Advanced Process Control for Selective Laser Sintering

Since its inception in 1986 Selective Laser Sintering (SLS) has been a predominant force within Additive Manufacturing (AM) sector, however there are several issues that have limited adoption and growth. The work presented in this thesis aims to address three challenges that the SLS process faces over the pre-processing and machine control phases; inefficiency of the pre-processing software leading to lengthy wait times for machine operators, expensive and wasteful calibration process for field distortion and dynamic laser scanning parameters and lastly the inadequate aspects of the produced parts including tensile strength and geometric accuracy while scanning at extremely high speeds. An appropriate software and control strategy for SLS was identified and a novel pre-processing algorithm, that converted a 3D STL model into machine compatible toolpath information that prioritised efficiency was presented. Features of the generated toolpath promoted beneficial material properties, including perimeter offset to maintain geometric accuracy, a rotated scan path to ensure high tensile strength and Identification of upward and downward facing surfaces for improved surface texture. A novel calibration method for field correction and finding the optimum dynamic scanning parameters using laser reactive paper instead of PA12 which is considerably more expensive. Lastly a software package capable of controlling the laser scanner system while interfacing with a SinterStation2000 basic control system to produce SLS parts, the pre-processing and control software allowed to produce high-quality parts up to 15,000mms-1 scan speed. The wider implication of this research is improvement in the control strategies of SLS, resulting in faster pre-processing software, less costly calibration procedure and higher quality parts with respect to geometric accuracy and tensile strength at high efficiencies, that can be applied to both new machines and upgrades on existing machines and positively impact SLS machine manufactures and the people who utilise them