Injection Molding Troubleshooting

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

• 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

• 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

• 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

• 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