5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014,
IIT Guwahati, Assam, India
535-1
APPLICATION OF ABRASIVE WATER JET MACHINING IN
FABRICATING MICRO TOOLS FOR EDM FOR PRODUCING ARRAY
OF SQUARE HOLES
Vijay Kumar Pal1*, S.K. Choudhury2
1*Ph.D. Scholar, Indian Institute of Technology Kanpur, Kanpur, 208016, Email: [email protected]
2Professor, Indian Institute of Technology Kanpur, Kanpur, 208016, Email: [email protected]
Abstract
In the field of Abrasive Water Jet (AWJ) machining, the current focus is on the fabrication of complex three-
dimensional features. The current work is aimed at using this strategy to manufacture micro-tools for machining
arrays of square holes using Electric Discharge Machining (EDM). Based on selected parameters of AWJ
process(step over, traverse speed, path strategy),micro tools were fabricated on brass sheet of 6 mm
thickness.The performance of such fabricatedtool was investigated by performing experiments on EDM
machine to make arrays of square blind holes( texture ) on stainless steel and Ti-6Al-4V alloy sheet. The depth
of texture was measured through 3D profilometer of FOV (2x) and objective (5x) embedded with vision 64
software.The textured square holes were obtained and its depth was achieved in the range of 10 to 60 microns
and thecorresponding depth obtained of the texture is less on titanium. Discrepancy between the tool dimension
(square) and work piece (textured) was found because of the tool wear on the electrode. Key words: AWJM, Texturing, EDM, Electrode (Tool)
1 Introduction
Micro-machining and miniaturization of products
has become the need of the industry. Currently in
commercial applications micro-machining is mostly
performed by non-conventional machining processes
like lasers, electro-discharge machining (EDM) and
chemical etching [1]. Now-a day’s texturing on the
surfaces is major interest of research because surface
texturing is an effective means to improve the
tribological properties [2]. It is mostly performed by
Cutting, Burnishing, Laser machining, Electron beam
writing, Lithographic methods, Thermal reflows,
Focused ion beam machining etc. Tool design and
mask fabrication are the major obstacles to perform
texturing by non-conventional machining processes as
EDM/ECM, lithography etc. because these masks
and micro-tools are costly and very less
sources/companies are available to fabricate
them.Abrasive Water Jet Machining (AWJM) is a
state- of –the- art non-traditional machining process
making use of high pressure water converted to high
velocity jet mixed with abrasives with an ability to cut
various materials ranging from soft material like
plastics, rubber, wood etc. to hard materials like
titanium and inconel. Originally AWJM technique
was only used for linear cutting and shape cutting of
difficult to cut materials [4]. Now, researchers have
also started experimenting on generating blind
features using AWJM. The literature study reveals
that the geometrical features, like channels (single
slot) and pockets (closed loop path) can be fabricated
using AWJ milling.
In the present study, a novel path strategy is
introduced to fabricate the micro-tool of different
shapes (here, array of square spikes) using the concept
of multi-pass linear traverse cutting. Here, the
distance between the two parallel passes was kept
more than the nozzle diameter [5].
The objective of the present work is to fabricate
micro-tools (electrode) for EDM process on brass
sheet by AWJM process. Primary experiments were
carried out to find out suitable range of process
parameters, based on these selected parameters, tools
were fabricated. EDM is one of the advantageous
methods to provide shape on very hard material.The
performance of such fabricated tool by AWJM
process wasshown by performing experiments on
EDM machine to make texture (arrays of square
holes) on stainless steel and Ti-6Al-4V sheet.
2 Methodology
2.1 Experiments to fabricate micro-tool
Experiments were performed using commercially
available abrasive water jet machine (OMAX Corp.).
Table 1 shows the specifications of the machine.In
AWJMprocess, highly pressurised water is mixed
APPLICATION OF ABRASIVE WATER JET MACHINING IN FABRICATING MICRO TOOLS FOR EDM FOR PRODUCING
with abrasive particles in a mixing tube
abrasive water jet is focused through a
before making an impact on the selected area on the
work material.
Table 1 Machine specification
Maximum traverse speed 4572mm/min
Jet impingement angle
Orifice diameter
Abrasive flow rate 0.226 kg/min
Mixing tube diameter
Mixing tube length
Maximum working
pressure
Figure 1 AWJM process (nozzle and mixing
chamber)
In this work brass sheet of 6 mm thickness is
considered as material. Test samples
before subjecting to AWJM in order
flatness of the resulting tool. Fig. 2 shows the surface
roughness profile of work piece.
