Study on Inhibition Mechanism of Polymer Parts in Selective Inhibition Sintering Process

The selective inhibition sintering (SIS) process is an additive manufacturing technique that builds parts based on powder sintering. In this process parts are made upon deposition of a solution, called inhibitor, at the boundary profile. The inhibitor prevents polymer particles to coalescence under heat exposure on each layer. The inhibited boundary profile acts as a sacrificial mold that can be easily removed, leaving a chemically pure part. One of the influential factors in fabrication resolution by SIS is the proper selection of an inhibitor. The best inhibition mechanism results in ease of separation of the part from undesired regions while maintaining part accuracy. In this paper, we investigate a framework for selecting an appropriate inhibitor for the process. Different experiments have been performed and inhibition theory has been studied on polyamide (PA) samples. Specifically, as an alternative to exhaustive experiments on solutions and polymers, a hybrid method based on crystallization is proposed to characterize the effectiveness of the inhibitor. Differential Scanning Calorimetry (DSC) tests are used to study changes in thermal properties of the samples. It is found that the sintering period increases as crystallinity of the polymer decreases. Results show that polymer samples exposed to sodium hypochlorite solution has longer sintering periods. Design of experiments has been used to study shrinkage behavior of polymer samples through bulk sintering.