Research on injection molding of micro parts using layered structure mold

This paper describes a new method of molding micro parts using a mold which was manufactured by layering metallic foils and plates. Coolant channels are circulated uniformly under the mold surface, at a depth sufficiently close to the surface. Hence, the mold temperature can be kept uniform over the large area of inserts of both the movable and fixed die plates. Two stainless steel foils in which micro-gates and cavities are machined by electrical discharge machining, respectively, are layered on the insert of fixed die plate. The space between the insert of movable die plate and the stainless foils, called sheet runner, is first filled with resin due to injection. Thereafter, the micro-cavities are filled with resin through the micro-gates due to the pressure rise in the sheet runner. The air vent effect due to the layered structure helps the resin to fill the cavity smoothly. The process conditions under which polypropylene micro disk of 200μm in diameter and 60μm in thickness can be formed uniformly over the sheet runner area of 40mm by 50mm were obtained changing the injected resin volume, resin temperature, and gate size. Besides, micro lens 200μm in diameter and 50μm in thickness were formed using molds manufactured by electrical discharge machining and electrolyte jet machining.