Injection Molding Troubleshooting

Problems	Possible Causes	Suggested Solutions
Insufficient material feeding	Caking at hopper bottom Back pressure insufficient or cylinder temperature too low causing inadequate melting Barrel temperature is too low causing inadequate material melting. Especially when 70% of the capacity is injected. Screw speed in too fast	Have cooling water pass hopper bottom adjust back pressure or increase barrel temperature Reduce screw speed
Short Shot	Poor melting of material Insufficient material flow Nozzle diameter, gate runner too small Injection pressure is too low Dwell time too short Insufficient charge volume in the barrel Air resistance, no gas escape Product too thin Abrasion of screw	Increase temperature of barrel and mold Use material with better flow properties Repair faulty part Increase injection pressure Lengthen dwell time Increase back pressure, charge volume Increase air vents Reconsider mold design Replace screw
Too much flash	Injection pressure too high Injection speed too fast Material flow too soft Clearance of mold surface Mold temperature too high	Lower injection pressure Adjust with flow control bulb Use hard flow material Make smaller clearance Lower mold temperature
Weld lines	Barrel temperature too low Injection pressure too low Air pockets Insufficient material flow Oil on mold surface Distance between gate and weld point too far	Increase barrel temperature Adjust injection pressure; widen runner, gate Increase air vents Use soft-flow material Remove mold and clean the oil on the mold Study gate position
Flow Mark	Un-uniform melting of material causing by low temperature of mould and barrel Gate too small	Increase temperature by step Widen the size of the gate Decrease the injection speed
Poor cavity filling	Barrel and mold temperature are too low Injection pressure and/or speed are too high Material flow is too high, i.e. material is too soft Injection starts before clamping pressure has been applied	Increase temperature of Barrel and mold Adjust injection pressure and flow control to fill cavity slowly Use harder material Delay injection starting time
Fragility	Melting temperature is too high Size of runner, sprue, gate are too small Material is too hard	Decrease barrel temperature Review the runner, spure and gate design Use softer material
Mold Shrinkage	The shorter the curing time is, the larger the molding shrinkage The shorter the dwell time is, the larger the shrinkage ratio The smaller the gate cross section area, the larger the shrinkage ratio