An experimental study on the burr formation in drilling of aluminum channels of rectangular section

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1 5 th International & 26 th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12 th 14 th, 2014, IIT Guwahati, Assam, India An experimental study on the burr formation in drilling of aluminum channels of rectangular section Das, R 1*, Barik, T 2 1,2 School of Mechanical Engineering, KIIT University, Bhubaneswar , Odisha, India * 1 ratankd@gmail.com, 2 tarakes18@gmail.com, Abstract Now-a-days precision manufacturing has gained it importance in all manufacturing industries. The best product dimensions and the minimization of time and cost of production has become a measure of concern. Drilling process takes care about 35% of all the machining processes and influences the acceptability of the products as the drilling process is at the most final processing stage in the production line. The burr, which is a plastically deformed material, generated during drilling is unnecessary output and often lowers the surface quality, reduces the product life and acceptability of the product. Total elimination of burrs during drilling process is a difficult task, however, with proper selection of process parameters it can be minimized. In the present experimental study, analysis on burr formation has been carried out on the aluminum channel in drilling process. The drill bit diameter and spindle speed are found to be most effecting parameters in burr formation. Drilling of aluminum flat drilling has been done for comparison of results. Keywords: Burr formation, Drill bit, Aluminum channel, 1 Introduction Drilling is one of the most commonly used machining processes in most of the manufacturing industries. Drilling takes acre about 35% of all the machining process. As the drilling process is followed at the end of all other machining processes, the acceptability of the products depends on the quality of the product. In describing the irregularities in drilling process, burr, which is the plastically deformed material, is being present at the entry and exit of the drilled hole. The removal of burr consumes about 15% of man power and cycle time of manufacturing. The earliest report about burr was with the punching operation. The other operations like turning, milling, grinding also produce burr during machining of materials. However, the mechanism of burr formation and the deburring processes followed are different for different materials. The problems associated with the burr are that they cause misalignment between adjacent parts and also reduction of fatigue life. The other problems are like danger to operator with the sharp edges of burrs, poor part aesthetics etc. The burr formation is dependent on many process parameters. The elimination of burr in any machining process is quite difficult. However, the proper selection of different process parameters can minimize the burr formation. 2 Literature review Pande and Releker (1986) carried out experimental investigation on reduction of burr formation in drilling of through-holes in metals and it was observed that the larger diameter of drill bit yields maximum burr height. For an optimum feed, the formation of burr is minimum and is independent of drill diameter. The burr formation in small diameter holes was carried out by Stein and Dornfeld (1997). They reported that in drilling of 0.91 mm hole in stainless steel, the burr height and the undeformed chip thickness ratio was constant in different level of feed rate and spindle speed. Dornfeld et al. (1999) carried out drilling on titanium alloy (Ti-6Al-4V) plate and investigated the effect of tool geometry and process condition on the drilling burr formation. The effect of different drill bit material (solid carbide and high speed cobalt) and application of coolant was studied. The different types of burr formations such as ring type, lean back burr, roll back burr and uniform burr were formed. They also observed that helical point drill produces small burrs than split point drill

