Theoretical and experimental investigations of magnetic field-assisted ultra-precision machining of titanium alloys

Abstract

Titanium alloys can be used in advanced engineering and biomedical applications. Their outstanding overall properties and high corrosion resistance make them indispensable structural materials for many industrial parts. They are biological implant materials that have been widely used in medicine. However, titanium alloys are poor in machinability in ultra-precision machining (UPM), their poor thermal conductivity results in high cutting temperature, which causes heat to accumulate in the cutting zone. Excessive heat causes most machining challenges because it accelerates tool wear and degrades the cutting tool edge, causing low surface quality. A magnetic field-assisted ultra-precision machining (MFUPM) system was developed in this study to boost the machinability of Ti6Al4V alloy concerning enhanced surface roughness and diamond tool life. A magnetic field-assisted ultra-precision machining (MFUPM) system was developed for creating the magnetic field. A setup of a magnetic field system with an adjustable intensity has been used to generate a uniform magnetic field in accordance with Maxwell's magnetic-field law. The selection of magnetic field intensity and the movable length for positioning magnets in the magnetic system is based on preliminary experimental results and a theoretical basis, yielding the optimal magnetic effect in UPM. The magnetic field density as well as the distribution of magnetic flux in the cutting zone are critical factors for MFUPM. For thermal analysis of MFUPM, finite element modeling (FEM) is built following the Johnson-Cook (JC) constitutive model and geometrical model, taking flow stress, strain, strain rate, and temperature into account, with the Johnson-Cook constitutive model serving as a link between material parameters, mechanical loading, effective stress, and heat at the tool/workpiece interface. The JC damage model was used, and the failure evolution-based fracture criteria were applied where the failure energy was taken into account. The geometric model includes tool settings, workpiece geometry, and machining conditions. An external magnetic field has been shown to improve Ti-6Al-4 V thermal conductivity during UPM. The experimental results in this study demonstrated that the magnetic field improves the UPM performance of the Ti-6Al-4V alloy, and the simulated and experimental outcomes were consistent. These findings revealed enhanced surface quality and increased diamond tool life. This thesis contributed to resolving the machining difficulties faced by UPM, which aims to uplift the precise level of products, especially for hard-to-cut materials such as Ti-6Al-4V. This study concluded that the machining of Ti-6Al-4 V alloy has been improved with the aid of the magnetic field. The relevant machining factors of tool wear, chip formation, and surface roughness of the machined work material were investigated, resulting in increased tool life and improved machined surface quality for diamond machining. In addition, MFUPM produced the lowest value for surface roughness. This work contributes significantly to supporting the MFUPM by FEM and producing high-quality machined Ti alloys in UPM for related research activities.