The time required to complete a single injection molding process is known as the molding cycle. It comprises several components, and the cycle duration directly impacts labor productivity and equipment utilization rates.
Therefore, during production, the aim is to minimize the various time intervals within the molding cycle while maintaining product quality. Among these intervals, injection time and cooling time are the most critical, as they decisively influence the quality of the finished product. Within the injection phase, mold-filling time is inversely proportional to the filling rate; in practice, this typically ranges from 3 to 5 seconds. The holding time-the duration during which pressure is applied to the plastic within the mold cavity-accounts for a significant portion of the total injection time, generally ranging from 20 to 120 seconds (though it can extend to 5–10 minutes for exceptionally thick parts). The duration of the holding phase affects dimensional accuracy only until the melt at the gate solidifies; once solidification occurs, the holding time has no further impact. There is an optimal holding time, which depends on factors such as melt temperature, mold temperature, and the dimensions of the sprue and gate. Assuming standard dimensions and processing conditions, the optimal duration is typically determined by identifying the pressure setting that minimizes fluctuations in product shrinkage.
Cooling time is primarily determined by the product's thickness, the plastic's thermal and crystallization properties, and the mold temperature. The cooling period should be long enough to ensure the part does not deform during demolding; typically, this ranges from 30 to 120 seconds. Excessive cooling time is unnecessary; it not only reduces production efficiency but can also complicate the demolding of complex parts, potentially inducing stress during forced ejection. Other time components within the molding cycle depend on the continuity and automation of the production process, as well as the degree to which these are implemented.