2 An experimental study on the burr formation in drilling of aluminum channels of rectangular section Kim and Dornfled (2001) carried out a cost estimation of drilling operation based on drilling burr control chart and Bayesian statistics. The cost of drilling operation consists of cost of hole making and cost of deburring. The procedure developed by them can be effectively used to minimize the total cost without sacrificing the hole quality and the productivity. A new concept drill was developed by Ko and Lee (2001) to improve the accuracy and productivity in drilling operation. The different point angles produce different types of burrs. They observed that larger point angles produce small burr height and the cap thickness is independent of feed but changes with material properties. Ko et al. (2003) proposed the use of step drill to minimize the burr formation as the step drill performs front edge cutting before step edge cutting. They also used laser sensor to measure the burr formed in drilling. Pena et al. (2005) proposed and evaluated the burr formation in drilling by monitoring the internal signals from the spindle torque. They developed an algorithm to distinguish the burr height with the established onset. A mathematical model based on the mechanics and dynamics of the drilling process was developed by Pritini and Lazoglu (2005) to predict the cutting forces and the drilled hole quality. Chang and Bone (2005) designed an ultrasonically vibrated workpiece holder and carried out drilling on A aluminum workpiece with uncoated and TiN coated drills. They observed that burr size can be effectively reduced at higher spindle speed and feed rate with ultrasonically assisted drilling. Gaitonde et al. (2008) carried out a study on the optimization of burr formation based on the cutting speed, feed, point angle and lip clearance angle. Some interesting observations were made by them. The point angle has major influence on optimal burr height for drill diameters of 4 mm, 10 mm and 28 mm. Lip clearance angle has significant effect in reducing the burr height for 20 mm drill bit diameter and large point angle is required to minimize the burr height for higher drill bit diameters. Aurich et al. (2009) carried out an extensive review on the burr formation and control. In the bird eye review of the research carried out for the period of 1965 to 2009, the authors indicated that the research findings have not yet been applied to industries. More focus to the drilling of small holes, micro products and products with high demands need must be given. A recent review work carried out by Liu et al. (2012) on the drilling of composite laminates. The thrust areas in the review include the high speed drilling, drill bit geometry, thrust force and tool wear. The literature review shows that the spindle speed and the feed force are important process parameters in burr formation. The review work carried out by Aurich et al. (2009) indicates that other than the flats, in the specimens like circular, the burr formation depends on many parameters. In the real practice, the use of rectangular channels is quite common and the dimension such as length, width, breadth and thickness also vary as per the requirements. The dimension of the holes to be drilled also fix or application based. This limits the process parameters to be controlled and care to be taken to avoid the bending of the channels due to excessive force applied during drilling. Thus, the objective of the present work has been set to have a systematic study to evaluate the effect of different process parameters in burr formation in the drilling of commercially available aluminum channels. 3 Experimental Procedure To comply with the objectives of the research, the work-piece specimens were taken in the form of rectangular channels of dimensions of 65 mm 45 mm 38 mm and 45 mm 45 mm 20 mm with thickness of 1 mm and 1.2 mm respectively [Make: Jindal Steel Ltd.]. The composition of the 1050 series aluminum channel is as follows, Mg- 0.05%, Si-0.2%, Mn-0.05%, Fe-0.45, Cu-0.07%, Zn- 0.05%, Ti-0.02% and Al-99.5%. The specimens were cut with the length of 50 mm for all experiments. As discussed in section 2, the drilling has to be carried out without bending of the channel. For this purpose, the bend test was carried out for the specimens. Figure 1. Bend test of the rectangular channel Figure 1 shows the bend test carried out on the rectangular aluminum channel. The specimen was put on the bottom platen of the Universal Testing Machine. On the top platen the drill bit was fixed with the help of one fixture which will make able the drill bit to be in the middle of the channel as shown in figure 1. The simple compression test was carried out and it was observed that at 20 N load, the channel starts bending. Before starting the experiments, some trials are carried out to get an approximate in hand experience of applying a load less than 20 N during the drilling process. The mere intention is to make the experiment as practicable as possible. The Channels were cut into the equal length of 50 mm. The high speed steel (HSS) drill bits of different diameter (2 mm, 4 mm and 6 mm) are used for drilling operation. The different spindle speeds of 625, 1250 and 2500 rpm have been used in drilling of different channels. All the operations are repeated twice. After each experiment, the drilled channel is 831-2

