Study and evaluation of abrasive water jet cutting ...

Machining Science and Technology An International Journal

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Study and evaluation of abrasive water jet cutting performance on AA5083-H32 aluminum alloy by varying the jet impingement angles with different abrasive mesh sizes Natarajan Yuvaraj & Murugasen Pradeep Kumar To cite this article: Natarajan Yuvaraj & Murugasen Pradeep Kumar (2017): Study and evaluation of abrasive water jet cutting performance on AA5083-H32 aluminum alloy by varying the jet impingement angles with different abrasive mesh sizes, Machining Science and Technology, DOI: 10.1080/10910344.2017.1283958 To link to this article: http://dx.doi.org/10.1080/10910344.2017.1283958

Published online: 20 Mar 2017.

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Date: 02 April 2017, At: 11:33

MACHINING SCIENCE AND TECHNOLOGY http://dx.doi.org/./..

Study and evaluation of abrasive water jet cutting performance on AA-H aluminum alloy by varying the jet impingement angles with different abrasive mesh sizes Natarajan Yuvaraj and Murugasen Pradeep Kumar Department of Mechanical Engineering, CEGC, Anna University, Chennai, India

ABSTRACT

This article describes the experimental investigation of abrasive water jet (AWJ) cutting on AA5083-H32 aluminum alloy. In this study, the influence of varying the jet impingement angles and abrasive mesh sizes with different water jet pressures, on the output parameters for the AWJ cutting of the aluminum alloy, was analyzed. The experimental results found that the output parameters, namely, the depth of penetration, top kerf width, kerf taper ratio, surface roughness, and abrasive contaminations, were strongly influenced by the combined effect of oblique jet impingement angles and abrasive mesh sizes on AWJ. Also, it is noticed that oblique jet impingement angles have more influence on the output cutting responses than the normal jet impingement angle, and consequently, each abrasive mesh size has an influence on the different output responses for the AWJ cutting of AA5083-H32. Scanning electron microscope and microhardness tester were used to examine the different cutting regions of the kerf wall surfaces. The Energy-dispersive X-ray spectroscopy analysis was used to confirm the amount of silicon particles embedded in the AWJ cut surfaces. The adequacy checking of the experimental data for the AWJ cutting performance models has been analyzed through the residual plots using the statistical software.

KEYWORDS

AWJ; AA-H; impingement angle; mesh size; performance evaluation; surface characterization

Introduction Aluminum alloys are widely used in aerospace and automotive applications for their light weight, better corrosion resistance, high strength-to-weight ratio, and relatively low cost (Totten and Mackenzie, 2003). Among these aluminum alloys, AA5083 is selected for its reasonable strength, suitability for low-temperature properties, better surface finish and weldability, and high corrosion resistance under extreme environmental conditions (Selvakumar et al., 2013; Stournaras et al., 2009). AA5083-H32 is one of the series of wrought aluminum–magnesium (Al–Mg) alloys with a weight of 4.73% Mg, because of its unique properties to produce typical components for CONTACT Natarajan Yuvaraj yuvaceg@gmail.com Department of Mechanical Engineering, CEGC, Anna University, Chennai , Tamil Nadu, India. Color versions of one or more of the figures in this article can be found online at www.tandfonline.com/lmst. ©  Taylor & Francis Group, LLC

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N. YUVARAJ AND M. P. KUMAR

marine and automotive applications (Kechagias et al., 2011; Stournaras et al., 2009), such as transport vehicles, railway applications, and ship-building structures. Precision machining processes are required to attain certain internal and external features of the typical components. Despite the superior mechanical and thermal properties of AA 5083-H32, poor machinability (Totten and Mackenzie, 2003) in terms of tool adherence, build up edge formation, various chip thicknesses, and worn-out tool are the major problems in the conventional machining process. A worn-out tool produces higher cutting forces and higher temperature in the cutting zone, and causes reduction of hardness and strength of the machined work material. AA5083-H32 is a strain-hardening alloy, which requires a higher rake angle of diamond cutting tool and higher cutting force (Jasinevicius et al., 2003). A higher rake angle reduces the strength of the cutting tool, and the higher cutting force generates a higher temperature. AA5083-H32 aluminum alloy is more sensitive to machining by other machining processes, because it is susceptible to stress corrosion cracking and fatigue crack growth, when it is exposed to temperatures more than 50°C, or for a very long time at room temperature, because the Mg content is more than 3% in the AA 5xxx series of aluminum alloys (Searles et al., 2001). This sensitization happened through the excess amount of Mg that tend to be distributed along the grain boundaries, and the formation of a Mg-rich phase. The formation of a Mg-rich phase in the aluminum alloy severely degraded the resistance to stress corrosion cracking and fatigue crack growth (Brosi and Lewandowski, 2010). So, the above material is chosen for the workpiece material and to overcome these problems using abrasive water jet (AWJ) cutting process, because it offers an extensive range of benefits, such as a lower cutting force on the parts, no thermal distortion on the machined surface, ability to cut all kinds of materials, and no contact tool to break, because water acts as the cutting tool. The mechanism of material removal is caused due to the erosion process (Momber and Kovacevic, 1998). Erosion is a type of wear, which occurs due to the mixing of the high kinetic energy of water jet with abrasive particles, wherein the abrasive particles are accelerated onto a workpiece surface, and the resulting erosion can be used for the removal of the material at the impact surface. In AWJ machining, erosion is caused by two different wear modes such as cutting wear and deformation wear (Arola and Ramulu, 1996; Bitter, 1963; Finnie, 1960; Hashish, 1988). In AWJ machining, the jet impingement angle, jet pressure, abrasive mass flow rate, traverse rate, stand-off distance (SOD), and the size and shape of the abrasive particles determine the erosion rate (Momber and Kovacevic, 1998). Researchers made efforts to enhance the cutting performance of AWJ through different techniques such as changing the jet impingement angle (Chen et al., 1998; Wang, 1999; Wang et al., 2003), abrasive mesh size and shape (Kanthababu and Chetty, 2006), recycling of abrasives (Kanthababu and Chetty, 2003), nozzle oscillation technique (Chen et al., 1998 2002; Keyurkumar, 2004), improvement in the cutting quality characteristics by physical models (Hlaváˇc, 1998; Hlaváˇc and Martinec, 1998), and finite element analysis (FEA) modeling (Junkar et al., 2006; Kumar and Shukla, 2012). These are the techniques developed without the

