parametric optimization of water jet machining characteristics of...

Parametric optimization of Water jet machining characteristics Of blended resin composites

Dr. Athimoolam[1], Rajan[2] & Dr. Thiyagu[3]

1. Associate Professor, Department of Mechanical Engineering, Agni College of Technology

2. Assistant Professor, Department of Mechanical Engineering, Agni College of Technology

3. Associate Professor, Department of Mechanical Engineering, Agni College of Technology

Abstract

Water jet machining(WJM) is basically a suitable process for post-manufacturing fabrication

of polymers and polymer composites as it produces zero or negligible change in thermal

strain in the materials. Polyurethane-Epoxy blended resin composites are widely used in the

shape memory applications. But not much literature available in the machining of these

composites. In the present work Epoxy-polyurethane, blended resin and the particulate

composites prepared with Nanoclay reinforcement are machined using plain WJM and the

optimization of the process is done for less energy consumption. The influence of input

parameters on the cutting time and cycle time are studied and the cutting conditions for

optimum energy consumption are identified. It is observed that if the water pressure is high,

stand-off distance is low and medium finish cut gives less cutting time and cycle time which

in turn reduces energy consumption. The Quality of cut surface is observed by visual

inspection using high- resolution camera and it has been found that the workpiece quality is

maintained for all types of composites prepared. The optimum cutting conditions from the

planned experimental trials are identified by using Grey relational analysis.

Keywords: Nanoclay, composites, machining, WJM, optimization,Grey,blend, resin

Introduction

There are various studies carried out in the field of water jet machining includes the study of

input parameters like water jet pressure, the mass flow rate of water between nozzle and work

piece and traverse and feed rate of the nozzle on the output parameters for instance rate of

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material removal (MRR) and roughness. Flow rate of abrasive particles and traverse speed

are identified as the major contributing factor for producing reduced kerfs and increased

metal removal rate in machining of cladded materials. [1] Better hole quality and surface finish

are obtained in addition to low thrust forces compared to conventional process when

machining carbon fiber-reinforced plastics using water jet cutting process. [2] The parameters

such as nozzle diameter, jet velocity ,water pressure and abrasive particle size are optimized

to get better surface roughness, MRR etc. are in Abrasive WJM using a special algorithm. [3]

The surface roughness is optimized by means of RSM technique for the input parameters of

jet speed, standoff distance and traverse speed. [4] It is observed that deformation type of wear

is the cutting mechanism because the jet penetrates into the work piece,. This can be related

to waviness formed in lower portion cut surface, eventhough the response is not fully

investigated. [5, 6] The taper and width of of laminates with thickness less than 5 mm are

minimised using low values of standoff distance. [7, 8] Less heat affected zone makes Water

jet machining a better option for machining composites. It has been observed that the standoff

distance is a major factor in deciding the machined surface quality. [9] Another study using

steel shows that low value of cutting speed yields good machined surface quality on either

side of the work piece. [10] In the fabrication of small and tiny structures, Water jet machining

technologies can be used with low pressures. This gives better surface finish in micro

machined parts if suitable value of standoff distance is selected. [11] The kerf width is

minimized by the optimization of pressure, abrasive flow rate and standoff distance by Anova

and Regression models.The pressure increase leads to increase of kerf width. [12]

K.S.Jai Aultrin et.al.[13]studied the effect of these parameters for machining of Aluminium

silicon carbide materials and obtained the variable bounds for the Abrasive water jet

machining process. Vijayakumar Pal et.al.[14] carried out the similar study including abrasive

size and standoff distance as variables for machining of blind pocket in Ti6Al4 and found that

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as the size of the abrasive particles increases, the depth achieved was more because of the

higher energy of the impact . The delamination behaviour on epoxy- graphite composite

materials when it is machined by WJM process is studied and it is observed that the erosion is

due to the collision of the shock wave from the water jet when pure water jet is used for

machining. [15] When the traverse speed of the jet is increased, will result in the increase in

the maximum value of the crack length .If the jet pressure is increased, will lead to decrease

in the maximum value of the crack length. Also if the value of the jet traverse speed is

decreased it leads to increase in the value of the depth of cut which inturn leads to decrease in

crack length as fewer particles penetrate the cracks. It has been identified that Material

removal micro mechanism throughout depth of the kerfs occurred by t he brittle fracture

when Epoxy-graphite laminates are machined. [16] J. Wang [17] studied that the cutting wear

process is analogous thereto within the conventional grinding process, and also the surface

generated is usually of a decent finish.

