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Common defects in MIM

Common defects in Metal Injection Molding
Injection molding defects in the MIM process can be apparent directly after molding or they may not be manifest themselves until after subsequent process steps. Molding is a multi-variable process where the variables are heavily interactive, thus, there are multiple ways to solve a problem. Also, the solution to one issue can cause defects of a different form. The below table is a guide to common defects and potential solutions.


Common defects and solutions for MIM molding
Defect Potential causes Potential solution
Blistering Improperly dried material Dry hygroscopic material
  Reduce humidity in plant
Blistering Poor heat removal from tool Increase cycle time
  Reduce mold temperature
  Reduce melt temperture
  More cooling channels in tool
  Higher thermal conductivity mold components
Blistering Localized shear heating Reduce injection speed
  Large gates to reduce shear heating
Blistering Polymer degradation Use higher MW polymers
  Use antioxidant in binder
Cracking Ejection issue Increase mold temperature
  Reduce pack pressure
  Decrease melt temperature
  Polish tool
Cracking after solvent Molded in stress Increase venting
  Increase mold temperature
  Post mold anneal
Flash Tooling not closed Adjust tooling for better clamping
  Worn tooling, dress parting line
  Clean mold faces of dirt
Flash Too low clamp tonnage Higher tonnage machine
  Reduce injection pressure by slowing injection
  Reduce pack pressure
Flash Material viscosity Increase viscosity by increasing solids loading (will cause shrinkage change)
  Increase viscosity by high molecular weight polymers
Gate blemish Powder/binder separation at gate Decrease injection speed
  Decrease pack pressure
Incomplete fill Insufficient material in cavity prior to gate freeze Increase shot size
Increase pack pressure
  Increase injection speed
  Increase venting
  Increase melt temperature
  Increase mold temperature
Incomplete fill Material feed issue Decrease backpressure on recovery
  Decrease size of feedstock and regrind
  Dry material for hygroscopic material
  Decrease fines in feedstock
Sinks Poorly filled part Increase pack pressure or pack time
  Increase gate size
  Increase backpressure for screw recovery
  Decrease melt temperature to decrease material shrinkage
  Increase melt temperature to allow greater fill
  Increase venting
Variable component mass Shot size variation Clean check ring
  Increase recovery backpressure
  Increase cushion
Voids Air entrapment Decrease injection speed
  Increase backpressure during recovery
  Increase pack pressure and pack time
Warpage Component distorts during ejection Increase cool time
Decrease mold temperature
  Better cooling in tool
Warpage Pressure gradient in component Decrease hold pressure
Weld lines Premature material solidification Increase injection speed
  Increase melt temperature
  Increase pressure for switchcover to pack control
Weld lines Gas entrapment in mold Increase venting on part and runner
  Decrease injection speed
Weld lines Premature material solidification Increase injection speed
    Increase melt temperature