3 5 th International & 26 th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12 th 14 th, 2014, IIT Guwahati, Assam, India removed from the machine and the burr heights are measured by using vernier caliper and micrometer. The standard deviations of the obtained butt heights are also calculated. For drilling operation, vertical bench drilling machine (Make: Hipat Machine tools, Cuttack, Odisha) is used. Before doing the experiments, a spring (spring constant is known) was fixed to the drill machine head and the lever. The deflection due to the load applied was measured and subsequently the load was calculated. The utmost care was taken to keep the load less than 20 N to avoid the bending of the channel. The time required to give feed was measured for the entire process using a stopwatch. of 2 mm and 4 mm. However this pattern changes with 6 mm drill bit diameter for same channel thickness. At low feed i.e. for 0.5 mm/sec, the effect of drill diameter is not significant in providing small burr height. However, the spindle speed of 1250 rpm produces minimum burr height. 4 Results and discussion Figure 2. Burr at the exit side of the channel after drilling Figure 2 shows the burr at the exit side of the channel. In the repetition of experiments, the different burr form and heights are obtained. The average burr height is plotted against the spindle speed. Figure 3. Burr height at different spindle speed in drilling on aluminum channel of 1.0 mm thickness at vertical feed of 0.5 mm/sec. Figure 3 shows the effect of spindle speed on the burr height while drilling of the channel of 1 mm thickness at vertical feed of 0.5 mm/sec. The vertical feed is calculated by using a stopwatch for all the experiments. It is observed that the average burr height is minimum at 1250 rpm for drill bit diameter Figure 4. Average burr height at different spindle speed of drilling on aluminum channel of 1.0 mm thickness at vertical feed of 3 mm/sec. Figure 4 shows the average burr height while drilling the channel at vertical feed of 3 mm/sec. The average burr height increases with increase in the drill bit diameter. The minimum burr height of observed for the drilling with 2 mm diameter drill bit. For the same drill bit diameter, the average burr height increase with increase in the spindle speed more than 1250 rpm. For the drill bit diameter of 6 mm, about 71% increase in the average burr height is there for the spindle speed 625 rpm when compared to 1250 rpm and about 60% increase in average burr height for the spindle speed of 2500 rpm when compared to 1250 rpm. This indicated that for a particular thickness, an optimum spindle speed exist which produces lowest burr height. With increase in vertical feed, the minimum burr height is observed for 2, 4, 6 mm drill bit diameters. At a particular spindle speed the cutting strain may be sufficient enough for separation of the burr a chip and goes away from the workpiece. As a result, the burr height decreases. At high cutting speed, the cutting operation by the both cutting edge of the drill bit will be influencing the burr height. Figure 5 and 6 show the burr height for the drilling of channel of 1.2 mm thickness. With the drill bit of 6 mm diameter, the burr heights increase upto 1250 rpm spindle speed and then decreases at 2500 rpm. This trend is not similar to that of the drilling of 1 mm thickness channel. It can be explained as follows. The 1.2 mm thickness channel requires more force to bending during drilling and therefore either more force can be applied to it or the vertical feed rate can be increased. From this observation, it observed that the force to be applied and the vertical feed applied during