But,the workdone on the cutting performance parameters and optimizing power consumption

is not given importance in most of study.So,This work focuses on optimizing the cutting

parameters for minimum power consumption within selected range of parameters for these

blended composites machining.

Materials and Methods

The specimens were Nanoclay reinforced Epoxy-Polyurethane blended Polymer Composites

made in the form of sheets by In-situ Polymerization process.

Table 1: Mechanical properties of blended composite material

Table 2: Experimental Parameters

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L9 orthogonal array with three parameters at three levels is studied. The range of input

parameter values are identified with the assistance of obtainable literature for the similar

materials and also the water jet machine available in MIT, shown in Figure 1. is employed for

the work.

Figure 1. Water jet Cutting Machine (Model: 1515 Max IEM)

At first, three variables at three levels are considered with an impact angle of jet 90° on the

three mm thick specimens. The range of water pressures in the machine is identified for

cutting, based on the properties of the materials and then it is divided into three levels, i.e. at

247, 254 and 261 MPa. The three levels of traverse speeds 1091, 1130, and 1497 mm/ min

are used for cutting and 2mm, 3mm and 4 mm stand-off distance levels are used between the

workpiece and nozzle. For these experiments, the rate of 0.1 kg/ min is employed. The choice

of the stand-off distance was done to stop delamination of the composites, even though a

smaller value of stand-off distance is preferred for accuracy of cutting. The machine is

configured for “hard” material processing and will not be reconfigured at the time of

experimenting because of the commercial and technical reasons. The performance of cutting

is evaluated by the number of measures in water jet cutting. The standard of the machined

surfaces gives the assesment as the rate of material removal isn't a serious concern within the

scope of the present work.

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Results and Discussion

The fabrication of the composite materials is doled out using Water jet because it produces

less damage to the workpieces. The post-manufacturing fabrication is successfully done using

Water jet machining process because it eliminates the issues related to the traditional

machining processes like crack formation because of machine vibration and thermal strain

because of friction between the machine and workpiece. Design of Experiments is completed

to reach the experimental trials. Since three independent variables like Water pressure,

Standoff distance and Quality of cut are considered and every at three levels. The variable

traverse speed is usually recommended by the machine betting on the standard of the cut

chosen. the subsequent Quality of cut options is offered within the machine. i) Q1-Rough cut

ii) Q2-Medium finish iii) Q3-Standard finish iv) Q4-finish cut and v) Q5-Super finish cut

The extremities such as Super finish cut and rough cut are omitted and the

remaining three options are considered for this study. The effect produced by the cutting

conditions on the machining time and total cycle time is studied.

Table 3 Experimental Trials for WJM

Q1-Rough cut; Q2-Medium finish; Q3-Standard finish; Q4-Finish cut; Q5-Super finish cut

With an increase in pressure the velocity of the jet decreases and hence the cutting time for

the composites increases at the given standoff distance. The graph shown in Chart 3 shows

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that the cutting time increases when the water pressure decreases. But it remains steady after

the water pressure reaches 254 MPa. It is evident from the graph shown in Chart 3 that the

cutting time remains constant when the standoff distance is maintained very small (2 mm) or

closer to the workpiece. When the standoff distance (SOD) increases cutting time also

increases. This increase is more when the water pressure is more. This is because the velocity

of jet decreases as the pressure of water through the nozzle increases.

Chart 1. Variation of cutting time Vs Traverse speed

The cutting time drastically increases with increase in values of SOD for a given

traverse speed as observed from the graph shown in Chart 1. Hence selection of minimum

standoff distance gives less cutting time with optimum traverse speed.The cycle time is

calculated by the addition of the four-time components such as i) time to approach the

workpiece by the jet travelling through standoff distance, ii) machining time or cutting time,

iii) dwell time and iv) the time for withdrawal of jet. The variation of cycle time also shows a

similar trend as that of the cutting time and they are shown in Chart 2.There is very little

widening at higher values of traverse speed with lower value of flow rate of abrasive particles

at the bottom owing to less interaction. The depth of cut (DOC) increases linearly with

pressure of water but the increase rate declines above a certain level of pressure setting.

