Author Topic: An experimental investigation on the machinability of powder formed silicon carb  (Read 1673 times)

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Author : Sujit Das, R. Behera,G. Majumdar,B. Oraon,G. Sutradhar
International Journal of Scientific & Engineering Research Volume 2, Issue 6, June-2011
ISSN 2229-5518
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Abstract-The paper attempts to study the machinability issues of aluminium-silicon carbide (Al-SiC) metal matrix composites (MMC) in turning using HSS cutting tool. SiCp-reinforced metal matrix composites (MMCs) containing SiC particles (5wt%-20wt %) of 400mesh size were prepared by powder metallurgy (P/M) route  and used as work material for turning. Experiments were conducted at various cutting speeds and depth of cuts at constant feed rate and parameters, such as cutting forces and surface roughness were measured. It was found that higher weight percentage of SiCp reinforcement produced a higher surface roughness and needs high cutting forces during machining operation of MMCs. It was also observed that surface roughness and the cutting forces are also depending upon the depth of cut and the cutting speed at constant feed rate. This paper present a reliable set of parameters as the result of an experimental investigation that demonstrate versatility, and numerous and diverse range based on experience and technology during the machining of aluminium-reinforced silicon carbide metal matrix composite (Al-SiCp MMC) which will provide valuable guidelines to the manufacturing engineers.
Keywords- Metal matrix composites, Machining, Surface roughness, cutting forces Machining, Depth of cut, Cutting speed.

Composite materials are a result of the continuous attempts to develop new engineering materials with low weight to strength ratios and improved properties. Composite materials are important engineering materials due to their outstanding mechanical properties. Metal matrix composite (MMC) materials are one of the widely known composites because of their superior properties such as high strength, hardness, lighter weight, stiffness, wear and corrosion resistances. Since 1970s, MMCs have successfully applied in the aeronautic and aerospace industries [1] and nowadays their use is gaining importance. As these composites contain very high hardness strengthening particles, the cutting tool tends to wear severely resulting in difficulties in machining [2]. Due to their superior strength and stiffness than those of conventional materials.MMCs have good potential for application in the automotive and aerospace industries [3-5]. Aluminium reinforced with SiC particles is one of the best materials to substitute the conventional structural alloys, which has more significance in the areas of aerospace and automotive engineering components and other diverse industries [6-9]. Powder forging is particularly attractive because it blends the cost and material-saving advantages compared to the conventional castings and forgings through better dimension and weight control. Powder forged parts can even outperform parts machined from a forged blank, probably as a consequence of fully dense, absolutely uniform and very fine grained microstructure. Machinability of metal matrix composites (MMCs) has received considerable attention because of the high tool wear associated with machining. Although efforts have made to produce MMCs by casting, or hot forging, the resulted near-net-shape products still have to machine into the designed shape, and dimension. MMCs reinforced with silicon carbide particles (SiCp), are notorious for high tool wear due to the inherent abrasiveness of the hard SiC particles. From some early conventional turning tests on Al-SiCp MMCs, it has found that the tool wear is excessive and surface finish is very poor while carbide tip tools are used for machining. The hard SiC particles of Al-SiCp MMC, which intermittently come into contact to the hard surface, are act as small cutting edges like those of a grinding wheel on the cutting tool edge which in due course is worn out by abrasion and resulting in the formation of poor surface finish during turning [10]. The processing parameters affecting machinability of a material are the values of cutting speed according to selected set of material properties of work piece and machining parameters. In the investigation of machinability, the cutting speed, feed rate and the cutting depth are important parameters. El-Gallab et al. has emphasized on the surface roughness in their study on the machinability of the 20% of SiCp reinforced Al-MMC. By performing dry turning tests with different cutting parameters, they have investigated the effect of processing parameters on surface roughness. They have found that large chip depths and high cutting speeds reduce the surface roughness. Bergman et al. investigated the machinability of Al-MMC by cutting tools. For this purpose, they used HSS and coated–uncoated hard metal cutting tools (WC) [11-13]. In addition, for many components, the production of good surface finish is essential Cutting speed is the most significant variable affecting tool life, while feed rate and depth of cut are less important. This leads to the softening of the metallic matrix enabling easier removal of the embedded SiC particle in the work piece [14-18].

2. Planning for experimentation:
2.1. Production of metal matrix composite:
Air atomized aluminum powder having an average particle of 400 mesh and SiC particulates with an average size of 400mesh are mixed corresponding to Al–5% SiCp, Al–10% SiCp, Al–15%SiCp and Al–20% SiCp were blended on a pot mill (diameter 40 mm, height 35 mm), at a constant speed of 1500 rpm for 1h to obtain a homogeneous powder blend.. Blending is one of the crucial processes in P/M where the metallic powders have mixed with the ceramic reinforced particles and the binder (Zinc Stearate). Several parameters such as particle size, blending speed and duration should be taken into consideration to ensure the SiCp particles distributing homogeneously in the matrix powders. The powder blending parameters are listed in Table 1. A mixture of the particles) has poured into a cylindrical die with 110 mm. high 25 mm. inner diameter and 75 mm outer diameter.

After pouring, the Green compacts of the powder blend were prepared on a hydraulic press (Manual Type, Capacity 8.0 KN. Ram stroke 300 mm.).The compacting pressure applied was2.1 KN, which has maintained for 5min to obtain green compacts for all composition of SiCp composites. The various steps involved in this experiment for manufacturing of P/M components has shown in Fig.1.The green compacts are then subsequently baked at
300˚C and followed by sintering in a induction type floor stand tube vacuum furnace . Fig.2,3,4 and 5 show the metallic die-and punch ,green compact , induction type floor stand vacuum furnace and sintered compact accordingly. To avoid the oxidation of Al alloy powders at high temperature and to abbreviate the preparation procedures, the degassing and sintering procedures of the green compacts were incorporated together. The stepped heating procedures of the degassing and sintering have introduced into the experiment. The sintering parameters have given in the Table2.

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