Workpiece surface quality when ultra-precision turning of SiCp/Al composites

Ultra-precision turning tests on SiCp/2024Al and SiCp/ZL101A composites were carried out to investigate the surface quality using single point diamond tools (SPDT) and polycrystalline diamond (PCD) cutters. Examined by SEM and AFM, the machined surfaces took on many defects such as pits, voids, microcracks, grooves, protuberances, matrix tearing and so on. It was found that cutting parameters, tool material and geometries, particle reinforcement' size and distribution, reinforcement' volume fraction and cooling conditions all had a significant effect on the surface integrity when ultra-precision turning this particular class of materials. And most of these defects were formed during the course of SiC particles being removed. The results showed that surface quality debased with increasing feed rate or using of high volume fraction materials. Dry cutting would deteriorate the surface finish. It was also pointed out that SPDT outperformed PCD tools although they produced the same surface roughness R-a. A lower surface roughness value can be produced when a positive tool cutting edge inclination, zero rake angle or bigger flank angle was selected. Microhardness measuring showed that the deformation layer was extended to 8-16 mu m below the machined surface. It was suggested that the surface finish was much better when the SiC particles were removed by pressed into or cut through mechanisms. (C) 2007 Elsevier B.V. All rights reserved.