Machinability of Single-phase Materials : Surface integrity and tool wear analysis
Abstract: The quality and performance of products are particularly important in sectors such as research facilities and in the nuclear, military and space industries. These sectors make use of high-performance materials that are uncommon in other contexts and therefore place high requirements on personnel, machines and tools. While tool manufacturers have readily available tool selection guides and cutting data recommendations for a wide range of materials, relying on many years of research, little information is available when selecting tools and cutting parameters for machining less common or exotic materials. Consequently, only a few highly specialized companies manufacture components using such materials. The aim of this dissertation is to create a knowledge base on machining single-phase materials, specifically oxygen-free copper, niobium, and tungsten. It builds on an understanding of the difficulties in achieving the required surface quality and suggests useful tooling solutions and cutting parameters, as exemplified for a longitudinal turning machining operation. Different aspects of surface integrity such as subsurface deformation, surface defects and damage are discussed. Such analysis relied on extraction, polishing, and examination of the machined samples with nanoindentation and SEM microscopy. Screening tests of several different tooling solutions for niobium and tungsten were also performed to evaluate machining performance and tool wear under different cutting conditions. Tool wear mechanisms were evaluated with SEM and TEM microscopy and further compared using the diffusion couple sample technique. The results of the research presented in this dissertation highlight the difficulties in achieving the targeted surface quality and selecting tooling solutions for these single-phase materials, while also highlighting potential successful pathways for the machining processes. These results can be used to further evaluate tool selection or to develop new tooling solutions to improve the surface quality of the finished product at a reasonable performance and therefore cost.
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