LOW Z-FORCE OCTASPOT™ SWEPT FRICTION STIR SPOT WELDS WELDING—
LOW Z-FORCE OCTASPOT™ SWEPT FRICTION STIR SPOT WELDS WELDING—
CONVENTIONAL TOOL AND PROCESS DEVELOPMENT APPROACH
A Thesis by
Tze Jian Lam
B.S.M.E., Wichita State University - 2005
Submitted to the Department of Mechanical Engineering and the faculty of Graduate School of
Wichita State University in partial fulfillment of the requirements of the degree of
Master of Science
May 2010
© Copyright 2010 by Tze Jian Lam
All Rights Reserved
LOW Z-FORCE OCTASPOT™ SWEPT FRICTION STIR SPOT WELDS WELDING—
CONVENTIONAL TOOL AND PROCESS DEVELOPMENT APPROACH
The following faculty members have examined the final copy of this thesis for form and content, and recommend that it be accepted in partial fulfillment of the requirement for the degree of
Master of Science with a major in Mechanical Engineering.
_____________________________________
George E. Talia, Committee Chair
_____________________________________
Dwight A. Burford, Committee Member
_____________________________________
Brian Driessen, Committee Member iii
DEDICATION
To my parents, my sister, my brothers, my relatives, and my friends iv
ACKNOWLEDGMENTS
As a graduate research assistant in the Advanced Joining and Processing Laboratory
(AJ&PL) of the National Institute for Aviation Research at Wichita State University, I would like to thank Dr. Dwight Burford, Director of AJ&PL, for giving me the opportunity and support to lead the project of Low Z-Force Octaspot™ Swept Friction Stir Spot Welds Welding—
Conventional Tool and Process Development Approach (CFSP07-WSU-03). This project was funded by the National Science Foundation’s (NSF) Center for Friction Stir Processing (CFSP), which is part of the Industry University Cooperative Research Center (IUCRC) program.
This project work is also my thesis, as part of the requirements for completing my Master of Science degree in Mechanical Engineering at Wichita State University. I would like to thank my advisor and committee chair, Dr. George Talia, for his guidance, and principal investigator and committee members, Dr. Dwight Burford and Dr. Brian Driessen, as well as Dr. Christian
Widener for their efforts and help with this thesis.
Also, I would like to recognize the hard work of students in NIAR’s AJ&PL, especially
James Gross, who developed much of the early low Z-force welding program. I would like to thank Kristie Bixby for her editorial efforts with this thesis.
I thank the Graduate School for supporting me financially throughout my Master’s degree. And I also thank my parents and family members for their encouragement in my studies. v
ABSTRACT
An investigation was conducted to develop low Z-force (normal/forge load) friction stir spot welds (FSSWs) using conventional tooling and process development approaches. Low Zforces can be achieved by studying the relationship between pin tool features, geometries, processing parameters, and resultant strength of coupons produced by friction stir spot welding
(FSSW). The effects of geometrical and feature changes of pin tool designs—including shoulder diameters, shoulder features, probe diameters, probe shapes, and probe features—on the joint properties of 0.040-inch-thick bare 2024-T3 aluminum alloy were evaluated. Welding tools included Psi™, Counterflow™, Modified Trivex™, and V-flute™ pin tools. A Box-Behnken design of experiments (DOE) approach was used to investigate the effects of three process parameters: spindle speed, Z-force (forge load), and travel speed. The goal of the investigation was to maintain the ultimate tensile load (UTL) in unguided lap shear coupons tested in tension while reducing the Z-force required for producing a sound joint. This goal was achieved on a specially built MTS Systems Corporation ISTIR PDS FSW gantry system. In addition to singlespot unguided lap shear tests, the performance of low Z-force FSSW joints was evaluated by optical metallographic cross-section analyses, which were then correlated with process parameters, UTL, and pin tool designs. The maximum Z-force spikes encountered during the initial plunge were reduced by an order of magnitude, and the Z-force processing loads were reduced by half for Octaspot™ swept FSSW, most effectively by controlling the plunge rate under force control. Additional reductions in Z-force were achieved by refining the conventional
FSSW tool shoulder and probe designs. Therefore, it was demonstrated that weld forces can be reduced to the point where it would be feasible to perform robotic low Z-force FSSW for at least some applications. vi
TABLE OF CONTENTS
Chapter Page
1.
INTRODUCTION ...............................................................................................................1
2.
LITERATURE REVIEW ....................................................................................................8
2.1
FSSW Process Controls ...........................................................................................8
2.2
Development of Process Parameters ......................................................................10
2.3
Tool Geometry .......................................................................................................12
2.4
Variation of FSSW .................................................................................................13
2.5
Material Flow .........................................................................................................14
3.
OBJECTIVE ......................................................................................................................16
4.
TEST PROCEDURE .........................................................................................................17
4.1
Pin Tool Designs ....................................................................................................17
4.1.1
Additional Pin Tool Designs .....................................................................21
4.2
Material Preparation...............................................................................................22
4.3
Weld Setup .............................................................................................................23
4.4
Weld Programs.......................................................................................................23
4.5
Mechanical Properties Testing ...............................................................................25
5.
RESULTS AND DISCUSSIONS ......................................................................................28
5.1
Achieving Low Z-Force .........................................................................................28
5.2
Concave Shoulder Tool Study (Phase 1) ...............................................................33
5.3
Concave Shoulder Diameter Study ........................................................................33
5.3.1
Psi™ Tool (0.30 Inch and 0.40 Inch) ........................................................34
5.3.2
Counterflow™ Tool (0.30 Inch and 0.40 Inch) .........................................37
5.4
Probe Design Study with 0.30-Inch-Diameter Concave Shoulder ........................41
5.4.1
Modified Trivex™ Tool ............................................................................41
5.4.2
Duo V-Flute™ Tool ...................................................................................44
5.4.3
Tri V-Flute™ Tool .....................................................................................45
5.5
Achievement in Concave Shoulder Study (Phase 1) .............................................47
5.5.1
Concave Shoulder Diameter Study ............................................................47
5.5.2
Probe Design Study....................................................................................47
5.6
Optimization Weld Parameters (DOE 2) ...............................................................51
5.7
Surface Preparation ................................................................................................54
5.8
Surface Finish ........................................................................................................55 vii
TABLE OF CONTENTS (continued)
Chapter Page
5.9
Scroll Shoulder Tool (0.30 Inch) Study (Phase 2) .................................................55
5.9.1
Achievement Duo V-Flute™ Scroll ..........................................................56
5.10
Featureless Probe Shape Study (Phase 3) ..............................................................57
5.10.1
Featureless Trivex™ ..................................................................................58
5.10.2
Featureless Pentagon™ ..............................................................................61
5.10.3
Featureless Octagon™ ...............................................................................63
5.11
Achievement in Featureless Probe Shape Study (Phase 3) ....................................65
5.12
Probe Diameter Study (Phase 4) ............................................................................66
6.
CONCLUSIONS AND FUTURE WORK ........................................................................74
REFERENCES ..............................................................................................................................78
APPENDICES ...............................................................................................................................83
A.
Detailed Calculation for Table 1 ............................................................................84
B.
Duration of Octaspot™ Swept FSSW ...................................................................85
C.
UTL Results ...........................................................................................................88 viii
LIST OF TABLES
Table Page
1.
Ratio of Probe Physical Unit Volume to probe Swept Unit Volume ................................12
2.
Pin Tool Matrix ..................................................................................................................20
3.
Average UTL and Corresponding Z-Force Applied Using Concave Shoulder
Psi™ Tool ..........................................................................................................................37
4.
Average UTL and Corresponding Z-Forces Applied using Concave Shoulder
Counterflow™ Tool ...........................................................................................................40
5.
Compilation of DOE 1 UTL Results for Probe Design Study of 0.30-Inch-Diameter
Concave Shoulder ..............................................................................................................49
6.
Compilation of DOE 2 UTL Results for Probe Design Study of 0.30-Inch-Diameter
Concave Shoulder ..............................................................................................................52
7.
Hooking Defect of Featureless Trivex™ Pin Tool ............................................................59
8.
Hooking Defect of Featureless Pentagon™ Pin Tool ........................................................61
9.
Hooking Defect of Featureless Octagon™ Pin Tool .........................................................63
10.
Summary of Hooking Defect and Ratio of Probe Physical to Swept Unit Volume ..........65
11.
Weld Radius Compensation for Probe Radius Reduction .................................................67
12.
Average UTL and Standard Deviation of DOE 1 for Probe Diameter Study ....................68
13.
Z-Force Reduction and Corresponding Pin Tools and Weld Parameters ..........................73 ix
LIST OF FIGURES
Figure Page
1.
2.
Friction Stir Spot Welding (FSSW) Process (courtesy of Kawasaki). ................................3
3.
4.
5.
6.
7.
ABB IRB 7600 Six-Axis Articulated Robot at AJ&PL NIAR WSU ..................................7
8.
Schematic Diagram of Process Controls of Octaspot™ FSSW ...........................................9
9.
10.
11.
Schematic Cross-Sectional Representation of Plunge and Swept FSSW ..........................15
12.
Flat Scrolls Shoulder on Duo V-Flute™ Pin Tool: (a) 0.40-Inch Diameter and
13.
Wiper™ Shoulder on Duo V-Flute™ Pin Tool: (a) 0.40-Inch Diameter and
14.
15.
16.
Reduced Shoulder and Probe Diameter Sizes of Duo V-Flute™ ......................................21
17.
18.
19.
x
LIST OF FIGURES (continued)
Figure Page
20.
21.
22.
Command and Feedback Plot for Typical Octaspot™ FSSW
23.
Command and Feedback Plot of 0.40-Inch-Diameter Psi™ Tool Welded with
24.
Command and Feedback Plot of 0.30-Inch-Diameter Psi™ Tool Welded with
25.
Command and Feedback Plot for Low Z-Force Swept FSSW ..........................................31
26.
27.
28.
Command and Feedback Plot for Low Z-Force Swept FSSW ..........................................33
29.
Main Effects Plot of 0.30-Inch-Diameter Concave Shoulder Psi™ Tool..........................34
30.
Main Effects Plot of 0.40-Inch-Diameter Concave Shoulder Psi™ Tool..........................34
31.
Low Z-Force Swept FSSW with 0.30-Inch-Diameter Psi™ Tool at 1,100 lbf .................35
32.
Low Z-Force Swept FSSW with 0.30-Inch-Diameter Psi™ Tool at 900 lbf ....................35
33.
Low Z-Force Swept FSSW with 0.30-Inch-Diameter Psi™ Tool at 700 lbf ....................35
34.
Low Z-Force Swept FSSW with 0.40-Inch-Diameter Psi™ Tool at 1,100 lbf .................36
35.
Low Z-Force Swept FSSW with 0.40-Inch-Diameter Psi™ Tool at 900 lbf ....................36
36.
Low Z-Force Swept FSSW with 0.40-Inch-Diameter Psi™ Tool at 700 lbf ....................36
37.
Main Effects Plot of 0.30-Inch-Diameter Concave Shoulder Counterflow™ Tool ..........38
38.
Main Effects Plot of 0.40-Inch-Diameter Concave Shoulder Counterflow™ Tool ..........38
xi
LIST OF FIGURES (continued)
Figure Page
39.
40.
41.
42.
43.
44.
45.
46.
47.
Joint Interface of Figure 46 (100X): (a) Right Side and (b) Left Side ............................43
48.
49.
50.
51.
52.
53.
xii
LIST OF FIGURES (continued)
Figure Page
54.
55.
56.
57.
58.
59.
60.
61.
62.
UTL Results Comparison of Low Z-Force Octaspot™ Swept FSSW for
Five Pin Tools with 0.30-Inch-Diameter Concave Shoulder in DOE 1 ............................50
63.
UTL Results Comparison of Low Z-Force Octaspot™ Swept FSSW for
Five Pin Tools with 0.30-Inch-Diameter Concave Shoulder in DOE 1 and DOE 2 ............53
64.
UTL Results Comparison of Low Z-Force Octaspot™ Swept FSSW for
65.
Low Z-Force FSSW with 0.30-Inch-Diameter Concave Shoulder with
66.
Low Z-Force FSSW with 0.30-Inch-Diameter Concave Shoulder with
67.
Low Z-Force FSSW with 0.30-Inch-Diameter Flat Scrolls Shoulder with
xiii
LIST OF FIGURES (continued)
Figure Page
68.
UTL Results Comparison of Low Z-Force Octaspot™ Swept FSSW for
0.30-Inch-Diameter Scroll Shoulder Duo V-flute™ in DOE 2 .........................................57
69.
70.
71.
72.
Featureless Pentagon™ Cross-Sectional Metallographic M19 .........................................61
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
xiv
LIST OF ABBREVIATIONS/NOMENCLATURES
AJ&PL
CFSP
CNC
DFT
DOE
FSP
FSW
FSSW
GKSS
HAZ
HCl
HF
HNO
3
HRS
IRB
ISTIR™
IUCRC
LOP
NIAR
NSF
PDS
Advanced Joining and Processing Laboratory
Center for Friction Stir Processing
Computer Numerically Controlled
Discrete Fourier Transformation
Design of Experiment
Friction Stir Processing
Friction Stir Welding/Weld
Friction Stir Spot Welding/Weld
Gesellschaft zur Förderung der Kernenergie in Schiffbau und Schiffstechnik
(German: Society for the Promotion of the Nuclear Energy in Shipbuilding and
Naval Technology)
Heat-Affected Zone
Hydrochloric Acid
Hydrofluoric Acid
Nitric Acid
High Rotational Speed
Industrial Robot
Intelligent Friction Stir Welding for Research and Production
Industrial University Cooperative Research Center
Lack of Penetration
National Institute for Aviation Research
National Science Foundation
Process Development System xv
PFSW
RPT
SEM
TMAZ
TWI
UTL
LIST OF ABBREVIATIONS/NOMENCLATURES (continued)
Plunge Friction Spot Welding/Weld
Retractable Pin Tool
Scanning Electron Microscope
Thermomechanically Affected Zone
The Welding Institute
Ultimate Tensile Load xvi
CHAPTER 1
Friction stir welding (FSW) was patented by The Welding Institute (TWI) in England in
1991 [1]. FSW is a solid-state joining technology, which differs from conventional fusion welding in that the joining process occurs below the melting temperature of the welded material
[2,5]. This new joining process is especially beneficial on materials such as 2XXX and 7XXX
series aluminum alloys, which are relatively difficult to join by conventional fusion welding. The use of aluminum alloys in automotive and aerospace industries gained popularity because of their high strength-to-weight ratio, resistance to corrosion, energy savings, etc. [3,4]. In recent years, research and development of FSW technology has made significant progress toward understanding the fundamentals of this joining technology [5].
The FSW process consists of four stages: rotate, plunge, translate, and retract. FSW was introduced as a linear weld with a non-consumable pin tool, which rotates about its own axis, plunges into a weld specimen to a specified depth, translates in a linear or curvilinear path along the joint line, and retracts
at the end of weld path (Figure 1). With this process, welding can
occur in a butt or lap joint configuration. One of FSW’s main variants is friction stir spot welding
(FSSW), which is similar to FSW only without the translation of a pin tool. FSSW is mainly
applied in lap joint configurations with only three stages: rotate, plunge, and retract (Figure 2).
The simplest form of FSSW, called poke or plunge FSSW, was patented by Mazda in 2003 [6] as
―plunge‖ friction spot welding (PFSW) [20]. Other variants of FSSW are Squircle™ [7],
Octaspot™ [25-28, 30-33], Stitch-FSW [5] or Stitch-FSSW from Gesellschaft zur Förderung der
Kernenergie in Schiffbau und Schiffstechnik (GKSS) [4,8,9], and swing-FSW [5] or swing-
FSSW from Hitachi [4,10,11,12], which increases the joint shear area. Another variant of FSSW
1
relates to the exit hole that is left when the pin tool retracts; thus, a process called ―refill‖ FSSW solves the issue by refilling the exit hole. The process of refill FSSW has been patented in Japan
[13] and in the United States [24]. Another variant of FSW, friction stir processing (FSP), was
developed to exploit the benefit of the FSW process to change the microstructure of cast materials to a void-free and fully recrystallized fine grain microstructure found in the weld
Figure 1. Friction Stir Welding (FSW) Process (courtesy of TWI).
2
(a) Rotate (b) Plunge (c) Retract
Figure 2. Friction Stir Spot Welding (FSSW) Process (courtesy of Kawasaki).
The microstructures of FSW and FSSW weld zones use the same terms: weld nugget, thermomechanically affected zone (TMAZ), heat-affected zone (HAZ), and unaffected zone or
parent material (Figure 3). The weld nugget, also called the stir zone, is the zone that the probe
has occupied and significantly processed, producing a fine, fully recrystallized grain structure.
