Method for molding plastic products comprising detecting surface area reduction before melting and injecting based on a pressure governing algorithm

摘要

A method of injecting plastic material into a mold cavity is proposed to accurately fill the mold cavity to low pressure and to avoid packing of the mold cavity with the plastic material. The plastic material is injected into the mold cavity at a sufficient rate to maintain an intact molten front and to avoid spraying or sprinkling of the plastic material in the mold cavity. After the initial intact melt front is defined, the rate at which the material is injected increases in proportion to the size of the melt front. After a certain amount of material enters the mold cavity, the material is ejected according to a rate governing control algorithm that maintains an intact melt front. After detecting signs of reduction of the surface area of the melt front, the material is injected in accordance with a pressure governing control algorithm in which the injection rate is adjusted as needed to prevent crossing the end of the mold process, to eliminate frying and to eliminate associated backflow problems. In order not to exceed the injection set limit. The injection pressure is monitored and controlled until the mold cavity is filled accurately, at which time the injection pressure is maintained until the plastic product is cured in the mold cavity. By accurately filling the mold cavity, the conventional problems associated with filling materials such as warping and flash are eliminated in the present invention and more uniform products are produced with less material.