How to Qualify a CNC Aluminum Casting Machining Service Provider

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  Key takeaways
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  Seven checks and what a good answer looks like
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  Process scope and alloy control
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  As-cast geometry and the machining allowance
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  Fixtures, datums and porosity screening
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  Quoting terms: MOQ, lead time and certifications
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  How to run a casting-plus-machining RFQ in six steps

The first question is not about price. It is whether the cnc aluminum casting machining service provider actually casts metal. Plenty of trading companies pass your file to a foundry, then to a machine shop, then back. Every handover adds a new datum reference and a new chance for the bore to drift. When one plant pours the part, cuts the fixture and machines the faces, the person who set the draft angle is the same person who sets the zero point.

GreatLight runs casting and machining in the same group, with 127 high-precision CNC machines across three wholly-owned plants and 7,600 m² of floor space. That matters most on parts where a cast pad becomes a machined mounting face. The fixture can be built against the actual as-cast surface rather than a nominal model that nobody checked.

Alloy is the second filter. Die casting usually means ADC12 or A380, which flow well and hold thin walls. Structural parts often move to 6061, 6082 or 7075, and those are typically gravity cast, sand cast or cut from billet instead. The two families machine at different feeds and behave differently after heat treatment. A supplier who quotes ADC12 and 7075 at the same cutting parameters has not run both.

Request mill certificates tied to the heat number, and ask whether positive material identification is available. For safety parts, a certificate that lists only the alloy grade is weak. You want the heat, the chemistry and the mechanical properties. If the shop cannot produce that on request, treat the alloy callout as unverified.

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  Ask earlyIs the casting poured in-house or bought in?
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  Check the alloy list6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075, ADC12 are all in our standard range.
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  Match process to alloyADC12 for thin-wall die casting; 7075 for high-strength structural work.
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  Require traceabilityHeat-number certificates plus PMI on request.

Casting tolerance and machining tolerance are not the same number, and confusing them is the most common quoting mistake. A die-cast surface typically lands within about ±0.5 mm of nominal. Machined faces on the same part can reach ±0.005 mm (±0.0002 in). If your drawing shows a tight tolerance on a face that stays as-cast, no supplier can hold it, and the quotes you get back will be guesses.

So decide which faces get cut. A practical rule is to leave 0.3-0.5 mm of stock on faces that will be machined, and to avoid machining a face that is already at final wall thickness. Draft angles of 1-2° on die cast walls and 1.5-3° on sand cast walls are normal. Sharp corners invite shrinkage porosity, so a small radius at every internal corner is cheaper than a repair weld later.

Wall thickness drives fill and cooling. For die casting, 1.5 mm is a reasonable floor for a part of moderate size, and 2.5-3.5 mm is comfortable. Ribs should be about 60-70% of the adjoining wall thickness. Thick sections cool slower and pull metal from thinner areas, which is how you get shrink voids in the middle of a boss that later shows up as a scrapped bore.

On the machining side, GreatLight works to 4,000 mm maximum part size, with travels of 4,000 × 400 × 150 mm on the large machines and 750 × 1,150 × 550 mm on the medium frames. A Ø400 mm rotary table covers most round castings that need bores on several axes. If your part needs more than that, say so before the design is frozen.

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  Stock allowanceLeave 0.3-0.5 mm on machined faces.
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  Draft1-2° die casting, 1.5-3° sand casting.
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  Walls1.5 mm minimum, 2.5-3.5 mm comfortable.
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  Ribs60-70% of the adjoining wall thickness.

Porosity is the reason cast-then-machined parts fail in service. Gas or shrinkage voids sit just under the skin, and the first cut opens them. A supplier who machines first and inspects later will ship a bore with a visible void and call it a finish defect. A better sequence screens the casting before the expensive operations run.

GreatLight inspects 100% of parts before shipment, covering raw material checks, in-process monitoring and final inspection, with reports on request. For castings, that means checking the as-cast blank at the gate and overflow areas, and pressure or dye testing any section that will become a sealed cavity. A qualification rate of 99.99% only holds if the screening happens before the finishing steps, not after.

Fixtures deserve their own line in the quote. A cast part has no reliable flat surface unless the shop makes one. The usual approach is a three-point nest on as-cast pads, then a first cut that establishes the datum face for every later operation. On a 4,000 mm part that fixture may cost more than the machining itself, and a supplier who leaves it out of the quote will recover it somewhere else.

For round parts, a Ø400 mm rotary table with a self-centering chuck lets the shop bore, face and turn multiple features in one setup. Fewer setups mean fewer datum shifts. Ask how many setups the part needs. If the answer is more than three for a part with two tight bores, the tolerance stack is already working against you.

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  Screen before machiningInspect the blank at gate and overflow areas.
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  Fixture in the quoteA three-point nest plus a datum cut.
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  Count setupsMore than three setups on a tight part is a warning.

A casting quote is only comparable when it uses the same basis. Price per kilogram sounds transparent but ignores machining hours, fixture cost, finishing and inspection. Ask for a piece price that includes the cast blank, the CNC operations, the surface finish you specified and the inspection report. Tooling should sit on its own line so you can see what you own.

MOQ is the next dividing line. GreatLight has no minimum order quantity, so one prototype and a 10,000+ part run are both workable. That is useful at the validation stage, when you want the real process rather than a machined lookalike. Production can start within 24 hours of a confirmed order, and parts ship in 3-5 days. Quotation and free DFM analysis come back within 12 hours.

Certifications tell you which markets the shop already serves. ISO 9001:2015 covers general quality management. IATF 16949:2016 applies to automotive and EV work. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security, which matters when you upload drawings. Ask for the current certificates and check the scope statement, not just the logo on the website.

Finishing is where costs quietly reappear. Anodizing, hardcoat, electroless nickel, powder coating, bead blasting, brushing and laser marking all add steps and handling. Laser marking has a minimum character height of 1.5 mm, so a 0.8 mm date code is not going to work. List every finish on the RFQ and ask whether it is done in-house or sent out, because outsourced finishing adds days and a second shipping step.

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  Quote basisPiece price plus tooling plus finishing, not per kilogram.
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  MOQNo minimum order quantity, from one part to 10,000+.
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  CertificatesISO 9001, IATF 16949, ISO 13485, ISO 27001 — check the scope.
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  FinishingName every finish; laser marking minimum 1.5 mm character height.