FINITE ELEMENT MODELING OF THE ORTHOGONAL MACHINING OF PARTICLE REINFORCED ALUMINUM BASED METAL MATRIX COMPOSITES

Abstract

2D finite element models (FEM) are developed to simulate orth- ogonal machining of particle reinforced aluminum based metal matrix composites (MMC). The models predict cutting forces, chip morphology, temperatures and stresses distributions. The simulations were carried out by developing a fully coupled temperature displacement model. In contrast to the equivalent homogeneous material (EHM) methodology, a heterogeneous model is developed based on reinforcement particle size and volume fraction. This allows models to simulate the local effects such as tool-reinforcement particle interaction, reinforcement particle debonding. The interface between the reinforcement particles and the matrix is modeled by using two approaches; with and without cohesive zone elements. Similarly the chip separation is modeled with and without using a parting line. The effect of different methodologies on the model development, simulation runs and predicted results have been discussed. The results are compared with experimental data and it has been found that the utilization of cohesive zone modeling (CZM) with the parting line approach seems to be the best one for the modeling of MMC machining. homogeneity and abrasive nature of reinforcement particles. Mostly MMC are fabricated with near net shape processes but some machining and finishing cuts are indispensable for final dimensions and surface finishes. Cutting tools such as high speed steel, cast cobalt alloys, cemented carbides and cermets cannot be used for machining of MMC due to high wear rate. Diamond cutting tools are found to be the best option for machining of MMC and they are being utilized in the last ten years for both particles and fibers based MMC (Looney 1992, Schwartz 1997, Muthukrishnan 2008). Fiber reinforced composites are anisotropic as fibers are not equi- axes, whereas particulate reinforced composites are isotropic like conventional metals. The later provide higher ductility and their isotropic nature make them a better choice as compared to fiber reinforced composites. Machinability of particulate reinforced composites depend on many factors like particulate type, its orientation, tool material, tool geometry and cutting conditions like cutting speed, feed etc. Numerous studies exist in the literature to analyze machining of MMC using experiments and mostly related to measure performance variables like tool wear, surface roughness, sub surface damage, cutting forces, cutting temperatures and chip morphology (Davim 2011). It has been found that parameters related to structure of composite greatly affect the machinability. These include reinforcement material, reinforcement type, volume fraction of the particles, base metal properties and overall arrangement of constituent phases. Polycrystalline diamond inserts (PCD) are commonly employed for their machining (Weinert 1993, Quigley 1994). Use of other ceramics materials like cubic boron nitride (CBN), alumina and silicon nitride are also reported but did not have a major success. Effects of cutting parameters (speed, feed and depth of cut) on machinability of MMC is almost similar to that found in machining of conventional metals with some differences due to abrasive nature of particles. The reinforced particles tend to expelled out from the base metal and slide in front of the cutting tool edge. This results in plowing through the newly generated machined surface and groove marks on it (El-Gallab 1998) (Manna 2003).