MACHINING SCIENCE AND TECHNOLOGY

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involvement of additional cost, and they can be used more effectively in the AWJ cutting of any materials. Some of the literature related to the improvement in the AWJ cutting of engineering materials through novel techniques, such as varying the jet impingement angle and abrasive mesh size are briefly presented below: researchers made a few investigations on the influence of the abrasive mesh size in the performance of AWJ cutting. Arola and Ramulu (1997) investigated the effect of the AWJ cutting process parameters on surface integrity and penetration depth, while machining different engineering materials. They noticed that the influence of the mesh size of the abrasives is found to be more significant than that of the waterjet pressure. Karakurt and Aydiner (2012) have studied the influence of the abrasive mesh size with other process parameters in the cutting of granite material. They observed that the garnet mesh size of #80 produced a higher depth of penetration. The abrasive mesh size of #80 had more energy to cut the material due to the presence of more number of coarse particles. Kulekei (2002) studied the effect of the AWJ cutting parameters on the penetration depth and Ra for stainless steel. It is observed that an increase in the waterjet pressure leads to a higher penetration depth. He also found that the depth of penetration increases as the average particle size of the abrasives increases up to 0.2 mm. Thereafter, there is not much significant variation observed in the depth of penetration, with the increase in the average particle size of the abrasives. Kanthababu and Chetty (2006) have performed experiments on AWJ cutting using single-mesh-size abrasives. They found that single-mesh-size abrasives produced a better cutting rate than multimesh-size abrasives. They concluded that the cutting behavior of single-mesh-size abrasives is analogous to that of the multimesh-size abrasives. Fowler et al. (2005) investigated the abrasive contamination on the milled titanium surface by the use of different abrasive mesh sizes. They reported that, the abrasive mesh sizes produced a similar contaminated area between 5% and 40% in the milled surface and, the abrasive contamination significantly affects the surface integrity of the milled component, which happens due to the high velocity of the abrasive particles, as reviewed by Kong et al. (2011). Researchers made some experimental studies on the influence of the jet impingement angle on the AWJ cutting performance. Wang et al. (2003) have investigated the influence of a jet impingement angle on cutting alumina ceramics. They found that the penetration depth and surface finish increased while decreasing the jet impingement angle. The result also indicates that an oblique jet impingement angle contributes more to the cutting performance than a normal impingement angle (90°). Wang (1999) conducted an experimental study to investigate the effect of the AWJ cutting performance in machining polymer matrix composites. They found an optimum jet impingement angle for the depth of penetration, kerf profile, and surface quality. The result shows that the jet impingement angle of 80° produced a better cutting performance while machining polymer matrix composites. The AWJ cutting performance in ceramic materials was evaluated by Chen et al. (1998). They observed that the impingement angle of the jet in the range of 80–85° produced the maximum penetration of depth and high surface quality. The result also indicates

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that striations in the lower cutting zone can be minimized. Manu and Babu (2008) have studied the effect of the jet impingement angle on the depth of penetration and surface topography of 6061-T6 parts geometry in AWJ turning. They observed that the normal impingement angle of the jet (90°) produced more penetration depth and better material removal rate, while the jet impingement angle of 30° yields a lower material removal rate and better surface finish when a higher water jet pressure is used. Keyurkumar (2004) conducted experiments on AWJ cutting to investigate the abrasive contamination in an aluminum alloy, using the nozzle head oscillation technique. He stated that the nozzle head oscillation technique reduced the abrasive contamination in the AWJ-machined surface. Chen et al. (2002) studied the nozzle oscillation technique for minimizing the embedded abrasive particles in the AWJ-machined surface in mild steel. They observed that the, nozzle oscillation technique reduces particle embedment, and the reduction of particle embedment in the machined surface will positively influence the fatigue property of the material. However, it is found that, the nozzle head oscillation technique does not influence the penetration depth, and it only improves the quality of the wall surface. Gudimetla et al. (2002) investigated the effect of the jet impingement angle in the AWJ cutting of ceramics. They found that tilting the cutting head was varied between 15° and 20° from the normal jet impingement angle, and it increased the smooth depth of penetration and diminished the deflection of the AWJ. Shipway et al. (2005) performed the milling of titanium alloy by AWJ with various jet impingement angles and abrasive mesh sizes. The results indicate that, higher material removal rate and better surface finish were obtained at the jet impingement angle of 60°, because the normal jet impingement angle generates high impulse and causes a severe impact on the cut surface. Some of the literature are related to the analysis of the AWJ erosion process by modeling techniques for improvement in the cutting performance. Erosion plays a significant role in the improvement of the AWJ cutting performance (Momber and Kovacevic, 1998). Erosive wear occurs through two predominant modes of mechanisms such as cutting wear (Finnie, 1960) and deformation wear (Bitter, 1963) and these analytical models predict that erosive wear occurs nearer to the normal impingement angle. Junkar et al. (2006) investigated the effect of abrasive particle rotation on the erosion process by the FEA. They observed that most of the abrasive grains get disintegrated in the nozzle cutting head during their acceleration process, and these particle fragmentations were also observed by Kanthababu and Chetty (2003). Kumar and Shukla (2012) conducted the simulation of multiabrasive particle impact on the erosion process in the AWJ machining of Ti-6Al-4V by the FEA. They observed that the erosion rate increased at a lower jet impingement angle value of 45°. They also found that the maximum crater depth is achieved at the normal impingement angle. From the literature, it can be noticed that the combined effect of the different jet impingement angles and abrasive mesh sizes was not investigated by the researchers. At the same time, it can be found that only a few researchers have experimentally investigated the influence of the jet impingement angle on ductile materials;


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Figure . AWJ cutting experimental setup. (a) normal jet impingement angle, (b) oblique jet impingement angle). Note: AWJ, abrasive water jet.

however, the lack of investigation and improvement in the AWJ cutting of ductile materials is observed. So, this study aims to investigate the influence of various jet impingement angles, along with different abrasive mesh sizes on the AWJ cutting performance of the AA5083-H32 aluminumt alloy. Experimental work The schematic experimental setup is shown in Figure 1. In this study, all the experiments were performed at the OMAX MAXIEM 1515 AWJ machine center, which can generate a maximum water jet pressure of 55,000 psi, and a traverse rate of 9 m/min; the cutting head travel movement in the X- and Y-axes of 1,575 × 1,575 mm2 , with a water discharge of 3.2 L/min. was used. For the experiments, garnet is used as an abrasive with different mesh sizes, as shown in Figure 2. The variable cutting parameters and their levels are given in Table 1, which also shows the other fixed parameters, such as the abrasive mass flow rate, traverse rate, SOD, focusing nozzle diameter, and orifice diameter. The variable cutting parameters were chosen based on the pilot test and the past literature with respect to the

Figure . Garnet abrasives with different mesh sizes. (a) # average particle size . mm, (b) # average particle size . mm, and (c) # average particle size . mm.

