Most plastic sourcing problems are not caused by bad suppliers. They are caused by a specification that left something open, and by a buyer who assumed the open item would be handled the obvious way. The ten pitfalls below account for the majority of the disputes that reach a claims stage, and each one is preventable at the enquiry stage for almost no cost.
The Ten Pitfalls
1. Quoting from a photo instead of a drawing
A photo shows the shape, not the tolerances, the material or the wall thickness. Two suppliers quoting from the same photo are quoting two different parts, and the cheaper one is usually the one that assumed less.
2. Leaving the material grade open
"PP" covers homopolymer, copolymer, talc-filled and flame-retardant grades with very different mechanical behaviour. Name the grade family and the filler content, or accept whatever is cheapest on the day.
3. Comparing prices at different incoterms
An FOB quote and a DDP quote are not comparable numbers. Fix the incoterm, the port and the packaging basis before comparing. Our explanation of Incoterms 2020 covers where the cost boundary actually sits.
4. Ignoring tooling ownership
If the mould is paid for by the buyer but titled to the supplier, switching suppliers later means paying for the tool twice. State ownership and the conditions for transfer in the tooling agreement.
5. Accepting a sample that came from a different process
A CNC-machined prototype proves the design, not the mould. Production samples must come from the production tool, on the production machine, at the production cycle time.
6. No agreed inspection standard
Without a written AQL level and a defect classification, "some flash" and "unacceptable flash" are both defensible positions. Define critical, major and minor defects before the first shipment.
7. Skipping the pre-production approval run
T1 and T2 exist to expose tool corrections while they are still cheap. Buyers who skip straight to mass production discover the problem in the container.
8. Underestimating packaging and loading
Carton size, pallet pattern and container utilisation change the landed cost more than a small unit-price difference. A quote without a packing specification is incomplete.
9. No change-control clause
Suppliers substitute materials, subcontract operations and move production between plants. A clause requiring written approval before any change protects the buyer at almost no cost.
10. Verifying the company but not the capability
A business licence confirms the company exists. It says nothing about whether the plant can hold the tolerance or run the resin. Factory verification and capability verification are different exercises, as set out in our guide to verifying a Chinese factory.
A Short Checklist Before the First Order
- Drawing with tolerances, material grade and surface requirement issued in writing
- Incoterm, port and packing specification agreed in the quotation
- Tooling ownership and transfer conditions documented
- Pre-production samples approved from the production tool
- Inspection standard with AQL and defect classes attached to the PO
- Change-control and traceability clauses in the supply agreement
None of these items is expensive to add at the enquiry stage. Each one is expensive to litigate later. Buyers running a competitive process should apply the same checklist to every supplier, so the comparison is between equals — the approach described in our note on supplier verification and audit checklists.
Where the Risk Actually Sits
Risk concentrates in the gap between what was quoted and what was specified. A supplier working from a vague brief is not being dishonest when the shipment differs from expectation; the expectation was never written down. The remedy is procedural, not adversarial, and it costs one extra page in the enquiry. The broader set of sourcing guides is collected under sourcing guide, and mould-related capability questions are best put to mould makers directly.
