Selection of optimal process parameters by Taguchi method for Drilling GFRP composites using Abrasive Water jet machining Technique

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ScienceDirect Materials Today: Proceedings 5 (2018) 19714–19722

www.materialstoday.com/proceedings

ICMPC_2018

Selection of optimal process parameters by Taguchi method for Drilling GFRP composites using Abrasive Water jet machining Technique. K. Siva Prasad, Dr. G. Chaitanya a

Assistant Professor,Department of Mechanical Engineering, V R Siddhartha Engineering College, Vijayawada-52007, India b Associate Professor,Department of Mechanical Engineering ,R V R& J C College of Engineering, Guntur-522019, India

Abstract Abrasive Water Jet Machining (AWJM) is an unconventional machining process which is employed for production of bolt holes on brittle and hard materials such as composite materials, alloys, ceramics and intricate electronics components, for assembly of structural frames. The strength of the assembled joint depends on the quality holes made by the abrasive water jet technique, so it is important to understand the applications of AWJM process on GFRP composites by the industry. The aim of present experimental work is to optimize the machining process parameters of abrasive water jet machining on Glass fiber reinforced plastic composite for making holes. In this work, experiments are carried out as per the taguchi experimental design and selected an L9 orthogonal array to study the influence of various process parameters on Material removal rate and surface roughness and hole quality. The selected machining process parameters are abrasive flow rate, pressure, standoff distance and fiber orientation. From the experimental results maximum material removal rate observed at a pressure of 225Mpa, mass flow rate of 400g/min ,standoff distance of 1.5mm and fiber orientation of 45o. Also observed optimum hole accuracy at pressure of 175Mpa, mass flow rate of 300g/min, standoff distance of 1.5mm and fiber orientation of 90o. From the experimental results it is found that material removal rate, hole accuracy and surface roughness are mainly influenced by the, standoff distance, pressure and abrasive flow rate . Taguchi technique is used for optimizing the effect of predicted variables on response variable. The experimental results are analyzed by using analysis of means. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization. Keywords: Abrasive water jet machining, Material removal rate, Surface roughness, accuracy,GFRP, Taguchi, orthogonal array.

* Corresponding author..

E-mail address: [email protected]

2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization.

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1. Introduction Glass fiber reinforced plastic (GFRP) composites are widely using in industrial applications because of their great advantages like high corrosion resistance, high modulus, high strength to weight ratio and high thermal resistance. In addition to those, easy to manufacture GFRPs which leads to low production cost, because of above advantages these are currently using in aircraft and automotive components. And also using for making of boat hulls, house hold appliances and building panels. Generally composites are brittle and hard which are difficult to machine by conventional machining methods. The non- traditional machining process used for machining of composites are Ultrasonic, Laser jet, Electron beam machining and Abrasive water jet machining (AWJM). Machining of Composite materials is challenge to conventional and non conventional machining technique due to anisotropy and inhomogeneity. The holes produced by USM have a tendency to break out at the bottom owing to the static load and high amplitudes. Difficulty associated with the laser beam and Electron beam machining process is thermal distortion, due to heat dissipation into the work piece thermal cracks and subsurface defects are propagated. Abrasive water jet machining (AWJM) is a non conventional machining method which is well suited for machining composite materials because of no thermal distortion, no vibrations and no chemical reaction. This process is particularly suitable for heat sensitive materials that cannot be machined by processes that produce heat while machining. R.Selvam et al. [1] had done investigation on performance of abrasive water jet in machining hybrid composites. The effects of cutting parameters on quality characteristics were optimized. From the experimental results it is observed that average surface roughness Ra is directly proportional to traverse speed and indirectly proportional to the water pressure. Surface roughness decreases with standoff distance. Kerf taper is indirectly proportional to both traverse speed and work pressure and decreases at moderate SOD. Ali Ibraheem et al. [2] had done investigation to assess the influence of abrasive water jet machining parameters in the hole making process on GFRP composites to find the optimum values of the process parameters. from the experimental results they observed that high level of cutting feed, abrasive flow rate and low level of jet pressure and stand-off distance lead to high cut quality, high dimensional accuracy, minimum cost and high productivity in hole making on composites. John Kechagias et al.[3]done experiments on trip sheet steels for quality characterization by abrasive water jet machining using taguchi technique. Influence of selected process parameters on response parameters are analyzed and observed that mean kerf width is affected mainly by nozzle diameter. On other hand nozzle diameter and standoff distance are mostly affect the surface roughness and also when the traverse speed is increased the mean kerf width decreased and the surface roughness increased. Lingaraj.N and Gajendran.S [4] had done work on optimization of process parameters by using Taguchi multi response method. From the results they observed that Traverse rate and Abrasive flow rate are the most significant control factors on (Multi Response Performance Index) MRPI and standoff distance is the sub- significant parameter on MRPI. Traverse rate and Abrasive flow rate are the most significant control factors on TPCI and standoff distance is the sub- significant parameter on TPCI. N. Jagannatha, et al,[5] done investigation on drilling of soda lime glass by abrasive hot air jet machining to find the effect on MRR and surface roughness. From the experimental results they identified that air temperature has the highest contribution of about 60.54% for MRR and 80.99% for Ra, the other parameters have less contributions. M.Ramulu et al,[6] done research on effect of process parameters on surface roughness and kerf taper of laminate specimens. Through ANOVA technique they find significant effect of process parameters on surface roughness and developed mathematical model to predict the surface roughness and kerf taper for cutting of 16mm thickness.. M. Chithirai Pon Selvan et,al.[7] conducted experiments to assess the influence of process parameters of abrasive water jet machining on stainless steel. They observed that increase of water pressure results in increase of depth of cut, depth of cut is directly proportional to the mass flow rate, increase of traverse speed decreases the

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depth of cut, Increase in nozzle standoff distance decreases the depth of cut .Sitarama Chakravarthy et al [8], done investigation on optimization of process parameters by using fuzzy logic and genetic algorithm on machining granite to a predetermined depth of cut. From the experimental results multi response optimization procedure suggests best set of process parameters to increase the productivity and thereby reducing the cost. D.V. Srikanth, M. Sreenivasa Rao, [9] done investigation on FRP composites by using Taguchi. From the investigation they observed that to minimize the width of cut, nozzle should be placed close to the work surface. By increasing the jet pressure, cut slot width also increasing. The taper of cut gradually varies with standoff distance. Standoff distance and work feed rate influencing on surface roughness. By increasing jet pressure, the surface roughness decreases.J wang et al,[10] done experimental investigation on polymer matrix composites to study the effect of input process parameters on machinability of kerf characteristics by abrasive water jet machine. From the experimental results recommendations are made to optimize the process control and process optimization. 2. Experimental work 2.1 Material The material selected for fabrication of work piece is Glass Fiber Reinforced Polymer composites (glass-138), Epoxy resin (3351) and hardener to fabricate the work pieces. 2.2 Sample Fabrication: Fibre Glass/Epoxy laminates was prepared by hand layup process. The fibre fabrics were cut into rectangular shape having dimensions of 100 mmx40 mm. The fiber orientations considered for experimentation are 0o, 45o, 90o and thickness of work pieces is 4 mm.

Fig1. (a) Geometrical model of specimen (b) Specimen made for experimentation 2.3 Design of experiments For this investigation hole operation performed with the diameter of 10mm on specimen of 4mm thickness. Experiments are conducted as per the Taguchi L9 orthogonal array. This L9 orthogonal array consists of 3 levels and 4 factors. The selected process parameters for experimentation are pressure, standoff distance, abrasive flow rate and fiber orientation and available range as shown in Table.1 Optimization is done for the response parameters of Material removal rate, Dimensional accuracy and surface roughness.