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Table . Process parameters of AWJ cutting process. Level Process parameter Water jet pressure (P), MPa Abrasive mesh size (#) Jet impingement angle (°) Abrasive mass flow rate Jewel orifice diameter Mixing tube diameter SOD Traverse rate

Level 

Level 

Level 

  

   . kg/min . mm . mm  mm  mm/min

  

AWJ, abrasive water jet; SOD, stand-off distance.

thickness of the target material and its properties (Brosi and Lewandowski, 2010; Searles et al., 2001). In the present study, the cutting experiments were performed under the traverse rate of 15 mm/min. This lower traverse rate compensates the AWJ cutting performance instead of using a maximum level of water jet pressure. In Figure 2, the abrasive mesh size #80 contains coarse particles, #100 has both coarse and fine, and #120 contains fine edges with smaller particles. The selection of the abrasive mesh size is based on the various features such as size and shape of the abrasive particles, jet nozzle, and orifice diameter, and these mesh sizes of the abrasives were used by the previous researchers (Jegaraj and Babu, 2005; Karakurt and Aydiner, 2012; Momber and Kovacevic, 1998) for the cutting operations. In this study, a constant level of SOD was considered for the experimentation. Because the changes in the SOD do not significantly influence the kinetic energy of the abrasive particles (Momber and Kovacevic, 1998). The optimum level of SOD was considered for the more material removal process and compensate the surface roughness and kerf width along with the variable cutting parameters were employed. AA5083-H32 aluminum alloy was selected as the workpiece material; its composition and mechanical properties are listed in Table 2. The aluminum alloy workpiece, which is trapezoidal, with a maximum thickness of 64.065 mm was cut (Figure 3), and the maximum penetration ability of the jet was determined. In the present work, three input parameters that varied at three levels are considered. Based on the input parameters and their levels, a typical orthogonal array of L27 was chosen. The experimental design for the L27 orthogonal array is given in Table 3. All these experimental conditions were conducted on the trapezoidal aluminum alloy, Table . Composition and properties of AA-H aluminum alloy. Chemical composition .% Al .% Mg .% Mn .% Si .% Cr .% Ti .% Cu .% Fe

Property

Value

Hardness vickers (HV.kg ) Density Ultimate tensile strength Yield strength Modulus of elasticity Shear strength Thermal conductivity Melting point

. HV . g/cm  MPa  MPa . GPa  MPa  W/mK –°C


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Figure . Trapezoidal AA-H workpiece.

and traversing a jet over the length of the workpiece until the splashing of the jet was observed by the operator. The jet splashes indicate the maximum depth of penetration of jet into the workpiece. The maximum penetration of depth was determined by measuring the inclined length (L) of the trapezoidal workpiece, using the following equation (Jegaraj and Babu, 2005; Srinivas and Babu, 2012): Depth of penetration = AB Sin 25◦

(1)

The surface quality of the AWJ workpiece surface was characterized by the roughness parameter (Ra ) which was measured using the Taylsurf 3+ Surftronic Table . Experimental design for AWJ cutting conditions. Ex. no.

Water jet pressure (MPa)

Abrasive mesh size (#)

Jet impingement angle (°)

                          

                          

                          

                           AWJ, abrasive water jet.

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Figure . Variation of depth of penetration with different jet impingement angles and mesh sizes of the abrasives. (a) #, (b) #, and (c) #.

profilometer, with a cut-off length of 0.8 mm and traverse length of 4 mm. The characteristics of the surface profile and 3-D surface topography were measured by Tally-Surf CCI profilometry equipment, with a magnification of 10×. The kerf width of the cut surfaces was measured by the tool maker microscope with a 0.005mm least count and a magnification of 10×. For each set of process parameters, the effect of the kerf taper ratio was measured, using the following relation (Momber and Kovacevic, 1998): Kerf taper ratio =

bT , bB

(2)

where b is top kerf width and bB is bottom kerf width. The scanning electron microscope (SEM) was used to examine the AWJ cut surfaces in three distinct regions. An energy-dispersive X-ray spectroscopy (EDS) analysis was used to perform the abrasive particle contamination in the top and middle cutting regions of the AWJ cut surfaces. In this analysis, abrasive particle contamination was studied through the amount of silicon particles embedded in the AWJ cut surfaces. The microhardness values were obtained by the Vickers hardness tester (Wolpert Group) equipped with a load of 100 g (HV0.1kg ) and 10-s dwell time. Microindentations were performed on the polished cut surfaces under ambient laboratory conditions. To produce accurate values, the optical finishes of the cut surfaces were obtained by fine mechanical polishing with diamond paste. All microhardness values were measured at the top (T), middle (M), and lower (L) cutting regions of the AWJ kerf wall surface, and in each cutting region, the hardness measurement was taken at three random locations. Results and discussion Influence of the AWJ cutting parameters on the depth of penetration

Figure 4 shows the influence of the jet impingement angles on the depth of penetration with various abrasive mesh sizes. This variation depends on three different water jet pressures with other fixed process parameters. From Figure 4a, it can


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be noticed that the depth of penetration increased with an increase in the water jet pressure for various levels of the jet impingement angle with an abrasive mesh size of #80. It is found that the maximum penetration depth can be achieved with a higher level of water jet pressure 150 MPa, at an impingement angle of 70°. The maximum depth of penetration that is achievable with this combination is found to be 58.32 mm. As indicated in Figure 4b (abrasive mesh size #100), the maximum depth of penetration can be achieved with a water jet pressure of 150 MPa and an impingement angle of 80°. The maximum depth of penetration achieved with this combination is found to be 49.50 mm. As seen in Figure 4c (abrasive mesh size #120), a higher depth of penetration can be achieved with water jet pressure of 150 MPa at an impingement angle of 90°. The maximum depth of penetration that can be achieved with this combination is found to be 47.75 mm. By comparing these levels of combinations, the highest depth of penetration is achieved with a jet pressure of 150 MPa, jet impingement angle of 70° along with an abrasive mesh size of #80. This particular behavior can be achieved by maintaining the velocity of the coarser abrasive particles effectively, while the depth of penetration is increased. It may be noticed that the depth of penetration increases with an increase in jet pressure along with various mesh sizes of abrasives. As a result, more amount of kinetic energy will be available to cut more material. The combination of a lower jet impingement angle with coarse abrasive particles (#80) can contribute to a reduction in the tangential force of the abrasive particles; however, it has sufficient kinetic energy to disintegrate the material with lower fractured abrasives, and consequently, increase the depth of penetration (Wang, 1999). It also reveals the cutting action of the abrasive particles, based on the size (density) and shape (coarse) of the abrasive particles (Karakurt and Aydiner, 2012). So, coarse particles of abrasive mesh size #80 have more kinetic energy to cut the material, and are able to produce the maximum depth of penetration. During the cutting action of the coarse abrasive particles, the effect of a lower jet impingement angle with a higher water jet pressure reduces the drag and centrifugal forces until the effective cutting energy of the AWJ was maintained. Increasing the water jet pressure increases the cutting volume of the coarse abrasive grains, and subsequently, increases the erosion rate and depth of penetration. If there is more amount of disintegration of the abrasives during the cutting and acceleration process, the abrasive particles lose their kinetic energy, and will not be able to cut the material, and this will induce localized plastic deformation, and leave burr formation on the exit side of the target material (Wang, 1999). Particle disintegration in the acceleration process was theoretically analyzed by Hlaváˇc et al. (2010), and they reported that the inlet abrasive particle is supplied perpendicular to the water jet axis, causing more particle disintegration and yielding a particle-size reduction, when the jet impingement angle of 90° and the coarse abrasive particles were used. And also, their physical modeling indicates that an increase in the stress of the abrasive particle due to the collision takes place in the mixing and acceleration process; hence, the abrasive particle is disintegrated (Hlaváˇc, 1996; Hlaváˇc and Martinec, 1998). It may reduce the cutting performance of AWJ along with the fractured abrasives in the cutting process. For the abrasive mesh size of #80, it is also

