Selection of time parameters for injection moulding process


The molding cycle of an injection mold refers to the ti […]

The molding cycle of an injection mold refers to the time required to complete an injection molding process. It includes all the time in the injection molding process. The molding cycle directly affects production efficiency and equipment utilization.
In the entire molding cycle, injection time and cooling time are the most important. They are not only the main component of the molding cycle, but also have a decisive influence on the quality of plastic parts. The filling time in the injection time is inversely proportional to the filling rate, and the filling rate is determined by the injection rate. In order to ensure the quality of plastic parts, the filling speed should be controlled correctly. For plastic parts with high melt viscosity, high glass transition temperature, fast cooling rate, glass fiber reinforced plastic parts and low foaming plastic parts, fast injection, ie high pressure injection, should be used.
In production, the mold filling time generally does not exceed 10s. The holding time in the injection time accounts for a large proportion of the entire injection time, generally about 20 ~ 120s (thick-wall plastic parts can reach 5 ~ 10min). The length of the dwell time is determined by the structural size, material temperature, main flow channel and gate size of the plastic part. In the case of normal process conditions and reasonable dimensions of the main flow channel and the gate, the optimal holding time is usually the minimum time within the fluctuation range of the shrinkage of the plastic part.
The cooling time is mainly determined by the wall thickness of the plastic part, the temperature of the injection mold, the thermal properties of the plastic and the crystallization properties. The cooling time should be based on the principle of ensuring that the plastic parts do not cause deformation when demolded. Excessive cooling time not only prolongs the molding cycle, reduces production efficiency, but also sometimes makes it difficult to demould plastic parts.