Drilling Uni-Directional Fiber-Reinforced Plastics Manufactured by Hand Lay-Up: Influence of Fibers

American Journal of Materials Science and Technology doi:10.7726/ajmst.2012.1001 Research Article Drilling Uni-Directional Fiber-Reinforced Plastics Manufactured by Hand Lay-Up: Influence of Fibers Dilli Babu 1, *, K. Sivaji Babu 2, B. Uma Maheswar Gowd 3 Received 19 July 2012; Published online 29 September 2012 The author(s) 2012. Published with open access at uscip.org Abstract Drilling composite materials is a very common and important process used in industry to assemble composite structures. However, drilling composite materials present a number of problems such as delamination associated with the characteristics of the material and the used cutting parameters. In order to reduce these problems, we present this study with the objective of evaluating the cutting parameters (cutting velocity and feed rate) and the influence of the fibers under delamination factor (F d). The approach is based on a combination of Taguchi techniques and on the analysis of variance (ANOVA). An experimental plan was performed involving drilling with cutting parameters in Natural Fiber Reinforced Plastic (NFRP) using a cemented carbide drill. The results of NFRP composite delamination factor (F d) were compared with Glass Fiber Reinforced Plastic (GFRP) composites. The objective was to establish a correlation between cutting velocity and feed rate with the delamination of different fiber-reinforced laminates. Keywords: Composites; Drilling; Delamination. 1. Introduction Fiber-reinforced polymer composites have played a dominant role for a long time in a variety of applications for their high specific strength and modulus. Fibers reinforcing plastics may be synthetic fiber-reinforced plastics or natural fiber-reinforced plastics. Previous studies have shown that only synthetic fibers such as glass, carbon, etc., have been used in fiber-reinforced plastics. Although glass and other synthetic fiber-reinforced plastics possess high specific strengths, their fields of application are very limited because of their inherent higher cost of production (Sanjay Kindo, 2010). *Corresponding author: 1Mechanical Engineering Department, V R Siddhartha Engineering College, Vijayawada-520 007, India Email: *gdillibabu@gmail.com 1 2Mechanical Engineering Department, P.V.P. Siddhartha Institute of Technology, Vijayawada-520 007, India 3Mechanical Engineering Department, J. N. T. U. college of Engineering, Anantapur-515 002, India

Natural fibers like jute, hemp, sisal, banana, coconut (coir) and bamboo in their natural form as well as several waste cellulosic products such as shell flour, wood flour and pulp have been used to reinforce different thermosetting and thermoplastic composites. Several authors have reported the chemical compositions and properties of natural fibers and their composites by incorporating the fiber in different matrices before and after treatment by different methods (Jain et al., 1992; Varghese et al., 1994; Geethamma et al., 1995; Ahlblad et al., 1994; Li et al., 2000). Murali Mohan Rao et al. (2010) investigated the effect of natural fibers on tensile strength and dielectric properties over different natural fiber-reinforced composites. Hakim et al. (2010) investigated load displacement behavior of glass fiber/epoxy composite plates with circular cutouts subjected to compressive load and concluded that as the cut-out size increases, the maximum load of the composite plate decreases. Kishore et al. (2009) studied the residual tensile strength after drilling in glass fiber-reinforced epoxy composites and determined the optimal machining conditions for drilling glass fiberreinforced epoxy composites. Palanikumara and Paulo Davim (2009) studied the some factors influencing tool wear on the machining of glass fiber-reinforced plastics by coated cemented carbide tools and concluded that cutting speed is a factor, which has greater influence on tool flank wear, followed by feed rate. Muthukrishnan and Paulo Davim (2009) studied the effect of machining parameters on turning metal matrix composites and concluded that the feed rate has the highest physical as well as statistical influence on surface roughness. Singh et al. (2008) carried out a study on drilling of uni-directional glass fiber-reinforced plastics and concluded that the thrust force depends on the drill point angle and the feed rate and increases directly with both the point angle and the feed rate. Tsao (2008) investigated the effects of drilling parameters on delamination by various step-core drills and concluded that drilling-induced delamination of various step core drills is inversely related to diameter ratio and spindle speed and directly related to feed rate. In this paper, an approach based on the Taguchi method is used to determine the desired optimum cutting parameters for minimized appearance of delaminations in drilled uni-directional natural fiber-reinforced composites and establish a correlation between a cutting speed and feed rate with delamination factor (F d). 2. Experimental setup and machining conditions 2.1 FRP specimen preparations The composite materials used in the tests were made with different fiber reinforcements, such as Hemp Fiber Reinforced Plastics (HFRP), Jute Fiber Reinforced Plastics (JFRP), Banana Fiber Reinforced Plastics (BFRP) and Glass Fiber Reinforced Plastics (GFRP). Resin polyester possessing a modulus of 3.25 GPa and density 1350 kg/m 3 was used in preparing the specimens with hand layup process. The required numbers of layers were stacked to give the intended thickness and a fiber volume fraction, which was determined later to be 0.52 using a weight loss method. 2

