English: Nimonic 90 Turbine Damper CNC Tooling Case: Curved Contact Pads and Thin Hook
A Nimonic 90 under-platform damper needs its tooling budget spent on contact geometry, not bulk stock. A tough Ø10 coated carbide cutter opens the forging, a Ø6 bull nose establishes uniform stock on two curved pads, and a necked Ø3 finisher reaches the thin hook without forcing it. The angled hole and edge breaks receive separate tools so work-hardened material is never rubbed twice.
Accessibility map from the drawing
Contact pad A seats against one blade platform; pad B is profile-controlled 0.025 mm to A and an angled Ø3 hole defines C. The hook is 2.10 ±0.05 mm thick, its root is R1.5 minimum, the relief pocket stops 0.30 mm from the contact envelope, and both pads require Ra 0.8 µm. Only three tool vectors can reach the underside without holder collision, so reach and shank clearance are part of the tolerance plan.
Tool assignments and life budget
| Cutting zone | Carbide tool, geometry and holder | Planned duty |
|---|---|---|
| Forged skin | Ø10 five-flute variable-pitch AlTiN micrograin carbide, 0.08 mm hone, R0.5, hydraulic holder | Adaptive roughing below 12% radial engagement; one edge set is reserved for skin only. |
| Curved pads semifinish | Ø6 five-flute TiAlN bull nose R0.5, 20 mm reach, shrink holder | Constant-cusp passes leave 0.18 mm normal stock on A and B. |
| Pad finish | Ø4 six-flute AlCrN ball nose R2, polished flute, 14 mm reach, high-accuracy shrink holder | Parallel-to-contact finishing with runout below 0.005 mm. |
| Thin hook and root | Ø3 four-flute AlTiN necked end mill R0.3, 28 mm reach, hydraulic micro chuck | Alternating hook faces in 0.4 mm axial bands; tool never removes bulk stock. |
| Scalloped relief | Ø5 four-flute chip-splitter carbide, AlTiN, 18 mm reach | Short trochoidal arcs keep chip thickness above rubbing range. |
| Angled Ø3 hole | Ø2.9 through-coolant solid-carbide drill, 140° point, reinforced margin, followed by Ø2 back-chamfer tool | One continuous feed after spot location; internal exit receives a measured break. |
| External edges | Ø6 four-flute AlTiN 90° chamfer mill, minimum projection | Creates 0.10 mm edges before the final pad pass. |
A ceramic cutter was considered for the open pad but rejected because the damper never offers a long continuous engagement; frequent entry, the forged-skin transition and the thin hook make tough coated carbide more predictable. A long ball nose was also rejected: it reaches the underside but adds compliance where the contact profile is most sensitive.
Five-axis fixture and cutting order
A contoured soft nest supports both future pads while two low clamps act on sacrificial forging tabs. The Ø10 tool opens the central relief and leaves the hooks joined by temporary bridges. Pad A is semifinished, the part is indexed, and pad B is brought to equal normal stock. Only then are bridges reduced and the hook faces alternated. Tool-axis smoothing limits rotary acceleration near the root; every finish path exits onto noncontact material.
High-pressure coolant remains directed at the active flute. Notch wear at the depth line, a brown heat tint, spindle-load slope and profile drift between pad scans form the tool-change rule. Feed is maintained through corners by lead/tilt and path-radius control; dwell or repeated spring passes would work-harden Nimonic 90. Chips are kept short and removed from the nest before indexing.
Inspection and FAQ
A CMM builds A-B-C in the nest and scans both pads on a common mesh. An optical system measures hook thickness and root radius without probe deflection; a borescope checks the angled-hole exit. Surface finish follows the pad contact direction. After unclamping, a free-state scan distinguishes fixture release from cutter error, and a qualified contact master checks seating only after geometry passes.
Which carbide end mill should rough Nimonic 90?
A tough variable-pitch five-flute AlTiN micrograin cutter with reinforced edge and controlled radial engagement is suitable here; the skin tool is not reused for finishing.
How is a thin turbine-damper hook finished without bending it?
Leave temporary support, use a necked Ø3 tool only for residual stock, alternate both faces in small axial bands and remove bridges late.
Why not use ceramic for the curved contact pads?
The engagement is short and repeatedly interrupted; carbide tolerates entry and changing contact more reliably in this hypothetical route.
Compare five-axis nickel-alloy tool-life control and tool choice under interrupted hard-alloy contact.
