Effect of tool nose radius and tool wear on residual stresses distribution while turning in situ TiB₂/7050 Al metal matrix composites

In situ TiB₂/7050 Al matrix composite is a new kind of particle reinforced metal matrix composite. With in situ synthesis method, a better adhesion at interfaces is achieved and hence improves mechanical properties. However, due to the presence of hard TiB₂ ceramic particles, the tool wear problem is severer while machining TiB₂/7050 Al composites compared with traditional metallic alloy. In order to have a deeper understanding of the residuals stress distribution during machining metal matrix composites, this paper investigates the effect of tool nose radius and tool wear on the residual stress distribution during turning TiB₂/7050 Al composites. Four CBN tools with different tool nose radius (0.4, 0.6, 0.8, and 1.0 mm) are used. The cutting force and residual stress distribution beneath the machined surface have been analyzed when the CBN tools are new or worn (0.26 mm VB). The results show that the residual compressive stress distribution is always obtained on the machined surface and subsurface no matter the tools are new or worn. The larger tool nose radius causes the increase of cutting force, lower surface residual compressive stress, and deeper residual stress penetration layer. As the tool wear, the location of maximum residual compressive stress transfers from the machined surface to the deeper subsurface. Compared with the tool nose radius, the tool wear has more significant influence on the cutting force and residual stress distribution.