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.
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
- 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
Challenges of hairpin technology
- Tolerances in bending and positioning
- Contact quality during welding
- Efficient cooling at high power density
- Minimisation of stray losses
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.
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.
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.