The TMAZ is the zone that receives some limited plastic deformation and is significantly affected by the thermal cycle of the process, while the HAZ experiences a thermal cycle that is only significant enough to change the properties and microstructure of the material. Finally, the unaffected zone experiences a minimal thermal cycle, which is not significant enough to change
the microstructure or mechanical properties [2]. Also, a small amount of asymmetry occurs
transverse to the weld direction. The advancing side of the weld panel (left side of Figure 1)
occurs when the tool rotation direction is the same as the tool travel direction, whereas, the
retreating side of weld panel (right side of Figure 1) is found on the side where the tool rotation
direction is opposite the tool travel direction.
The advancing side of a transverse metallographic sample is shown in Figure 3. The
right side of this figure has a clear distinctive line between the TMAZ and HAZ, but on the retreating side, there is no such clearly discernible line between the TMAZ and HAZ. The weld
3
nugget properties, such as fatigue, deformation, and tensile load, are generally superior to the
surrounding parent material due to the nugget’s fine grain microstructure [2]. In a typical FSW
lap joint configuration, the weld zones mentioned above can also be observed, as shown in
Retreating
Side
Parent
Material
HAZ
TMAZ Nugget TMAZ
HAZ
Advancing
Side
Parent
Material
Figure 3. Typical FSW Butt Joint with Fixed Pin Tool.
Retreating
Side
Parent
Material
HAZ
TMAZ
Nugget
TMAZ
HAZ
Advancing
Side
Parent
Material
Figure 4. Typical FSW Lap Joint with Fixed Pin Tool.
Conventional FSW tools are non-consumable pin tools, which consist of a body, a shoulder, and a probe or pin. These tools are also known as fixed-pin tools, where the length of
eliminate the potential for lack of penetration (LOP) in the weld and apply minimal net force normal to the part assembly, since the down force of the upper shoulder is opposed by the upward force of the lower shoulder. Similarly, FSSW typically uses fixed pin tools but also uses refill or retractable FSSW pin tools, which consist of an independently moveable probe and
shoulder with an optional containment ring (Figure 5b). The probe of FSW or FSSW tools
typically consists of different features such as threads, flutes, and/or flats, which help to channel the flow of material. In order to promote material movement, the shape of the probe can be in the
4
form of a circle, triangle, square, pentagon, etc.. The shoulder captures material displaced by the probe and exerts a forging force (normal load) to consolidate the material. The body of the pin tool is inserted into the pin tool holder, which is attached to the forge spindle of the FSW machine. The probe of both retractable and self-reacting pin tools is attached to an independent pin axis in an FSW machine in order to control pin force and pin position separately from the forge axis.
Body
Containment
Ring
Shoulder
Body
Upper
Shoulde r
Probe
(a) Fixed Pin Tool
Probe
(b) Retractable Pin Tool
Lower
Shoulde r
(c) Self-Reacting Pin Tool
Figure 5. Schematic Representation of Pin Tools.
Applications and designs lead to various definitions of pin tools such as fixed pin tool or conventional pin tool, retractable pin tool or refill pin tool (RPT), and self-reacting pin tool or bobbin pin tool. A fixed pin tool is where the probe and shoulder do not move relative to each
the end of the weld, whereas a retractable pin tool is designed not to produce an exit hole. The relative motion of the probe and shoulder in an RPT tool set enables it to refill the exit hole. A self-reacting pin tool has an additional lower shoulder attached to the probe, and both the upper shoulder and lower shoulder create a nominally zero net force while clamping the weld material
5
to keep it from escaping from the joining region (Figure 5c) [17]. The design of a self-reacting
pin tool requires no backing anvil, eliminates the lack of penetration defect, and increases the travel speed due to heating from both shoulders [16,17].
FSW machines are usually gantries for stiffness, with three to five-axes of motion for two- or three-dimensional welding, position and load control capability, and intelligence and sensing capability. The multi-purpose gantry FSW machine used in this study was an MTS
Systems Corporation’s ISTIR™ Process Development System (PDS) (Figure 6), which is
capable of a wide range of process development parameters such as high Z-force (normal load) up to 20 kip with the stiffness of the gantry system.
Figure 6. MTS System Corp. ISTIR™ PDS Five-Axis FSW Machine at AJ&PL NIAR WSU.
This FSW machine can be programmed using position control, load control, or a combination of both. The intelligence and sensing capability enables the capture of data on weld parameters and feedback forces that can be analyzed to ensure weld quality. Articulated-arm robots equipped for
6
FSSW, such as the ABB IRB 7600 (Figure 7), is desirable for this manufacturing process
because of high flexibility and low capital investment. However, articulated-arm robots have a lower degree of stiffness and normal force, both of which present challenges for the transition of
FSSW technology to articulated robots, such as methods to decrease the required Z-force.
Figure 7. ABB IRB 7600 Six-Axis Articulated Robot at AJ&PL NIAR WSU.
7
CHAPTER 2
The process controls of FSSW have improved over the decades with the advancement of computing, sensing, and measuring. Advancement in machining technology directly benefits
FSSW because, from its inception, FSW was developed using computer numerically controlled
(CNC) machines. The more capabilities of FSSW machines mean that the more varieties of process controls can be developed.
Position control is normally applied to FSSW. This is the simplest process control and requires the least amount of processing monitoring by the machine controller. A position control weld program uses a command of known weld depths to maintain a constant tool depth
throughout the weld (Figure 8a) [4,18]. Another process control of FSSW is load control, which
involves a force-feedback process. It requires more intelligence for measuring, sensing, feedback, and command controls for loading and positioning. A load-control weld program begins by establishing a nominal load command based on a feedback load obtained from a preliminary weld using a position-control weld program. This load is typically maintained at a
constant load throughout the weld (Figure 8b) [4,18]. Variation of FSSW process control can be
a combination of position control and load control, known as hybrid control. The hybrid-control weld program operates with the position control as the initial command control, beginning with the plunge step controlled to a specified weld depth. Once the plunge phase is complete, the program switches to load control as command control to maintain a predetermined constant
forging load during the weld (Figure 8c) [26].
8
Load Load Load
Position Position Position
Time
Command
Time
Feedback
Time
(a) Position Control (b) Load Control (c) Hybrid Control
Figure 8. Schematic Diagram of Process Controls of Octaspot™ FSSW.
The feedback reaction force of a position-control weld program increases during the plunge stage, due to displacement of material when the probe is plunged into the joint material, and increases significantly when the tool shoulder comes in contact with the top surface of the joint material. As the pin tool is moved in the Octaspot™ path, if the weld coupon has irregular thickness or if the backing fixture is uneven, a position control weld will produce poor weld
quality due to not maintaining a sufficient forging force (Figure 8a). Since the Z-force acts as the
forging force, which is an important factor to ensure a fully consolidated weld, load control as command control can ensure a constant load level throughout the weld. However, the increased
position of the pin tool that travels causes lifting because the predetermined load is low (Figure
8b) [Note: the position values in Figures 8b and 8c can be either negative, when the tool plunges
into the material (predetermined load too high), or positive, when the tool rises above the material (predetermined load too low)]. In the hybrid-control weld program, position control is utilized to ensure that a sufficient weld depth is reached in the plunge stage of the weld; then the program is changed to load control to ensure a consistent forging force for the rest of the weld.
However, the high-reaction load due to the control position during the plunge phase is not favorable for low Z-force FSSW research. A low Z-force weld program based on load control is
9
used to eliminate high-reaction loads, known as Z-force spikes, in the plunge step of the weld
2.2 Development of Process Parameters
The process parameters of Octaspot™ swept FSSW are similar to FSW and include spindle speed (rpm), travel speed (ipm), plunge speed (ipm), tilt angle (degree), dwell time (sec), and forge load or normal load (lbf). The process parameters of plunge FSSW include spindle speed, plunge speed, and dwell time, whereas an Octaspot™ swept FSSW has a closed-loop path
(Figure 10) involving the additional process parameters of travel speed and tilt angle. A hybrid-
control weld program (Figure 8c) includes the initial plunge under position control and the tool
movement under load control.
In a low Z-force weld program, plunge depth is defined by a constant-plunge spindle speed and a constant-plunge dwell time, both introduced to reach specific plunge depth within a range of low forge load. For a low Z-force weld program developed from the hybrid-control weld program of Octaspot™ swept FSSW, all process parameters are held constant. These include the tilt angle, dwell time, plunge speed, plunge dwell time, and plunge spindle speed. For this research, the effects of variation and interaction of process parameters such as normal load, weld spindle speed, and travel speed are of main interest for characterizing the weld properties of low Z-force Octaspot™ swept FSSW.
Each process parameter has its own role; therefore, the investigation of certain, more significant process parameters is more desirable for research that is constrained by time and budget. Since three factors (k = 3) or process parameters were selected for this study, two general design of experiments (DOEs), either two-level with k factors (2 k
) or three-level with k factors
(3 k
) designs are appropriate DOEs. A three-level DOE with 27 runs has a higher resolution than a
10
two-level DOE with 8 runs. In addition, a three-level DOE can be a second-order model.
However, a three level DOE will increase the cost and time. A model that provides a response surface can be used to optimize the process parameters for maximizing the ultimate tensile load
(UTL) of lap shear coupons. Therefore, statistical development of process parameters using a response surface method, such as a Box-Behnken DOE, can significantly reduce time and cost compared to a full factorial DOE. For example, a Box-Behnken or Central Composite DOE has only 15 or 16 runs, compared to 27 runs in a three-level full design with three factors 3
3
.
Compared to a Box-Behnken DOE, a Central Composite DOE contains points on the corners of the design space cube, which can represent factor-level combinations that are either expensive or impossible to test because of physical process constraints [19]. In certain situations, these corner points can be extreme process parameters, which ultimately can damage the pin tools.
The three process parameters chosen as the main interest of investigation in this study were selected because FSSW was treated as a thermo-mechanical controlled process. Weld spindle speed and travel speed are controlled variables in a weld program, and they directly
affect thermal input to the work piece [2, page 71]. The term ―cold‖ weld is typically associated
with a weld that is made with a relatively high travel speed and low spindle speed. A ―hot‖ weld is typically described as a weld with a relatively low travel speed and high spindle speed. These
relative terms of cold and hot welds do not correlate with peak temperature [2, page 37]. One
would assume a ―hot‖ weld should reach a higher peak temperature compared to a cold weld, but the high conductivity of aluminum tends to disperse the heat of a ―hot‖ weld because of the slow travel speed, thus resulting in a lower peak temperature. A final controlled variable chosen to be
investigated in this study was normal load because a ―controlled path extrusion‖ [2 pp 301,20]
11
FSSW need a consistent normal load to produce a good FSSW joint. All other process parameters were kept constant in this research but may be investigated in future work.
FSW and FSSW tools have similar characteristics, such as body, shoulder, and probe
(Figure 5), which may have a range of different features and shapes. Features on the probe, such
as flats, flutes, and threads, can promote the flow of material around the probe. A concave shoulder traps material that is displaced by the probe. A shoulder with a flat face and scrolls will tend to capture the material displaced by the probe and redirect it inward toward the probe.
Probes with different cross-sectional shapes are shown in Figure 9. These shapes serve to
change the ratio of the physical volume of the probe to the swept volume of the probe. Table 1 provides the volume per unit length (or unit volume) of each probe.
(a) (b) (c) (d) (e) (f) (g)
Figure 9. Different Probe Shapes with Same Effective Swept Area:
(a) Rectangular, (b) Triangular, (c) Square, (d) Pentagon, (e) Hexagon, (f) Octagon, and (g) Circular
TABLE 1
RATIO OF PROBE PHYSICAL UNIT VOLUME TO PROBE SWEPT UNIT VOLUME
Probe Shape a b c d e f g
Probe Physical Unit
Volume
Ratio of Probe
Physical to Swept
0.010 0.013 0.020 0.024 0.026 0.028 0.031
0.308 0.413 0.637 0.757 0.827 0.900 1.000
Unit Volume
Detailed calculation refers to Appendix A.
12
In plunge FSSW, the plunge stage creates a hooking defect at the lap joint interface due to displacement of the probe’s volume of material. In addition, features on the probes, such as threads, which provide an augering effect that causes material to recirculate toward the shoulder, further increase the lifting and hooking, and create a large weld nugget. However, the Octaspot™ swept FSSW process includes a closed-loop path that consumes the hooking feature and simultaneously creates a larger stir zone compared to the plunge FSSW process.
The shoulder of a pin tool has three main functions: (1) to capture material displaced by the probe, (2) to apply Z-force or forging force, and (3) to create frictional heat. Shoulder
features, such as flat scroll or Wiper™ [21] (Figure 12 and Figure 13), are designed to capture
material and direct it toward the probe. A concave shoulder (Figure 14), which has a small
pocket of volume, captures the displaced material and keeps it pressed against the probe.
For thin-gage material, an optimum shoulder diameter is favorable to create adequate frictional heat and avoid a large heat-affected zone. A large shoulder diameter creates a wider
HAZ, compared to a small shoulder diameter. Since low Z-force is the primary goal of this research, the pin tool shoulder diameter needs to be reduced for low process forces but yet provide sufficient forging force to ensure consolidation of the weld nugget. A large shoulder diameter requires more Z-force compared to a small shoulder diameter to create similar forging pressure for sufficient consolidation of the weld nugget.
Existing fastening methods such as rivets and resistance spot welds have been widely applied in the automotive and aerospace industries for decades. FSSW has been introduced recently as an alternative fastening method for thin-gauge materials. The simplest type of FSSW, referred to as plunge FSSW or poke FSSW, is an attractive alternative replacement for existing
13
discrete fastening methods because it can be produced rapidly and with a simple motion. Plunge
FSSW has shown many benefits and already has been implemented in the automotive industry
[22]. Besides plunge spots, refill FSSW can fill the exit hole and leave a nearly flush surface with an opposing pin and shoulder [23,24]. Swept FSSW, such as the Squircle™ disclosed by
TWI [7] and developed at Wichita State University (WSU) as an Octaspot™, has been shown to
be up to 250 percent stronger than rivets and resistant spot welds in a single-spot lap shear [25].
Plunge and refill FSSW differ from swept FSSW. Swept FSSW has an additional closed-loop
translation movement (Figure 10). This closed-loop translation increases the joint shear area and
has been demonstrated at WSU to have better mechanical properties compared to plunge or refill
Figure 10. Octaspot™ Travel Path.[25,27]
Plunge FSSW cross-sections tend to exhibit an upward flow of material from the bottom sheet causing an uplift of the faying surface, called hooking. The hooking caused by the vertical translation of material creates a thinning of the effective thickness of the top sheet. In contrast,
14
Plunge (Poke) Spot
swept FSSW consumes the hook by sweeping around the perimeter, giving it better control of the
faying surface geometry and increasing the effective shear area of the nugget (Figure 11).
Swept Spot
Figure 11. Schematic Cross-Sectional Representation of Plunge and Swept FSSW.[26]
For single-pass linear FSW lap welds, placing the advancing side or retreating side in the load path significantly affects the mechanical properties measured by the unguided lap shear
coupons [26,29]. Hooking is typically observed on the advancing side of lap welds and sheet
lifting along the retreating side of lap welds (Figure 21). Both defects can be significantly
affected by probe design. Prior related work involving the Counterflow™ tool was found to produce excellent unguided lap shear mechanical properties on both the advancing side and
retreating side when placed directly on the loading path [29].
In making an Octaspot™ swept FSSW, the advancing side is typically placed directly on
the loading path because it produces a clearly distinctive line between the TMAZ and HAZ [26].
This distinctive line on the advancing side is placed on the outside of the Octaspot™ swept
FSSW weld nugget to ensure that there is no sheet thinning or hooking around the joint. In this study, the retreating side of an Octaspot™ swept FSSW was placed inside the weld nugget and not directly subjected to a tensile lap-shear test load. The hooking defect on the advancing side and joint interface oxide remnant line (sheet lifting) on the retreating side can be eliminated by appropriate probe designs.
15
CHAPTER 3
Friction stir spot welding development work has commonly been used on a gantry-type system because of the wide range of Z-forces, also known as ―forging forces‖ or ―normal forces,‖ required to produce a sound FSSW. However, articulated robots, which are limited to lower Z-forces, are preferred for implementation in manufacturing plants because of their potential to produce three-dimensional structures with more flexibility and lower capital costs than a conventional gantry system. Thus, for robotic applications, an investigation into low Zforce FSSW using conventional tools and process development is crucial for the development of this technology. Lower Z-forces can be achieved by studying the relationship between pin tool features, geometries, and process parameters measured by UTL, and optical metallographic cross-sections. FSSW must maintain a significant joint strength with lower Z-force and be comparable to existing FSSW joint strength. The weld cycle time must be minimized to achieve a lower manufacturing time and thus be competitive with other fastening technologies. This research helps to indentify the portability issues associated with moving FSSW technology from gantries to robots and provides a path for implementation of FSSW utilizing articulated robots in the automotive and aerospace industries.
