Mask Projection Stereolithography (MPSLA) is a manufacturing process capable of fabricating high resolution, three dimensional parts out of photopolymer resin. The process has potential applications in a variety of fields like MEMS packaging, micro-fluidics, tissue scaffolding, etc.  Since the MPSLA technoology  is less than a decade old, most work in it has been experimental in nature. The process has not been analytically modeled and is still at the "proof of concept" stage. The broad aim in my PhD is to study the MPSLA process in order to mature it into a micro fabrication technology.  

          As a part of my research, I have designed and assembled a MPSLA system. The optical schematic of the system is shown in Figure 1. The MPSLA process starts with the CAD model of the object to be fabricated. The CAD model is sliced at various heights to obtain its cross sections. The cross sections are converted into bitmaps. These bitmaps are displayed on a dynamic mask. I am using the Digital Micromirror Device (DMD) from Texas Instruments as the dynamic mask. The bitmap dispayed on the mask is imaged onto the photopolymer contained in a vat to cure a layer. This layer is coated with a fresh film of resin and the next layer, corresponding to the next cross section is cured on it. Likewise, by curing layers over each other, the entire part is built.

Figure 1. Optical Schematic of the MPSLA system realized as a part of this research

Research Objective

          Suppose the micro nozzle shown in Figure 2 needs to be fabricated using the MPSLA process in less than 10 minutes. The micro nozzle has constriants on dimensions, surface finish as well as build time. What should be the layer thickness used to build this part? What bitmaps should be imaged onto the resin surface to cure these layers? How long should these bitmaps be imaged? In order to answer such questions, we need a process planning method for MPSLA. Process planning becomes even more complicated because a Stereolithography resin's cure parameters have an inherent randomness associated with their values. Process planning needs ot be done in such a way that the variations in resin parameters would still keep the cured part's dimensions within the prescribed tolerances.

Figure 2. Motivating example problem: Fabrication of a micro nozzle

          The micro nozze in Figure 2 is representative of the class of parts whose fabrication would be enabled  by this research. The research objective for my PhD is this scoped out as: "To formulate a process planning method to cure Mask Projection Stereolithography parts with constraints on dimensions, surface finish and build time, under parameter uncertianty".

PhD proposal         

          In my PhD proposal, a strategy to attain the research objective presented above has been presented. The research objective has been broken down into research questions. Hypotheses are presented for these research questions and tasks to be undertaken to test these hyypotheses are presented. Click here to download my PhD proposal.

Pictures

          The MPSLA system realized as a part of this research is presented in Figure 3. The pictures of some micro parts cured using this systems are presented in Figure 4 and 5. In Figure 4, the close up of the teeth of a micro spur gear is shown. The gear is a three layer part, each layer 50 micron thick. Figure 5 shows the top view of four wheels and axle of a micro SUV. This is a 9 layer part, each layer 50 micron thick.