What is hairpin technology in the electric motor?
Hairpin technology is an innovative winding process for the manufacture of stators for electric motors. It uses rectangular copper wires, so-called hairpins, which are bent into a U-shape and inserted into the stator slots. The open ends are then contacted by means of laser welding. The process enables precise, repeatable production for series manufacturing.
How does hairpin winding work?
The automated process comprises several steps: preforming the hairpins, mechanically inserting them into the stator slots, connecting the ends on a second level and final impregnation for electrical insulation. Each step is designed for reproducibility and tight tolerances.
Benefits of the hairpin stator
- Higher fill factor than round-wire windings, with more copper in the slot cross-section
- Lower electrical losses and better efficiency
- Improved thermal properties through denser packing
- Higher process reliability and reproducibility in series production
- Optimal for traction drives of electric vehicles
Difference from conventional windings
In contrast to classic round-wire windings, hairpin winding offers a geometrically defined, structured winding with high density instead of a chaotic winding. The standardised wire shapes enable automated production with tight tolerances, which is particularly critical for large-series production in e-mobility.
The role of the stator in hairpin motors
The stator is the heart of every electric motor, including the hairpin motor. It generates the electromagnetic field that sets the rotor, the rotating component, in motion. In hairpin stators, the current flow is particularly efficient thanks to lower losses.
Influence of the stator on power density
The more compact the stator and the higher the copper fill factor, the better the power density. Hairpin technology enables compact designs with high efficiency, a real advantage where installation space in electric vehicles is limited.
Components of the hairpin stator
- Laminated core: layered, insulated electrical steel sheets
- Hairpin windings: U-shaped rectangular copper wires
- Insulating materials: slot insulation, phase insulation
- Connection systems: contacting and wiring
Materials for hairpin winding
- Copper for the hairpins (high conductivity)
- Electrical steel for the stator laminated core, for example M270-50A or comparable grades
- Epoxy resin or vacuum impregnation agents for fixation
- Insulating films or paper for the turn insulation
Assembly process
The manufacturing of a hairpin stator comprises six main steps:
- Bending the hairpins into the desired U-shape
- Inserting into the stator slots
- Stripping the wire ends
- Positioning and alignment
- Laser welding of the contact points
- Electrical testing and impregnation
Process reliability during assembly
- Use of laser measurement technology for position verification
- Inline quality controls
- Automated assembly lines with camera-based monitoring
Technologies used in the assembly process
- Laser welding for precise contacting
- Robotics for parts handling
- CNC bending machines for hairpin preparation
- Thermography for testing thermal performance
Challenges of hairpin technology
- Tolerances in bending and positioning
- Contact quality during welding
- Efficient cooling at high power density
- Minimisation of stray losses
Influence of tolerances on manufacturing
Even small deviations in bending or inserting the hairpins can lead to contact problems. Process-reliable production therefore relies on high-precision manufacturing machines and real-time measurement systems.
Methods for minimising losses
- Optimised welding process to reduce contact resistances
- Use of high-purity copper
- Thermal simulation, for example with ANSYS, for cooling design
Efficient winding design
Individual hairpins are arranged in a planar layout, creating a uniform electric field. This ensures low losses, especially at high frequencies. Wave winding additionally improves the thermal balance.
Importance for e-mobility
Hairpin technology enables compact, powerful motors with higher efficiency, lower energy consumption and less waste heat. These properties are decisive for range and efficiency of electric vehicles. The automotive industry is increasingly adopting hairpin stators for its traction drives.
Role in the automotive industry
Hairpin windings are state of the art in modern traction motors. Major OEMs use them to achieve higher torque with a smaller footprint, especially in electric vehicles and plug-in hybrids.
Use in commercial vehicles
In commercial vehicles, high continuous load capacity is decisive. Hairpin motors deliver exactly that: high thermal load capacity, low losses and a long service life.
Wave winding
In wave winding, the current path runs continuously in a spiral pattern across several slot areas. This enables optimal use of space, improved heat distribution and uniform current distribution in the stator. This technique is also known as continuous hairpin.
Technologies for producing wave winding
- 3D bending machines
- Simulation software for design
- Automated insertion systems
Influence of wave winding on thermal performance
The uniform current flow and the large contact area between copper and heat sink significantly improve thermal dissipation. This is decisive for high continuous output and efficient temperature management.
GOBA Takeaway
Hairpin winding is a key technology for the next generation of electric drives. It combines a high fill factor, superior thermal properties and automated manufacturability. For the electrical insulation in hairpin stators, high-quality insulating materials and clean processing are indispensable.