Aluminum silicon carbide Metal Matrix Composites (Al-MMC) are widely used in aeronautical and automobile industries due to their excellent mechanical and physical properties. However machining this composites find difficult because of the reinforcement particles. Tools wear more quickly and reduce the life of the tool. This paper presents the experimental investigation on machining two different A356 matrix metal reinforced with 10 % and 20 % by weight of Silicon carbide (SiCp) particles is fabricated in house by stir casting method. Fabricated samples are turned on medium duty lathe with Poly crystalline Diamond (PCD) insert of 1600 grade at various cutting conditions. Parameters such as power consumed by main spindle, machined surface roughness and tool wear are studied and influence of SiC particles percentage on tool wear also discussed. Scanning Electron Microscope (SEM) images support the result. It is evident that, tool wear is strongly dependent on reinforcement percentage.
Key words: A356 Alloy, PCD, Power consumed, Surface roughness, SiC percentage
1. Introduction
Metallic matrix composites have found considerable applications in aerospace, automotive and electronic industries [1] because of their improved strength, stiffness and increased wear resistance over unreinforced alloys [2]. However, the final conversion of these composites in to engineering products is always associated with machining, either by turning or by milling. A continuing problem with MMCs is that they are difficult to machine, due to the hardness and abrasive nature of the reinforcing particles [2]. The particles used in the MMCs are harder than most of the cutting tool materials. Most of the researchers reported diamond is the most preferred tool material for machining MMCs [3-8]. Most of the research on machining MMCs is concentrated mainly on the study of cutting tool wear and wear mechanism [9,10]. Heat and coworkers [4,5,8] investigated the performance of polycrystalline diamond in machining MMCs which containing aluminum oxide fiber reinforcement. They compared the tool life of cemented carbide with PCD and concluded that sub-surface damage is greater with cemented carbide than that of PCD tools. Lane [3] studied the performance of different PCD tools grain size. He reported that, PCD tools with a grain size of 25µm are better withstand of abrasion wear than tools with grain size 10 µm. He also reported that further increases in the grain size do not have any influence on the tool life but it cause significant deterioration in the surface roughness. The works carried out by Andrews et al [11] characterize the wear mechanisms of PCD and CVD diamond tools in the machining MMCs. The conclusions can be applied to the design of better diamond tools and optimization of machining process. In the view of above machining problems, the main objective of the present work is to investigate the influence of cutting parameters on surface finish and power consumption. The results are analyzed to find the best machining parameter. Now by setting this parameter and tool flank wear was studied for time duration of 60 minutes and also to study the tool wear pattern.
2. Experimental Procedure
Fabricated cylindrical bars having 10% and 20% of SiC particles on matrix of Al 356, using stir casting method of diameter 50 mm and 175 mm long are turned on self centered three jaw chuck, medium duty lathe of spindle power 2 KW. Fig -1 shows the microstructure of 10% and 20% SiC particles reinforced workpiece. Table -1 shows the chemical composition of the work piece for experimentation. Table -2 shows the physical and mechanical properties of Al-SiC10p-MMC.Parameters such as power consumed by main spindle was measured using digital wattmeter (make-Nippon Electrical Inst.Co, Model 96x96–dw 34 Sr.No:070521485 CTR 5A/415 V AC F.S 4 KW). The machined surface was measured at three different positions and the average surface roughness (Ra) value was taken using a Mitutoyo surf test (Make-Japan –Model SJ-301) measuring instrument with the cutoff length 2.5 mm. According to Taguchi method, three machining parameters are considered as controlling factors (cutting speed, feed rate and depth of cut) and each parameter has three levels. Table -3 shows the cutting parameters.
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Al 356 reinforced with 10% SiC Al 356 reinforced with 20% SiC
|Cutting Speed |75,120, and 180 m/min |
|Feed Rate |0.1,0.2, and 0.32 mm/rev |
|Depth of Cut |0.5, 0.75 and 1.0 mm |
|Tool holder |PCLNR 25*25 M 12 |
|Tool Insert |CNMA 120408 (1600 Grade) |
3. Power Consumed
Fig 2, 3 shows the plot between cutting speed and power consumed for depth of cut 0.5 mm and 1.0mm. It was observed that power consumed decreased as cutting speed increased for all combinations of machining conditions for both the work pieces. Power consumed is more in machining the work piece having more reinforcement particles (20p) at lower cutting speed and at the higher cutting speed. It was observed that more power is required to pull the particles rather than cutting it [18]. Power was more generally with the reinforcing particles are more. At higher cutting speeds removal of hard particles from aluminium matrix becomes easier [5] . [pic]
Fig 2 Cutting speed Versus Power consumed (Depth of cut 0.5 mm)
Fig 3.Cutting speed Versus Power consumed (DOC=1.0mm)
4. Surface Roughness
Fig4.Cutting speed Versus Surface Roughness (DOC=0.5mm)
The turning operation was performed at feed rates 0.1, 0.2 and 0.32 mm/rev with depth of cut 0.5, 0.75 and 1.0 mm.The influence of surface finish on cutting speed is represented in fig 4 and 5. The figures show the relation ship pertaining to depth of cut 0.5 mm and 1.0 mm respectively for machining the samples. General trend of the graphs show that surface roughness value Ra decreasing as the cutting speed increases. Similar trend exist for depth of cut.
5. Tool Wear:
From the above observations best machining parameter was cutting speed 180 m/min, feed rate 0. 1mm/rev and depth of cut 0.5 mm. Now setting this cutting condition as a constant parameter and machined the samples having 10% and 20% SiC particles for a time duration of 60 minutes and the tool flank study was carried out. Tool was monitored for normal types of wear namely flank wear, crater wear and nose wear using a tool maker’s microscope. Tool flank wear was caused by abrasive nature of the hard particles present in the work piece. At low cutting speed worn flank encourages the adhesion of work piece material on the tool insert and formed Built-Up-Edge (BUE)[1]
Tool flank wear on PCD insert after machining Al-SiC (10p) & Al-SiC (20p)
Fig -6 shows the plot between tool flank wear and time duration. From the plot it was understood that, the tool flank wear of PCD machining composite having less percentage by weight of SiC particles having uniform increase in the wear land as compared to composite having more percentage weight of SiC particles. For the first 15 minute duration tool wear on machining both the pieces having constant increase in tool wear land. After that there was sudden increase in the wear land of PCD insert machining 20% SiC particles. This was clearly understood that weight percentage of SiC particles on composites accelerated the tool wear [19].
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Fig 6 Tool wear versus time duration
6. Conclusions 1. Power consumed is less at higher cutting speeds because of less friction between tool and workpiece interface 2. Volume fraction of Silicon carbide particles influencing tool wear 3. Primary wear mechanism is believed to be abrasion between reinforcing particles and cutting tool material 4. Tool wear is more in Al-SiC (20p) under the selected cutting condition 5. Surface finish improves at higher cutting speeds
7.References
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G.lane,The effect of different reinforcement on PCD tool life for aluminium composites, in: Proceedings of the Machining of Composites Materials Symposium, ASM Materials Week, Chicago, IL, 1992,pp3-15.
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Muthukrishnan N., Paulo Davim J 2009., Optimization of machining parameters of Al-SiC –MMC with ANOVA and ANN analysis. J. Mater. Process Techno. Vol,209. Pp 225-232,
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Tool flank Wear
Tool flank Wear
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Fig5.Cutting speed Versus Surface Roughness(DOC=1.0) mm)
