Curing Characteristics of the Photopolymer Used in the Solid Laser-Diode Plotter RP System

Abstract

Most stereolithography (SL) processes employ ultraviolet (UV) or diode pumped solid state lasers to cure the associated photopolymer to build a 3D part. A UV or diode pumped solid state laser is more expensive in initial cost and maintenance than a semiconductor laser. A semiconductor laser is used in the solid laser-diode plotter (SLP) rapid prototyping system to cure a specific photopolymer (DF2000). The DF2000 photopolymer is formulated from a based resin, hardening agent, and powder. The wavelength of the semiconductor laser used in the SLP system is 680 nm and is in the range of red colour light. In this work, the curing effect of the visible wavelength spectrums generated by a lamp on the DF2000 photopolymer was investigated, using differential scanning photo calorimetry (DSPC). The DSPC result indicates that the curing degree of the photopolymer using blue light is better than that when using red light. The result also seems showing that the shorter the wavelength, the better the curing effect of the photopolymer. Hence, a blue semiconductor laser (405 nm) or a shorter wavelength laser or even a higher-power lamp, instead of a red laser, can be employed to increase the curing degree of the photopolymer used in the SLP system, The quantitative effect of the SLP processing parameters on the curing degree of DF2000 photopolymer and the mechanical property of the SLP test specimen was studied using the Taguchi method. The results show that the mechanical property of a fabricated part is proportional to the curing degree of the photopolymer. The results also indicate that the scanning pitch of processing parameters is the most sensitive parameter of the SLP system affecting the curing degree and, hence, also affecting the mechanical property. Therefore, the curing characteristics of the photopolymer used in SLP system could be used as an index of the mechanical property of a fabricated part. Also, the employment of a shorter wavelength laser rather than red laser can further improve the part mechanical property and fabrication speed of the part.