2.2 Machining setup The carbide drill bit used in the experiments was 5 mm in diameter. Drilling tests were conducted on the CNC machining center supplied by MTAB, India. The laminate composite specimen was held in a rigid fixture attached to the machine table. The experimental setup is shown schematically in Fig. 1. 2.3 Design of experiments Fig. 1. Schematic diagram of experimental setup. The cutting speed and the feed rate are the two most important parameters characterizing the drilling operation and have been selected for investigation. Table 1 indicates the factors to be studied and the assignment of the corresponding levels. An L9 orthogonal array was selected for the present investigation, which has nine rows corresponding to the number of tests (eight degrees of freedom) with two columns at three levels, as shown in Table 2. The experimental plan comprises nine tests (array rows) in which the first column was assigned to the cutting velocity (v) and the second column to the feed rate (f) and the remaining were assigned to the interactions. The response to be studied is the delamination factor (F d) in four different fiber-reinforced composites. The treatment of experimental results is based on the analysis average and the analysis of variance (ANOVA). Table 1: Levels of the variables used in the experiment. Process parameters Low (1) Center (2) High (3) Cutting speed (A) in m/min 16 24 32 Feed rate (B) in mm/rev 0.10 0.20 0.30 3

Table 2: Orthogonal array L 9 (2 4 ) of Taguchi (Ross P. Taguchi, 1996) L 9 (2 4 ) Test 1 2 3 4 1 1 1 1 1 2 1 2 2 2 3 1 3 3 3 4 2 1 2 3 5 2 2 3 1 6 2 3 1 2 7 3 1 3 2 8 3 2 1 3 9 3 3 2 1 3. Measurement of delamination factor (Fd): The differing extent of intrinsic hole machining defects (delamination) caused by drilling of each specimen were determined using the Mitutoyo TM 500 toolmakers microscope of 1 µm resolution with 30X magnification. It was employed to measure the delamination damage of holes and each trial was replicated twice. The value of the delamination factor (F d) can be calculated using the following equation: F d = D max / D (1) where D max is the maximum diameter of the damage around the hole periphery and D is the diameter of the drill, as shown in Fig. 2. Fig. 2. Schema of the measurement of the maximum diameter (D max). 4. Experimental results and discussion 4.1 Influence of the cutting parameters in the delamination factor The average readings of two trials of delamination factor were taken as process response. Table 3 presents the experimental layout plan and the computed values of delamination factors of the drilled four different fiber-reinforced composites. 4

In Figs. 3 and 4 we observe the evolution of the delamination factor (F d) with different cutting speed and feed rate values. Table 3: Experimental results of the L 9 orthogonal array experiments: v f Delamination factor (F d) Test (m/min) (mm/rev) Glass Hemp Jute Banana 1 16 0.10 1.87 1.79 1.92 1.80 2 0.20 2.19 2.50 2.93 2.27 3 0.30 2.87 2.90 3.80 3.03 4 24 0.10 1.60 1.15 1.70 1.61 5 0.20 1.97 1.70 2.39 1.95 6 0.30 2.14 2.10 2.95 2.24 7 32 0.10 1.36 1.08 1.35 1.49 8 0.20 1.96 1.70 2.10 1.74 9 0.30 1.97 1.85 2.12 1.95 3 3.5 Delamination factor (Fd ) 2.5 2 1.5 Glass Hemp Jute Banana Delamination factor (Fd ) 3 2.5 2 1.5 Glass Hemp Jute Banana 1 16.00 24.00 32.00 Speed (m/min) 1 0.10 0.20 0.30 feed (mm/rev) Fig. 3. Delamination factor F d compared (v). Fig. 4. Delamination factor F d compared to feed to cutting speed rate (f). In Fig. 3 we see that the delamination factor (F d) decreases with the cutting speed. We also observe in Fig. 4 that the delamination factor (F d) increases with the feed rate. According to the graphs, we observe that the HFRP Composite performs better than the other fiberreinforced composites. The JFRP composite always results in a bigger delamination factor, which means higher damage in the composite laminate. Physical properties and geometrical differences between the fiber types of different composites may be the reason for this observation. In the orthogonal array experiments analysis, we see evidence that the feed rate and cutting speed contribute the most to the delamination effect. Generally, the use of high cutting speed and low feed favor minimum delamination on drilling fiber-reinforced composites. 5

