Quick answer: Buying from an OEM plastic case manufacturer means buying execution, not ideas. Once the drawing is frozen, four things belong in the contract: who owns the tool, which 18 dimensions sign off the first article, whether a material change forces re-approval, and how tooling and payment are carried.
Table of contents
- Quotation Breakdown for an OEM Plastic Case Manufacturer
- Tooling Ownership and Drawing Freeze
- First-Article Approval and Process Discipline
- Lead Time, Payment Terms and Quote Traps
- FAQ
1. Quotation Breakdown for an OEM Plastic Case Manufacturer
A thin drawing package produces a guessed price. The enquiry pack is three documents: frozen drawings, technical conditions, acceptance criteria. They must state an external size of 585 x 420 x 230 mm, a 3.2 mm wall, a finished weight of 6.4 kg, and IP67 to IEC 60529: 1 m of still water, 30 minutes, no ingress. Drop and vibration follow MIL-STD-810H methods 516.7 and 514.7.
Then the quotation from an OEM plastic case manufacturer has to be itemised.
| Quotation line | Basis | Deliverable | Usual omission |
|---|---|---|---|
| Tooling | Per set, by cavities | Tool drawing, cavities | Frame parts excluded |
| Trials | Per trial | Samples, size report | Fourth trial charge |
| Moulding | Per piece, machine hour rate | Moulded part only | Runner scrap |
| Secondary ops | Per operation | Drilling, tapping, printing | Operations merged |
Resin stays separate. PP copolymer at 9.2 CNY per kg on a 6.4 kg case is about 59 CNY, half the unit price; a flame-retardant grade adds 23. A quote with no grade or shot weight is a bundle.
2. Tooling Ownership and Drawing Freeze
For an OEM plastic case manufacturer, who pays for the tool decides the position three years later. A single-cavity tool runs 98,000 CNY and is never buried in the unit price. The contract carries a tool schedule: tool number, cavity count, cavity steel, weight, storage bay. Invoice, acceptance sheet and schedule together form the ownership record. The tool stays in the supplier's plant, inspected every 5,000 shots, records handed over on transfer. Design life is 500,000 shots; who pays for new cores beyond that is written down. If the programme stops, the buyer gives 30 days' notice and collects the tool.
Drawing freeze means a version number, a stamp and a file. This project sits at revision V1.3, every change runs through a numbered ECN, and tool modification is charged at 180 CNY per hour.
3. First-Article Approval and Process Discipline
A first article is not a sample. It is a chain of evidence that can be reproduced.
- Report: 18 critical dimensions measured, tolerances at plus or minus 0.3 mm
- Material certificate: grade, lot and melt flow index matching the drawing
- Parameter card: melt and mould temperature, packing pressure, cooling time locked
- Colour: against the signed master, difference no greater than 1.5
- Signed samples: two pieces, one kept at the plant, one shipped
- Patrolling check: five pieces every 2 hours, wall thickness recorded
Process discipline reduces to one line: nobody changes a parameter alone.
Raise the melt temperature from 215 to 230 degrees Celsius and the part fills more easily while warp grows. Drop the mould temperature by 5 degrees Celsius and the cycle shortens by 8 seconds, but the latch gap can drift from 0.4 mm to 0.7 mm. So a material change, a machine change, a tool repair, or any stoppage over 4 hours triggers a fresh first article at an OEM plastic case manufacturer. Writing that into the quality agreement beats arguing after a reject.
4. Lead Time, Payment Terms and Quote Traps
Lead time counts from the day the drawing is frozen, not the signing date. Tool build takes 22 days, the T1 trial 3, first-article approval 5 and production 12, 42 days in total. Compress a block and the schedule must show which task was displaced; removed time returns as rework.
Payment terms run 30 percent deposit, 60 percent before shipment and 10 percent within 30 days of acceptance. Ratios are negotiable; the order is not.
Four traps cover most of the gap:
| Trap | How it appears | What to do |
|---|---|---|
| Tooling amortised | Low piece price, tool written off over years | Keep tooling on its own line |
| Trials unbounded | Trials included, count unstated | Fix the first three in the fee |
| Secondary ops bundled | Drilling, tapping, printing as one price | Split and price each step |
| Working-day lead time | 42 days written as 42 working days | Use calendar days |
Ask those four and the cost structure surfaces. The hard part is never the unit price but the unwritten items at volume. An OEM plastic case manufacturer that puts the tool schedule, first-article report and ECN log on the table beats two points of discount.
Conclusion
Build-to-print sourcing tests one skill: translating drawing language into settlement language. Tool ownership, first-article approval, process discipline and payment terms each need a record; a missing one becomes an argument at volume. Put the 18 dimensions, the 42-day chain and the 30-60-10 rhythm in the contract, and prices become comparable. Choosing an OEM plastic case manufacturer is really choosing a partner that keeps evidence.
This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.
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