For SLS rapid prototyping process, it is difficult to achieve the SLS prototype with good surface quality and dimensional accuracy and high strength at the same time. Therefore, in order to make up for the inherent defects of SLS prototype in accuracy and strength, post-processing process is generally required. The shortcomings of SLS prototype are as follows;
(1) SLS is a process of powder sintering. As the powder particles are heated to its glass transition temperature, the adjacent particles are bonded, and part of the powder particles remain solid during the sintering process, which makes the sintered parts inevitably have gaps. Compared with the traditional injection processing, the strength is poor, which needs post-treatment to strengthen.
(2) The SLS prototype is surrounded by the unfired powder. Due to the secondary sintering phenomenon, it is inevitable that some powder will stick to the sintered parts, which affects the accuracy of the sintered parts. Therefore, after sintering and cooling, post-treatment is needed to remove floating powder and sticky powder.
(3) For SLS For the specific application of prototype, for some non bearing capacity structural parts, resin coating can be selected to improve their surface strength; the other is for investment casting. In order to meet the surface quality requirements of wax pattern in investment casting, especially for large-scale complex models, it also needs to meet its own strength requirements, so post-treatment is needed. Generally, wax immersion post-treatment is selected.
In view of the above shortcomings, the main measures for SLS prototype post-treatment at this stage include painting, immersion and surface finish. Generally, resin is chosen as the coating material, and the surface strength of SLS prototype can be improved by filling the gap of SLS prototype. Wax is commonly used to immerse SLS prototype into reinforcement materials. The post-treatment process is mostly used in investment. After wax immersion, not only the wax liquid enters into the SLS prototype gap and improves the overall strength, but also the surface quality of SLS prototype is significantly improved after the second wax immersion, so that it can meet the needs of investment casting. However, due to the entry of high temperature wax, the volume of SLS prototype changes to a certain extent. At the same time, due to the excessive wax adhering to the surface of SLS prototype, the final wax pattern has a certain size error.