A short shot is a part that doesn’t completely fill. Most short shots are process or tooling problems, but if the part used to fill and now doesn’t, or a thin-walled part never fills reliably, the resin may be the issue.
Check the process and tool first
- Shot size and cushion
- Melt and mold temperature
- Injection speed and pressure limits
- Blocked or undersized vents (trapped air stops flow)
- Cold or undersized gates and runners
Signs the resin is the problem
- It started with a new lot. Compare the melt flow on the new COA to the old one. A drop in MFI means a stiffer melt.
- The part is thin-walled or has long flow paths and has always been marginal.
- You switched suppliers or grades and the “equivalent” was matched on the data sheet, not on actual flow.
- The material is wet or degraded, which can change flow either way.
Material fixes
- A higher-MFI grade of the same resin. Watch the trade-off: higher flow usually means somewhat lower toughness. How to read MFI
- An easy-flow or thin-wall grade made for long flow lengths.
- Tighter lot-to-lot consistency, so the window you dialed in stays put.