4 An experimental study on the burr formation in drilling of aluminum channels of rectangular section the drilling operation also effect the burr height along with the drill bit diameter and the spindle speed. evident that the variation exists in the burr height while drilling many specimens at same conditions of operation. It is observed that the burr formation is unavoidable in drilling process. However, the minimization is possible by selecting some process parameters. The segmented (broken) burrs are hazardous and also create problems during the assembly. Another experiment is carried out to study the effect of any back support in the nature of burr formation. For this, aluminum flat of 6 mm thickness is drill having a support at the bottom as shown in figure 5. Figure 5. Average burr height at different spindle speed of drilling on aluminum channel of 1.2 mm thickness at vertical feed of 0.5 mm/s (a) (b) Figure 5 (a) and (b). Burrs with the holes on aluminum flat Figure 6. Average burr height at different spindle speed of drilling on aluminum channel of 1.2 mm thickness at vertical feed of 3 mm/s Table 1. Standard deviation of burr heights in drilling of 1.2 mm thickness channel using 3 mm diameter drill bit. Specimen no Avg. burr height (mm) Max. burr height (mm) Standard deviation The drill bit diameter of 3 mm is used for drilling holes. The holes are drilled at different locations starting from the clamp support towards the middle of the flat. The burr at the entry side of the hole is not observed. It can be observed from the figure 10 that the burrs at the exit side of the holes are not segmented. The holes located towards the clamped side, the un-segmented burr is formed. The holes at the middle of the flat have some small fragmented burrs but compared to the channels, it is very less. The clamping helps in providing the better quality holes. The selection of the support (in the present case is wood) is also a matter if issue. When the drill bit leaves the hole and enters into the wood, there may be transmission of force and this will allow the burrs to get segmented. This can be studied further in details for producing a better hole quality. Table 1 shows the maximum, average and standard deviation of burr heights for the drilling of 1.2 mm channel using 3 mm drill bit. The standard deviation ranges from as low as 0.37 to as high as It is 831-4

5 5 th International & 26 th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12 th 14 th, 2014, IIT Guwahati, Assam, India 5 Conclusions Based on the above discussions, following conclusions can be drawn. The burr formation in channels highly depends on the spindle speed. The thickness of the channels also effect the burr formation i.e. the higher thickness channel needs more force during drilling. There an optimum spindle speed exists for a selected channel thickness, for which the average burr height is lowest. The prevention of bending increases the time taken for drilling operation to complete and the applied force will be limited. In case of drilling of flats, the support at the bottom part helps in producing unsegmented burr, which is less hazardous. The proper clamping force can also produce a better quality hole on flat. International Journal of Machine Tool Design and Research, Vol. 26 (3), pp Penaa, B., Aramendia, G., Rivero, A. and Lacalle, L., (2005), Monitoring of drilling for burr detection using spindle torque, International Journal of Machine Tools & Manufacture, Vol. 45, pp Pirtini, M. and Lazoglu, I., (2005), Forces and hole quality in drilling, International Journal of Machine Tools & Manufacture, Vol. 45, pp Stein, J.M. and Dornfled, D. A. (1997), Burr formation in drilling of miniature holes, Annals of the CIRP, Vol. 46, pp References Aurich, J.C., Dornfeld, D., Arrazola, P.D., Franke, V., Leitz,V. and Min, S., (2009), Burrs Analysis, control and removal, CIRP Annals-Manufacturing Technology, Vol. 58, pp Chang, S. and Bone, G.M., (2005), Burr size reduction in drilling by ultrasonic assistance, Robotics and Computer-Integrated Manufacturing, Vol. 21, pp Dornfeldl, D.A., Kim, J.S., Dechow, H., Hewson, J. and Chen, L.J., (1999), Drilling Burr Formation in Titanium Alloy, li-6ai-4v, Annals of the CIRP, Vol. 48, pp Gaitonde, V.N., Karnik, S.R., Achyutha, B.T. and Siddeswarappa, B., (2008), Taguchi optimization in drilling of AISI 316L stainless steel to minimize burr size using multi-performance objective based on membership function, Journal of materials processing technology, Vol. 202, pp Kim, J. and Dornfeld, David A. (2001), Cost Estimation of Drilling Operations by a Drilling Burr Control Chart and Bayesian Statistics, Journal of Manufacturing Systems, Vol. 20, pp Ko, Sung-Lim and Lee, J., (2001), Analysis of burr formation in drilling with a new concept drill, Journal of Materials Processing Technology, Vol. 113, pp Ko, Sung-Lim., Changa, J. and Yang,G., (2003), Burr minimizing scheme in drilling, Journal of Materials Processing Technology, Vol. 140, pp Liu, D., Tang, Y. and Cong, W. L. (2012), A review of mechanical drilling for composite laminates. Composite structures, Vol. 94, pp Pande, S. S. and Relekar, H. P., (1986), Investigations on reducing burr formation in drilling,