Injection Molding in China: Tooling Costs, T1 Samples, and DFM

Injection molding projects in China succeed or fail on decisions made before any plastic is molded: the tool steel, the cavity layout, the DFM review, and the contract language on mold ownership. This guide explains what actually drives tooling cost, how to read a DFM report critically, what the T1 and T2 sampling process should look like, and which clauses must be in writing before you pay a tooling deposit.

What You Are Actually Paying For in a Mold

A quotation line that reads "tooling: one injection mold" hides a long bill of materials and labor. Understanding the components lets you compare quotes on substance rather than on the bottom-line number.

• Mold base and core/cavity steel. The mold base is largely standardized, but the core and cavity inserts — the parts that form your geometry — are cut from tool steel whose grade drives both cost and tool life. P20 is the baseline pre-hardened steel for moderate volumes. 718 (a nickel-improved P20 family steel, often listed as 718H) polishes better and lasts longer. S136 is a hardenable stainless tool steel used for high-polish surfaces, optical parts, medical work, and corrosive resins such as PVC. Hardened steels like H13 appear when glass-filled resins will abrade the tool. Each step up this ladder adds material cost and machining and heat-treatment time.
• Cavitation. A single-cavity tool molds one part per cycle; a 4-cavity or 8-cavity tool multiplies output and tooling cost together, requiring more insert machining, a balanced runner system, and a larger mold base and press.
• Runner system. A cold runner is simple and cheap but produces runner waste each cycle and can limit gate placement. A hot runner system keeps the melt channel heated, eliminating runner waste and improving cycle time, but the manifold and hot tips are precision purchased components that add substantially to tool cost. For high-volume production the hot runner usually pays for itself; for short runs it rarely does.
• Actions and mechanisms. Undercuts require sliders, lifters, or unscrewing mechanisms, each adding machined components, fitting labor, and lifetime maintenance. Redesigning a part to eliminate one slider is often the cheapest engineering hour you will ever spend.
• Surface finish and texture. Mirror polishing (for example to SPI A-level finishes) and chemical etching of textures are skilled manual or subcontracted processes billed on top of the base tool.

Why Tooling Quotes Span Orders of Magnitude

Quotes for "a plastic part mold" can differ by ten times or more between suppliers. The spread is usually rational once you decompose it.

1. Tool life class. A soft aluminum or P20 prototype tool guaranteed for a few thousand shots and a hardened production tool warranted for hundreds of thousands of shots are different products that happen to mold the same part. Ask every bidder to state the guaranteed shot life in writing.
2. Cavitation and runner assumptions. One bidder quotes 1-cavity cold runner, another 4-cavity hot runner. Fix these parameters in your RFQ or the quotes cannot be compared.
3. Steel and standard components. Imported steel and brand-name hot runner systems, ejector components, and interlocks cost more than domestic equivalents. Neither choice is wrong, but you should know which one you are buying.
4. Who carries the engineering risk. Some shops quote assuming your part is moldable as drawn; others include the DFM iterations, gate trials, and texture samples they know from experience the job will need.
5. Factory positioning. A precision mold maker serving medical and connector customers has a cost structure and quality system that a general-purpose shop does not. If your part is a simple enclosure, you may be paying for capability you do not need; if it is a tight-tolerance gear, the cheap quote is the expensive one.

Shortlisting suppliers whose existing customer base matches your part complexity — visible in the equipment lists and product photos on profiles in the rubber and plastic products sector — narrows the spread before you ever request numbers.

Reading the DFM Report

Before cutting steel, a competent supplier issues a design-for-manufacturing report. Treat it as an engineering document to be reviewed, not a formality to be approved. Focus on these items.

