Laser Sintering is an Additive Manufacturing technology that uses digital files to construct 3-dimensional parts by depositing and consolidating layers of powdered material. Application of the technology for metal and ceramic powders is common but the focus of this work was on polymer laser sintering. A significant drawback for polymer laser sintering is the limited selection of materials currently available for use compared with more conventional processes such as injection moulding. This constrains the usefulness of the technology for designers and engineers. A primary reason for this is a lack of detailed understanding of the development process for new materials for laser sintering. This PhD investigation examines some of the key attributes and requirements needed for successfully implementing new polymer-based laser sintering materials.
A strategic method for characterizing and identifying new polymer materials was created utilizing thermal measurements, practical and analytical methods to quantify sintering rate, and degradation studies. Validation of this work occurred through the successful integration of a new laser sintering material at industrial project partner Burton Snowboards. Thermal degradation as a result of the laser sintering process was studied in detail and resulted in the creation of a proposed new parameter: Stable Sintering Region (SSR). The term acknowledges and defines the region above the melting point that is the minimum requirement for sintering to occur and an upper limit beyond which polymer deterioration impedes on mechanical properties. A quantitative approach to define the SSR was developed and explored with three different laser sintering materials, two of which were flexible elastomers. The ability to specifically interpret laser sintering process parameters from thermal degradation characterization was created and used to explore the effects of high energy input on tensile properties and molecular weight. The results of these tests showed the potential to identify an Optimum Sintering Range based on maximizing mechanical properties through the control of energy input and molecular weight.
This thesis makes a significant contribution to the knowledge and understanding of polymer laser sintering, especially in the context of materials development. Novel concepts such as the Stable Sintering Region were developed using a theoretical approach and practical measurements and were also thoroughly explored for verification. Additionally, a new method to use a powder characterization technique to predict the actual machine parameters of a material in the laser sintering process was quantified. This has several implications for testing new materials for laser sintering and efficiently identifying appropriate processing conditions.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.