The Genesis of Tool Wear in Machining

Abstract

This paper presents a series of experimental and theoretical efforts that we have made in unraveling the tool wear mechanisms under steady state conditions in machining for the last few decades. Two primary modes of steady state tool wear considered in this paper are flank and crater wear. We preface this paper by stating that flank wear is explained as abrasive wear due to the hard phases in a work material while crater wear is a combination of abrasive wear and generalized dissolution wear which encompasses both dissolution wear as well as diffusion wear. However, the flank wear was not a function of the abrasive cementite content when turning low alloy steels with pearlitic microstructures. The machined surfaces of these alloys are examined to confirm the phase transformation (ferrite to austenite), which diminishes the effect of cementite content. In particular, the cementite phase present in low alloy steels dissociates and diffuses into the transformed austenitic phase during machining. Dissolution wear is claimed to describe the behavior of crater wear at high cutting speeds. The original dissolution mechanism explains the crater wear in the machining of ferrous materials and nickel alloys at high cutting speeds, but the generalization of the dissolution wear is necessary for titanium alloys. In machining titanium alloys, the original dissolution mechanism did not show a good correlation with experimental results; generally the diffusivity of the slowest diffusing tool constituent in titanium limits the wear rate. The phase transformation from alpha (HCP) to beta (BCC) phases can also take place in machining titanium alloys, which drastically increases the crater wear due to the few orders of magnitude increase in diffusivity. The most puzzling issue is however the presence of the scoring marks even though no hard inclusion is typically present in titanium alloys. This is finally explained by the heterogeneity in the microstructure due to the anisotropic hardness of alpha (HCP) phase (the hardness in c-direction is 50% higher than the hardness in other directions) and the presence of lamellar microstructure (alternating layers of alpha and beta). The lamellar microstructure has not only the in-plane anisotropic hardness but also a greater hardness than other phases. Even though we cannot claim to fully understand the physics behind tool wear, our combined approaches have unveiled some elementary wear mechanisms.

Analysis of tool wear and surface roughness in high-speed milling process of aluminum alloy Al6061

“…In the theoretical modelling method, the tool wear and surface roughness were modeled by theoretical method depending on the physical, chemical, and geometrical phenomena such as friction, temperature, cutting, etc. [11,12]. This approach is often quite difficult to perform because too many factors that should be considered to add into the tool wear and surface roughness models [13,14].…”

“…This study was carried out to verify the change in surface roughness of the workpiece due to increasing tool wear [10]. The neural approach was conducted to investigate the effect of cutting condition of tool wear and surface roughness in turning process under minimum quantity lubrication (MQL) environment [11]. The response surface method was applied to analyze the effect of the technological parameters on the tool wear and surface roughness.…”

A Study on the Tool Wear in Milling Process of the Gleason Spiral Bevel Gear

“…In the first direction, the tool wear and other machining characteristics were modeled depending on the physical, chemical, and geometrical phenomena such as friction, temperature, cutting, Etc. [8,9]. This approach is quite difficult to perform because many factors that influence on the wear of tool and other output parameters.…”