On the machinability of directed energy deposited Ti6Al4V

Current class Directed Energy Deposition (DED) techniques used for component manufacture and repair have inherently poor geometrical tolerance. Hence, there remains a requirement to apply conventional machining strategies post build in order to achieve finished components. In contrast to wrought materials, parts produced this way have markedly different localised material properties. This in turn results in non-uniform machinability within these. The present work investigates the effect of traditional machining approaches on the processability and resultant surface integrity of Ti6Al4 V produced by DED. Here, heat treatments are applied post DED in order to homogenise the microstructure and in turn improve the overall machinability of the material. Fundamental metallurgical analysis reveals grain coarsening which is consistent with standard heat treatments used for wrought Ti6Al4 V. Investigation of the stress condition of specimens machined from the ‘as-built’ condition and the heat treated condition show a 22% increase in compressive residual surface stress, a reduction in cutting forces of 40% in the beta condition and 24% in the alpha condition at a low machining speed of 50m/min. Furthermore, heat treatment and machining strategies are proposed which demonstrate performance improvements over standard machining techniques in the ‘as-built’ condition

An Evaluation of Tool-Chip Contact Phenomena and Tool Wear in High Speed Machining

Metal cutting still accounts for a high percentage of available manufacturing techniques. For this process, high speed machining (HSM) is now recognised as a key technology of particular relevance to the mould and die and aerospace industries. In HSM the material deformation process takes place in an narrow region and in an environment that is associated with highly inhomogeneous plastic flow, complex contact conditions, extreme temperatures and pressures. Although research has focused largely on the mechanics of the metal cutting process, contact phenomena and friction conditions at the tool-chip interface remains challenging. A sound understanding of the tool-chip contact phenomena in metal cutting is important for the finite element simulation of machining processes as well as for the development of new tool coatings. This paper contributes towards a fundamental understanding of the tool-chip contact phenomena in conventional and high speed dry machining using uncoated WC-TiC-Co cutting tools. The results of extensive machining tests supported by use of a scanning electron microscopy, followed by chemical analysis by energy-dispersive spectrometry on the contact area are reported. The tool-chip contact phenomenon was quantified, and metallic adhesion (seizure) was elucidated.</p