At Hella Saturnus d.o.o., there is a strive to predict the deformation of headlight lenses during the lacquering process in the development phase, which occur due to the force of gravity under long-term thermal stress near the glass transition temperature of the polymer. The knowledge of time-dependent mechanical properties of the materials used is of paramount importance for accurately predicting such deformations.
In the first step, we prepare samples of the selected material type and perform experimental measurements to determine the material properties and shear relaxation. Using time-temperature superposition and the CFS algorithm a summary curve is created. Based on the obtained summary curve, Prony series parameters are determined for chosen material. Numerica simulation is performed to verify the appropriateness of the selected parameters on the simulation model, that is set up same as the experimental measurements. When the simulation results correspond adequately with the measurement results, we shift our focus to evaluating the method used on an example of a simplified lacquering process in production. Subsequently, as the second step of our task, we conduct controlled tempering of three light lenses, taken directly from ongoing serial production, and meticulously document all deformations. We then compare the obtained deformation values with the results of the numerical simulation, which describes the tempering process of the lenses. The final conclusion is that the use of the simulation method is practical in predicting the deformation of headlight lenses.
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