Dimensional accuracy and strength comparison in hole making of GFRP composite using Co 2 laser and abrasive water jet technologies

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1 Indian Journal of Engineering & Materials Science Vol. 21, April 2014, pp Dimensional accuracy and strength comparison in hole making of GFRP composite using Co 2 laser and abrasive water jet technologies Hussein Mohammed Ali a *, Asif Iqbal b & Majid Hashemipour b a Department of Refrigeration and Air-condition, Technical College of Mosul, Foundation of Technical Education, Mosul, Iraq b Department of Mechanical Engineering, Eastern Mediterranean University, Gazimagusa, Northern Cyprus, Via Mersin 10, Turkey Received 12 October 2012; accepted 20 January 2014 The dimensional accuracy and strength of a part is of critical importance in the manufacturing industry, especially for precision assembly operation. In the manufacturing process, the designed part will be presented in a drawing with all dimensions normally given within a certain range of tolerances. The tolerance defines the limits of induced deviation for which allowance should be made in the design, and within which actual size is acceptable. In laser and abrasive water jet cutting, dimensional accuracy is one of the important parameters to define the quality of produced part. The aim of the present work is to compare experimentally the influence of cutting parameters on dimensional accuracy and strength of hole making in GFRP by using laser beam and abrasive water jet cutting technologies. Full factorial design is used as a statistical method to study the effects of predictor variables on the response variables. The results show that abrasive water jet cutting gives a less out of roundness in cutting hole diameter, less reduction in strength and large difference between upper and lower diameter compared to the laser cutting technology of hole making in the type of the glass fiber reinforced plastic composite material used in the present work. Keywords: Abrasive water jet machining, CO 2 laser, Cutting parameters, Dimensional accuracy, Strength, Laminated GFRP Glass fiber reinforced polymer (GFRP) composites are used in a large number of industrial applications because of the advantages they have compared to other materials. These advantages are high strength to weight ratio, high modulus, high fracture toughness, and corrosion and thermal resistance. As well as the relative ease of manufacture of components using GFRPs 1. As structural materials, joining composite laminates to other metal materials structures could not be avoided 2, and bolt joining efficiency and quality depend critically on the quality of machined holes. Various cutting processes are extensively used for producing riveted and bolted joints during assembly operation of composite laminates with other components. For rivets and bolted joints, damagedfree and precise holes must be made in the components to ensure high joint strength and precision 3,4. Conventional machining of hole making in fiber-reinforced composites is difficult due to diverse fiber and matrix properties, fiber orientation, inhomogeneous nature of the material, and the presence of high-volume fraction (volume of fiber over total volume) of hard abrasive fibers in the *Corresponding author ( hrlha@yahoo.com) matrix. Abrasive water jet machining (AWJM) and laser beam machining (LBM) processes have been used for processing composite materials because of the advantages offered by these technologies as compared to traditional techniques of processing. Laser beam machining (LBM) process has a wide range of applications in different manufacturing processes in industry due to its advantages of high cut quality and cost effectiveness through massproduction rate 5. LBM is particularly suitable for making accurately placed holes. The material to be cut is locally melted by the focused laser beam. The melt is then blown away with the aid of assist gas, which flow coaxially with the laser beam, in the cutting procedures, different types of assist gases are used such as oxygen and nitrogen. It is suitable for fine cutting of sheet metal at high speed 6. Abrasive water jet machining (AWJM) has been used for processing composite materials because of the advantages (no heat affected zone, ability to cut any shape, limited tooling requirements, etc) offered as compared to traditional techniques of processing composite materials has created an opportunity for abrasive water jet machining. Abrasive water jet cutting technology uses a jet of high pressure and

