CNC machining in mobile phone manufacturing

• 1
  Why phone parts go on a CNC at all
• 2
  What tolerances and finishes phone parts actually need
• 3
  Wall sections, pockets and features that cause trouble
• 4
  Material choices and what they do to the cut
• 5
  Fixturing, 5-axis work and where errors creep in
• 6
  When CNC is the wrong process for a phone part
• 7
  CNC vs casting vs stamping for phone parts

A phone is mostly plastic, glass and battery. The metal around them is the part that carries the load. A mid-frame ties the display to the board, a camera housing holds three lenses in alignment, and antenna inserts sit within a few tenths of a millimetre of the radio path. Cutting metal gives you that geometry in one setup.

Die casting and stamping can make a phone body cheaper per unit. They struggle with two things: a 0.6 mm wall beside a 4 mm boss, and holes that must line up with a lens stack. CNC machining in mobile phone manufacturing is used where a cutter removes material from a solid block or a near-net casting, so the finished wall can vary in thickness without a draft angle fighting you.

The trade-off is cycle time. A phone frame machined from a 6061-T6 block may take 15 to 40 minutes per part on a 3-axis machine, depending on pocket depth and how many faces need work. A 5-axis machine can finish several faces in one setup, which removes refixturing error but adds programming hours.

So the practical question is not whether CNC is good. It is which parts justify the cutting time and which should stay cast, stamped or moulded.

A phone mid-frame often needs ±0.02 mm on the display seating face, because a 0.05 mm gap shows up as a visible shadow line. Boss heights that contact the battery cover usually hold ±0.05 mm. Camera lens bores are tighter: ±0.01 mm on diameter and concentricity within 0.01 mm, or the lens tilts and corner sharpness drops.

GreatLight works to ±0.005 mm on critical features where the drawing allows it, and ±0.0002 in in imperial drawings. That is not a claim that every phone part needs it. It means the machine and metrology can hold it when the function depends on it, such as a lens barrel seat or a hinge knuckle.

Surface finish matters for different reasons. As-machined Ra 1.6–3.2 μm is fine for internal brackets and shields. Mating faces and visible chamfers usually sit at Ra 0.8–1.6 μm. Lens bores and sliding surfaces go to Ra 0.2–0.8 μm so a seal or a light path behaves predictably.

Finish choice follows the same logic. Anodising adds 5–15 μm per surface depending on type, which can close a tolerance. If a bore must stay 3.00 mm, mask it or cut it undersize before coating. Laser marking needs a minimum character height of 1.5 mm to stay legible after anodising.

The classic phone-part problem is a thin wall next to a thick boss. When you cut a 0.6 mm wall, tool pressure pushes it sideways. The cutter deflects, the wall bows, and the measured thickness varies along the length. Cut the wall in two passes with a smaller radial engagement rather than one heavy pass.

Deep pockets are the second problem. A pocket 8 mm deep with a 2 mm corner radius needs a long, thin cutter. Length-to-diameter above 4:1 invites chatter. Chatter shows up as a rippled floor and a finish that fails on the shop floor. If the design allows a 3 mm corner radius, the cutter gets stiffer and the cycle gets shorter.

Sharp internal corners are not free. A cutter leaves its own radius, so a true 90-degree internal corner needs EDM or a broach. For most phone brackets, a 0.5 mm corner radius is invisible and saves a secondary operation.

Threaded bosses under M1.2 are another boundary. Below M1.2, thread milling is fragile and tapping breaks taps. If the design can use a press-fit insert or a self-clinching nut, the machined part gets simpler.

6061-T6 aluminium is the default for phone frames and housings. It machines fast, anodises cleanly and holds ±0.02 mm without drama. 7075 machines to a better strength-to-weight ratio but is less forgiving of thin walls and can show tool marks after hardcoat anodising.

Stainless 304 and 316L appear in hinge parts and structural brackets. They work-harden, so a light pass with a dull cutter will polish the surface instead of cutting it. Feed per tooth has to stay above a floor, or the tool rubs. 17-4PH is used where a phone part needs corrosion resistance plus higher yield strength after heat treatment.

Copper and brass show up in antenna contacts and thermal spreaders. C101 and C110 cut easily but are gummy; sharp tools and high rake angles help. Beryllium copper is used for spring contacts and needs dust control during machining.

Plastics are common for prototype housings and internal carriers. ABS and PC cut cleanly. PEEK and carbon fibre need carbide tools and slower feeds. Carbon fibre dust is abrasive and conductive, so it is kept away from aluminium chips in the shop.

A phone frame is thin, so clamping it is half the job. Soft jaws machined to the part profile hold it without denting the anodised surface. Vacuum plates work for flat covers but lose grip on a curved back. Every refixture adds a datum shift of 0.01–0.03 mm, which is why 5-axis machines help.

On a 5-axis centre, the tool reaches five faces of a frame without the operator moving the part. A rotary table of Ø400 mm covers most phone and camera module sizes. GreatLight runs 16 simultaneous 5-axis machining centres, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centres, so the setup matches the part rather than the other way around.

The largest travel is 4,000 × 400 × 150 mm. That is not a phone part, but it matters for the fixtures and trays that hold phone parts during finishing, and for the camera test rigs built alongside them.

Heat is the quiet error source. Aluminium expands about 23 μm per metre per degree Celsius. A frame that measures 150.00 mm at 20 °C will measure 150.02 mm at 26 °C. For ±0.01 mm work, the shop and the CMM need to be at a stable temperature, and the part should cool before final inspection.

If a part is a simple flat cover with no tight hole pattern, stamping is faster and cheaper at volume. If the geometry is a thin shell with a uniform 0.8 mm wall and no machined feature, injection moulding or die casting wins on cost per unit.

If the part needs internal channels that a cutter cannot reach, metal 3D printing or die casting with a slide may be the only route. If the surface must be a mirror without tool marks, polishing or a moulded surface beats a machined one on cost.

CNC stays the right answer when the part is a prototype, when the quantity is low to mid, when a hole pattern must align with another machined part, or when the material is one that cannot be cast cleanly, such as 7075 or 17-4PH.

There is also a tolerance boundary. If the drawing allows ±0.1 mm everywhere, a casting plus a light finish pass will do. If it calls out ±0.01 mm on a lens bore and 0.01 mm concentricity, the part belongs on a CNC.