16
CHAPTER 4
A conventional fixed-pin tool design used for a lap-joint weld requires an adequate probe length to penetrate through the first sheet of material and partially breaking the surface interface of the second sheet material to create a joint. Whereas, a lap-joint weld with different material thicknesses to be welded required a two-piece pin tool, a body, and a detachable probe with different probe lengths or a retractable pin tool. In this study, a conventional pin tool with a fixed probe length will be utilized to lap weld bare aluminum alloy 2024-T3 sheet with a thickness of
0.040 inch. Since AJ&PL has ongoing research involving short, continuous, linear FSW and
Octaspot™ swept FSSW lap weld joints using a similar thickness of material, a few existing pin tool designs were utilized in this research. A comparison of existing data with low Z-force data on mechanical properties such as single-spot unguided lap shear weld UTL were analyzed based on Z-forces and pin tool designs.
Each pin tool has a few unique features designed on the probe such as threads, flutes, and flats. A new pin tool design has two opposing flutes and resembles the letter V in the alphabet;
hence, it is named the V-flute™ (Figure 12). Typical shoulder designs are concave, flat, and
convex. In this experiment, pin tools were designed with a five-degree concave shoulder with no features. The material displaced by the probe in the plunge process was captured mostly under the concave shoulder. Another pin tool shoulder was designed with grooved features on a flat shoulder, hence named flat scrolls, and was used in this experiment to capture displaced material,
17
in the design stage. However, a reduction of the shoulder diameter from 0.40 inch to 0.30 inch
(Figure 13b) prevented its use, and the flat scrolls design with a similar shoulder feature (Figure
(a) (b)
Figure 12. Flat Scrolls Shoulder on Duo V-Flute™ Pin Tool: (a) 0.40-Inch Diameter and
(b) 0.30-Inch Diameter.
(a) (b)
Figure 13. Wiper™ Shoulder on Duo V-Flute™ Pin Tool: (a) 0.40-Inch Diameter and
(b) 0.30-Inch Diameter.
Five pin-tool designs were included in this research. Three pin tools were extensively investigated for short linear lap FSW, plunge FSSW, and Octaspot™ swept FSSW. Two preferred pin tools for Octaspot™ swept FSSW were the Counterflow™ [28,29,30,31] and Psi™
tool [25,30,31,32,33] designs developed at WSU, whereas a Modified Trivex™ tool [26,30,31]
has been shown to be successful for plunge and Octaspot™ FSSW (Figure 14a to 14f). In
addition, a new pin tool design named the V-flute™ [30]—Tri V-flute™ and Duo V-flute™
(Figure 14g to 14j)—was included in this research. A Tri V-flute™ pin tool has three sets of V-
flutes™ and a Duo V-flute™ has two sets of V-flutes™. The two designs were developed to study the effects of multiples V-flutes on UTL joint strengths for an Octaspot™ swept FSSW.
Two pin tool shoulder diameters of 0.30 inch and 0.40 inch were included in this research to investigate the effects of shoulder sizes on Z-force applied, corresponding to the UTL of joint
18
strength. The pin tool probes had base diameters of 0.135 inch and a seven-degree taper angle.
All the pin tools included in this research had a five-degree concave shoulder.
(a) (c) (e) (g) (i)
(b) (d) (f) (h) (j)
Pin Tool Shoulder Diameters: Top row 0.40 inch and bottom row 0.30 inch.
Probe Design: Counterflow™ Tool (a) and (b), Psi™ Tool (c) and (d), Modified Trivex™ Tool (e) and (f),
Tri V-Flute™ (g) and (h), and Duo V-Flute™ (i) and (j).
Figure 14. Pin Tools with Five-Degree Concave Shoulder.
Although all pin tools were designed with a seven-degree tapered cylindrical probe, each of the pin tools shown in Figure 14 has at least one or more features on the probe for its identity and functionality. The features on the probe add an additional factor, which leads to the study of different probe designs on the mechanical properties of the weld. The Counterflow™ tool has a
combination of two features: thread and counterflow flutes on the probe (Figure 14a and 14b).
The Psi™ tool has a combination of two features: inclined flats and vertical flutes on the probe
design included in this research, the V-flute™, has a seven-degree tapered cylindrical probe designed with the feature of two opposing flutes. The Tri V-flute™ pin tool was designed with
19
The matrix of the pin tools had a combination of two shoulder sizes and two shoulder features, and the five probe designs created a total of 20 pin tools (Table 2). Thus, this research was divided into two phases: that involving the concave shoulder (phase 1) and that involving the flat scrolls (phase 2). Phase 1 involved the pin tool matrix with two different shoulder diameters to study the effects of shoulder diameter on Z-forces and five probe designs to study the effects of probe designs on mechanical properties. However, the Modified Trivex™, Tri Vflute, and Duo V-flute™ tools with 0.40-inch-diameter shoulders in phase 1 and all 0.40–inchdiameter shoulders in phase 2 were not made because the 0.40-inch-diameter shoulder required a higher Z-force. In phase 2, the pin tool matrix was reduced to one probe design (Duo V-flute™) to study the effects of the flat scrolls shoulder feature and the concave shoulder feature on the
0.3-inch-diameter shoulder on mechanical properties (UTL).
TABLE 2
PIN TOOL MATRIX
Shoulder
Diameter Counterflow Trivex
0.3 inch
Concave
PSI
0.4 inch
Counterflow Trivex
Scroll
PSI
0.3 inch
0.4 inch
Tri V-Flute Duo V-Flute
Tri V-Flute Duo V-Flute
Phase 1 study
Phase 2 study
Pin tools not made
20
4.1.1 Additional Pin Tool Designs
Further investigation led to a phase 3, which consisted of three probe shape designs with
Octagon™ (Figure 15c) with a 0.135-inch-diameter probe base and 0.30-inch-diameter five-
degree concave shoulder. This additional investigation studied the relationship between the ratio of physical volume to swept volume and the hooking defect of Octaspot™ swept FSSW.
The Duo V-flute™ pin tool design was selected to further reduce the Z-force from a
was the final design of a small 0.25-inch-diameter shoulder with a small 0.10-inch-diameter
force and UTL of Octaspot™ swept FSSW.
(a) (b) (c)
Figure 15. 0.3-Inch-Diameter Probe Shapes: (a) Concave Shoulder Trivex, (b) Pentagon, and (c) Octagon.
(a) (b) (c)
Figure 16. Reduced Shoulder and Probe Diameter Sizes of Duo V-Flute™.
21
The weld coupon used in this study was a lap joint configuration with 1.0-inch overlap in
0.040-inch-thick, bare 2024-T3 aluminum alloy. The specimen coupon configuration is shown in
Figure 17. Both top and bottom sheets were 2024-T3 aluminum alloy, 1.0 inch wide and 4.0
inches long. Grain direction was parallel to the mechanical tensile shear test direction. The
Octaspot™ path began in the center, moved to the positive X-axis, circulated 450 degrees, and returned to center from the positive Y-axis.
Figure 17. Single-Spot Unguided Lap Shear Specimen.
Prior to FSSW, the surface oxide layer of the weld coupon at the joint interfaces and tool contact interface was removed with a dual-action (DA) sander, also known as a random orbital sander, with a 180-grit disk. The weld coupon was also wiped with methyl ethyl ketone (MEK) to remove any remaining sanded oxide particles. Surface oxide was removed, unless it was indicated that there was no prewelding preparation or only MEK wipes were used for cleaning.
Surface oxide can remain in the FSSW nugget if its dispersion is insufficient. A separate investigation could be initiated to correlate the effects of surface preparation and UTL of FSSW.
22
All FSSW setups were made with a five-axis ISTIR™ PDS FSW machine from the MTS
Systems Corporation. Welding was supported with a 0.50-inch-thick steel backing plate with a
0.040-inch machined step for lap welds (Figure 18). Steel bars were spaced 0.75 inch apart,
clamped with finger clamps spaced 6.0 inches apart, and tightened with a torque wrench to 40 ftlbf, providing approximately 900 lbf down force. The weld fixture position was set up so that the lower sheet was on the positive X-axis side of the machine, and the start of the first spot through
the fifteenth spot from negative to positive was on the Y-axis (Figure 18). In this setup, the
metallographic cross-section of each spot was consistently processed (Note: Steel backing support was removed from time to time to accommodate other projects).
0.04”
2024-T3
0.5” x 1”
4130 Steel Bar
~ 900 lbf
+ Y-axis into slide
0.75”
~ 900 lbf
0.04”
Spacer
+ X-axis
0.04”
2024-T3
4130 Steel Backing Support
Figure 18. Experimental Weld Setup.
Weld programs used on the MTS FSW machine were written using a combination of load control and position control. This capability of the MTS software provides an advantage to researchers to further investigate FSSW with low Z-force with innovative weld schedules tested in this research. The first weld program utilized position control, which commanded the pin tool to plunge into the weld coupon at a specified depth. The second weld program utilized a hybrid weld program with a partial initial plunge using position control and then switched to load control for the remainder of the weld. In addition to controlling maximum weld forces, load-
23
control FSSW has been shown to have more consistent ultimate tensile load results with lower
standard deviations [26]. However implementation of a full load-control weld program has a few
obstacles with which to be concerned, such as uncontrolled plunge depth and weld program modification. Modification of the weld program to load control introduced additional parameters, such as plunge dwell time and plunge spindle speed. However, the weld program was modified with minimal changes, and most of the constant values remained the same.
Process parameters vary in a weld program and depend on the types of FSSW. In plunge
FSSW, the main process parameters are spindle rotational speed, plunge speed, plunge depth, and dwell time. In a hybrid weld program written for Octaspot™ FSSW, additional process parameters included in the hybrid weld program are travel speed, tilt angle, spot radius, and Zforce. A low Z-force weld program modified from a hybrid weld program introduced a new process parameter, plunge spindle speed, and substituted dwell time with plunge dwell time and removed the plunge depth. Selecting which process parameters to hold constant and which to be varied requires a literature review on process parameters. The process parameters selected to be varied in this research were spindle speed, travel speed, and forge load. The process parameters matrix used a Box-Behnken DOE approach to determine the process parameters window and the significance of each process parameter with response to ultimate tensile load of Octaspot™-
FSSW.
Since the hybrid weld program has a position control in the plunge section, feedback of the normal load spiked up to 3,000 lbf at the time of pin tool shoulder contact with the weld coupon. Prior to changing the hybrid weld program to the low Z-force weld program, several solutions were suggested to reduce the spike of the Z-force feedback. Pre-welding solutions suggested for reducing normal load, such as preheating and predrilling the weld coupon, were
24
not practical and not tested. However, modification of the process parameters, such as reducing the plunge speed, reducing the plunge depth, increasing the spindle speed, and increasing the dwell time, were more practical solutions.
The position-control weld program was utilized to approximate the Z-force value for the load-control weld program from feedback force data. Three selected process parameters were varied using the Box-Behnken DOE approach and run with the low Z-force weld program to investigate the effect of process parameters and pin tools designs on the mechanical properties of low Z-force Octaspot™ FSSW.
4.5 Mechanical Properties Testing
There are two different types of mechanical properties tests: destructive and nondestructive. Destructive tests, such as the tensile shear test, fatigue test, cross-tension test, crosssectional optical metallographic test, cross-sectional hardness test, impact or dynamic or crash test, and corrosion test have been established and used to determine mechanical properties. Nondestructive tests, such as the phased-array ultrasonic test, X-ray test, surface hardness test, laser test, surface optical metallographic test, scanning electron microscopy (SEM), and discrete
Fourier transformation (DFT) software that analyzes feedback forces, can be very time and cost effective for quality assurance.
In this research, destructive testing using the tensile shear test of a single spot on unguided lap shear coupons was used to evaluate the UTL mechanical properties of low Z-force
FSSW. The 2024-T3 aluminum alloy required a minimum of four days or 100 hours of post-weld
natural aging treatment to allow the weld nugget to stabilize [2 pp74,34]. The microstructure of
the weld nugget went through a by-product heat-treatment process after FSSW, since weld nuggets require time for grain growth and recrystalization to reach a stable temper.
25
In addition to the tensile shear test, optical metallographic analyses of FSSW crosssections were used to qualitatively evaluate the welds. Repeated welds were milled close to the center and mounted into clear epoxy resin for polishing. The orientation of the Octaspot™ weld path with respect to the machine axis was as follows: starts from the center, moves out to the positive X-axis, travels counter clockwise 450 degrees, and returns to center from the positive to
the negative Y-axis (Figure 10 and Figure 17). Keller’s reagent is a chemical etching was used to
enhance the difference of the weld nugget, TMAZ, HAZ, and parent material due to different grain structures. Keller’s reagent consists of 2.5% nitric acid (HNO
3
), 1.5% hydrochloric acid
(HCl), 1% hydrofluoric acid (HF), and 95% distilled water. Finally, pictures of the optical metallographic were documented and examined to reveal certain weld defects, nugget size, and joint interface defects. Weld defects, such as lack of consolidation or lack of fill, which looks
downward movement of the joint interface, both hooking and sheet lifting create a sheet-thinning defect on the upper or lower sheet of the welded coupon. Sheet thinning defects do appear in
Octaspot™ swept FSSW since it is a lap joint configuration, and changes of the loading path to a thinner sheet leads to premature failure in mechanical testing. Optical metallographic digital images and failure analysis of low Z-force Octaspot™ FSSW coupons on the tensile shear test were categorized and documented.
26
Figure 19. Worm Hole Defect in Octaspot™ FSSW.
Figure 20. Kissing Bond Defect in Plunge FSSW.
Figure 21. Sheet Lifting (left) and Hooking (right) in Lap FSW.
27
CHAPTER 5
Previous research has been performed using a 0.40-inch-diameter probe shoulder. This data was beneficial in taking steps toward effective low Z-force FSSW. Octaspot™ swept FSSW using the hybrid weld program consisted of position control in the plunge process and switching to load control in the sweep stage. Feedback from the Z-force (forge force) of the position control welds had two distinctive Z-force spikes, the probe spike and the shoulder spike, as the material was in contact with the pin tool during the initial plunge, which reached up to 2,000 lbf
(1,100 lbf spike of Z-force in addition to 900 lbf command force (Figure 22)). The Z-force spike
can be as high as 1,500 lbf to 2,000 lbf in addition to the command Z-force. The high Z-force spike created by the pin tool shoulder was undesirable for this low Z-force study because it is beyond the force capability of most robotic arms.
FSW07079_01_9
2500
2000
1500
1000
500
0
347 348 349 350
Forge Force Cmd, lbf
351
Time (sec)
352 353 354
Forge Force Fbk, lbf
355 356
Forge Fbk, in
357
0
0.1
0.05
0.3
0.25
0.2
0.15
Figure 22. Command and Feedback Plot for Typical Octaspot™ FSSW
(Hybrid Weld Program).
28
Therefore, a few possible solutions to reduce these spikes were considered: predrilling before FSSW, preheating before FSSW, decreasing initial plunge depth, increasing spindle speed, increasing dwell time, and decreasing plunge rate. Most of these possible solutions were tested using the existing hybrid weld program, and the data from feedback forces was compared directly with existing FSSW data. Predrilling and preheating before FSSW were not investigated because the additional steps required for drilling and heating would increase the cycle time to complete a spot weld. The remaining solutions were unsuccessful when implemented with the existing hybrid weld program. Plunge depth was decreased from 0.005 inch to 0.001 inch, but Zforce spike was not eliminated. Spindle speed increased up to 2,000 rpm created a hotter weld and decreased the Z-force spike but was unable to eliminate it. Plunge rate decreased from 17 ipm to 1 ipm, which created a slower weld at the plunge stage and a distinctive probe spike and shoulder spike. Dwell time increased from 1 second to 5 seconds before the swept stage tended to reduce the Z-force spike. The Z-force spike was not eliminated, but trends of lower Z-force spike were observed from the feedback forces plots. Therefore, the final option was to modify the hybrid weld program to a load control weld program. Existing data of the 0.40-inch-diameter shoulder weld using the hybrid weld program was used as a benchmark for Z-force and UTL comparison.
A position-control weld program was used to determine an appropriate Z-force for a corresponding hybrid weld program. The position-control weld program was also used to estimate a required Z-force to maintain the tool depth while in the swept stage of the weld. The
0.40-inch-diameter shoulder created a spike up to 3,000 lbf, which decreased to an average of
1,700 lbf during the sweep stage of the FSSW (Figure 23), whereas the 0.30-inch-diameter
shoulder spiked up to 3,500 lbf and continuously dropped to an average of 800 lbf at the end of
29
the sweep stage (Figure 24). The reduction of Z-force at the end of the sweep stage for the 0.30-
inch-diameter shoulder showed that a lower Z-force could be achieved simply by reducing the shoulder diameter. The data also suggest that all position control aspects of the weld program should be eliminated and performed under load control in order to eliminate the Z-force spike in
Octaspot™ FSSW.