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Dimensional accuracy (DU-DL): it is the difference between upper diameter and lower diameter. A high value of these terms represents low dimensional accuracy. Where DU: Upper Diameter D L: Lower Diameter Table 1. Available process parameters for experimentation Selected process parameters

Level 1

Level 2

Level 3

Pressure (Mpa)

125

175

225

Standoff Distance (mm)

1.5

2.5

3.5

Mass flow rate (g/min)

200

300

400

Fiber orientation( Degree)

0

90

2.4 Experimental setup The equipment used for machining the samples was CNC Abrasive Water jet cutting machine with direct drive pump of 30hp with designed pressure of 345MPa (50,000 psi). The machine is equipped with a vacuum feed type of abrasives from the hopper, which is pneumatically controlled. For the nozzle assembly, it has an orifice of 1.01mm diameter of sapphire jewel and a focusing tube of 1.01 mm internal diameter of carbide with a focus length of 4 inch. Throughout the experiments, the nozzle was frequently checked and replaced with a new one if the nozzle was worn out significantly. Experimental Diagram as shown in fig.1 the diameter of the hole size is measured by profile projector along the x-axis and y-axis and taken as average. Surface roughness is measured by Tomlinson surface meter along the depth of hole at four points and taken as average as shown in below Fig 2 and Fig 3.

Fig.2 Experimental setup of abrasive water jet machining

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Fig.3 Specimens after machining by the abrasive water jet machining process 3. Results and Discussions 3.1 Effect of different input process parameters on Material Removal Rate Selected input process parameters for analysis of material removal rate are Pressure (C1), standoff of distance (C2), flow rate (C3), fiber orientation (C4) and selected response parameters are Material removal rate (C5) and signal to noise ratio (C6). From the table 2, it is observed that Maximum Material Removal Rate is 1.8190gm at a pressure of 225 MPa, standoff distance of 1.5 mm, abrasive flow rate of 400gm and fiber orientation of 45o. Table 2. Experimental results for Material Removal Rate S.No.

Pressure (Mpa)

Stand-off distance(mm)

Flow rate (g/min)

Fiber orientation

MRR

SNRA

(gm/min)

(Degrees) C1

C2

C3

C4

C5

C6

1

125

1.5

200

0

0.8967

-0.94706

2

125

2.5

300

45

1.3450

2.57445

3

125

3.5

400

90

1.7934

5.07354

4

175

1.5

300

90

1.3876

2.84529

5

175

2.5

400

0

1.4148

3.01390

6

175

3.5

200

45

1.2553

1.97495

7

225

1.5

400

45

1.8190

5.19665

8

225

2.5

200

90

1.6139

4.15753

9

225

3.5

300

0

1.7840

5.02790

Plots are drawn for the analysis of material removal rate, it is observed that for minimum mean value 0.8967gm MRR for flow of 200 g/min, again 1.3450gm for 200 to 300g/min and again is increasing to 1.7934 gm for 300 to 400 g/min. this is due to fact that increase in mass flow rate leads to increase in weight of abrasive particles for constant time, thereby increasing the Material removal rate. Again the graph drawn for mean of means and pressure as shown in fig.3 In this case the mean value is maximum at 225Mpa which is 1.75 then decreases up to 1.35 from 225Mpa to 175Mpa after that to 1.33 from 175Mpa to 125Mpa. This is due to increase in air pressure increases the energy of abrasive particles and strike of the material with high energy level and cut the more material. Graphs drawn for mean of means and standoff distance as shown in fig.3 Here the mean is maximum at standoff distance of 3.5mm for 1.68 thereafter decrease in mean 1.48 from 3.5 to 2.5 standoff distance and also decrease in mean 1.35 from 2.5 to 1.5mm. here increase in standoff distance increasing the mean value up to certain extent, beyond that limit generally decrease in MRR because of loss of kinetic energy of abrasive particles. From ranking parameters based on means, standoff distance showing least influence on Material removal rate and occupying third rank as shown in below 3 and above Table 1 and table 2.

