Dynamic mold surface temperature control using induction heating and its effects on the surface appearance of weld line

Electromagnetic induction heating combined with coolant cooling is used to achieve dynamic mold surface temperature control. A simulation tool was also developed by integration of both thermal and electromagnetic analysis modules of ANSYS, and capability and accuracy were verified experimentally. To evaluate the feasibility and efficiency of induction heating on the mold surface temperature control, a mold plate (roughly about an inset size of cellular phone housing) with four cooling channels was utilized for two demo experiments with varying mold surface temperature between 110 and 180 degrees C, and 110 and 200 degrees C, respectively. During induction heating/cooling, it takes 4 s to increase mold surface temperature from 110 to 200 degrees C and 21 s for mold surface to return to 110 degrees C. The mold plate surface temperature can be raised at about 22.5 degrees C and cooled down at 4.3 degrees C/s within the aforementioned temperature range. Mold plate temperature distribution exhibits good uniformity as well in all stages of the heating/cooling process. Finally, mold surface temperature of a double-gated tensile test part mold was induction heated to above glass transition temperature for few seconds prior to melt injection. The surface mark of weld line was eliminated, and the associated weld line strength enhanced. (c) 2006 Wiley Periodicals, Inc.