A lid binds on three compacts from the same sample box. The other lids close cleanly. If the three tight lids share a cavity mark, the mark gives you a group to investigate. The useful question is which parts bind, under which assembly conditions, and how often the same pattern appears.

Build the comparison around the mating parts

Ask the molder to identify the mark and confirm the mold and revision it refers to. A number molded into the plastic could also be a part or revision code. Record the marks on both the lid and the base, the sample lot, and where in the motion the lid starts to bind. Include passing samples in the same log. Without them, a cavity that supplied most of the shipment can look disproportionately responsible.

Compare suspect lids and passing lids against the same known-good bases, then repeat with bases from the suspect group. Use compatible revisions and keep the assembly method the same. If the problem follows the lid across several bases, measure the lid features that actually meet the base. If it occurs only with one pairing, look at the combined clearances and how the components seat. Where production samples are available, repeat the comparison across multiple parts from each group.

A pattern tied to one cavity helps narrow inspection to dimensions, surface condition, or process history associated with that cavity. Decoration thickness or assembly sequence may still account for the result if those changed with the sample group. Photograph the contact area and agree on a measurable acceptance check before requesting a tooling change. The SamBound packaging catalog is available at sambound.com.

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