Metal Die Casting Makers: How to Compare Them Like an Engineer

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  Key takeaways
• 2
  What Each Type of Metal Die Casting Maker Is Good At
• 3
  Process Fit: Which Casting Route Your Part Needs
• 4
  Tooling: Simulation, Draft, and Who Owns the Die
• 5
  Secondary CNC Machining: The Step Most Buyers Underestimate
• 6
  Tolerances, Inspection, and What the Report Must Show
• 7
  MOQ, Lead Time, and Quote Depth for Metal Die Casting Makers
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  Seven Checks Before You Issue a Purchase Order

Die casting is four processes wearing one name. High-pressure die casting (HPDC) pushes metal into the cavity at high velocity and suits thin walls, tight as-cast detail, and volumes where tooling amortizes. Low-pressure and gravity casting fill more slowly, which reduces porosity in thick sections and costs less in tooling. Squeeze casting sits between them for parts that need density in specific zones.

Start with wall thickness and projected area. A 2 mm wall over a 300 mm span is HPDC territory. A 12 mm boss feeding a structural node usually is not, because the same die that fills the thin web will shrink-cavitate in the boss. Engineers who skip this step order tooling for a geometry that no machine can fill at a sane cycle time.

Alloy narrows the choice further. A380 and ADC12 flow well and machine cleanly, which is why they dominate aluminum housings. A360 offers better corrosion resistance. Zinc alloys cast to tighter as-cast tolerance but weigh more, so they rarely win on a handheld product. Magnesium AZ91D is light but needs tighter process control on the melt.

Ask the maker which process they would pick and why. A useful answer names the alloy, the wall range, and the draft angle they plan to use. A vague answer usually means the quote is being routed to whoever has capacity that month.

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  Thin walls and high volumeHPDC with A380 or ADC12
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  Thick sections, low porosityGravity or low-pressure casting
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  Local density demandSqueeze casting
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  Light weight priorityMagnesium AZ91D with tight melt control

Tooling decides your launch date. A die that is gated wrong shows it at first shot, and fixing gating after the steel is cut can add weeks and rework. Before any cutting starts, ask for mold-flow simulation output: fill pattern, air entrapment, and predicted shrinkage. A maker who simulates as standard is cheaper in the long run than one who quotes lowest and debugs on your schedule.

Draft angle and parting line are the other quiet cost drivers. Typical draft runs 1–3° on as-cast walls, more on textured surfaces. If your design has a zero-draft face because a mating part sits flush there, that face will need machining after casting, which changes the drawing and the price. Decide that before tooling, not after.

Ownership matters too. Confirm in writing who holds the die, where it is stored, and what it costs to transfer it. Some makers amortize tooling into the piece price and keep the die; others bill it as a separate line item. Both are workable. What is not workable is discovering the arrangement at the end of the program.

Finally, check die life assumptions against your volume. Tool life is quoted in shots, and a program that runs well past the quoted life will need maintenance or a second cavity. Ask for the number in the quote.

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  Get simulation outputFill, air entrapment, shrinkage
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  Lock draft before cutting steel1–3° typical on as-cast walls
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  Confirm die ownership in writingStorage and transfer cost
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  Match die life to volumeAsk for quoted shots

Almost no functional casting ships as-cast. Sealing faces, bearing bores, threaded holes, and dowel locations need machining after the part cools. When the foundry and the machine shop are different companies, you own the interface: the cast datum, the stock allowance, and the blame when a bore comes out undersized. That interface is where schedules slip.

The practical fix is to ask what stock allowance the maker leaves for machining and how they hold the casting for the second op. A common allowance is 0.3–0.8 mm on faces that will be milled, tighter on faces that only need a skim. If the casting arrives with 1.5 mm of stock on a face that must finish flat, every part costs extra cycle time.

This is why an integrated shop changes the economics. GreatLight casts the blank and finishes it on the same floor, with 16 simultaneous 5-axis machining centers and 12 four-axis mills, so a housing can be cast near net shape and then have its sealing surfaces cut to ±0.005 mm under one quality system. Nothing gets lost between vendors.

It also changes what is possible. A cast aluminum housing with machined sealing faces and threaded inserts is one purchase order instead of three, and the inspection report covers the finished part rather than the raw casting.

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  Agree stock allowance first0.3–0.8 mm on machined faces
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  Define the cast datumSame datum feeds the CNC fixture
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  Keep finishing in houseOne quality system, one report

As-cast tolerance and machined tolerance are different numbers, and quotes that blur them cause arguments later. Casting alone typically holds a wider band that depends on alloy, wall, and die condition. Features that mate or seal need machining, and that is where tight bands come from. GreatLight holds ±0.005 mm (±0.0002 in) on machined features and finishes critical surfaces to Ra 0.8–1.6 μm.

Ask what is inspected and how often. A credible answer separates raw material check, in-process monitoring, and final inspection, and it names the instruments. A CMM report on the features called out on your drawing beats a generic certificate every time. GreatLight inspects 100% of parts before shipment and supplies reports on request.

Porosity is the casting-specific risk that machined parts do not have. It shows up as a leak, a rejected anodize batch, or a void under a machined face. X-ray or dye penetrant on critical zones costs money, so decide early which zones are critical and put them in the drawing. Otherwise you are inspecting by luck.

Certification sets the floor here. ISO 9001:2015 covers general quality management. IATF 16949:2016 is what automotive programs audit against, and ISO 13485:2016 covers medical devices. If your product falls in those categories, a supplier without the matching certificate is not a candidate, regardless of price.

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  Separate cast from machined toleranceThey are not the same band
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  Name critical zonesX-ray or penetrant on those only
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  Match certificate to industryIATF for automotive, ISO 13485 for medical

Volume assumptions drive tooling cost, so the first question is how many parts you actually expect in twelve months. If the answer is under a few thousand, a hard die may never amortize and you should be looking at soft tooling, vacuum casting, or machining from billet. A maker who pushes die casting at 200 pieces is selling tooling, not solving your problem.

Lead time has three parts: tooling, first article, and production. Ask for each separately. A single quoted date hides which stage is the constraint. GreatLight returns a quotation with free DFM analysis within 12 hours, can start production within 24 hours on released work, and ships parts in 3–5 days, with no minimum order quantity from one prototype to 10,000+ piece runs.

Quote depth is the tell. A useful quote lists alloy, process, draft, stock allowance for machining, secondary operations, finish, inspection, and tooling treatment. A single number with a lead time attached is a budget figure, not a purchase order. Compare quotes line by line, not total to total.

Finally, check the confidentiality terms before you upload drawings. Secure upload and an NDA on request are standard for serious suppliers. If a maker hesitates on an NDA, treat that as a signal about how the rest of the project will go.

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  Under a few thousand partsSoft tooling, vacuum casting, or CNC from billet
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  Split the lead timeTooling, first article, production
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  Compare line itemsAlloy, draft, allowance, finish, inspection
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  Settle NDA and upload security firstBefore drawings leave your network