Fragmentation of particles at higher pressure level is the cause for decrease in rate of increase

2.5

4.5

6.5

8.5

10.5

12.5

14.5

1470.000 1478.000 1470.000

Cut

ting

tim

e in

sec

Traverse speed in mm/min

Traverse speed Vs Cutting time

SOD 4 mm

SOD 3 mm

SOD 2 mm

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of cut depth. For Opening a narrower slot, at higher values of traverse speedswith lower flow

rates, very few particles are participating in erosion.

Chart 2. Variation of Cycle time Vs Traverse speed

Excessive loading exerted because of more water pressure applied on the material

leads to bonding failure or delamination due to factors like workpiece vibration, in the bottom

portion of the workpiece while cutting. Hence,Water pressure is controlled properly in order

to avoid this problem which will reduce mechanical defect. However, through cuts are

obtained at a high water pressure when the traverse speed selected is reasonably high. When

the SOD is increased to 3 mm the cutting time initially increased to 0.070 min at 254 MPa

and maintains at the same value even if the water is pressure increased to 261 MPa. The same

pattern is repeated at the SOD 4mm. This is shown in Chart3 and the variation of cycle time

with water pressure is shown in Chart 4.

8.0

13.0

18.0

23.0

28.0

33.0

1470.000 1478.000 1470.000

Cyc

le t

ime

in s

ec

Traverse speed in mm/min

Traverse speed Vs Cycle time

SOD 4 mm

SOD 3 mm

SOD 2 mm

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Chart 3.Variation of cutting time Vs Water pressure

Chart 4. Variation of Cycle time Vs Water pressure

The influence of Water pressure and Standoff distance on another cutting parameter of

Traverse speed is also an important aspect to be studied because the traverse speed value is

generated by the machine at a given water pressure for the Quality of cut chosen. Charts 5

and 6 indicates that there is no change in traverse speed for low water pressure of 247 MPa

and low standoff distance of 2mm. There is slight variation in the traverse speed for 3 mm

SOD and at a pressure of 254 MPa.

0

1

2

3

4

5

6

245 250 255 260 265

Cut

tin

g ti

me

in s

ec

Water pressure in MPa

Pressure Vs Cutting time

SOD 2 mm

SOD 3 mm

SOD 4 mm

0

2

4

6

8

10

12

245 250 255 260 265

Cut

ting

tim

e in

sec


Pressure Vs Cycle time

SOD 2 mm

SOD 3 mm

SOD 4 mm

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Chart 5. Variation of Traverse speed Vs Water pressure

Chart 6. Variation of Traverse speed Vs Standoff Distance

As the composite materials are brittle it generally doesn’t present burrs. It is

observed that if water pressure used is high, smooth exit edge without any burrs are formed in

the machined samples. However, if the water pressure used is low then burrs are visible in

the machined samples especially on the exit side. Also, it is observed that small hairline burrs

are present on the materials when high values of traverse speed is used for cutting. Hence it is

inferred that the burr formation in the specimen or finish of the cut surface depends on the

energy level of the jet on the exit side of the specimen. It is observed in this study that at

0

200

400

600

800

1000

1200

1400

1600

245.00 250.00 255.00 260.00 265.00

Tra

ver

se s

pee

d i

n m

m/m

in


Pressure Vs Traverse speed

SOD 2 mm

SOD 3 mm

SOD 4 mm

600

800

1000

1200

1400

1600

0 2 4 6

Tra

vers

e sp

eed

in

mm

/min

Standoff distance in mm

SOD Vs Traverse speed

WP 247 MPa

WP 254 MPa

WP 261 MPa

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938.5 mm/min traverse speed or 261MPa water pressure are used then there is no burrs

present on the machined surface.

The crack generation process followed the mode I method of fracture. At first, crack

tips are formed followed by the penetration of water into the already developed crack tips

causes a wedge action of water results in the crack propagation. Wedging action occurs

because of particle embedment inside the existing material crack.

When the traverse speed is increased then the value of crack length also reaches maximum

value. But if the jet pressure is increased then the maximum value of crack length will

decrease. This is due to increase in kinectic energy of the jet because of increase in water

pressure. As the jet deflection is reduced, the flow of water into the cracks is also reduced.

This in turn leads to a decrease in maximum value of a crack length. If the the jet traverse

speed value is deccreased then the rate of mass flow increase causes more shearing action.

