Cooling Down Process Effects on the Mechanical and Crystalline Properties of PA12 Parts Produced by Selective Laser Sintering

Selective laser sintering is one of the most popular additive manufacturing techniques used in recent years, due to its capability to build complicated geometries without the support structure. Thermal history plays a major role in the mechanical properties of the final product. In this research, the effects of different cooling down processes on mechanical properties of PA12 parts produced by selective laser sintering have been investigated. For this purpose, temperature changes of different points inside the powder bed during the built and cool down process have been monitored and recorded. Crystallization kinetics for the produced parts has been investigated by the non-isothermal crystallization model to help the interpreting of the results. Differential scanning calorimetry and X-ray powder diffraction (XRD) analysis were performed to find the degree of crystallinity and its possible correlation with mechanical properties. The results indicated that the parts cooled with the lower cooling rate showed 5% higher tensile strength and 10% more crystalline structure fraction comparing with the other two cool down methods. The results of crystallization kinetics for the produced parts by non-isothermal crystallization model showed that a lower cooling down rate led to slower crystallization in the component. The degree of crystallinity of the slow cooling down parts was about 10 percent more than the other samples. Based on the XRD results, the crystalline structure of the parts in all cooling down processes was the same (γ form crystal).