Injection Molding
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Underfilling/Short Shot of Low-Density Polyethylene Injection Molded Products (Variant: Strengthened Measures)
Fenómeno do problema
The product fails to completely fill the cavity, with material-missing parts, incomplete edges, or local voids.
Short shot directly leads to product scrapping, and usually occurs first in parts with long flow distance, thin walls, or poor venting.
In particular, extra attention is needed on the original basis; this problem is more prominent and requires key attention.
Análise das causas
（1）The injection pressure is insufficient or the injection speed is too slow, and the melt solidifies prematurely during mold filling
（2）The barrel temperature is too low (below the 160-220°C lower limit), the melt viscosity is high, and the flowability is poor
（3）The mold temperature is too low, the melt cools rapidly after contacting the mold wall, and the flow distance is shortened
（4）The gate size is too small or the runner is too long, and the melt flow resistance is large
（5）The cavity venting is poor, and the trapped gas hinders the melt filling
（6）On the original basis, extra attention is needed: process parameter fluctuations or equipment status changes have aggravated this problem
Solução
（1）Increase the injection pressure to 80-150MPa, increase the injection speed, and shorten the mold filling time
（2）Increase the barrel temperature to a higher value within the 160-220°C range to reduce the melt viscosity
（3）Increase the mold temperature to a higher value within the 30-60°C range to delay melt cooling
（4）Increase the gate and runner sizes, shorten the runner length, and reduce the flow resistance
（5）Check and improve the mold venting, and add vent grooves or vent pins at the filling end
（6）And strengthen process monitoring; on the original basis, extra attention is needed, with special attention to parameter stability
Conclusão principal
Short shot is the result of insufficient melt flowability or excessive mold filling resistance, and needs to be solved by increasing the temperature, pressure, and improving the gating and venting system.
Targeted preventive measures need to be taken in different production scenarios.
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