Influence of drilling parameters on thrust force in drilling of sic and graphite reinforced aluminium matrix composites by step drill

Transcription

1 Influence of drilling parameters on thrust force in drilling of sic and graphite reinforced aluminium matrix composites by step drill A. Muniaraj 1, a, Sushil Lal Das 2, b and K. Palanikumarr 3, c 1 Dept. of Mechanical Engineering, Sathyabama University, Chennai, India. 2 Dept. of Mechanical Engineering, Jeppiaar Engineering College, Chennai, India. 3 Dept. of Mechanical Engineering, Sri Sai Ram Institute of Technology, Chennai, India. a raniraj5@gmail.com, b sushil_das@rediffmail.com and c palanikumar_k@yahoo.com Abstract Hybrid metal matrix composites (MMCs) find diverse applications in many engineering fields. applications of these composite materials are among the most important developments in materials engineering in recent years. Metal matrix composites have became the necessary materials in various engineering applications like aerospace,marine, automobile and turbine-compressor engineering applications, because of their light-weight, high strength, stiffness and resistance to high temperature. MMCs should continue to focus on two important aspects, including improving the properties of MMCs and finding more economical techniques to produce mmcs. Machining is a material removal process and therefore is important for the final fabrication stage prior to application, consequently the development of effective machining methods leading to a reduction. In overall cost of component is one of the major challenges yet to be solved. Drill geometry is considered the most important factor that affects drill performance. A major concern in drilling of composite materials is the delamination that occurs in the exit as well as in the entrance planes. The delamination damage caused by the tool thrust is known as one of the major concerns during the drilling process. This paper discusses the influence of cutting parameter on Thrust force of when drilling aluminum alloy reinforced with silicon carbide and graphite hybrid metal matrix composite. The experiments are conducted to study the effect of spindle speeds: 1000, 2000 and 3000 rpm, feed rate: 0.05, 0.10 and 0.15mm/rev and different diameter of drill: 4 mm, 8 mm and 12 mm. This study included dry drilling with TiN coated solid carbide step drills. Keywords: Hybrid metal matrix composites, Drilling, Step drill, Thrust force 1. Introduction Metal matrix composites (MMC) are the new class of materials and are rapidly replacing conventional materials in various engineering applications such as the aerospace and automobile industries. Some of the typical applications are bearings, automobile pistons, cylinder liners, piston rings, connecting rods, sliding electrical contacts, turbocharger impellers, space structures, etc. The performance of MMCs is superior to conventional materials in terms of improved physical, mechanical, and thermal properties that include high specific strength and modulus, low density, high abrasion and wear resistance and high thermal conductivity [1 3]. The most popular reinforcements are silicon carbide (SiC) and alumina (Al 2 O 3 ). Aluminum, titanium, and magnesium alloys are commonly used as the matrix phase. The density of most of the MMCs is approximately one third that of steel,resulting in high-specific strength and stiffness [4].SiCp-reinforced aluminium composites have found many applications in the aerospace and automotive industry. However, due to hard ceramic reinforcing components in metal matrix composites (MMCs), they are difficult to machine and attempts to do so frequently results in accelerated tool wear and premature failure in accelerated tool wear and premature failure [5 7]. Coating is also used on cutting tools to provide improved lubrication at the tool/chip and tool/ tool/workpiece interfaces and to reduce friction, and consequently reduce the temperatures at the cutting edge. During machining, coated carbide tools ensure higher wear resistance, lower heat generation and lower cutting forces, thus enabling them to perform better at higher cutting conditions than their uncoated counterparts. The use of coated tools to machine difficult-to-cut materials actually represents state of the art machining technology and today s machining processes are becoming increasingly demanding upon cutting tool materials. Therefore, the available literature concentrated on the study of wear characteristics of various tool materials during machining aluminium-based composites [8 15]. In drilling of composite materials is the delamination that occurs in the exit as well as in the entrance planes. The delamination is primarily a function of feed rate and tool geometry [16].Numerous studies have examined cases in which delamination in drilling have been correlated to the thrust force during exit of the drill [17]. The delamination zone for twist drill has been shown to be related to the chisel edge [18].Usually, a step drill is employed to make holes of different diameters in a single drilling operation. The function of a step drill in drilling of composite materials is similar to the pre-drilled pilot hole that can reduce the delamination [19]. The influences of drill size and cutting conditions for step drilling have been studied by [20]. Most of the changes in the characteristics of the thrust force were influenced by the smaller drill of the step drill 435