An analysis of variance of the data with the delamination factor (F d) in four different fiberreinforced composites was performed, with the objective of analyzing the influence of the cutting velocity (v) on feed rate (f ). The data was statistically analyzed in two phases. The first phase was concerned with the analysis of variance and the effects of the factors and interactions. The second phase allowed us to determine the correlation between the parameters (v and f). Tables 4 7 show the results of the analysis of variance with the delamination factor (F d) in four different fiber-reinforced composites. From the analysis of Table 4, we observe that the cutting velocity (% contribution = 34.83%) and the feed rate factor (% contribution = 55.42%) have statistical and physical significance for the delamination factor (F d) obtained. The factors (v and f) present a statistical significance test F > F α = 5%. Notice that the error associated with the table ANOVA for the F d was approximately 9.75%. From the analysis of Table 5, we observe that the cutting velocity factor (% contribution = 47.72%) and the feed rate factor (% contribution = 50.93%) have statistical and physical significance for the F d obtained. The factors (v and f) present a statistical significance test F > F α = 5%. Notice that the error associated with the table ANOVA for the F d was approximately 1.35%. From the analysis of Table 6, we observe that the cutting velocity factor (% contribution = 34.99%) and the feed rate factor (% contribution = 57.29%) have statistical and physical significance for the F d obtained. The factors (v and f) present a statistical significance test F > F α = 5%. Notice that the error associated with the table ANOVA for the F d was approximately 7.72%. From the analysis of Table 7, we can observe that the cutting velocity factor (% contribution = 37.41%) and the feed rate factor (% contribution = 52.25%) have statistical and physical significance for the F d obtained. The factors (v and f) present a statistical significance test F > F α = 5%. Notice that the error associated with the table ANOVA for the F d was approximately 10.34%. From the reasons above presented, the feed rate and cutting speed are seen to make the largest contributions to the delamination effect. Generally, the use of high cutting speed and low feed favor minimum delamination on all four composites of the drilling, leading to better quality holes. 6

Table 4: ANOVA of the delamination factor to the GFRP Source DF Seq SS Adj SS Adj MS F F α =5% P % contribution Speed 2 0.4907 0.4907 0.24537 7.14 6.94 0.048 34.83 Feed 2 0.7807 0.7807 0.39034 11.36 6.94 0.022 55.42 Error 4 0.1374 0.1374 0.03436 9.75 Total 8 1.4089 DF - degrees of freedom, SS - sum of squares, MS - mean squares, P-values Table 5: ANOVA of the delamination factor to the HFRP Source DF Seq SS Adj SS Adj MS F F α=5% P % contribution Speed 2 1.30027 1.30027 0.650136 70.52 6.94 0.001 47.72 Feed 2 1.38811 1.38811 0.694053 75.28 6.94 0.001 50.93 Error 4 0.03688 0.03688 0.009219 1.35 Total 8 2.72526 DF - degrees of freedom, SS - sum of squares, MS - mean squares, P-values Table 6: ANOVA of the delamination factor to the JFRP Source DF Seq SS Adj SS Adj MS F F α =5% P % contribution Speed 2 1.5822 1.5822 0.79108 9.06 6.94 0.033 34.99 Feed 2 2.5906 2.5906 1.29528 14.84 6.94 0.014 57.29 Error 4 0.3492 0.3492 0.08731 7.72 Total 8 4.522 DF - degrees of freedom, SS - sum of squares, MS - mean squares, P-values Table 7: ANOVA of the delamination factor to the BFRP Source DF Seq SS Adj SS Adj MS F F α =5% P % contribution Speed 2 0.6409 0.6409 0.32043 7.24 6.94 0.047 37.41 Feed 2 0.8953 0.8953 0.44766 10.11 6.94 0.027 52.25 Error 4 0.177 0.177 0.04426 10.34 Total 8 1.7132 DF - degrees of freedom, SS - sum of squares, MS - mean squares, P-values 4.2 Correlation (delamination factor/cutting parameters) The correlations between the factors (cutting velocity and feed rate) and the delamination factor (F d) in different fiber-reinforced composite laminates were obtained by multiple linear regression using Minitab 16 software. The equations obtained were as follow: Glass Fiber Reinforced Plastics (GFRP): F d = 2.10-0.0345 Speed + 3.58 Feed R = 87.1% (2) 7

