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
  • 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