2 [20]. The step drill performs front-edge cutting before step-edge cutting. The delamination formed in the primary stage cutting by the front cutting edge can be removed in secondary stage cutting by the step edge. The aim of this paper is to analyze the cutting parameters on thrust force in drilling of Al- 15%/SiC-4% Graphite metal matrix composites by tin coated solid carbide step drill of 4 mm, 8 mm and 12 mm diameter with different spindle speed and feed conditions.. Taguchi s orthogonal array is used for conducting the experiments. The experimental results are analysed and presented in this study. 2. Experimental procedure 2.1 Preparation of the composite In this study dry drilling tests were performed on a (CNC) ARIX vertical machining centre. The hybrid composite comprises 6061 aluminum alloy as matrix and SiC and Graphite are reinforcements. Aluminum alloy reinforced with 15% volume fraction of SiC and 4 % volume fraction of graphite with a particle size of 50µm was used as a reinforcement material. The composite were fabricated by stir casting method. The melting was carried out in electrical resistance furnace. The aluminium scraps of 6061 were first preheated at 600 C before melting. The SiC and graphite were also preheated at the required temperature. The preheated aluminum scraps were first heated above liquidus temperature to melt them completely, They were then slightly cooled below the liquidus temperature to maintain the slurry in semi-solid state. The Preheated reinforcement were mixed manually then composite slurry were heated to a liquid state, The final temperature was controlled to be within 800 C and pouring temperature was controlled to be around 820 C. The melt was poured in to steel moulds and allowed to cool to obtain 110mm x110mm x 5 mm size of plate. Table 1 shows the chemical composition of the Al 6061 alloy used. The fabricated Al-15%SiC-4%Gr composite chemical composition is presented in Table 2. The microstructure of the composite is shown in Fig. 1. Aluminum Graphite SiC Fig 1. Microstructure of Al-15%SiC-4%Graphite Table 1. Chemical composition [wt %] of Al 6061 alloy Al Mg Si Iron Cu Zn Ti Mn Cr others Balance Max Max 0.25 Max 0.15 Max Table 2. chemical compositions [wt %] of Al -15%SiC-4%Graphite Fe Si Mn Cu Cr Ti V Pb Mg Al Remainder 436

3 2.2 Machining Table 3 shows the various experimental parameters and their levels. The experiments were performed at different feed rates of 0.05 mm/rev, 0.10 mm/rev and 0.15 mm/rev, speeds of 1000 rpm,2000 rpm, and 3000 rpm and diameters of 4 mm, 8 mm and 12 mm as given in Table 4. The drilling tests are performed on ARIX-CNC machining center manufactured by ARIX CNC machine Co. Ltd., Taiwan. Coolant was not used in all of the drilling tests. The drill bits used for the experiments are presented in Fig. 2. Table 3 Experimental parameters and their values Parameters Drill Type Drill Size Values Solid carbide TiN coated step drill Ø 4mm, Ø 8mm and Ø 12mm Feed rate (mm/rev) 0.05,0.10,0.15 Spindle speed (rpm) 1000,2000,3000 Table 4. Variable factor levels S. No Feed rate, mm/rev Spindle speed, rpm Drill size, mm The thrust forces during drilling were measured with a Piezoelectric-dynamometer mean while the signals of the thrust force from the dynamometer was amplified and fed through a data acquisition system for electronic storage. The data-acquisition System is based on the dynaware software. The experimental setup is shown in Fig

4 Fig 2 Drills used for the experimentation Drill Head Composite [a] [b] Fig 3 Experimental set-up [a] Machine center and data acquisition system [b] Experimental device 3. Taguchi method The Taguchi method can economically satisfy the needs of problem solving and product/process design optimization in industry.for conducting the experiments Taguchi method is used. Taguchi method is experimental design tool used in analysing and designing of experimental results in manufacturing engineering. Taguchi method uses a special design of orthogonal arrays to study the entire parameter space. Taguchi method is used for analysing the main effects and interaction effects in experimental analysis and is a powerful tool, which provides a simple, efficient and systematic approach to determine optimal cutting parameters. Compared to the conventional approach of experimentation, this method reduces drastically the number of experiments that are required to model the response functions [21, 22]. Table 5 shows the factors to be studied and the assignment of the factors to the corresponding Levels. The array chosen was the L 27 [3 13 ].which has 27 rows corresponding to the number of tests (26 degree of freedom) with 13 columns at three levels. The factors and the interactions are assigned to the columns. The plan of Experiments made of 27 tests in which first column is assigned to feed rate [f], the second column to spindle speed [n], the fifth column to drill diameter [d] and the remaining columns were used interaction and other effects. 438

