Start troubleshooting by identifying the observed symptom and the equipment state. A machine alarm, a hot-material leak and a rejected molded part require different responses. Do not assume that every problem can be corrected by lubrication, clearing an obstruction or changing one setting.
Record a Useful Baseline
Keep the machine and injection-unit identity, material grade and lot, preparation, mold and cavity, approved process, alarms and the last acceptable samples. Link current part findings and available traces to the same cycle or period. Note recent changes before proposing a cause.
Identify the Part Defect
- Flash: unwanted material at a mold gap. Map the location and review tooling, support, process response and material evidence.
- Short shot: an incompletely filled part. Record the cavity, pattern, material delivery, recovery, filling and transfer information.
- Sink marks: local surface depressions. Compare their position with thickness changes and the packing and cooling records.
- Dimensional shrinkage or warpage: separate a size difference from shape distortion; state the measurement time and conditioning.
- Internal void or bubble: record location and available inspection evidence. Do not assume that every internal empty region is trapped gas; contraction-related and gas-related findings need to be distinguished.
- Weld line: a region where melt flow fronts meet during molding, rather than necessarily a joint made by a later welding operation. Review its location and specified strength or appearance requirements.
- Discoloration, dark marks or brittleness: preserve samples and review grade, preparation, contamination, thermal history and process evidence without assigning one universal cause.
Distinguish Process Trials from Repair
Use a planned trial within the material and machine limits to evaluate a process hypothesis. Define the changed inputs and the required quality results. Material substitution, tooling changes and revised recipes can affect the approved product and need their own review.
Lubricate only the points and with the products specified in the machine procedure. Access to moving parts, removal of obstructions, nozzle work, electrical checks and component replacement require the applicable competent personnel, stop and isolation arrangements. A general guide is not authorization for a do-it-yourself repair.
Verify the Result
Check repeated samples and affected cavities for the original defect and other required dimensions, appearance or functional results. Record the conditions and unresolved findings. One visually acceptable shot does not demonstrate a stable production process.
Detailed Investigation Guides
Use the flash checklist, intermittent short-shot checks, sink, shrinkage and warpage review and fault event record for the corresponding evidence.
Troubleshooting Questions
Should I Change Pressure, Speed and Temperature Together?
Use an approved investigation plan that preserves a baseline and makes the effects of changes assessable. An unrecorded group of changes can obscure the cause.
Does Removing One Surface Defect Complete Validation?
No. Confirm all relevant acceptance requirements and repeatability.
