Developing process capabilities for selective laser melting

Selective Laser Melting (SLM) is an Additive Manufacturing (AM) technique which is able to fabricate complex functional 3-Dimensional (3D) parts of high densities from the complete melting and fusion of powdered materials. SLM parts possess superior properties compared to parts produced by conventional manufacturing processes due to enhanced microstructure obtained from the rapid solidification process in SLM. However, the SLM process is difficult to control because of the mechanical properties of the parts fluctuate easily with different forming parameters. Furthermore, SLM exhibits complex physical and chemical processes and is accompanied with complicated heat and mass transfer that are not fully understood. This research aims to develop new and better SLM process capabilities to address the process control difficulties with a representative metallic alloy, M2 High Speed Steel (HSS). M2 HSS is a popular tool material valued for its excellent hardness, toughness and wear resistance and is also a material new to the SLM process. Hence, this research also paves the way to better understand and control the SLM process through M2 HSS as well as introducing it as a tool material for SLM. Firstly, the SLM process was modelled so as to study and understand the microstructure evolution in M2 HSS SLM parts through MATLAB programming and simulations. As a result, the resultant microstructure, in particular, the Heat Affected Zones (HAZs) were successfully characterised with a novel approach based on a proposed analytical solution developed from a double ellipsoidal density heat source. The simulated HAZs were validated where characterisation results were very close to the experimental results. This indicated that the HAZs in SLM parts could be desirably controlled with appropriate process parameters. In addition, cooling rates within the simulated theoretical HAZs were calculated to be in the range of 105 K/s.Doctor of Philosophy (MAE