ANALYSIS OF EFFECTS OF USING ALUMINIUM AS MOLD MATERIAL IN
PLASTIC INJECTION MOLDING FOR AUTOMOTIVE HVAC DUCTS
Sri Srinivasa Muktevi
B.Tech., Jawaharlal Nehru Technological University, India, 2007
PROJECT
submitted in partial satisfaction of
the requirements for the degree of
MASTER OF SCIENCE
in
MECHANICAL ENGINEERING
at
CALIFORNIA STATE UNIVERSITY,SACRAMENTO.
FALL
2011
ANALYSIS OF EFFECTS OF USING ALUMINIUM AS MOLD MATERIAL IN
PLASTIC INJECTION MOLDING FOR AUTOMOTIVE HVAC DUCTS
A Project
by
Sri Srinivasa Muktevi
Approved by:
________________________________, Committee Chair
Dongmei Zhou, Ph. D.
_________________________
Date
ii
Student:Sri Srinivasa Muktevi
I certify that this student has met the requirements for format contained in the university
format manual and this project is suitable for shelving in library and credit is to be
awarded for the project.
________________________, Graduate Coordinator
Akihigo Kumagai, Ph. D.
Department of Mechanical Engineering
iii
_____________________
Date
Abstract
of
ANALYSIS OF EFFECTS OF USING ALUMINIUM AS MOLD MATERIAL IN
PLASTIC INJECTION MOLDING FOR AUTOMOTIVE HVAC DUCTS
by
Sri Srinivasa Muktevi
Aluminum injection molds, primarily used in the past for prototypes are being
investigated for use as production molds with the advent of a new generation of
aluminum materials specifically tailored for this application.
This project investigates the effects of using aluminum tooling while comparing the
importance of other contributing factors in molding performance through the use of
Moldflow software and Taguchi methods.
The large number of variables studied, 13 at three different levels, contributed to some
interesting results that were not seen on other published studies with smaller numbers of
variables. The main focus, the mold material was found, not surprisingly, to be an
important contributor in molding performance. However, unexpectedly the aluminum
tooling in this instance was found to perform poorer than steel while beryllium-copper
was found to be far superior to both.
Factors such as melt temperature and mold
iv
temperature were important contributors.
Other variables that were the focus of
experiments with fewer variables, such as waterline geometries were found to be of little
importance in comparison.
________________________________, Committee Chair
Dongmei Zhou, Ph. D.
_________________________
Date
v
ACKNOWLEDGMENTS
While working on this project, some people helped me to reach where I am today and I
would like to thank all for their support and patience.
Firstly, I would like to thank Professor Dr. Dongmei Zhou for giving me an opportunity
to do this project. Her continuous support was the main thing that helped me to develop
immense interest on the project that led to do this project. Dr.Dongmei Zhou helped me
by providing many sources of information that needed from beginning of the project till
the end. She was always there to talk and answer the questions that came across during
the project.
Special thanks to my advisor Dr Akihigo Kumagai for helping me to complete the writing
of this dissertation, without his encouragement and constant guidance I could not have
finished this report.
Finally, I would also like to thank all my family, friends and Mechanical engineering
department who helped me to complete this project work successfully. Without any of
the above-mentioned people the project would not have come out the way it did. Thank
you all.
vi
TABLE OF CONTENTS
page
Acknowledgments…………………………………………………………………….. .viii
List of Tables…………………………………………………………………………….x
List of Figures……………………………………………………………………………xii
Software Specifications………………………………………………………………….xv
Chapter
1. INTRODUCTION…………………………………………………………………......1
1.1 Background…………………………………………………………………………1
1.2 Objectives…………………………………………………………………………..2
1.3 Procedure and Methodology……………………………………………………….4
1.4 Computer Simulation Parameters for Taguchi Method DOE……………………..5
2. VARIABLE PARAMETERS OF INJECTION MOLDING ........................................ 6
2.1 Mold Parameters ...................................................................................................... 6
2.1.1 Mold Dimensions .......................................................................................... 6
2.1.2 Mold Material................................................................................................ 7
2.1.2.1 Aluminum Alloy (Injection Molding Grade) - QC-10 ...................... 11
2.1.2.2 Tool Steel - P-20 ................................................................................ 12
2.1.2.3 Copper Alloy - Be-Cu C18000 .......................................................... 12
2.2 Waterline Parameters ............................................................................................ 13
2.2.1 Waterline Diameter..................................................................................... 14
2.2.2 Waterline Pitch........................................................................................... 15
vii
2.2.3 Waterline Depth ......................................................................................... 16
2.3 Gating ..................................................................................................................... 18
2.4 Part Design Parameters ........................................................................................... 19
2.4.1 Plastic Types .................................................................................................. 19
2.4.2 Plastic Families ............................................................................................ 20
2.4.3 Fillers ........................................................................................................... 24
2.4.4 Plastics Grades ............................................................................................. 24
2.4.5 Part Thickness ............................................................................................. 25
2.5 Processing Parameters ............................................................................................ 26
2.5.1 Coolant Parameters ....................................................................................... 26
2.5.2 Coolant Flow Rate ....................................................................................... 27
2.5.3 Coolant Temperature .................................................................................. 28
2.6 Mold Surface Temp .............................................................................................. 29
2.7 Melt Temp ............................................................................................................ 30
2.8 Ejection Temp....................................................................................................... 32
2.9 Frozen Percentage ................................................................................................ 33
3. TAGUCHI METHOD ORTHOGONAL ARRAY ....................................................... 35
3.1 Setup .................................................................................................................... 36
3.1.1 Equipment .................................................................................................... 36
3.2 Finite Element Model ......................................................................................... 36
viii
4. RESULTS AND DISCUSSIONS ................................................................................. 39
4.1 Dimensional Stability ............................................................................................ 39
4.1.1 Deflection – Combined Effects.................................................................... 40
4.1.2 Deflection – Corner Effects ......................................................................... 42
4.1.3 Deflection – Differential Cooling ................................................................ 43
4.1.4 Deflection – Differential Shrinkage ............................................................ 44
4.1.5 Deflection – Orientation Effects .................................................................. 45
4.1.6 Residual Stresses ......................................................................................... 46
4.2 Cooling ............................................................................................................... 48
4.2.1 Coolant Circuit Temperatures .................................................................... 48
4.2.2 Mold Temperatures .................................................................................... 50
4.2.3 Part Temperatures ...................................................................................... 53
4.2.4 Time to Reach Ejection Time .................................................................... 55