This results in increased depth of cut, leaving very few particles for penetration of the cracks.

Chart 7. Variation of Cutting time Vs Standoff Distance

Another important aspect of this machining process is that when the water pressure is kept

constant then the cutting time and cycle time are varying linearly for standoff distance. It is

shown in Chart 7 and Chart 8.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.000 2.000 4.000 6.000

Cut

ting

tim

e in

sec

Stand off Distance in mm

SOD Vs Cutting time

WP 247 MPa

WP 254 MPa

WP 261 MPa

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Chart 8. Variation of Cycle time Vs Standoff Distance

Figure 2. WJM -work piece after Cutting

Figure 3. WJM -Removed material samples after Cutting

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0 2 4 6

Cyc

le t

ime

in s

ec

Stand off Distance in mm

SOD Vs Cycle time

WP 247 MPa

WP 254 MPa

WP 261 MPa

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The variation is more pronounced if the standoff distance or water pressure is

increased further. The machined samples for EP/PU, EP/PU/1%NC, EP/PU/2%NC,

EP/PU/3%NC, EP/PU/4%NC and EP/PU/5%NC composites are shown in Figure 2 and the

cut-outs or removed pieces during machining are shown in Figure 3. The machined samples

show good quality cuts as evidenced in the figures with no deviation in dimensions of the

hole. Also, it is observed from the removed materials the burr formation is limited and hence

it can be used for machining of these composites successfully.

Grey Relational Analysis

Optimum process parameters for cutting the composites are identified among the

experiments conducted by using Grey Relational Analysis. Lower the better criterion is used for

the cutting time to identify the optimum process parameters setting. The Maximum and

Minimum entry values are identified for the cutting time and cycle time and the deviation

between them is calculated.

Table 4. Calculation of Rank based on Grey Relational Coefficient

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The deviation between the maximum value and the cell value is computed. The actual deviation

divided by the maximum deviation will give the Grey relational coefficient. These values are

given in Table 4.There is Rank deficiency due to the presence of empty cells, unbalanced

nesting, and therefore further analysis is not carried out. The optimum values of Input

parameters are calculated based on the experimental values shown in Table 3.Grey Relational

Analysis is done to find out the optimum values of input parameters to obtain less cutting

time and it is found that the cutting time is minimum (0.05 min) for the pressure of 261 MPa,

SOD 2 mm and with Quality of cut Q2 (medium finish) i.e. traverse speed 1470 mm/min.

Thus the optimum cutting parameters for machining of these composites with less cutting

time and cycle time has been identified.

Conclusion

The property values of the materials and the limitations of the water jet cutting machine are

used as constraints to select input parameter values.The phenomenon of cutting mechanism is

decided by the bond strength and amount of deformation. The mechanism of cutting in the

middle portion of the hole involves the plastic deformation. This phenomenon of erosion

usually occurs in ductile materials. This mechanism is also seen in the erosive process of

brittle materials. The Epoxy-polyurethene blended composites, contains several Nanoclay

particles embedded on the material. It is recommended to use higher levels of water pressure

to reduce the size of the crack but technological constraints are imposed in order to utilize

minimum cutting time and energy. Similarly, the traverse speed of the machine table is

reduced as it is linked with reduction in the number of machined samples or cutting rate.

Water jet machining process machined accuracy and the quality of cut are very good as

observed and it is an advantageous and more suitable cutting process for these types of

composites. The Water jet machining process is optimized by Grey Relational Analysis for

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less cutting time and cycle time. Experiments show that Water jet machining may be

successfully employed for machining E/PU/NC composites.

References

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waterjet cutting of cladded material: kerf taper and MRR analysis. Mater. Manuf.

Processes.,2019,34,544-553.

[2] Massimo Durante; Luca Boccarusso; Dario De Fazio;Antonio Langella, Circular

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[3] Shankar Chakraborty ;Ankan Mitra. Parametric optimization of abrasive water-jet

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[4] Arvind Kumar; Hari Singh; Vinod Kumar. Study the parametric effect of abrasive

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[5] Gnanavelbabu, A.; Kaliyamoorthy Rajkumar; Saravanan, P. Investigation on the

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hybrid metal matrix composites. Mater. Manuf. Processes.,2018, 33, 1313-1323.

