Tool Wear, Surface Integrity and Dimensional Accuracy in Turning Al2124SiCp (45%wt) Metal Matrix Composite using CBN and PCD Tools

Abstract

The focus of this study is the turning of Al2124SiCp (45% wt) Metal Matrix Composite using PCD, CBN-coated and CBN-uncoated tools. The machinability of Al2124SiCp (45% wt) Metal Matrix Composite is evaluated by measurement of tool wear, surface finish and dimensional accuracy of the work-piece. Wear mechanisms and patterns of tools in turning of Al2124SiCp (45% wt) Metal Matrix Composite are discussed. The experimental setup involved turning Al2124SiCp (45% wt) 78.0 mm long and 31.8 mm diameter on a precision lathe at fixed feed rate, different depth of cut and cutting speed using PCD, CBN-coated and CBN-uncoated tools. The reinforcement of the matrix consists of SiC 5-8 μm in diameter. Experimental results reveal that abrasion and adhesion presented the most prevalent mode of wear among all the tools. Fracture was observed among CBN tools while chipping on PCD tools. Flank and crater wear were observed in all tools with flank wear more prevalent in both CBN-coated and CBN-uncoated. Wear among PCD tools was low as compared to CBN tools. Further analysis reveal that the outer layer of the CBN-coated tools wear off fast creating a good platform for adhesion of matrix material on to the tool. This further increases wear of the tool due to adhesive wear as the built-up edge breaks off from the tool. PCD tool presented better surface finish than CBN tools with CBN-coated performing better than CBN-uncoated. Due to high SiC content, discontinuous chips are formed which are also curled due to increase in temperature at cutting zone causing bimetallic effect on the chip. On dimensional accuracy it was observed that PCD tool produced lowest diameter error followed by CBN-uncoated and finally CBN-Coated. It is concluded that in machining Al2124SiCp (45% wt) Metal Matrix Composite PCD tools are the best followed by CBN-coated and lastly CBN-uncoated.