4.3 Pressure............................................................................................................. 56
4.4 Weld Lines ........................................................................................................ 57
4.5 Air Traps............................................................................................................ 58
4.6 Fiber Orientation............................................................................................... 59
4.7 Economics and Performance............................................................................. 60
5. CONCLUSION AND FUTURE WORK……………………………………………63
5.1 Conclusion.......................................................................................................... 63
5.2 Future Work ........................................................................................................ 64
Bibliography ..................................................................................................................... 65
ix
LIST OF TABLES
page
1. Table 1 Thermal properties of mold materials………………………………………...10
2. Table 2 Variables selected-waterline diameters……………………………………....15
3. Table 3 Variables selected-waterline pitch……………………….………………..…16
4. Table 4 Variables selected-waterline depth……………………………………..……17
5. Table 5 Typical processing parameters for generic classes of resins……………....…21
6. Table 6 Materials selected with filler type and percentage……………………………25
7. Table 7 Selected part thickness……………………………………………………….26
8. Table 8 Selected flow rates as measured by Reynolds numbers……………….……..28
9. Table 9 Selected collant temperatures…………………………………………….…..29
10. Table 10 Selected mold surface temperatures………………………………………30
11. Table 11 Recommended mold surface temperatures (molfdlow)…………………..30
12. Table 12 Selected melt temperatures…………………………………………...……31
13. Table 13 Recommended melt temperatures (mold flow)…………………………...32
14. Table 14 Selected ejection temperatures…………………………………….……....33
15. Table 15 Recommended ejection temperatures……………………………………..33
16. Table 16 Select frozen temperature……………………………………………...…34
x
17. Table 17 Resulting L27 orthoginal array (taguchi method)……………………..….35
18. Table 18 Hardware & software used………………………………..….……………36
19. Table 19 Finite element model statistics…………………………………………….37
20. Table 20 Results considered……………….…………………………………….......39
21. Table 21 Deflection and Ejection time compared for aluminium,steel and copper
tool…………………………………………………………………………62
xi
LIST OF FIGURES
page
1. Figure 1 HVAC duct ...................................................................................................... 3
2. Figure 2 L27 (13 factors with 3 levels) orthogonal array .............................................. 5
3. Figure 3 Mold geometry ................................................................................................ 7
4. Figure 4 Thermal diffusivity as a function of endurance limit of mold materials .......... 9
5. Figure 5 Thermal conductivity vs Thermal diffusivity of engg materials at room
temperature…………………………………………………………………10
6. Figure 6 Modulus versus strength of engineering materials ........................................ 11
7. Figure 7 Typical dimensions for cooling channels…………………………………..14
8. Figure 8 Waterline depth as measured for this project. …………………………….17
9. Figure 9 A typical view of the mold with part and waterlines connected in series….18
10. Figure10 Part with various gate locations…………………………………………20
11. Figure 11 Processing window for melt temperature of generic plastics…………..23
12. Figure 12 Processing window for mold temperature of generic plastics…………..24
13. Figure 13 Recommended ejection temperatures of generic plastics……………….24
14. Figure 14 Finite Element Model…………………………………………………..39
15. Figure 15 An example of dimensional deflection……………………………………41
16. Figure 16 Effect of studied parameters on combined deflection effects…………....41
17. Figure 17 An example of corner effects on a box shape. ………………………….42
xii
18. Figure 18 Effect of studied parameters on corner effects………………………….43
19. Figure 19 Effect of studied parameters on differential cooling…………………….44
20. Figure 20 Effect of studied parameters on all differential shrinkage………………..45
21. Figure 21 Effect of studied parameters on orientation effect……………………....46
22. Figure 22 Effect of studied parameters on all 1st residual stress…………………….47
23. Figure 23 Effect of studied parameters on 2nd residual stress……………………….47
24. Figure 24 Effect of studied parameters on highest circuit cooling temperature
bottom…………………………………………........................................49
25. Figure 25 Effect of studied parameters on highest circuit cooling temperature
top..............................................................................................................49
26. Figure 26 Effect of studied parameters on highest mold temperature - top…………50
27. Figure 27 Effect of studied parameters on lowest mold temperature – top…………51
28. Figure 28 Effect of studied parameters on mold ∆T - top…………………………..51
29. Figure 29 Effect of studied parameters on highest mold temperature – bottom……52
30. Figure 30 Effect of studied parameters on lowest mold temperature - bottom……..52
31. Figure 31 Effect of studied parameters on mold temperature ∆T– top…………….53
32. Figure 32 Effect of studied parameters on temperature differential………………..54
33. Figure 33 Effect of studied parameters on heat flux - bottom………………………54
34. Figure 34 Effect of studied parameters on heat flux - top…………………………..55
35. Figure 35 Effect of studied parameters on time to reach ejection temperature……..56
36. Figure 36 Effect of studied parameters on pressure at the V/P switchover…………57
xiii
37. Figure 37 Weld lines are indicated by the multicolored lines………………………58
38. Figure 38 Fiber orientation with air traps…………………………………………..59
39. Figure 39 Typical Fiber Orientation………………………………………………..60
xiv
SOFTWARE SPECIFICATION
The
work was performed utilizing Autodesk Moldflow software.
The exact
configuration is detailed in below.
Hardware and Software Used
Computer
Dell Dimension 9100
Processor
GenuineIntel x86 Family Model 15 Stepping 6 ~2393 x2
Memory
2045 Mbytes
Operating
Windows XP Service Pack 3
System
Software
Autodesk Moldflow (ami2010-main (Build 09114-001) 32-bit
build
xv
1
Chapter 1
INTRODUCTION
1.1 Background
As discussed in the article “exploration of use of advanced aluminium alloys for
improved productivity in plastic injection molding”( Nerone et. al,. 2000) for many years,
the automotive industry has used both aluminum molds and steel molds for injection
molding. Aluminum molds have been used primarily for prototype tooling. Due to the
relative softness of aluminum compared to steel, aluminum tools are able to be quickly
and cheaply manufactured which is an advantage for a prototype tool. Unfortunately, the
types of aluminums used were prone to wear and fatigue issues.
Aluminum tools
generally were assumed to last in the range of hundreds of parts rather than the tens of
thousands of parts needed for an automotive production application. Thus, automotive
parts required the use of steel tooling for production parts. Additionally, the different
thermal properties of aluminum compared to steel made it difficult to apply the lessons
learned in the processing of the prototype parts to production parts.
Recently, aluminum companies such as Alcoa and Alcan have introduced new grades of
aluminum that are purported to be a viable replacement to steel as a mold material in
many applications.
The new aluminum tools hold the promise of reducing tool
manufacturing time and cost, decreasing cycle time and thereby piece cost, and
improving part quality.In a paper by name exploration of use of advanced aluminum
2
alloys for imporved productivity in plastic injection molding, a comparision of the
thermal conductivity of new aluminium alloys and tool steel is been made, so as an
extension to the project I have conducted an experimental investigation of the effect of
these two mold materials in molding performance,This project focuses on dimensional
stability of part produced when these mold materials have been used and also the effects
of variuos parameters on molding performance.
1.2 Objectives
This study had two objectives:

Investigate the effect on the part molding process of aluminum tooling while
investigating whether the contribution of the tooling or other factors such as
design or molding parameters are more important

Investigate the molding performance of aluminum tooling versus steel tooling
The focus of this study was to examine an automotive part that would be a prime
candidate for the use of the new aluminum molds. The largest downside with the new
aluminum molds appears to be they still do not retain texture on the mold as well as a
steel mold; therefore, non-visible parts which will not have texture are great candidates.
