CNC Machining (Milling & Turning)
Also known as: CNC Milling, 5-Axis Milling, CNC Turning, Post-Machining, Hybrid Machining
CNC machining removes material from near-net-shape AM parts to bring critical features — datums, mating faces, bores, threads, sealing surfaces — to final tolerance and surface finish that the AM process alone cannot hold. Milling (3- and 5-axis) addresses prismatic and freeform features; turning addresses axisymmetric features (shafts, flanges, bores). Because AM tolerances are typically ±0.1–0.3 mm and as-built Ra is 5–25 µm, machining is required wherever drawings call for tight GD&T (±0.01–0.05 mm) or fine finishes (Ra <1 µm).
Why AM parts need this
AM is a near-net-shape process. Functional interfaces — bearing seats, O-ring grooves, threaded ports, flange faces, optical datums — almost always need machining to tolerance. Best practice is to design AM preforms with explicit machining stock (typically 0.5–1.5 mm) on critical surfaces, then fixture off an as-built datum and machine only what the drawing requires. Machining hardened AM parts (e.g. aged MS1 at 50–54 HRC, IN718) requires rigid setups, carbide or ceramic tooling, and conservative feeds — these alloys are abrasive and work-hardening. Hybrid machines (DMG MORI LASERTEC) combine DED and milling in one setup, eliminating refixturing between additive and subtractive steps.
Achievable surface finish
Typical input Ra
15 µm
Achievable Ra
0.4–1.6 µm
Machined surfaces only — applies to the specific features machined, not the whole part. Unmachined as-built surfaces retain their original Ra.
Key parameters
Designed onto AM preform critical surfaces. Too little risks as-built defects breaking through; too much wastes machining time.
5-axis milling: ±0.01–0.02 mm. Turning: ±0.005–0.02 mm. Far tighter than the ±0.1–0.3 mm of as-built AM.
Finish milling/turning: Ra 0.4–1.6 µm. Fine boring and reaming: Ra <0.4 µm.
Fixture off an as-built feature or a sacrificial datum printed into the part — never assume the build plate face is square to the part.
Compatible AM processes
Compatible materials
Limitations
- Requires accessible setups — internal channels and lattice interiors cannot be reached by a cutting tool (use AFM or electropolishing instead)
- Hardened AM alloys (aged MS1, IN718, CoCr) are abrasive and work-hardening — tool wear is high, feeds must be conservative
- Fixturing AM parts is non-trivial — irregular as-built surfaces give poor clamping references; design in datums or sacrificial fixturing tabs
- Machining removes the compressive surface layer from shot peening — sequence carefully if both are specified
- Not applicable to most polymer AM functional surfaces (handled by vapor smoothing / mass finishing instead)
Related tools
Providers
GF Machining Solutions (AgieCharmilles)
Georg Fischer AG machining division — AgieCharmilles wire EDM and die-sink EDM alongside high-speed milling centres for AM post-processing, hybrid additive-subtractive workflows, and precision finishing of LPBF parts.
Geneva, CH
DMG Mori Lasertec
DMG Mori's AM division — Lasertec 65, 125, and 3D DED hybrid systems combining 5-axis precision milling with laser metal deposition in a single machine setup.
Bielefeld, DE
Relevant standards
Tolerance and stock-allowance ranges from DfAM best-practice literature and GF Machining Solutions / DMG MORI hybrid-machining application notes (manufacturer tier). General machining tolerances per ISO 2768 / ISO 286.
All post-processing