OEM Metal Die Casting Service: What to Check Before You Commit
This guide is for engineers and sourcing managers choosing an OEM metal die casting service. It covers the five checks that decide whether a casting project ships on time at the tolerance you specified, and when a single-source supplier is the wrong choice.
In this article
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Key takeaways
Separate vendors versus one integrated OEM metal die casting service
Each row is a decision point you can verify during a supplier audit, not a marketing claim.
| Check point | Separate die caster + CNC shop | Integrated OEM metal die casting service |
|---|---|---|
| Tolerance ownership | Each stage quotes its own window | One quoted window across casting and machining |
| Porosity found at | After the part is already machined | Before it enters the CNC cell |
| Blame on a bad lot | Split between two purchase orders | Held by the supplier you paid |
| Prototype to production | Second supplier, second DFM round | Same process chain, same fixturing logic |
| Surface finish | Outsourced again to a coater | Anodizing and plating in the same building |
| Documentation | Two sets of reports to reconcile | One inspection report per shipment |
| Change response | Days lost to email between vendors | Design change handled inside one plant |
| Traceability | Heat number may be lost in transit | Material and lot tied to the part |
When a single-source OEM metal die casting service is the right call
Choose one supplier when the part has tight functional features, a sealing surface, or a short path from prototype to volume. Keep vendors separate when the design is still fluid and each stage can be re-quoted without penalty.
Where the tolerance stack-up actually comes from
The ±0.001 mm promise is the most common lie in outsourcing. No single stage in a die casting chain holds that number end to end. The casting itself typically lands in a ±0.1 mm window. CNC machining on a good fixture holds ±0.005 mm. Anodizing or powder coating adds another 0.02 to 0.05 mm of build-up. Add those and your 'high precision' part drifts by nearly 0.2 mm at the critical feature.
The fix is not a tighter promise. It is deciding which feature carries the function and controlling only that one. A mounting boss for an M4 screw needs position, not size. A bearing bore needs roundness and size, not position. When you send a drawing to an OEM metal die casting service, mark the functional features and leave the rest at general tolerance. Vendors who ask which features matter are usually the ones who can hold them.
Ask for the combined stack-up in writing. A supplier who answers with a single stage number is either guessing or hoping you will not add the stages yourself. With our own 16 simultaneous 5-axis machining centers and 127 CNC machines, the casting and the machining window are set together before the die is cut, so the number we quote is the number the part sees.
- 1General casting toleranceAround ±0.1 mm on as-cast features, tighter only where the die allows it.
- 2Post-machining toleranceDown to ±0.005 mm (±0.0002 in) on fixtured features.
- 3Coating build-up0.02–0.05 mm per side for anodizing or powder coat. Plan for it.
- 4What to sendA marked-up drawing naming the functional features and their datums.
Porosity: why a good-looking casting can still leak
Gas porosity forms when air or gas is trapped in the shot sleeve and does not escape before the metal solidifies. The part looks fine. Then the CNC opens the skin and a hairline pocket appears on a sealing face. On a pressure housing that is a leak. On a cosmetic part it is a reject you already paid to machine.
You cannot inspect your way out of this after machining, because the cost is already sunk. The controls sit upstream: vacuum-assisted filling, correct die venting, controlled shot profile, and a first-article X-ray or section cut on the thick sections. For parts that must hold pressure, vacuum casting and a documented porosity acceptance level are worth the extra tooling cost.
Ask the supplier where porosity is checked and what happens to a suspect lot. If the answer is 'we check after machining', the risk is on your invoice. If the answer is 'we cut a section from the first shots and check before the run', the process is being controlled rather than sorted.
- 1Thick sectionsSlow cooling and shrink porosity. Keep walls uniform where you can.
- 2Sealing facesKeep them out of the last-filled region of the die.
- 3Acceptance levelAgree a porosity class and an inspection method before tooling starts.
Communication and who owns the risk
A split supply chain creates a communication gap that costs days. You send the CAD file to a die caster. They send a casting to a machine shop. The machine shop finds the datum is not where the model assumed. Emails go out. Nobody wants to move the datum because that changes the fixture and the quote. Two weeks disappear.
We run a different structure. GreatLight was set up in Dongguan in 2011 and now runs 3 wholly-owned plants across 7,600 m² with 150 technicians. Die design, casting, 5-axis machining, and finishing sit on the same site, and the same engineering team owns the datum from the die drawing to the final inspection report. When a casting has micro-porosity, we catch it before it reaches the CNC cell. We own the risk, so we have a reason to control it.
The practical test during a supplier visit is simple: ask who signs off when the casting and the machining drawing disagree. If two different companies sign, you are the project manager whether you wanted the job or not.
From one prototype to a 10,000-piece run
Most projects die in the gap between proof of concept and mass production. The prototype came from a machined billet or a 3D print. The production part is a die casting. The geometry that worked in the prototype may not fill in a die, and the draft angles the die needs change the fit of the part next to it.
A supplier who can run both ends of that range removes the gap. We hold no minimum order quantity, so a single prototype and a 10,000+ piece run come out of the same process chain with the same fixturing logic. Production can start within 24 hours of a released order, and parts typically ship in 3–5 days once the die is proven.
Before you commit, ask three questions. Can they machine the prototype and the production casting on the same equipment? Will the DFM analysis cover draft, wall thickness, and gate location, not just the CNC toolpath? And is the quote built from the production process, or from a prototype process that will change later?
- 1DFM scopeDraft angles, wall uniformity, gate and vent position, parting line.
- 2Tooling planSingle cavity for low volume, multi-cavity only when volume justifies it.
- 3Quote basisMake sure the price assumes the die-cast route, not a billet route.
Certifications, material traceability, and confidentiality
Certificates only matter if your part actually runs under the system. IATF 16949:2016 is the one automotive buyers ask for, and it drives PPAP-style documentation, change control, and traceability. ISO 13485:2016 is the medical device standard, and it changes how records are kept and how non-conformances are handled. ISO 9001:2015 covers the general quality system, and ISO 27001:2022 covers information security, which matters when you send CAD files and drawings across borders.
Material traceability is the part engineers forget. Ask whether the heat number or alloy lot is recorded against your parts and printed on the inspection report. For aluminum work, the common die casting alloy is ADC12, while machined parts may use 6061, 7075, or 6082. Mixing them in one document set is a real risk on mixed programs.
Confidentiality is a commercial check as much as a legal one. If the design is not public, ask for an NDA before you upload. We sign one on request, and file transfers stay on controlled systems. Do not send a proprietary housing to a broker who forwards it to three unknown shops.
- 1Automotive and EVIATF 16949:2016 plus a documented change-control path.
- 2Medical devicesISO 13485:2016 and inspection records retained per the standard.
- 3Alloy recordHeat or lot number tied to the shipment, not to the month.
- 4NDASigned before files move, not after the first quote.
Step by step: auditing an OEM metal die casting service
Run these in order. Each step can end the conversation early, which saves you the cost of a bad tool.
- 1Send the drawing with functional features markedName the datums and the features that carry load, seal, or fit. Leave cosmetic surfaces at general tolerance. A supplier who cannot work from a marked drawing will not hold the tight features either.
- 2Ask for the combined tolerance stack-upRequest one number covering casting, machining, and coating. Compare it against your functional requirement. If the answer is a single-stage figure, ask again.
- 3Request the porosity control planAsk for the filling method, the venting approach, and where porosity is inspected. For pressure-tight parts, ask for vacuum assistance and a defined acceptance class.
- 4Confirm the machining is in-houseAsk how many machining centers are on site and what the largest travel is. Our largest 5-axis travel is 4,000 × 400 × 150 mm, with a Ø400 mm rotary table for round parts.
- 5Check the certification scope against your industryMatch IATF 16949:2016 or ISO 13485:2016 to your program. Ask to see the certificate scope, not just the logo on a web page.
- 6Confirm MOQ and the prototype pathAsk whether one piece is possible. A no-MOQ supplier can build the prototype and the production run on the same chain, which removes the second DFM round.
- 7Agree the inspection and reporting formatDecide up front which dimensions are reported, in what units, and whether 100% inspection before shipment is included. Reports should be available on request.
- 8Sign the NDA before files moveIf the design is confidential, get the agreement signed first. Controlled file transfer and access limits should be part of the deal, not a favor.
Questions buyers ask before tooling starts
What wall thickness is practical for a die-cast housing?
For aluminum die casting, 2 to 4 mm is a comfortable range on a part of typical electronics-housing size. Thin walls below about 1.5 mm fill poorly and tend to run cold, which raises porosity and short-shot risk.
Thick sections above roughly 6 mm cool slowly and pull shrink porosity into the middle. If the design needs a thick boss, core it out or expect a slower cycle and a section check on the first shots.
Can you machine a die casting to ±0.005 mm?
Yes, on the machined features, using fixtured 5-axis work. Our quoted machining tolerance is ±0.005 mm (±0.0002 in) and fine finishes run Ra 0.2–0.8 μm.
The limit is not the machine, it is the datum. If the casting datum is unstable because of draft or parting-line flash, the machining window moves with it. That is why datum selection is agreed before the die is cut.
Do you have a minimum order quantity?
No minimum order quantity. We run from one prototype to 10,000+ part runs, and the prototype and production parts come off the same process chain.
Which surface finishes can be applied after casting?
Anodizing in clear, color, hardcoat, and conductive versions; electroless nickel, zinc, silver, and gold plating; powder coating and black oxide; plus bead blasting, tumbling, brushing, and polishing.
Laser marking is available down to a minimum character height of 1.5 mm. If a marked area will be anodized, plan the masking and the mark depth together, because anodizing can wash out a shallow mark.
How fast can a quote and a first article come back?
Quotation and a free DFM analysis come back within 12 hours. Production can start within 24 hours of a released order once tooling is proven, and parts typically ship in 3–5 days.
Lead time on the die itself depends on part size and cavity count, and it is quoted per project.
What documentation should I expect with each shipment?
Raw material verification, in-process monitoring records, and a final inspection report, with 100% inspection before shipment. Reports are provided on request.
For automotive programs, the documentation follows the IATF 16949:2016 system. For medical parts, records follow ISO 13485:2016.
Send the drawing and get a combined tolerance answer
Upload your file and we will return a quote with a DFM analysis within 12 hours, covering casting, machining, and finish in one number.
12-hour quote and DFM100% inspection before shipmentNDA on request
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