Research on the Control of Mechanical Properties of Selective Laser Sintering PA12 Based on Heat Treatment(Invited)

Additive manufacturing plays an indispensable role in the field of complex structure forming, which enables the precise manufacturing of complex products directly through digital models. Among them, Selective Laser Sintering (SLS) technology, as an advanced technology for powder-based additive manufacturing, PA12 is an ideal material that can be used in SLS technology. However, during the forming process, the particles are connected by sinter necks, which often results in microporous parts and high surface roughness, which prevents the intrinsic properties of the material from being achieved. In order to improve the mechanical properties of SLS molded parts, three methods are usually applied: first, the process parameters are optimized, which is a relatively simple method, but usually the material properties are not greatly improved; the second is to enhance the performance of the part by introducing reinforcement, which can indeed bring about the improvement of the performance of the molded parts, but it is usually difficult to form, and at the same time will cause many problems such as the surface quality of the molded parts; finally, this situation is improved by post-treatment of the formed parts, which is also a good way to improve the mechanical properties of the molded parts, which are commonly improved by heat treatment, but this method often leads to the deformation of the parts after heat treatment, which is usually caused by overheating and slow cooling. In order to solve this problem, this paper independently developed a uniform heating and rapid cooling device for heat treatment of SLS-printed PA12 materials and complex structural parts. It aims to achieve the intrinsic mechanical properties of the material by improving the internal structural defects of the material. The properties of the heat-treated sample were greatly improved at room temperature, with a maximum tensile strength of (57.6 +/- 1.9) MPa and an elongation at break between 293 degrees o and 297 degrees o. In addition, the material still maintains good tensile properties in high and low temperature environments, with a tensile strength of up to 110.5 MPa and an elongation at break of 22 degrees o to 25 degrees o at -80 degrees C . The tensile strength at +80 degrees C is (53.1 +/- 3.3) MPa, and the elongation at break is up to 578.6 degrees o. The load-bearing capacity of the heat-treated samples with Triply Periodic Minimal Surfaces (TPMS) structures increased by up to 19 degrees o in the elastic stage. Among them, the heat-treated D-type TPMS performed excellently, with a maximum load-bearing capacity of 7.3 kN in the elastic stage and excellent energy absorption performance. At the same time, this study found that with the gradual increase of temperature, the tensile properties basically increased first and then decreased. There is little difference between the crystallinity and the peak melting temperature of the unheat-treated specimen and the specimen under different heat-treated temperatures, and the crystal form does not change. With the gradual increase of heat treatment temperature, the surface roughness value of the sample showed a gradual downward trend, and the roughness was the lowest at 230 degrees C . After heat treatment, the porosity and defects in the cross-section of the sample basically disappeared, and the plastic deformation occurred during the tensile process. At the same time, it can promote the molten growth and microstructure densification of SLS-formed PA12 specimen particles, eliminate internal pore defects, and improve the mechanical properties of the material.