multi-performance optimization of abrasive water jet...

Indian Journal of Engineering & Materials Sciences Vol. 25, August 2018, pp. 406-416

Multi-performance optimization of abrasive water jet machining of carbon epoxy composite material

Ajit Dhanawadea & Shailendra Kumarb*

aDepartment of Mechanical Engineering, B S College of Engineering and Research, Pune 411 041, India bDepartment of Mechanical Engineering, S V National Institute of Technology, Surat 395 007, India

Received 7 March 2016; accepted 8 November 2017

Carbon epoxy composite material is widely used in naval, aerospace, transportation, structural applications. Traditional machining of carbon epoxy composite is difficult due to improper surface features and kerf geometry, delamination, high tool wear, etc. In the present paper, research work involved in multi-performance optimization of abrasive water jet machining (AWJM) of carbon epoxy composite is described. Taguchi approach and analysis of variance are used to experimentally investigate the influence of process parameters on surface roughness and kerf taper. Four AWJM process parameters namely hydraulic pressure, traverse rate, stand-off distance and abrasive mass flow rate are considered for this study. It is found that two parameters, hydraulic pressure and traverse rate are most significant to control surface roughness and kerf taper. Analysis of scanning electron microscope images of machined surface of work-piece has been carried out to evaluate its microscopic features. The process is optimized for minimum surface roughness and kerf taper using Taguchi based grey relation analysis approach. Confirmation tests are carried out to verify improvement in the response characteristics using optimum set of AWJM process parameters.

Keywords: Abrasive water jet machining, Carbon epoxy composite, Optimization, Surface roughness, Kerf taper

Abrasive water jet machining (AWJM) is one of the unconventional machining processes which are widely used in many industrial applications. This process can machine hard materials efficiently at reasonable speeds with better quality characteristics. AWJM uses high speed water jet mixed with abrasive particles. The high speed abrasive water jet erodes work-piece material to cut or machine the work-piece. This process is versatile and flexible. It is suitable for hard and sensitive materials because it machines with almost no heat and chatter, and also results in low stresses. But high initial cost and noisy operations are the limitations of this process1.

Composite materials are widely used in advanced technological applications because of their good mechanical properties such as high strength, low density, corrosion resistance, high stiffness and good impact resistance. Composite materials have high strength to weight ratio. Nowadays, composites are being used in marine and aerospace applications, transportation and construction applications, sport equipments, and more recently in infrastructure2. Carbon-fiber-reinforced polymer (CFRP) is an extremely strong and light weight material. It has

excellent mechanical properties including high strength to weight ratio, high modulus of elasticity, high tensile strength, high fatigue strength etc.3,4

The machining of CFRPs by conventional techniques is very difficult because of excessive tool wear, delamination, and excessive cutting forces and high rise in temperature. Further their direct measurement is difficult, especially in conventional machining processes where the cutting tool rotates or conceals inside the work-piece. Quality of machined work-piece and productivity is generally improved by minimizing tool wear and delamination with high production rates. This is often very difficult in machining of composites by conventional means simply because of the fact that tool wear increases with increase in cutting speed and feed rate. AWJM offers certain advantages over conventional machining methods. These include high production rates, flexibility, and capability to produce complex contours and shapes. In addition, this process requires no cutting tool and very minimum fixturing5.

Some researchers have made efforts to investigate the cutting performance of AWJM of composites for response characteristics such as surface roughness and kerf taper. Ramulu and Arola6 carried out an experimental investigation to determine the influence

————— *Corresponding author (E-mail: [email protected])

DHANAWADE & KUMAR: ABRASIVE WATERJET MACHINING

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of cutting parameters on the surface roughness and kerf taper of an abrasive waterjet machined graphite epoxy laminate. Arola and Ramulu7 investigated kerf geometry, kerf wall features and cutting front characteristics of graphite epoxy laminates machined by abrasive water jet. Investigations on the effects of cutting parameters on kerf characteristics also carried out to develop empirical models for kerf profile and features of three distinct microscopic regions, i.e., jet entry region, centre region and jet exit region. An experimental investigation of the machinability and kerf characteristics of polymer matrix composite sheets using AWJM is carried out by Wang8. Wang and Liu9 carried out experimental investigation of various cutting performance measures such as kerf taper and depth of cut in profile cutting of alumina ceramics by abrasive water jet. Experiments and investigations to assess the influence of AWJM process parameters on surface roughness and kerf taper ratio of aramid fibre reinforced plastics (AFRP) composite is carried out by Azmir et al.10 Azmir and Ahsan11 conducted experiments to assess the influence of AWJM process parameters on surface roughness of glass fiber reinforced epoxy composites using Taguchi’s method and analysis of variance approach. The study on surface roughness and kerf taper ratio characteristics of an abrasive water jet machined glass epoxy composite laminate was carried out by Azmir and Ahsan12. Miron et al.13 performed machining of composite material by water jet and abrasive water jet cutting processes to analyse the possibilities for water jet cutting of complex composite parts. Haddad et al.14 investigated the defects generated by different machining processes including AWJM and their impact on the mechanical behavior of CFRP in quasi-static and tensile–tensile fatigue tests.

A number of researchers have made efforts to investigate the influence of different process parameters in AWJM of composites. But experimental investigation on cutting performance of AWJM of carbon epoxy composite has not been reported. This paper presents a study of surface roughness and kerf taper in AWJM of carbon epoxy composite. Taguchi approach is used to optimize single response characteristic. Because of higher-the-better performance of one response may affect the lower-the-better performance of other response. In the present study, grey relational analysis approach (GRA) is used to optimize multiple performance characteristics of kerf properties in the form of surface roughness and taper.

There are several related parameters and factors of AWJM process that can influence the kerf properties of the AWJ machined surfaces15. However, in the present study four parameters namely, stand-off distance, pressure, traverse rate and abrasive mass flow rate, each with four levels are considered for analysis. Experiment Procedure

The AWJM setup used for the present work is shown in Fig. 1. It is a flying arm CNC abrasive water jet cutting machine with designed pressure of 300 MPa and traverse speed upto 10000 mm/min. This machine is equipped with automatic abrasive feeding. The cutting area of the machine is 1300 mm, 1300 mm and 150 mm along with X, Y and Z axis, respectively. The positional and repeat accuracy of the machine is ±0.04 mm. As the objective of present work is to minimize surface roughness and kerf taper, good quality of garnet abrasives of mesh size #80 were used for the experiments. Reverse osmosis (RO) water purifier tank is used to supply pure inlet water for machining. The work-piece used for the present work was 22 mm thick. The work-piece specimen consists of carbon fibers with 6 µm diameter. Thermoset epoxy resin matrix is used along with fast hardener at ratio of 4:1. The mechanical properties of carbon epoxy composite material are given in Table 1.

Table 1 — Mechanical properties of carbon epoxy composite material

Property Value

Carbon percentage by weight 60 Compressive strength - longitudinal 570 MPa Density 1.5 g cm-3 Young's modulus - longitudinal 70 GPa

Fig. 1 — AWJM setup

INDIAN J. ENG. MATER. SCI., AUGUST 2018

408

Experimental design Surface roughness and kerf taper in AWJM can be

influenced by numerous parameters and factors of the process. Figure 2 shows the mechanism of AWJM of composite material with fiber orientation. Figure 3 shows material removal and kerf geometry in AWJM. At the top region of the kerf, the material removal takes place by low impact of abrasives; however at the bottom region of kerf it is because of plastic failure. It is characterized by a small curvy corner at the top edge due to plastic deformation of material produced by high speed abrasive water jet occurrence. Therefore, the kerf is wider at the top region as

compared to the bottom region, which results the formation of a taper.

