Mold temperature variation for assisting micro-molding of DVD micro-featured substrate and dummy using pulsed cooling

Variable mold temperature for micro-molding has been a new trend, assisting in both the micro-feature replication accuracy and in holding cycle time increases down. Although various mold temperature controls have been proposed and proven useful in improving micro-feature dimensional accuracy, the required increases in cycle time hinder commercial application. Cycle time is particularly important in molding thin-wall parts such as cellular phone housings, CDs, and DVD substrates, for which the cycle times range from less than 10 s to about 4 s. In this study, pulsed cooling is evaluated and employed in the injection molding of DVD-R substrate and dummy. For pulsed cooling, coolant circulation is usually stopped during the melt-filling process and the opening and closing period of the mold. This may lead to additional cavity surface temperature increases of 10–15 °C in the melt-filling stage, depending on the overall cycle time and cooling circuit design. It helps to improve the microgroove replication accuracy by about 6% in molding micro-featured substrate and results in a 4–6% reduction in radial and tangential deviation in the molding dummy. If pulsed cooling is employed with original coolant temperature lowered by 8–10 °C, cycle times can be reduced from 4 s to 3.5 s and from 4 s to 3.2 s, respectively, for substrate and dummy molding, while holding microgroove accuracy and geometry deflection properties at their previous levels. Pulsed cooling technology has been successfully employed in low cycle time molding cases to either reduce cycle time or improve part qualities without a cycle time increase, or both.