Hemp Fiber Reinforced Plastics (HFRP): F d = 2.20-0.0534 Speed + 4.72 Feed R = 89.4% (3) Jute Fiber Reinforced Plastics (JFRP): F d = 2.60-0.0642 Speed + 6.50 Feed R = 91.0% (4) Banana Fiber Reinforced Plastics (BFRP): F d = 2.20-0.0400 Speed + 3.86 Feed R = 88.0% (5) 5. Confirmation tests Table 8 shows the machining conditions and results obtained from comparing the foreseen values by the models developed in the present work equations (2 5) with the experimentally obtained delamination factor (F d) values. From the analysis of the referenced table, we notice that the actual model has a maximum error of about 2%. We also consider that equation (2 5) correlates the evolution of the delamination factor (F d) in the different fiber-reinforced composite (GFRP, HFRP, JFRP, AND BFRP) laminates, with the machining parameters (spindle speed and feed rate) having a good degree of approximation. Table 8: Cutting conditions used in drilling confirmation tests. Speed Feed F d (Measured F d (Model Error Specimen Test (m/min) (mm/rev) Values) equations) (%) GFRP 1 20 0.08 1.66 1.70 2.15 2 30 0.25 1.98 1.96 1.02 HFRP 3 20 0.08 1.5 1.51 0.64 4 30 0.25 1.77 1.78 0.45 JFRP 5 20 0.08 1.85 1.84 0.76 6 30 0.25 2.32 2.30 0.91 BFRP 7 20 0.08 1.72 1.71 0.66 8 30 0.25 1.96 1.97 0.25 6. Conclusions An experimental analysis for drilling induced delamination associated with various machining parameters (cutting speed and feed rate) on different fiber-reinforced composites is presented in this study. The following conclusions can be drawn from the above investigation: (1) As seen in this study, the Taguchi design of experiment method provides a systematic and efficient methodology for the design optimization of the process parameters resulting in minimum delamination with far less effect than would be required for most optimization techniques. 8

(2) The quality of the hole produced in the natural fiber-reinforced composites tested were found to compare favorably with the corresponding quality of GFRP. The delamination factor of the drilled natural fiber-reinforced composite were in some cases better than those of glass fiberreinforced composite. This suggests that natural fiber composites have the potential to replace glass fiber composites in many applications where machining is needed. (3) The Hemp Fiber Reinforced Composites promote less damage than other fiber-reinforced composites, i.e., the delamination factor (F d) is smaller. (4) The feed rate and cutting speed are seen to contribute the most to the delamination effect. Generally, the use of high cutting speed and low feed favor minimum delamination on drilling for all four fiber-reinforced composites. (5) Confirmatory experiments were conducted to compare the predicted delamination factor with the experimental values of delamination factors, and good agreement between the predicted and experimental results were observed. Acknowledgements The first author expresses his gratitude to V R Siddhartha Engineering College, Vijayawada, Andhra Pradesh, India, for experimental facilities provided to carry out this research work. References Ahlblad, G., Kron, A., Stenberg B., 1994. Effects of plasma treatment on mechanical properties of rubber/cellulose fibre composites. Polym Int. 33, 103 9. http://dx.doi.org/10.1002/pi.1994.210330112 Geethamma, V.G., Joseph, R., Thomas S., 1995. Short coir fibre-reinforced natural rubber composites: effects of fibre length, orientation and alkali treatment. J App Polym Sci. 55, 583 94. http://dx.doi.org/10.1002/app.1995.070550405 Hakim S. Sultan Aljibori, W.P. Chong, T.M.I. Mahlia, W.T. Chong, Prasetyo Edi, Haidar Al-qrimli, Irfan Anjum, R. Zahari, 2010. Load displacement behavior of glass fiber/epoxy composite plates with circular cut-outs subjected to compressive load. Materials and Design. 31, 466 474. http://dx.doi.org/10.1016/j.matdes.2009.07.005 Jain, S., Kumar, R., Jindal, U.C., 1992. Mechanical behavior of bamboo and bamboo composite. J Mater Sci. 27, 4598 604. http://dx.doi.org/10.1007/bf01165993 Kishore R A, R. Tiwari, A. Dvivedi, I. Singh, 2009. Taguchi analysis of the residual tensile strength after drilling in glass fiber reinforced epoxy composites. Materials and Design. 30, 2186 2190. http://dx.doi.org/10.1016/j.matdes.2008.08.035 Li, Y., Mai, Y-W., Lin, Y., 2000. Sisal fibre and its composites: a review of recent developments. Compos Sci Technol. 60, 2037 55. http://dx.doi.org/10.1016/s0266-3538(00)00101-9 Murali Mohan Rao, K., Mohana Rao, K., Ratna Prasad A.V., 2010. Fabrication and testing of natural fibre composites: Vakka, sisal, bamboo and banana. Materials and Design. 31, 508 513. http://dx.doi.org/10.1016/j.matdes.2009.06.023 9

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