CNC Machining of Aluminum Shell for Mobile Phone

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  What makes a phone shell different from other machined parts
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  Alloy choice for CNC machining of aluminum shell
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  How five-axis workholding holds a thin wall steady
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  Cutting parameters and the roughing-to-finishing sequence
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  Deburring, anodizing and the steps after machining
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  When a machined shell is the right call

Most machined parts are judged on size and hole position. A phone shell is judged on how it feels in the hand. The wall between the outer surface and the battery pocket often runs 0.6 to 1.2 mm, and the outer surface is cosmetic on all four sides plus the rim. That combination drives every decision downstream.

The part is also long and thin. A typical shell is 150 to 165 mm long, 70 to 78 mm wide and 7 to 9 mm tall. The length-to-wall ratio on the side walls can reach 200:1. Any cutting force that pushes the wall sideways shows up as chatter marks, or as a wall that measures thin in one spot and thick in the next.

Flatness matters more than most drawings suggest. A phone shell that bows 0.05 mm will not sit flush on the display module or the back panel. Gaps of that size are visible under a light box and audible when the phone is squeezed. That is why shell drawings usually call out flatness on the mating face, not just overall length and width.

So the process is not really about removing metal fast. It is about removing metal without bending the part, then holding the shape through anodizing and assembly. Every step below serves that goal.

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  Thin walls0.6–1.2 mm between outer skin and battery pocket
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  Cosmetic facesFour sides plus rim are visible after assembly
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  FlatnessMating face flatness controls gap and feel

Not every aluminum grade machines into a good shell. The common picks are 6061-T6, 6063, 6082 and 7075. Grade 6061-T6 is the default for prototypes and mid-volume runs: it cuts cleanly, holds a thread, and anodizes to a consistent clear or colored finish. Grade 6063 is softer and extrudes well, so it suits shells that start as extruded tube and get light machining.

Grade 7075 gives the highest strength of the group, roughly double 6061 in yield. It also machines to a sharper edge and takes a hardcoat anodize well. The trade-off is cost and corrosion behavior. Grade 7075 is more sensitive to the anodize bath, and color matching across a batch is harder. Use it when the shell is a structural member, not just a housing.

Grade 6082 sits close to 6061 in strength with slightly better machining response on thick sections. For a production shell where you also need anodize consistency, 6082 and 6061-T6 are the safe pair.

One more point. Shells are often machined from bar or from a near-net forging. Bar stock wastes more material on a 160 mm part, but it removes the porosity risk you get in castings. If the shell carries a camera boss or an antenna slot, bar stock is usually the better starting point.

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  6061-T6Default for prototypes, threads and anodize consistency
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  6082Similar strength, good response on thick sections
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  7075Highest strength, harder anodize color control
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  Bar vs forgingBar avoids porosity at the cost of more waste

A shell has features on six sides: outer skin, battery pocket, camera cutout, button slots, speaker holes, antenna lines. Three-axis machining needs a flip for each face, and every flip re-clamps the part. On a 0.8 mm wall, re-clamping is where the part goes out of tolerance.

A simultaneous 5-axis center cuts the outer profile and the pocket in one setup. The part stays in one fixture from roughing to finishing. That removes the re-datum error between operations, which is often 0.03 to 0.05 mm on a flipped thin-walled part. It also lets the tool approach the side walls at an angle, so the cutter engages the wall along its length instead of pushing straight into it.

Workholding for the pocket side usually means a vacuum plate or a soft-jaw fixture machined to the part contour. Both spread the clamping load over a large area. Bolting through a small boss concentrates force and leaves a witness mark that shows through anodizing.

Where a magnetic chuck or a low-melt fixturing compound is used, plan the release step. Thermal release at 60 to 90 °C can move a thin wall if the part is not supported during cooling.

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  One setupOuter profile and pocket cut without a flip
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  Vacuum or soft jawsSpread load, avoid witness marks
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  Angled approachEngage the wall along its length, not head-on

Roughing removes most of the material and leaves 0.3 to 0.5 mm on every cosmetic face. On 6061-T6, a 10 mm three-flute carbide end mill at 12,000 rpm and 2,000 mm/min with a 0.5 mm radial step keeps the load low. Climb milling on the finishing pass gives a cleaner wall.

Finishing is where the finish callout is met. For Ra 0.8 to 1.6 μm, a sharp 6 mm end mill at 0.1 mm radial step and 0.05 mm axial step is normal. For Ra 0.2 to 0.8 μm on a visible face, plan a separate finishing cutter and a fresh edge. A worn tool will smear the surface and show as a dull patch after anodizing.

Heat is the enemy of a thin wall. Coolant through the spindle keeps the part near room temperature and flushes chips out of the pocket. If the part warms 10 °C during a long pass, it can grow 0.02 mm over 160 mm and spring back when it cools.

Measure between operations. A shell that is 0.02 mm off after roughing will be 0.02 mm off after finishing, and the finishing pass cannot pull it back. In-process checks on the wall thickness and on the mating face flatness catch drift before the part is scrapped.

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  Roughing stockLeave 0.3–0.5 mm on cosmetic faces
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  Finish step0.1 mm radial, 0.05 mm axial for Ra 0.8–1.6 μm
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  CoolantThrough-spindle flow holds part temperature
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  In-process checksWall thickness and flatness after roughing

Machined edges on a shell are handled by hand or by vibratory tumbling. A 0.2 mm edge break is typical on a cosmetic rim. Leaving a sharp edge looks wrong after anodizing because the coating builds on the corner and darkens it.

Bead blasting sets the surface texture that the anodize will follow. A uniform blast across the whole shell is what makes a matte finish look even. Blasting one face longer than the others creates a sheen difference that only shows up after the bath.

Anodizing adds 5 to 15 μm per side, depending on the process. Type II clear or colored anodize is the common choice for phone shells. Hardcoat gives a thicker, harder layer but shifts dimensions more and can change the color. If the shell has a press-fit feature, allow for the coating in the pre-anodize dimension.

Laser marking is often added for logos, regulatory text or an IMEI field. Keep character height at 1.5 mm or more so the mark stays legible after anodizing. After coating, the part should be checked again for flatness, since the bath and the drying step can relax a thin wall.

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  Edge break0.2 mm on cosmetic rims before coating
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  Bead blastingUniform texture across all visible faces
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  Anodize growth5–15 μm per side, allow in the dimension
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  Laser markingMinimum character height 1.5 mm