Investigation into crystallinity and degree of particle melt in selective laser sintering

Selective Laser Sintering (SLS) is a manufacturing process which has emerged from numerous other technologies as the leading process considered viable for Rapid Manufacturing. SLS of polymers has found use in a wide range of industries ranging from aerospace to medicine. The ability to easily manufacture previously difficult or impossible to produce parts, without tooling, has proved invaluable. This industry backed manufacturing engineering PhD investigation examined material properties of Nylon-12 parts produced by the SLS process. Crystallinity relates to and determines mechanical properties in traditionally processed polymers. The nature of crystallinity in SLS processed Nylon-12 has been examined in this study and shown to be fundamentally different to that of traditionally processed polymers. Rather than depending primarily upon crystallisation factors such as cooling rate, it was shown to depend on the degree of particle melt (DPM). DPM was shown to be quantifiable by DSC measurements (by the degree of crystallinity and Core Peak Height) and distinct relationships between the quantified DPM and mechanical properties were found. Additionally, this study showed for the first time that parts remain above the crystallisation onset temperature even after build completion. This work has expanded the knowledge base of SLS by shedding light on critical aspects of the process. The ability to quantify the degree to which particles melt (DPM) provides a new level of understanding into the causes of changes in mechanical properties with changes in process parameters. This new understanding can lead to improved process modelling and could aid in the development of new processes and materials. DPM could be implemented into new quality control methods and the knowledge of post build crystallisation shows that post build cool down is an aspect of the build process that requires control for improved consistency of properties.