The machining of titanium alloys with polycrystalline diamond tools

摘要

The excellent mechanical properties and unrivalled corrosion resistance of Titanium have led to the successful application of Titanium alloys in aerospace industry. However, the inherent properties of low thermal conductivity and high chemical reactivity of Titanium alloys cause poor machinability. They adversely affect tool life, cause premature tool failure, and eventually lead to extremely low machining efficiency. Recently, Polycrystalline diamond (PCD) tools have been successfully used in the turning of Titanium alloys. The significant hardness and the excellent thermal conductivity of PCD make it the most advantageous tool material for the machining of Titanium alloys, in particular Ti6Al4V. This research investigated the application of PCD tools in the end milling of Ti6Al4V by using customized cutting tools. The discharge characteristics of PCD was analysed; the mathematical relationship between cutting force and cutting parameters was developed; tool life, tool wear, and causes that lead to tool failure were discussed. A cutting temperature model was developed and validated to investigate the relationship between cutting temperature and machining parameters. To analyse tool wear and cutting temperatures, residual chemical components on the PCD tool were examined with X-ray diffraction method, while surface integrity of cutting tools was inspected based on the images taken by the scanning electrical microscope. Finite element analysis models were developed to simulate the initiation of cracks under different loading cycles. It was found that brittle chipping and fatigue were the two major modes of failure, and feed rate was the dominant factor that causes large cutting forces. Evidences of material diffusion and chemical reaction on PCD tools showed that some region of cutter suffered from higher than detected temperature. Based on SEM photos of serrated chips, serration frequency was investigated. Results from chip morphology scanning illustrated that serration frequency changed on each single chip.