As an emerging hole-machining methodology, helical milling process has become increasingly popular in aeromaterials manufacturing research, especially in areas of aircraft structural parts, dies, and molds manufacturing. Helical milling process is highly demanding due to its complex tool geometry and the progressive material failure on the workpiece. This paper outlines the development of a 3D finite element model for helical milling hole of titanium alloy Ti-6Al-4V using commercial FE code ABAQUS/Explicit. The proposed model simulates the helical milling hole process by taking into account the damage initiation and evolution in the workpiece material. A contact model at the interface between end-mill bit and workpiece has been established and the process parameters specified. Furthermore, a simulation procedure is proposed to simulate different cutting processes with the same failure parameters. With this finite element model, a series of FEAs for machined titanium alloy have been carried out and results compared with laboratory experimental data. The effects of machining parameters on helical milling have been elucidated and the capability and advantage of FE simulation on helical milling process have been well presented.

Abstract:With a significant growth in use of titanium alloys in aviation manufacturing industry, the key challenge of making high quality holes in aircraft assembly process needs to be addressed. In this work, case studies deploying traditional drilling and helical milling technologies are carried out to investigate the tool life and hole surface integrity for hole-making of titanium alloy. Results show that , the helical milling process leads to much longer tool life, lower cutting force, generally lower hole surface roughness and higher hole subsurface microhardness. In addition, no plastically deformed layer or white layer have been observed in holes produced by helical milling. In contrast, a slightly softened region was always present on the drilled surface. The residual stress distributions within the hole surface, including compressive and tensile residual stress, have also been investigated in detail.