Alloy Precision CNC Machining Services

Cutting metal alloys on computer-controlled mills and lathes to tolerances tight enough that the part fits without hand work: that is the short definition of alloy precision cnc machining. In our shop the tight band runs to ±0.005 mm on critical features, with surface finish held between Ra 0.2–0.8 μm and Ra 0.8–1.6 μm depending on the feature. Not every dimension on a drawing needs that. We mark the ones that do and leave the rest at general tolerance.

The alloy choice drives almost everything downstream. Aluminum 6061 and 7075 cut fast and hold a good finish, so they suit housings, brackets and heat sinks. Stainless 303 and 316L machine clean but work-harden if you dwell in the cut, which is why we keep feed per tooth up and never let the tool rub. Titanium TC4 and Inconel sit at the other end: low thermal conductivity, high cutting temperature, short tool life. Those parts need rigid setups, flood coolant and a conservative stepover.

Tolerance is a process decision, not a machine spec. A ±0.005 mm bore in a 200 mm long aluminum part behaves very differently from the same callout in a 40 mm stainless block. Thermal growth, residual stress and clamping force all move the part between roughing and finishing. We rough, let the part stabilize, then finish in a separate setup when the geometry allows it.

A three-axis machine cuts one face per setup. That is fine for plates, manifolds and any part where all critical features are reachable from a small number of directions. We keep 27 three-axis machines for exactly that work, plus 12 four-axis mills for parts that need indexing around one axis, such as shafts with cross holes.

Five-axis work earns its cost when the part has compound angles, deep pockets or features on five sides that must stay in one datum. Our 16 simultaneous five-axis centers hold that datum through the whole cut, so hole-to-hole position does not drift across setups. Impellers, turbine blades, robotic joints and bone plates are typical. If a part can be made in three setups on a three-axis machine, moving it to five-axis adds cost without adding much.

Mill-turn centers handle parts that are turned and milled in one program. We run 16 of them. A stainless valve body with a turned bore and milled ports usually comes off a mill-turn in one cycle instead of two, which removes a re-chuck and the concentricity error that comes with it.

Heat is the main enemy. Aluminum expands roughly twice as fast as steel per degree, so a part that measures on size at 25 °C can drift out of tolerance by the time it cools. We measure critical features after the part reaches room temperature, not straight off the machine. For long parts we sometimes leave a finishing allowance and take the last cut cold.

Tool wear shows up as a slow drift, not a sudden jump. On a 500-part run of 17-4PH, the first and last parts can differ by more than the tolerance band if nobody watches the offset. Our operators check dimensions at set intervals and adjust the wear offset; the inspection record travels with the job.

Fixtures matter as much as the spindle. Thin-walled aluminum housings deflect under clamping force. We use soft jaws, vacuum plates or sacrificial tabs so the part is supported where it is weak. If a wall is under 1 mm, we say so before quoting and propose a different holding strategy.

We inspect 100% of parts before shipment, covering raw material check, in-process monitoring and final inspection, with reports on request. Across production the qualification rate sits at 99.99%.

CNC wins on tight tolerance, complex geometry and modest volumes. It loses on cost per part once volumes climb into the tens of thousands and the geometry is simple. A die-cast or vacuum-cast blank that is then finish-machined only on the critical faces is often cheaper at that point, and we run both processes in-house, so the comparison is honest.

Sheet metal is the better answer for enclosures and brackets under about 3 mm thick. Cutting and forming a flat pattern beats milling a pocket out of solid plate on material cost and cycle time. We keep sheet metal fabrication separate from the machining cells for that reason.

If the alloy itself is the problem, changing it may beat changing the process. A 7075 bracket that keeps cracking in service may be better in 6061-T6 with a thicker section, or in 17-4PH if strength is the driver. Send the drawing and the load case, and we will say which route we would take.