OPTIMAL PROCESS PARAMETERS FOR DIRECT METAL LASER SINTERING OF TI64 FOR MEDICAL IMPLANT PRODUCTION

Abstract

Direct Metal Laser Sintering (DMLS) is a layer-by-layer Additive Manufacturing (AM) process that creates physical metal parts from three-dimensional (3D) Computer Aided Design (CAD) data. For DMLS to be generally accepted by industry as a manufacturing technology, high mechanical integrity of final components needs to be demonstrated. Properties of manufactured components are directly affected by the quality of each individual laser sintered track of each consecutive layer. The purpose of this work is to study the geometrical characteristics of single tracks produced through DMLS and determine the optimal process parameters for three of the most influential process parameters in order to process Titanium-6Aluminium-4Vanadium(Ti-6Al-4V) powder namely: appropriate laser power, scanning speed and powder layer thickness. State of the art metal powder-based technology, the commercialisation process and current DMLS systems are presented. Properties and applications of titanium and its alloy in aerospace, marine and energy industry, consumer market and biomedical applications are described. Powder material characteristics were defined by scanning electron microscopy and the use of an optical granulomorphometer. The DMLS experiments were conducted on an EOSINT M270 machine. Geometrical characteristics of single tracks, their shape and stability varied significantly when process parameters changed. To estimate to what extent laser power and scanning speed have an influence on Ti-6Al-4V material fusion, several experiments were conducted on a Ti-6Al-4V substrate without powder. For 150-170 W laser power and 600-2000 mm/s scanning speed, different regimes of laser track were found: “keyhole” mode, “conductive” mode and “humping” mode. The empirical data were compared to a melt pool width and depth prediction simulation program in order to verify its predictive capability. This model is useful for estimating geometrical characteristics of single tracks in “conductive mode”. Single tracks of Ti-6Al-4V powder from TLS Technik GmbH were produced at 15, 30 and 45 μm powder layer thicknesses. More stable tracks were obtained at 15-30 μm layer thickness, 150-170 W laser power and scanning speeds between 1000 and 1200 mm/s where powder deposition imperfections, roughness of the substrate and even some variation in laser scanning speed did not result in large differences in geometry of the tracks. An analysis of each single track’s shape, width and height of tracks, melting depth into the substrate and track melted surface area permitted the estimation of some of the optimal process parameters.