TL;DR

Part dimensional variation is usually a holding pressure drift, a cooling time change, or a mold temperature non-uniformity. Check shot weight consistency and mold temperature first.

What you might see

part dimensions outside specification on CMM or go/no-go gauge
shot weight variation above 0.5% between shots
sink marks or warpage on critical part features
part dimensions trending over time during the production run

Likely causes

Tap to mark as ruled out

Holding pressure or holding time drift from servo parameter shift
Mold cooling channel scale buildup causing non-uniform mold temperature
Resin lot viscosity change between batches altering fill and pack behavior
Check ring wear allowing backflow during packing, reducing pack pressure

Required tools

Precision balance for shot weight measurement
Contact thermometer or mold temperature data logger
CMM or dimensional gauges per part print
Mold cooling flush kit

Safety first

The mold surface temperature during production can exceed 100 degrees C for engineering resins. Use insulated gloves when inspecting the mold or handling parts immediately after ejection.
Medical device components require GMP documentation of all process changes. Record all parameter changes and any material deviations in the batch record.

Procedure

7 steps · ~60 min

1
Weigh 10 consecutive shots and calculate the shot weight mean and standard deviation. Variation above 0.5% indicates a process inconsistency.[1]
2
Review the holding pressure and holding time set-points against the validated process record. Correct any deviation.
3
Check the mold temperature at the inlet and outlet of each cooling circuit with a contact thermometer or mold temperature sensor. A delta above 5 degrees C between circuits indicates a blocked channel.
4
Flush or descale any blocked cooling circuit following the mold maintenance procedure.
5
Check the melt temperature consistency by measuring the cushion position on consecutive shots. Inconsistent cushion indicates check ring wear.[1]
6
Replace the check ring assembly if cushion variation exceeds the specification.
7
Verify the resin lot viscosity if a new material lot was introduced. Run a new viscosity-curve and adjust injection speed if needed.

Sources

Sumitomo SHI Demag Sumitomo IntElect Med Medical Injection Molding Machine general technical documentation, Sumitomo SHI Demag
Sumitomo IntElect Med injection molding machine general process optimization and mold maintenance procedures (general)

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