Process Parameters

Optimizing process parameters is essential for producing high-quality molded parts consistently. This guide covers the key parameters and their effects on part quality.

Key Parameters

Melt Temperature

Each material has an optimal processing temperature range. Too low = incomplete filling, weld lines; too high = material degradation, burns. Typical ranges: ABS (200-260°C), PP (200-280°C), PC (280-320°C), Nylon 66 (280-310°C).

Mold Temperature

Controls cooling rate and crystallinity. Higher mold temperatures improve surface finish and dimensional stability but increase cycle time. Lower mold temperatures reduce cycle time but may cause warpage or poor surface quality.

Injection Speed & Pressure

Multi-stage injection profiles are used for complex parts: fast fill for thin sections, slow fill near gates to prevent jetting, controlled packing to minimize sink marks. Injection pressure must overcome flow resistance through the runner, gate, and cavity.

Packing Pressure & Time

After filling, packing pressure compensates for material shrinkage. Typical packing pressure is 50-70% of injection pressure. Insufficient packing causes sink marks; excessive packing causes flash and high internal stress.

Cooling Time

Determined by part wall thickness and material thermal properties. Rule of thumb: 1-2 seconds per mm of wall thickness for most materials. Inadequate cooling causes warpage and shrinkage variation.

Back Pressure

Pressure applied to the screw during retraction. Improves melt homogeneity and de-gassing. Typical range: 5-20 bar for free-flowing materials, higher for temperature-sensitive materials.

Troubleshooting by Parameter

Defect	Likely Parameter Issue
Short shot	Low injection speed/pressure, low melt temp, insufficient shot size
Flash	High injection pressure, low clamp force, worn mold
Sink marks	Insufficient packing pressure/time, high mold temp, thin walls
Weld lines	Low melt/mold temp, slow injection speed, poor gate location
Warpage	Uneven cooling, high mold temp differential, excessive packing
Jetting	Gate size too small, injection speed too fast at gate