The most important process conditions in the injection molding process are the temperature, pressure, speed and corresponding action time that affect the plasticizing flow and cooling. However, these factors influence and restrict each other. For example, if the melt and mold temperature are increased, the injection pressure and speed can be reduced. Otherwise, the injection pressure and speed need to be increased. The core of the influence of various process conditions is the viscosity change of plastics, which is very important for the reasonable selection of parameters and the influence of each other in the injection process.
Characteristics of injection speed
High speed injection has the following advantages in the injection process:
(1) reduce the injection time and shorten the molding cycle;
(2) improve the plastic process, which is conducive to the molding of thin-walled parts;
(3) improve the surface gloss of products;
(4) improve the strength of the welding line, so that the welding line is not obvious;
(5) prevent the cooling deformation.
Low speed injection has the following advantages in the injection process:
(1) to prevent the forming products from flying edge;
(2) to prevent jet and flow lines;
(3) to prevent burning marks;
(4) to prevent the plastic melt from air entrainment;
(5) to prevent the molecular orientation deformation, etc.
Injection processing speed is closely related to product quality. The advantages of injection are the disadvantages of low-speed injection, and vice versa.
Therefore, the combination of high-speed and low-speed in the injection process can make full use of their advantages and avoid their disadvantages, so as to ensure product quality and process economy. This is what we usually refer to as multi-stage injection technology, which has been widely used in modern injection molding machines.
At present, most medium-sized and above injection molding machines have five to six stages of injection pressure, speed change and three to four stages of pressure maintaining pressure change (because at the pressure maintaining stage, the melt has filled the cavity, at this time, the feeding material flowing into the cavity through the pressure maintaining pressure has been limited, so the impact of pressure maintaining speed is not significant).