An example of a larger non-visible part is an HVAC defroster duct. The traditional
HVAC duct is generally made from two halves (Figure 1) that are attached together
forming a tube, often with considerable bends and twists to go around other components
2
3
or to reach distant window demister locations. Generally both halves are formed in a
family mold and warp in nearly all directions is a very real concern.
This study utilized mold flow software and Taguchi methods to determine whether
replacing steel tooling with aluminum tooling makes sense from a molding performance
point of view. At the same time, this study investigated many input parameters from the
design stage, though the tooling stage, and finally to processing to determine what were
the key contributors.
Figure 1 HVAC duct
4
1.3 Procedure and Methodology
The primary focus was to study the two parts using Moldflow software. The effect of
different mold design, part design, and processing considerations were considered in
terms of part quality and cycle time. Using information gained from the CAE analysis
performed, a discussion of whether aluminum tooling is feasible in terms of molding
performance will be discussed.
Autodesk Moldflow plastic injection molding simulation software, part of the Autodesk
solution for Digital Prototyping, is a tool that help manufacturers validate and optimize
the design of plastic parts and injection molds, and study the plastic injection molding
process. Auto desk mold flow simulation software helps to reduce the need for costly
physical prototypes, avoid potential manufacturing defects, and get innovative products
to market faster.
To analyze if aluminium can be replaced with steel as mold material in plastic injection
molding, the following parameters have been supplied to autodesk mold flow software as
input variuables: mold parameters, part design parameters, process parameters.The output
of simulation would be the effects of dimensional stability of the part, varying pressures
in part, weld lines, fiber orientation are being studied as output’s of simulation which are
discussed in chapter 4 of this report.
5
1.4 Computer Simulation Parameters for Taguchi Method DOE
The first section of the report, chapter 2 and part of chapter 3 will explain many of the
important parameters that effect the final part condition. Each parameter will be grouped
into either a mold parameter, part design parameter, or process parameter. The study
explains the reason for choosing or not choosing a parameter and if chosen what factor
levels will be used. Finally, a full L27 (13 factors with 3 levels) orthogonal array (
Figure 2) will be presented with a discussion of the results .
Figure 2 L27 (13 factors with 3 levels) orthogonal array
6
Chapter 2
VARIABLE PARAMETERS OF INJECTION MOLDING
2.1 Mold Parameters
A tool engineer when designing a mold will make key decisions that influence the
molding process. Primarily, the key considerations to be made by the mold engineer are
the mold size, what mold material will be selected, how the waterlines will be laid out,
and the method of runners and gates.
2.1.1 Mold Dimensions
There are many considerations for a mold engineer to consider when choosing the core
and cavity block size such as packaging any actions and ensuring structural integrity of
the mold. The mold itself can act as a heat sink, and affect the molding process. But,
typically other considerations such as mass and cost of the mold material and the ability
to fit the mold between the platens and tie rods of the molding machine, dictate that the
smallest mold possible be used. The mold dimensions for this project are fixed and are
based on the actual cavity and core dimensions of the real life part. The die draw of the
mold is shown in Figure 3. For clarity, the two mold halves are referred to as top and
bottom rather than cavity and core.
7
Figure 3 Mold geometry
2.1.2 Mold Material
Selection of the mold material is an important decision for any mold engineer. Two
typical scenarios can explain the importance of mold material selection.
In the first scenario, a prototype mold to produce a prototype part needs to be constructed
quickly. Build time and fabrication cost are important considerations for a prototype
mold. An aluminum mold is often selected because of the ability to quickly and cheaply
fabricate the mold due to relative ease of machining aluminum.
However, there are
drawbacks. The aluminum mold typically wears relatively quickly and therefore is not
suitable for production volumes.
Additionally, when the part is eventually built on a
8
production tool, it is often observed that the processing characteristics of the part are
quite different than what was observed on the prototype tool. Typically this is attributed
to the substantial differences in thermal properties of the aluminum prototype mold
versus the steel production mold.
In the second scenario, a production mold is built. Cost and timing are important, but
when weighed against the possibility of premature wearing and ultimately the failure of
the tool, which could shut down production of an automotive assembly line, durability is
the key factor. For this reason, tool steels are typically chosen for production injection
mold tools. While machining can be onerous by comparison, creating higher cost and
taking longer to manufacture, steel molds are durable and can produce a very high
quantity of parts.
Typically mold material selection is a tradeoff of mechanical property versus thermal
properties. High mechanical properties are desired as well as high thermal properties.
Unfortunately, as can be seen from Figure 4 through Figure 6 and in Table 1, typical
mold materials such as steel, aluminum, and copper do not meet all the requirements
simultaneously.
Steel typically has high mechanical properties whilst low thermal
properties and copper and aluminum typically have high thermal properties but low
mechanical properties.
Three different mold materials were chosen as variables. The first is a new generation of
high strength aluminum professed to be engineered to meet the requirements of a
9
production injection mold, QC-10.
The second is the workhorse material of injection
molding, P-20 (Kazmer, 2007, p. 85). Third is a copper alloy C18000, which is typically
used in molds for its very high thermal properties.
Figure 4 Thermal diffusivity as a function of endurance limit of mold materials
(Kazmer, 2007, p. 85)
10
Table 1 - Thermal Properties of Mold Materials
Figure 5 - Thermal conductivity vs Thermal diffusivity of engg materials at room
temperature
(Ashby M. F., 2005, p. 66)
11
Figure 6 - Modulus versus strength of engineering materials
(Ashby, Shercliff, & Cebon, 2010, p. 118)
2.1.2.1 Aluminum Alloy (Injection Molding Grade) - QC-10
Aluminum alloys have traditionally been used in injection molding for prototype
tooling. While having thermal properties superior to steel, they typically are not
suitable to meeting the high number of cycles of an injection mold. Aluminum
manufacturers, notably Alcoa with its QC-10 grade and Alcan with its Alumold
500 line have attempted to break into the production mold market with new
aluminum alloys specifically engineered to be used in high cycle production
12
molds. While still not matching the strength of steel, it is noted to be sufficiently
strong and offers the advantages over steel of easy tool manufacturing and
superior thermal properties (Skillingberg, 2004).
2.1.2.2 Tool Steel - P-20
P-20 steel is a commonly chosen high grade forged tool steel for injection molds.
Basically, P-20 is an AISI-4130 or AISI-4140 steel (sometimes this group of
chromium-molybdenum steels is referred to chrome moly steels) with more
stringent requirements resulting in less impurities and a more homogenous
microstructure. It is a good mold material due to its high toughness, lack of
internal defects, uniformity, pre-hardened state, and ability to be textured or
polished to nearly any finish. (Rosato, Rosato, & Rosato, 2000, pp. 334-7)
2.1.2.3 Copper Alloy - Be-Cu C18000
Copper alloys such as that shown in Error! Reference source not found., have a
lace in mold manufacturing due to their high heat transfer which can be 10 times
that of tool steels.
Unfortunately, they have low resistance to wear, low
toughness, and low compressive strength. (Rosato, Rosato, & Rosato, 2000, p.
343) Traditionally they are an alloy of Beryllium-Copper (Be-Cu).
More
recently, health concerns with the machining of beryllium have caused the
creation of beryllium free alloys in which nickel replaces the beryllium. (Baranek)
Some Be-Cu thermal conductivity copper alloy. (Engelmann & Dealey,
13
Maximizing Performance Using Copper Alloys, 1999) Be-Cu C18000 , having
both good mechanical and thermal properties whilst being beryllium free was
chosen for this study.alloys typically chosen for mold cores are Be-Cu C17200, a
high hardness Be-Cu; Be-Cu C17510, a high thermal conductivity Be-Cu; and BeCu C18000 a Ni-Si-Cr hardened high
2.2
Waterline Parameters
Waterline geometry is an important consideration when designing a mold. One of the
primary functions of the mold is its ability to efficiently and evenly pull heat from the
part to solidify it. Different geometry choices of waterlines result in different cooling
performances depending on which mold materials are used. Three important geometry
choices are waterline diameter, depth, and pitch (Figure 7). (Shoemaker, Hayden,
Engelmann, & Miller, 2004)
14
Figure 7 Typical dimensions for cooling channels
2.2.1 Waterline Diameter
Waterlines are typically circular due to the fact that machining a feature for a
waterline in a mold is most efficiently performed with a gun drill. This leaves the
diameter to be the only variable.
Previous studies have indicated that waterline
size “was not found to have a significant effect on temperature uniformity of the
molding surface” but “did significantly affect the average temperature of the
molding surface.” (Shoemaker, Hayden, Engelmann, & Miller, 2004, p. 824)
National Pipe Thread (NPT) sizes are typically used in mold construction in the
US; the sizes used in this study are in
Table 2. (Rees, 2002, p. 298)
15
Table 2 – Variable selected - Waterline diameters (ANSI/ASME B1.20.1 - 1983 (R1992))
Drilled Waterline Diameter
Pipe Size (in)
2.2.2
Drill Size
(in)
(mm)
1/4 NPT
7/16"
0.4375
11.1
3/8 NPT
9/16"
0.5625
14.3
1/2 NPT
11/16"
0.6875
17.5
Waterline Pitch
Waterline pitch is the spacing between each waterline as shown in Figure . The
pitch is often calculated as a multiple of the waterline diameter (Rees, 2002, p.
300). While waterline pitch is fairly standardized in steel molds, it has been
shown that the introduction of mold materials with high thermal conductivity
creates a need to reevaluate waterline pitch and depth. Typically larger pitch can
be used to achieve equal or improved surface temperature uniformity due to the
higher thermal conductivity. (Shoemaker, Hayden, Engelmann, & Miller, 2004)
The waterline pitch values investigated in this study are listed in table 3.
16
Table 3 – Variable selected - Waterline pitch as measured by multiple of waterline
diameter
Waterline Pitch
2.5 x Diameter
5 x Diameter
10 x Diameter
2.2.3
Waterline Depth
Waterline depth is often measured as a multiple of waterline pitch which is itself a
multiple of waterline diameter. (Rees, 2002, p. 300) Typically the depth of the
waterline is calculated such that the waterline is as close to the surface as possible
while maintaining adequate distance from the surface in order to ensure the
structural integrity of the mold. The waterline depths investigated in this study
are listed in table 4. However, as 27 unique waterlines were required for this
experiment, it was beyond the scope of this study to optimize waterlines for each
scenario. The Moldflow waterline wizard was used which only allows one level
and no baffles.
While perhaps a thickness of only 8.3mm of steel between
waterline and part would be judged by a tooling engineer to be insufficient in a
real mold due to structural integrity, for the purpose of this study it was judged
adequate. The 8.3mm was an acceptable compromise as the dimension measured
17
is to the closest point of waterline and part which only occurred in a small
localized area.
In the case of the largest distance, the waterline depth was
35mm.
Table 4 – Variable selected - Waterline diameter as measured by multiple of
waterline diameter
Waterline Depth
0.75 x Diameter
1.5 x Diameter
2 x Diameter
Refer to Figure 8 andFigure 9 for actual examples of waterline diameter, pitch, and depth
from this study.
Figure 8 Waterline depth as measured for this project.
Note that because the waterlines reside in one plane, waterline depth is measured to the
closest point from the plane in which the waterlines are to the part.
18
Figure 9 - A typical view of the mold with part and waterlines connected in series.
Note-diameter, pitch, and depth vary.
2.3
Gating
The gating location of the part is an important consideration. Typically the flow length of
the material determines how many gates are needed and the gates are then spread out in a
manner such that each gate fills approximately the same amount of material volume. The
gate positions for this project were positioned to have equal filling amounts from the
center of the tool along the parting line (Figure 10). Different gating geometries were not
investigated as part of this study.
19
Figure10 Part with various gate locations
Arrows indicate gate location and colored zones are typical fill regions for each gate
2.4 Part Design Parameters
The design engineer makes many choices during the engineering of a plastic part that will
affect molding results such as cycle time and part warpage. Two important items the
design engineer will select are material and geometry. While material is easier to define
for the purpose of this study, geometry is not as an infinite amount of shapes could be
chosen. However, one very important geometry parameter, thickness (assuming that it is
uniform) is easy to define.
2.4.1
Plastic Types
One of the biggest decisions any design engineer has is the selection of material.
Injection molded parts are no different. A basic introductory course in plastics will
introduce the general rule of thumb that amorphous parts are typically more
20
dimensionally stable then semi-crystalline parts. Also, fillers, especially fiber fillers, can
create complex anisotropic properties.
Therefore it is logical that to examine the
influence of material selection.
2.4.2
Plastic Families
For this study, generic plastic families were chosen based on two primary criteria,
common usage in the automotive industry and a similar processing window. The
first criteria being important as the part under investigation is automotive, the
latter being important so as to be able to consider processing parameters as
variables and use similar process settings regardless of the specific material being
used on a sample.
The first step to determine the material choices was to consult a table of common
generic plastics (Table 5). Polypropylene is a very common commodity plastic
used in HVAC parts. Two additional materials were then sought with similar
processing criteria in terms of melt temperature, mold temperature, and ejection
temperature(Figure 1 - Figure 3).
ABS
has nearly identical processing
parameters. It is a common automotive material and as a bonus for this study, it is
an amorphous plastic as opposed to the semi-crystalline polypropylene allowing
for the study of whether this may have influenced the results. Finally polystyrene
was chosen to have a third material; while not as typical of an automotive
21
material, the very similar processing characteristics made it a workable choice for
this study.
Table 5 - Typical processing temperatures for generic classes of resins with the choices
for this project
are highlighted in green (Shoemaker, 2006, p. 289)
Ejection
Melt Temp (°C)
Generic
Mold Temp (°C)
Temp (°C)
Name
Min.
