An observed molding defect can have several causes. Begin with a documented, previously accepted process if one exists, the selected grade’s processing data and the machine documentation. Do not treat a general symptom list as an instruction to increase pressure, speed or temperature.
Record the Defect and the Conditions
Identify the affected cavity, feature and stage, when the problem began and what changed. Keep representative samples and record material lot, conditioning, machine and screw configuration, tooling, cycle, inspection results and relevant process trends.
Checks for Common Symptoms
- Short shot: review material supply, actual shot and cushion behavior, filling conditions, flow path, gates and vents, and any machine or tooling limit. Establish the cause before selecting a change.
- Flash: review the parting line, mold condition, insert location, clamping and filling/packing behavior. More clamping force is not a universal remedy.
- Burn marks or discoloration: review material condition, residence and thermal history, contamination and venting. Confirm the relevant grade and process limits.
- Sink or voids: review geometry, gating, packing/holding behavior and thermal conditions with the tooling and material requirements.
- Warp or dimensional variation: review actual dimensions and measurement conditions, material variation, filling/packing, thermal balance, demolding and any post-molding conditioning.
Use a Controlled Investigation
Check measurement validity and maintenance condition before attributing a result to a setting. Work within the approved machine, mold and material limits. Document the proposed change, rationale, trial conditions and acceptance criteria; preserve the accepted setup and compare resulting samples and process records.
Verify the full component and relevant performance after a change, not only the appearance of one symptom. Record accepted-part output and rejects under stated conditions rather than assuming that a shorter cycle improved production.
Frequently Asked Questions
Should Final Pressure Always Be Set to 100% of Primary Pressure?
No. Pressure definitions, control stages, material and tooling vary. There is no universal pressure ratio or fixed setting supplied by this article.
Should Every Short Shot Be Fixed with Higher Speed and Pressure?
No. Material supply, flow restrictions, venting, measurement, machine limits and tooling condition can require different responses. Identify the cause and confirm the applicable limits first.
For terms and units, see the cycle and parameter guide. For a project review, prepare the part, material and mold checklist. This guide does not replace model-specific service or operating procedures.