Using the estimated average load of 900 lbf from position control and applying it to the load control weld program successfully produced Octaspot™ FSSW with a small Z-force spike.
The Z-force spike was lowered to 1,000 lbf; with command force of 900 lbf with additional
shoulder spike of 100 lbf (Figure 25).
3500
3000
2500
CFSP08302_1_5
3000 lbf
0.3
0.25
Average 1700 lbf
0.2
2000
0.15
1500
0.1
1000
0.05
500
0
197 199 201
Forge Force Fbk, lbf
203
Time (sec)
205
Forge Fbk, in
207
Forge Cmd, in
209
0
Figure 23. Command and Feedback Plot of 0.40-Inch-Diameter Psi™ Tool Welded with
Position Control.
30
CFSP08301_1_5
4000
3500
3000
2500
2000
1500
1000
500
0
210
3500 lbf
800 lbf
0.3
0.25
0.2
0.15
0.1
0.05
212 214 216
Time (sec)
218 220 222
0
Forge Force Fbk, lbf Forge Fbk, in Forge Cmd, in
Figure 24. Command and Feedback Plot of 0.30-Inch-Diameter Psi™ Tool Welded with
Position Control.
CFSP08301_11
1200
1000
800
600
400
0.3
0.25
0.2
0.15
0.1
200 0.05
0
53 55 57
Forge Force Cmd, lbf
59
Time (sec)
61 63
Forge Force Fbk, lbf
65
Forge Fbk, in
67
0
Figure 25. Command and Feedback Plot for Low Z-Force Swept FSSW.
The load-control weld program, known as the low Z-force weld program, successfully created Octaspot™ FSSW with a low Z-force of 900 lbf, desirable joint interface, and a fully consolidated weld nugget. The weld joint interface of low Z-force Octaspot™ FSSW is shown in
31
Figure 26, using a Psi™ tool with a 0.30-inch-diameter shoulder, and corresponds to the Z-force
feedback shown in Figure 25. The weld also exhibited a desirable joint interface with minimal or
no hooking, as shown in Figure 27.
Figure 26. Low Z-Force Cross-Sectional Metallographic (1.2X).
(a) (b)
Figure 27. Joint Interface of Figure 26 (100X): (a) Left Side and (b) Right Side.
Using the same tool and lowering the commanded Z-force to 700 lbf, the command and
feedback force plot shows no spike of Z-force and only fluctuation of 50 lbf (Figure 28). The
load-control weld program significantly reduces the spike of Z-force, and a combination using a low-commanded Z-force below 700 lbf can eliminate the Z-force spike. The surface faying interface has minimal to no hooking for the swept FSSW welded with 700 lbf of commanded Zforce.
32
CFSP08301_12
800
700
600
500
400
300
200
100
0
54
0.3
0.25
0.2
0.15
68
0
0.1
0.05
56 58
Forge Force Cmd, lbf
60 62
Time (sec)
Forge Force Fbk, lbf
64 66
Forge Fbk, in
Figure 28. Command and Feedback Plot for Low Z-Force Swept FSSW.
5.2 Concave Shoulder Tool Study (Phase 1)
To further investigate strategies for reducing the Z-force, three essential process parameters—Z-force, spindle speed, and travel speed—were studied in further detail while all other parameters were held constant. Process parameters were investigated using Box-Behnken
DOE to show correlations between UTL and these three process parameters. The first DOE had a process parameter low and high range of 4 ipm to 8 ipm for travel speed, 700 lbf to 1,100 lbf for
Z-force, and 800 rpm to 1,200 rpm for spindle speed with a midpoint (three levels). The UTL of unguided single spot lap shear was used to correlate with the process parameters.
5.3 Concave Shoulder Diameter Study
In this part of the research, two pin tool designs were used to study the effects of shoulder diameter on Z-force process parameter. Pin tool designs included Psi™ and Counterflow™ with two five-degree concave shoulder diameter sizes of 0.30 inch and 0.40 inch.
33
5.3.1 Psi™ Tool (0.30 Inch and 0.40 Inch)
Low Z-force specimens were welded with two pin tool diameters, 0.30 inch and 0.40 inch, using a concave shoulder with a Psi™ tool probe. UTL increased for the 0.30-inch-
diameter shoulder specimens as the Z-force decreased (Figure 29). On the other hand, as the
UTL decreased, the Z-force decreased for the 0.40-inch-diameter shoulder (Figure 30).
UTL
Figure 29. Main Effects Plot of 0.30-Inch-Diameter Concave Shoulder Psi™ Tool.
UTL
Figure 30. Main Effects Plot of 0.40-Inch-Diameter Concave Shoulder Psi™ Tool.
34
Cross-sectional metallographic analysis using optical microscopy provided more evidence to support this trend. The 0.30–inch-diameter concave shoulder with the Psi™ pin welded at Z-force of 1,100 lbf over-plunged, which created sheet thinning in the top sheet and an
Figure 31. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Psi™ Tool at 1,100 lbf.
Figure 32. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Psi™ Tool at 900 lbf.
Figure 33. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Psi™ Tool at 700 lbf.
The 0.40-inch-diameter concave shoulder of the Psi™ Tool welded at Z-force of 1,100 lbf and 900 lbf created a wide weld nugget, a wide flow arm with adequate plunge depth, and no
35
0.050 in
Figure 34. Low Z-Force Swept FSSW with 0.40-Inch-Diameter Psi™ Tool at 1,100 lbf.
0.050 in
Figure 35. Low Z-Force Swept FSSW with 0.40-Inch-Diameter Psi™ Tool at 900 lbf.
Figure 36. Low Z-Force Swept FSSW with 0.40-Inch-Diameter Psi™ Tool at 700 lbf.
From the metallographic inspection shown in Figures 34 to Figure 36 , the pin tool with
the wider shoulder diameter created a deeper flow arm and wider TMAZ and HAZ zones (V-
shaped nugget, as shown in Figure 34 and Figure 35), with sufficient Z-force of 1,100 lbf and
900 lbf, respectively. The 0.40–inch-diameter shoulder showed less sensitivity at a higher and wider range of Z-force from the metallographic observation and ultimate tensile load. At Z-force of 700 lbf, the pin tool shoulder without sufficient Z-force created a worm hole, and lack of contact of the shoulder with the weld coupon created no flow arm with minimal TMAZ and HAZ
zones (U-shaped nugget, as shown in Figure 36), whereas the 0.30-inch-diameter shoulder
36
showed higher sensitivity at a similar range of Z-force compared to the 0.40-inch-diameter shoulder in metallographic observation and UTL.
Table 3 shows the results of average UTL for respective shoulder diameters and Z-forces, which indicates that at a high Z-force of 1,100 lbf, the average UTL of the 0.30-inch-diameter shoulder is low at 816 lbf, and at a low Z-force of 700 lbf, the average UTL of the 0.40-inch-
diameter shoulder is low at 1,050 lbf. Table 3 agrees with the main effect plots shown in Figure
TABLE 3
AVERAGE UTL AND CORRESPONDING Z-FORCES APPLIED USING CONCAVE
SHOULDER PSI™ TOOL
Shoulder Diameter\
Average UTL 700 lbf
Z-Forces Applied
900 lbf
0.30 inch
0.40 inch
1,119 lbf
1,050 lbf
Average UTL results refer to Appendix C
5.3.2 Counterflow™ Tool (0.30 Inch and 0.40 Inch)
1,113 lbf
1,192 lbf
1,100 lbf
816 lbf
1,216 lbf
Counterflow™ tool welded joints with two shoulder diameter sizes of 0.30 inch and 0.40 inch. The main effects plot shows a similar trend to the results of the Psi™ tool when welded with similar weld parameters. The 0.30-inch-diameter concave shoulder shows better
performance at low Z-force compared to the 0.40-inch-diameter shoulder (Figure 37 and Figure
37
UTL
Figure 37. Main Effects Plot of 0.30-Inch-Diameter Concave Shoulder Counterflow™ Tool.
UTL
Figure 38. Main Effects Plot of 0.40-Inch-Diameter Concave Shoulder Counterflow™ Tool.
Metallographic cross-sectional analysis of the 0.30-inch-diameter concave shoulder of the
Counterflow™ tool shows similar trends as that which occurred with the Psi™ tool. Figure 39
shows that over-plunging created sheet thinning at the exit hole, and the top sheet indicating
flash at Z-force of 1,100 lbf is similar to what is shown in Figure 31. Figure 40 shows slightly
over-plunging with minimal amount of flash at Z-force of 900 lbf, which is similar to what is
shown in Figure 32. Figure 41 shows a good weld nugget with adequate plunge at Z-force of 700
lbf, similar to what is shown in Figure 33.
38
Figure 39. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Counterflow™ Tool at 1,100 lbf.
Figure 40. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Counterflow™ Tool at 900 lbf.
Figure 41. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Counterflow™ Tool at 700 lbf.
Figure 42 and Figure 43 showing welds with a 0.40–inch-diameter concave shoulder with
the Counterflow™ tool at Z-force of 1,100 lbf and 900 lbf, respectively, show wider HAZ and
TMAZ zones (V-shaped nuggets), similar to what occurred with the 0.40–inch-diameter Psi™ tool. A 0.40-inch-diameter shoulder creates excessive heat and wider TMAZ and HAZ zones, which changes the properties of the parent material and can significantly reduce overall strength of the weld nugget.
39
0.050 in
Figure 42. Low Z-Force Swept FSSW with 0.40-Inch-Diameter Counterflow™ Tool at 1,100 lbf.
0.050 in
Figure 43. Low Z-force Swept FSSW with 0.40-Inch-Diameter Counterflow™ Tool at 900 lbf.
Table 4 shows the results of average UTL for respective shoulder diameters and Z-forces.
At a high Z-force of 1,100 lbf, the average UTL of a 0.30-inch-diameter shoulder is low at 1,013 lbf. At low Z-force of 700 lbf, the average UTL of a 0.40-inch-diameter shoulder is not available.
Table 4 agrees with the main effect plots shown in Figure 37 and Figure 38.
TABLE 4
AVERAGE UTL AND CORRESPONDING Z-FORCES APPLIED USING CONCAVE
SHOULDER COUNTERFLOW™ TOOL
Shoulder Diameter\
Average UTL 700 lbf
Z-Forces Applied
900 lbf 1,100 lbf
0.30 inch
0.40 inch
1,165 lbf
NA
1,184 lbf
1,178 lbf
1,013 lbf
1,166 lbf
Average UTL results refer to Appendix C
The Counterflow™ tool with different shoulder diameters of 0.30 inch and 0.40 inch has similar results and trends compared to the Psi™ tool. The 0.40–inch-diameter Counterflow™ tool was unable to plunge at 700 lbf Z-force because the tip of the probe has a larger surface area
40
compared to the Psi™ tool. The 0.30-inch-diameter shoulder pin tool for both the Psi™ tool and
Counterflow™ tool showed a better performance and achieved comparable UTL to the 0.40inch-diameter shoulder pin tool at lower Z-force using a low Z-force weld program. Since the shoulder diameter investigation confirmed that the small shoulder can achieve lower Z-force, the remaining pin tool design of the Modified Trivex™, Duo V-flute™, and Tri V-flute™, all with
0.40-inch-diameter shoulders was not investigated. Phase 2 of the study of shoulder features used one tool selection based on phase 1 results with the 0.30-inch-diameter shoulder only. The remaining phase 1 of this project was an investigation into different probe designs affecting the
Z-force and mechanical properties of swept FSSW using a 0.30-inch-diameter concave shoulder.
5.4 Probe Design Study with 0.30-Inch-Diameter Concave Shoulder
In the remainder of phase 1 (probe design study), the Modified Trivex™, Duo V-flute™, and Tri V-flute™ pin tools with 0.30-inch-diameter concave shoulders were included in the study and welded with the low Z-force weld program with similar weld parameters as the Psi™ and Counterflow™ tools. The different probe designs affected the nugget joint area and joint interface morphology, both of which significantly affect UTL.
The Modified Trivex™ tool welded joints with similar weld parameters had a significantly lower average UTL of 911 lbf in the first DOE. The weld nugget metallographic
defect created sheet thinning on the upper sheet, which carried a significantly lower UTL. All four metallographic cross-section specimens had hooking defects.
41
Besides metallographic analysis and UTL values, failure mode was another indication of
the hooking defect. All coupons tested in DOE 1 showed plug pull-out failure (Figure 48). The
Wankel’s triangular probe shape of the Modified Trivex™ tool promoted volumetric side material movement due to the probe’s small physical to swept unit volume ratio. The triangularshaped probe tip area of the Modified Trivex™ was smaller compared to the circular-shaped
probe tip area of the Psi™ and Counterflow™ tools (Figure 14) (see Figure 9 and Table 1). This
finding led to an investigation of correlations of the probe’s physical to swept unit volume ratio with different probe shapes to reduce volumetric side material movement. Volumetric side material movement may promote hooking defects in a lap joint weld.
Metallographic analysis for DOE 1 shows that the 0.30-inch-diameter concave shoulder
over-plunged at 1,100 lbf Z-force creates excessive flash (Figure 44), slightly over-plunged at
900 lbf Z-force creates some flash (Figure 45), and an adequate plunge at 700 lbf Z-force (Figure
46). This trend is similar to that of Psi™ and Counterflow™ tools.
Figure 44. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Modified Trivex™ Tool at 1,100 lbf.
42
Figure 45. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Modified Trivex™ Tool at 900 lbf.
Figure 46. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Modified Trivex™ Tool at 700 lbf.
(a) (b)
Figure 47. Joint Interface of Figure 46 (100X): (a) Right Side and (b) Left Side.
0.250 in
Figure 48. Plug Pull-Out Failure Mode.
43
The Duo V-flute™ tool welded joints with similar weld parameters as in first DOE had a similar trend of weld nugget as that of the 0.30-inch-diameter Psi™, Counterflow™, and
some flash, and Figure 51 shows adequate plunging at 700 lbf Z-force. Since the magnification
of 1.2X is not enough to reveal hooking defects, the 100X magnification of metallographic
analysis shown in Figure 52 indicates that no hooking occurred at the faying surface interface.
Figure 49. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Duo V-Flute™ Tool at 1,100 lbf.
Figure 50. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Duo V-Flute™ Tool at 900 lbf.
44
Figure 51. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Duo V-Flute™ Tool at 700 lbf.
(a) (b)
Figure 52. Joint Interface of Figure 51 (100X): (a) Right Side and (b) Left Side.
The Tri V-flute™ tool welded joints with similar weld parameters as the first DOE had a similar weld nugget trend as that of the 0.30-inch-diameter Psi™, Counterflow™, Modified
magnification of 1.2X is not enough to reveal hooking defects, the 100X magnification of
metallographic analysis shown in Figure 56 indicates that no hooking occurred at the faying
surface interface.
45
Figure 53. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Tri V-flute™ Tool at 1,100 lbf.
Figure 54. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Tri V-flute™ Tool at 900 lbf.
Figure 55. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Tri V-flute™ Tool at 700 lbf.
(a) (b)
Figure 56. Joint Interface of Figure 55 (100X): (a) Right Side and (b) Left Side.
46
5.5 Achievement in Concave Shoulder Study (Phase 1)
5.5.1 Concave Shoulder Diameter Study
Position control was found to be not suitable for low Z-force application on Octaspot™ swept FSSW due to the sudden increase in Z-force spikes. Using position control, the 0.30-inchdiameter shoulder shows a promising decrease of Z-force at the end of Octaspot™ swept FSSW.
The weld program was modified to load control, and Z-force spikes were reduced significantly and even eliminated. The 0.30-inch-diameter shoulder welded with the load-control weld program performed better than the 0.40-inch-diameter shoulder at low Z-force. Although performance of the 0.30-inch-diameter shoulder was better, sensitivity of the Z-force increased significantly, thus affecting variation in plunge depth. The average UTL of low Z-force weld coupons with a 0.30-inch-diameter shoulder were comparable with average UTL of high Z-force spike weld coupons with a 0.40-inch-diameter shoulder. Since the 0.40-inch-diameter shoulder requires higher Z-force, it was delineated from further study.
Using the same weld parameters as in the DOE 1 for five different probe designs showed no significant increase of weld nugget area for Octaspot™ swept FSSW using the low Z-force
weld program (Figure 57 to Figure 61). Since the path and radius of Octaspot™ was similar, the
weld nugget size was similar across the five pin tool designs. The variation of weld nugget size was due to different depths of polishing. Probe designs were analyzed for two main categories: shape and features. The Modified Trivex™ has a Wankel’s triangular-shaped smaller probe tip area compared to the other four pin tools that have a circular-shaped probe. The Psi™ tool with three inclined flats slightly reduced the probe-tip area. A small probe-tip area is recommended to further reduce the Z-force required for FSSW. Although a small probe-tip area reduced the
47
plunging Z-force, the small ratio of the probe’s physical to swept unit volume increased the swept volume, which in turn promoted side material movement, thus creating the hooking defect.