5 Table 5 Orthogonal array of L 27 [3 13 ] Trial A B AXB AXB C AXC AXC BXC D AXD BXC BXD CXD 4 Result and Discussion 4. 1 Thrust force Figure 4 (a), (b) and (c) shows the influence of feed rate on the thrust force in drilling of Al/SiC/Graphite hybrid metal matrix composites without use of coolant. The drilling tests are performed at different cutting speed, feed rate. Spindle speed and feed rate are the two major drilling parameters that are considered in the experiments Figure 4(a) shows the influence feed rate on thrust force when drilling at spindle speed 1000, 2000 and 3000 rpm. The result indicated that thrust force increase with increase in feed rate. From the figure it can be observed that the thrust force is (57.50 N) lower at higher cutting speed (3000 rpm) than lower cutting speed (1000 rpm). 439

6 Thrust force [N] Feed [mm/rev] 1000 rpm 2000 rpm 3000 rpm Fig 4 (a) Variation of Thrust force with feed rate at different drill Speed Figure 4 (b) shows the influence of feed rate and the drill diameter on thrust force in drilling of Al/SiC metal matrix hybrid composites. The feed rate verses thrust force graph shows consistently thrust force is lower at lower diameter of drill than at higher diameter of drill. Thrust force is low (65 N) at low feed rate, i.e.0.05 mm / rev and thrust force is high ( N) at high feed rate, i.e.0.15mm / rev. The reason being the increase of feed rate increases the load on the tool subsequently increases the thrust force in drilling of hybrid composites Thrust force [N] Feed [mm/rev] 4 mm 8 mm 12 mm Fig 4 (b) Variation of Thrust force with feed rate at different drill diameter Figure 4 (c) show the influence of cutting speed and the drill diameter on thrust force. The speed Vs thrust force graph shown thrust force gradually decreases by increasing cutting speed from 1000 rpm to 3000 rpm during drilling of Al / SiC/ graphite hybrid metal matrix composite. The feed rate is the predominant factor and as the feed rate increases the thrust force increases for the composite. Davim and Baptista [32]. were under the opinion that regardless of the tool material and work material, the thrust is highly dependent on feed rate, while cutting speed was found to have insignificant influence on the degree of drilling forces. Charles Lane [33] was under the opinion that the feed rate was determined to be the most significant parameter affecting the drill life and tool forces. increasing the feed rate increases cutting force significantly. 440

7 Thrust force [N] Speed [rpm] 4. 2 SEM image investigation 4 mm 8 mm 12 mm Fig 4 (c) Variation of Thrust force with speed at different drill diameter Fig 5 SEM image of showing rough drilled surface at a feed rate of 0.05 mm/rev and a speed of 1000 rpm Fig 6 SEM image of showing fine drilled surface at a feed rate of 0.05 mm/rev and a speed of 2000 rpm Fig 5 shows the SEM image of rough drilled surface of Al-15% SiC-4% Graphite hybrid metal matrix composites under cutting conditions of feed rate 0.05 mm/rev and spindle speed 1000 rpm. In this case, it can be seen that feed mark is visible on the surface of the composites. Surface layer is highly sheared. Alumina and silicon particles are severely fragment and pulled out of the surface during drilling operations; the particles rub against the tool causing the surface finish as shown in figure. Fig 6 shows the SEM image of fine drilled surface of Al-15% SiC-4% Graphite hybrid metal matrix composites under cutting conditions of feed rate 0.05 mm/rev and spindle speed 2000 rpm, the contact duration of the tool with work piece material is reduced, hence the tool wear is decreased, feed mark is not visible, Surface finish is comparatively better at a speed of 2000 rpm and 0.05 mm/rev. CONCLUSIONS The experiments are conducted on computer numerical control machining centre to study the influence of cutting parameters on drilling of hybrid metal matrix composites. Based on the experimental results and analysis the following conclusions are drawn: 1. Feed rate is the main factor, which influence the thrust force in drilling of Al/SiC/Gr hybrid metal matrix composite and as the feed rate. 441