Considering the range of available AWJM set-up and reviewing published literature, machining parameters and their levels as listed in Table 2 are selected as control factors for present study. Four machining parameters namely stand-off distance, jet pressure, traverse speed and abrasive mass flow rate with four respective levels are selected. Other machining parameters namely impact angle, nozzle diameter, orifice diameter, and focusing length were kept constant as 90°, 0.76 mm, 0.25 mm, and 70 mm, respectively.

With full factorial design, number of experiments to be carried out for the present study would be 256 (i.e. 44 = 256). It is time consuming and uneconomical. Also it may result in high experimental error. Taguchi orthogonal array design is a type of general fractional factorial design. It is a highly fractional orthogonal design that is based on a design matrix proposed by Dr. Genichi Taguchi (16). In the present work, Taguchi’s approach i.e. orthogonal array is used to plan the experiments and subsequent analysis of the collected data. Based on selected four control factors with their respective levels, L16 orthogonal array (OA) was used for the experimentation depending upon the Taguchi’s approach as shown in Table 3.

Table 3 — L16 orthogonal array with results

Expt. Control factors Avg. surface roughness

Kerf taper angle

SOD P TR AMFR 1. 1.0 200 50 600 3.415 0.750 2. 1.0 220 100 700 3.038 0.733 3. 1.0 240 150 800 3.036 0.700 4. 1.0 260 200 900 3.082 0.633 5. 1.5 200 100 800 3.042 0.950 6. 1.5 220 50 900 2.912 0.633 7. 1.5 240 200 600 3.083 0.750 8. 1.5 260 150 700 2.973 0.733 9. 2.0 200 150 900 3.471 1.133

10. 2.0 220 200 800 3.289 1.033 11. 2.0 240 50 700 2.515 0.466 12. 2.0 260 100 600 2.629 0.500 13. 2.5 200 200 700 3.998 1.350 14. 2.5 220 150 600 3.239 1.033 15. 2.5 240 100 900 2.763 0.833 16. 2.5 260 50 800 2.392 0.433

Table 2 — Selected machining parameters and their levels

Sr. No. Machining parameter Level 1 Level 2 Level 3 Level 4

1. Stand-off distance (SOD) (mm) 1.0 1.5 2.0 2.5 2. Jet pressure (P) (MPa) 200 220 240 260 3. Traverse rate (TR) (mm/min) 50 100 150 200 4. Abrasive mass flow rate (AMFR) (g/min) 600 700 800 900

Fig. 2 — Mechanism of AWJM of carbon epoxy compositework-piece

Fig. 3 — Material removal and kerf geometry in AWJM


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Surface roughness and kerf taper measurement In the present work, the response characteristics for

experiment are surface roughness (Ra) and kerf taper angle. Surface roughness is measured by using surface roughness tester (Model -Mitutoyo SJ-210 ISO 1997). The cut off length for measurement is set as 0.8 mm and total sampling length as 4 mm. Traverse speed is kept as 0.5 mm/s throughout the measurement of surface. For measuring the roughness value, stylus is traversed in horizontal direction on the work-piece surface. Surface roughness at three different regions is measured. Then the average of three different values of surface roughness is calculated for further analysis.

Kerf widths of machined samples are measured by using vision measuring system (model: Sipcon SDM-TRZ5300). In this measurement process, video edge detection with pointer is used for selecting point on cut edge with active crosshair. Then the taper is calculated using Eq. (1). Specifications of vision measuring system are given in Table 3.

Kerf Taper tan … (1)

Where, Wt is kerf top width, Wb is kerf bottom width and t is work-piece thickness. Analysis

After experimentation, the influence of process parameters is analyzed through ANOVA (Minitab 16). Tables 4 and 5 show the ANOVA, F-ratio values and P values in surface roughness and kerf taper of machined samples respectively. The analysis is carried out at 95% confidence level.

SOD- stand-off distance, P- pressure, TR- traverse rate, AMFR- abrasive mass flow rate, DOF- degree of freedom; SS- sum of squares; MS- mean square; F- F ratio; P- p value.

