Sustainability and tool wear of titanium alloy thread cutting in dry and cryogenic conditions

Anna Zawada-Tomkiewicz,Filip Szafraniec,Dariusz Tomkiewicz,Łukasz Żurawski

doi:10.1007/s00170-021-07034-1

Anna Zawada-Tomkiewicz, Filip Szafraniec + Show 2 more

Open Access

https://doi.org/10.1007/s00170-021-07034-1

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Abstract

The article is devoted to the study of the effect of cryogenic cooling on the tool wear in thread turning tests. The tool wear and its influence on the thread accuracy were investigated. Two different grades of titanium alloys were used for comparative purposes. The excellent performance characteristics of titanium alloys pose machining problems, causing high unit forces at the edge of the tool leading to chipping and premature tool failure. In turn, the low thermal conductivity of pure titanium affects the heat distribution in the cutting zone. The heat is not absorbed by the material being machined but accumulates in the tool, causing an increase in diffusion and chemical wear. The results of cutting tests using liquid nitrogen showed lower values of wear on the major and minor tool flank. The edge reduction of the tool was also significantly less during cryogenic machining. The analysis of the formation of wear marks and the blade wear mechanisms was carried out for the tool rake face. The tests were carried out using the SEM method and confirmed by EDS analyses. In order to compare the course of tool wear over time, a mathematical model was developed, which results from the course of phenomena during cutting. It consists of two complementary equations. The first equation is characteristic for the first cutting phase and results from the loads imposed on the blade and aims at thermodynamic equilibrium. It is a period of stable tool operation and constant wear intensity. The second equation concerns crossing the equilibrium point followed by the process of accumulation of elementary wear phenomena. These phenomena accumulate until the blade is completely worn-out. The use of blade wear development models to determine the expected blade life allowed to confirm the beneficial effect of cryogenic cooling on the course of the blade wear process when cutting threads for two different titanium alloys.

Highlights

Materials for medical uses, including titanium alloys, require a manufacturing process with controlled properties and precision for both internal and external threads
The machinability of titanium alloys is strongly dependent on the cutting parameters, which in turn determine the amount of heat released and the temperature in the cutting zone
When examining titanium alloys in thread turning tests at room temperature and cryogenic conditions, the tool failure mechanism was recognized as adhesion-diffusion and all tools were subjected to this failure mode

Summary

Introduction

Materials for medical uses, including titanium alloys, require a manufacturing process with controlled properties and precision for both internal and external threads. The high corrosion resistance and high temperatures of titanium alloys during operation result in accelerated tool wear, vibration, and low material removal rate (MMR) during their processing. The machinability of titanium alloys is strongly dependent on the cutting parameters, which in turn determine the amount of heat released and the temperature in the cutting zone. As stated in [2], the heat generated during the machining of Ti6Al-4V alloy has been identified as the cause of increased tool wear and surface finish degradation, which is characterized by burr formation. The machined surface during cutting is thermally softened and, an unfavorable, brittle alpha phase is formed. Even under conditions where phase change was not observed, the

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