Inconsistent Shot Weight: Practical Troubleshooting Steps

Shot weight variation is one of the most useful early signals in process diagnosis. If the molded part weight is not repeating, visible defects such as short shot, flash, bubbles, and dimensional variation may be symptoms of the same unstable material or machine condition.

Quick Answer

Weigh parts before changing many settings. Use the same cavity, same trim condition, and same timing. Then compare weight variation with material feeding, recovery, temperature, pressure, and visible defects.

What You May See

• Part weight changes beyond the normal inspection range.
• Short shot, flash, bubbles, or dimensional variation appears with weight changes.
• The variation is stronger during startup, after material refill, or after changeover.
• One cavity or one station shows a different weight pattern.
• Recovery time, cushion, or pressure response changes together with weight.

Likely Cause Areas

• Material feeding may be inconsistent because of bridging, empty hopper, contamination, or moisture.
• Drying or material batch condition may change material density and flow behavior.
• Screw recovery or shot preparation may not repeat consistently.
• Temperature variation may change viscosity and fill response.
• Leakage, nozzle contact, or check behavior may affect delivered material.
• Mold resistance or insert position may cause one cavity or station to fill differently.

Safe Checks Before Adjustment

Stop automatic operation if movement, alarm, guarding, or operator safety is uncertain. Do not place hands in the mold, table, injection, or guarded area while movement is possible. Use photos, controller screenshots, cycle logs, and safe observation before changing several settings.

Diagnosis Path

1. Define a consistent weighing method before collecting samples.
2. Separate samples by cavity, table station, time, and startup or running condition.
3. Check material feeding continuity, hopper level, drying record, and batch change.
4. Review recovery time, screw position, cushion, and pressure response.
5. Check temperature alarms or drift during the sample period.
6. Compare weight change with visible defects and part location.
7. Inspect whether the issue follows one station, fixture, or mold cavity.
8. Document original settings before making one controlled adjustment.

Evidence to Collect

Check	Why It Matters	Evidence to Collect
Sample method	Consistent weighing prevents false conclusions	Same trim state, same timing, same cavity notation
Weight trend	Trend shows whether variation is random or station-based	Weight log by cavity and cycle
Material feed record	Feeding changes often create shot variation	Hopper, drying, refill, and batch notes
Recovery data	Recovery repeatability affects shot preparation	Controller screenshots and cycle observations
Defect correlation	Visible defects help identify the effect of weight change	Defect photos linked to sample weights

What Not to Change Too Quickly

• Do not compare weights from parts trimmed differently.
• Do not ignore startup samples if the problem is mainly during warm-up.
• Do not change multiple process values before measuring a stable baseline.
• Do not assume weight variation is acceptable because the part looks filled.

When to Contact Deboge

Contact Deboge when weight variation connects to recovery, pressure fluctuation, station pattern, or machine alarms. Send weight logs, defect photos, material records, machine model, controller screenshots, and recent change notes.

Related Reading

• Process Issues
• troubleshootingprocess issuesmaterial feeding problems
• Engineering Plastics
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