CNC Machining of Die Cast Parts
What machining adds to a casting
Die casting produces near-net shape, but a casting is rarely a finished part. Sealing faces, mounting pads, threaded holes, connector windows and any bore that mates with a shaft are normally machined after casting. Our process runs five-axis CNC centres in the same facility as the casting cells, holding ±0.05 mm where the drawing calls for it. Keeping both operations under one roof means the datum established at the casting stage is the same datum used in the finishing programme, rather than one that has to be re-established by the next supplier.
The useful question at DFM stage is not how tight the machine can hold, but which features genuinely need it. A blanket tolerance note forces tight machining across the whole part, adds setups and inspection time, and usually raises cost without improving function. Mark the features that mate, seal or locate, and let the rest of the casting stay as-cast. That single distinction typically moves more cost than any negotiation on piece price.
Datums, stock and draft
Machining starts from a datum, and on a die casting that datum has to survive ejection. Draft angles, parting line position and where the gate and overflow wells sat all affect how much material is left for the cutter. Too little stock and the tool breaks through into an as-cast, possibly porous, surface; too much and you remove the dense skin that makes the casting sound in the first place. Agreeing the datum scheme and the stock allowance during DFM is far cheaper than discovering a breakthrough on the first production batch.
Where machining will open a face that must hold pressure or keep a gasket seated, that is also the moment to decide the casting route. Vacuum die casting reduces the gas entrapped ahead of the metal front, so the material exposed by the cutter is sounder than it would otherwise be. The two decisions - casting route and machining stock - belong in the same conversation, not in two separate ones held weeks apart.
Inspection and documentation
Verification runs in our QC laboratory with CMM inspection, and full batch reports are issued with the parts. Because casting, machining, surface treatment and inspection sit in the same 22,000 square metre facility, a dimensional finding can be traced back through its batch instead of being argued across separate suppliers. For automotive programmes, inspection reports and PPAP documentation are available alongside ISO 9001 and IATF 16949 certificates.
Send the STEP, IGES or DXF model with the machined features marked and the annual volume stated. DFM review is free and we reply with costing within 24 hours; prototype samples follow in about 7 days and volume production in 30 to 45 days after approval. If you are unsure which faces to machine, say so at enquiry stage - that is exactly the sort of question the review is meant to settle.
FAQ
What tolerance can you hold on machined castings?
General machining is quoted at ±0.05 mm where the drawing specifies it. Achievable tolerance depends on feature size, wall thickness and how the part is located, so the datum scheme and stock allowance are agreed during DFM review rather than assumed afterwards.
Should every surface be machined?
No. Machining every surface adds setups and cost without improving function. Mark the faces that mate, seal or locate and leave the rest as-cast; a blanket tolerance note is the most common cause of unnecessary machining cost on a die cast part.
Does machining create porosity problems?
It can expose them. Cutting into a face that must seal opens pores that were closed below the surface, which is why the casting route and the machining stock should be decided together, and why porosity limits belong on the drawing alongside dimensional tolerances.
Can you machine and finish in the same facility?
Yes. Die casting, five-axis CNC machining, anodising, powder coating, plating, chromate conversion and QC inspection all run in one facility, so traceability, scheduling and any dimensional query stay with a single supplier.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.