Troubleshooting Insufficient Clamping Force in Plastic Molds
Insufficient clamping force causes flash, overflow, oversized parts, and mold damage. Many flash issues are mistakenly solved by increasing clamping force without identifying the real cause. This article provides a step-by-step method to diagnose and resolve insufficient clamping force.
Confirm True Clamping Force Shortage
Genuine flash from low clamping force:
Appears on parting lines, slides, inserts
Worsens with higher holding pressure
Improves significantly on larger machines
Local flash near gates may be caused by high temperature or speed, not clamping force.
Clamping Force Calculation and Setting
Basic formula:Clamping force (tons) = Projected area (cm²) × Cavity pressure (300–500 kg/cm²) / 1000
Set clamping force to the minimum value that eliminates flash, not maximum.
Step-by-Step Adjustment Procedure
Check clamping force setting on the controller
Recalibrate clamping force
Verify mold closing position and high-pressure locking
Check parallelism and cleanliness of parting surfaces
Increase clamping force gradually until flash disappears
Parallelism and Uneven Pressure
Uneven clamping often causes flash on one side. Clean mold mounting surfaces, align mold center, and adjust tension evenly on four tiebars.
Mold-Related “False” Flash Issues
Flash may occur even with sufficient clamping force due to:
Particles or dirt on parting surfaces
Worn slides or inserts
Insufficient mold support or stiffness
Excessively deep vents
These require mold maintenance, not machine adjustment.
Process Optimization to Reduce Clamping Demand
Lower barrel temperature, reduce injection speed, decrease holding pressure, and optimize fill profile to reduce cavity pressure.
Machine Capacity and Safety
Ensure mold projected area matches machine rating. Avoid continuous operation above 85–90% of rated clamping force.
Conclusion
Effective troubleshooting requires distinguishing real clamping force issues from mold or process problems. Correct calibration, parallelism, mold condition, and parameter settings eliminate flash while protecting molds and machinery.
