PRIMARY AND SECONDARY PROCESSING OF METAL MATRIX COMPOSITES

Abstract

The growing steel prices have significantly affected the manufacturing expenditure in automobile and house hold industries, thus making a strong case for substituting steels with materials having light weight and high strength to weight ratio. The aluminium and its alloys have outstanding properties like light weight, wear and corrosion resistance that make them suitable in numerous industrial applications. These materials being comprehensively used in automobile and aerospace industries have nearly touched their limit of practicality. Therefore, substantial investigations in the area of materials science and engineering have been focused towards the growth of newfangled materials. Among the newfangled materials, Metal Matrix Composites (MMCs) has numerous industrial as well as defense related applications. The superior properties of MMCs over the monolithic materials such as, high specific strength, improved wear and corrosion resistance, are source of attraction for industries and researchers. Solid, liquid and vapor state processing methods are used for the production of MMCs. Stir casting route has been prominently used as a production process technique but it faces technical challenges as well. The main research challenge is to get a uniform distribution of the reinforcement in the matrix with minimum porosity. The poor wettability of the abrasive reinforcement with the molten matrix is the major problem in the stir casting route. It causes weak interfacial bonding and deterioration of the mechanical properties. The presence of hard abrasive particles as reinforcement limits the machinability of MMCs and consequently they have limited applications. Both conventional and - unconventional machining processes have been used for machining of MMCs. The factors that affect the machinability of MMCs are work material, percentage of reinforcement, tool iv material, tool profile and cutting parameters like cutting speed and feed rate. These parameters also affect the drilling behavior of MMCs in terms of thrust force, torque, chip formation, surface roughness, and associated problems like built-up edge (BUE) formation, tool wear, burr formation, out of roundness etc. Unconventional machining processes like electric discharge machining (EDM), powder mixed-EDM, wire-EDM, abrasive water jet machining have also been employed for machining of MMCs. However, their material removal rate is significantly less as compared to the conventional machining processes. Therefore, there is an imminent need to explore the processing techniques for 4. MMCs in order to produce net-shape or near-net-shape products to avoid the problems associated with the machining of MMCs. Selected machining processes; particularly drilling is still required for joining and assembly of MMC products. Therefore, there is a necessity to investigate the process of processing and machining of MMCs in order to produce industrial components of good quality at reasonable price. The present experimental investigation is divided into two main sections, primary processing and secondary processing of metal matrix composites. The primary processing comprises of development of the 'stir-squeeze-quench' setup for the production of nearnet- shape of MMC components. The distribution of the SiC particles in the metallic matrix affects the variations in physical, mechanical and tribological properties of the developed metal matrix composites. Uniform distribution of the SiC particles along with appropriate wetting of SiC particles with matrix causes enhanced physical and mechanical properties such as, high density or minimum porosity, increased tensile strength, hardness and wear resistance. The secondary processing deals with the machining aspects of the developed materials. Drilling behavior of metal matrix composites has been experimentally V investigated using the solid carbide drill point geometries of different profiles (twist, parabolic and Jo-drill) as well as modified drill point geometry. The drilling performance has been evaluated in terms of cutting forces, surface finish, tool wear, burr formation and chip formation during the hole making of MMCs at different cutting conditions. Modifications in the drill point geometry and drilling process have been attempted to improve the quality characteristics. Exhaustive experimentation has been carried out to explore the drilling behavior of the developed MMCs. The drilling experimentation has been divided into three Phases. IPhase I explore the drilling behavior of inter drill point geometry (cutting profile of geometry) along with machine tool parameters. It has been found that the drill point geometry plays a significant role for the output quality characteristics such as; thrust force, torque, surface roughness, burr formation and tool wear. Modified drill point geometry has been designed and developed for burr free drilling in MMCs in the Phase 11 of experimentation. The intra drill point geometry investigation of the modified drill point geometry has been carried out using response surface methodology (RSM). An experimental setup named Abrasive Assisted Drilling (AAD) has been designed and developed in Phase Ill of experimentation for improvement in surface roughness. A significant improvement in the surface roughness of the drilled hole wall surface has been observed using the AAD process. Some of the prominent objectives of the present experimental investigation have been under: To develop a setup for near-net-shape manufacturing of MMCs products by stir casting having modified features of squeezing action, bottom pouring and water/oil quenching. vi • To characterize the developed Al-SiC composite by optical micrographs, hardness and mechanical strength tests to ascertain the feasibility and reproducibility of the material. Experimental investigation using design of experiments for understanding the wear behavior of the fabricated MMCs to determine the wear rate. These results can be used to establish the wear characteristics of the developed MMCs. Experimental investigation using design of experiments for understanding the drilling behavior of Al-SiC using different drill point geometries. Quantification of quality characteristics like Thrust force (TF) Torque (TQ) Surface Roughness (SR) Tool wear and Burr formation. • To develop and validate predictive models for the various output responses with help of statistical methods. • To optimize drilling process parameters for drilling of Al-SiC composites. The intra-drill point geometry investigation will be carried out for the optimized drill point geometry. • To conceptualize, design, development and optimize a modified drilling process for enhancing the quality characteristics (surface roughness) during drilling on MMCs.