Figure 57. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Counterflow™ Tool at 700 lbf.
Figure 58. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Psi™ Tool at 700 lbf.
Figure 59. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Modified Trivex™ Tool at 700 lbf.
Figure 60. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Duo V-Flute™ Tool at 700 lbf.
48
Figure 61. Low Z-Force Swept FSSW with 0.30-Inch-Diameter Tri V-Flute™ Tool at 700 lbf.
Table 5 shows the first DOE UTL minimum, maximum, average, and standard deviation
values for five different probe designs. Figure 62 shows the average UTL with standard
deviation comparison between a 0.30-inch-diameter concave shoulder with five different probe designs and high Z-force spike 0.40-inch-diameter benchmark UTL value. From the first DOE, the average UTL of all tools was comparable to the average UTL of high Z-force, except the
Modified Trivex™ tool. Figure 62 shows no significant effect of the five probe designs to
variation in UTL of Octaspot™ FSSW due to a large standard deviation.
TABLE 5
COMPILATION OF DOE 1 UTL RESULTS FOR PROBE DESIGN STUDY OF 0.30-INCH-
DIAMETER CONCAVE SHOULDER
Pin Tools\UTL Min Max Average
Standard
Deviation
Psi™
Counterflow™
Modified
Trivex™
Duo V-Flute™
624 lbf
905 lbf
785 lbf
600 lbf
Tri V-Flute™ 847 lbf
UTL results refer to Appendix C
1,208 lbf
1,261 lbf
1,036 lbf
1,231 lbf
1,240 lbf
1,036 lbf
1,133 lbf
911 lbf
1,016 lbf
1,063 lbf
163 lbf
102 lbf
61 lbf
175 lbf
127 lbf
49
Low Z-force Swept FSSW 0.30 inch Shoulder Diameter
1400
1200
1000
800
600
400
200
0
Psi
Counterflow
Trivex
Duo V-flute
Tri V-flute
High Z-force
DOE 1
Figure 62. UTL Results Comparison of Low Z-Force Octaspot™ Swept FSSW for
Five Pin Tools with 0.30-Inch-Diameter Concave Shoulder in DOE 1.
Since the first DOE was designed to accommodate the wide variation of probe designs and shoulder diameters, optimization of the weld parameters was required to achieve higher and precise UTL. Other factors include metallographic analysis to avoid over-plunging by reducing the maximum Z-force from 1,100 lbf to 950 lbf and reduction in cycle time by increasing the maximum travel speed from 8 ipm to 13 ipm. Statistical analysis of weld parameters also played a minor role in weld parameter selection. The main effects plots of DOE 1 for all tools were
analyzed. The main effects plot shown in Figure 29 indicates that Z-force had a quadratic trend
line with a maximum point between 700 lbf and 1,100 lbf, travel speed had a quadratic trend line with a minimum point between 4 ipm and 8 ipm, and spindle speed had a linear trend line with a maximum point at 800 rpm and minimum point at 1,200 rpm. The main effects plot shown in
Figure 37 indicates that Z-force had a quadratic trend line with a maximum point between 700
lbf and 1,100 lbf, travel speed had a quadratic trend line with a minimum point at 4 ipm and maximum point at 8 ipm, and spindle speed had a quadratic trend line with a maximum point between 800 rpm and 1,200 rpm. From these two main effects plots, extrapolation of weld
50
parameters did not stand true but indicated that an increase in travel speed will further increase
UTL. Increase of travel speed is another factor that contributed to the reduction of cycle time of welding. Weld program optimization also contributed to a reduction in weld cycle time, and dwell time was reduced by an increase in acceleration rate of spindle rotational. Dwell time was reduced from 7 seconds to 5 seconds and finally to 2 seconds by optimization of weld programs
(refer to Appendix B).
5.6 Optimization Weld Parameters (DOE 2)
The first DOE was created to find the process window, and the second DOE was created to achieve maximum UTL for all tools. Using Box-Behnken DOE, weld parameters in both a low and high range were selected, travel speed was 7 ipm to 13 ipm, Z-force was 750 lbf to 950 lbf, and spindle speed was 800 rpm to 1,100 rpm with a mid-point. The coupons were naturally aged for a minimum of four days before tensile testing. The weld panels contained a total of 21 spot welds, with six coupons having repeated weld parameters for metallographic analysis.
In addition to optimizing the weld program, the weld cycle time was further reduced as a result of optimizing the weld parameters in DOE 2. The low travel speed range (4-8 ipm) was increased to a high travel speed range (7-13 ipm). This increase of travel speed reduced its weld time significantly: an increase in travel speed from 4 ipm to 13 ipm reduced the weld time from
15 seconds to 7 seconds (refer to Appendix B). A total cycle time of five welds was analyzed and compared and resulted in a total reduction of five seconds (refer to Appendix B). The fastest
Octspot™ swept FSSW was completed in a total time of nine seconds for each weld: two seconds dwell time and seven seconds weld time.
51
Table 6 shows that the reduction of the standard deviation for all tools increases the precision and repeatability of Octaspot™ FSSW by optimization through the response surface method. Only the Psi™ tool had the highest standard deviation, almost double or triple compared to the other tools. Hooking defects in all metallographics of the Modified Trivex™ tool contributed to the low UTL values in DOE 2. The Wankel’s triangular-shaped Modified
Trivex™ tool with a small probe physical to swept unit volume ratio had a large side volumetric displacement. Side volumetric displacement created the hooking defect in all welded coupons.
TABLE 6
COMPILATION OF DOE 2 UTL RESULTS FOR PROBE DESIGN STUDY OF 0.30-INCH-
DIAMETER CONCAVE SHOULDER
Pin Tool\UTL Min Max Average
Standard
Deviation
Psi™
Counterflow™
731 lbf
1,049 lbf
Modified Trivex™ 874 lbf
Duo V-Flute™ 976 lbf
1,234 lbf
1,204 lbf
1,024 lbf
1,255 lbf
1,143 lbf
1,117 lbf
958 lbf
1,176 lbf
129 lbf
45 lbf
44 lbf
76 lbf
Tri V-Flute™ 1,021 lbf
UTL results refer to Appendix C
1,245 lbf 1,173 lbf 63 lbf
Figure 63 shows that the Psi™ tool was able to match the average UTL of the
Counterflow™ tool on the second DOE with a slightly reduced standard deviation, whereas the average UTL of the Counterflow™ tool dropped 16 lbf but the standard deviation was reduced by half. The average UTL of the Duo V-flute™ and Tri V-flute™ increased, and the standard deviation was reduced by half. The precision and repeatability of Octaspot™ swept FSSW increased as the range of weld parameters decreased by optimization of the process parameters.
Metallographic cross-sections show minimal to no over-plunging, with minimal to no hooking defects, except for the Modified Trivex™ tool.
52
Low Z-force Swept FSSW 0.30 inch Shoulder Diameter
1400
1200
1000
800
600
400
200
Psi
Counterflow
Trivex
Duo V-flute
Tri V-flute
High Z-force
0
DOE 1 DOE 2
Figure 63. UTL Results Comparison of Low Z-Force Octaspot™ Swept FSSW for
Five Pin Tools with 0.30-Inch-Diameter Concave Shoulder in DOE 1 and DOE 2.
Four tools showed the least significant effect of probe design to variation in UTL for
Octaspot™ swept FSSW, except the Modified Trivex™ tool. The radical probe shape of the
Modified Trivex™ tool with a small physical to swept unit volume ratio contributed to the variation of UTL due to the hooking defect. However, features on the probe, such as vertical flutes, inclined flats, threads, and opposing inclined flutes, contributed minimally to the variation of UTL in both DOEs. The features on the probes, such as threads, flutes, and flats, had a minimal effect on the tensile load due to the identical closed-loop path achieving closer values of the tensile load results. Features such as inclined flutes are preferred, due to the clean shear on the advancing side and minimal or no hooking at the joint interface. In Octaspot™ swept FSSW, the shape of the probe with the small ratio of physical to swept unit volume may promote the side displacement of material, which creates the hooking defect.
53
Surface oxide of the weld coupon at the joint interface and pin tool contact interface was removed using a dual-action sander. Different operators removed a varied amount of surface oxide, which may have contributed to the reduction of the weld quality. However, all pin tools, except the Modified Trivex™, were welded with surface oxide remaining on the weld coupons.
MEK wipes remove dirt and oil without removing surface oxide.
Figure 64 shows that there was no reduction in average UTL, the amount of surface oxide
removed are not significant to the variation of UTL for Octaspot™ swept FSSW. The standard deviation of UTL for all tools increased slightly except for the Psi™ tool, where the standard deviation decreased. Therefore, reducing the surface preparation step in the manufacturing process can significantly save time as well as the cost of labor and consumables without sacrificing UTL.
Low Z-force Swept FSSW 0.30 inch Shoulder Diameter
1400
1200
1000
800
600
400
200
0
DOE 2 No Prep
Figure 64. UTL Results Comparison of Low Z-Force Octaspot™ Swept FSSW for
Four Pin Tools with No Surface Preparation in DOE 2.
Psi
Counterflow
Trivex
Duo V-flute
Tri V-flute
High Z-force
54
The surface finish of each spot weld is very important, as the excessive expulsion of aluminum, known as flash generation, creates debris and requires post-weld touchup. Since the shoulder diameter was reduced from 0.40 inch to 0.30 inch for a lower Z-force, the small
shoulder was unable to capture material displaced by the probe, thus creating a flash (Figure 65).
Modifying the tilt angle weld parameter from half a degree to one degree significantly reduced
the amount of flash (Figure 66). In the manufacturing process, the elimination of debris and post-
weld touchup can significantly reduce cost and manufacturing time.
Figure 65. Low Z-Force FSSW with 0.30-Inch-Diameter Concave Shoulder with
Half-Degree of Tilt Angle.
Figure 66. Low Z-Force FSSW with 0.30-Inch-Diameter Concave Shoulder with
One-Degree of Tilt Angle.
5.9 Scroll Shoulder Tool (0.30 Inch) Study (Phase 2)
In the second phase, the flat scrolls shoulder was studied for comparison with concave shoulder pin tools. The effects of flat scrolls were also observed on the surface finish, crosssectional metallographic, and UTL. Only one pin tool probe design, Duo V-flute™, was selected for this study due to budget and time constraints. From the concave shoulder diameter study and probe design study results in phase one, it was not necessary to study the effects of the features of flat scrolls on all pin tool designs.
55
5.9.1 Achievement Duo V-Flute™ Scroll
Weld parameters used for the Duo V-flute™ Scroll pin tool were selected from a 0.30inch-diameter concave shoulder DOE 2, at 800 rpm to 1,100 rpm, 7 ipm to 13 ipm, and 750 lbf to 950 lbf. Using the same weld parameters and probe features, the flat scrolls feature compared fairly against the concave feature. The surface finish of Octaspot™ swept FSSW welds of flat scrolls is not as smooth as the concave shoulder because the flat scrolls feature extends out of the
shoulder lip (Figure 67). The amount of flash generated using the flat scroll shoulder was less
compared to the concave shoulder welded with similar weld parameters (Figure 65). The flat
scrolls shoulder captured and directed material inward, generating a smaller amount of flash. The concave shoulder tool required changing the tilt angle to one degree to reduce the amount of
flash generation (Figure 66), whereas the flat scrolls shoulder generated no flash with a half-
degree of tilt angle.
Figure 67. Low Z-Force FSSW with 0.30-Inch-Diameter Flat Scrolls Shoulder with
Half-Degree of Tilt Angle.
The average UTL of the Duo V-flute™ Scroll was 1,147 lbf, with a standard deviation of
50 lbf. The average UTL of the Duo V-flute™ Scroll was comparable to the Psi™,
Counterflow™, Duo V-flute™, and Tri V-flute™ concave shoulder tools. The standard deviation
of the flat scrolls shoulder was lower compared to the concave shoulder (Figure 68).
56
Low Z-force Swept FSSW 0.30 inch Diameter Shoulder
1400
1200
1000
800
600
400
200
0
Psi
Counterflow
Trivex
Duo V-flute
Tri V-flute
High Z-force
Duo V-flute
Scroll
DOE 2
Figure 68. UTL Results Comparison of Low Z-Force Octaspot™ Swept FSSW for
0.30-Inch-Diameter Scroll Shoulder Duo V-flute™ in DOE 2.
The Z-force feedback plot shows no Z-force spike to a maximum spike of 100 lbf, in addition to the commanded Z-force. The fluctuation of Z-force about 50 lbf was observed in all
15 welds. Metallographic analysis showed some degree of hooking at the surface interface up to
0.008 inch. The Duo V-flute™ with concave shoulder showed no sign of the hooking defect, but the Duo V-flute™ with flat scrolls shoulder had hooking defects. The flat scrolls features might promote a more aggressive flow arm directing material inward, thus creating hooking defects.
Recent discovery that the pin tool holder had worn out and because the pin tool had run out up to
0.010 inch might also be another cause for the hooking defect. Flat scroll features do not reduce the Z-force compared to the concave shoulder with the same shoulder diameter.
5.10 Featureless Probe Shape Study (Phase 3)
The results of low average UTL coupled with metallographic analysis of the Modified
Trivex™ tool confirmed the hooking defect in all 15 welds of the DOE. The concave pin tool study of different features on probe designs led to a study of probe shape, which showed that all four pin tools with circular-shaped probe designs performed better than the triangular-shaped
57
Trivex™ pin tool. Therefore, a full parametric study of probe shape was initiated to investigate the relationship of the probe physical to swept unit volume ratio and the hooking defect. It was hypothesized that increasing the number of sides of the probe to make it closer to a circular shape, or a ratio of probe physical to swept unit volume closer to 1, might reduce the hooking
defect (Figure 9 and Table 1). Due to budget and time constraints, three pin tools were selected
for this study: octagon, pentagon, and Trivex™ (Figure 15). The following weld parameters from
DOE 2 were utilized: 800 rpm to 1,100 rpm, 7 ipm to13 ipm, and 750 lbf to 950 lbf.
The Featureless Trivex™ pin tool achieved average UTL of 915 lbf with a standard deviation of 50 lbf. The corresponding UTL and hooking defect ranged from 0.006 to 0.015 inch for the respective metallographic cross-sectional shown in Table 7. UTL values do not directly represent the severity of the hooking defect but more likely represent the set of process parameters. Metallographic analysis showed a similar size of the weld nugget area, except for the
presence of the hooking defect (Figure 69, Figure 70, and Figure 71). Since these metallographic
metallographic image corresponds to the right side of the metallographic sample. The threaded
Trivex™ probe in the phase 1 design study showed that it achieved a similar average UTL of 958 lbf with a standard deviation of 44 lbf. Thus, the threaded features on the edge of the Trivex™ probe did not significantly enhance the UTL value.
58
Featureless Trivex™
M16
M17
M18
M19
M20
TABLE 7
HOOKING DEFECT OF FEATURELESS TRIVEX™ PIN TOOL
Corresponding UTL
(lbf)
864
940
991
922
910
Hooking Defect (1/1000 inch)
Left Right
7
10
11
15
10
6
6
11
13
9
Figure 69. Featureless Trivex™ Cross-Sectional Metallographic M19.
Figure 70. Right Side of Figure 69 with 0.015 Inch Hooking Defect.
59
Figure 71. Left Side of Figure 69 with 0.013 Inch Hooking Defect.
60
The Featureless Pentagon™ pin tool achieved an average UTL of 1,093 lbf with a standard deviation of 66 lbf. The corresponding UTL and hooking defect ranged from 0 inch to
0.006 inch for the respective metallographic cross-sectional shown in Table 8. As with the
Trivex™ pin tool, severity of the hooking defect did not represent the UTL trend and depended on the set of process parameters. Metallographic analysis showed the presence of the hooking
defect, but this was less severe than with the Trivex™-shaped pin tool (Figure 72, Figure 73, and
Figure 74). These metallographic images were taken using an inverted microscope; therefore, the
left side of Figure 72 corresponds to the right side of the metallographic sample.
HOOKING DEFECT OF FEATURELESS PENTAGON™ PIN TOOL
Featureless Pentagon™
TABLE 8
Corresponding UTL
(lbf)
Hooking Defect (1/1000 inch)
Left Right
M16
M17
M18
M19
M20
988
1,038
1,072
1,119
1,134
2
6
2
5
4
0
2
2
2
1
Figure 72. Featureless Pentagon™ Cross-Sectional Metallographic M19.
61
Figure 73. Right Side of Figure 72 with 0.005 Inch Hooking Defect.
Figure 74. Left Side of Figure 72 with 0.002 Inch Hooking Defect.
62
The Featureless Octagon™ pin tool achieved an average UTL of 1,033 lbf with a standard deviation of 23 lbf. The corresponding UTL and hooking defect ranged from 0.002 to
0.009 inch for the respective metallographic in the cross-sectional shown in Table 9. UTL values do not directly represent the severity of the hooking defect but are more representative of the set of process parameters. Metallographic analysis showed a similar size of weld nugget area, except
for the presence of the hooking defect (Figure 75, Figure 76, and Figure 77 ). Since these
metallographic images were also taken with an inverted microscope, the right side of the image is the left side of the metallographic sample.
TABLE 9
HOOKING DEFECT OF FEATURELESS OCTAGON™ PIN TOOL
Featureless Pentagon™
M16
M17
M18
M19
M20
Corresponding UTL
(lbf)
1028
1029
1066
1015
1012
Hooking Defect (1/1000 inch)
Left Right
5
5
6
9
8
2
2
6
8
5
Figure 75. Featureless Octagon™ Cross-Sectional Metallographic M19.
63
Figure 76. Right Side of Figure 75 with 0.009 Inch Hooking Defect.
Figure 77. Left Side of Figure 75 with 0.008 Inch Hooking Defect.
64
5.11 Achievement in Featureless Probe Shape Study (Phase 3)
Table 10 shows the trend and summary of the hooking defect and its relationship to the ratio of probe physical to swept unit volume. The hooking defect values were recorded from five metallographic samples within the DOE weld parameters range. The hooking defect was averaged from four circular probes: Counterflow™, Psi™, Duo V-flute™, and Tri V-flute™. All hooking defect images were taken with an inverted microscope and measured using PaxIt™ image software. The depth of samples in a mount may vary, and the different amount of grinding and polishing of different mounted samples can affect the measurement of the hooking defect.
Therefore, a direct comparison of the hooking defect across different pin-tool metallographic samples becomes less accurate, and metallographic samples within the same pin tool but mounted in different setting cups will skew the hooking defect values. The hooking defect was recorded in a two-dimensional or one cross-sectional segment. All metallographic samples were polished as close to the center of the spot weld or slightly passed the center. In this study, metallographic analysis found that the hooking defect could be three-dimensional, which may vary around the weld nugget.
TABLE 10
SUMMARY OF HOOKING DEFECT AND RATIO OF PROBE PHYSICAL
Probe Shape
TO SWEPT UNIT VOLUME
UTL +/- Standard
Deviation (lbf)
Ratio of Probe
Physical to Swept
Unit Volume
Hooking Defect
(1/1000 inch)
Circular with Features
Featureless Octagon™
Featureless Trivex™
Threaded Trivex™
~ 1,150 +/-78
1,033 +/-23
Featureless Pentagon™ 1,093 +/-66
915 +/-50
958 +/-44
UTL results refer to Appendix C
1.000
0.891
0.764
0.414
0.414
~0-5
2-9
0-6
6-15
3-15
65
The hypothesis of reducing the hooking defect by increasing the ratio of probe physical to swept unit volume turned out to be false for this particular DOE set. Increasing the ratio of probe physical to swept unit volume was similar to increasing the number of sides from triangular, pentagon, and octagon, and did not show any trend supporting this hypothesis. However, the hypothesis is still plausible because from the Trivex™-shaped tool to the Pentagon-shaped tool, the hooking defect was reduced. Therefore, a full parametric investigation should be able to confirm this hypothesis. Hooking defects can be reduced or eliminated by features on the probe, such as the flutes, threads, flats, or combinations of more than one feature with the proper set of process parameters. Locations of features on the probe are also crucial to eliminating the hooking defect because threads at the edge of the Trivex™ pin tool did not reduce the hooking defect. A combination of features is also important because the probe with threads alone creates sheet thinning, but with additional features, the Counterflow flute reduces sheet thinning in the linear lap weld.
5.12 Probe Diameter Study (Phase 4)
In phase 1, the concave shoulder pin tool study, a probe with a 0.135-inch diameter was unable to plunge at certain weld parameters of low Z-force of 700 lbf, low spindle speed of 800 rpm, and high travel speed of 13 ipm. Probe designs with a small probe tip area, such as the
Psi™ tool with three inclined flats and the Trivex™ tool with a triangular-shaped probe were able to plunge at the lower extremes of the set of weld parameters mentioned previously.
Therefore, a reduction of probe diameter from 0.135 inch to 0.100 inch will further reduce the required Z-force to plunge below 700 lbf. During the design step of reducing probe diameter size, it was determined that shoulder diameter could be reduced from 0.30 inch to 0.25 inch
66
(Figure 16c). This pin tool with the Duo V-flute™ probe was designed to reduce the Z-force
below 700 lbf.
Although the pin tool was designed to achieve a lower Z-force, another main objective of this study was to maintain static UTL of 1,100 lbf. In Octaspot™, the spot radius was held constant with the same probe diameter, but the total weld radius had to be increased to compensate for the smaller probe diameter (Table 11). Increasing the spot radius to 0.100 inch with a 0.050-inch probe radius created a total weld radius of 0.150 inch, slightly higher than the current probe’s total weld radius of 0.148 inch.
TABLE 11
WELD RADIUS COMPENSATION FOR PROBE RADIUS REDUCTION
Pin Tool Probe Probe Radius Spot Radius Total Weld Radius
Current Probe
Small Probe
0.068 inch
0.050 inch
0.080 inch
0.080 inch
0.148 inch
0.130 inch
Small Probe 0.050 inch 0.100 inch 0.150 inch
Since this study used a new pin tool, new weld parameters range were selected to achieve a lower Z-force with a higher spindle speed range of 1300 rpm to 2000 rpm, travel speed range of 7 ipm to 13 ipm, and Z-force range of 450 lbf to 700 lbf. In addition to investigating spindle speed, travel speed, and Z-force weld parameters, tilt angle and spot radius were included.
Earlier investigations in phase 1 showed that an increase in the tilt angle improved the surface finish for a shoulder-diameter modification from 0.4 inch to 0.3 inch. The weld spot radius was increased to compensate for the decrease of probe radius to remain comparable to the weld radius to achieve a UTL of 1,100 lbf.
The average UTL results shown in Table 12 consist of a work order from CFSP09307_4,
5, and 6, with weld parameters of 1,300 rpm to 2,000 rpm, 7 ipm to 13 ipm, and 450 lbf to 700 lbf and optimization in work order CFSP09307_7 with weld parameters of 1,500 rpm to 1,800
67
rpm, 8 ipm to 12 ipm, and 500 lbf to 600 lbf. The average UTL with wide standard deviation was unable to provide significant results to confirm that the increase of tilt and spot radius increased the average UTL. Metallographic results provided additional information to explain the slightly lower average UTL and wide standard deviation.
TABLE 12
AVERAGE UTL AND STANDARD DEVIATION OF DOE 1
FOR PROBE DIAMETER STUDY
Work Order Average UTL (lbf) Standard Deviation
(lbf)
Tilt, Spot Radius
(degree, inch)
CFSP09307_4
CFSP09307_5
CFSP09307_6
813
872
909
291
300
245
0.5, 0.08
0.5, 0.10
1.0, 0.10
CFSP09307_7
UTL results refer to Appendix C
1,025 149 1.0, 0.10
One metallographic image (Figure 78) showed that a high spindle speed of 1,650 rpm
with a combination of slow travel speed of 7 ipm and high Z-force of 700 lbf caused the tool to
over plunge and the sheet to thin. Another metallographic image (Figure 79) showed that at a
low spindle speed of 1,300 rpm with a mid-travel speed of 10 ipm and low Z-force of 450 lbf, it was not possible create a consolidated weld nugget. An unconsolidated weld is one of the main reasons for a low average UTL and wide standard deviation. Good process parameters at a spindle speed of 1,650 rpm, travel speed of 10 ipm, and Z-force of 575 lbf corresponded to a
spindle speed of 2,000 rpm, travel speed of 13 ipm, and Z-force of 575 lbf, which yielded a UTL of 662 lbf. Obvious defects due to an improper combination of weld parameters was another contribution to lower average UTL and wide standard deviation. Metallographic images with
68
microdefects, which can only be detected at higher magnification with slightly reduced UTL to
1,000 lbf, were more difficult to analyze.
Figure 78. Metallographic Image of CFSP09307_6_M21.
Figure 79. Metallographic Image of CFSP09307_6_M17.
Figure 80. Metallographic Image of CFSP09307_6_M19.
Figure 81. Metallographic Image of CFSP09307_6_M23.
Although this DOE consists of weld parameters that can achieve a low Z-force of about
575 lbf with a high spindle speed up to 2,000 rpm, metallographic analysis showed defects, a surface oxide line defect, and a confirmed lower UTL value. Since the FSSW process is highly
69
dependent on the amount of heat input, spindle speed and travel speed can significantly affect the amount of Z-force that should be applied to obtain a sound FSSW. The concave shoulder diameter study in phase 1 revealed that shoulder diameter is another factor affecting the amount of Z-force required to produce a sound FSSW using the same weld parameters. Therefore, a second DOE was initiated with a lower spindle speed range of 800 rpm to 1,100 rpm, travel speed range of 7 ipm to 13 ipm, and Z-force range of 600 lbf to 800 lbf, similar to that used in the concave shoulder diameter study DOE except for the Z-force. UTL results showed that the Zforce at 600 lbf and a combination of low spindle speed of 800 rpm or 950 rpm and travel speed of 10 ipm or 13 ipm, respectively, were unable to produce a sound FSSW and was confirmed
with a metallographic image that looks similar to Figure 79. In the DOE 2, weld parameters in
combination with a Z-force of 700 lbf produced FSSW with a UTL above 1,000 lbf up to 1,100 lbf. Results showed that reduction of the shoulder diameter from 0.3 inch to 0.25 inch did not significantly reduce the amount of Z-force to produce a sound FSSW.
Optimization of the weld parameters by changing the Z-force range from 650 lbf to 750 lbf with a similar spindle speed and travel speed range yielded an average UTL of 1,091 lbf with a standard deviation of 45 lbf. Reduction of the shoulder diameter can increase the sensitivity of weld parameters: a Z-force range of at least 300 lbf for a 0.3-inch-diameter shoulder was reduced to 100 lbf for a 0.25-inch-diameter shoulder. The amount of heat input through frictional heat of the shoulder and probe can also affect the Z-force. A pin tool with a 0.1-inch-diameter probe with a 0.25-inch-diameter shoulder produced less frictional heat than a 0.135-inch-diameter probe with a 0.3-inch-diameter shoulder, which can increase the Z-force required to produce a sound FSSW. An optimum shoulder diameter can reduce sensitivity of weld parameters, lower the Z-force, and produce a sound FSSW.
70
In the DOE 2, the metallographic image in Figure 82 confirmed its respective UTL value
of 1,111 lbf showing no sign of defects. However, at high magnification, the metallographic
image in Figure 83 provided further details, which the UTL results were unable to detect, such as
microdefects and a surface oxide line. These are defects that cannot be detected by static shear testing because the defects are protected by the weld nugget, which is strengthen by fine, dynamically recrystallized grains. Some metallographic images from both DOEs showed some microdefects and surface oxide lines in the weld nugget. These microdefects and surface oxide lines can be a source of crack initiation, which can be detrimental in fatigue tests. Further investigation will be required to eliminate voids, and surface oxide line defects using more aggressive probe flute depths, and inadequate overlap of the probe radius and spot radius.
Figure 82. Metallographic Image of CFSP09307_12_M20.
71
Figure 83. Right Side of Nugget in Figure 82.
Although the Z-force was reduced by changing the weld parameter, pin tools have a unique range of weld parameters, which dictate the Z-force range. Pin tools with different shoulder and probe diameters and different probe designs with flutes, threads, flats, and shapes can also contribute to and limit the range of weld parameters. The second DOE using a 0.25inch-diameter shoulder and 0.1-inch-diameter probe welded with a similar spindle speed and travel speed of 0.30-inch-diameter shoulder and 0.135-inch-diameter probe achieved a reduction of 150 lbf Z-force. The change from a 0.4-inch-diameter shoulder to a 0.3-inch-diameter shoulder achieved a reduction of 250 lbf Z-force. The Counterflow™ tool reached the same UTL value, regardless of shoulder size, with a similar Z-force.
Pin tools have unique weld parameters because 0.4-inch-diameter and 0.3-inch-diameter shoulders have the same UTL with the same weld parameters, regardless of the difference in
72
shoulder size such as Counterflow™ (Table 13). However, for the Psi™, Duo V-flute™ and, Tri
V-flute™ tools with a 0.3-inch-diameter shoulder share a similar weld parameter set providing an average UTL of 1,200 lbf Octaspot™ swept FSSW (Table 13). Optimum weld parameters for the Counterflow™ tool with the same weld parameters can be welded with different shoulder sizes and achieve the same UTL. In general, a reduction of shoulder diameter will reduce the Zforce to obtain a sound FSSW (Table 13).
Table 13 shows a reduction of Z-force as the pin-tool shoulder size was reduced from 0.4 inch to 0.3 inch, and the UTL remains at about 1,200 lbf, based on three coupons from DOE 1 or
2. A reduction of the probe diameter to 0.1 inch and shoulder diameter to 0.25 inch for the Duo
V-flute pin tool dropped the UTL to 1,090 lbf. Microdefects and surface oxide defects could contribute to a reduction of UTL. A reduction of 150 lbf Z-force was noticeable as the shoulder diameter was reduced from 0.3 inch to 0.25 inch. An increase of spindle speed from 950 rpm to
1,650 rpm also reduced the Z-force another 125 lbf, while maintaining the UTL at 1,090 lbf.
Table 13
Pin Tool
Psi
Counterflow
Counterflow
Psi, Duo, and
Tri V-Flute
Duo and Tri
V-Flute
Z-FORCE REDUCTION AND CORRESPONDING PIN TOOLS
AND WELD PARAMETERS
Shoulder
Diameter
Probe
Diameter Rpm
Weld Parameters
Ipm Z-Force
0.40
0.40
0.40
0.30
0.30
0.135
0.135
0.135
0.135
0.135
800
1,500
1,000
950
1,100
Counterflow 0.30 0.135 1,000
Duo V-Flute Scroll 0.30 0.135 1,100
Duo V-Flute
Duo V-Flute
0.25
0.25
UTL results refer to Appendix C
0.100 950
0.100 1,650
6
12
6
10
10
6
10
10
10
1,100
1,100
900
850
850
900
950
700
575
73
UTL
<1,200
<1,187
<1,200
<1,200
<1,200
<1,200
<1,200
<1,090
<1,090
CHAPTER 6
The results of this study show that programmable load control enables low Z-force
FSSW. Conversely, a position-controlled weld program’s feedback forces cannot be controlled to produce low Z-force FSSW. This is due to the sudden increase in normal force (Z-force spike) when the tool shoulder comes into contact with the material using position control. Different possible solutions were tried independently with a hybrid weld program without success of eliminating the Z-force spike. However, the solution using a load-controlled weld program provided significant reduction in Z-force spike from 1,500 lbf to 300 lbf and maintained FSSW quality. Furthermore, reduction of shoulder diameter significantly reduced the required Z-force while simultaneously maintaining good mechanical properties of Octaspot™ FSSW. A 0.30inch-diameter shoulder requires 850 lbf Z-force and performs better than a 0.40-inch-diameter shoulder that requires 1,100 lbf Z-force.
Four pin tool designs—Psi™, Counterflow™, Duo V-flute, and Tri V-flute—coupled with a low Z-force weld program and appropriate process parameters created a sound Octaspot™
FSSW, except for the Modified Trivex™ pin tool. Mechanical properties of low Z-force
Octaspot™ FSSW were investigated using unguided single-spot lap shear. The average UTL
(1,117 lbf to 1,173 lbf) of low Z-force Octaspot™ swept FSSW was comparable to the average
UTL (1,210 lbf) of high Z-force Octaspot™ FSSW. Probe designs with smaller probe tip areas, such as Psi™ and Modified Trivex™, required less Z-force to plunge. Therefore, an investigation of small probe diameters of 0.1 inch with a 0.25-inch-diameter shoulder successfully lowered the Z-force below 700 lbf.
74
Modified Trivex™ pin tools that created weld coupons with a hooking defect were excluded from the analysis of probe features. The initial hypothesis suggested that a probe design such as the Modified Trivex™ with a small ratio of probe physical to swept unit volume creates hooking defects. A separate investigation of probe shape was initiated to correlate the hooking defect with the probe physical to swept unit volume ratio. However, the featureless probe shape investigation was unable to confirm that an increase of probe physical to swept unit volume ratio will reduce hooking defects. However, a weld parameter set tends to produce an aggressive hooking defect across three different probe shapes. Features on probes, such as flutes, can eliminate the hooking defect effectively if designed properly.
