A short shot in injection molding happens when molten plastic does not completely fill the mold cavity. Common causes include low injection pressure, low melt temperature, restricted gates, poor venting, thin walls, long flow length, premature freeze-off, material viscosity or an unbalanced mold design.
Short shots are not only a machine setting problem. If the part has very thin walls, long flow paths, sharp transitions or blocked vents, raising pressure may not solve the root cause. A supplier should review the part design, mold design, resin flow behavior and process window together.
Common Causes of Short Shots
| Cause / material | Typical sign or use | Buyer or engineering action |
|---|---|---|
| Low injection pressure | Cavity not fully filled | Increase pressure within safe mold and machine limits |
| Low melt or mold temperature | Flow freezes before filling | Adjust temperatures according to resin and part geometry |
| Thin wall or long flow length | End-of-fill areas missing | Review wall thickness, gate location and resin flow |
| Poor venting | Gas blocks melt flow | Improve vents in end-of-fill or trapped air zones |
| Small or restricted gate | Material cannot enter fast enough | Review gate size, type and location |
Part Design Checks
- Check whether the thinnest wall can be filled with the selected resin.
- Avoid sudden wall reductions near the end of fill.
- Review ribs, windows and thin clips that restrict flow.
- Use flow simulation or DFM review for long, thin or complex parts.
- Confirm that the gate location supports balanced filling.
Material and Process Considerations
| Material / case | Main concern | Selection note |
|---|---|---|
| High-viscosity engineering plastics | Harder to fill thin sections | Review melt temperature and wall thickness |
| Glass-filled nylon | Flow and fiber orientation matter | Balance strength, flow and warpage |
| PC | Needs controlled heat and pressure | Avoid forcing poor flow with excessive stress |
| PP | Good flow but shrinkage risk | Balance fill, packing and warpage |
| TPE | Soft material behavior varies by grade | Confirm hardness and flow grade |
Buyer RFQ Details for Short Shot Prevention
For a useful review, send the 3D model or 2D drawing, resin grade or target material, part photos if the defect already exists, machine and mold information if available, expected annual volume, cosmetic requirements, critical dimensions, application environment and any inspection standard. Nylon Plastic can review the design, material and molding route before tooling or production changes are made.
Related Engineering Guides
Request a Quote or Design Review
Share your plastic part drawing, material requirements, production quantity and defect or DFM concern. Nylon Plastic can help compare material choices, tooling changes, process adjustments and production risks for custom molded plastic parts.
FAQ
What is a short shot in injection molding?
A short shot is an incomplete molded part caused when molten plastic does not fully fill the mold cavity.
What causes short shots in molded plastic parts?
Common causes include low injection pressure, low melt temperature, restricted gates, poor venting, thin walls, long flow length and high material viscosity.
Can part design cause short shots?
Yes. Very thin walls, long flow paths, sharp transitions and poorly placed gates can cause short shots even when machine settings are adjusted.
How should buyers request help with short shots?
Buyers should provide the CAD model, wall thickness, material grade, defect location, photos, target quantity and any current mold or machine information available.
