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