Rec.
Max.
Min.
Rec.
Max.
Rec.
ABS
200
230
280
25
50
80
88
PA 12
230
255
300
30
80
110
135
PA 6
230
255
300
70
85
110
133
PA 66
260
280
320
70
80
110
158
PBT
220
250
280
15
60
80
125
PC
260
305
340
70
95
120
127
PC/ABS
230
265
300
50
75
100
117
PC/PBT
250
265
280
40
60
85
125
HDPE
180
220
280
20
40
95
100
LDPE
180
220
280
20
40
70
80
PEI
340
400
440
70
140
175
191
PET
265
270
290
80
100
120
150
PETG
220
255
290
10
15
30
59
22
PMMA
240
250
280
35
60
80
85
POM
180
210
235
50
70
105
118
PP
200
230
280
20
50
80
93
PPE/PPO
240
280
320
60
80
110
128
PS
180
230
280
20
50
70
80
PVC
160
190
220
20
40
70
75
SAN
200
230
270
40
60
80
5
Melt Temperature of Generic Plastics
Temperature °C
450
400
350
300
Melt Temp (°C) Max.
250
200
Melt Temp (°C) Min.
150
Melt Temp (°C) Rec.
Generic Plastics
Figure 11 Processing window for melt temperature of generic plastics
23
Mold Temperature of Generic Plastics
Temperature °C
200
150
100
Mold Temp (°C) Max.
50
Mold Temp (°C) Min.
0
Mold Temp (°C) Rec.
Generic Plastics
Figure 12 Processing window for mold temperature of generic plastics
Ejection Temperatures
150
100
50
Ejection
Temp (°C) Rec.
0
SAN
PETG
PVC
LDPE
PS
PMMA
ABS
PP
HDPE
PC/ ABS
POM
PBT
PC/ PBT
PC
PPE/ PPO
PA 6
PA 12
PET
PA 66
PEI
Temperature (°C)
200
Generic Plastics
Figure 13 Recommended ejection temperatures of generic plastics
24
2.4.3
Fillers
Fillers were chosen as a key part design criteria that could affect both cooling
time and warpage.
Materials were sought with common filler and loading
percentages of 0, 10, and 30%. Glass fiber was chosen as the filler due its
common use and because it was predicted that the high aspect ratio of glass fiber
as opposed to other common fillers such as talc or glass beads would play an
important role. (Fischer, 2003, p. 29) Unfortunately even with common materials,
common fillers, and common loading percentages, it was not possible to find
examples of all the materials with each filler type and loading percentage in the
Moldflow library. In the case of PS, a 10% mineral filled PS had to be substituted
for a 10% glass filled PS. For ABS, a 15% glass filled ABS had to be substituted
for a 10% glass filled ABS.
2.4.4
Plastics Grades
Given the criteria of plastic families and fillers presented above. Materials were
chosen from the Moldflow library. They are listed in table 6
25
Table 6 – Materials selected with filler type and percentage
FILLER
Generic Name
Manufacturer
Trade Name
FILLER
%
PP
Basell
Pro-fax SD242
N/A
N/A
PP
Arkema
Pryltex V4010HL12
Glass Fiber
10%
PP
Arkema
Pryltex V4030HL12
Glass Fiber
30%
PS
Chevron Phillips
MC3200
N/A
N/A
PS
SABIC
CM-3260
Mineral
10%
PS
RTP
RTP 0405
Glass Fiber
30%
ABS
DOW
Magnum 3404
N/A
N/A
ABS
SABIC
Thermocomp AF-1003M
Glass Fiber
15%
ABS
LG Chemical
Lupos GP-2300
Glass Fiber
30%
2.4.5
Part Thickness
The geometry of a part is important, especially in terms of warpage. Consider the
difficulties in molding a five sided box with no warpage. (Bakharev, Zheng, Costa, Jin, &
Kennedy, 2005) However, to study the effects of different geometries was too large in
scope to attempt due to the need to create models for each unique geometry and an
infinite amount of geometries to choose from. One aspect of geometry, part thickness, is
easy to model in Moldflow when using mid-plane analysis. Part thickness was chosen
26
for its obvious effect on cooling time and less obvious effects on warpage such as
different shear stress and orientation effects.
A typical range of part thickness for automotive HVAC parts of 2.0 to 3.0mm was
selected. The parts are modeled with standard injection molding guidelines of uniform
thickness. (Malloy, 1994, pp. 64-65)
Table 7 – Selected part thickness
Part Thickness (mm)
2.0
2.5
3.0
2.5 Processing Parameters
The processing engineer has the complicated task of selecting the proper settings for the
injection molding process. Some of the more important parameters were chosen as
variables and the details of each are explained below.
2.5.1
Coolant Parameters
While the coolant can be various fluids, water and oil are the most common. In the case
of using the coolant only to cool the mold (as opposed to heating coolant material for this
experiment. Water is often recirculated in a closed loop system that typically has two
27
variables, coolant flow rate and coolant temperature.it), water is commonly used although
ethylene glycol and oil are sometimes used. Water is selected as the
2.5.2
Coolant Flow Rate
Coolant flow rate needs to be sufficient enough to prevent the water from raising
in temperature a significant degree while it is in the mold.
If the water
temperature rises too much, it could cause different amounts of cooling across the
part. Typical recommendations are to keep the coolant temperature from rising
more than 6○C between the inlet and outlet. (Rees, 2002, p. 303) However, it
should be noted that some sources advocate keeping the temperature delta to less
than 0.1○C for precision parts. (Kazmer, 2007, p. 208) Additionally, liquids cool
less efficiently with laminar flow than with turbulent flow. Because the diameter
is also a variable thereby complicating any use of volumetric rate as a variable, it
then made most sense to use the Reynolds number to describe the flow rate. In
laminar flow with water, the outer layer can prove to be significantly higher in
temperature at the outer laminate than near the core. Turbulence begins in circular
cooling channels at a Reynolds number about Re 2300. (Osswald, Turng, &
Gramann, 2008, p. 302) To ensure efficient cooling a Reynolds number of Re
4000 (Kazmer, 2007, p. 209) to 10000 (Osswald, Turng, & Gramann, 2008, p.
302) is recommended. This study used Re 4000, Re 10000, and Re 20000 to
determine the effect of lower versus higher turbulence (Table 8).
28
Table 8 – Selected flow rate as measured by Reynolds numbers
Flow Rate (Reynolds Number)
4000
10000
20000
2.5.3
Coolant Temperature
Setting coolant temperature is a balance between cycle time and part quality. The
lower the coolant temperature, the lower the cycle time. However, lower coolant
temperature can result in higher residual stresses.
Typically the coolant
temperature is selected to be slightly above the freezing temperature of the liquid.
