Dimensional instability means the dimensional changes of a molded part exceed the tolerance limit, for which the reasons might lie in the injection molding machine, the mold or the injection molding process.
(1)Injection Molding Machine
①The application of different types of injection molding machine leads to the differences in injection molding conditions;
②Melt temperature fluctuation – check for failure of the thermocouple or the temperature controller;
③Instable screw speed – check the hydraulic system;
④Instable injection pressure – check whether there’s consistent buffering during each cycle, or whether the plastic non return valve leaks, repair or change it when necessary;
①Check whether the gate is blocked by residue;
②Check whether the mold temperature is stable, whether the coolant flows smoothly, and whether the mold cooling circuit is correctly connected;
③Check for failure of molding components;
(3)Injection Molding Process
①Non-uniform mold temperature or unreasonable cooling circuit leads to improper mold temperature control – make adjustments accordingly;
②Injection pressure is too low – raise injection pressure;
③Appropriately increase injection time and holding time;
④Material barrel temperature or nozzle temperature is too high – make adjustments accordingly;
⑤Filling speed is too low – increase injection speed, or adopt multistage injection.