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CHAPTER 4
EXPERIMENTAL SETUP
4.1
INTRODUCTION
This chapter describes the experimental setup used to conduct
the experiments. A brief description of the tool material, workpiece
material, measuring instruments have also been included. Experimental
design methods used to select the level of parameters are explained in
detail. Central composite rotatable design matrix that has been employed
for conducting experiments are described and presented in this chapter.
4.2
EXPERIMENTAL SETUP
The experiments were conducted on a HASS vertical machining
centre as shown in Figure 4.1. The detailed view of cutting operation is
displayed in Figure 4.2. Figure 4.3 shows the workpiece material AISI 304
steel which is used for experiment. The dimensions of the workpiece
specimen were taken as 32 mm × 32 mm in cross section and 50 mm in
length. As per experimental design 31, identical specimens were cut to the
above specified dimensions. The workpiece is placed at the centre of the
machine and held using machine vice. The technical details of
experimental setup for conducting experiments are shown in Table 4.1.
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Table 4.1
Technical details of experimental setup
Parameter
Value
Power of spindle motor
5.6 kw
Speed range of spindle motor
0 - 4000 rpm
Feed rate (F) m/mm
5.1 m/mm
Torque of spindle and feed motor
45 Nm @ 1200 rpm
Feed (X & Y dir)
0 - 450 mm/min
Machine tool
Hass vertical machining
centre TM1
Machine weight
1470 kg
Material of cutter
Uncoated solid carbide
end-mill
Number of flutes
4
Diameter of cutter
12 mm
Axial rack angle of cutter
18°
Nose radius
0.4 mm
Size of the workpiece
32 × 32 × 50 mm
Radial depth of the cut
2.5 mm
Workpiece material
AISI 304 steel
Surface roughness measuring
Mitutoya SJ-201 surf
instrument
tester @ 28±1 C
Tool wear measuring instrument
microscope
Cutting force measuring
Syscon tool
instrument
dynamometer
53
Figure 4.1
Figure 4.2
HASS vertical machining centre
A detailed view of end-mill and workpiece setup
54
Figure 4.3
Workpiece material (AISI 304 steel)
The tool material used was the uncoated solid carbide tools.
Solid carbide tool is inexpensive when compared to other tool materials.
It can be easily shaped and contains excellent fracture toughness, fatigue
and shock resistance. Five end-mill cutters with different helix angles have
been utilized for conducting experiments, as shown in Figure 4.4.
The shank type end-mill is available in wide variety of sizes, flute
configurations and lengths. The specifications of geometry of the end-mill
used for conducting experiments are as follows:
(i)
Number of flutes
4
(ii)
Diameter of cutter
12 mm
(iii)
Shank length
70 mm
(iv)
Rake angle of flute
12°
(v)
Helix angle of flutes
25°, 30°, 35°, 40° & 45°.
(vi)
Coating type
Uncoated
55
25
Figure 4.4
4.3
30
35
40
45
End-mill cutters with different helix angles
SURFACE ROUGHNESS MEASUREMENT PRINCIPLE
The average roughness value was measured using Mitutoyo
Surftest SJ201 as shown in the Figure 4.5. The Surftest SJ201 is a shop
floor type surface roughness-measuring instrument, which traces the
surface of various machine parts, calculates their roughness standards, and
displays the result. The measuring instruments consist of a detector unit
with stylus for tracing. A pickup or stylus of the detector unit will trace the
minute irregularities of the workpiece surface. The vertical stylus
displacement produced during tracing the work surface is converted into an
electrical signal. The electrical signals are subjected to various calculation
processes and the results of calculations (measurement result) are displayed
on the instrument liquid crystal display. RS 232 port is available in the
instruments to acquire the measured surface roughness value using
Mituotyo version 3.0 software. The cut-off length used during the
measurement was 2.5 mm and the measurement were taken at three places
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on the machined surface and the averages of those values were noted.
The certificates of inspection of the measured values are attached in
Appendix III.
4.3.1
Mituotyo Surface Test SJ201
The range and features of Mitutoyo SJ 201 P are presented
below:

Portable for easy measurement

The detector/drive unit can be detached from the display unit for
effortless measurement

Contain wide 350 µm (-200 µm to + 150 µm) measurement
range

Can be auto-calibrated

10 Measurement data can be retained in memory even after the
power is turned off

RS-232C interface enables data transfer to computer or other
devices using an external device

A dedicated carrying case is included for safe transport
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Figure 4.5
Mitutoyo
SJ-201
setup
for
surface
roughness
measurement
4.4
TOOL WEAR
The tool wear was measured using Metzer tool
microscope on the flank surface of the end-mill cutter specimen as shown
in Figure 4.6. The tool makers microscope consist of 150 mm × 150 mm
measuring stage, travel of 25 mm and extendable up to 50 mm with slip
gauges, Gonimeter eyepieces 10X with scale, base illumination (diascopic)
12V/20W (variable intensity) incident illumination 12V/20W (variable
intensity), Magnification 30X with field of view 12 mm and working
distance 80 mm. The tool after milling is kept in the measuring stage.
The tool wear is measured on the flank surface with the help of vernier
scale and cross wire.
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Figure 4.6
measurement
4.5
CUTTING FORCE
The cutting forces such as infeed force, crossfeed force and
thrust force are measured using syscon instruments milling tool
dynamometer. The instruments work based on the strain gauge wheat-stone
bridge principle. RS232 port is available in the instruments to acquire data
while machining. The workpiece is mounted on the specially-designed
machine with strain gauges to measure the cutting force in all three (axial,
radial and tangential) directions. The experiment setup of Syscon tool
dynamometer connected with CNC machine to measure the cutting forces
are shown in Figure 4.7. Moreover, a specially designed vice is used for
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measuring the cutting forces as shown in Figure 4.8. A Cutting force online
measurement system is shown in Figure 4.9.
Figure 4.7
Experimental setup - Syscon tool dynamometer connected
with CNC machine
Figure 4.8
Experimental setup - specially designed vice for cutting
force measurement
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Figure 4.9
4.6
Cutting force online measurement system
EXPERIMENTAL DESIGN PROCEDURE
Experimental design is a critically important tool in designing
and analyzing an experiment. It is an approach which gives a clear idea of
exactly what is to be studied, how the data are to be collected and a
qualitative understanding of how these data are to be analyzed in advance.
The various steps in the experimental design procedure are as
follows:

Identifying of factors and responses

Finding the limits of the process variables

Development of design matrix
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4.6.1 Identification of Factors and Responses
The identification of correct process parameters is of paramount
importance in obtaining better surface finish. Desired surface roughness,
tool wear and cutting forces may be achieved by properly selecting the
independently controllable process variables or factors, which influence the
responses. Among the many independently controllable process parameters
affecting surface roughness, tool wear and cutting forces, helix angle ( )
spindle speed (S), feed rate (F) and depth-of-cut (D) are selected as factors
to carry out the experimental works and the development of mathematical
models.
4.6.2
Finding the Limits of the Process Variables
The working ranges of all process variables selected had to be
determined to fix their levels and to develop the design matrix. A large
number of trial runs were conducted at different machining parameters.
While conducting the experiments, the upper limit of a factor was coded as
+2 and the lower limits as -2, and the coded values for intermediate values
were
calculated
from the following relationship
Equation
(4.1)
(Montgomery 1976).
Xi
2(2X (X max X min ))
(X max X min )
where
Xi is the required coded value of a parameter X
X is any value of the parameter from Xmin to Xmax
(4.1)
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Xmin is the lower limit of the parameter and
Xmax is the upper limit of the parameter
The different parameters and levels in end-milling process are
presented in Table 4.2.
Table 4.2
Parameters and
Notations
Parameters and levels in end-milling
Units
Degree(º)
Levels
-2
-1
0
1
2
25
30
35
40
45
Spindle speed (S) rpm
700 1400 2100 2800 3500
Feed rate (F)
mm/rev
0.03 0.06
0.09
0.12
0.15
Depth of cut (D)
mm
0.2
0.6
0.8
1.0
4.6.3
0.4
Development of Design Matrix
The central composite design, which is a particular design of the
Box-Wilson central composite design, has an incorporated factorial or
fractional factorial design. It has center points augmented that has a
collection of star points that permits estimation of curvature. There are
usually twice as many as star points as there are factors in the design of a
central composite design. Two extreme values (low and high) for each
factor in the design are represented by the star points (NIST/SEMTECH
2014).
Table 4.3 represents the central composite second order
rotatable design for k = 3, 4, 5, 6. The size of the experiment is reduced
using a half-replicate of the 2k factorial. If the different treatment
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combinations are applied one after another, the order in this sequence
should be randomized.
Table 4.3
Components of central composite design
No. of
Number of points in
Total
x-variables k
2k factorial
Star
Center
N
3
8
6
6
20
4
16
8
7
31
5
16
10
6
32
6
32
12
9
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This design matrix comprised of a full replication of 2 4 (=16)
factorial design plus seven center points and eight star points (Kannan &
Yoganandh 2010). All the machining parameters at the intermediate levels
(0) constituted the center points and the combination of each machining
three parameters of the intermediate level (0) constitute the star points. For
four process parameters and five levels, 31 experimental runs have been
selected for this investigation.
These variables are identified to be the controllable potential
design factors that influence the machining performance, such as surface
roughness, tool wear and cutting force during milling. It is important to
choose the ranges over which these machining variables will be varied and
the specific levels at which the runs will be made. After conducting trial
runs, the range of these machining variables influencing the machining
performance were found to be 25° - 45° for helix angle, 700 rpm -
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3500 rpm for spindle speed, 0.03 mm/rev - 0.15 mm/rev for feed rate and
0.2 mm - 1.0 mm for depth-of-cut.
The experimental design matrix for this research work is shown
in Table 4.4.
Table 4.4
Central composite rotatable design matrix
Machining parameters by coded form
Experiment
Number
Helix angle
-1
Spindle
speed (rpm)
-1
Feed rate
(mm/rev)
-1
Depth of
cut (mm)
-1
01
02
1
-1
-1
-1
03
-1
1
-1
-1
04
1
1
-1
-1
05
-1
-1
1
-1
06
1
-1
1
-1
07
-1
1
1
-1
08
1
1
1
-1
09
-1
-1
-1
1
10
1
-1
-1
1
11
-1
1
-1
1
12
1
1
-1
1
13
-1
-1
1
1
14
1
-1
1
1
15
-1
1
1
1
16
1
1
1
1
17
-2
0
0
0
18
2
0
0
0
19
0
-2
0
0
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Table 4.4 (Continued..)
Machining parameters by coded form
Experiment
4.7
Number
Helix angle
0
Spindle
speed (rpm)
2
Feed rate
(mm/rev)
0
Depth of
cut (mm)
0
20
21
0
0
-2
0
22
0
0
2
0
23
0
0
0
-2
24
0
0
0
2
25
0
0
0
0
26
0
0
0
0
27
0
0
0
0
28
0
0
0
0
29
0
0
0
0
30
0
0
0
0
31
0
0
0
0
SUMMARY
The experimental setup and procedures are explained in this
chapter. Significant input parameters are identified. Then, the limits and
levels of the process variables are fixed. Further, design matrix of 31 runs
is selected and presented.