Figure 2 Surface roughness profile of
brass sheet
2.2 Path strategy used to fabricate (square
pattern) shaped tool
APPLICATION OF ABRASIVE WATER JET MACHINING IN FABRICATING MICRO TOOLS FOR EDM FOR PRODUCING
ARRAY OF SQUARE HOLES
with abrasive particles in a mixing tube (Fig. 1). The
abrasive water jet is focused through a focusing tube
before making an impact on the selected area on the
Table 1 Machine specification
4572mm/min
900
0.33 mm
0.226 kg/min
0.762 mm
101.6 mm
45 kpsi
1 AWJM process (nozzle and mixing
brass sheet of 6 mm thickness is
Test samples were grinded
to improve the
. Fig. 2 shows the surface
2 Surface roughness profile of grinded
cate (square
A novel path strategy is introduced to fabricate
micro-pillars by AWJM process. The resulting
machined surface is to be used as a tool in the EDM
process. The path strategy is derived from the work of
(Pal and Chaudhury, 2014) and briefly
the help of Fig.3. Here machining was carried by
keeping the distance between two successive passes
(also known as step-over (SO))
diameter of jet such that there was no superimposition
of the parallel passes of the jet. By this manner some
material in the form of strip was retained between two
consecutive passes during machining, as shown
first and second raster paths (Fig. 3). Both the raster
paths cross each other perpendicularly
It can be clearly seen that, the two crossed raster
paths generate thearrays of square on the same area.
The cross motions of nozzle along these raster
leave some material in between their consecutive
passes which results in the square pillars
implicit that the height of these square lands is
essentially the depth of the slots created due to metal
removal during the AWJ passes.
Figure3 Path strategy to fabricate
square pins)
Based on the present strategy, four different tools
were fabricated with different geometric
configurations by varying process parameters
associated with the AWJM. The quantitative features
of these tools are listed in Table 2.and the tools are
shown in Fig. 4. If one changes the step over distance,
the number density of the resulting features changes.
Similarly by varying the traverse speed, the depth of
cut (hence height of the features) can be varied.
APPLICATION OF ABRASIVE WATER JET MACHINING IN FABRICATING MICRO TOOLS FOR EDM FOR PRODUCING
535-2
is introduced to fabricate
pillars by AWJM process. The resulting
machined surface is to be used as a tool in the EDM
is derived from the work of
and briefly explained with
achining was carried by
distance between two successive passes
more than the
diameter of jet such that there was no superimposition
of the parallel passes of the jet. By this manner some
trip was retained between two
, as shown in the
). Both the raster
ly.
It can be clearly seen that, the two crossed raster
on the same area.
these raster paths
in between their consecutive
the square pillars. It is
implicit that the height of these square lands is
the slots created due to metal
Path strategy to fabricate tool (Array of
four different tools
with different geometric
configurations by varying process parameters
associated with the AWJM. The quantitative features
nd the tools are
. If one changes the step over distance,
he resulting features changes.
Similarly by varying the traverse speed, the depth of
cut (hence height of the features) can be varied.
5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014,
IIT Guwahati, Assam, India
535-3
Figure 4 Fabricated tools by AWJM
Table 2 Parameters considered for AWJM
T1 T2 T3 T4
Step over
(mm)
1.1 1.3 1.3 1.5
Traverse
speed
(mm/min)
3500 3500 2500 2500
Area (mm2) 15x25 15x25 15x25 25x25
3 Performance of Textured Tool in
Electric Discharge Machining
The surfaces machined using the AWJM processes
were used as tool (electrode) in the Electric Discharge
Machine (EDM). Since these surfaces could not be
directly fitted into an EDM, they were brazed at one
end of the copper cylinders so that they could be
inserted into the tool holder. This arrangement is
pictorially presented in Fig.5.The performance of
tools thus fabricated was investigated in an EDM
setup. The process parameters for this machining were
taken based on micro features machining and
presented in Table 3.
Figure5 EDM set up for texturing
Table 3 EDM parameters in present work
S.No. Parameter Value
1 Current 5 Amps
2 Voltage 75 volts
3 Pulse on time 150 micro sec
4 Duty Factor 72%
The experiments were conducted on Ti-6Al-4V
alloy and stainless steel sheets of 1 mm thickness.
This work aims to achieve textured arrays of square
holes on sheets. All the four tools developed in the
previous section were used here to machine these
materials.