2 190 INDIAN J ENG MATER SCI., APRIL 2014 velocity water and abrasive slurry to cut the target material by means of erosion 7. The quality of the cutting hole in a GFRP is strongly dependent on the appropriate choice of the cutting parameters in machining process. The studies on AWJM and LBM of composite materials have been carried out by many researchers. Ho-Cheng 8 discussed an analytical approach to study the delamination during drilling by water jet piercing. Their model predicted an optimal water jet pressure for no delamination as a function of hole depth and material parameter. Ramulu et al. 9 reviewed and investigated the AWJ drilling for various materials (steel, aluminum, glass, titanium and polycarbonate). It was found that water pressure, abrasive flow rate and drilling time significantly affected the dimensions and accuracy of the AWJ drilled holes. Hocheng and Sao 10 studied various non-traditional drilling techniques and observed that water jet drilling can be effectively used to make fine holes of medium to large diameter, by contour cutting at very high speeds. They found that delamination can be eliminated by reducing the jet speed but on the other hand, the piercing capability deteriorates. This research presents a comprehensive approach to select optimal cutting parameters for high dimensional accuracy and strength, of hole making in laminate GFRP composite type 3240 by AWJM and LBM processes. A numerical optimization has been performed using Derringer-Suich multi-criteria decision modeling approach. A set of experiments regarding the two machining techniques were conducted, with cutting parameters prefixed on glass fiber reinforced plastic (GFRP) laminate. The predictor variables namely, hole diameter, material thickness, cutting speed and feed rate are optimized based on the statistical analyses performed and user s preferences sought. and abrasive slurry to cut the target material by means of erosion. It was shown from the scanning electron microscopy (SEM) analysis for the cut surfaces of polymer matrix composites that the erosive process for the matrix material (resin) involves shearing and ploughing as well as intergranular cracking. Shearing or cutting was found to be the dominant process for cutting the fibers in the upper cutting region, but the fibers are mostly pulled out in the lower region of the cutting surface 7. Materials For the experimental study, a sheet of woven laminated glass fiber reinforced plastic (GFRP), Type 3240 produced by Jinhao Material Co., China was used as shown in Figs 1 and 2. This material is mainly used in aerospace, transportation tools and electrical Fig. 1 Laminated GFRP with the two thicknesses Experimental Procedure Cutting mechanism by LBM and AWJM Glass fiber reinforced plastic (GFRP) composite materials are the combination of two materials, glass fiber and polymer matrix, that have significant different characteristics. Since each of these materials oxidizes at a different temperature, the laser beam process used to cut the glass fibers would cause the epoxy resin to decompose and melt resulting in a flow of the fibers within the resin and charring and tearing of the resin layer 11. While abrasive water jet cutting technology uses a jet of high pressure, velocity water Fig. 2 Cross-sectional view

3 ALI et al.: GFRP COMPOSITES 191 appliances as insulation materials. The properties of the laminated GFRP material used are given in Table 1. Design of experiments Some of the control parameters are selected based on the available literature, availability of the machine specifications, and the experience of the authors and the others, and are selected based on the preliminary trial runs. Some of the control parameters, which are the parameters, related to the machining process are determined by trial runs. A preliminary trail runs were carried out using abrasive water jet for determining the minimum or maximum values of jet pressure, feed rate and standoff distance that is required for the GFRP material to cut through. With those trail runs it was determined that the jet pressure should be not less than 150 MPa, standoff distance should be not more than 3 mm and with feed rate not less than 0.2 m/min. Using laser beam cutting process, preliminary tests were conducted to determine the range of laser power, feed rate and standoff distance. In this study, it was determined that the GFRP material was cut through with laser power not less than 1.5 kw, standoff distance not more than 2 mm and feed rate not less than 0.1 m/min. The predictor variables ranges are carefully provided between the levels for comparison purpose. A five factor, two-level, full-factorial design Table 1 Major properties of Laminated GFRP Type 3240 Property Value Fiber density 0.82 g/cm 3 Fiber volume fraction 45% Max. working temperature 200 o C Tensile strength MPa Layer thickness 0.5 mm Table 2 High and low settings of control parameters in AWJM Code Input factor Unit Level 1 Level 2 A Nominal hole diameter (D) mm 6 8 B Material thickness (t) mm 8 16 C Cutting feed (V c ) m/min D Jet pressure (P) Mpa E Standoff distance (Sod.) mm 2 3 Table 3 High and low settings of control parameters in LBM Code Input factor Unit Level 1 Level 2 A Nominal hole diameter (D) mm 6 8 B Material thickness (t) mm 8 16 C Cutting feed (V c ) m/min D Laser power (LP) kw E Standoff distance (Sod.) mm 1 2 of experiments (2 5 = 32 tests) was developed for each cutting technology (AWJM and LBM). High and low, levels of the control parameters for the AWJM and LBM are shown in Tables 2 and 3, respectively. Following is the description of the response variables (performance measures) to be measured in 32 tests for each type of cutting: Dimensional accuracy In the manufacturing process, the designed part will be presented in a drawing with all dimensions normally given within a certain range of tolerances. The dimensional accuracy taken in terms of out of roundness (OOR) and the difference between the upper and lower diameters (D u -D L ). High values of these terms represent low dimensional accuracy. OOR = (L 1 +L 2 +L 3 ) / 3 Where L 1, L 2 and L 3 are the deviation distances at three different points measured from the optical microscope image for each hole. Tensile strength Tensile strength measured in MPa. 64 tensile test of hole specimens (32 holes cut each by AWJM and LBM ) according to ASTM D were carried using Universal Tensile Testing Machine, Type WDW-300, made by Changchun Kexin Com., China. The experimental setup for the tensile test is shown in Fig. 3. Experimental setup AWJM experiments were conducted on ultra high pressure water cutting machine produced by Nanjing Hezhan Microtechnic Co. Ltd., China with a maximum pressure of MPa, abrasive flow rate 3.7 g/min and water flow rate L/h. The type of abrasive used was Garnet. In all the AWJM experiments, the nozzle diameter used was 1 mm. LBM experiments were conducted on Rw 6015 X cantilevered flight optical path laser cutter produced by Nanjing Nanchuan Laser Equipment Ltd., China. CO 2 continuous beam laser was used with laser power range (2-4 kw); maximum speed (50 m/min) and table size 2500/1250 mm. In all the laser experiments, the nozzle (orifice) diameter used was 1.5 mm. The dimensions of the work piece material to be cut in the two types of cutting processes were 200 mm 200 mm 8 mm and 200 mm 200 mm 16 mm. Arithmetic surface roughness (R a ) taken along the depth of cutting hole at four points was measured by Mahr Perthometer M1. Optical Microscope of type Leica DVM500, having

