EFFECTS OF COOLING TIME AND MOLD TEMPERATURE ON QUALITY OF MOLDINGS WITH PRECISION CONTOUR

Injection molding is now used to mold plastic parts with precision con tours such as lenses. Cooling conditions have critical effects on the quality and productivity of such precision parts. This article is devo ted to investigate the effects of mold temperature and cooling time on quality. A two-cavity mold for molding convex lenses with square-loop ed cooling channels was used. Samples molded with different mold tempe ratures and cooling times were collected, and their contour conformity to those of the cavity was evaluated. Contour errors were defined. Th e correlation between mold temperature and cooling time and contour er rors was analyzed. It has been found that for a given mold temperature , two critical cooling times can be defined at which the thermal and r igidity states pass through a transition. Most dramatic improvements i n part conformity occur around such critical points. (C) 1996 John Wil ey & Sons, Inc.