Dimensional instability in plastic injection molding process

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;

 

(2)Mold

①Check whether the gate is blocked by residue;

②Check whether the mold temperature is stable, whether the coolant flows smoothly, and whether the 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.