Injection molding defects can affect part appearance, strength and function. Understanding the common defects and their causes helps you design better parts and work more effectively with your mold maker. Here are the most common injection molding defects and how to avoid them.
1. Sink Marks
Sink marks are shallow depressions that appear on thicker sections where the material shrinks as it cools. They are caused by thick walls, insufficient packing or high mold temperature. To avoid sink marks, keep wall thickness uniform, add ribs instead of thick sections, and ensure proper packing pressure.
2. Warpage
Warpage is the distortion of a part after ejection, caused by uneven shrinkage, poor cooling or excessive internal stress. To reduce warpage, use uniform wall thickness, balanced cooling and consider mold flow analysis to predict and correct shrinkage.
3. Flash
Flash is excess material that escapes along the parting line or around ejector pins, caused by insufficient clamping force or worn mold surfaces. It is controlled by proper mold fit, clamping force and mold maintenance.
4. Short Shots
A short shot occurs when the mold cavity does not fill completely, often caused by insufficient injection pressure, material that is too viscous or a gate that is too small. Correct gate size, material temperature and injection speed to resolve.
5. Weld Lines
Weld lines form where two flow fronts meet, creating a visible line or weak spot. They can be minimized by adjusting gate location, improving material flow and increasing mold and melt temperature.
6. Burn Marks
Burn marks are dark discoloration caused by trapped air that overheats during injection. They are resolved by adding or improving venting, reducing injection speed or lowering melt temperature.
How We Prevent Defects
D-top Mould prevents most defects in the design phase through DFM review and mold flow analysis, and validates molds through careful trials and inspection before shipment. Send your drawings and our engineering team will help you avoid these common issues from the start.
