The influence of the crystallographic orientation when micro machining commercially pure titanium: a size effect

Abstract Micro machining processes are characterized by the influence of size effects like the influence of the workpiece micro structure on the process and ultimately on the process results. So far, the influence of grain orientation on the process results is state of the art and mostly investigated on single-crystal materials, but the influence of the grain orientation on the process and process results in micro machining of polycrystalline materials with a hexagonal close packed (hcp) crystal structure like commercially pure (cp)-titanium is, to the best knowledge of the authors, not completely understood. Within this research, the correlation between the grain orientation and the surface topography, process forces, and chip formation is researched by orthogonal cutting. This process offers the possibility of clearly linking the cutting behavior with the resulting surface and the influences of the size effect. The results show a clear correlation between the grain orientation and the topography height, the ripping out of material, and the resulting surface. A correlation between the grain orientation and the forces in the X-, Y-, and Z-directions could also be shown. The chip formation and thus the resulting chip thickness differs depending on the grain orientation. In addition, micro milling tests were conducted and influences on burr formation and process forces are shown. At low spindle speeds the burr width or the burr shape are a function of the grain orientation. At high spindle speeds this effect can no longer be observed. With the results of this research, it is possible to compensate the influence of the grain orientation on the process results and to enhance the efficiency and the resulting surface quality of micro machining processes.