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Figure . Variation of the average top kerf width with different jet impingement angles and mesh sizes of the abrasives. (a) #, (b) #, and (c) #.

found that, the combination of a higher water jet pressure with a higher impingement angle generates a lower depth of penetration, which occurs due to the fractured abrasives when the tangential force is much higher than the critical energy, and this causes more particles to be deflected away from the target surface, which is opposite to the movement of the cutting head direction. These fractured abrasives lead to reduce the velocity of the abrasive particles (kinetic energy) in the form of jet deflection, after it is difficult to penetrate into the work material. It can be noticed that, the fractured abrasives occur due to the interaction of a higher water jet pressure (150 MPa), higher impingement angle (90°) along with coarse abrasive particles (#80). This combined level of energy exceeds the critical level of the cutting energy, and as a result the depth of penetration is reduced. Furthermore, it may be noticed that with a mesh size of #120, the oblique jet impingement angles of 70° and 80° are found to be insignificant. This combined effect of the higher impingement angle with fine mesh sizes of abrasives, produces the maximum depth of penetration. When there is an interaction of fine abrasives with lower impingement angles, it reduces the cutting efficiency of the work material due to the over compensate action of the abrasive particles in the lower cutting region. Therefore, the optimum condition for the depth of penetration exists with a jet impingement angle of 70°, abrasive mesh size of #80 along with the water jet pressure of 150 MPa. It has been concluded that the influence of the water jet pressure, jet impingement angle, and abrasive mesh size offers the maximum depth of penetration, based on the target material properties. Influence of the AWJ cutting parameters on the average top kerf width

Figure 5 shows the influence of the jet impingement angles on the average top kerf width with different abrasive mesh sizes, which depend on three different water jet pressures. The average top kerf width is obtained by the measurement at three different locations of the target material. To minimize the loss of material in AWJ cutting, a lower kerf width is desirable as it is more effective. The geometry of the kerf width is characterized by a wider entry at the top than on the bottom side (Wang, 1999; Wang et al., 2003). From Figure 5a (abrasive mesh size #80), it is observed that the average top kerf width decreased with an increase in the water jet pressure for


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different levels of the jet impingement angles. It is found that a lower average top kerf width can be achieved with a medium level of water jet pressure 125 MPa with an impingement angle of 90°. The minimum average kerf width that is achievable with this combination is found to be 0.905 mm. As indicated in Figure 5b (abrasive mesh size #100), a lower average top kerf width can be achieved with a higher water jet pressure of 150 MPa and an impingement angle of 80°. It can be noticed that the lower average top kerf width achieved with this combination is found to be 0.77 mm. Figure 5c (abrasive mesh size #120) indicates that a lower average top kerf width can be achieved with a jet pressure of 150 MPa at an impingement angle of 70°. The lower average top kerf width that can be achieved with this combination is found to be 0.857 mm. By comparing these levels of combinations, a lower average top kerf width of the AWJ cutting is obtained with a medium water jet pressure (125 MPa), lower jet impingement angle (70°) along with a medium abrasive mesh size (#100). This result is attributed to the effect of a lower jet impingement angle with medium pressure, which offers convergent AWJ in the entry of the cutting zone more effectively while using medium size abrasive particles (#100) rather than other abrasive mesh sizes of #80 and # 120. The abrasive particle size (coarser #80 or finer #120) does not show any significant influence on the average top kerf width. From the above results, it can be noticed that a medium pressure with a lower jet impingement angle produces sufficient jet energy to enter and exit the aluminum alloy. The result also indicates that a higher pressure and coarse abrasives (#80) increase the top kerf width. This happens probably because of the increment of the drag force in the boundary of the jet (Haghbin et al., 2015). This result is also well correlated with that of Hlaváˇc et al. (2015), who reported that the difference between the top and the bottom kerf width in the ductile materials increased, due to the lesser wear resistance of the target material. In contrast, the low pressure of the AWJ negatively influences the average top kerf width, due to the less capable AWJ, which is more divergent at the entry of the top surface in the target material. It has been concluded that the water jet pressure was significant, which is observed by other researchers (Jegaraj and Babu, 2005; Kanthababu and Chetty, 2006; Khan and Haque, 2007; Momber and Kovacevic, 1998; Wang, 1999), when it interacts with a few input cutting parameters such as traverse speed, abrasive mass flow rate, SOD, and focusing nozzle diameter, and additionally it is clear that the role of the abrasive mesh size and oblique jet impingement angles is also found to be significant in average top kerf width. Influence of the AWJ cutting parameters on the kerf taper ratio

The kerf taper ratio is characterized as a nondimensional ratio between the average top kerf width and the average bottom kerf width. It is noticed that the formation of the kerf taper is not desirable in the AWJ cut surfaces, because it affects the accuracy of the cut. The minimum kerf width is desirable to achieve precision on the AWJ cut surfaces. More researchers (Jegaraj and Babu, 2005; Kanthababu and Chetty, 2006; Maros, 2012) have studied the taper ratio on ductile materials and brittle materials (Arola and Ramulu, 1996; Wang, 1999) with different input process parameters. For

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Figure . Variation of kerf taper ratios with different jet impingement angles and mesh sizes of the abrasives. (a) #, (b) #, and (c) #.

