THE ROOT CAUSE OF NOSE AND FLANK WEAR AND THEIR BEHAVIOR IN TURNING TI-6AL-4V WITH CARBIDES AND PCD INSERTS

摘要

This paper addresses the root cause for flank and nose wear when machining Ti alloys. In machining ferrous metals, at least the cementite (Fe_3C) phase is present as the abrasive contributing to the flank wear. However, most titanium alloys possesses no significant hard phase, which questions the root cause for those wear. In this study, a Ti-6Al-4V bar was turned under various conditions with few grades of uncoated carbide and PCD-insert type tools. The cutting tools were retrieved sporadically after stopping the tuning process in order to examine the wear patterns and their evolution on the tools. The nose and flank wear patterns on the tool inserts were investigated with a confocal microscope. The microstructure of the bar was characterized using Orientation Image Microscope with Electron-Backscattered Diffraction Scan (EBDS). Two distinct types of damages were identified, (a) Micro-fracture at the cutting edge and (b) Scoring markings. Based on the microstructure and the tool wear patterns, this paper claims that both types of damages were caused primarily by the hard orientation of the alpha (a or Hexagonal Closed Packed) crystalline phases and secondarily by the adhesion layer detaching parts of the tool material from the nose and flank surfaces.