Microfluidic Chip Control Injection Molding Mold Release System

Injection molding is one of the most important methods to produce microfluidic chip. As an important stage in injection molding, demolding determines the final quality of formed components to a great extent. Microfluidic chip may be fractured, deformed and even destroyed in the demolding process, if demolding system is designed improperly or unsuitable process parameters are chosen. The main work carried out in this paper, as listed below, aims to devise a better micro-fluidic chip demolding system after an in-depth and systematic analysis of the demolding process by taking the chip warpage and demolding stress as the measuring indexes of demolding quality.Firstly, in order to improve the demolding quality of injection molded parts, an in-depth analysis of micro-fluidic chip demolding process was done and thermal shrinkage and demolding stress distributions were obtained through numerical simulation. Three different demolding setups using ejector pins were designed to improve the uniformity of demolding force distribution. Variation patten of demolding stress in the three setups was studied. Results revealed that an increase in the number of ejector pins leads to a decrease of demolding stress but also causes worse surface quality and even an interference between ejector pins and cooling channels. Based on the above results, an automatic non-destructive demolding system integrating porous steel as media was developed, which served as a platform to verify the feasibility of porous steel as a pneumatic demolding media.Secondly, based on numerical simulation results, injection molding experiments were performed to study the influence of demolding temperature on the chip warpage. It was observed that the increase of demolding temperature leads to a gradual decrease of demolding stress and a gradual increase of warpage, and that fracture occurred at a mold temperature of 90℃.According to the results, the optimum temperature is suggested to be within 70-80℃.Finally, ejector pin demolding and pneumatic demolding were compared in terms of chip demolding quality through experiments under the same processing conditions, in which the warpage of molded covers ejected by those two demolding mechanisms was compared. Results indicated that porous steel based pneumatic demolding is effective in reducing warpage of the cover by as much as 38% compared to ejector pin demolding.