Aluminum CNC Milling Service Guide

Aluminum cuts fast. A sharp carbide cutter runs at high surface speed and takes deep passes without the chatter you fight in stainless or titanium. That is the main reason a milling supplier can hold a ±0.005 mm band on a feature while still removing material at a rate that keeps the part affordable. Chips clear easily, and the low cutting temperature means less thermal drift between roughing and finishing.

The material is not uniform across alloys, though. Soft tempers such as 5052 or 6063 gum up on fine flutes and leave a built-up edge. Harder grades like 7075 machine cleanly but spring back more, so a heavy radial pass can pull the wall off size. 2024 sits in between and machines well in T4, yet it corrodes faster than 6061 if you leave bare surfaces exposed.

For most brackets, housings and fixtures, 6061-T6 is the default pick. It welds, anodizes predictably, and holds tight tolerances after stress relief. Reach for 7075-T6 only when you need yield strength near 500 MPa and the part is thin or highly loaded. ADC12 is a die-casting alloy and shows up here mainly when a machined prototype has to match a casting later.

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  6061-T6General purpose. Good weldability and anodizing response.
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  7075-T6High strength. Poor weldability, slower to cut, higher cost.
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  2024-T4Fatigue resistance. Needs corrosion protection on bare faces.
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  5052 / 5083Formable and corrosion resistant. Gummy on small end mills.

A job starts with a STEP or IGES model and a 2D drawing that carries the tolerances, datums and finish callouts. If the model and drawing disagree, the drawing wins unless you say otherwise. We run a DFM pass on the geometry before quoting: wall thickness, tool reach, corner radii and hole depth all get checked against the cutters we actually own.

Roughing removes the bulk with a large indexable or carbide tool, leaving 0.3–0.5 mm of stock for finishing. Then a semi-finish pass equalizes the load, and the finish pass cuts the final geometry. On a three-axis machine the part is usually held in soft jaws or a vise; on a four-axis setup a rotary table lets us index the part without re-clamping, which protects the datum.

Five-axis work is where undercuts, deep pockets and compound angles become practical. A Ø400 mm rotary table on a simultaneous five-axis center reaches features that would need three separate setups otherwise. Each re-clamp adds stack-up error, so fewer setups usually means a tighter part and a shorter schedule.

After milling, parts go through deburring, then any secondary operation: anodizing, plating, bead blasting, laser marking. We inspect 100% before shipment and can send dimensional reports on request. Raw material certificates are checked on arrival, and in-process checks catch a drifting tool before it ruins a batch.

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  Setup countEach re-clamp adds error. Fewer setups, tighter result.
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  Tool reachDeep pockets need long, thin cutters that deflect. Split the depth.
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  Corner radiiMatch radii to standard cutter sizes to avoid slow, tiny tools.

A standard milled feature lands around ±0.05 mm without special effort. Push to ±0.005 mm and the part needs stable fixturing, sharp tooling and temperature control. That number is achievable, but put it only on the dimensions that matter. Calling out tight tolerance across a whole drawing raises cost and slows inspection without improving function.

Surface finish follows the same logic. As-machined faces sit around Ra 1.6–3.2 μm, a good finish pass reaches Ra 0.8–1.6 μm, and fine work gets to Ra 0.2–0.8 μm. If a face is a sealing surface or a bearing seat, specify the finish. If it is a clearance face, leave it as-machined.

Thin walls are the usual failure point. A 0.8 mm wall in 6061 will deflect under cutting force, so we often adjust the toolpath and take lighter passes rather than let the wall bow. Tell us which walls are functional and which are just packaging. The functional ones get the care.

Datum strategy matters as much as the tolerance number. Pick three stable faces that survive every operation and reference the critical dimensions to them. When datums move mid-process, even a generous tolerance can fail first article.

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  Critical features onlyTighten the few dimensions that drive function.
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  Finish calloutsSpecify Ra where a seal or bearing seats.
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  Wall thicknessFlag functional thin walls before quoting.

Ask what machines the shop owns and how many axes each one has. A supplier with only three-axis mills will quote the same part but plan more setups, which adds cost and error. Sixteen simultaneous five-axis centers, twelve four-axis mills and twenty-seven three-axis machines give room to route a job to the setup that fits it.

Ask how inspection is handled. A shop that checks 100% before shipment and keeps reports will catch a bad batch before it ships. One that samples at random is a different risk. For regulated work, look for ISO 9001, IATF 16949, ISO 13485 or ISO 27001 depending on your industry.

Turnaround claims are worth checking too. A shop that returns a quotation and DFM notes within 12 hours and can start production within 24 hours is set up to move. That does not replace quality, but it tells you the front office and the floor are connected.

Confidentiality should be settled early. Uploads are secure and confidential, and we sign an NDA on request. If your drawings are proprietary, get that in place before the first RFQ, not after.

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  Machine mixMore axes means fewer setups for complex geometry.
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  Inspection100% check and reports on request.
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  Industry certsPick the cert that matches your market.
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  NDASign it before drawings leave your building.