Aluminum alloy CNC processing: how the process actually runs

The work is subtractive. A saw cuts bar, plate or extruded profile to a rough length, then a machining center removes material until the geometry matches the CAD model. Nothing is formed or added, so every feature has to fit inside the starting stock envelope. That constraint drives the first decision on any job: which stock form and thickness to buy.

Programming comes next. A CAM toolpath is generated from the model, with tool diameter, stepover, stepdown and feed rate chosen for the alloy. For most 6061 work, three-axis milling handles the flats and pockets, then a fourth or fifth axis reaches the side holes and angled faces in the same setup. Fewer setups mean fewer datum shifts and tighter position tolerances.

Roughing removes the bulk of the material with larger cutters, leaving 0.3–0.5 mm of stock on finished surfaces. Semi-finishing and finishing follow with smaller tools and lighter passes. Thin walls and long, unsupported sections are the usual trouble spots; they deflect under cutting force and spring back after the tool passes.

Inspection closes the loop. Critical dimensions are checked against the drawing, and a first-article report can be issued before the run continues. For production volumes, in-process checks catch drift before a whole batch is cut to the wrong size.

The alloy decides more about the job than the machine does. 6061-T6 is the default for structural brackets, housings and fixtures: it machines cleanly, welds, anodizes well and holds moderate strength. When a part needs higher strength, 7075-T6 is the usual step up, but it cuts differently and is less forgiving of poor chip evacuation.

2024-T4 and 2024-T351 offer good fatigue resistance and are common in aerospace work. They are harder to weld and corrode more readily without a coating, so the drawing should say what protection is required. 5052 and 5083 are selected for formability and corrosion resistance rather than machined strength; they are gummy and produce long chips that wrap around the tool.

For die-cast housings that need secondary machining, ADC12 is common. It cuts easily but can contain porosity that shows up as a pitted surface after facing. If a cosmetic surface matters, tell us the alloy is die-cast stock so we can plan around it.

We machine 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12 on a routine basis. If your drawing names an alloy outside that list, send the specification and we will confirm before quoting.

General machining tolerance on aluminum is ±0.005 mm where the geometry allows it. Tight tolerances are easier on small, well-supported features and harder on long, thin parts, because thermal growth and cutting force move the material during the cut. If a 300 mm part carries a ±0.01 mm callout, that is a different job from a 30 mm bushing at the same number.

Surface finish follows the toolpath. As-machined faces land around Ra 1.6–3.2 μm, a good general finish sits at Ra 0.8–1.6 μm, and fine finishing reaches Ra 0.2–0.8 μm. Finer finishes cost time, so specify them only on faces that touch something or show on the product.

Aluminum scratches easily after machining. Bead blasting, brushing or polishing hides tool marks, and anodizing adds a hard layer that resists handling damage. Clear, color, hardcoat and conductive anodizing are all available. Laser marking needs at least 1.5 mm character height to stay legible after coating.

Aluminum is not a universal answer. If the part sees sustained temperatures above roughly 150 °C, or needs high wear resistance at a bearing surface, steel or titanium will serve better. Aluminum has no fatigue limit, so a part under millions of cycles needs a generous safety factor or a different material.

Some shapes are simply not efficient to machine from solid. Deep pockets, long bores and complex internal channels remove most of the stock as chips, which drives cost and cycle time. In those cases, die casting or a fabricated assembly is often cheaper than a solid machined block.

Tool breakage is the other real risk. Wrong feed and speed, poor chip evacuation, or vibration on a long tool all end the same way. Aluminum's low melting point makes it prone to built-up edge, so we run sharp, polished cutters with high rake angles and generous coolant. That is a process choice, not a preference.

Our shop runs 127 high-precision CNC machines across three wholly-owned plants, with a total floor area of 7,600 m² and 150 technicians. Sixteen simultaneous 5-axis machining centers handle angled faces and contoured surfaces in one setup, and twelve four-axis mills cover the side-drilling work that would otherwise need a second operation.

Size limits matter early. The largest travel is 4,000 × 400 × 150 mm, and medium machines cover 750 × 1,150 × 550 mm and 600 × 600 × 600 mm. Compact machines handle 500 × 500 × 450 mm and 500 × 310 × 200 mm. A Ø400 mm rotary table supports round parts that need indexing.

The plant has been running since 2011 and holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. Every part is inspected before shipment, covering raw material check, in-process monitoring and final inspection. Reports are available on request, and uploads stay confidential under NDA.