Research On Tensile Strength Of Parts In Mask Projection Stereolithography

Rapid prototyping is a kind of new advanced manufacture technology based on additive manufacturing principle, with which the physical prototype of the parts can be produced rapidly form its CAD models, thus it is an indispensable technology for the research and development of new products. Mask projection stereolithography, a new rapid prototyping technology raised in recent years, the process of which involves: CAD solid models of the parts are sliced with professional software, after that the dates obtained are stored as view files which are able to generate a series of cross-sectional layers. Then photo-sensitive resin is selectively solidified with an image mask on resin surface which is produced by a dynamic pattern generator driven by the file.Mask projection stereolithography is mainly used to produce miniature parts whose strength is greatly required to satisfy practical engineering application. Aiming at the insufficient strength of the parts fabricated with this technology, the tensile test specimens were designed according to the requirements of the national standards, fabricated with the mask projection stereolithography system under varies conditions of fabrication parameters and the orientations of build layers, and the tensile strength of specimens were tested. The experimental results show that the tensile strength gradually increases from 2.21 to15.94 Mpa with the exposure time extending from 60 to 360 s and the tensile strength decreases from 17.33 to 1.90 Mpa with the layer thickness increasing from 0.05 to 0.5mm.The tensile strength of the specimens varies with orientations of build layers while waiting time of liquid level had no significant effect on tensile strength.During the process of the solidification of epoxy resin, the strength of the parts can be affected by the contraction deformation caused by residual stress between the layers, so the influences of new exposure modes on the tensile strength of the parts were identified in this paper. The survey reveals that the tensile strength of the specimens fabricated in transverse crisscross exposure mode(the length direction of the grid parralls with that of the tensile specimen), is larger than that fabricated in longitudinal crisscross exposuremode(the length direction of the grid perpendiculars with that of the tensile specimen).And the tensile strength of the specimens produced in transverse crisscross exposure mode,longitudinal crisscross exposure mode and cross laminated crisscross exposure mode respectively, all gradually increased with the exposure time extending from 60 to 360 s.However, grid width, exposure time slot and waiting time of liquid level had less impact on tensile strength.Furthermore, to improve the tensile strength of the parts, an experimental investigation on the basis of Taguchi method were carried out to determine and optimize impact factors for maximum tensile strength. Among all the impact factors, exposure time(factor A), layer thickness(factor B), resin temperature(factor C), exposure mode(factor D) and orientation of build layers(factor E) are included in the present study. By an intuitive analysis together with an variance analysis, it is found out that factor A, factor B,factor D and factor E all have remarkable effects on tensile strength, and the interaction between A and B, A and C, A and D, also factor C have less influence on tensile strength.According to the experimental results, an optimum factor combination of33313 EDCBA which contributes a lot to the tensile strength was concluded, through the use of which the tensile strength of the parts fabricated with the mask projection stereolithography system got significantly increased.Finally, based on the orthogonal array data, an empirical regression relationship between impact factors mentioned above and the tensile strength of parts was established with orthogonal polynomial regression modeling method, with which the tensile strength of the parts can be accurately predicted before they are produced under the help of a given set of factors combination.