From the F-test and P value, for both the response characteristics, it has been found that stand-off distance (SOD) and abrasive mass flow rate (AMFR) are failed in the test of significance and hence these are insignificant process parameters. Results and Discussion

Effect of pressure and traverse rate on surface roughness The maximum Ra value is observed at 200 MPa,

and the value of Ra decreases with increase in pressure as shown in Fig. 4(a). This implies that surface roughness decreases with increase in pressure. The increase in pressure causes increase in particle velocity at nozzle exit and particle fragmentation inside the nozzle. This fragmentation reduces the size of impacting particle. Also an increase in pressure increases kinetic energy of jet. The increased kinetic energy helps the jet to cut the surface at the lower part of surface with minimum roughness. Figure 4(b) shows the effect of pressure on SN ratio.

It is observed that, increase in traverse rate results in increased surface roughness as shown in Fig. 4(c). The maximum value of Ra is observed at 200 mm/min of TR. Increase in traverse rate allows less overlap machining action and also allows fewer abrasive particles to impinge the surface. It results in increase in surface roughness. A slow traverse rate increases the number of abrasive particles impinging the surface which results in minimum surface roughness. Figure 4(d) shows the effect of traverse rate on SN ratio. Surface morphology

Figure 5 shows a typical AWJ machined surface. The machined surface reveals three distinct regions, i.e., top region (damaged at jet entry), middle region (smooth finish) and bottom region (rough and uncut at jet exit). The surface roughness at these three regions varies as shown in Fig. 6.

A few samples are examined using SEM to evaluate the microscopic features of the AWJ machined surfaces at top damaged region, middle smooth region and bottom rough cutting region as shown in Fig. 7. It is observed that fibers are cut smoothly, without fracture, pull off and abrasives embedment with first combination as shown in Fig. 7 (a). However fibers are fractured and pulled off and resulted in rough surface with second combination as shown in Fig. 7 (b). This is

Table 4 — ANOVA table for surface roughness

Source DOF SS MS F P %P

SOD 3 0.6364 0.2121 1.00 0.501 3.4767 P 3 9.6633 3.2211 15.12 0.026 52.7919 TR 3 6.7652 2.2551 10.59 0.042 36.9592 AMFR 3 0.6005 0.2002 0.94 0.520 3.2807 Error 3 0.6391 0.2130 3.4915 Total 15 18.3045 100

Table 5 — ANOVA table for kerf taper

Source DOF SS MS F P %P

SOD 3 5.7515 1.9172 1.56 0.363 4.9408 P 3 61.0635 203545 16.52 0.023 52.4559 TR 3 45.0510 15.0170 12.19 0.035 38.7007 AMFR 3 0.8466 0.2822 0.23 0.871 0.7273 Error 3 3.6963 1.2321 3.1753 Total 15 116.409 100


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because the jet with low pressure tends to deflect upward after impinging the work-piece and hence results in fiber fracture with rough surface. Also high traverse rate decreases number of abrasive particles impinging the surface. In the middle region of both samples as depicted in Fig. 7(c) and (d), smooth surface is observed, however fiber fractures are

observed with fibers pulled off with some abrasives embedment in the second sample. The low pressure decreases the kinetic energy of jet and reduces its capability of material removal. As a result the surface increases with decrease in jet pressure. After that, the surface of bottom region deteriorates due to the jet energy loss during particle impact and jet-material interaction. Figure 7(e) and (f) shows the surface

Fig. 4 — Effect of pressure and traverse rate on surface roughness (a) surface roughness v/s pressure, (b) SN ratio v/s pressure, (c) surface roughness v/s traverse rate and (d) SN ratio v/s traverse rate

Fig. 5 — Typical AWJ machined surface

Fig. 6 — Surface roughness v/s depth of measurement


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deterioration at the bottom region of both the samples. It is observed that the surface is more deteriorated in sample cut with second combination as compared to that of cut with first combination.