ductile materials, the traverse speed, jet pressure, SOD, and abrasive mass flow rate are found to be significant (Shanmugam and Masood, 2009), while the other process parameters are not (Hashish, 1988). Only a few specific data are available on the kerf taper ratio while varying the jet impingement angles along with different abrasive mesh sizes in metals and nonmetals. Figure 6 indicates the effect of the jet impingement angles and abrasive mesh sizes on the kerf taper ratio along with different water jet pressures. From Figure 6a, it is noticed that the kerf taper ratio decreases with an increase in the jet pressure for the abrasive mesh size of #80. It is observed that the minimum kerf taper ratio can be achieved with a higher level of water jet pressure (150 MPa) at a lower impingement angle (70°). The minimum kerf taper ratio that is achievable with this combination is found to be 1.030. For the abrasive mesh size of #100, the minimum kerf taper ratio can be achieved with a water jet pressure of 150 MPa and an impingement angle of 90°. It is found that the minimum kerf taper ratio achieved with this combination is 1.006 as seen in Figure 6b. Figure 6c (abrasive mesh size #120) indicates that the minimum kerf taper ratio achieved with the combined effect of a water jet pressure of 150 MPa at an impingement angle of 70° is found to be 1.017. By comparing these levels of combinations, the lower kerf taper ratio is achieved with a water jet pressure of 150 MPa, and a jet impingement angle of 90° along with an abrasive mesh size of 100. It can be observed that the abrasive mesh size is found to be more significant in the kerf taper ratio, irrespective of the cutting material thickness. It is also noticed that the jet impingement angle of 80° produces a minimum kerf taper ratio (1.007), even if the penetration depth reached the maximum level. Jet impingement angles of 70° and 80° with high pressure do not lose the kinetic energy of the abrasive particles while the penetration depth was increased, and finally, become a linear kerf profile when abrasive mesh sizes of #80 and #100 were used. On the bottom side of the kerf width, the cutting wear mode is more effective, and causes a parallel kerf width in the cut surfaces. However, lower jet impingement angles are found to be less significant when they interact with the lower water jet pressure due to the cutting energy of the abrasive particles lower than the threshold energy of the AWJ cutting. The trend also noticed that a poor kerf taper ratio occurs when the pressure is increased from a lower to a higher level. This


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Figure . AWJ kerf profile. (a) Top surfaces and (b) Bottom surfaces. Note: AWJ, abrasive water jet.

particular trend is observed when the impingement angle varies from a lower to a higher value, and the abrasive particles get disintegrated during the cutting process, which leads to deflect the cutting direction of the AWJ, while the penetration depth is increased, and consequently, a taper is formed when the bottom kerf width is narrower than the top kerf width; the top and bottom kerf width cut surfaces are shown in Figure 7. It has been concluded that the effects of the pressure (Guptaa et al., 2014; Shanmugam and Masood, 2009), abrasive mesh size, and jet impingement angle offer more kinetic energy, which helps to improve the cutting wear mode in the lower cutting region, and subsequently reduces the taper formation in the AWJ cut surfaces. Influence of the AWJ cutting parameters on the average surface roughness

Figures 8–10 show the influence of varying the jet impingement angles with different mesh sizes of the abrasives on the average surface roughness. In this experimental study, an AWJ cut surface is characterized by three distinct zones such as the upper zone (smooth surface), middle zone (rough surface), and lower cutting zone (waviness) (Kovacevic, 1991). These cutting zones are measured at three distinct locations of the AWJ cut surface as follows: the upper zone is measured at a point 2 mm from the top of the cut surface, and the other zones are measured at 4 and 6 mm, respectively. In the upper zone (Figure 8a), it is observed that a lower roughness is achieved with the combined effect of the jet impingement angle of 70°

Figure . Variation of the upper zone average surface roughness with different jet impingement angles and mesh sizes of the abrasives. (a) #, (b) #, and (c) #.

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Figure . Variation of the middle zone average surface roughness with different jet impingement angles and mesh sizes of the abrasives. (a) #, (b) #, and (c) #.

with an abrasive mesh size of #80 along with water jet pressure of 100 MPa, and the lower Ra is found to be 2.67 µm. As indicated in Figure 8b, it is observed that, the (abrasive mesh size #100), a lower roughness can be achieved with a low water jet pressure of 100 MPa and an impingement angle of 90°. It can be noticed that the lower roughness achieved with this combination is found to be 2.05 µm. Figure 8c (abrasive mesh size #120) indicates that a lower roughness can be achieved with a lower water jet pressure of 100 MPa at an impingement angle of 80°. The lower roughness achieved with this combination is found to be 1.85 µm. By comparing these levels of combinations, the lower roughness of the AWJ cutting is obtained with a low water jet pressure of 100 MPa, jet impingement angle of 80° along with an abrasive mesh size of #120. This particular result occurs due to a lower water jet pressure and oblique jet impingement angle, producing a lower cutting force, which causes a smooth surface, and also, this happens when the fine-mesh-size abrasive particles impact with the target material. However, it is noticed that the combined effect of a jet impingement angle of 90° with abrasive mesh sizes of #80 and #100 involves particle disintegration, and consequently, reduces the energy density of the AWJ; it may generate a smooth surface finish on the top kerf wall cut surface.

Figure . Variation of the lower zone average surface roughness with different jet impingement angles and mesh sizes of the abrasives. (a) #, (b) #, and (c) #.


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In the middle zone (Figure 9a), it is indicated that a lower surface roughness is achieved with the combined effect of the jet impingement angle of 90° with an abrasive mesh size of #80 along with a water jet pressure of 100 MPa, and the lower Ra is found to be 2.95 µm. As indicated in Figure 9b, it is seen that (abrasive mesh size #100) a lower roughness can be achieved with a combination of a low water jet pressure of 125 MPa and an impingement angle of 80°. It can be noticed that the lower roughness achieved with this combination is found to be 2.25 µm. Figure 9c (abrasive mesh size #120) indicates that a lower roughness can be achieved with a lower water jet pressure of 100 MPa at an impingement angle of 80°. The lower roughness value achievable with this combination is found to be 2.10 µm. By comparing these levels of combinations, the lower roughness of the AWJ cutting is obtained with a water jet pressure of 125 MPa, and a lower jet impingement angle of 80° along with an abrasive mesh size #120. The result attributed to the same trend occurs in the upper zone of the AWJ cut surface. For the abrasive mesh sizes of #80 and #100, it is noticed that a better surface finish is also obtained with the influence of a low water jet pressure (100 MPa) and lower jet impingement angle (70°). In the lower zone (Figure 10a), it is observed that a better surface finish is achieved by the combination of a water jet pressure of 100 MPa and a jet impingement angle of 70° along with an abrasive mesh size of #80. The lower surface roughness achieved with this combination is found to be 2.87 µm. It is seen from Figure 10b that the influence of a medium mesh size abrasive of #100, a water jet pressure of 125 MPa, and a jet impingement angle of 80° yields a lower surface roughness value and is found to be 2.09 µm. Figure 10c shows that the lower surface roughness is achieved with the combined effect of a jet impingement angle 80° and water jet pressure of 100 MPa, and an abrasive mesh size of #120, and the roughness is found to be 2.01 µm. By comparing these levels of combinations in the lower cutting region of the AWJ cut surface, a better surface finish is achieved with a effect of lower water jet pressure, jet impingement angle of 80°, and the fine number of abrasive particles, which contribute to the smooth surface finish on the AWJ cut surface. It is noticed that fine abrasive particles with lower water jet pressure produce a smooth surface finish; additionally, the jet impingement angles of 70° (at mesh size #80) and 80° (at mesh size #120) maintain the stability of the jet in the lower cutting region and reduce the striations in the lower cutting region of the AWJ cut surface and consequently, a high surface quality is achieved in the cut surface than with the normal jet impingement angle. It has been concluded that, oblique jet impingement angles, medium and fine mesh sizes of the abrasives (Kanthababu and Chetty, 2006; Karakurt and Aydiner, 2012), and a low water jet pressure contribute to the better surface quality in the AWJ cut surface. It is widely known that aluminum alloy easily erodes the material while compared to the other difficult to cut materials, so that a higher pressure produces rough surfaces in the cutting region along with coarser abrasives. Because of that, the lower water jet pressure with medium- or fine-size abrasive particles produces sufficient kinetic energy (cutting force), which helps to induce the microscopic level of deformation (smaller dislocation motion) in the target material. Due

