Machining of directed energy deposited Ti6Al4V using adaptive control

Abstract

Additively manufactured (AM) components possess microstructures different from conventional forms in the same material and as a consequence, the mechanical properties and machinability of components produced using these technologies differ. Also, the microstructures from these processes are often anisotropic and as such different regions possess varying properties and hence varying response during post process machining. An adaptive control (AC) machining system for addressing this variation in microstructures during post process machining is developed here and its use demonstrated in this paper.The adaptive control system is used in milling and drilling trials for machining components manufactured by Directed Energy Deposition (DED). Surface roughness and residual stress analysis in the ‘as built’ state and after post process machining with the prevailing cutting forces are also presented here. Microstructures of the deposited material and the subsurface effects at the machined region due to the action of the cutting tool is also analysed.Milling trials are investigated from the standpoint of the use of adaptive machining for the removal of the outermost layer of DED produced Ti6Al4V and in the machining of bulk regions after preliminary machining of the undulating layer. Drilling experiments are carried out for investigating the effects of the machining process on the resulting surface condition, comparing the process with and without adaptive control. The effects of variation in cutting forces during drilling through the different material systems comprising of the DED region and the wrought substrate is also discussed. The effect of periodic changes in cutting forces during machining due to the variation in microstructure along the build direction is analysed and discussed. The use of adaptive control machining for post processing is shown to improve surface finish as it reduces the initiation and generation of chatter marks on the machined surface resulting from material anisotropicity.