K.Siva Prasad et al./ Materials Today: Proceedings 5 (2018) 19714–19722 Main Effects Plot for SN ratios

Main Effects Plot for Means

Data Means

Data Means

pressure

1.8

sod

flow rate

fiber angle

pressure

5.0

sod

flow rate

fiber angle

4.5

Mean of SN ratios

1.7

Mean of Means

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1.6

1.5

1.4

4.0 3.5 3.0 2.5

1.3

2.0

1.2

125 125

175

225

1.5

2.5

3.5

200

300

400

0

45

90

175

225

1.5

2.5

3.5

200

300

400

0

45

90

Signal-to-noise: Larger is better

Fig. 4 (a) Main effect plots for mean of means (b) Main effect plots for S/N ratio (Material Removal Rate) To find the influence of fiber orientation on material removal rate drawn graphs between mean and fiber orientation. The mean is maximum at 1.60 for 90o and decreasing to 1.48 from 90oto 45o there after decreasing to 1.35 from 45o to 0o. The Ranking parameters based on Means, fiber orientation influencing the material removal rate and occupying fourth rank. Table 3. Ranking of parameters based on means for MRR Level

Pressure

Standoff distance

Flow rate

Fiber angle

1

1.345

1.368

1.255

1.365

2

1.353

1.458

1.506

1.473

3

1.739

1.611

1.676

1.598

Delta

0.394

0.243

0.420

0.233

Rank

2

3

1

4

3.2 Eeffect of different input process parameters on surface roughness. From the table 4, it is found that minimum surface roughness of 3.48 microns at a pressure of 175 Mpa, 200 mass flow rate of 200g/min, standoff distance of 3.5mm and fiber orientation of 45o.To find out the effect machining process parameters on surface roughness, graphs are between mean of means to pressure, standoff distance, and flow rate and fiber angle. Table 4. Experimental results for Surface roughness S.No.

Pressure

Flow rate

Fiber orientation

Surface roughness (microns)

SNRA

(Mpa)

Stand-off distance(mm)

C1

C2

C3

C4

1

125

1.5

200

0

3.91

-11.8435

2

125

2.5

300

45

4.41

-12.8888

3

125

3.5

400

90

4.60

-13.2552

4

175

1.5

300

90

4.34

-12.7498

5

175

2.5

400

0

4.26

-12.5882

6

175

3.5

200

45

5.84

-15.3283

7

225

1.5

400

45

3.83

-11.6640

8

225

2.5

200

90

5.27

-14.4362

9

225

3.5

300

0

4.86

-13.7327

(g/min)

(Degrees)

C5

C6

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From the experimental results it is observed that least surface roughness at a pressure of 225Mpa, standoff distance of 1.5mm and fiber orientation of 45o. Plots drawn between mean of means to pressure, SOD, mass flow rate and fiber angle. standoff distance is directly proportional to the surface roughness, this is due to that increase in SOD results in increase in jet diameter this reduces the kinetic energy density of the jet due to impingement, this results increase in surface roughness. Lower standoff distance produces smoother surface due to increased kinetic energy. Pressure is proportional to surface roughness up to some extent there by decrease in surface roughness. This is due to higher pressure energy increases the kinetic energy of the abrasives and cutting operation is carried out without any jet deflection there by minimizes the waviness of the pattern. Mass flow rate is directly proportional the surface roughness which is observed from the plots. This is because of higher the abrasive flow rate means higher the number of particles involved in cutting process thereby inter-collision of particles among themselves and hence increases in surface roughness. Fiber orientation is also influencing the surface roughness. From the plots is observed that surface roughness increases with increase in fiber angle, this is up to some extent. Least surface roughness observed at an angle of 0o. This is depending on microstructure of material, type of fiber and shear fracture. From the table 5 of ranking parameters based on mean of means for surface roughness, it is observed that Standoff distance and mass flow rate are the most significant parameters on surface roughness after that pressure and fiber orientation are subsequent significant parameters on surface roughness.