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to the microscopic level of movement, the AA5083-H32 strain-hardening alloy has the ability to produce a better surface finish under a lower cutting force. It may also be noticed that the effect of varying the water jet pressure, and maintaining a normal impingement angle irrespective of the mesh size of the abrasives, produces a poor surface finish in the work material, which occurs due to the kinetic energy of the AWJ being more than the critical energy in the top cutting region, and lower than the threshold energy in the lower cutting region. A few results also show that the normal impingement angle with a higher water jet pressure offers a better surface finish; this particular behavior can happen when particles get disintegrated into fine particles when an abrasive mesh size of #100 is used in the AWJ cutting. In this combination, every individual particle gets the minimum threshold energy, which helps to mitigate the deflection of the jet in the lower cutting region of the AWJ cut surface. It is also observed that the average surface roughness in the middle cutting region is higher than that in the lower cutting region. This can happen, because the coarse abrasive particles strongly adhere to a few regions of the middle kerf wall surface of the aluminum alloy. Influence of the various jet impingement angles on the 3-D surface topography

Furthermore, to assess the surface characteristics of AWJ on the lower kerf wall cutting region (6 mm from the top kerf wall cut surface), a 2-D roughness profile and 3D surface topography were performed. These surface characteristic measurements are conducted on varying the jet impingement angle with the mesh size of the abrasive of #80 and a water jet pressure of 150 MPa. In each Figure 11a–c, the horizontal axis constitutes the focusing area of 3,250 µm along the AWJ kerf wall cut-surface direction, and the vertical axis constitutes the amplitude value of the surface roughness profile. Figure 11a shows the up and down variations in the roughness profile, and also that more number of peaks and valleys are present in the corresponding 3D surface topography. It means that the cutting force of the AWJ produced a higher plastic deformation in the lower cutting region, in which the velocity of the abrasive particles was maintained. Due to this, the surface roughness value is found to be 3.07 µm. As seen in Figure 11b, only a small variation in the 3-D surface profile and the roughness value is found, namely, 1.62 µm. A jet impingement angle of 80° produced a sufficient cutting force with the disintegration of abrasive particles, causing a less deformation effect, so it leads to produce a smooth finish on the kerf wall surface in the lower cutting region. As indicated in Figure 11c, minimum fluctuations, and peaks and valleys are present in the 2-D roughness profile and 3-D surface topography, and these variations are lesser than those of the jet impingement angle of 70°. The minimum roughness value is found to be 1.96 µm. The normal impingement angle produced a fragmentation of abrasives with a lower cutting force; after that it impacts on the lower cutting region of the kerf wall surface. These lower cutting forces with the disintegration of abrasives produce a lower roughness in the lower kerf wall cut surface due to the microscopic movement of dislocations (lower deformation) in the AA5083-H32 strain-hardening aluminum alloy. However, the


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Figure . Variation in surface topography of the kerf wall cut surface with mesh size # and different jet impingement angles. (a) °, (b) °, and (c) °.

bottom of the lower kerf wall surface has more striations (curvatures) when the jet impingement angle of 90° is used rather than jet impingement angles 70° and 80°, as noticed in Figure 12a–c). This is because, the oblique jet impingement angles maintain the stability of the AWJ by reducing the jet retardation until it reaches the maximum penetration depth in the target material; as a result, the deflection of the jet is minimized and produces a very less striation defect, such as curvatures on the kerf wall cut surfaces. And the theoretical model of this result was proposed by Hlaváˇc et al. (2012). They reported that the tilting of the cutting head from the normal jet impingement angle improves the quality of the kerf wall cut surfaces through a reduction in the jet retardation and it is also found that the formation of striation is based on the target material type and the limit of the traverse rate was used (Hlaváˇc, 2009). Due to the limit of traverse rate, the jet need not use sufficient exposure to the material; as a result, a lower penetration depth and poor formation of the kerf

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Figure . AWJ cut surfaces with mesh size # and different jet impingement angles. (a) °, (b) °, and (c) °. Note: AWJ, abrasive water jet.

were observed due to the lagging effect of the jet in the bottom region of the cut. During AWJ cutting, the AA5083-H32 strain-hardening aluminum alloy ability to take a better surface finish, when the cutting forces are minimum in the lower kerf wall surface, has been confirmed.

Influence of the various jet impingement angles on the surface morphology

In this study, erosion surface analysis was performed on AA 5083-H32 aluminum alloy using SEM. The effect of varying the jet impingement angle on the AWJ cut surfaces with a pressure of 150 MPa and an abrasive mesh size of #80 is shown in Figure 13. These analyses were performed on the top, middle, and bottom AWJ cut surfaces. Erosion is a complex phenomenon in which the material is removed through different mechanisms, such as microcutting, microchipping, plowing, and rubbing (Arola and Ramulu, 1997; Momber and Kovacevic, 1998). For ductile materials, erosion occurs in the cutting and deformation wear modes (Bitter, 1963; Finnie, 1960). In the top cutting region, usually referred to as the damaged region (Hascalik et al., 2007), more wear tracks (bright lines of the SEM image) are present due to the particle disintegration, in which each particle uses the minimum threshold energy to be involved in the cutting action of work material, and also embedded abrasive particles were seen in the top kerf wall surface. This particular behavior is attributed to the normal jet impingement angle, in which the high kinetic energy of the abrasive particles interacts with the top kerf wall surface. It may also be observed that at the jet impingement angles of 70° and 80°, less wear tracks were present in the traverse direction of the jet than those at the normal jet impingement angle. Due to the reduction of the AWJ tangential force, high dislocation movements were restricted to the crystal structure of the material. As a result, a less damaged surface can be obtained even at the top kerf wall surface, when oblique jet impingement angles were used. It is noticed that wear tracks are randomly oriented at the normal jet impingement angle, which constitutes the distribution of abrasive particles that generate more wear tracks with a nonuniform width. This nonuniform width of the wear tracks was produced by the size and shape of the fractured abrasives and their fragmentation. In the middle region, it is indicated that the abrasive particles were sticking more to the kerf wall surface at the jet impingement angle 90° along with the wear tracks.


