Quick answer
An injection molding quotation is only comparable line by line. Ask every supplier to quote the same five blocks — tooling, part price, secondary operations and assembly, packaging and logistics, and commercial terms — and to state the assumptions behind each one: resin grade, shot weight, cycle time, cavity count, tool life, MOQ, and who pays for engineering changes. A quotation that cannot be decomposed into those blocks is a price, not an offer, and the cheapest number on the page is usually the one with the most assumptions hidden inside it.
Most sourcing decisions in this industry are made on a single number: the unit price. That number is the end of a long chain of engineering and commercial assumptions, and two suppliers can quote the same part at €1.84 and €2.37 with both of them being honest. The difference is not usually greed. It is cavity count, resin grade, cycle time, inspection level, and whether the tool is quoted to last 300,000 shots or 1,000,000.
This guide is written for buyers and program engineers who receive three or four quotations for an automotive interior plastic part and need to decide which one is actually lower cost. It walks through each block of a quotation, what the numbers should look like, and the questions that turn a price sheet into a comparable offer.
Block 1 — Tooling: the block that decides the part price
Tooling is quoted once and paid once, but it sets the part price for the life of the program. Three parameters in the tooling block drive everything downstream:
| Parameter | Why it changes the part price | What to ask |
|---|---|---|
| Cavity count | Doubling cavities roughly halves machine time per part but raises tool cost 60–90% and increases tonnage | How many cavities, and what annual volume did you assume to justify it? |
| Tool life / steel grade | A P20 tool and a hardened H13 tool are both "a mold" and differ by a factor of two in cost and service life | What is the guaranteed shot count, and what is the maintenance plan to reach it? |
| Hot runner vs cold runner | Hot runner removes runner scrap and shortens cycle on thin walls, at the cost of a higher tool and higher maintenance | Is the runner system included, and who owns the controller? |
Two details are worth insisting on in writing. First, the tooling quotation should state whether it covers T1 samples, correction loops, and the checking fixture. A tool quoted €12,000 lower than the others frequently excludes two correction loops and the fixture, which then arrive as change orders. Second, it should state the ownership and delivery terms of the tool: an automotive buyer who does not hold title to the mold has an expensive dependency rather than an asset.
The practical test: for a program of 40,000 parts per year over four years, the tooling block is typically 6–12% of total cost of ownership. A 20% difference in tooling is worth less than a 5% difference in part price, and far less than one unplanned tool repair that stops a customer line.
Block 2 — Part price: five inputs, not one
A part price quoted as a single figure cannot be audited. Ask for the build-up in these five inputs, which are the same five the supplier uses internally:
- Resin grade and price basis — not "PP" but the grade and the price date. PP homopolymer, PP copolymer with talc, and PC/ABS sit in different price bands, and resin is commonly 45–65% of the part price. A quotation that does not name the grade is not a quotation for a defined part.
- Shot weight including runner — the material consumed per cycle, not the finished part weight. On a cold-runner tool the runner can add 15–30%.
- Cycle time — in seconds, with the assumed wall thickness. Cycle time is the single largest lever on machine cost per part and the parameter most often optimised on paper rather than in the tool.
- Machine hourly rate and tonnage — a 250 t machine and a 1,300 t machine are not interchangeable, and the quoted tonnage should match the projection area and clamp force requirement.
- Yield and scrap allowance — the percentage built in for start-up, rejects, and colour changes. Ask whether scrap is charged at full part price or at material cost.
A useful sanity check that any buyer can run without a supplier's data: divide the part price by shot weight. For unfilled PP interior parts in the 100–600 g range, a material-plus-conversion ratio outside roughly 1.8–3.2 times the raw material cost per kilogram signals either a very small volume, a very complex tool, or an assumption that has not been disclosed.
Block 3 — Secondary operations and assembly
On interior trim, the moulded part is often not the delivered part. The quotation must list, as separate lines with separate prices, everything that happens after ejection:
- Deflashing, trimming, and gate removal (manual vs fixture-based)
- Grain or texture repair, and any post-mould texturing on class-A surfaces
- Painting, soft-touch coating, or laser etching
- Ultrasonic welding, heat staking, or clip and fastener insertion
- Sub-assembly with foam, fabric, or electrical components
- Functional and cosmetic inspection, and whether it is 100% or AQL sampled
These lines are where quotations most often diverge without appearing to. A supplier who quotes 100% cosmetic inspection against a boundary sample is quoting a genuinely different product from one who quotes AQL 2.5 visual sampling, and the difference can be 8–15% of the part price. Neither is wrong; the buyer needs to know which one the assembly line will accept.
