Short Shot / Incomplete Fill
Causes, Solutions & Prevention in Injection Molding
Short shot is failure to completely fill the mold cavity during injection.
Below you will find general information about this defect. To get a pinpoint solution tailored to your specific machine, material, and process parameters using the world’s most comprehensive injection molding troubleshooting database — sign up and access AI-powered troubleshooting, 7 engineering calculators, and detailed project tracking.
🔍Symptoms & Visual Identification
⚠️Root Causes by Category
⚙️ Process
- Cushion at zero
- Shot size too small
- Injection speed too low
- Barrel temperatures too low
🔲 Mold
- No vent at last-fill point air trap blocks fill
- Gate runner sprue undersized
- No cold slug well
- Mold temperature too low
🧪 Material
- MFI too low high viscosity
- Material not dried steam pockets
- Non-uniform granule size
📋 General
- Complex geometry with no flow leader ribs
- Jetting effect material sprays into cavity
✅Solutions & Corrective Actions
⚙️ Process
- Check cushion first fix if zero
- Increase shot size in 2% increments
- Raise injection speed
- Increase barrel temperatures zone by zone
🔲 Mold
- Add vent at last-fill point CRITICAL
- Enlarge gate runner sprue
- Add cold slug well
- Increase mold temperature
- Add flow leader ribs on reverse side
📋 General
- Jetting reduce speed gate must direct material at wall
- Add lubricant additive for better flow
🛠Step-by-Step Troubleshooting
Check Process Parameters
Check cushion first fix if zero
Inspect the Mold
Add vent at last-fill point CRITICAL
Verify Material Condition
MFI too low high viscosity
❓Frequently Asked Questions
What causes short shot / incomplete fill in injection molding?
Short Shot / Incomplete Fill is caused by several factors including: Cushion at zero; Shot size too small; No vent at last-fill point air trap blocks fill; Gate runner sprue undersized; MFI too low high viscosity; Material not dried steam pockets.
How do you fix short shot / incomplete fill in injection molding?
Start by checking key parameters: Injection pressure, Shot size / cushion, Melt temperature, Injection speed. Check cushion first fix if zero
Which plastics are most affected by short shot / incomplete fill?
Common materials include: PC, PA6-GF30, PPO, PPS, LCP. Pay special attention to drying, shrinkage and mold temperature for each grade.
How do I prevent short shot / incomplete fill in future production runs?
Prevention relies on three pillars: (1) process optimisation — verify Injection pressure, Shot size / cushion; (2) mold maintenance — check gates, vents and cooling channels; (3) material control — ensure correct drying and virgin/regrind ratio.
What is the difference between short shot / incomplete fill and similar defects?
Part is partially formed. Thin sections or far-from-gate areas not filled. Part is lighter than normal. This distinguishes it from related surface defects during visual inspection.
📐Related Calculators
Run these engineering calculators to verify your process parameters and prevent this defect.
🔗Related Defects
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