Aluminum CNC Treatment: Game Changers in Modern Manufacturing

Most aluminum problems we see start with an alloy picked for price instead of function. 6061-T6 is the default for a reason: it machines cleanly, welds, anodizes evenly and holds ±0.005 mm on a stable setup. If your part is a fixture plate, a housing or a bracket, stop there unless something specific pushes you off it.

2024-T4 cuts to a better finish and has higher fatigue strength, but it corrodes without protection and is harder to weld. 7075-T6 gives you roughly double the yield strength of 6061, which matters for thin ribs and load paths, yet it is more prone to stress cracking after hard anodizing and costs noticeably more per kilogram.

Casting alloys sit in a different category. ADC12 flows well into thin die-cast walls and is cheap at volume, but porosity shows up the moment you machine into it. If a part needs pressure tightness or a cosmetic finish, billet stock is the safer path even at higher material cost.

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  6061-T6General machining, housings, brackets, fixture plates
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  7075-T6High-load ribs, aerospace structure, tight weight budgets
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  2024-T4Fatigue-critical parts that can be coated or plated
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  ADC12High-volume die cast housings with generous wall thickness

Aluminum is soft, so it deflects under cutting force before it breaks. A wall thinner than about 0.8 mm will chatter on a standard three-axis setup, and the finish will show it. On a five-axis machine with light radial cuts and supported fixturing we hold 0.5 mm walls regularly, but the feature has to be designed so the tool can reach it from both sides.

Deep pockets are the other common trap. A pocket deeper than four times its cutter diameter needs a long-reach tool, and long-reach tools bend. We usually step down to a smaller cutter, reduce the radial engagement and accept a longer cycle. Redesigning the pocket or adding a corner radius saves more money than any cutting parameter change.

Threads below M2 in aluminum strip easily, especially in 6061. Rolled threads hold better than cut threads at that size. If your design has more than a few M1.6 holes, expect a higher scrap rate on the first run and plan a test batch.

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  Minimum wall, 3-axisAbout 0.8 mm with stable support
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  Minimum wall, 5-axisAbout 0.5 mm with light radial cuts
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  Pocket depth ruleKeep under 4× cutter diameter when possible
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  Small threadsBelow M2, specify rolled threads over cut

Anodizing builds oxide into the surface rather than sitting on top of it. Type II clear anodizing grows roughly 5–10 μm per side, and hardcoat can reach 25–50 μm depending on the process. That growth goes outward and inward, so a bore sized to ±0.005 mm before anodizing will not measure the same afterward.

The fix is simple but has to be planned at quoting time. Either mask the critical diameters, machine them undersize to allow for growth, or run the finish before the final boring pass. We ask for a drawing with the finish callout on it for exactly this reason.

Bead blasting gives a matte, uniform look and hides tool marks well. It also rounds sharp edges slightly, which is fine on a cover but not on a sealing face. Brushing keeps a directional grain and is usually chosen for visible panels. Polishing reaches the lowest roughness but shows every handling mark after assembly.

Laser marking is the cheapest way to add a logo, serial or part number. Minimum character height is 1.5 mm. Below that the mark gets fuzzy and inconsistent, so shrink the layout or drop characters instead of shrinking the text.

Plating options include electroless nickel, zinc, silver and gold. Electroless nickel adds a hard, uniform layer with good corrosion resistance and holds tight tolerances better than anodizing because the deposit is thinner and more even.

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  Type II anodizeAbout 5–10 μm growth per side
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  Hardcoat anodizeAbout 25–50 μm growth per side
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  MaskingSpecify critical diameters on the drawing
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  Laser marking1.5 mm minimum character height

A three-axis mill handles most flat parts, plates and open pockets. It is the fastest and cheapest option when the part can be reached from one direction. Twenty-seven of our machines are three-axis, and they run the bulk of simple production work.

Four-axis makes sense when a part has features on multiple faces that can be indexed around one axis. It removes a second setup and the position error that comes with it. Twelve four-axis mills in the shop cover most of this work.

Five-axis earns its cost in two situations: contoured surfaces that a ball nose cannot reach in three axes, and parts with features on five or more faces that would otherwise need three or four setups. Sixteen simultaneous five-axis centers handle impellers, medical housings and complex brackets. The trade-off is cycle time and programming cost, so it is not the default for a simple plate.

For parts up to 4,000 mm long, we run a large-travel machine with a 4,000 × 400 × 150 mm envelope. Beyond that, splitting the part or switching to fabrication is usually cheaper than finding a bigger machine.

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  Three-axisPlates, open pockets, single-direction features
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  Four-axisMulti-face parts indexable around one axis
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  Five-axisContoured surfaces, five-plus face features
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  Large travelUp to 4,000 × 400 × 150 mm