Block 4 — Packaging and logistics
Interior parts are large, light, and easily scratched, which makes packaging a real cost rather than a rounding error. The quotation should state the pack quantity per carton or returnable rack, the packaging type (expendable carton, returnable EPP tray, or bulk), and the Incoterm. A supplier quoting FOB with expendable cartons and a supplier quoting DDP with returnable racks are quoting two different supply chains, and the difference in landed cost per part is frequently larger than the difference in unit price.
Ask also for the container loading quantity. For bulky interior components, freight is often limited by volume rather than weight, and a design or nesting change that fits 12% more parts per container is worth more than a 3% price reduction.
Block 5 — Commercial terms that change the total
| Term | What to pin down | Typical trap |
|---|---|---|
| MOQ and lot size | Minimum order quantity and minimum lot per run | A low unit price that requires 20,000 parts per run against a 4,000-part annual demand |
| Price validity | How long the resin price basis holds | A 90-day validity on a four-year program |
| Resin price adjustment | The index and the pass-through formula | A one-way clause that adjusts upward but never down |
| Payment terms | Tooling milestone schedule and part payment terms | Full tooling payment before T1, with no acceptance milestone |
| Engineering change | The hourly rate and minimum charge for ECN work | No rate quoted, so every change is negotiated from zero |
| Warranty and PPM | The quality target and the cost of containment | No stated PPM commitment, and no agreement on who pays for a sort |
A comparison method that survives a review meeting
Score the quotations on landed cost per part over the program life, not on unit price. The formula is short enough to build in a spreadsheet in ten minutes:
Landed cost per part = (tooling + validation + packaging development) ÷ program volume + part price + secondary operations + freight per part + expected cost of quality escapes.
The last term is the one buyers omit and the one that decides programs. If a supplier's PPM history is unknown, use the cost of one containment event — a sort at the customer, an expedited replacement shipment, a line-stop penalty — and multiply it by the probability of occurrence. On a program with 40,000 parts a year, a single line stop at a tier-one customer usually exceeds the entire annual saving from a 3% price difference.
Red flags on the page
- No resin grade named. The part is undefined, so the price is undefined.
- Tooling quoted without a shot-count guarantee. You are buying an object, not a capability.
- No cycle time and no cavity count. The two numbers that determine the part price are missing.
- One total for "samples and production". T1, correction, and PPAP are different deliverables with different costs.
- Identical prices across parts of different size and complexity. Usually a copy-paste quotation, and usually a sign nobody reviewed the drawing.
- A price far below the others without an explanation. Either the grade, the cavity count, or the inspection level is different from what you asked for.
What a good quotation looks like
A quotation that can be compared has four properties: it repeats the drawing revision it was priced against, it names the resin grade and the price date, it separates tooling from part price from secondary operations, and it states its MOQ, validity, and change-rate assumptions. Everything else is negotiation; those four are the offer.
We quote automotive interior programs this way because it is the only version of a quotation that survives a supplier-quality audit and a cost-down review eighteen months later. If you are comparing quotations for a door panel, a side guard strip, or a wiring harness bracket, the fastest way to shorten the comparison is to send us the drawing pack and let us return the same five blocks, line by line.
Comparing quotations for an interior plastic part? Send the drawing, the annual volume, and the target vehicle programme. We will return a quotation broken into tooling, part price, secondary operations, packaging, and commercial terms — with the resin grade and cycle time stated, so it can be put next to the others line by line. Request a quotation or review the Auto Parts range we currently mould.
Related reading
- How to Read a Drawing and Set Tolerances That Actually Hold — the drawing pack that any quotation should be priced against.
- PP, ABS or PC/ABS? Choosing Material for Automotive Interior Parts — how the resin grade named in Block 2 changes the part price.
- From DFM to PPAP: The Mold Development Workflow — what the tooling block is actually paying for.
- OEM, ODM or Private Label: Who Owns the Mold, the Drawing and the Part — the ownership terms to settle before tooling is released.