Research On Model Reconstruction Method And Building Processes For Additive Manufacturing

With the globalization and marketization of the modern manufacturing industry, to develop a new product in a shorter time and put it on the market is more and more important for a company, which can help them keep competitive strength. Application of additive manufacturing technology for product design can shorter the developing period and lower the verification cost. Different from the traditional process of removing material, additive manufacturing is a process of adding materials. By change the three dimensional model into two dimensional plane or points and lines, there is no restrictions for building complicated parts.From the invention of additive manufacturing process in later last80s, there have been lots kinds of fabrication technologies, with many kinds of materials, like photosensitive resin, metal and ceramic powder, etc. But there is still a big gap between the additive manufacturing process and traditional processes on the fabrication accuracy, surface quality, and the physical properties of the built parts. Also, compared with the traditional methods, it’s much more expensive for the additive manufacturing process to fabricate one part, resulting to its improper usage for mass production. Based on these problems, the topic of this thesis is research on integrated computer numerical control accumulation process and mask image projection stereolithography apparatus based additive manufacturing process, aiming for improving the part quality and extending the using area of additive manufacturing process. The main contents and results are as follows:(1) Research on the modeling digitalizing method based on two-axis rotation micro-mirror. For the purpose of setting up an additive manufacturing system integrated with three dimensional scanning system, a three dimensional scanning system is developed based on the TALP1000b two-axis rotation micro-mirror form Texas Instruments and a simple web camera. By control the movement of the laser dot by the rotation mirror, a rectangle area can be scanned one time. So it can be easily integrated into the additive manufacturing system and measure the surface of the part to be built on immediately. A layered based discrete method was used for the camera calibration and laser position calibration. By using the bi-linear interpolation algorithm, the world coordinates of the pixels in the captured images and the world coordinates of the laser dots from the rotation mirror can be computed, which defines two spatial lines both passing through the scanned points. Then by calculating the intersection between these two lines, we can get the world coordinates of the scanned point. By doing some experiments, the reasons of the measured errors are analyzed and the improvement methods are proposed.(2) Research on the model reconstruction algorithm based on algebraic point set surface (APSS) and layered depth normal images (LDNls). First, by fitting the scanned points into APSS surface, the noisy points can be removed and smoothed. Then, by using the projecting operation, convert the APSS surface into LDNIs models, which can be converted into mesh based surface by contouring algorithm and finishing the model reconstruction process.(3) Research on the integrated computer numerical control accumulation manufacturing system. There is much non-uniformity of their physical properties between different directions in the parts built by layered fabrication processes. To solve this problem, a new non-layered additive manufacturing process based on computer numerical control system was developed. By integrating the designed three dimensional scanning system and the model reconstruction algorithm into this process, it can get the model of the unknown surface online. Together with the Boolean and offsetting computation based on layered depth normal images, the tool path of the laser can be generated. With the computer numerical control system, it can build parts on the given surface.(4) Research on large-area and micro-structure fabrication system based on mask image projection stereolithography apparatus. Some research job was done on the principle of MIP-SLA based additive manufacturing process, its building steps and system structure, especially the bottom-up projection based MIP-SLA process. A new system for large-area and micro-structure fabrication was designed, with its mask image generation and building process planning. In the system, a commercial projector was used, and the optical system was rebuilt to make the image focused in a very small area. By extending the optical path and building base in the X and Y directions, parts of large area with micro-structures can be built.(5) Research on mask image generation algorithm based on LDNIs. A new algorithm of mask image generation based on LDNIs was proposed. First, the LDNIs models are generated by discrete sampling of a solid model, and then use one dimensional Boolean operation instead of contouring intersecting to generate the mask image. This algorithm is much more efficient in processing complicated models with small layer thickness than the contour intersection based algorithm. A DLP based projector was spatially calibrated by layered database, which can be used for the mask image compensation and reverse computation. A new smooth surface fabrication process was introduced, which uses the mask image reverse computation algorithm to generate the second exposure images.(6) Design of MIP-SLA prototyping systems. A new prototyping system for large-area and micro-structure fabrication was built, and the curing time, building resolution of the micro fabrication system was tested by doing some experiments. Also a bottom-up projection based MIP-SLA prototyping system was developed using the EtherMAC motion control system and Windows CE embedded system, which contains an online measuring system of the peeling force during the building process. Some experiments were made to verify the accuracy, the curing time of the system. Also the relationship between the peeling force and the area of the part is established by the online force measuring system.In this thesis, an integrated computer numerical control accumulation system was developed with the research on three dimensional model digitalizing technology and the model reconstruction algorithm. This system can be used for fabricating parts without layers, which is helpful in improving the physical properties of the part in different directions. The proposed mask image generation algorithm based on LDNIs is much more efficient in the slicing operation of complicated models than the traditional algorithm based on contouring method. The designed large-area and micro-structure fabrication system overcomes the contradictions between the building resolution and building area by MIP-SLA process, which can build large-area parts with micro-structures on them. This ability is significant for extending the usage of MIP-SLA process and improving the accuracy of its fabricated parts.