CNC aerospace and defense components: what drives the process

Most CNC aerospace defense components we cut are aluminum, titanium or stainless. Aluminum covers brackets, housings, ribs and panel supports. Titanium covers loaded fittings, engine-side hardware and anything that sees heat plus vibration. Stainless and 17-4PH cover actuator parts, fasteners and valve bodies where corrosion resistance matters more than weight.

Grade choice matters more than most drawings admit. For aluminum, 6061-T6 is the default because it machines clean and welds well. Moving to 7075 buys strength but costs tool life and adds stress-corrosion risk if the part sees salt spray. For titanium, TC4 (Ti-6Al-4V) is the workhorse. It cuts slowly, generates heat fast, and needs sharp tooling and heavy coolant. Budget more cycle time and expect more tool changes than an aluminum job of the same shape.

Inconel and magnesium sit at the edges. Inconel is used for hot-section brackets and exhaust-side hardware; it is machinable but slow, and it work-hardens if the cutter rubs. Magnesium AZ31B and AZ91D cut fast and light, but the chips burn, so the shop has to treat them as a separate process with its own housekeeping.

Plastics show up in panels, insulators and mockups. PEEK and carbon fiber are the two we see most in defense work. PEEK holds dimension at temperature and resists chemicals. Carbon fiber is abrasive and eats cutters, so it is usually routed rather than milled with standard end mills. If a part does not need metal, saying so early saves money.

• 1
  Aluminum 6061-T6, 7075, 2024Brackets, housings, ribs. Good strength-to-weight, easy to anodize.
• 2
  Titanium TC4 (Ti-6Al-4V), TA1, TA2Loaded fittings and heat-side hardware. Slow cutting, sharp tooling required.
• 3
  Stainless 17-4PH, 316L, 15-5 style gradesActuators, valve bodies, fasteners. Corrosion resistance first.
• 4
  Inconel, magnesium AZ31B / AZ91DHot sections and weight-critical housings. Both need special handling.

A five-axis machine earns its cost when the part has features on more than three faces, or when a compound angle has to be cut without a fixture that costs more than the part. We run 16 simultaneous five-axis machining centers, 12 four-axis mills and 27 three-axis machines. The right answer is not always five axes. On a simple plate with holes and a pocket, a three-axis machine with a good fixture is faster and cheaper.

The real gain is setup count. Every time a part moves between machines, the datum shifts and the tolerance stack grows. Cutting five faces in one setup removes those moves. On a thin-wall rib or a housing with a bore that must stay concentric to a face, that is the difference between holding ±0.005 mm and chasing it.

Tool access drives the decision too. Deep pockets, undercut flanges and contoured channels are hard to reach with a three-axis spindle. A tilting head or trunnion lets a short, rigid cutter reach the feature at the right angle. Short tools deflect less, so the surface finish improves without a second pass.

We work from 3D models, not just 2D prints. STEP and IGES files let us check wall thickness and tool reach before quoting. If the model shows a 0.5 mm wall in titanium, we will say so. That is a conversation worth having before the chips fly, not after.

We hold ±0.005 mm (±0.0002 in) on critical features. That is a floor, not a target for every dimension. Putting a tight tolerance on a non-functional face adds cost and inspection time without adding value. Mark the features that matter and let the rest run to general tolerance.

Surface finish is specified by function. A sealing face or a bearing bore wants Ra 0.2–0.8 μm. A mating face that just needs to sit flat wants Ra 0.8–1.6 μm. An internal pocket that nobody touches can run at Ra 1.6–3.2 μm as machined. Calling out a fine finish everywhere is a common and expensive habit. Call it where the drawing needs it.

Inspection is not an afterthought. We check raw material certificates on arrival, monitor dimensions in process, and run a final inspection on 100% of parts before shipment. Reports are available on request. If your program needs first article inspection or a specific report format, tell us at quote time so the inspection plan matches.

Material traceability travels with the job. Heat lot numbers are recorded, and the certificate chain stays with the part record. For defense work, that paper trail is often as important as the part itself.

Machining is usually the first step, not the last. Aerospace and defense parts often need anodizing, plating, powder coating or laser marking. Doing the finish in-house keeps the sequence under one roof and avoids shipping parts out and back, which is where damage and lost traceability happen.

Anodizing comes in clear, color, hardcoat and conductive types. Hardcoat adds wear resistance on sliding surfaces but builds dimension, so mask the bores that must stay tight. Conductive anodize is used where the part needs a ground path. Electroless nickel, zinc, silver and gold plating cover the rest.

Laser marking needs at least 1.5 mm character height to stay legible after finishing. If your part number or lot code is smaller than that, it will not survive a coating. Tell us the marking requirement at quote time so it is cut before the finish, not after.

The order matters. Bead blasting before anodizing gives a uniform matte look. Polishing before plating gives a brighter surface. Black oxide on steel is quick, but it does not add corrosion protection on its own, so it usually needs an oil or wax topcoat. Each of these steps adds a day or two. Plan for it.

Machining is not always the right process. A part with a hollow internal cavity that no cutter can reach is better cast or printed. A large, thin, single-curve panel is often cheaper as sheet metal. A part needed in the hundreds with a simple shape may be a die casting job. Saying this early saves everyone money.

Very thin walls in titanium are a known problem. Below about 0.8 mm, the part moves during cutting and after stress relief. The fix is usually a design change, not a tighter tolerance. Add a rib, thicken the wall, or accept a softer tolerance on the non-critical face.

Long slender parts are another limit. A 4,000 mm part is within our travel, but the length-to-diameter ratio decides whether it can be held straight. If the part is long and thin, it may need a support fixture or a different process. Send the model and we will tell you which.

Prototypes and low-volume runs are our normal work. There is no minimum order quantity, from one piece to 10,000+ parts. Quotation and free DFM analysis come back within 12 hours, and production can start within 24 hours. Parts ship in 3–5 days on standard jobs. The goal is to catch the design issues before the first cut, not after.