Inconel 718 Impeller 5-Axis CNC Machining Case Study

Project Overview

This impeller brought together three constraints that are individually manageable but difficult in combination: a nickel-based superalloy with poor machinability, blade geometry that severely restricts tool access, and blade-to-hub relationships that could not tolerate datum transfer between setups.

The part is a 248 mm diameter impeller with 17 curved blades, machined from solid rather than from a casting. Machining from solid removes the variables that come with cast blanks — porosity, inconsistent allowance, and the datum ambiguity of a near-net shape — but it puts the entire material removal burden onto the cutting strategy.

Rather than present this as a showcase, this page is written as an engineering record: what the customer asked for, what made the part difficult, which decisions were taken and why, and what evidence was produced. If you are evaluating whether the same discipline can be applied to your own geometry, the Inspection & Verification and Final Result sections are the ones that matter.

Xiamen Goldcattle Plastic & Metal Products Co., Ltd. has been manufacturing custom precision components since 1998, operating under an ISO 9001:2015 certified quality management system.

Engineering Challenges

Four constraints shaped every downstream decision. Each one on its own is routine; together they determined the machine, the setup count and the toolpath strategy.

1. 1

   Restricted blade access

   The gap between adjacent blades limits both cutter diameter and shank clearance. As the cutter works toward the hub, the available approach angle narrows and the risk of shank or holder collision against the neighbouring blade rises sharply. Tool length had to be kept as short as the geometry allowed while still reaching the root of each passage, and every toolpath was checked against the full holder assembly — not just the cutting flutes.

2. 2

   Complex curved surfaces

   Each blade is a compound-curved airfoil, not a ruled surface. Holding a consistent Ra 0.8 µm finish across the blade requires continuous control of the tool orientation relative to the surface normal. An indexed 3+2 approach would have left facet marks and inconsistent cusp heights between passes, so continuous simultaneous motion was required rather than a series of fixed-angle cuts.

3. 3

   Datum stability

   The dimensional relationship between the hub, the bore and the blade tips cannot be re-established accurately once the part is unclamped. Any secondary setup introduces a datum transfer error that would show up as blade-to-blade profile variation. The blade-to-hub relationship therefore had to be maintained within a single clamping, from roughing through to finishing.

4. 4

   Inconel 718 machinability

   Inconel 718 work-hardens rapidly and retains strength at elevated cutting temperatures. Cutting forces and heat concentrate at the tool edge, which makes chip evacuation and thermal load the controlling variables. Poor parameter selection in this material produces surface integrity problems — tensile residual stress, a work-hardened layer, or micro-cracking — that are not visible to the eye but matter on a rotating part.

Material — Inconel 718

* Hardness and mechanical properties are taken from the mill certificate for the specific batch supplied, not quoted from a generic datasheet.

Inspection & Verification

Three distinct activities. They are often conflated in supplier marketing — they are not the same thing.

• CMM profile scan

  The blade airfoil surfaces were scanned on a coordinate measuring machine and compared against the nominal geometry. The point of a scan, as opposed to discrete point measurement, is that deviation is evaluated across the whole surface — so a localised high spot between measured points is still detected. This is the only practical way to verify a compound-curved airfoil.

• Dimensional inspection

  Critical features — bore, mounting datum and hub dimensions — were measured against the drawing and recorded in the inspection report. This covers the features that govern how the impeller locates and seals in its assembly, which is where fit problems originate if they are wrong.

• First Article Inspection per AS9102

  A first article inspection documenting measured results for the characterised features. One clarification we make deliberately: AS9102 is a first article inspection standard, not a certification. We report "FAI per AS9102" because that is accurate. A supplier claiming to be "AS9102 certified" is describing something that does not exist.

What This Case Demonstrates

What a buyer can reasonably infer about our capability from this one part — and what they should still ask about their own.

• Complex geometry held in one setup

  Seventeen curved blades with restricted access were completed around a single primary datum. This is the capability that matters when your part cannot tolerate re-fixturing — see our 5-axis CNC machining services.

• Nickel superalloys cut under control

  Inconel 718 was machined with attention to tool engagement and thermal load, not simply at reduced parameters. We cut 718, 625, 600, X-750 and Hastelloy C-276 under the same discipline.

• Verification that matches the geometry

  Compound curves were verified by CMM scan rather than point sampling, and dimensional features were measured separately against the drawing. Reports ship with the part.

• Honest documentation language

  We state "FAI per AS9102" because that is what it is, and we do not claim certifications we do not hold. On a supplier evaluation, the way a vendor describes its own documentation is itself a signal.

• Prototype through to production

  The same planning and inspection approach applies whether the order is a single first article or a repeat run — the process does not change when the quantity does.

• Material traceability from the start

  EN 10204 3.1 certification is standard on every batch, so composition and mechanical properties are documented before cutting begins rather than reconstructed afterwards.

Frequently Asked Questions