Investigation of the milling of Ti6Al4V alloy manufactured by selective laser melt under micro conditions

In this doctoral thesis, the micro-millability of commercial Ti6Al4V (Ti64) alloy, which is frequently used in the aerospace, defense industry and healthcare industry, and the micro-millability of Ti64 alloy, which is additively manufactured by selective laser melting (SLM) method using Ti64 alloy powders, were experimentally compared. For this purpose, two Ti64 alloy test materials with different manufacturing methods were compared mechanically and metallographically by performing microstructure examinations along with tensile and hardness tests. Both test materials were subjected to micro milling under the same selected cutting conditions with a TiAlN coated micro milling tool with two cutting edges of 502 µm diameter. For both test materials, the change in cutting forces, surface roughness, burr width and tool wear during micro milling with different feed rate, cutting speed and depth of cut were measured. According to the experimental results, it was determined that low cutting speeds and high depths of cut caused an increase in cutting forces for both test materials. Additionally, in micro milling of both test materials, it has been determined that the minimum chip thickness can be achieved with a feed rate fz: 1 µm/tooth in order to avoid the scraping of the tool, which causes dramatic cutting forces. It was concluded that high cutting forces accelerated abrasive wear in the micro milling tool and increased the burr width in the machined channel. Increasing the machining length caused both axial and circumferential wear on the tool and a sudden change in the edge radius. It was concluded that especially the change in edge radius negatively affects the surface roughness. Additionally, it has been observed that the burr width on the machined channel edges varies depending on the material and cutting parameters. In this context, the lower hardness and strength of the commercial Ti64 alloy increases the burr width in the machined channel, and a tendency to smear the tool has been observed, and wider burrs have been observed in the channel processed by scraping with a feed rate smaller than fz:1 µm/tooth.