Depending on whether the water is cooled from a central location or press side,
and depending on the season, coolant temperature may vary. (Osswald, Turng, &
Gramann, 2008, p. 303) Coolant temperatures of 10, 20, and 30○C were selected
for this study to range from a temperature above freezing to the room temperature
of a hot summer day (table 9)
29
Table 9 - Selected Coolant Temperatures
Coolant Temperature ○C
10
20
30
2.6 Mold Surface Temp
High mold surface temperatures can allow a processing window of lower pressure
resulting in lower shear stress. The effect of mold surface temperature on pressure and
shear stress is usually found to be lower than that of melt temperature. (Shoemaker,
2006, p. 22) Additionally, lower injection speed can be used with higher mold surface
temperatures due to slower cooling of the melt flow. Mold surface temperatures of 35,
50, and 65○C were chosen for this study (table 10) to fall within the range of
recommended mold surface temperatures for each material studied (table 11)
Table 10 – Selected Mold Surface Temperatures
Mold Surface Temperature ○C
35
50
65
30
Table 11 - Recommended Mold Surface Temperatures (Moldflow)
Min.
Rec.
Max.
Mold
Mold
Mold
Surf.
Surf.
Surf.
Temp.
Temp.
Temp.
○C
○C
○C
Generic
Manufacturer
Trade Name
FILLER
FILLER %
Name
PP
Basell
Pro-fax SD242
-
-
20
50
80
PP
Arkema
Pryltex V4010HL12
Glass Fiber
10%
40
50
60
PP
Arkema
Pryltex V4030HL12
Glass Fiber
30%
20
40
60
PS
Chevron Phillips
MC3200
-
-
25
48
70
PS
SABIC
CM-3260
Mineral
10%
20
50
70
PS
RTP
RTP 0405
Glass Fiber
30%
40
50
65
ABS
DOW
Magnum 3404
-
-
25
50
80
ABS
SABIC
Thermocomp AF-1003M
Glass Fiber
15%
40
60
80
ABS
LG Chemical
Lupos GP-2300
Glass Fiber
30%
25
50
80
2.7 Melt Temp
Melt temperature is an important process variable. Low melt temperatures will result in
higher viscosity melt, requiring a higher pack pressure and resulting in high shear
stresses. High melt temperatures reduce the pressure needed, but also results in high
volumetric shrinkage.
If temperatures are too high, the material can also degrade.
Additionally, higher melt temperatures result in longer cooling time, but not as markedly
31
as higher mold temperatures. (Shoemaker, 2006, p. 22) Melt temperatures of 210, 230,
and 250○C (table 12) were chosen for this study , which span the recommended melt
temperature processing window of the three main material families (table 13)
Table 12 - Selected Melt Temperatures
Melt Temperature ○C
210
230
250
Table 13 -Recommended Melt Temperatures (Moldflow)
Rec.
Max.
Melt
Melt
Temp.
Temp.
○C
○C
Min.
Generic
Manufacturer
Trade Name
FILLER
FILLER %
Melt
Name
Temp. ○C
PP
Basell
Pro-fax SD242
-
-
200
230
280
PP
Arkema
Pryltex V4010HL12
Glass Fiber
10%
220
235
290
PP
Arkema
Pryltex V4030HL12
Glass Fiber
30%
200
240
300
PS
Chevron Phillips
MC3200
-
-
200
230
300
PS
SABIC
CM-3260
Mineral
10%
180
230
320
PS
RTP
RTP 0405
Glass Fiber
30%
210
230
265
ABS
DOW
Magnum 3404
-
-
200
230
320
ABS
SABIC
Thermocomp AF-1003M
Glass Fiber
15%
220
240
280
ABS
LG Chemical
Lupos GP-2300
Glass Fiber
30%
200
230
320
32
2.8 Ejection Temp
Ejection temperature is the surface temperature of the part when ejected. Because it
would take many minutes for the part to reach an equilibrium state, with a uniform
temperature throughout the part, the part is often ejected as soon as the part has reached a
temperature cool enough to maintain its shape during and after ejection. The part will
continue to shrink during the cooling phase, so by keeping the part in the mold longer
(lowering the ejection temperature), it can help to prevent warp. However, the longer it is
kept in the mold, the longer the cycle time, so a balance must be reached. The ejection
temperature is usually recommended by the material manufacturer (table 15). For this
project, ejection temperatures of 80, 90, and 100○C were chosen (table 14)
Table 14 - Selected Ejection Temperatures
Ejection Temperature ○C
80
90
100
33
Table 15 -- Recommended Ejection Temperatures (Moldflow)
Generic
Manufacturer
Trade Name
FILLER
Name
FILLER
Rec. Eject.
%
Temp. ○C
PP
Basell
Pro-fax SD242
-
-
116
PP
Arkema
Pryltex V4010HL12
Glass Fiber
10%
113
PP
Arkema
Pryltex V4030HL12
Glass Fiber
30%
95
PS
Chevron Phillips
MC3200
-
-
86
PS
SABIC
CM-3260
Mineral
10%
80
PS
RTP
RTP 0405
Glass Fiber
30%
89
ABS
DOW
Magnum 3404
-
-
88
ABS
SABIC
Thermocomp AF-1003M
Glass Fiber
15%
95
ABS
LG Chemical
Lupos GP-2300
Glass Fiber
30%
88
2.9 Frozen Percentage
An alternative method of determining when to eject plastic is by checking the frozen
percentage. This is easy to do in a software simulation, but less easy to do in reality.
How can one on a processing floor instantly cut into a part and then measure how much
has solidified and how much is liquid? But, it is an interesting observation to check not
only the surface temperature from the previous section, but also to check solidification on
a volumetric temperature approach, which in this case is how much of the part has
reached a temperature below the melt temperature in cooling. Frozen percentages of 100,
95, and 90 were selected table 16.
34
Table 16 -- Selected Frozen Percentage
Frozen Percentage
100%
95%
90%
35
Chapter 3
TAGUCHI METHOD ORTHOGONAL ARRAY
The previously described variables in chapter 2 result in a L27 (13 factors with 3 levels)
orthogonal array. The array is shown in Table 17 below. Taguchi methods were used to
analyze the results and are described in this chapter. The taguchi method is used over
here to come up with a optimum set of parameters to achieve otpmised results in the
simulation.
Table 17 - The resulting L27 (13 factors with 3 levels) orthogonal array for the
experiment
36
3.1 . Setup
3.1.1 Equipment
The study was performed utilizing Autodesk Moldflow software.
The exact
configuration is detailed in table 18.
Table 18 - Hardware and Software Used
Computer
Dell Dimension 9100
Processor
GenuineIntel x86 Family Model 15 Stepping 6 ~2393 x2
Memory
2045 Mbytes
Operating
Windows XP Service Pack 3
System
Software
Autodesk Moldflow (ami2010-main (Build 09114-001) 32-bit
build
3.2 Finite Element Model
A mid-plane mesh of the part was created and is shown in Figure . A midplane mesh was
chosen for this experiment primarily due to the ability to vary the part thickness in
Moldflow which is not possible in a full 3d mesh. Additionally the mid-plane mesh
37
keeps the computing time reasonable as some runs can take up to 8 hours and full 3-D
analysis would have extended the computing time needed even further. Information
regarding the mesh is provided in table 19.