Effect of pressure and traverse rate on kerf taper The maximum kerf taper angle is observed at the

pressure of 200 MPa. Kerf taper angle decreases with increase in pressure as shown in Fig. 8(a). An increase in pressure results in increase in width of the jet. The jet with increased width has adequate energy to cut the lower part of cutting front. Therefore the

corresponding kerf width increases and the kerf taper reduces. Figure 8(b) depicts the effect of pressure on SN ratio of kerf taper.

The increase in traverse rate results in increase in kerf taper angle. The minimum value of kerf taper angle is observed at traverse rate of 50 mm/min as shown in Fig. 8(c). An increase in the traverse speed is associated with decrease in the jet contact with the area of material. This allows less overlap machining action and fewer abrasive particles to impinge the surface. It results in minimum machining of material.

Fig. 7 — SEM images (at 1000X) of machined surface (a) top region at 260 MPa and 50 mm/min, (b) top region at 200 MPa and200 mm/min, (c) middle region at 260 MPa and 50 mm/min, (d) middle region at 200 MPa and 200 mm/min, (e) bottom region at260 MPa and 50 mm/min and (f) bottom region at 200 MPa and 200 mm/min


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It consequently increases the taper of surface. Therefore, cutting at a low traverse speed results in small kerf taper angles. Figure 8(d) shows the effect of traverse rate on SN ratio of kerf taper.

Some surfaces of machined samples are examined using vision microscope to evaluate the microscopic feature of kerf geometry of AWJ machined samples as shown in Fig. 9. As this process produces no heat, no any heat affected zone is observed in any of the samples. Uncut portion, striation effect and abrasive embedment

In AWJM process, the cutting power of the jet decreases as it penetrates into the work-piece and striations are formed at the lower portion of the cut surface. In the present investigation, striations are observed at bottom region of work-piece.

It is found that striations are observed at bottom part of machined surfaces of many samples as shown in Fig. 10. Striations are repeatedly found in samples machined at high SOD and high traverse rate. However, samples machined at high pressuresare found with negligible striation marks. It is also observed that for low traverse rate, the influence of AMFR on surface roughness is almost

negligible. At the end of a cut, a small nib (Fig. 10) may remain on the bottom portion of machined surface in lead-in/lead-out area. Because of lagging effect, when jet reaches at the end of cut, the top portion of jet finds the path of least resistance, and hence jet jumps over a small bit of material, leaving a nib on machined surface. Also some abrasive particles are embedded in the cut surfaces as shown in Fig. 11. Multi-Performance Optimization Criteria

GRA approach is used to optimize a set of AWJM process parameters for surface roughness and kerf taper. For both response characteristics, i.e., surface roughness and kerf taper which are lower is better type performance variables, the equation for normalized values is given in Eq. (2)16.

𝑥 ∗ , , ……

, , …… , , ……For j

1,2,3, … … .9 … (2)

Where, 𝑥 ∗ is the normalized value of the lower-the-better type of response variable of the jth trial, j= 1,2,3, …..9.

Fig. 8 — Influence of pressure and traverse rate on kerf taper angle (a) kerf taper angle v/s pressure, (b) SN ratio v/s pressure, (c) kerftaper angle v/s traverse rate and (d) SN ratio v/s traverse rate


413

The maximum of the normalized values is obtained using Eq. (3), 𝑅 max

,, , ……

, ,

𝑥 ∗ 13) ... (3)

The absolute difference between each normalized value and the reference value R, regardless of the

response variables, trials and replications is computed using Eq. (4),

∆ 𝑥 ∗ 𝑅 , i 1,2, j 1,2,3, … .32. and k 1,2,3 ... (4)

The GRCs are obtained using formula as shown in Eq. (5),

Fig. 9 — Microscopic images of kerf quality (50X) (a) kerf edges at different pressures, (b) kerf quality at 220 MPa pressure and (c) kerf quality at 260 MPa pressure

