A drawing specifies the part; a quality agreement specifies how the part will be proven. Programmes that rely on the drawing alone discover at the receiving dock that two suppliers met the same drawing differently, and the difference was never a dimension. The quality agreement is the cheapest risk control in a plastics programme, and it works only when it states what will be measured, by whom, and what happens when it fails.
What belongs in the agreement
Six clauses carry most of the value. The first is the specification hierarchy: drawing first, then the referenced standards, then the agreed deviations, so there is one answer when documents conflict. The second is the inspection plan: which characteristics are controlled at the moulder, which at the buyer, and which by a third party, with the sampling plan stated. The third is the documentation set per lot: what travels with the goods, typically a lot card with material, process and measurement data. The fourth is the change control: no material, colour, tool or process change without notification, because an undisclosed change is the failure mode this clause exists for. The fifth is the nonconformance route: containment, disposition and the cost boundary. The sixth is the retention: how long the moulder keeps reference samples and records.
| Clause | Question it answers | Common gap |
|---|---|---|
| Specification hierarchy | Which document wins | Two revisions of the same drawing |
| Inspection plan | Who checks what, how often | 100 percent at buyer, nothing at moulder |
| Lot documentation | What proves the lot | Certificate without measurement data |
| Change control | When the buyer is told | Silent resin grade substitution |
| Nonconformance route | What happens on failure | Sorting cost dispute after the fact |
| Retention | How long records live | Reference sample discarded early |
Change control is the clause that pays
If only one clause survives negotiation, make it change control. The expensive failures in plastics programmes are not the parts that were made wrong; they are the parts that were made right against a specification that quietly changed. A resin grade substitution, a colourant switch, a tool refurbishment that moved a gate, a move to a second cavity in the same tool: each of these can produce parts that pass the drawing and fail the programme, and each is invisible without a notification obligation. The clause should name the change categories and require written notification before the changed material ships.
Writing one a moulder will sign
The agreements that get signed are short, specific and reciprocal. They name the characteristics that matter with their tolerances rather than referencing the whole drawing, because a moulder who reads a hundred control points applies none of them. They state the sampling plan the buyer will actually run, because an inspection clause the buyer cannot staff is theatre. And they put the cost boundary in numbers before the failure, because the argument about who pays for sorting is unwinnable after the container has landed.
Where it fits in the programme
The agreement is signed at qualification, not at the first order, and it is reviewed at the first production lot rather than filed. The reference samples from that lot, signed by both sides, are what the change-control clause compares against for the life of the programme, and a programme without signed reference samples is negotiating from memory the first time a lot is disputed.
Related reading
Our bagged and kitted parts programme with lot traceability shows the lot-documentation clause in production, the third party inspection guide covers the external option, and the sample approval process note covers the qualification step before the agreement is signed.
Related product categories
The materials and part types discussed above are grouped in our sourcing directory:
