Understanding injection molding defects is essential for troubleshooting and improving part quality. This guide covers the most common defects, their root causes, and practical solutions.
Incomplete cavity fill. Causes: insufficient injection pressure or speed, low melt temperature, inadequate shot size, blocked gate or nozzle, trapped air in cavity. Solutions: increase injection pressure and speed, raise melt temperature, increase shot size, improve venting, adjust gate location.
Thin film of plastic escaping at the parting line. Causes: insufficient clamp force, mold damage at parting line, excessive injection pressure, low clamp tonnage, mold deflection. Solutions: increase clamp force, repair damaged parting line surfaces, reduce injection pressure, increase mold stiffness.
Surface depressions opposite thick sections. Causes: insufficient pack pressure or time, gate freeze-off before full packing, inadequate cooling in thick sections, material shrinkage too high. Solutions: increase pack pressure and time, move gate location to thick section, increase cooling in thick areas, consider gas-assist molding.
Visible lines where two flow fronts meet. Causes: material temperature too low at flow front, flow fronts meeting at low pressure, insufficient venting at weld location, contamination or moisture in material. Solutions: increase melt and mold temperature, improve venting at weld area, increase injection speed, relocate gate to move weld line to non-critical area.
Discolored or charred areas on the part surface. Causes: trapped air heating to combustion temperature, material degradation from excessive temperature or residence time, contaminated material. Solutions: improve venting at last-fill locations, reduce melt temperature, reduce injection speed at problem areas, verify material drying.