Reduction of Pressure Distribution Variation in Press Mold Based on Variable Lattice Optimization

Abstract

Hot molding is one of the efficient techniques for shaping viscoelastic materials such as glass. However, to prevent surface quality defects caused by the contact between molds during the shaping process, the mold should be carefully designed to provide unifying contact pressure. In this study, to reduce the distribution of contact pressure of molds, the mold's internal stiffness distribution was controlled using variable lattice optimization via molding. Control of stiffness in the contact direction was achieved using unit cell shapes that included beam structures, and the range of effective stiffness was expanded by combining multiple types of unit cells. In addition, contact and linear elastic calculations were performed separately to address the boundary nonlinearity problem in the contact analysis. The linear elastic calculation was performed by mapping the displacement distribution obtained in the contact analysis, and sensitivity calculation was performed for the linear elastic calculation. Using two examples with modified contact surface shapes, the proposed method's effectiveness and validity are discussed through numerical calculations with effective material properties, reproduced detailed shapes, and experimental verification. The numerical simulations revealed a reduction in the variance of contact pressure by 74% in the 2.5D examples and 68% in the 3D examples. Experimental results demonstrated a decrease in the variance of contact pressure by 29% in both the 2.5D and 3D examples.