PCD Cutting Insert Behavior on Turning (Al-SiC15p) MMC

Transcription

1 PCD Cutting Insert Behavior on Turning (Al-SiC15p) MMC S.Santha Kumar, V.Thenappan and G.Srinath Abstract--The paper presents the results of an experimental investigation on the machinability of Aluminum metal matrix composite AL-SiC-MMC (A356/SiC/15p) during continuous turning of composite rods using medium grade Polycrystalline Diamond (PCD 15) inserts. MMC s are very difficult to machine and PCD tools are considered by far, the best choice for the machining of these materials. Experiments were conducted at medium duty lathe using PCD 15 grade insert at various cutting conditions and parameters such as surface roughness, specific power consumed, and tool wear were measured. The influences of cutting speed on the insert wear and built-up edges (BUEs) formation were studied. The present results reaffirm the suitability of PCD for machining MMCs. The worn out tool is also analyzed under optical scanning microscope. The result provides some useful information. Keywords-- Machinability, Metal Matrix Composite, Tool Wear, PCD inserts. I I. INTRODUCTION NCREASING quantities of metal matrix composites (MMCs) are being used to replace conventional materials in many applications, especially in the automobile and recreational industries. The most popular types of MMCs are aluminum alloys reinforced with ceramic particles. These low cost composites provide higher strength, stiffness and fatigue resistance [1,2,3] with a minimal increase in density over the base alloy. Owing to the addition of reinforcing materials, which are normally harder and stiffer than the matrix, machining becomes significantly more difficult than in the case for conventional materials, as reported in the earlier publications [1-6]. The type of MMC studied in this paper for its machinability is an Al-SiC composite. The Al356 reinforced with 15 % by weight of particulate of Silicon carbide. Aluminium is acted as matrix. A typical microstructure of work piece is shown in fig - 1. The chemical composition of work piece is shown in table - 1. S.Santha kumar is with the Mechanical Engineering Department, Sri Venkateswara College of Engineering, Sriperumbudur, CO 6215 INDIA (phone: ; shantha_wolvy@ahoo.co.in). V.Thenappan is with the Mechanical Engineering Department, Sri Venkateswara College of Engineering, Sriperumbudur, CO 6215 INDIA(phone: ; thenappanvairavan@gmail.com). G.Srinath with the Mechanical Engineering Department, Sri Venkateswara College of Engineering, Sriperumbudur, CO 6215 INDIA. Fig. 1 Microstructure of the specimen (Al-SiC) The grain size of the cutting tools has significant influence on the tool wear during machining of MMC. While a tool with coarse grain posses a high abrasion resistance required for increased performance, increasing the size of the grains could result in substantial drop in the fracture resistance, which has a significant negative influence on overall tool performance [7, 8]. Al Si Fe M g Silicon carbide TABLE 1 CHEMICAL COMPOSITION OF THE MATERIAL Zn Pb Ni Zr Mn V Li and Seah [9] observed that tool wear becomes acute when the percentage of reinforcement in the MMC substrate exceeds a critical value, which is determined by the density and size of the particles. El-Gallab and Sklab [1] found that the built-up edge that is formed during machining could protect the cutting tool from abrasion wear. However, the unstable built-up edge may induce tool chipping and adversely affect the surface finish. [1,11]. The good surface finish is produced when the particles are cut cleanly instead of being pulled from the matrix material [12]. K 2 inserts showed better wear resistance and produced better surface finish than High-speed steel tools [12,13]. This was due to the higher hardness of the carbide tools and the lower affinity with the MMC material. The main objective of the present work is to analyze the optimum cutting conditions of the MMC with K2 insert. 133

2 Work piece material Machine Tool insert TABLE 2 EXPERIMENTAL CONDITIONS Al/SiC (15p) 5 mm * 175 mm long dia billet Self Centering Lathe CNMA 1248, Nose radius.8 mm Holder size 25 * 25 (PCLNR 2525 M12) Cutting parameters Surface equipment texture Cutting speed 1,2,3,4, and 5 m/min Feed rate.1, and.2 mm/rev Depth of cut.25,.5 and.75 mm Surf test 31, Make - Mitutoyo II. EXPERIMENTAL PROCEDURE The Al-SiC (MMC) of dia 5 mm * 175 mm long billet was machined with Poly Crystalline Diamond (PCD) carbide insert at five different cutting speeds (1,2,3,4, & 5 m/min) with two different feed rates (.1 &.2 mm/rev) and three depth of cuts (.25,.5 &.75 mm). Table- 2 summarizes the details of the experimental conditions. The use of K 2 carbide insert in this study is due to its better performance compared with High-speed steel tool when machining aluminum MMC [5] The surface roughness was measured at predetermined intervals. Other parameters like material removal rate, power consumption, and cutting force were calculated using the cutting speed, feed and depth of cut. All trials were performed for one-minute duration III. RESULTS AND DISCUSSION EFFECT OF CUTTING SPEED ON MRR From fig.2 it is clearly understood that cutting speed increases the MRR also increase. It is a general rule that MRR depends on feed and depth of cut. If feed and depth of cut are high, the volume of metal removal rate is more, because the area of contact of insert on the work piece is more. EFFECT OF CUTTING SPEED ON MAIN CUTTING FORCE From fig-3 it is clearly observed that main cutting force is decreasing when cutting speed increases. This has happened due to the stability of the cutting insert at high cutting speed and it is also very easy to chip material from the parent material at high cutting speed. EFFECT OF POWER CONSUMPTION From fig.4 it is noticed that power consumed is more at high cutting speed. It is obvious that power requirement is more at high feed rate and depth of cut. It is a general rule that power consumption is fully dependent on the feed and depth of cut. FEED.18 DOC.25 FEED.18 DOC.5 FEED.18 DOC.75 FEED.2 DOC.25 MRR ( Cu mm/min) FEED.2 DOC.5 FEED.2 DOC Cutting Speed (m/min) Fig 2 Cutting speed Versus MRR 134

