Wear Mechanisms Of Carbide Tools Research Articles

Chip/Tool Interaction during Dry Machining of the TA6V Alloy

During chip formation, material is subjected to high deformations and high strain rates which generate high pressures and temperatures. Cutting fluids have an important role but produce many constraints: cleaning of parts, environment quality degradation, cost increase, diseases as identified by the European Agency for Safety and Health at Work. Dry machining is one of the future challenges although its implementation remains delicate, in particular for TiAl6V alloy. This paper aims at correlating the contact conditions at the tool/chip interface with the tool wear to understand the wear mechanisms of carbide tools in dry machining. Numerical simulations, experimentally validated, allow pointing out that the temperature distribution at the tool/chip interface depends on chip type (continuous, serrated). For continuous chips, the temperature is fairly uniform and stationary throughout the interface. For segmented chips, a cold zone between two temperature peaks is observed and moves along the tool rake face during the formation of a chip segment. The evolution of the normal stress at the interface is similar for both types of chips at the beginning of the localization phenomenon. These pressure and temperature fields allow the titanium to diffuse into the tungsten carbide and form the mixed carbide (Ti, W)C, which is very sensitive to oxidation above 500°C. This could explain the attrition of the tool, due to the brittleness of the oxycarbides. Contact conditions and tool wear are finally correlated.

鋼切削時の超硬工具の摩耗機構

Turning test was performed by a carbide tool on several carbon steels having various carbon contents and the worn surface of the tool and its cross-section were surveyed by the electron probe X-ray micro-analyzer in order to estimate the wear mechanism of carbide tools. Relation among the tool wear, cutting temperature, thickness of the diffused layer and the hardness of work material was investigated through the experimental findings concerning the decrease of cobalt content on the tool surface, the diffusion of carbon, and the weakening of tool.It is found that the tool wear is caused mainly by the diffusion of carbon from the carbide constituents of the tool material into the work steel, which changes the structure of carbides and weakens the tool crystals.From both the experimental data and the theory, it is proved that the wear velocity of carbide tool is resticted by the diffusion velocity of carbon through the matrix of the tool. And the thickness of the diffused layer beneath the tool surface increases as the cutting temperature is raised such that the hardness of work material is decreased, and as the carbon content of the work material is decreased.