Variation of Part Wall Thicknesses to Reduce Warpage of Injection-Molded Part: Robust Design Against Process Variability

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Abstract
This article introduces a concept for deliberately varying the wall thicknesses of an injection-molded part within prescribed dimensional tolerance to reduce part warpage. The “warpage” described is measured from warpage simulation so as to represent various deformation behaviors of the molded part. Considering the variation in molding process as noise factors, a wall thickness model that minimizes the effect of these noises on warpage characteristics is obtained using the Taguchi method. The warpage characteristics of this model are compared with those of the constant-wall-thickness models that comply the general rule of an uniform wall thickness in part design. Each wall thickness model is then simulated for plausibly small process fluctuations against the best process conditions of each model that would occur in the actual molding operation. It is seen that varying wall thicknesses obtained by the present study exhibits better warpage characteristics in terms of warpage mean and variance against this mean, compared to the constant wall thicknesses.