• Draft angles. Every face parallel to the direction the mold opens needs draft, typically at least 1 degree, and more on textured surfaces because texture depth increases the draft needed for clean ejection. The DFM should mark every zero-draft face and propose a value; your job is to confirm the added taper does not break fit with mating parts.
• Wall thickness uniformity. Thick sections cool slowly and sink; abrupt thickness changes cause warpage. The report should flag sections outside the resin supplier's recommended range and propose coring-out. Ribs are conventionally kept to roughly half to two-thirds of the adjoining wall to avoid sink marks on the cosmetic side.
• Sink and void risk. Bosses, rib junctions, and thick lettering are the usual suspects. A good DFM shows the specific locations, often with mold-flow simulation images, and offers concrete fixes rather than a generic warning.
• Gate location and weld lines. The gate position determines where weld lines (knit lines) form and where gate vestige appears. Confirm the vestige lands on a non-cosmetic surface and weld lines avoid high-stress or sealing areas.
• Ejection and undercut handling. The report should show ejector pin locations (their witness marks are permanent) and how each undercut is released. If a proposed slider surprises you, that is the moment to discuss a design change, not after steel is cut.
• Tolerance feasibility. Molded-part tolerances depend on resin shrinkage, which varies with glass fill, gate design, and process. Ask the supplier to identify any drawing tolerance they consider at risk and how they plan to steel-safe those dimensions, leaving material to adjust after first shots.

Respond to the DFM in writing, item by item. A supplier who receives a blanket "approved" owns none of the risk you just accepted.

T1, T2, and Sample Acceptance

The first trial of the finished mold is called T1. Expect T1 parts to be imperfect: unpolished surfaces and dimensions that need steel adjustment are normal. What matters is the discipline around the loop.

1. T1 delivers parts plus data. You should receive sample parts from each cavity, individually labeled, along with a dimensional report against the drawing and the molding parameters used. Photos and videos of the trial are reasonable to request.
2. You return a disposition list. Classify every issue: dimensional, cosmetic (polish, texture, gate vestige), and functional (fit, assembly, mechanical tests on your side). Distinguish mold corrections from process tuning; the first requires machine-shop time, the second only trial time.
3. T2 verifies the corrections. The second trial should close the specific items on your list, again with a dimensional report. Complex tools may legitimately need a T3; a tool that is still chasing basic dimensions at T4 signals a deeper problem in the tool design or the shop's metrology.
4. Define acceptance before T1. Agree in advance on the criteria that end sampling: all critical dimensions within tolerance across all cavities, cosmetic standard met on agreed surfaces under agreed lighting and viewing distance, and a capability run — for example a continuous production run of some hours — demonstrating stable cycling without operator intervention. Tie the tooling payment milestone to this acceptance, not to "T1 samples shipped."

Keep golden samples: signed, dated reference parts from the accepted trial, one set held by each party. They are the arbitration reference for every future cosmetic dispute during production, whether you later manage orders directly or through listings on product sourcing pages.

Mold Ownership: Put It in the Contract

The near-universal commercial arrangement is that the buyer pays for the mold and owns it, while the supplier possesses and maintains it for production. Custom and verbal assurances are worthless here; the tooling agreement must state the terms explicitly.

• Ownership. Name the buyer as owner of the mold upon payment, ideally with the mold permanently tagged with your name and an asset number, and photographs of the tag on file.
• Exclusivity. Prohibit using the mold to produce parts for any other party, and prohibit copying the mold or the part design.
• Maintenance and shot count. Make routine maintenance the supplier's responsibility, require shot-count records, and state the guaranteed tool life and who pays for refurbishment or a replacement tool when it is reached.
• Transfer rights. State that the buyer may take possession of the mold, with a defined handover package (the tool itself, 2D and 3D mold drawings, hot runner documentation, spare parts) and a defined preparation period. Expect friction in practice — settle any open invoices first and specify the condition the tool must be in at handover.
• Storage after production ends. Define how long the supplier must store an idle mold and what notice is required before scrapping it.

Sign the tooling agreement with the entity that actually invoices you, and verify that name against the registered company profile — a check that a structured manufacturer listing makes considerably easier than a trading company's business card.

Key Takeaways

• Tooling cost is driven by steel grade (P20, 718, S136, H13), cavitation, hot versus cold runner, undercut mechanisms, and finish — fix these variables in the RFQ so quotes are comparable.
• Always get the guaranteed shot life in writing; a prototype tool and a production tool are different products at very different prices.
• Review the DFM report item by item — draft, wall thickness, sink risk, gates, ejection — and respond in writing.
• Define T1/T2 acceptance criteria before the first trial and tie the final tooling payment to acceptance, keeping signed golden samples afterward.
• The mold ownership clause — buyer pays, buyer owns, supplier maintains, transfer terms defined — belongs in a signed tooling agreement with the invoicing entity.

This guide is editorial reference material, not legal or transactional advice. Verify supplier claims and regulatory requirements independently. See our data sources and editorial policy.