Research On Optimization Of The Building Parameter For Mask Projection Stereolithography System

Rapid prototyping is a kind of brand-new advanced manufacture technology, which isdifferent from the process method of traditional remove material in manufacturing principle.The principle of the Mask Projection Stereolithography (MPSLA) is that the CAD model ofthe object is sliced by a computer and the cross-sections of the slices are stored as the viewfiles. The view files are displayed with a dynamic pattern generator and are imaged ontothe resin surface.Dynamic pattern generator is the core component of the MPSLA system, the opticalsystem’ performance has enormous influence on building accuracy of the system. Theoptical system has a certain degree of optical distortion in imaging process, because ofmanufacture errors and assembling errors of the optical system. The optical system indynamic pattern generator has a certain degree of optical geometric distortion in imagingplane, and the geometric distortion will cause changes of image mask in dimension andshape. So the accuracy of dimensions and shape of cured single-layer will be lost.Therefore, we have to calibrate geometric distortion image caused by the optical system. Toimprove the building accuracy of the MPSLA system, the distortion model of binary cubicpolynomial interpolation is established with least-square method. The gray scale rebuildingis implemented with space-variable linear interpolation by using VC++6.0. Taking theimage after being corrected to calibrate the view generator, which can ensure to obtain anaccurate2D image section on resin surface and improve the accuracy of building part.In the building process of MPSLA, the part is build through accumulation of the layers,which is the smallest unit. The phenomenon of print through can be reduced and improvedthe building accuracy of the parts by controlling the depth of a thin layer. The major factorsaffecting the print through include the exposure time interval, irradiation and the area ofmask. Through the research of the thin layer cure model, the parameters DPS, DPLand Ecareto be determined. And the relationship is determined between cure depth and the energy.Based on above, it is found that exposure time interval influences cure depth. Due to effectof diffusion of radicals and oxygen, it will reduce energy of the bottom, which is relatedwith exposure time interval. Therefore, exposure time interval has certain positive role oncontrolling the print through. In addition, it is found that the cure depth has relation to irradiation and the area of mask. When exposure energy is established, cure depth reducesas the irradiance reduced. But the exposure time is longer, when the irradiance is lower,which leads to the production efficiency reduced. Therefore, the right irradiance valuechose is important. Mask design is the view of manufacture, which is the slicing pictureafter Anti-color process. The reason of mask design influenced on the cure depthis related to energy stack. The experiment model shows that the phenomenon of printthrough is improved of by controlling the above factors affecting cure depth.In order to improve the dimension accuracy in exposure plane, the signal-to-noise (SN)ratio in Taguchi method is used to optimize the four main influence factors including theirradiation (factor D), exposure time (factor C), exposure time interval (factor B) and thecoefficient of surface shrinkage compensation (factor A). Adopting orthogonal table of theL27(313), the signal-to-noise ratio of the part’ dimension error is obtained with the respondof different level of these factors. Through analysis of intuitive and analysis of variance inthe orthogonal table, it is found that A, B, D and A×D in exposure plane significantly affectthe dimension accuracy, the interaction between A and B also have effect on the dimensionaccuracy. The experimental results indicate that the dimension error has been reached in±10μm with the optimum combination of factors. The research obviously improvesbuilding accuracy of the Mask Projection Stereolithography system.Finally, this paper based on the above research detailedly introduces productionprocess of the MPSLA system. To make through the three-dimensional model of chessshows that the phenomenon of print through is significantly improved. In addition, a planefeature test is made. The measurements of the test and the results of analysis show that theRMSE of measurement on the plane is0.011mm, and the dimensionerror on the planewithin±0.020mm is95.6%of the measurements. The accuracy of part is improvedobviously, which is great significance for promotion of the MPSLA technique.