Lap joints are more likely to have a hooking defect on the faying surface interface, which will affect UTL because of sheet thinning. V-flute™ pin tools with features such as flutes performed excellently, not creating a hooking defect in the Octaspot™ FSSW. The threaded pin tool created a hooking defect if it was not coupled with Counterflow™ flutes. A reduction of shoulder diameter and Z-force created a preferable weld nugget with smaller TMAZ and HAZ regions. Metallographic images were correlated with process parameters and pin tool designs to further justify sound FSSW.
UTL and metallographic images should not be the only measures for good Octaspot™
FSSW. Surface finish was another criterion for this research, since reduction of shoulder diameter increased the sensitivity of the process parameters, specifically Z-force, which can cause flash generation. Surface finish of the FSSW should be level and without flash generation, which can be adjusted with tilt angle and Z-force. A flat scrolls shoulder design also significantly reduced flash generation, compared to the concave shoulder, without adjustment of process parameters. Aluminum with surface oxide was welded as is and did not affect the UTL for four
75
different pin tools, thus potentially reducing a step of surface oxide removal in the manufacturing process. Another objective was to reduce the processing time of each Octaspot™ swept FSSW, through optimization of process parameters, and weld program. Optimization of the weld program by reducing the dwell time and increasing the rate of acceleration reduced the weld cycle time by at least five seconds. Optimization of weld parameter such as travel speed coupled with statistical analysis showed that at a high travel speed, the UTL of Octaspot™ FSSW was not compromised and was able to further reduce the weld time to 7 seconds.
Statistical analysis software (Statgraphics
®
) was used to correlate the UTL of the lap shear coupons with respective process parameters for optimization of UTL. Four pin-tool designs showed the least significant effect on the average UTL for different probe features with similar weld process parameters. However, the Trivex™ probe shape significantly affected the average
UTL due to the hooking defect for similar weld process parameters. The optimization of weld parameters increased the average UTL and reduced standard deviation UTL to achieve higher repeatability with a wide range of weld parameters. The performance of the new pin tool design,
V-flute™, was comparable to Psi™ and Counterflow™. Besides optimization of weld parameters, a balanced pin tool with optimized geometries such as shoulder and probe diameters can avoid an unnecessary increase of weld parameter sensitivity.
These low Z-force FSSW results indicate that it is possible to produce sound FSSW joints within the Z-force capability range of a typical articulated robot. Since the automotive and aerospace industries are moving toward automation to improve production rate and quality control simultaneously, the investigation of low Z-force FSSW will accelerate and bridge the implementation of FSSW for articulated robots in those industries. Standards and specifications for low Z-force FSSW will also be important to generate reproducible design data, such as
76
mechanical properties for a design engineer handbook. Application-based research, such as surface sealant and surface treatment in low Z-force FSSW, is also important. Future work should investigate the transfer of low Z-force FSSW knowledge to robotic applications, the further reduction of Z-force through high rotational speed FSSW, and the impact of low Z-force
FSSW on joints with sealants.
77
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78
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82
APPENDICES
83
APPENDIX A
DETAILED CALCULATIONS FOR TABLE 1
FORMULAS
Area of rectangular
Area of a triangle
Area of a cirle
Unit Volume
Ratio
Angle (rad)
CONSTANTS
(PI) = radius = m=n=radius = o = angle (rad) t = thickness = diagonal = 2*m =
Area=t*l
Area=0.5*m*n*sin(o)
Area=(PI)*m^2
Vol=1*Area
Unit volume/0.03142
Angle=2*(PI)/# Triangle
3.142
0.100
0.100
0.050
0.200
l ~ diagonal =
Actual l =
ASSUMPTIONS:
Radius is 0.100 inch
0.200
0.194
Rectangular thickness is 0.050 inch
Rectangular length is close to diagonal length since its thickness is very small
CALCULATIONS
Shape
Rectangular
Triangular
Square
Pentagon
Hexagon
Octagon
Circle
Table 1 Ref.
# Triangle Angle (rad) Area of a Triangle Total Area Unit Volume Ratio a 0.010
0.010
0.308
b c d
3
4
5
2.095
1.571
1.257
0.00433
0.00500
0.00476
0.013
0.020
0.024
0.013
0.020
0.024
0.413
0.637
0.757
e f g
6
8
1.047
0.786
0.00433
0.00354
0.026
0.028
0.031
0.026
0.028
0.031
0.827
0.900
1.000
84
APPENDIX B
DURATION OF OCTASPOT™ SWEPT FSSW
DURATION OF FSW07079_1 FOR SPOTS 3 AND 4
DURATION OF CFSP08310_1 FOR SPOTS 3 AND 4
85
APPENDIX B (continued)
DURATION OF CFSP08310_2 FOR SPOTS 3 AND 4
Spot 3,
7 ipm, 10 sec
2 sec dwell
Spot 4,
13 ipm, 7 sec
SUMMARY OF INDIVIDUAL WELD DURATION FOR SPOTS 3 AND 4
SPOT 3 SPOT 4
DOE DWELL TIME IPM WELD
TIME
IPM WELD
TIME
FSW07079_1
CFSP08310_1
CFSP08310_2
7 SEC
5 SEC
2 SEC
8.45
6
7
7 SEC
11 SEC
10 SEC
10.45
4
13
6 SEC
15 SEC
7 SEC
86
APPENDIX B (continued)
DURATION OF CFSP08310_2 FOR 5 SPOTS
CFSP08310_2.dat
1200 0.3
1000
0.25
800
0.2
600
0.15
400
0.1
200
0
100
-200
120 140 160 180 200 220 240
Forge Force Cmd, lbf
Seconds
Forge Force Fbk, lbf Forge Fbk, in
SUMMARY OF WELD DURATION FOR FIVE SPOTS
DOE Spot 3 to 8 (5spots)
FSW07079_1 115 to 300 sec =185 sec
CFSP08310_1 111 to 286 sec = 175 sec
CFSP08310_2 121 to 281 sec = 160 sec
260 280
0.05
300
0
Cycle time for each spot
(300-115)/5=37 sec
(286-111)/5=35 sec
(281-121)/5=32 sec
87
APPENDIX C
UTL RESULTS
0.3 INCH PSI™ TOOL DOE 1
Upper Shoulder
Lower Shoulder
CFSP08301
08-0055-0300-05-SN1 n/a
Weld Number
CFSP08301_14
Pin
Plate Thickness
Tensile # RPM IPM Pin Load (lbs)
T01
T02
T03
T04
T05
T06
T07
T08
800
1000
800
1000
800
1000
800
1200
6
4
6
8
6
6
4
6
900
900
1100
1100
700
900
900
700
Advanced Joing Lab x5205
Psi Tool
Material 0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
St. Dev
1190
1049
1005
747
1094
1138
1143
1080
1035.5
163.2
T09
T10
T11
T12
T13
T14
T15
1200
1200
1000
1000
1200
1000
1000
8
4
4
6
6
8
8
900
1100
1100
700
900
700
900
1135
624
889
1095
1050
1208
1087
0.3 INCH PSI™ TOOL DOE 2
Upper Shoulder
Lower Shoulder
Weld Number
CFSP08301
08-0055-0300-05-SN1 n/a
Tensile # RPM IPM
Pin
Advanced Joing Lab x5205
Psi Tool
Plate Thickness 0.040
Pin Load (lbs)
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
T01 950 13 750 1023
Date
Material
St. Dev
CFSP08301_19
T02
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
13
7
13
10
10
13
7
7
10
10
7
10
10
10
950
1100
800
800
800
1100
950
950
950
950
800
1100
950
1100
950
850
850
950
750
850
950
750
850
850
850
950
850
750
1220
1223
1126
1215
731
1181
1091
1156
1234
1220
1193
1204
1213
1113
1142.8
128.8
Room 110
2024-T3
Failure Location
TOP
BOTTOM
TOP
TOP
TOP/NUGGET SHEAR
BOTTOM
BOTTOM
BOTTOM
TOP
TOP
TOP
BOTTOM
TOP
BOTTOM
BOTTOM
Room 110
July 22 2008
2024-T3
Failure Location
Top & Bottom(Nugget Pullout)
Bottom
Bottom
Bottom
Top
Top & Bottom(Nugget Pullout)
B/Nugget Pullout
Bottom
Bottom
Top & Bottom(Nugget Pullout)
Bottom
Top
Top
Top
Bottom
88
APPENDIX C (continued)
0.4 INCH PSI™ TOOL DOE 1
Upper Shoulder
Lower Shoulder
CFSP08302
08-0055-0400-15 SN2 n/a
Weld Number
Pin
Plate Thickness
Tensile # RPM IPM Pin Load (lbs)
T01
T02
T03
T04
T05
T06
800
1000
800
1000
800
1000
4
6
6
8
6
6
900
900
1100
1100
700
900
Advanced Joing Lab x5205
Psi Tool
Material 0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
St. Dev
1187
1154
1219
1172
951
1165
CFSP08302_3
T07
T08
800
1200
4
6
900
700
1250
1129
1160.7
84.9
T09
T10
T11
T12
T13
T14
T15
1200
1200
1000
1000
1200
1000
1000
8
8
4
6
8
4
6
900
1100
1100
700
900
700
900
1191
1229
1243
997
1210
1124
1189
0.3 INCH COUNTERFLOW™ TOOL DOE 1
CFSP08304 upper shoulder lower shoulder
08-0055-0300-01-SN1 n/a pin plate thickness
Weld Number Tensile # RPM IPM Pin Load (lbs)
Advanced Joing Lab x5205
Counterflow Tool
0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
Material
St. Dev
T01 800 8 900 1228
CFSP08304_03
T02
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
1000
800
1000
800
1000
800
1200
1200
1200
1000
1000
1200
1000
1000
6
6
4
6
8
8
4
4
6
6
8
6
6
4
900
1100
1100
700
900
900
700
900
1100
1100
700
900
700
900
1176
1032
954
1138
1208
1197
1127
1120
905
1159
1234
1100
1161
1261
1133.3
101.5
Room 110
2024-T3
Failure Location
Top/Nugget Shear
Bottom
Bottom
Bottom
Nugget Shear
Bottom
Nugget Shear
Bottom
Bottom
Bottom
Bottom
Top/Nugget Shear
Bottom
Bottom
Bottom
Room 110
2024-T3
Failure Location
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
89
APPENDIX C (continued)
T01 950 13 750
0.3 INCH COUNTERFLOW™ TOOL DOE 2
Upper Shoulder
Lower Shoulder
Weld Number
CFSP08304
08-0055-0300-01-SN1 n/a
Tensile # RPM IPM
Pin
Advanced Joing Lab x5205
Counterflow Tool
Plate Thickness 0.040
Ultimate
Pin Load (lbs) Tensile Load
(lbs)
Avg UTL
(ksi)
1126
Date
Material
St. Dev
T02
T03
950
1100
13
7
950
850
1158
1051
T04
T05
T06
800
800
800
13
10
10
850
950
750
1204
1159
1108
CFSP08304_05
T07
T08
1100 13
950 7
850
950
1122
1049
1117.1
45.1
T09
T10
T11
T12
T13
T14
T15
950 7
950
950
10
10
800 7
1100 10
950 10
1100 10
750
850
850
850
950
850
750
1082
1151
1135
1134
1059
1139
1079
0.4 INCH COUNTERFLOW™ TOOL DOE 1
CFSP08305
Upper Shoulder
Lower Shoulder
08-0055-0400-11 SN1 n/a
Pin
Plate Thickness
Weld Number Tensile # RPM IPM Pin Load (lbs)
Advanced Joing Lab x5205
Counterflow
0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
Material
St. Dev
T01 800 8 900 1180
CFSP08305_1
T02
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
6
6
4
6
8
8
4
4
6
6
8
6
6
4
1000
800
1000
800
1000
800
1200
1200
1200
1000
1000
1200
1000
1000
900
1100
1100
700
900
900
700
900
1100
1100
700
900
700
900
1307
1261
1139
-
1311
1092
-
1130
1066
1199
-
1025
1119
1202
1169.3
91.4
Room 110
2024-T3
Failure Location
Nugget Pullout
Top
Bottom
Top
-
Bottom
Top
-
Top
Top
Top
-
Top
Top/Bottom
Bottom
Room 110
July 22 2008
2024-T3
Failure Location
TOP
TOP
TOP
TOP
TOP
TOP
TOP
BOTTOM
TOP
TOP
TOP
TOP
TOP
TOP
TOP
90
APPENDIX C (continued)
0.3 INCH TRIVEX™ TOOL DOE 1
Upper Shoulder
Lower Shoulder
CFSP08308
08-0055-0300-0-SN2 n/a
Weld Number
Pin
Plate Thickness
Tensile # RPM IPM Pin Load (lbs)
T01
T02
T03
T04
T05
T06
800
1000
800
1000
800
1000
4
6
6
8
6
6
900
900
1100
1100
700
900
Advanced Joing Lab x5205
Trivex Tool
Material 0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
St. Dev
1036
970
931
903
870
925
CFSP08308_1
T07
T08
800
1200
4
6
900
700
947
932
911.4
60.5
T09
T10
T11
T12
T13
T14
T15
1200
1200
1000
1000
1200
1000
1000
8
8
4
6
8
4
6
900
1100
1100
700
900
700
900
0.3 INCH TRIVEX™ TOOL DOE 2
Upper Shoulder
Lower Shoulder
Weld Number
CFSP08308
08-0055-0300-03-SN2 n/a
Tensile # RPM IPM
Pin
Advanced Joing Lab x5205
Trivex Tool
Plate Thickness 0.040
Ultimate
Pin Load (lbs) Tensile Load
(lbs)
Avg UTL
(ksi)
Date
Material
St. Dev
T01
T02
950
950
13
13
750
950
936
952
885
850
785
903
842
962
930
CFSP08308_2
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
13
7
7
10
10
7
10
10
10
7
13
10
10
1100
800
800
800
1100
950
950
950
950
800
1100
950
1100
850
850
950
750
850
950
750
850
850
850
950
850
750
936
1008
1006
955
967
874
943
971
993
1024
877
987
940
957.8
43.7
Room 110
2024-T3
Failure Location
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Room 110
August 28 2008
2024-T3
Failure Location
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
Top Sheet
91
APPENDIX C (continued)
0.3 INCH DUO V-FLUTE™ TOOL DOE 1 upper shoulder lower shoulder
CFSP08310
08-0055-0300-09-SN1 n/a pin plate thickness
Weld Number Tensile # RPM IPM Pin Load (lbs)
T01 800 8 900
Advanced Joing Lab x5205
Duo V-flute Tool
Material 0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
St. Dev
1141
T02
T03
1000
800
6
6
900
1100
998
979
T04
T05
T06
1000
800
1000
4
6
6
1100
700
900
876
1137
966
CFSP08310_1
T07
T08
800
1200
4
6
900
700
1095
1231
1016.3
174.7
T09
T10
T11
T12
T13
T14
T15
1200
1200
1000
1000
1200
1000
1000
8
8
4
6
8
4
6
900
1100
1100
700
900
700
900
1206
600
790
1181
911
1159
974
0.3 INCH DUO V-FLUTE™ TOOL DOE 2
CFSP08310 Advanced Joing Lab x5205
Upper Shoulder
Lower Shoulder
08-0055-0300-09-SN1 n/a
Pin
Plate Thickness
Duo V-flute Tool
Weld Number Tensile # RPM IPM Pin Load (lbs)
0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
T01 950 13 750 976
Date
Material
St. Dev
CFSP08310_2
T02
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
950
1100
800
800
800
10
10
1100 13
950 7
950 7
950
950
10
10
800 7
1100 10
950 10
1100 10
13
7
13
950
850
850
950
750
