TL;DR
Short shots are usually insufficient injection speed, a cold or blocked gate, or insufficient shot volume. Check the gate temperature and injection speed profile before increasing hold pressure.
What you might see
- incomplete part visible after mold open
- parts missing thin-wall features
- shot weight consistently below nominal
- melt temperature lower than set-point
Likely causes
Injection speed too low for the part geometry and resin viscosity
Gate temperature too cold, causing premature freeze-off before fill is complete
Shot size set too small, leaving insufficient material for the part and runner
Barrel temperature too low causing high melt viscosity and resistance to flow
Required tools
- Precision balance for part weight
- Melt temperature probe or pyrometer
- Resin processing datasheet
Safety first
- The mold and nozzle area are at melt temperature. Use heat-resistant gloves and face shield when manually purging the barrel or inspecting the nozzle.
- Do not reach into the mold space while the machine is in automatic mode. Engage the mold protection interlock before any manual mold inspection.
Procedure
- 1
Weigh a short-shot part and compare to the full-part weight to estimate the missing volume.
- 2
Verify the barrel temperature set-points against the validated process record and the resin datasheet recommended processing range.[1]
- 3
Increase barrel temperature by 5 degrees C increments if it is below the lower processing limit. Allow 3 cycles to stabilize after each change.
- 4
Review the injection speed profile. Increase the speed in the thin-wall or last-to-fill section of the profile.
- 5
Check the hot runner or gate temperature set-point (if applicable). Increase the gate temperature by 5 degrees C if the gate is frequently freezing before fill.[1]
- 6
Verify the shot size and cushion on the machine display. Increase the shot size by 1 to 2% if the cushion reaches zero before pack is complete.
- 7
Run 5 shots after each change and inspect parts visually before measuring dimensions.
Sources
Sumitomo SHI Demag Sumitomo IntElect Med Medical Injection Molding Machine general technical documentation, Sumitomo SHI Demag
Sumitomo IntElect Med injection molding machine general fill study and barrel temperature optimization (general)
More guides for Sumitomo SHI Demag Sumitomo IntElect Med
How to fix flash defect on parts from a Sumitomo IntElect Med injection molding machine
Flash is usually excessive pack pressure or clamping force loss from mold wear or incorrect set-point. Verify clamping force and pack pressure before inspecting the mold parting line.
How to fix part dimensional variation on a Sumitomo IntElect Med injection molding machine
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.
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