Sink marks, flow marks and weld lines
Sink marks usually appear near thick ribs, bosses and material accumulation zones. The solution may include reducing local wall thickness, changing rib ratio, improving holding pressure, adjusting gate position or extending cooling time. Flow marks and weld lines are often related to melt temperature, filling speed, gate design and air venting.
For cosmetic plastic housings, a defect that is acceptable on an internal rib may be unacceptable on a visible surface. That is why appearance grading should be defined before mold design.
Warpage and dimensional drift
Warpage can be caused by uneven wall thickness, unbalanced cooling, material shrinkage, poor ejection or an unstable process window. If a part is flat or has tight assembly requirements, cooling design and ejection balance become just as important as machine settings.
Dimensional drift during batch production may come from material moisture, mold temperature change, unstable holding pressure or tool wear. Huanze uses first article inspection, patrol inspection and process records to track these changes.
Flash, short shots and weak snap fits
Flash may be caused by excessive injection pressure, worn parting surfaces, insufficient clamping force or poor mold fitting. Short shots often appear in thin areas, long flow paths or poorly vented positions. Weak snap fits are usually connected to material choice, fiber orientation, sharp corners or insufficient radius.
How to prevent defects before mass production
A structured trial process helps prevent repeated problems. Review T1 samples for appearance, dimensions, assembly fit and function. Record the process window, update the mold if needed and confirm stable samples before batch production. For high-volume products, mold maintenance and cavity balance checks should be part of the production plan.
Related pages: custom injection molding services, quality management and automotive plastic parts case study.