Thermoforming is the process of shaping heated sheet against a cooled mold. Products range from very thin packaging disposable packaging to very thick transportation components. Thermoformed parts are recognized as having very large surface area-to-thickness ratios. They are also know for nonuniform wall thicknesses across their surfaces. As with other single-surface processes such as blow molding and to some extent, rotational molding, commercial thermoformed part wall thickness variation is typically +/- 20-30%. Three areas of computer aids have grown in popularity recently. Computer-aided multi-axis CNC trimming machines are being extensively used in heavy-gauge thermoforming to ensure accurate peripheral and mating surface dimensions. Computer programs are now available for predicting heating and cooling cycles for diverse polymers, thus allowing for more rapid material and mold changeover. And finite element analysis is used to predict local part wall thickness and plug design, among other facets. The impact of these newer developments on part-to-part dimensional reliability is discussed in this paper.
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