Table 19 -- Finite Element Model Statistics
Mesh type
Midplane
Number of nodes
17778
Number of beam elements
1342
Number of triangular
31494
elements
Number of tetrahedral
elements
0
38
Figure 14 - Finite Element Model
39
Chapter 4
RESULTS AND DISCUSSIONS
The results considered are listed in Table 20 below. The results discussed are obtained
from computer simulation done in autodesk mold flow software.
Table 20 - Results Considered
4.1 Dimensional Stability
Dimensional stability or as some may refer to it, deflection or warpage is the difference
between the nominal position and actual molded position.
In terms of dimensional
stability, the smaller the deflection, the better the quality of the part. When it comes to
40
the automotive industry today, it is not uncommon for parts to have tolerances in the
tenths of millimeters.
Dimensional stability will be evaluated by measuring the distance from nominal position
to the as molded position of a point at the extreme edge of the part which was seen to
have some of the worst warpage issues (figure 5).
Figure 15 An example of dimensional deflection
The measurement for all deflection values is the difference between the nominal and
actual values of a key point at the extremity of the upper arm.
4.1.1
Deflection – Combined Effects
Deflection is one of the primary considerations in this report. The Deflection –
Combined Effects result (Figure 6) is the most important deflection result as it
41
shows the final part condition and incorporates all the other deflection categories
into a sum total.
Somewhat surprisingly, the variable with the largest effect is melt temperature.
Plastic type, mold material, and fillers also all have significant contributions.
Waterline and coolant made almost no difference. Also, as it is typically taught
that the longer the part is held in the mold, the more dimensionally stable it is, one
would have expected ejection temperature or frozen percentage at ejection to
make a larger contribution, but they didn’t. Also unexpectedly, the QC-10 had
higher deflection then the P-20.
Figure 16- Effect of studied parameters on combined deflection effects
42
4.1.2 Deflection – Corner Effects
Corner effects, is the condition in molding which causes a part to shrink to the
warmer side of the part. Consider a curve with thickness. The outside of the
curve has more length then the inside of the curve. In a mold, the outside of the
curve has more mold material to cool the plastic then the inside of the curve does.
The inside of the curve takes longer to cool and causes the part to warp to the
inside. An example is shown in figure 17.
The Deflection – Corner Effects result is similar to the Combined Affects (Figure
6) result, except ejection temperature is less of a contributor (figure 18).
Figure 17 - An example of corner effects on a box shape.
The black is the nominal shape and the red is the molded shape due to corner effects
43
Figure 18 Effect of studied parameters on corner effects
4.1.3 Deflection – Differential Cooling
Differential cooling is caused by different cooling rates at different locations of
the plastic part. Differential cooling can be caused by either the part or the mold.
For instance, if a part has both thick and thin areas, the thick areas will take longer
to cool then the thin areas. Also, a certain area of the mold may be more difficult
to cool causing differential cooling.
The Deflection – Different cooling result (Figure 19) shows a much tighter
grouping of contributors then the Combined Effects result(Figure 6)However
melt temperature and plastic type are still the strongest contributors along with
mold temperature. The waterlines and coolant temperature make a difference, but
not nearly as much as I would have thought.
44
Figure 19 Effect of studied parameters on differential cooling
4.1.4 Deflection – Differential Shrinkage
Differential shrinkage can be thought of as differences in shrinkage of certain
areas caused by factors such as the position relative to key factors such as the gate
location or end of fill. (Shoemaker, 2006, p. 161)
The melt temperature and plastic type make significant contributions to the
Deflection – Differential Shrinkage result (Figure 0) while mold material and
fillers are also important. The graph is very similar to the Combined Effects
result (Figure 16), except the contributions of the top four variables are even
stronger in comparison to the other variables.
45
Figure 20 Effect of studied parameters on all differential shrinkage
4.1.5 Deflection – Orientation Effects
Orientation effects are attributed to the alignment of the plastic molecules and
fiber fillers due to the flow direction of the injected material.
The orientation effects (figure 21) was strongest with the melt temperature and
plastic type.
Mold material and not surprisingly fillers also were strong
contributors. What is somewhat surprising is that the fillers were not stronger
contributors.
46
Figure 21 Effect of studied parameters on orientation effect
4.1.6 Residual Stresses
Residual stress is a state in which a part is mechanically stressed while there are
no applied external forces. Residual stress is typically caused by differential
cooling. (Potsch & Michaeli, 2007, pp. 147-148)
Moldflow generates reports for biaxial stress. For 1st residual stresses (
Figure 2) there were only two strong contributors, melt temperature and mold
material. It makes sense that melt temperature was a strong contributor since it
was also a strong contributor in differential cooling. Interestingly, the aluminum
and Be-Cu material caused higher stresses then the steel. The 2nd residual stress
results (figure 23) had no clear strong contributors, other than melt temperature.
47
Figure 22 Effect of studied parameters on all 1st residual stress
Figure 23 - Effect of studied parameters on 2nd residual stress
48
4.2 Cooling
For the cooling section, the study will look at results the input variables have in terms of
the cooling circuit temperatures, mold temperatures, part temperatures, and heat flux.
While none of these are characteristics of the final part, they can shed important light
onto how some of the characteristics of the final part came to be.
4.2.1
Coolant Circuit Temperatures
As previously noted, coolant circuit temperatures are important because they can
affect the temperature of the mold and the mold affects the temperature of the part
and how quickly it can cool. It is recommended that the temperature differential
between coolant inlet and outlet be small in order to make dimensionally stable
parts.
The strongest factor in the highest coolant temperature is the inlet temperature.
However, this is really not of any interest since of course a higher inlet coolant
temperature results in a higher outlet coolant temperature. The only other factor
making a strong contribution is the Reynolds number. Low Reynolds numbers,
which correspond with low flow rates, experienced a strong correlation with high
outlet temperature. The longer residence time seems to be a stronger contributor
then the higher turbulence. Results of coolant circuit temperatures are shown in
figure 24 and figure 25.
49
Figure 24 Effect of studied parameters on highest circuit cooling temperature bottom
Figure 25 Effect of studied parameters on highest circuit cooling temperature top.
50
4.2.2
Mold Temperatures
For mold temperatures, a series of results are presented on figure 26 through
figure 31. Shown in these results are the highest mold temperature during the
cycle, the lowest mold temperature during the cycle, and the difference between
the two values. The highest mold temperature is dominated by the mold material
and mold temperature setting.
The lowest mold temperature is primarily
dependant on the coolant temperature. The difference between these two values
is dependent on the three previously noted variables.
Figure 26 Effect of studied parameters on highest mold temperature - top
51
Figure 27 Effect of studied parameters on lowest mold temperature – top
Figure 28 Effect of studied parameters on mold ∆T - top
52
Figure 29 - Effect of studied parameters on highest mold temperature – bottom
Figure 30 Effect of studied parameters on lowest mold temperature - bottom
53
Figure 31 - Effect of studied parameters on mold temperature ∆T– top
4.2.3
Part Temperatures
Shown in Figure 2 through Figure 35 are graphs related to the part temperature
properties. The temperature differential of the part is mostly dependant on the
coolant temperature and the mold temperature. The heat flux shows a strong
correlation with the mold material, coolant temperature, and mold temperature.
