Injection molding machines and methods for accounting for changes in material properties during injection molding runs

摘要

A method and a machine that account for changes in material properties of molten plastic material during an injection run. If viscosity of the molten plastic material changes during an injection run, a controller alters a step time of the injection cycle to ensure that molten plastic material completely fills and packs a mold cavity to prevent part flaws such as short shots or flashing.

主权项

1. A method of automatically adjusting a step time for an injection molding cycle to adapt for variations in the flowability of a molten plastic material, the method comprising:
(a) during a first molding cycle, injecting a first shot of molten plastic material into a mold cavity; (b) during the first injection molding cycle, measuring a first time for the molten plastic material to reach a flow front sensor that is configured to sense the presence of a flow front of the molten plastic material at a particular location in the mold cavity; (c) comparing the first time to a predetermined time to determine a first comparison result; (d) determining a first step time, based, at least in part, on the first comparison result; and (e) during the first molding cycle, removing injection pressure from the first shot of molten plastic material so that the first injection molding cycle has the first step time, wherein the step time is the time from initiation of injection of molten plastic material to just before the mold is opened for ejection.