4 192 INDIAN J ENG MATER SCI., APRIL 2014 (a) (b) Fig. 3 (a) Standard hole specimen for tensile test and (b) universal tensile testing machine accuracy mm was used to measure the cut profile. The experimental setup is shown in Fig. 4 Results and Discussion The experimental layout and results for the two types of cutting processes are presented in Tables 4 and 5, respectively. Experimental data have been analyzed using ANOVA and numerical optimization has been performed using Derringer-Suich multicriteria decision modeling approach. ANOVA is a basic statistical technique for determining the influence of an input parameter on response parameter(s). Different desirability functions have been used in Derringer-Suich, multi-criteria optimization technique to find the maximization or minimization of the response parameters (variables). More details are given elsewhere 12. All the statistical analyses, including ANOVA and numerical optimization, were performed using commercial statistical software called Design-Expert. Analysis of variance Tables 6 and 7 present ANOVA performed on the data related to the response variables of hole making by AWJM and LBM processes. The effects of all the individual input variables have been shown. The effects of all the possible interactions among the input variables were analyzed and only the significant interactions have been shown in the plots. This is to be mentioned, with respect to ANOVA table, that effect of any parameter is considered to be significant if p-value 0.05; and insignificant, otherwise. As there are many predictor and response variables included in this study for both AWJM and LBM process, it means a large number of ANOVA tables will take a big space, for that reason, only F- and p- values were included in the ANOVA tables. The bold numbers of p-values represent the parameters having significant effects. Analysis of hole making by AWJM and LBM processes The columns F-value and p-value in Table 6, which is shown the identification of significant input parameters in AWJM process, suggest that effect of material thickness to be cut and stand of distance are significant upon out of roundness. Whereas the significant factors upon the difference in hole diameter are the thickness of the material, pressure of water jet, interaction between hole diameter and stand of distance, interaction between material thickness and feed rate and finally the interaction between material thickness and jet pressure. The analysis also shows that the significant factors upon the tensile strength are the material thickness to be cut and the interaction between material thickness and jet pressure. While the columns F-value and p-value in Table 7, which is shown the identification of significant input parameters in LBM process, suggest that material thickness and laser power are significant factors upon out of roundness. The analysis also shows that the significant factors upon the tensile

