Rotor Shafts

Electric vehicle powertrains present different mechanical engineering challenges compared to traditional powertrain architectures. These challenges come in many forms, including higher working RPM’s, to lower noise limits, to increased heat transfer capabilities and so on.

Rotor shafts have evolved over recent years. Originally solid machined forgings, shafts moved to lighter weight designs through additional center drilling. This in turn evolved to hollow shafts that provide greater weight reduction. The latest step in rotor shaft evolution is to increase their function from solely supporting the laminates, to additional activities such as cooling management or integrated differential gears. NETFORM has developed novel manufacturing processes that allow the cost-efficient production of advanced rotor shafts with integral cooling and component consolidation.

NETFORM’s Flowforming and Press Forming technologies help overcome the product design limitations that come with using a shaft preform designed from traditional manufacturing processes. Using NETFORM’s advanced forming processes, product engineers can achieve part consolidation, weight reduction, cooling system incorporation and cost reductions not
previously possible.

Product Domain



Flowformed Motor Shafts

NETFORM’s flowforming approach to manufacturing rotor shafts provides many options for part optimization. With the correct design and manufacturing approach, weight can be reduced and cooling performance increased, while still meeting or beating cost and weight targets.

In addition, the usage of a forged preform allows for the incorporation of
traditionally-separate components. The key factor is having design discussions (at concept stage) with all parties involved – manufacturing, product engineering, assembly. This way the optimum design can be achieved at the lowest cost.

Manufacturing Process

Forged Preform



Video courtesy of WF Maschinebau

Rotor Shafts – Flowformed Design Options


  • Flowformed rotor shaft
  • Machined cap
  • Laser-welded

One-Piece Rotor Shaft

  • Flowformed forging
  • Cooling unit inserted – optional
  • End “necked” as required

One-Piece With Cooling Tube

  • Tubular preform
  • Outer tube reduced, trapping inner tube
  • Process repeated to the other end
  • Uni-directional coolant flow
Rotor Shaft with cooling insert

Two-Piece Longer Shaft

  • Two flowformed rotor shafts
  • Center laser-weld
  • Coolant control cylinders and center support are an optional addition

One-Piece With Internal Cooling Tube

  • Flowformed forging
  • Cooling tube inserted
  • Shaft reduced, trapping tube
  • Bi-directional coolant flow

Flowformed Rotor Shaft Features

Integrated Traditionally Separate Components

The process also allows for the incorporation of traditionally separate components into the shaft itself, such as reluctor wheels/speed sensors.

Cooling Unit Integration

The cooling unit is placed inside the rotor shaft before being necked down.

Heat Transfer Improvements

One key product feature is the ability to integrate cooling fins on the inside of the tube. The inside surface area of the tube increases by up to 70%, improving heat dissipation.

Keyway-Driven Weight Reduction

In applications where maintaining cross-sectional thickness is critical for the structural integrity of the rotor shaft, NETFORM can offer formed internal features where wall thickness can be held consistently throughout the shaft, even when keyways are required for laminate retention.

Technical Information 

  • Materials: Low Carbon Steels
  • Diameter: 40 mm min – 250 mm max
  • Max Length: Up to 350 mm
  • Work Hardening: Up to 2-3X original strength.
  • Forming capabilities:
    • Formed Diameters ±0.10mm
    • Tooth Space ±0.05mm
    • Runout between Inside Diameters 0.05mm


Flowforming is a cold forming process in which a set of roller tools apply pressure to a rotating workpiece over a mandrel tool to form a symmetrical part. The rollers deform the preform, forcing it against the tool (also known as a mandrel), axially lengthening and radially thinning the material.

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Blog Article

NETFORM has created a hollow rotor shaft design that works well for both low and high torque applications. This advanced, light-weight rotor shaft is made up of two flowformed half shafts that are laser-welded together in the center.

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The NETFORM approach can help you reduce emissions, improve performance and drive profitability.

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