3 1 9 Cutting Force (newtons) FEED.18 DOC.25 FEED.18 DOC.5 FEED.18 DOC.75 FEED.2 DOC.25 FEED.2 DOC.5 FEED.2 DOC.75 Cutting Speed (m/min) Fig-3 Cutting Speed Versus Cutting force Gross Power (watts) rpm.18 feed 315 rpm.18 feed 5 rpm.18 feed 775 rpm.18 feed 12 feed.18 feed 224 rpm.2 feed 315 rpm.2 feed 5 rpm.2 feed 775 rpm.2 feed 12 rpm.2 feed Depth of Cut (mm) Fig 4 Depth of Cut versus Power Consumed 135

4 Surface Finish (Ra in microns) rpm.18 feed 315 rpm.18 feed 5 rpm.18 feed 775 rpm.18 feed 12 rpm.18 feed 224 rpm.2 feed 315 rpm.2 feed 5 rpm.2 feed 775 rpm.2 feed 12 rpm.2 feed Depth of Cut (mm) Fig 5 Depth of cut Versus Surface Finish It is essential to see the trend at various feed rates at various depth of cut, fig- 5 is drawn between Depth of cut and Surface finish. When the depth of cut and feed rate increase the surface finish obtained is poor. It is evident that surface finish is strongly dependent on the depth of cut and feed rate. It is also noticed that the surface finish is good when the insert is slightly worn out rather than sharp edge, ie nose radius is slightly larger than.8 mm. Flank wear Fig 6 PCD insert after machining Nose region Fig 7 PCD insert before machining (5X) It is also seen in Fig-5, at lower depth of cut and lower feed rate the gross power required is less. It is increasing linearly when the depth of cut and feed rate increase. This is happened due to the more power requirement to chip the material from the parent material. It is advisable to machine this material at lower feed rate with less depth of cut. IV. CONCLUSION The following conclusions can be drawn from the results of this investigation: The main type of tool wear during machining Al- SiC Metal matrix take place on flank and the rake surfaces. The primary mechanism of wear formation is believed to be the abrasion between reinforcement particles and cutting tool material. The surface finish of the machined samples deteriorates with increasing feed rates. PCD insert performed well in all aspects. REFERENCE [1] J.T. Lin, D.Bhattacharyya, and C.Lane, Machinability of a silicon carbide reinforced aluminium metal matrix composite Wear, (1995) [2] M.C.Shaw, Metal cutting principles, Clarendon, Oxford, [3] D.Bhattacharyya, M.E.Bowis and J.T.Gregory, The influence of micro sphere reinforcement on the mechanical behavior and edibility of a 661 aluminium metal matrix composite, ASM.Int. symp. Machining of composite materials, Chicago, November 1992, pp [4] C.Lane, The effect of different reinforcements on PCD tool life for aluminium composites, ASM.Int. symp. Machining of composite materials, Chicago, November 1992, pp [5] C.Lane, Machinability of aluminium composite as a function of matrix alloy and heat treatment, ASM.Int. symp. Machining of composite materials, Chicago, November 1992, pp [6] N.Tomac and K.Tonnessen, machinability of particulate aluminium matrix composites, Ann. CIRP, 41(1) (1992) [7] L.Cronjager and D.Meister, machining of fibre and particulate reinforcement aluminium, Ann. CIRP, 41(1) (1992) [8] E.J.A Armarego and R.H.Brown, The machining of metals, Prentice Hall, NJ, [9] M. El-GALLAB. M. Sklad. Machining of Al/SiC particulate metal matrix composites. Part I: Tool performance. J. Mater. Process. Techno. 83 (1993)

5 [1] M. El-GALLAB. M. Sklad. Machining of Al/SiC particulate metal matrix composites. Part II: Workpiece surface integrity, J. Mtaer. Process. Techno. 83 (1998) [11] C.F. Chenng, K.C. Chan, S. To. W.B. Lee, Effect of reinforcement in ultra-precision machining of Al661/SiC metal matrix composites, Scripta Mater, 47 (22) [12] R.M. Hooper, J.L. Henshall, A. Klopfer. The wear of polycrystalline diamond tools used in the cutting of metal matrix composites. Int. J. Refract. Matal Hard. Mater. 17 (1999) [13] A.R. Chambers, The machinability of light alloy MMCs, Composites part A 27A (1996)