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Figure . Surface morphology of the AWJ cut surfaces. Note: AWJ, abrasive water jet.

A small fracture and microchipping action was observed on the surface when the jet impingement angle of 70° was used. These particular results occur due to the cutting action of the high-energy coarse particles that adhere strongly at some places in the middle cutting region. It is also noticed that less particle disintegration was observed with the jet impingement angle of 80°. And it was also found that only a few abrasive particles interact with the middle region of the kerf wall surface, which is observed from the AWJ cut surfaces at various jet impingement angles. These few abrasives alone induce the microscopic deformation movement in the AA5083-H32 aluminum alloy at oblique jet impingement angles, and consequently, a smooth finish was produced. It has been concluded that, the middle region was not effective in the normal impingement angle, due to the kinetic energy of the AWJ becoming lower when the penetration depth is increased, and it produced a particlecontaminated surface.

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In the bottom cutting region of the AWJ cut surfaces, a damaged profile was observed at the normal jet impingement angle, where plowing deformation is the principal mechanism. In this deformation wear mode, the material is removed through the orientation of the abrasive particles as it impacts on the target surface (Momber and Kovacevic, 1998). A damaged profile was obtained due to the fractured abrasive grains. It may also be noticed that a crater was produced around the fractured abrasives. The jet impingement angle of 80° produced a better surface finish with lesser wear tracks present along the target surface than with the normal impingement angle. On the contrary, the jet impingement angle of 70° shows more wear tracks, which happen due to the shearing action of the abrasive particles, and also the evidence of microcutting action was noticed. The results revealed that AWJ maintains sufficient kinetic energy in the lower cutting region, causing a cutting wear mode in the crystal structure of the material; as a result, a considerable amount of material is removed when the abrasive particles adhere well to the lower kerf wall surface, and it leaves less striations on the target surface. It has been concluded that cutting wear plays a crucial role in the top to bottom cutting region, and it is also found that less striations were observed at oblique jet impingement angles. In contrast, more striations and their angles were observed (Figure 12c) at a normal jet impingement angle, due to the deflection of the jet, and consequently, changes the mode of material removal from cutting wear into deformation wear, when the penetration depth is increased. A similar trend is observed by Strnadel et al. (2013). According to their theoretical model, striations and their angles increased due to the increase in strength and hardness of the target material, caused by the lower energy of the penetration of abrasive particles which occurred when the jet impingement angle of 90° and abrasive mesh size of #80 were used. The strength and hardness of the target material increased while the plastic deformation occurred due to the interaction of the lower energy of the abrasive particles with the target material. It has been concluded that a continuous lower mobility of dislocations occurs in the normal jet impingement angle, and the material continues to strain harden; however, it can be removed due to the continuous impingement of abrasive particles in the lower cutting region and it produced striations on the AWJ cut surface by the act of plastic deformation through the lower energy of the penetration of the abrasive particles. Figures 14 and 15 show the EDS images of the top and middle cutting regions of the AWJ cut surfaces at varying jet impingement angles with a pressure of 150 MPa, and abrasive mesh size of #80. This analysis has confirmed that a certain amount of fractured silicon particles are embedded in the top and middle cutting regions of the kerf wall cut surfaces. It indicates that, the jet impingement angle of 90° has caused more number of silicon particles to be embedded in the top cutting region than the oblique jet impingement angles, due to more number of fractured abrasives generated by the critical energy of the jet, which happened through the action of the coarser abrasive grains at a higher water jet pressure. This contamination produces severe problems with the other operations of these cut surfaces, such as grinding and coating (Keyurkumar, 2004). Due to the abrasive contamination, the usage


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Figure . EDS analysis at top cutting region of the AWJ cut surfaces. Note: AWJ, abrasive water jet; EDS, energy dispersive X-ray spectroscopy.

of the AWJ process has been limited to certain applications (Shipway et al., 2005). The higher level of abrasive particle contamination may happen due to the low traverse speed of the jet used. Similar results were reported by Fowler et al. (2005) and they also reported that severe abrasive contamination was observed at the jet impingement angle of 90° with different abrasive mesh sizes such as #80 and #200, because a high impulse of particle impingement occurred on the target material. From the results, it has been confirmed that the oblique jet impingement angles

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Figure . EDS analysis at middle region of the AWJ cut surfaces. Note: AWJ, abrasive water jet; EDS, energy-dispersive X-ray spectroscopy.

achieve a better kerf wall cut surface quality with less contamination than the jet impingement angle at 90°. Because the oblique jet impingement angles maintain the velocity of abrasive particles in the cutting regions, less number of abrasive particles was embedded in the cut surfaces. Influence of the various jet impingement angles on the microhardness

Figure 16 shows the influence of the various jet impingement angles on the microhardness using water pressure and an abrasive mesh size of #80. The result indicates


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Figure . Microhardness of the AWJ cut surfaces at different cutting regions. Note: AWJ, abrasive water jet.

that the jet impingement angle of 90° shows lower hardness than the base material hardness (100.34 HV0.1kg ). All the measurements were taken in the top cutting zone (or entry), middle cutting zone (or half of the depth of penetration), and lower cutting zone (or exit) of the cut surface. The entry of the AWJ at an jet impingement angle of 90° has produced a higher cutting force than the other jet impingement angles of 70° and 80°, and frequently it causes high local temperature in the interaction zone, in which the higher energy of the coarser abrasive particles impact the top kerf wall surface. Those localized temperatures affect the vicinity of the workpiece immediately in the impact region, and therefore, reduce the hardness of the machined surface. No increase in hardness was found in the middle (M1, M2, M3) and lower (L1, L2, L3) cutting regions of the AWJ cut surface. Because the high thermal conductivity of the aluminum alloy produces a higher temperature in the impact region, and this heat in the cutting region is rapidly conducted into the inner regions (or uncutting regions), it reduces the cooling effect of the jet while the depth of penetration is increased (Kovacevic et al., 1996), and therefore, the hardness was lower in the inner cutting regions. Ohadi et al. (1992) investigated the temperature distribution on the workpiece, measured during the AWJ machining process, and they found that the temperature can be raised up to 70°C. Therefore, this peak temperature affects the hardness of the AA5083-H32 aluminum alloy, because this aluminum alloy performs better under low temperature (Searles et al., 2001; Stournaras et al., 2009). The peak temperature occurs in the lower cutting region of the AWJ cut surface due to the higher frictional forces caused by the continuous deflection of the jet, when a normal jet impingement angle along with coarser abrasive particles and higher water jet pressure was used. It is found that the hardness of the exit region is lower than the entry region of the AWJ, because the maximum temperature occurs in the lower cutting region. These temperatures reduce the dislocation density within the work material; as a result, lower hardness was found. It may also be noticed that the heat was developed due to the combined effect of the lower traverse rate, higher water jet pressure, and normal jet impingement angle, where increasing the number of impingement of the abrasive particles (exposure time) with critical energy on the target surface; as a result the peak temperature was found in the inner cutting regions.