Figure 6 Textured images by various tools
The responses of texturing tools were characterized
by the depth and geometry of the texture obtained on
these sheets. The images of the surfaces machined
using the four tools enlisted in Table 2 are shown in
Fig.6. The numbering is in accordance with the tool
numbers in the Table 2. For the first two images (Fig.
APPLICATION OF ABRASIVE WATER JET MACHINING IN FABRICATING MICRO TOOLS FOR EDM FOR PRODUCING
ARRAY OF SQUARE HOLES
535-4
6), the work piece is stainless steel while for the later
two titanium alloy work piece was used. Tool 1 (T1)
had a smaller step over distance than tool 2 (T2). This
resulted in smaller fins on the tool and subsequently
the features produced during EDM. This is apparent
from the Fig.6. Similarly, tool 3 had smaller step over
than tool 4, thus producing smaller features on the
corresponding work piece. It can also be observed
from these figures that the shapes produced on these
sheets correspond to the texturing on the tool.
Figure 7 Enlarge view of texure obtained by Tool
(T4)
Enlarged image of one of the surfaces machined
(corresponding to tool 4) is shown in the Fig. 7. The
measurement shows that the produced features are of
an approximate dimension of 700 µm x 700 µm. The
image of the corresponding tool is shown in Fig.
8.The area of the top surface of each square fin in 600
µm x 600 µm. This discrepancy between the tool
dimension and work piece can be explained as
follows: As shown in Fig. 8 (a), the tool produced by
AWJM has taper along the height of the fins. During
EDM, the tool also undergoes some wear. Because of
these, the tool area responsible for ED machining
increases in time and produces features larger than the
initial tool dimensions.
Figure 8 Images of fresh and wear tool
This image of the tool wear is shown in Fig 8. Fig 8
(a) shows a new tool and Fig 8(b) shows the
corresponding worn out tool. Because of this
taperness in the tool, the resulting feature is also
expected to be tapered along the depth direction. This
is confirmed by the optical image of the machined
work piece surface as shown in Fig. 9.The depth of
texture was measured through 3D optical profilometer
of FOV (2x) and objective (5x) embedded with vision
64 software.
Figure 9 (3D) Optical image of the square hole
texture
Since titanium alloy is difficult to machine
compared to stainless steel surface, therefore
corresponding depth obtained after machining
(texturing) was found less on titanium. This fact is
also reflected by larger tool wear while machining the
titanium alloy surface. These comparisons can be
justified since the same machining parameters were
used while working on all these surfaces and tools.
Based on these arguments, the following trends are
expected.
• Tool wear should be more while machining
titanium surface (compared to stainless steel
surface).
• Because of larger tool wear, the ratio of
obtained textured profile area to the tool
surface area should be larger on titanium.
• Depth of features should be less on titanium.
• For same operating parameters and machined
surfaces, fractional wear should decrease
with tool cross section.
Quantitatively, machining of stainless steel using tool
cross sections 200x200 µm and 400x400 µm give
features of dimensions 290x290 µm and 480x480 µm
respectively.
Similarly, tools of dimensions 400x400 µm and
600x600 µm produced features of cross sections
450x450 µm and 700x700 µm, accordingly, while
machining titanium surface.
Depth of cut on titanium was found in the range 10-20
µm which was quite less than stainless steel
machining (50-60 µm). This proves that stainless steel
is easier to machine.
5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014,
IIT Guwahati, Assam, India
535-5
Thus, all the expected trends are also obtained
experimentally.
4 Conclusions
From the advancement of technology, the capability
of AWJM process can be extended to fabricating
micro-tool (electrode) for EDM. Present work shows
the path strategy to fabricate tool (arrays of square
pin) on brass sheet. Performance of tools were
analysed by conducting experiments on stainless steel
and Ti-6Al-4V sheet. Based on the observations of
present investigation following conclusions can be
drawn:
• Smaller step-over produces the smaller fin (top
area) e.g Tool 1 (T1) has a smaller step over
distance than tool 2 (T2). This result in smaller
fins on the tool and subsequently the features
produced during EDM.
• This discrepancy between the tool dimension and
work piece was found because of taperness of
tool. The tool produced by AWJM has taper
along the height of the fins.
• Because of taperness in the tool, the resulting
textured feature on the surface was also found
tapered along the depth direction.
• Titanium alloy is difficult to machine compared
to stainless steel surface therefore, corresponding
depth (texture) obtained of the features is less on
titanium
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