54
Figure 32 Effect of studied parameters on temperature differential
Figure 33 Effect of studied parameters on heat flux - bottom
55
Figure 34 Effect of studied parameters on heat flux - top
4.2.4
Time to Reach Ejection Time
Figure
shows the effect on the time to reach ejection temperature, more
commonly referred to as the cycle time. This is one of the key performance
indictors in terms of the economic viability of a part as the quicker the cycle time;
the more parts can be made. Mold material, mold temperature, coolant flow rate,
and part thickness were all important contributors. It was expected that mold
material, mold temperature, and part thickness, would play important results in
ejection time. Unexpectedly, ejection temperature and frozen percentage were of
little importance. Also unexpectedly, the QC-10 tended to take longer to reach
ejection temperature then P-20. The coolant flow rate had some unusual results
with both high and low Reynolds number resulting in relatively high cycle time,
56
while the Reynolds number of 10000 showed significant improvement in cycle
time.
Figure 35 Effect of studied parameters on time to reach ejection temperature
4.3 Pressure
Pressure is equivalent to describing how hard the injection molding machine must work
to force the plastic into the mold. A recommendation for pressure is that to mold a part it
should not take more than fifty percent of the pressure that the injection molding machine
can create. (Shoemaker, 2006, p. 28) Not surprisingly, the melt temperature especially,
but also the fillers were strong contributors to pressure (figure 36).
57
Figure 36 Effect of studied parameters on pressure at the V/P switchover
4.4 Weld Lines
Weld Lines are areas where two flow fronts meet forming a weaker area know as a weld
line or knit line.
Moldflow presents weld lines as a graphical representation (figure 37). There was little
difference between weld lines based on different processing parameters.
58
Figure 37 Weld lines are indicated by the multicolored lines.
4.5 Air Traps
Air traps are areas that plastic failed to fill. Typically they are created because either a
flow front reaches an area of the mold that has inadequate venting or two flow fronts
meet head on trapping a pocket of air between the flow fronts.
The data Moldflow is able to report for air traps is a graphical representation of the
locations of air traps. Shown in Error! Reference source not found., one can see there is
little distinguishable difference between a part judged to have a high amount of air traps
and one that has a low amount of air traps. Therefore, the processing parameters will not
be investigated as to the affect on air traps. What can be noted is that the air traps are
well aligned to weld lines shown in the previous section.
59
4.6 Fiber Orientation
Fiber orientation was checked for each part containing fillers.
Fiber orientation is
reported by Moldflow graphically. There was no distinguishable difference for fiber
orientation with the given variables. Typical fiber orientation is presented in Figure 39 .
Figure 38 fiber orientation with air traps
This figure shows there is little difference between what can be considered a part exhibiting high
quantity of air traps (top set, run 25) and a part exhibiting low quantity of air traps (bottom set,
run 23). The red circles show the areas of highest concentrations of air traps.
60
Figure 39 Typical Fiber Orientation
4.7 Economics and Performance
The justification for manufacturing a mold from high grade aluminum (QC-10) rather
than traditional mold steel (P-20) in this case is difficult to justify based on the results.
This report was meant to study the general effects of various part, mold, and processing
parameters, not to choose the optimal set of conditions to make a specific part. One
61
cannot say that for any specific part whether aluminum or steel may make a better mold
choice based on these results. However, the evidence from Figure and Figure shows
that whether aluminum or steel is chosen, the part should have nearly the same deflection
and ejection time results with the steel having slightly better results in both cases.
Certainly this was unexpected, as one would have thought the superior heat transfer
characteristics of the aluminum would at minimum cool the part quicker. Additionally
there is case study evidence that would have led one to predict the aluminum to perform
better. (Nerone, Iyer, & Ramani, 2000)
The data obtained from the Taguchi experiment was looked at for further explanation.
There were 27 experiments run, 9 for each mold material. The mean, minimum, and
standard deviation were examined for each set of nine runs in Table 21. Since this data
came from an orthogonal array set up for a Taguchi experiment, it was not intended to be
set up to examine data from each run as though it was an independent optimized run so
one might question the validity of examining these results in such a way. But it is
illustrative that only in the case of minimum ejection time, did QC-10 perform better then
P-20 and that BE-CU performed better than either.
So, unless two Moldflow simulations are performed on a part, one for aluminum and one
for steel, and the results compared, one should not assume that aluminum will perform
better. Moreover, the recommendation should be to make the tool of steel for the
superior wear and large amount of experience molders and toolmakers have with it unless
62
substantial improvements can be shown to exist for using aluminum through Moldflow
simulation.
Finally, while aluminum was not shown to have substantial advantages over steel, Be-Cu
was and more investigation would be warranted in this material. Some studies have
already suggested this (Engelmann, Dawkins, Shoemaker, & Monfore, 1997) , but real
world use in terms of full molds seemed to be even less common then aluminum tooling.
Typically, any use was restricted to small inserts.
Table 21 - Deflection and Ejection Time Compared for Aluminum, Steel and Copper
Tools.
QC-10:aluminium alloy
P-20: Tool Steel
Be-CU :beryllium copper alloy
63
Chapter 5
CONCLUSION AND FUTURE WORK
5.1 Conclusion
As predicted the mold material was a strong contributor in many aspects of the molding
criteria. However, the QC-10 did not show the favorable results that were predicted. At
the same time, some of the other criteria showed their importance while others were
determined to be of little significance.
From the variables studied, several proved to be dominant contributors. Melt temperature
proved to be especially important in the deflection and stress criteria along with the
material choice and to a lesser degree the mold material. The mold material and mold
temperature proved to be especially important in terms of cycle time and heat removal
from the part.
Unexpectedly, there were several variables that when compared at the same time with
other variables, made little or no difference in comparison to the dominant variables in
any of the results studied.
Amongst such variables were the waterline variables;
diameter, depth and pitch as well as ejection signal variables; ejection temperature and
frozen percentage. So while some studies, such as that by Shoemaker et al. (Shoemaker,
Hayden, Engelmann, & Miller, 2004) found important the waterline variables, when
compared against more variables, their significance was reduced.
64
5.2 Future Work
 An automotive hvac duct part is choosen to conduct of the tests to investigate the
effects of replacing steel with aluminium alloy. With aluminium alloy as the
mold material, it is being said that the high qualities of tetures of part cannot be
achieved. So work can be extended to do a comparison of surface texture obtained
when using steel as mold material to aluminum..
 Work can be extended by investing the effects on various products manufactured
through injection molding process.
 Work can be extended by doing finite element analysis on parts generated from
different mold materials, to have a better understanding of their behavior.
 FEA analysis of the mold can be conducted using CAE software's like catia, solid
works etc.
65
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