Main Effects Plot for Means

Main Effects Plot for SN ratios

Data Means

pressure

5.2

sod

Data Means

flow rate

fiber angle

-12.0

Mean of SN ratios

5.0

Mean of Means

pressure

4.8

4.6

4.4

4.2

sod

flow rate

fiber angle

-12.5

-13.0

-13.5

-14.0

4.0

125

125

175

225

1.5

2.5

3.5

200

300

400

0

45

90

175

225

1.5

2.5

3.5

200

300

400

0

45

90

Signal-to-noise: Smaller is better

Fig. 5 (a) Main effect plots for mean of means (b) Main effect plots for S/N ratio (Surface roughness) Table 5. Ranking of parameters based on means for fiber angle Level

Pressure

Standoff distance

Flow rate

Fiber angle

1

4.307

4.027

5.007

4.343

2

4.813

4.647

4.537

4.693

3

4.653

5.100

4.230

4.737

Delta

0.507

1.073

0.777

0.393

Rank

3

1

2

4

3.3 Effect of different input process parameters on Accuracy of drilled hole. Effect of process parameters on drilled hole accuracy are observed from the following table.6 From the experimental results optimum dimensional accuracy observed at pressure of 175Mpa, standoff distance of 1.5mm, flow rate of 300g/min and fiber angle of 90o. Graphs drawn between mean of means to pressure, standoff distance, and mass flow rate and fiber angle. From the graphs it is finding that dimensional accuracy is decreases with increase of standoff distance and pressure. This is due to Increasing the standoff distance results in increase in jet

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diameter thereby decrease in abrasive density , so top surface hole diameter & bottom surface hole diameter are not equal this leads to decrease in accuracy. Increase of hydraulic pressure leads to increase the kinetic energy of abrasive particles. Abrasive particles with high kinetic energy impinging on top surface there onwards decrease in energy levels to cut throughout depth of cut. So this leads to dimensional inaccuracy as shown in below table 7.

Main Effects Plot for Means

Main Effects Plot for SN ratios

Data Means

Pressure

0.0375

Sod

Data Means

Flow rate

Fiberangle

0.0350

Sod

Flow rate

Fiberangle

34

Mean of SN ratios

0.0325

Mean of Means

Pressure

35

0.0300 0.0275 0.0250 0.0225

33

32

31

30

0.0200

29 125

125

175

225

1.5

2.5

3.5

200

300

400

0

45

90

175

225

1.5

2.5

3.5

200

300

400

0

45

90

Signal-to-noise: Smaller is better

Fig. 6 (a) Main effect plots for mean of means (b) Main effect plots for S/N ratio (DimensionalAccuracy) Table 6. Experimental results for Material Removal Rate S.No.

Pressure

Stand-off distance(mm)

(Mpa)

Flow rate (g/min)

C2

C1

C3

Fiber orientation

Accuracy

(Degrees)

C5

SNRA

(Du-DL)