[6] Bimla Mardi, K. ; Dixit, A. R. ; Mallick, A. ; Alokesh Pramanik; Beata Ballokova;

Pavol Hvizdos; Josef Foldyna; Jiri Sucka; Petr Hlavacek; Michal Zelenak, Surface

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[7] Mustafa Armagan; Armagan Arici, A. Cutting performance of glass-vinyl ester

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[8] Selvam, R. ; Karunamoorthy, L.; Arunkumar, N. Investigation on performance of

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[9] Vasanth. S.; Muthuramalingam. T.; Vinothkumar, P.; Geethapriyan, T.; Murali, G.

Performance Analysis of Process Parameters on Machining Titanium (Ti-6Al-4V)

Alloy Using Abrasive Water Jet Machining Process. Procedia CIRP.,2016,46,139 –

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[10] Piotr Loschnera; Krzysztof Jarosz; Piotr Nieslonya. Investigation of the effect of

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[11] Matus Molitoris; Jan Pitel; Alexander Hosovsky; Maria Tothova; Kamil Zidek.

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[12] Deepak Doreswamy; Basavanna Shivamurthy; Devineni Anjaiah; Yagnesh, N. An

Investigation of Abrasive Water Jet Machining on Graphite/Glass/Epoxy Composite.

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[13] Jai Aultrin,K.S.; JaiAultrin,M.; DevAnand,P.;Jerald Jose. Modelling the cutting

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[14] Vijaya Kumar Pal.S.K.; Choudhury. Surface characterization and machining of blind

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Figures and Tables

Figure 1. Water jet Cutting Machine (Model: 1515 Max IEM)

Figure 2. WJM -work piece after Cutting

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Figure 3. WJM -Removed material samples after Cutting

Table 1: Major properties of the Test material Mechanical property Test value

1%NC 2%NC 3%NC 4%NC 5%NC Impact strength(J/m) 13.76 13.35 12.94 12.53 12.12 Compressive strength(MPa) 17.81 14.91 12.00 09.10 06.19 Shear strength(kPa) 05.76 04.79 03.82 02.85 01.88 Tensile Strength(MPa) 08.75 10.52 10.55 08.85 05.42 Flexural strength(MPa) 20.01 26.10 28.13 26.09 20.00 Table 2: Experimental Parameters Water pressure(MPa) Traverse speed(mm/min) Standoff distance(mm)

247 1470 2

254 1176 3

261 938 4

Table 3 Experimental Trials for WJM

Expt.No Water pressure (MPa)

Standoff Distance

(mm)

Traverse speed (mm/min)

Machining time

(sec)

Total cycle time

(sec)

1 247 2 Q2(1470) 3.00 9.00

2 247 3 Q3(1130) 3.60 9.60

3 247 4 Q4(1091.8) 4.20 10.20

4 254 2 Q2(1478) 3.00 9.00

5 254 3 Q3(1117.5) 4.20 10.08

6 254 4 Q4(904.96) 5.40 11.22

7 261 2 Q2(1470) 3.00 8.88

8 261 3 Q3(1156) 4.20 9.90

9 261 4 Q4(938.5) 5.40 10.98

Q1-Rough cut; Q2-Medium finish; Q3-Standard finish; Q4-Finish cut; Q5-Super finish cut

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Table 4. Calculation of Rank based on Grey Relational Coefficient

Max M/c ing Time -M/c ing time

Max Cycle Time -Cycle time

Lower the better (Machining time)

Lower the better (Total cycle time)

Grey relational coefficient 1

Grey relational coefficient 2

GRC1+ GRC2

Grey relational grade

R a nk

0.04 0.037 1 0.9487 1.0000 0.9070 1.907 0.9535 2

0.03 0.027 0.75 0.6923 0.6667 0.6190 1.287 0.6429 3

0.02 0.017 0.5 0.4359 0.5000 0.4699 0.969 0.4849 6

0.04 0.037 1 0.9487 1.0000 0.9070 1.907 0.9535 2

0.02 0.019 0.5 0.4872 0.5000 0.4937 0.994 0.4968 5

0 0 0 0.0000 0.3333 0.3333 0.667 0.3333 8

0.04 0.039 1 1.0000 1.0000 1.0000 2.000 1.0000 1

0.02 0.022 0.5 0.5641 0.5000 0.5342 1.034 0.5171 4

0 0.004 0 0.1026 0.3333 0.3578 0.691 0.3456 7

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