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Figure . Residual plots for depth of penetration.

During the cutting process, the oblique jet impingement angles maintain the hardness of the workpiece, and some of the regions of the AWJ cut surface show a higher hardness than the base material, which is attributed to the work-hardening property of the aluminum alloy. For oblique jet impingement angles, it is found that an increase in the hardness of the AA5083-H32 aluminum alloy due to the fact that plastic deformation occurs at a low temperature in the impact region of the AWJ, and consequently, increases the density of dislocations after the dislocation starts blocking in the work- or strain-hardening condition. The results of the jet impingement angle of 70° did not show significant variations in the three distinct AWJ cutting regions, and it is found that the aluminum alloy has reached the strain-hardening limit. It has been concluded that the hardness of the machined surface depends upon the work material, process parameters, and machining operations. Model adequacy of the AWJ cutting responses by a statistical analysis

The adequacy of the AWJ cutting response models was studied by investigating the residuals between the observed and predicted responses of each cutting performance in the AWJ cutting process. A comparison of the residuals between the experimental values and predicted values is presented in Figures 17–22. This statistical analysis (residual plots) was performed on the observed experimental data of the AWJ cutting performance characteristics, such as depth of penetration, top kerf width, kerf taper ratio, upper zone roughness, middle zone roughness, and lower zone roughness obtained through the Taguchi L27 orthogonal array using the MINITAB 14 statistical software. The difference between the residuals of the experimental and predicted values was examined by various residual plots


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Figure . Residual plots for average top kerf width.

(Makadia and Nanavati, 2013; Pradhan, 2013), such as the normal probability of the residuals, residual versus the fitted values, histogram of the residuals, and residual versus the order of the data. For Figures 17–22, the correlation between the responses and experimental values indicates the goodness-of-fit and suggests that a better adequate model was obtained in the AWJ cutting process, because the normal

Figure . Residual plots for kerf taper ratio.

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Figure . Residual plots for upper zone roughness.

probability plots confirm that the residues of each cutting performance were closely fitted to the straight line and form the structural pattern. Similarly, the residual versus the fitted values plot shows that the residues were randomly distributed, and no

Figure . Residual plots for middle zone roughness.


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Figure . Residual plots for lower zone roughness.

obvious residue pattern, i.e., structure-less formation was observed, so that a nonlinear relationship and no outliers were existed in the data, since variance in the measurement was constant. The histograms of the residual plots revealed that the different frequency level of residues was formed at each of the AWJ cutting responses. It proves that the frequency of each residue acted independently and follow the normal distribution pattern; the exact bell-shaped pattern was observed in the depth of penetration model, because the process variables influenced the AWJ cutting performance characteristics more. It implies that the residues were normally well distributed on both sides of the median, and a desired skewed shape was obtained; as a result, the model of the depth of penetration is an excellent goodness-of-fit and adequate model rather than the other models. The residual versus the order of the data plots confirm how the observed residues were distributed in each experiment. The observed residues of each experiment in the AWJ cutting responses reveal that no noticeable pattern was found. This implies that, the residue of each experiment depends on different combinations of the process parameters, and their interaction effects in the cutting conditions in a standard order. Finally, the results conclude that, the proposed model for the AWJ residue analysis is adequate for the different cutting performance characteristics. Conclusion The present work, discusses the combined effect of different jet impingement angles and abrasive mesh sizes on the AWJ output parameters, namely, the depth of penetration, average top kerf width, kerf taper ratio, different zones of roughness, surface

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topography, and surface morphology, on AA5083-H32 aluminum alloy by AWJ cutting. The major conclusions are drawn and the experimental results are correlated with the theoretical modeling of the past researchers (Hlaváˇc, 1998, 2009; Hlaváˇc et al., 2010; Strnadel, 2013). The results are as follows: 1. At a higher water pressure (150 MPa), the combination of a lower jet impingement angle (70°) with coarser abrasives (#80) has achieved a higher depth of penetration than the normal jet impingement angle (90°) due to the higher impulse force and particle disintegration. 2. In the average top kerf width and kerf taper ratio, oblique jet impingement angles (70° and 80°) with different mesh sizes of the abrasives (#80 and #100) are found to play a more influential role along with the water jet pressure. 3. The surface roughness in the three cutting zones, such as the upper, middle, and lower, is found to be lower when fine abrasive particles (#120) were used along with the jet impingement angle of 80° at a water jet pressure of 100 MPa. 4. Considering 2-D roughness profile and 3-D surface topography, it is observed that the jet impingement angle of 80° produced a better surface finish in the lower kerf wall cut surface than the other jet impingement angles. It is also noticed that oblique jet impingement angles produced less striations on the kerf wall surface due to the reduction in jet retardation. 5. The SEM analysis confirms that the oblique jet impingement angles maintain the cutting wear mode in the top and bottom cutting regions, due to a reduction in the particle disintegration. 6. In the top cutting region of the AWJ cut surface, the level of abrasive contamination was found to be as low as 2.54% at the jet impingement angle of 70° and abrasive mesh size of #80. Due to the existence of a threshold level of abrasive particle velocity by oblique jet impingement angles, the abrasive contamination was reduced significantly. 7. In the microhardness examination, hardness was reduced at the normal jet impingement angle and improved at the oblique jet impingement angles. It is observed that hardness variations in the AA5083-H32 aluminum alloy are subject to the plastic deformation and the temperature. 8. From the residual plot analysis, it is found that the models for the cutting responses, such as the depth of penetration, top kerf width, kerf taper ratio, upper zone roughness, middle zone roughness, and lower zone roughness were adequate for the AWJ cutting process, and therefore produce better consistent results for future predictions. The overall effect of the oblique jet impingement angles and different mesh sizes of the abrasives with water jet pressure is that it increases the penetration ability of the AWJ and hardness of the cut surface, decreases the kerf taper ratio, and also, a lower roughness and less striations on the kerf wall surface were obtained. From this study, the overall efficiency of the AWJ cutting can be improved through the novel technique of oblique jet impingement angles with different abrasive mesh sizes. These suggestions help the manufacturing industries in cutting AA5083-H32


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aluminum alloy by AWJ, to achieve a higher depth of penetration, lower top kerf width and taper ratio, and better surface finish, along with less-damaged surfaces and hardness. Acknowledgments The authors acknowledge the Head, Department of Production Technology, Madras Institute of Technology (MIT) campus, Anna University, Chennai, for providing the experimental facilities to conduct the research work. The authors express their sincere thanks to the editor and the reviewers for their greatest support by the valuable comments and suggestions on this manuscript.

Funding N. Yuvaraj thanks the Council of Scientific and Industrial Research (CSIR), Government of India, New Delhi, for the research fund under the scheme of Senior Research Fellowship (Grant file no. 9/468(479)/2014-EMR I).

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