Briefly Describe Which Types of Parts Are Suitable for Treatment With CNC Machine Tools

The clearest fit is a part whose shape cannot be produced by a simpler process. Think of a housing with pockets on five faces, a manifold with intersecting bores, or a bracket with angled mounting pads. A CNC machine tool moves a rotating cutter along a programmed path, so almost any shape that fits inside the work envelope can be cut. There is no mold to make and no draft angle to add.

Tolerance is the second filter. When a drawing calls for ±0.005 mm on a bore spacing, or a flatness that must hold across a 300 mm face, machining is usually the only route that keeps the number honest. Castings and forgings start close, then need a finishing cut anyway. Sheet metal holds position well but cannot hold a ground bore.

Thin walls deserve a warning. A wall under 0.8 mm on aluminium will deflect under cutting force, and the finished part may spring back after unclamping. Deep pockets narrower than four times the cutter diameter force the use of long, slender tools that chatter. If the feature is unavoidable, expect slower feed rates and a higher unit price.

Curved surfaces and freeform shapes are where simultaneous 5-axis work earns its place. An impeller blade, a turbine vane or a contoured mold insert cannot be reached by a 3-axis spindle without repeated refixturing. Each refixture adds setup error. Cutting the part in one setup removes that error stack.

Our 16 simultaneous 5-axis machining centers cover this class of work, with a Ø400 mm rotary table and travels up to 4,000 × 400 × 150 mm. For smaller prismatic parts we run 12 four-axis mills and 27 three-axis machines.

Aluminium is the easiest starting point. Grades 6061 and 7075 cut fast, hold tolerance and take an anodized finish without special handling. We also machine 2024, 5052, 5083, 6063, 6082 and ADC12 die-cast blanks that need only a light finishing pass on the sealing faces.

Stainless steels are common but less forgiving. Grades 303 and 304 machine cleanly; 316L and 17-4PH work-harden if the tool dwells in the cut. The rule is simple: keep the cutter moving, take a real depth of cut, and never rub. A sharp tool with a positive rake and a rigid setup solves most of it.

Titanium and nickel alloys are where the process slows down. TC4 (Ti-6Al-4V) conducts heat poorly, so the cutting edge absorbs most of the temperature. Inconel is worse. Both cut fine with correct speeds and generous coolant, but expect longer cycle times and more tool changes than an aluminium part of the same size.

Copper, brass and beryllium copper machine easily but are gummy. C36000 brass and C110 copper produce stringy chips that need chip-breaking geometry and steady coolant flow. Plastics behave differently again: POM and PEEK hold tight tolerances, while ABS and PP flex and are better used for covers and fixtures than for bearing fits.

A part that is mostly a thin sheet with a few holes is usually not a CNC milling job. Laser cutting plus a press brake will be cheaper. Machining wins once the part needs a pocket, a thread, a bore or a face that must be flat to a few microns.

CNC machining has no tooling cost, so the first part and the thousandth part share the same setup logic. That is why a single prototype is a normal job for us, not a favor. We hold no minimum order quantity, and a one-off bracket costs the same to program as the first piece of a 10,000-part run.

At higher volume the economics shift. Once a part is simple enough and the annual quantity is large, die casting, investment casting or stamping can beat machining on unit price. Machining still wins when the part is complex, when the quantity is moderate, or when the design is still changing.

A common middle path is to machine the first batch, prove the design in the field, then move the part to a casting tool with machined interfaces. We do both, so the transition is a conversation about which faces must stay machined.

Mixed batches are routine here. A single order can hold 20 different part numbers with quantities from 1 to 500. Setup time is shared across the batch, which keeps small lots affordable.

Size is a hard limit. Our largest travel is 4,000 × 400 × 150 mm. A part longer than that needs a different supplier or a different process. Compact work up to 500 × 500 × 450 mm runs on smaller machines with better access for the operator.

Geometry sets another boundary. A closed internal cavity cannot be cut by a rotating tool, no matter how many axes you add. Undercuts that face away from every tool approach need an EDM pass or a redesign. Sharp internal corners are impossible with a round cutter; the corner radius equals the tool radius, so a 2 mm corner needs a 4 mm cutter at most.

Surface finish has a floor as well. We hold Ra 0.8–1.6 μm as a standard machined finish, reach Ra 0.2–0.8 μm with fine finishing, and leave Ra 1.6–3.2 μm where the drawing allows. A mirror finish on a large face is possible but slow, and it is worth asking whether the function truly needs it.

Quantity and tolerance together decide the process. A tight tolerance on a million parts points to a dedicated process. A tight tolerance on fifty parts points to a CNC machine tool. Most parts sit somewhere between, and the answer usually comes from the drawing rather than from the process list.

Before any of this reaches a spindle, we check the drawing. Upload a STEP or PDF file and we return a quotation with a free DFM analysis within 12 hours. Production can start within 24 hours of approval, and parts usually ship in 3–5 days.