Fig. 10 — Uncut portion and striation effect


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Table 6 — Grey relation grades

Expt. Control factors

GRG SOD P TR AMFR

1. 1.0 200 50 600 0.515495 2. 1.0 220 100 700 0.579329 3. 1.0 240 150 800 0.59346 4. 1.0 260 200 900 0.617061 5. 1.5 200 100 800 0.511333 6. 1.5 220 50 900 0.651616 7. 1.5 240 200 600 0.485321 8. 1.5 260 150 700 0.592342 9. 2.0 200 150 900 0.411222

10. 2.0 220 200 800 0.452756 11. 2.0 240 50 700 0.900014 12. 2.0 260 100 600 0.822345 13. 2.5 200 200 700 0.333333 14. 2.5 220 150 600 0.459913 15. 2.5 240 100 900 0.609029 16. 2.5 260 50 800 1

Level 1 0.576336 0.442846 0.766782 0.570769

Level 2 0.560153 0.535904 0.630509 0.601255 Level 3 0.646584 0.646956 0.514234 0.639387 Level 4 0.600569 0.757937 0.472118 0.572232

𝜉

⎝

⎛

, …, , ……

, , ….

∆ ς

∆ ς

⎠

⎞ , i 1,2,3 … p, j

1,2,3 … q, k 1,2,3 … . r ... (5)

Where, ξijk is the GRC for the ith response variable, jth trial and kth replication, ς is distinguishing coefficient in the range 0 to 1

(0.5 widely accepted). The GRGs are computed by averaging GRCs of

each performance characteristic, i.e., GRCs for surface roughness and kerf taper. The GRG values are given in Table 6 with orthogonal array L16. The

higher GRG signifies that the experimental results are closer to the supremely normalized value.

The mean GRGs for each level of machining parameters are graphically represented in Fig. 12. The graph shows that for level 3 of SOD, level 4 of pressure, level 1 of traverse rate and level 3 of AMFR give the highest value of GRG. Higher GRG signifies that the experimental results are closer to the supremely normalized value. Therefore, levels of process parameters giving highest value of GRG are selected as optimum levels. In the present study it is observed that SOD - 2.0 mm, P - 260 MPa, TR - 50 mm/min, AMFR - 800 g/min are optimum levels.

Effect of control factors on GRGs Figure 12 shows the effect of machining

parameters on GRGs and consequently on surface roughness and kerf taper angle.

Fig. 11 — Abrasive particles embedded in material

Fig. 12 — Effect of process parameters on GRGs (of surfaceroughness and kerf taper)


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Effect of stand-off distance The maximum value of GRG at level 3 of SOD

(i.e. 2.0 mm) implies that it gives minimum surface roughness and minimum kerf taper at 2 mm SOD. It is observed that there is no significant effect of SOD on surface roughness and kerf taper. After 2 mm, increasing the SOD resulted in increase in surface roughness and kerf taper (Fig. 12). This is due to the fact that the water jet diverges and loses its energy when spreading out from the mixing tube. The divergence results in increased kerf taper and surface roughness. Effect of pressure

The minimum GRG value is observed at level 1 of pressure (i.e. 200 MPa), and the value of GRG increases with increase in pressure as shown in Fig. 12. The maximum GRG value is observed at level 4 (i.e. at pressure 260 MPa). It is found that surface roughness and kerf taper decreases with increase in pressure value. Hence higher the pressure, better the kerf quality is achieved. This is due to the fact that the increase in pump pressure increases abrasive water jet kinetic energy. This excess energy cuts the lower part effectively and makes the surface smooth and straight. Effect of traverse rate

An increase in the traverse speed causes a constant decrease in GRG and consequently increases surface roughness and kerf taper. The maximum value of GRG is observed at level 1 of TR (i.e. 50 mm/min) as shown in Fig. 12. It is apparent that the increase in the traverse speed results in increase in kerf taper angle. This is because the increase in traverse speed is associated with less overlap machining action and reduced abrasive particles impingement on the surface.

