Aluminum Processing 101: A Beginner's Guide

The term covers a family of operations that turn stock into a usable part. On a shop floor it usually means subtractive work: a rotating cutter removes material from a block, plate or extrusion until the geometry matches the drawing. Casting, forging, extrusion and sheet forming belong to the same family, and most parts touch two or more of them before they ship.

These alloys behave differently from steel, and that changes how you cut them. Heat travels through aluminum about five times faster than through steel, so it leaves the cutting zone quickly and the part stays relatively cool. It is also soft and gummy at low silicon content, which means a sharp edge and a free-cutting geometry matter more than brute force.

The upside is speed. Aluminum cuts fast, tools last a long time, and a machine that struggles with 304 stainless will run this metal all day without complaint.

Alloy selection drives everything downstream: tooling, cutting parameters, finishing, and how the part behaves in service. Most first projects land on 6061-T6 because it welds, machines cleanly and holds tight tolerances without drama. It is a general-purpose choice, and it is rarely wrong for brackets, housings and fixtures.

When strength matters more than weldability, 7075-T6 is the usual next step. Its yield strength sits close to some mild steels, which makes it common in aerospace brackets and high-load fittings. The trade-off is that 7075 does not weld well and costs more per kilogram, so it should be reserved for the parts that need it.

Copper-bearing 2024-T4 offers excellent fatigue resistance and is common in aircraft skins and structural panels. It has poor corrosion resistance on its own, so it is normally clad or anodized. For marine and chemical exposure, 5052 and 5083 are the corrosion-resistant picks, and 5083 keeps useful strength after welding.

Extrusions such as 6063 and 6082 are common in frames and enclosures because the profile is already close to final shape. The die cost is the reason: a custom extrusion only pays off at higher volumes. One prototype is almost always cheaper cut from plate.

Cast alloys are a separate track. ADC12 is a die-casting alloy, not a wrought one, and it machines differently. If the drawing specifies ADC12, the part is probably meant for high-volume casting, and machining is a secondary operation rather than the primary one.

• 1
  6061-T6General purpose. Welds, machines well, holds ±0.005 mm.
• 2
  7075-T6High strength. Poor weldability, higher cost.
• 3
  2024-T4Fatigue resistant. Needs cladding or anodizing.
• 4
  5052 / 5083Marine and chemical service. 5083 keeps strength after welding.

CNC milling is the workhorse. A spindle carries a rotating tool along three or more axes, and material is removed in passes until the shape is complete. Three-axis machines handle flat parts, plates with pockets, and anything that can be reached from one direction. They are the cheapest way to remove metal.

Four-axis machining adds rotation about one axis, usually the X axis. That lets the tool reach several faces of a part in a single setup, which cuts the number of fixtures and the chance of stacking error. Shafts, cylinders and parts with features on four sides are the usual candidates.

Five-axis machining adds two rotary axes at once, so the tool can approach the part from almost any angle. This matters for contoured surfaces, deep pockets with steep walls, and parts that would otherwise need three or four separate fixtures. A Ø400 mm rotary table covers most of the work we see, and our 16 simultaneous 5-axis centers run these jobs daily.

Turning is the other main family. A single-point tool feeds into a rotating workpiece, which suits round parts like shafts, bushings and connectors. Mill-turn centers combine both operations, so a part with a turned body and milled flats comes off one machine without being re-chucked.

For sheet parts, the process changes completely. Laser cutting, punching and bending form enclosures and brackets from flat stock, often faster and cheaper than milling from plate. If your part has a constant wall thickness and bends, sheet metal is usually the right answer.

Tolerance is the range a dimension is allowed to vary. General machining holds ±0.1 mm without much effort. Tightening to ±0.05 mm adds inspection and slower feeds. At ±0.005 mm you are in precision territory, and the cost comes from temperature control, tool wear management and more frequent measurement, not from the cut itself.

Surface finish is measured as Ra, the average roughness of the surface. As-machined aluminum typically lands at Ra 1.6–3.2 μm. A finer pass brings it to Ra 0.8–1.6 μm, and careful work with the right tool and coolant reaches Ra 0.2–0.8 μm. Below that, you are usually paying for a polishing operation rather than a cutting one.

Both numbers should be applied only where the part needs them. A mounting face may need ±0.02 mm and a fine finish. The clearance pocket next to it probably does not. Call out tight tolerances on the features that matter, leave the rest general, and the price drops without any loss of function.

Wall thickness is the other cost lever. Thin aluminum walls deflect under cutting force and vibrate, so the shop has to take lighter passes and more of them. Walls under 1 mm are possible but slow. If the design allows 2 mm or more, the part gets cheaper and more stable.

Finally, think about how the part will be held. A shape with no flat face for the vise, or with features that require five re-fixtures, costs more than one designed around two setups. A short conversation with the shop before you freeze the model often saves more than any parameter tweak.

Aluminum is not a universal answer. It has a low melting point, roughly 660 °C, so parts that see sustained heat above a few hundred degrees will lose strength or creep. Steel, titanium and Inconel hold up where aluminum cannot.

Wear resistance is another limit. Bare aluminum is soft, and sliding contact against another metal will gall and wear quickly. Hardcoat anodizing helps by building a ceramic oxide layer, but if the part needs a hardened raceway or a cutting edge, a steel insert is the practical route.

Fatigue is the third issue. Aluminum has no true endurance limit, so a part loaded in cyclic tension will eventually crack no matter how low the stress. Steel can be designed to run forever below its endurance limit. For high-cycle applications, this difference decides the material.

Cost is not always on aluminum's side either. The raw metal is cheap and cuts fast, but if the part is a simple flat plate in large volume, stamping or die casting will beat machining per unit once tooling is amortized. Machining wins when geometry is complex, volumes are low to medium, or the design is still changing.