Custom 600mm Metal Cross-Flow Impellers: 65, 75 and 80mm Case Study

What the OEM specified

A European OEM building compact HVAC systems needed three metal cross-flow impeller sizes, each 600mm long. Diameters of 65mm, 75mm and 80mm would give it three performance tiers inside one product family.

The request covered six samples of each diameter, full technical drawings, and a quotation including tooling. In other words, a proper NPI project intended to validate a design before anyone commits to volume.

Here the tolerances tell you what kind of application this is.

• Overall length 600mm, held to plus or minus 0.5mm.
• Residual unbalance under 300 mg across that 600mm length.
• A shaft bore of 8mm with a tight fit tolerance.
• Blade-to-blade chord length varying by no more than 0.5mm.
• Radial runout at the shaft end capped at 0.10mm.
• Unmarked tolerances to GB/T 1804-V.

Metal rather than plastic was chosen on purpose. Plastic wheels are cheaper and lighter, yet they flex and they creep when warm. When you are chasing a 300 mg balance figure, a stiff metal cross-flow impeller is what makes the number reachable at all.

Building the metal cross-flow impeller family

We logged this as light development with a material quote, since it makes new sizes of a metal cross-flow impeller we already build.

Extrusion or riveted assembly

This was the choice that shaped everything. Aluminum extrusion gives a lovely, even blade shape. We turned it down anyway.

The reason is tooling. Extrusion needs its own costly die for each of the three sizes, and it fixes the length. Any later change means new tooling again.

So the team picked riveted assembly instead. Blades are pressed from aluminum sheet, then riveted to pressed end plates and fitted to a steel shaft. One blade die serves all three sizes, and only the end-plate tools change. Consequently samples come faster, and later length changes stay cheap.

Aluminum rather than steel

Steel was available and was not chosen. Aluminum gives a better strength-to-weight ratio, which lowers rotational inertia and eases the load on the motor bearings.

More to the point, lower mass is what makes the balance figure reachable. Unbalance is a mass moment, so a lighter wheel starts nearer the target before any correction. That is how LWMI-φ65X600-01, LWMI-φ75X600-01 and LWMI-φ80X600-02 hit the 300 mg limit every time, not now and then.

We approved those drawings, added a costed proposal with the NRE tooling fee, and sent the lot to the customer.

Technical Specifications

Three diameters share one length and one bore. The tolerances below, rather than the dimensions, are what turned this metal cross-flow impeller job into a development project.

Technical Documentation

Meanwhile the following documents were generated as final deliverables during the engineering phase. They provide the necessary data for OEM system integrators and quality assurance teams.

The document package contains the final approved technical specification sheets for the 65mm, 75mm, and 80mm metal cross-flow impellers, required by OEM design engineers for system integration.

Here the annotated engineering drawing shows the key dimensional requirements and tolerances for the custom 80mm cross-flow impeller, serving as a master reference for quality control.

Why this NPI came here

Custom fan parts are where NPI work usually stalls. Either on speed, on tooling cost, or on test. Four things helped here.

• Drawings and a full quotation in days. The project ran from enquiry to approved drawings and a costed proposal, tooling included, inside our standard 90-day NPI framework. European suppliers commonly quote 12 to 18 months for custom-tooled parts.
• Tooling that does not punish three sizes. Developing three diameters normally means three sets of tools. Sharing a blade die across all three, and building in Ningbo, puts both tooling and unit price materially below European equivalents.
• Samples before commitment. Six pieces of each size for fit and performance testing is a normal step here, not a favor. It lets the OEM finish design validation before raising a production order.
• Tolerances that are actually held. A 0.10mm runout limit needs process control, not just a final check. Ours runs under ISO 9001, with performance testing audited against AMCA 210/211.

Browse our cross-flow impeller range, or the impeller section for other types. Balance quality grades are defined in ISO 21940.

Questions about custom impellers

How long do custom impeller samples take when new tooling is needed?

Expect 46 to 70 days from kickoff for a new metal cross-flow impeller, covering final design, tooling fabrication and the first sample run. Once tooling exists, repeat production runs on a normal make-to-order lead time of 15 to 25 days.

Can you supply the complete fan, not just the impeller?

Yes. This case study covers the LWMI metal cross-flow impeller on its own, but we build complete assemblies including scroll housing and motor. The impeller can be paired with a traditional AC shaded-pole motor or with a SmartEC brushless DC motor carrying 0-10V, PWM and RS485 control.

Is there a tooling charge, and is any of it returned?

Yes, a new diameter carries a one-time NRE charge for stamping and assembly tooling, typically USD 12,000 to 40,000 depending on complexity. Under our standard NPI terms we credit half of it back against your first mass production orders.

Why does residual unbalance matter so much on a 600mm impeller?

Because unbalance force rises with the square of speed and with the distance from the axis. On a long, slender wheel a small mass error at one end produces a couple rather than a simple force, which shakes the bearings at both ends. That is why the specification is written as a figure for the full 600mm length rather than per plane.