Effect of abrasive mass flow rate The maximum value of GRG is observed at level 3

of AMFR (i.e. 800 g/min) as shown in Fig. 12. Although high AMFR results in increased cutting ability of jet, but at high AMFR abrasives collide with each other and lose their kinetic energy. It results in increased surface roughness and kerf taper. ANOVA for GRG

The sum of squares of GRGs of all factors of conducted experiments is given in Table 7.

The ANOVA of the GRGs is carried out to identify the significance of parameters. The results of ANOVA are summarized in Table 8.

From Table 8, it is clear that factors pressure and traverse rate have significant effect on GRGs and apparently on surface roughness and kerf taper. The SOD and AMFR are insignificant parameters. Confirmation tests

The confirmation experiments are performed to verify the optimized set of process parameters. The confirmation tests also validate the experimental analysis. In the present study, conformation tests are carried out using optimum levels. Total four samples are prepared using the optimum levels of SOD - 2.0 mm, P - 260 MPa, TR - 50 mm/min, AMFR - 800 g/min. The results of confirmation tests are given in Table 9. It is found that optimized set of process parameters gives optimum solution to minimize

Table 8 — ANOVA for GRGs

Source SS DF Mean SS Fcal Ftable (0.05) Remark SOD 0.017005 3 0.005668 1.037525 3.29 Insignificant P 0.22355 3 0.074517 13.64031 3.29 Significant TR 0.209557 3 0.069852 12.78638 3.29 Significant AMFR 0.012447 3 0.004149 0.759473 3.29 Insignificant Error 0.016389 3 0.005463 Total 0.478948 15

Table 9 — Confirmation tests of optimum levels for surface roughness

Sample Optimum cutting parameters SOD - 2.0 mm, P – 260 MPa, TR - 50 mm/min, AMFR - 800 g/min

Surface roughness Kerf taper 1 2.521 0.413 2 2.497 0.450 3 2.509 0.433 4 2.541 0.410

Table 7 — Sum of squares of GRGs of all factors

Sum of GRGs Level 1 2.305345 1.771383 3.067126 2.283075 Level 2 2.240613 2.143615 2.522035 2.405019 Level 3 2.586337 2.587824 2.056937 2.557549 Level 4 2.402275 3.031748 1.888472 2.288928


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surface roughness and kerf taper. The values of surface roughness and kerf taper of confirmation tests are smaller than those observed in experiments. Hence the objective of minimizing the surface roughness and kerf taper is accomplished by optimization of process parameters. Conclusions

A study of AWJM of carbon epoxy composite has been presented in this paper. Four AWJM process parameters namely hydraulic pressure, traverse rate, stand-off distance and abrasive mass flow rate are considered for this study. Plausible trends of surface roughness and kerf taper with respect to process parameters have been analyzed. From the present study, it is observed that:

(i) Pressure and traverse rate are the most significant factors which influence surface roughness and kerf taper.

(ii) Surface roughness and kerf taper decreases with increase in water pressure.

(iii) Machined surfaces reveal three distinct regions. The surface roughness at bottom region is maximum along with striations.

(iv) Fiber fractures and pull off are prominent in samples machined with high traverse rate and low pressure.

(v) Increase in traverse speed causes increase in surface roughness and kerf taper.

A set of process parameters is optimized in order to minimize surface roughness and kerf taper. The confirmation tests show that the optimized set of parameters give optimum surface roughness and kerf taper angle. Overall it may be stated that AWJM is an effective technology for machining and cutting of carbon epoxy composite with commercially acceptable kerf quality.

Acknowledgement Authors acknowledge the financial support being

provided by Naval Research Board (NRB), Govt. of India, for the project “Investigation on the Influence of Machining Parameters in the Machining of Carbon Epoxy Composite with Abrasive Water Jet Machining to Improve Surface Finish and Minimize Defects” NRB/4003/PG/341. References

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