850
950
750
850
850
850
950
850
750
1217
1177
1187
1168
1131
1255
1043
1187
1231
1243
1217
1205
1228
1181
1176.4
75.9
10/17/2008
2024-T3
Failure Location
Bottom
Bottom
Top
Bottom
Bottom
Bottom
Bottom
Top
Top
Top
Nugget Pullout
Top
Top
Bottom
Bottom
Room 110
10/18/2008
2024-T3
Failure Location
Nugget Pullout
Bottom
Bottom
Top
Bottom
Top
Nugget Pullout
Bottom
Bottom
Bottom
Bottom
Bottom
Top
Bottom
Bottom
92
APPENDIX C (continued)
0.3 INCH TRI V-FLUTE™ TOOL DOE 1 upper shoulder lower shoulder
CFSP08312
08-0055-0300-07-SN1 n/a
Weld Number pin plate thickness
Tensile # RPM IPM Pin Load (lbs)
T01
T02
T03
T04
T05
T06
800
1000
800
1000
800
1000
4
6
6
8
6
6
900
900
1100
1100
700
900
Advanced Joing Lab x5205
Tri V-flute Tool
Material 0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
St. Dev
1157
1038
1016
892
1145
1057
CFSP08312_1
T07
T08
800
1200
4
6
900
700
1094
1200
1063.0
126.8
T09
T10
T11
T12
T13
T14
T15
1200
1200
1000
1000
1200
1000
1000
8
8
4
6
8
4
6
900
1100
1100
700
900
700
900
1240
847
868
1169
970
1208
1045
0.3 INCH TRI V-FLUTE™ TOOL DOE 2
CFSP08312 Advanced Joing Lab x5205
Upper Shoulder
Lower Shoulder
08-0055-0300-07-SN1 n/a
Pin
Plate Thickness
Tri V-flute Tool
Weld Number Tensile # RPM IPM Pin Load (lbs)
0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
T01 950 13 750 1155
Date
Material
St. Dev
CFSP08312_2
T02
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
950
1100
800
800
800
10
10
1100 13
950 7
950 7
950
950
10
10
800 7
1100 10
950 10
1100 10
13
7
13
950
850
850
950
750
850
950
750
850
850
850
950
850
750
1194
1145
1200
1086
1156
1245
1021
1201
1230
1237
1208
1129
1243
1151
1173.3
62.7
10/18/2008
2024-T3
Failure Location
Bottom
Bottom
Top
Bottom/Nugget Pullout
Top
Bottom
Bottom
Bottom
Nugget Pullout
Top
Bottom
Bottom
Nugget Pullout
Bottom
Bottom
Room 110
10/18/2008
2024-T3
Failure Location
Top
Bottom
Bottom
Top
Bottom
Top
Top
Bottom
Bottom
Bottom
Bottom
Bottom
Bottom
Bottom
Bottom
93
APPENDIX C (continued)
T01 950 13 750
0.3 INCH DUO V-FLUTE™ SCROLL TOOL DOE 2
Upper Shoulder
Lower Shoulder
Weld Number
CFSP09303
09-0055-0300-10-SN1 n/a
Tensile # RPM IPM
Pin
Advanced Joing Lab x5205
Duo V-flute Scrolls Tool
Plate Thickness 0.040
Ultimate
Pin Load (lbs) Tensile Load
(lbs)
Avg UTL
(ksi)
1102
Date
Material
St. Dev
T02
T03
950
1100
13
7
950
850
1103
1168
T04
T05
T06
800
800
800
13
10
10
850
950
750
1121
1142
1165
CFSP09303_1
T07
T08
1100 13
950 7
850
950
1141
1171
1147.2
49.3
T09
T10
T11
T12
T13
T14
T15
950 7
950
950
10
10
800 7
1100 10
950 10
1100 10
750
850
850
850
950
850
750
1116
1121
1106
1147
1301
1132
1172
0.3 INCH FEATURELESS OCTAGON™ TOOL DOE 2
CFSP09304 Advanced Joing Lab x5205
Upper Shoulder
Lower Shoulder
09-0055-0300-27-SN1 n/a
Pin
Plate Thickness
Octagon Tool
Weld Number Tensile # RPM IPM Pin Load (lbs)
0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
T01 950 13 750 1028
Date
Material
St. Dev
CFSP09304_1
T02
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
950
1100
800
800
800
10
10
1100 13
950 7
950 7
950
950
10
10
800 7
1100 10
950 10
1100 10
13
7
13
950
850
850
950
750
850
950
750
850
850
850
950
850
750
1046
1029
1040
1066
987
1015
1038
1012
1039
1047
1068
1053
1030
998
1033.2
23.0
Room 110
4/29/2009
2024-T3
Failure Location
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Room 110
4/29/2009
2024-T3
Failure Location
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
94
APPENDIX C (continued)
0.3 INCH FEATURELESS PENTAGON™ TOOL DOE 2
Upper Shoulder
Lower Shoulder
Weld Number
CFSP09305
09-0055-0300-25-SN1 n/a
Tensile # RPM IPM
Pin
Advanced Joing Lab x5205
Pentagon Tool
Plate Thickness 0.040
Ultimate
Pin Load (lbs) Tensile Load
(lbs)
Avg UTL
(ksi)
T01 950 13 750 988
Date
Material
St. Dev
T02
T03
950
1100
13
7
950
850
1021
1038
T04
T05
T06
800
800
800
13
10
10
850
950
750
1045
1072
1007
CFSP09305_1
T07
T08
1100 13
950 7
850
950
1119
1137
1092.8
65.5
T09
T10
T11
T12
T13
T14
T15
950 7
950
950
10
10
800 7
1100 10
950 10
1100 10
750
850
850
850
950
850
750
1134
1097
1094
1115
1187
1118
1221
0.3 INCH FEATURELESS TRIVEX™ TOOL DOE 2
CFSP09306 Advanced Joing Lab x5205
Upper Shoulder
Lower Shoulder
09-0055-0300-03-SN1 n/a
Pin
Plate Thickness
Trivex Tool
Weld Number Tensile # RPM IPM Pin Load (lbs)
0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
T01 950 13 750 864
Date
Material
St. Dev
CFSP09306_1
T02
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
950
1100
800
800
800
10
10
1100 13
950 7
950 7
950
950
10
10
800 7
1100 10
950 10
1100 10
13
7
13
950
850
850
950
750
850
950
750
850
850
850
950
850
750
954
940
955
991
826
922
906
910
924
949
963
840
932
844
914.7
49.8
Room 110
4/29/2009
2024-T3
Failure Location
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Room 110
4/29/2009
2024-T3
Failure Location
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
95
APPENDIX C (continued)
0.25 INCH DUO V-FLUTE™ TOOL WITH 0.1 INCH PROBE
Upper Shoulder
Lower Shoulder
Weld Number
CFSP09307
09-0055-0250-09-SN1 n/a
Tensile # RPM IPM
Pin
Advanced Joing Lab x5205
0.25 Duo V-flute 0.1 Pin
Plate Thickness 0.040
Ultimate
Pin Load (lbs) Tensile Load
(lbs)
Avg UTL
(ksi)
Date
Material
St. Dev
T01 1650 13 700 1012
T02
T03
2000 10
1300 10
700
450
907
1
T04
T05
T06
1650
2000
7
7
1300 13
450
575
575
562
1003
967
CFSP09307_4
T07
T08
1650 10
1650 10
575
575
1035
1035
813.1
290.5
T09
T10
T11
T12
T13
T14
T15
1650 10
1650 13
1650 7
2000 10
1300 10
1300 7
2000 13
575
450
700
450
700
575
575
1008
466
889
645
984
962
721
0.25 INCH DUO V-FLUTE™ TOOL WITH 0.1 INCH PROBE
CFSP09307 Advanced Joing Lab x5205
Upper Shoulder
Lower Shoulder
09-0055-0250-09-SN1 n/a
Pin
Plate Thickness
0.25 Duo V-flute 0.1 Pin
Weld Number Tensile # RPM IPM Pin Load (lbs)
0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
Date
Material
St. Dev
T01 1650 13 700 1101
CFSP09307_5
T02
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
2000 10
1300 10
1650 7
2000 7
1300 13
1650 10
1650 10
1650 10
1650 13
1650 7
2000 10
1300 10
1300 7
2000 13
700
450
450
575
575
575
575
575
450
700
450
700
575
575
960
89
693
1100
1035
1107
1118
1086
554
932
635
1007
1091
576
872.2
300.0
Room 110
4/30/2009
2024-T3
Failure Location
Top
Top
N/A
Nugget Shear
Top
Top
Top
Top
Top
Nugget Shear
Bottom
Nugget Pullout
Top
Top/ Nugget Shear
Nugget Pullout
Room 110
4/30/2009
2024-T3
Failure Location
Nugget Pullout
Top
Nugget Shear
Top
Top
Top
Top
Top
Top
Nugget Shear
Nugget Pullout
Top
Bottom/Nugget Pullout
Nugget Pullout
Nugget Pullout
96
APPENDIX C (continued)
0.25 INCH DUO V-FLUTE™ TOOL WITH 0.1 INCH PROBE
Upper Shoulder
Lower Shoulder
Weld Number
CFSP09307
09-0055-0250-09-SN1 n/a
Tensile # RPM IPM
Pin
Advanced Joing Lab x5205
0.25 Duo V-flute 0.1 Pin
Plate Thickness 0.040
Ultimate
Pin Load (lbs) Tensile Load
(lbs)
Avg UTL
(ksi)
Date
Material
St. Dev
T01 1650 13 700 1058
T02
T03
2000 10
1300 10
700
450
967
290
T04
T05
T06
1650
2000
7
7
1300 13
450
575
575
750
1057
1055
CFSP09307_6
T07
T08
1650 10
1650 10
575
575
1114
1094
908.6
244.8
T09
T10
T11
T12
T13
T14
T15
1650 10
1650 13
1650 7
2000 10
1300 10
1300 7
2000 13
575
450
700
450
700
575
575
1099
581
950
781
1096
1076
662
0.25 INCH DUO V-FLUTE™ TOOL WITH 0.1 INCH PROBE
CFSP09307 Advanced Joing Lab x5205
Upper Shoulder
Lower Shoulder
09-0055-0250-09-SN1 n/a
Pin
Plate Thickness
0.25 Duo V-flute 0.1 Pin
Weld Number Tensile # RPM IPM Pin Load (lbs)
0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
Date
Material
St. Dev
T01 1650 12 500 658
CFSP09307_7
T02
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
1650 10
1500 10
1650 8
1650
1800
8
8
1800 10
1650 10
1500 8
1800 10
1650 12
1500 12
1500 10
1800 12
1650 10
550
600
600
500
550
600
550
550
500
600
550
500
550
550
1058
1169
1139
999
1151
1071
1092
1098
1024
1078
1031
704
990
1105
1024.5
149.3
Room 110
4/30/2009
2024-T3
Failure Location
Nugget Pull Out
Top
Nugget Shear
Top
Top
Top
Top
Top
Top
Nugget Shear
Bottom
Top
Bottom
Top
Nugget Pull Out
Room 110
4/30/2009
2024-T3
Failure Location
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
97
APPENDIX C (continued)
0.25 INCH DUO V-FLUTE™ TOOL WITH 0.1 INCH PROBE
Upper Shoulder
Lower Shoulder
Weld Number
CFSP09307
09-0055-0250-09-SN1 n/a
Tensile # RPM IPM
Pin
Advanced Joing Lab x5205
0.25 Duo V-flute 0.1 Pin
Plate Thickness 0.040
Ultimate
Pin Load (lbs) Tensile Load
(lbs)
Avg UTL
(ksi)
Date
Material
St. Dev
T01
T02
T03
950
1100
10
7
1100 10
700
700
800
1105.9
1089.8
1014.2
T04
T05
T06
T07
950
950
950
950
13
7
7
10
800
800
600
700
1118.9
1163.4
1041.1
1097.0
CFSP09307_12 1024.7
160.7
T08
T09
T10
T11
T12
T13
T14
T15
1100 13
950 10
800
800
950
800
800 13
1100 10
7
10
13
10
700
700
700
800
600
600
700
600
1093.0
1103.8
1072.8
1111.4
765.9
545.7
1017.9
1029.1
0.25 INCH DUO V-FLUTE™ TOOL WITH 0.1 INCH PROBE
Upper Shoulder
Lower Shoulder
CFSP09307
09-0055-0250-09-SN1 n/a
Advanced Joing Lab x5205
Pin
Plate Thickness
0.25 Duo V-flute 0.1 Pin
0.040
Date
Material
Weld Number Tensile # RPM IPM Pin Load (lbs)
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
St. Dev
T01
T02
1100 10
950 7
750
650
1122
1085
CFSP09307_13
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
800
950
10
10
1100 13
1100 7
800
950
13
13
950 7
800
800
7
10
1100 10
950 13
950
950
10
10
750
700
700
700
700
750
750
700
650
650
650
700
700
1124
1119
1085
1086
1090
1129
1145
1113
959
1065
1047
1098
1090
1090.5
44.5
Room 110
6/15/2009
2024-T3
Failure Location
TOP
TOP/BOTTOM
BOTTOM
TOP/ BOTTOM
TOP
TOP
TOP
TOP
TOP
TOP
TOP
TOP/BOTTOM/NUGGET
NUGGET
TOP/BOTTOM/NUGGET
TOP
Room 110
6/15/2009
2024-T3
Failure Location
TOP/BOTTOM
TOP
TOP
TOP
TOP
TOP/BOTTOM
TOP
TOP
BOTTOM
TOP
TOP/NUGGET
TOP
TOP
TOP
TOP
98
APPENDIX C (continued)
T01 950 13 750
0.3 INCH PSI™ TOOL DOE 2 (NO PREPARATION)
Upper Shoulder
Lower Shoulder
Weld Number
CFSP08301
08-0055-0300-05-SN1 n/a
Tensile # RPM IPM
Pin
Advanced Joing Lab x5205
Psi Tool
Plate Thickness 0.040
Pin Load (lbs)
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
1063
Date
Material
St. Dev
CFSP08301_20
T02
T03
T04
T05
T06
T07
T08
950
1100
800
800
800
1100
950
10
10
13
7
13
7
13
950
850
850
950
750
850
950
1231
1140
1171
1253
1074
1154
1105
1174.7
68.0
T09
T10
T11
T12
T13
T14
T15
950
950
950
800
1100
950
1100
7
10
10
7
10
10
10
750
850
850
850
950
850
750
1226
1258
1268
1233
1164
1174
1108
0.3 INCH COUNTERFLOW™ TOOL DOE 2 (NO PREPARATION)
CFSP08304 Advanced Joing Lab x5205
Upper Shoulder
Lower Shoulder
08-0055-0300-01-SN1 n/a
Pin
Plate Thickness
Counterflow Tool Date
Material
Weld Number Tensile # RPM IPM Pin Load (lbs)
0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
St. Dev
T01 950 13 750 1165
CFSP08304_06
T02
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
950
1100
800
800
800
10
10
1100 13
950 7
950 7
950
950
10
10
800 7
1100 10
950 10
1100 10
13
7
13
950
850
850
950
750
850
950
750
850
850
850
950
850
750
1142
1037
1222
1197
1222
1097
1120
1139
1215
1197
1169
1036
1154
1071
1145.4
62.8
Room 110
October 29 2008
2024-T3
Failure Location
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Room 110
Oct 29 2008
2024-T3
Failure Location
Nugget Pullout
Nugget Pullout
Bottom
Top
Bottom
Nugget Shear
Nugget Pullout
Bottom
Bottom
Bottom
Bottom
Nugget Pullout
Top
Top &Bottom
Bottom
99
APPENDIX C (continued)
0.3 INCH DUO V-FLUTE™ TOOL DOE 2 (NO PREPARATION)
Upper Shoulder
Lower Shoulder
Weld Number
CFSP08310
08-0055-0300-09-SN1 n/a
Tensile # RPM IPM
Pin
Advanced Joing Lab x5205
Duo V-flute Tool
Plate Thickness 0.040
Ultimate
Pin Load (lbs) Tensile Load
(lbs)
Avg UTL
(ksi)
Date
Material
St. Dev
T01 950 13 750 1039
T02
T03
950
1100
13
7
950
850
1178
1157
T04
T05
T06
800
800
800
13
10
10
850
950
750
1162
1170
959
CFSP08310_3
T07
T08
1100 13
950 7
850
950
1234
1040
1163.3
85.7
T09
T10
T11
T12
T13
T14
T15
950 7
950
950
10
10
800 7
1100 10
950 10
1100 10
750
850
850
850
950
850
750
1213
1235
1247
1217
1216
1232
1152
0.3 INCH TRI V-FLUTE™ TOOL DOE 2 (NO PREPARATION)
CFSP08312 Advanced Joing Lab x5205
Upper Shoulder
Lower Shoulder
08-0055-0300-07-SN1 n/a
Pin
Plate Thickness
Tri V-flute Tool Date
Material
Weld Number Tensile # RPM IPM Pin Load (lbs)
0.040
Ultimate
Tensile Load
(lbs)
Avg UTL
(ksi)
St. Dev
T01 950 13 750 891
CFSP08312_3
T02
T03
T04
T05
T06
T07
T08
T09
T10
T11
T12
T13
T14
T15
950
1100
800
800
800
10
10
1100 13
950 7
950 7
950
950
10
10
800 7
1100 10
950 10
1100 10
13
7
13
950
850
850
950
750
850
950
750
850
850
850
950
850
750
1194
1159
1193
1189
1104
1256
1029
1229
1263
1247
1233
1185
1258
1152
1172.3
100.4
Room 110
10/29/2008
2024-T3
Failure Location
Nugget Pullout
Bottom
Bottom
Top
Bottom
Nugget Pullout
Bottom
Bottom
Bottom
Bottom
Bottom
Bottom
Top
Bottom
Bottom
Room 110
10/29/2008
2024-T3
Failure Location
Nugget Pullout
Bottom
Bottom
Top
Bottom
Nugget Shear
Bottom
Bottom
Bottom
Bottom
Bottom
Bottom
Top
Bottom
Bottom
100
