Development and Experimental Validation of a Hybrid Selective Laser Melting and CNC Milling System

Relatively low dimensional accuracy and poor surface quality have been the major drawbacks for selective laser melting (SLM). A hybrid SLM and computer numerical control (CNC) milling system that operates in an alternating manner may have the capability of improving the dimensional accuracy and surface quality to a comparable level to conventional CNC processes. However, very few studies have been conducted on the machine development and experimental applications of this hybrid process. In this study, we developed a hybrid SLM/CNC milling system based on the fundamental understanding of the hybrid process. Key technological challenges are analyzed including the mechanical design of the hybrid machine to solve the design contradictions in hybridizing the two processes, the adaption of laser scanning system to avoid structural interferences between SLM and CNC, and the process planning and data processing to coordinate SLM and CNC milling. Solutions are proposed to address these challenges. The hybrid system developed in this study was then validated with commonly used stainless steel 316 L. Nearly full dense 316 L parts with relative density >= 99 % were fabricated. Excellent tensile properties with yield strength >= 540 MPa, ultimate strength >= 650 MPa and elongation >= 44.5 % that are comparable to the conventional solely SLMed ones were obtained. Meanwhile, the dimensional accuracy and surface roughness were also significantly improved with this hybrid system. This systematic study further suggests that the hybrid SLM/CNC milling system can be an effective and promising tool for the manufacturing of high-quality metal parts.