VARIATION OF PART WALL THICKNESSES TO REDUCE WARPAGE OF INJECTION-MOLDED PART - ROBUST DESIGN AGAINST PROCESS VARIABILITY

This article introduces a concept for deliberately varying the wall th icknesses of an injection-molded part within prescribed dimensional to lerance to reduce part warpage. The ''warpage'' described is measured from warpage simulation so as to represent various deformation behavio rs of the molded part. Considering the variation in molding process as noise factors, a wall thickness model that minimizes the effect of th ese noises on warpage characteristics is obtained using the Taguchi me thod. The warpage characteristics of this model are compared with thos e of the constant-wall-thickness models that comply the general rule o f 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 b y the present study exhibits better warpage characteristics in terms o f warpage mean and variance against this mean, compared to the constan t wall thicknesses.