CNC Machining for Aerospace: AS9100D, Traceability and the Parts That Carry the Load

Aerospace parts fly. When a bracket or fitting fails in service, it is not a warranty claim; it is an investigation, and the paperwork follows the part for decades. That is why aerospace buyers want more than tight tolerances. They want proof: material certificates, controlled processes, first article reports, and a supplier whose quality system survives an audit, not just a quotation.

Why Aerospace Machining Is Different

Three things separate aerospace work from commercial machining. First, materials are certified and traceable to their heat lot. Second, the processes are documented and controlled, from tooling to coolant. Third, the first part off the line is inspected and documented in a first article report, and the standard that defines how is AS9102, currently revision C, published by SAE in 2023. Close enough is not a phrase in this vocabulary.

The Materials That Define the Work

Titanium 6Al-4V shows up wherever the part must be light and strong, and it earns its reputation: hard on tooling, prone to heat, and slow to machine. 7075-T7351 aluminum covers structure that does not see extreme temperature. 17-4PH stainless handles actuators and fittings, and nickel alloys like Inconel take the hot sections.

Aerospace parts also carry brutal buy-to-fly ratios. On many machined components, 70 to 90 percent of the raw material ends up as chips. That much removal is where heat and residual stress live, and it decides the machining strategy more than any other factor.

Heat, Residual Stress and Thin Walls

Machining is a controlled way of releasing stress. Remove material unevenly and the part moves: it warps off the machine, then warps again when the next layer is cut. Aerospace tempers exist for this. T7451 and T7351 aluminum are stress relieved at the mill, but the shop still works in a sequence: rough, stress relief where the drawing or process calls for it, semi-finish, then finish. Thin ribs that carry load are machined last, so the heat of earlier cuts cannot pull them out of shape.

Five-axis machining earns its cost here. A part with thin walls and compound surfaces needs the tool to stay short and stiff, and it needs all critical features completed in one setup so datums do not move between operations.

What AS9100D Changes in the Shop

AS9100D is the aerospace quality management baseline, and it changes daily habits: risk-based thinking in planning, control of records and calibration, documented nonconformance handling, and audit readiness at any moment. The visible outputs are material traceability at lot level and a first article report per AS9102 that accounts for every characteristic on the drawing, with the measurement data to back it.

What We Do at KGL

KGL holds AS9100D certification and machines titanium alloys, aluminum alloys and stainless steel on 3, 4 and 5-axis centers. First article inspection follows the AS9102 process, with CMM data and material certificates kept with the lot records. Twelve years of precision CNC work show up in the parts that carry the documentation: thin-walled, tightly toleranced components that arrive with the proof the buyer's quality department will ask for anyway.

Conclusion

For aerospace, the machining capability is table stakes; the quality system is the product. Choose a supplier whose shop floor habits match the brochure, whose first article reports survive review, and whose material traceability is real. The part that flies is the one that can prove where it came from.

FAQ

Q: Do all aerospace parts require an AS9100D supplier?

A: Prime contractors and most Tier 1 suppliers require AS9100D as the baseline, and a first article inspection per AS9102 is standard on new parts. Some commercial and tooling work falls outside that, but the quality habits should not.

Q: How do you keep thin-walled titanium parts from distorting?

A: With stress-relieved stock, a controlled rough-to-finish sequence, fixtures that support the thin sections, and 5-axis one-setup machining so the tool stays short and stiff. Distortion is managed by process, then verified by measurement.

Q: What documentation comes with an aerospace part?

A: Material certificates with heat lot traceability, a first article report per AS9102 covering the drawing characteristics, CMM inspection data, and process records. The documentation is part of the deliverable, not an extra.