Real-time monitoring technology of plaster-based three-dimensional printing system for quality determination of model structure

Using plaster-based three-dimensional printing (3DP) technology, calcium phosphate powder can be bonded together and become a model when a liquid adhesive is injected into the powder. This technology has many advantages, such as no need for support materials and fast setting times. However, the accuracy, surface flatness, and resolution of this technology are not equal to those of other manufacturing processes. These parameters can be analyzed from an image of each layer using a real-time monitoring module. Hence, in this study, light-emitting diode (LED) lights with four different wavelengths were used to irradiate a working platform, and the contour of the bonded region was obtained from images before and after the adhesive injection. The results show that the model irradiated by ultraviolet (UV) light (405 nm) has a higher image contrast from the powder than the model irradiated by visible (VIS) light (660 nm) and near-infrared (NIR) light (890 nm), the contrast rate of which was 0.92. In addition, four volumes and four viscosities of adhesive were used to investigate the setting time and diffusion ratio of the model. The diffusion ratio was approximately 1.37 ± 0.04 times using four volumes of adhesive, but the setting time was in conjunction with the adhesive volume. In addition, the diffusion ratio of the model increased with the viscosity of the adhesive, which increased from 1.39 to 1.60 times and extended 70 s for setting compared with that with an adhesive without stickiness. By using a real-time monitoring system, the accuracy and quality of the model can be immediately controlled in the 3DP process, and the printing process can be interrupted to prevent wasting the material if the model becomes seriously distorted.