What a short shot tells you
A short shot is an incomplete part caused by the cavity failing to fill before the melt freezes or the machine reaches its limits. The missing area is often at the end of flow, but the root cause may be upstream in the shot size, runner, gate, material condition or venting.
1. Start with the machine and material
Confirm that the actual shot size, cushion and transfer position are stable. Check hopper loading, material level and whether the selected grade matches the job. Moisture-sensitive resins should have a verified drying history. A cold slug, blocked nozzle or inconsistent check ring can also reduce the amount of melt reaching the cavity.
2. Check the flow path
Inspect the nozzle, sprue, runner and gate for restriction or premature freezing. A cold mold or low melt temperature increases viscosity and can make a previously stable process short-shot. Compare the defect with a fill-only study if the machine supports one. This shows whether the problem occurs before or after the packing stage.
3. Air and process checks
Trapped air at the last-fill region can stop the flow or create a burn. Clean and verify vents, especially after a mold has been polished or modified. Increase injection speed carefully only after confirming that the mold can vent safely. Raising pressure without checking the flow path may hide a restriction and increase flash risk elsewhere.
Record the corrective change that restores filling, then challenge the process with several cycles and a part-weight check. A short shot that disappears for only one cycle is not a stable correction.
How to use this guide
This page is designed to explain the relevant material, process, decision point or failure mode in practical terms. It is meant to support understanding, not replace a current supplier datasheet, process validation, regulatory requirement or engineering sign-off.
Typical material behavior, common process logic, defect patterns, material comparisons and practical decision framing.
Exact product specifications, grade-specific values, regulatory opinions, food-contact validation or factory-specific trials.
Before a production or commercial decision is made, check the exact grade, processing window, standards and local rules that apply to your application.
What to record during a short-shot investigation
Record shot size, cushion, transfer position, peak pressure, fill time, melt temperature and mold temperature. Also note the cavity location of the missing area. These observations separate a material or machine problem from a restricted gate, poor vent or unbalanced runner.