C4

C6

1

125

1.5

200

0

0.019

34.4249

2

125

2.5

300

45

0.023

32.7654

3

125

3.5

400

90

0.029

30.7520

4

175

1.5

300

90

0.017

35.3910

5

175

2.5

400

0

0.024

32.3958

6

175

3.5

200

45

0.036

28.8739

7

225

1.5

400

45

0.020

33.9794

8

225

2.5

200

90

0.026

31.7005

9

225

3.5

300

0

0.041

27.7443

Table 7. Ranking of parameters based on means of dimensional accuracy Level

Pressure

Standoff distance

Flow rate

Fiber angle

1

0.02367

0.01867

0.02700

0.02800

2

0.02567

0.02433

0.02700

0.02633

3

0.02900

0.03533

0.02433

0.02400

Delta

0.00533

0.01667

0.00267

0.00400

Rank

2

1

4

3

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Also observed from the plots, dimensional accuracy increased with increase in Mass flow rate and fiber angle. This is due to that higher the mass flow rate means higher the number of particles involved in cutting process that leads to proportionate increase in depth of cut thereby increase in dimensional accuracy. Fiber orientation is also increasing the dimensional accuracy this is depending upon interstitial matrix, type of fiber and shear fracture, from the experimental results dimensional accuracy observed fiber orientation at 90o. Conclusions: The present study inteded to provide technical information related to material removal rate, surface roughness and dimensional accuracy,by hole making on GFRP compisites with abrasive water machining. The following points are observed from the investigation. (1) Standoff distance, pressure, mass flow rate and fiber orientation are the influential parameters in the machining process of GFRP composites using abrasive water jet technique. (2) Material removal is directly proportional to the mass flow rate. The maximum material removal rate observed at a pressure of 225Mpa, mass flow rate of 400g/min, standoff distance of 1.5mm and fiber orientation of 45o. (3) Surface roughness affected by the Standoff distance. While increasing flow rate surface roughness was decreasing. The minimum surface roughness observed at a pressure 225Mpa and flow rate of 300g/min. (4) Dimensional accuracy influenced by the standoff distance and pressure. optimum dimensional accuracy observed at a pressure of 175Mpa and mass flow rate of 300g/min and standoff distance of 1.5mm. (5) The experimental results shows that abrasive water jet cutting is viable process for cutting this type of composites. References [1] R.Selvam, L.Karunamoorthy and N.arunkumar, “investigation on performance of abrasive eater jet in machining hybrid composites, material and manufacturing process,2017,vol.32,No.6,PP700-706. HM Ali Ibraheem,A Iqbal,H Majid, numerical optimization of hole making in GFRPcomposite using abrasive water jet machining process,journal of the Chinese Institute of Engineers, Vol.38, No.1,2015. pp 66-76. [2] HM Ali Ibraheem,A Iqbal,H Majid, numerical optimization of hole making in GFRPcomposite using abrasive water jet machining process,journal of the Chinese Institute of Engineers, Vol.38, No.1,2015. pp 66-76. [3] John Kechagias , George Petropoulos and Nikolaos Vaxevanidis, “Application of Taguchi design for quality characterization of abrasive water jet machining of TRIP sheet steels”, Int J Adv Manuf Technol (2012) 62:635–643. [4] Lingaraj.N and Gajendran.S, study of optimization of abrasive water jet machining process using hybrid multi response techniques, International Journal of Applied Engineering and Technology, pp.16-22 January-March, 2016 Vol. 6 (1). [5] N. Jagannatha, S.S. Hiremath and K. Sadashivappa, Analysis and parametric optimization of abrasive hot air jet machining for glass using taguchi method and utility concept, international journal of mechanical and materials engineering (ijmme), vol. 7 (2012), no. 1, 9–15. [6] Ramulu, M.; Arol, D. (1994) The influence of abrasive water jet cutting conditions on the surface quality of graphite/epoxy laminates. International Journal of Machine Tools and Manufacture, 34(3): 295-313. [7] M. Chithirai Pon Selvan and Dr. N. Mohana Sundara Raju, “Assessment of Process Parameters in Abrasive Waterjet Cutting of Granite” International Conference on Trends in Mechanical and Industrial Engineering (ICTMIE'2011) Bangkok , 2011, pp 140-144. [8] P. Sitarama Chakravarthy and N. Ramesh Babu, “A New Approach for Selection of Optimal Process Parameters in Abrasive Water Jet Cutting” Materials and Manufacturing Processes, 1999, Vol. 14, No. 4, pp581-600, [9] D.V.Srikanth, M.Sreenivasa Rao, Machining of FRP Composites by abrasive jet machining optimization using Taguchi, International journal of mechanical, Aerospace, industrial and mechatronics engineering Vol.8,No.3,2014 [10] Wang, J. (1999) A machinability study of polymer matrix composites using abrasive waterjet cutting technology. Journal of Materials Processing Technology, 94(1): 30-35.