Plastic Injection Troubleshooting

Below is a list of plastic injection defects. This troubleshooting guide offers some potential ways to correct the defect listed. Adjustments might require that one, several or all of the changes listed.Before making adjustments, CLEAN MOLD and verify fill only shot is at 95-98% with no pack or hold applied. Adjustments should always be made with an understanding of why the change is being made, and that other defects might occur. If in doubt, ask a process engineer or technical support employee for best practice. This is a primary list, and does not offer all solutions for defect correction. For in-plant consulting, contact Garrett MacKenzie at:
    • PHONE: 404-793-9834

    Parts for review can be mailed to:

    • Garrett MacKenzie 2103 Willow Shore Drive SE
    • Suite 201 Kentwood, MI 49508


    • Examine mold for parting line damage
    • Clean mold and vents
    • Verify that process has been decoupled
    • Lower hold pressure
    • Raise Cut-off
    • Slow injection speed in area of fill
    • Lower melt temperature (Refer to MSDS for melt range prior to change
    • Increase tonnage
    • Lower mold temperature
    • Use bluing agent to verify parting line seal off


    • Check material moisture content
    • Verify melt Temperature is within melt temperature window, as established by MSDS supplied by material manufacturer
    • Check mold for water/ oil leak
    • Slow down injection speed overall, or in area of fill
    • Inspect nozzle tip for damage
    • Lower heat profile
    • Reduce back pressure
    • Check material for over drying
    • Inspect nozzle tip for proper size
    • Check for consistent cushion (cracked/ damaged check ring)
    • Check mold for signs of damage/ burring


    • Apply cooler mold temperature to warp face. Molecules will move away from cold side towards heat
    • Longer cool time to allow part to set in mold longer
    • Review water circuit set up. Measure mold steel temp to review large swings in mold temperature
    • Review mold open and ejection process for signs of part sticking

    Part Sticking

    • Slower Breakaway speed
    • Reduce pack/ hold pressure
    • Verify mold is clean, and free of gas build up
    • Slow ejection speed, increased ejection pressure
    • Inspect mold for tool damage

    Color Too Light or Dark

    • Verify colorant ratio
    • Too dark, decrease mold temp. Too light, increase mold temp.
    • Too dark, lower barrel temperature. Too light, increase barrel temperature
    • Too light, increase pack/ hold. Too dark, decrease pack/ hold pressure
    • Verify material has not been overdried
    • Verify regrind percentage isn’t too high

    Length/ Dimensions

    • Too small or short is a sign of excessive shrink. Longer cool time, or lower mold/ barrel temperatures can correct condition
    • Too big or long can be sign of low shrink rate. Faster cycle, or higher mold/ barrel temps can correct condition
    • Increasing pack/ hold pressures can reduce part shrinkage. Decreasing pack hold pressures can increase part shrinkage

    Voids/ Bubbles

    • Over pack condition. Molecules are too densely packed causing a resistance condition. Reduce pack/ hold to correct
    • Under pack condition. Fill speeds too slow, or hold/ pack to low, causing gas to be trapped due to a failure to force gas from cavity through vents. Increase fill speed or higher pack/ hold to correct
    • High moisture content. Verify material has been correctly dried

    Lamination (Flaking)

    • Contaminated material
    • Regrind percentage too high
    • Material overdried

    Ribs/ Details Sticking

    • Inspect for tool damage
    • Melt temp too low, leading to increased packing of rib/ detail
    • Injection speed too low, causing rib/ detail to be overpacked
    • Ejection speed/ pressure too high
    • Check material moisture

    Contamination/ Color Swirl

    • Poorly purged hot runner
    • Material overdried
    • Contaminated material
    • Tool/ tip damage causing shear
    • dirty nozzle tip
    • cracked check ring
    • Poorly purged barrel
    • screw- carbon deposits
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Plastic Injection Expert Network