5 ALI et al.: GFRP COMPOSITES 193 Fig. 4 Experimental set-up strength are laser beam power and the interaction between laser beam power and the stand of distance (Sod). The analysis shows that there are no significant factors upon the difference between upper and lower diameter. The effects of influential parameters upon out of roundness, difference between upper and lower diameter and tensile strength respectively for AWJM process, is represented in graphical form as shown in Figs 5-7. It is clear from Fig. 5(a) that as the feed rate of abrasive water jet increased, the quality characteristic (reducing out of roundness) of the cutting surface will improve. This phenomenon is depending on kinetic energy absorption by work piece due to hydrodynamic friction of abrasive water jet 13. While Fig. 5(b) shows that by increasing the standoff distance the material surface is exposed to the downstream of the jet. At downstream, the jet starts to diverge losing its coherence thereby reducing the effective cutting area that directly affects the kerfs taper angle 14. Figure 6 shows that difference between upper and lower diameters is increased with the decrease in material thickness to be cut and water jet pressure. This depends on kinetic energy absorption by work piece due to hydrodynamic friction of abrasive water jet 13. While Fig.6(b) shows that by increasing the standoff distance the out of roundness is increased. This is because the surface of the material is exposed to the downstream of the jet. At downstream, the jet starts to diverge losing its coherence thereby reducing the effective cutting area that directly affects the kerfs taper profile 14. Figure 7(a) shows that the thickness of material to be cut and the interaction between material thickness and water jet pressure are affective factors on the strength of the composite material. Figures 8 and 9 show the effects of influential parameters upon out of roundness and tensile strength respectively for LBM process. It is clear from Fig. 8(a) that increase in material thickness leads to increase in cut path deviation around the hole diameter. This is because of the thermal conduction of the thicker GFRP material, which results in thermal stresses at the circumference of the hole causes distortion in the work piece leading to out of roundness in the hole diameter. While the increase in the laser power at constant feed rate and a given thickness of material results in the lower out of roundness as shown in Fig. 8(b). This is due to the

6 194 INDIAN J ENG MATER SCI., APRIL 2014 Predictor variables Table 4 Experimental results for AWJM Response variables S.N D (mm) A t (mm) B V c (m/min) C P (MPa)D Sod (mm) E OOR (mm) Du-DL (mm) TS (MPa) increase in the stability of laser beam in the work piece 11. It is clear from Fig. 9(a) that strength of the composite decreases with the increase in laser power. With increase the laser power, the volume of heataffected zone (HAZ) is increased. This is because with increasing the laser power, the heat-affected zone (HAZ) is increased and a large volume of fibers in the composite is vaporized, causing a change in the properties of the material, which lead to reduction in the strength of the composite 12. Discussion The woven laminated GFRP composite, type 3240 which is used in many industrial applications was machined by AWJM and LBM processes. The aim of the research is to investigate the effects of the predicted variables upon deviation in the cutting profile (out-of-roundness), difference between upper and lower diameter, tensile strength. It is obvious from Tables 3 and 4 that in AWJM process the minimum value of the hole surface roughness which is equal to µm was obtained by using low settings of water jet pressure and the standoff distance result in increasing the hole surface roughness. A microscopic analysis was used to determine the value of the deviation (out-of-roundness) in the upper cut hole diameter in contrast with the required nominal hole diameter, the microscopic analysis was also used to measure the difference between upper and lower hole diameter, A sample of microscopic pictures for the holes cutting by AWJM and LBM processes are shown as Figs 10 and 11, respectively. Figures 10 (a) and (b) represent the upper and lower surfaces optical picture

7 ALI et al.: GFRP COMPOSITES 195 Predictor variables of exp. no. 32 in Table 4 cut by AWJM process. It can be shown from this figure that, BC1 represents the cut hole diameter while BC2 represents the diameter that includes the defects in both upper and lower surfaces respectively. The difference between BC1 and BC2 which represent the difference between upper and lower holes diameters is equal to mm, while the difference between upper and lower holes diameters, which was cut by LBM process as shown in graphs (a) and (b) of Fig. 11, is equal to mm. It means that the difference between upper and lower holes diameters in the case of LBM process is lesser than that in the case of AWJM process. This is due to inertia experience by AWJM nozzle, as the nozzle is unable to maintain a true curved path that causes the Table 5 Experimental results for LBM Response variables S.N D (mm) A t ( mm) B Vc (m/min) C LP (kw) D Sod (mm) E OOR (mm) Du-DL (mm) TS (MPa) jet to decrease in energy resulting in a very narrow cut at the bottom. As it was found by Shanmugam et al. 14 when the kinetic energy of the water jet decreased, the jet at the bottom will become narrow. The deviation distances (out-of-roundness) at three different points were measured from the optical microscope picture for each hole as shown in Figs 10 and 11. It was found that the measured value of the deviation by AWJM process is equal to mm while that for LBM process is mm. This was due to the laser power action. As the power is increased, the heat gets intensified and thermal effect on the surface of the hole is increased. From Fig. 11 (a, b), it was observed that an inadequate heat dissipation during cutting by laser beam resulted in

