Impact testing of stereolithographic models to predict natural frequencies

Stereolithography (SLA) is a rapid-prototyping method which is used primarily to display the three-dimensional geometry of designed parts. In this paper, impact testing of SLA models is examined as a tool for the prediction of the natural frequencies of prototype aluminum parts. If the SLA model is ideal, its frequencies and those of the corresponding aluminum prototype will be related by simple ratios of material parameters and dimensions. However, the effects of properties of the SLA model which are non-ideal or qualitatively different from aluminum have not been examined. Impact tests of SLA beams, plates, and complex shapes (models of motor end shields) were performed to quantify the effects of differences such as increased mass loading (due to the lightness of SLA parts), possible anisotropy due to the "laminated" nature of the model, and mismatches between the damping, non-linearity, and the Poisson ratio of the SLA material and the corresponding properties of aluminum. The natural frequencies predicted from SLA models were compared to those measured from corresponding aluminum parts. Comparisons generally showed good agreement and suggest that carefully performed impact testing of SLA models is a useful method to predict the natural frequencies of prototype parts. These predictions may be used directly in the design process, or to validate and refine finite-element models.