8 2. Thrust forces vary with feed, feed rate affects drilling forces but cutting speed has not much effect over the range of spindle speeds. 3. Thrust forces decreases with increase in cutting speed and vice versa. 4. Lower speed shows comparatively more thrust force than higher spindle speed. 5. Due to the abrasive action of the SiC particles, the coating on the tool material is removed REFERENCES 1. Suresh S, Mortensen A, Needleman A (1993) Fundamentals of metal-matrix composites. Butterworth-Heine -mann, Stoneham, MA. 2. Taya M, Arsenault RJ (1989) Metal-matrix composites-thermo mechanical behavior. Pergamon Press, Newy York. 3. Ibrahim A,Mohammed FA, Lavernia EJ (1991)Metal-matrix composites-a review.j Mater Sci 26: QuanY,Ye B (2003) The effect of machining on the surface properties of SiC/Al composites. J Mater Process Process Technol 138: M.K. Brun, M. Lee, F. Gorsler, Wear characteristics of various hard materials for machining SiCp reinforced aluminium alloy, Wear 104 (1985) A.R.Chambers, S.E.Stephens, Machining of Al 5Mg reinforced with 5 vol. % Saffil and 15 vol.% SiC fibres, J. Mater. Sci. Eng. A 135 (1990) M. El-Gallab, M. Sklad, Machining of AlySiCp metal matrix composites part-i: tool performance, J. Mater. Process. Technol. 83 (1998) Y.M. Quan, Z.H. Zhou, B. Y. Ye, Cutting process and chip appearance of Al matrix composites reinforced by SiC particles,j. Mater. Process. Technol. 91 (1999) Q. Yanming, Z. Zehna, Tool wear and its mechanism for cutting SiCp reinforced Al matrix composites, J. Mater. Process. Technol. 100 (2000) N.P. Hung, F.Y.C. Boey, K.A. Khor, C.A. Oh, H.F. Lee, Machinability of cast and powder formed alumini -um alloys reinforced with SiC particles, J. Mater. Process. Technol. 48(1 4) (1995) J.T. Lin, D. Bhattacharyya, C. Lane, Machinability of a silicon carbide reinforced aluminium metal matrix composite, Wear 181 (1995) L.A. Looney, J.M. Monaghan, P. O Reilly, D.M.R.Taplin, The turning of an AlySiC metal composite, J. Mater. Process.Technol. 33 (1992) X. Li, W.K.H. Seah, Tool wear acceleration in relation to workpiece reinforcement percentage in cutting of metal matrix composites, Wear 247 (2001) Q. Quigley, J. Monaghan, P. O Reilly, Factors affecting the machinability of an AlySiC metal matrix composites, J. Mater.Process. Technol. 43 (1994) K. Weinert, D.Biermann, Turning of fibre and particulate reinforced aluminium, in: Processing of Internati -onal Conference. 16. Jain S, Yang DCH (1993) Effects of feedrate and chisel edge on delamination in composite drilling. ASME J Eng Ind 115: Sakuma K, Yokoo Y, Seto M (1984) Study on drilling of reinforced plastics-relation between tool material and wear behavior. Bull JSME 27(228): Won MS, Dharan CKH (2002) Chisel edge and pilot hole effects in drilling composite laminates. ASME Manuf Sci Eng 124: Tsao CC, Hocheng H (2003) The effect of chisel length and associated pilot hole on delamination when drilling composite materials. Int J Mach Tools Manuf 43(11): Xia RS, Mahdavian SM (2005) Experimental studies of step drills and establishment of empirical equations for the drilling process.int J Mach Tools Manuf 45(2): Yang WH, Tang YS (1998) Design optimization of cutting parameters for turning operations based on the taguchi method. J Mater Process Technol 84, Taguchi G (1990) Introduction to quality engineering. Asian Productivity organization, Tokyo. 23. Davim, J.P., Baptista, A.M., Cutting force, tool wear and surface finishing drilling Metal matrix composites.proc.inst.mech eng. E 215, Lane. C., (1993).International conference on advanced composite materials. In; Chandra, T., Dhingra, A.K, (Eds), The Minerals, Metals and Materials society, pp