8 196 INDIAN J ENG MATER SCI., APRIL 2014 Table 6 ANOVA details for R a, OOR, DU-DL and TS and identification of significant input parameters in AWJM process Source OOR DU-DL TS F-value p-value F-value p-value F-value p-value Model A- (D) B- (t) C- (V c ) D- (P) E- (Sod) A B A C A D A E B C B D B E C D C E D E Table 7 ANOVA details for R a, OOR, DU-DL and TS and identification of significant input parameters in LBM process Source OOR DU-DL T.S. F-value p-value F-value p-value F-value p-value Model A- (D) B- (t) C- (V c ) D- (LBP) E- ( Sod ) A B A C A D A E B C B D B E C D C E D E the delamination around the cut holes. On the other hand, some degree of delamination can also be observed (from Fig. 10) for GFRP cut by AWJM process but it was of very low magnitude as compared to the LBM process. It is obvious from the experimental results Tables (4 and 5), that cutting holes by AWJM process results in less reduction in tensile strength of GFRP as compared to LBM process. This is because AWJM technology is less sensitive to material properties as it does not cause chatter, has no thermal effects, impose minimal stresses on the work piece. The results of the Fig. 5 Factorial plots showing the effects of (a) cutting feed and (b) standoff distance upon out of roundness in AWJM

9 ALI et al.: GFRP COMPOSITES 197 Fig. 6 Factorial plots showing effects of (a) material thickness, (b) water jet pressure, (c) interaction between nominal hole diameter and standoff distance, (d) interaction between material thickness and cutting feed and (e) interaction between material thickness and water jet pressure upon difference between upper and lower diameters in AWJM Fig. 7 Factorial plots showing effects of (a) material thickness and (b) interaction between material thickness and water jet pressure on tensile strength in AWJM Fig. 8 Factorial plots showing effects of (a) material thickness and (b) laser power upon out of roundness in LBM study show that CO 2 laser cutting is not a viable method for cutting this composite. This is because of the conductive nature of the composites, which increases heat transfer to the materials causing increasing in the dimension of the HAZ that reflects the quality of laser cutting on composite materials. Numerical optimization The AWJM and LBM cutting processes are widely used in manufacturing industry. The two technologies have procured many overlapping applications. Thus, Fig. 9 Factorial plots showing effects of (a) laser power and (b) interaction between feed rate and it is important for the industry to understand both processes, in order to select the optimum method in different situations. The comprehensive knowledge on cut quality, strength would help the users to judge which method is more appropriate for each type of application. Therefore, it is better to find out the optimal cutting conditions at which the desirable cut quality and strength can be achieved. Optimization criteria can be set to find out the optimum cutting conditions. Hence, three optimization criteria have been introduced for each of the two cutting technologies (AWJM and LBM) as given in Tables 8 and 9, namely: (i) minimize the difference between upper and lower diameters, (ii) minimize out of roundness and (iii) maximize tensile strength (i.e. reducing the reduction in tensile strength) Tables 8 and 9 present optimized values (within tested range) of the predictor variables for different objectives in the two cutting technologies. Last column of the table shows the actual results of confirmation experiments performed against each optimized values. Table 8 shows that minimum out of roundness, minimum difference between upper and lower diameters and maximum tensile strength inawjm can be achieved by cutting at high settings of cutting

10 198 INDIAN J ENG MATER SCI., APRIL 2014 Fig. 10 Microscopic pictures for hole no.32, group 2 of AWJM process (a) upper hole surface and (b) lower hole surface Fig. 11 Microscopic pictures for hole no.32, group 2 of LBM process (a) upper hole surface and (b) lower hole surface Table 8 Recommendations and predictions of multi-objective optimization against each set of objectives and comparison with experimental results in AWJM process Fixed Parameters Optimized Parameters Objectives t (mm) D (mm) V c (m/min) P (MPa) Sod (mm) Predicted values Experimental values Minimize (OOR) mm mm Minimize (D U -D L ) mm mm Maximize (T.S) MPa MPa Table 9 Recommendations and predictions of multi-objective optimization against each set of objectives and comparison with experimental results in LBM process Fixed parameters Optimized parameters Objectives t (mm) D (mm) V c (m/min) LP (kw) Sod (mm) Predicted values Experimental values Minimize (OOR) mm mm Minimize (D U -D L ) mm 0.01 mm Maximize (TS) MPa MPa

11 ALI et al.: GFRP COMPOSITES 199 feed, low settings of jet pressure and low settings of stand of distance. Table 9 shows that minimum value of out of roundness can be achieved by cutting at low settings of cutting feed, low settings of stand of distance and high settings of laser power. Minimum value of the difference between upper and lower diameters of the cutting hole can be achieved by high setting of cutting feed, high stand of distance and low setting of laser power. Finally, reducing the reduction in strength will be achieved if low setting of cutting feed, laser power and stand of distance is applied. Conclusions The present study is intended to provide initial technical information related to the cut quality (deviation in hole cut profile or out-of-roundness and difference between upper and lower holes diameters), strength of hole making in GFRP using two cutting processes, these are abrasive water jet machining and laser beam machining. Comprehensive statistical analyses were performed to investigate the effects of the major AWJM and LBM cutting parameters upon the selected response parameters mentioned above. The detailed analyses reveal that abrasive water jet cutting system offers a better cut quality, less reduction in tensile strength as compared to the laser cutting technology. The following conclusions can be drawn: In AWJM process, improving dimensional accuracy (reducing out-of-roundness, difference between upper and lower diameters of the cutting hole) can be done by reducing the stand-off distance. Reducing the loss in the strength of the cutting material can be achieved by reducing the water jet pressure and increasing the feed rate and standoff distance. In LBM process, improving dimensional accuracy (reducing out-of-roundness) can be done by reducing cutting feed, stand-off distance and increasing laser power whereas reducing the difference in the upper and lower diameters of the cutting hole can be done by increasing cutting feed, stand-off distance and decreasing laser power. Reducing the loss in the strength of thecutting material can be achieved by reducing the laser power, feed rate and stand-off distance. Abrasive flow rate and stand-off distance are more influential machining parameters in AWJM process while cutting feed, laser power, stand-off distance and assist gas flow rate are more influential machining parameters in LBM process. CO 2 laser beam cutting is not a viable method for cutting this composite material in contrast with AWJM process. This work is likely to prove beneficial for generating superior quality holes by AWJM and LBM in GFRP composites used in different manufacturing applications. Acknowledgements The authors wish to thank the managers of AWJM and Laser companies for their helps to do the experiments. The authors would like also to acknowledge the help and support provided by the staff of College of Mechanical and Electrical Engineering, Nanjing University of Aeronautic and Astronautic, China, in performing the measurements required for this work. Nomenclature GFRP = glass fiber reinforced plastic LBM = laser beam machining AWJM = abrasive water jet machining D = nominal hole diameter (mm) t = mmaterial thickness (mm) V c = cutting feed (m/min) P = water jet pressure (MPa) AF = abrasive flow rate (g/min) Sod = stand-off distance (mm) LP = laser beam power (kw) V = assist.gas flow rate (L/h) R a = arithmetic surface roughness (µm) OOR = out of roundness (mm) D U = upper surface diameter (mm) D L = lower surface diameter (mm) TS = tensile strength (MPa) C = cost per hole (USD) Pr = productivity (no. of holes per min) HAZ = heat affected zone References 1 Lemma E, Chen L & Siores E, Compos Struct, 57 (1-4) (2002) Hufenbach W, Dobrzan ski L A, Gude M, Konieczny J & Czulak A, J Achieve Mater Manuf Eng, 20 (2007) Teti R, CIRP Ann Manuf Technol, 51 (2002) Abrao A M, Faria P E, Campos Rubio J C, Reis P & Davim J P, J Mater Process Technol, 186 (2007) Eltawahni H A, Hagino M, Benyounis K Y, Inoue T & Olabic A G, Opt Laser Technol, 44 (2012) Dubey Avanish Kumar & Yadava Vinod, Int J Mach Tools Manuf, 48 (2008) Wang J, Int J Adv Manuf Technol, 15 (1999) Hocheng H, Int J Mach Tools Manuf, 30(3) (1990) Ramulu M, Young P & Kao H, J Mater Eng Performance, 8(3) (1999) Hocheng H & Tsao C C, J Mater Process Technol, 167 (2005) laser cutting composite materials. Laser cutting of composite materials. 12 Derringer G & Suich R, J Qual Technol,12 (1980) Hloch Sergej, Fabian Stanislav & Rimár Miroslav, Nonconvent Technol Rev, 2 (2008). 14 Shanmugam D K & Masood S H, J Mater Process Technol, 209 (2009)