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2025-05-08
Hairpin motors have become more common in electric cars. They are easier to make. They are more efficient and better thermal and power performance than other electric engines.
Hairpin motors make electric vehicles competitive with both combustion engines and previous generations of EVs.
This article will cover the following topics.
· What is the working of electric motors?
· What is a hairpin motor?
· Hairpin Stators: Benefits
· Protective Varnish & Coating for Hairpin Motors
· Hairpin Motor Manufacturing
· Laser Stripping & Welding - To Form a Complete Electric Circuit
· Process of Hairpin Impregnation & Connecting to E-Motor
It's crucial to know how electric motors function before we can understand hairpin motors. These EV motor principles are essential to understanding why hairpins motors make a difference.
Electric motors are used in hybrid and electric cars to convert electricity from batteries into movement. The rotor and stator magnetize in opposite directions to create motion. Rotation is caused by the push-pull force that exists between the stator, and the rotor.
The magnetic field in the stator is created by electricity flowing through the copper coils.
In the rotor it is a completely different situation. In the rotor, the two types of motors that are most common generate magnetic forces differently:
· Magnets in the motor rotor create a magnetic field permanent.
· The magnetic field of the rotor is inducted by motors. Aluminum or copper bars are used in the rotor to induce this magnetic field. These bars, being in the magnetic field of the stator, induce an electric current in them. This then creates the magnetic field in the rotor.
Hairpin motors are electric motors whose stator is wound with round wires, but whose winding uses hairpins. The hairpins, which are large and rectangular compared with wires, have a larger diameter. The rectangular shape of hairpins allows for better space utilization (20% better) due to the better fill factor. A rendering of a hairpin. Hundreds of hairpins are used in the stators of electric drive systems.
The technology of hairpin winding offers a number of advantages:
· The additional copper creates a more powerful magnetic field due to its better fill factor. The rotor can rotate faster and the torque on the wheels is increased.
· Stators can be made smaller if they have a higher fill factor.
· Copper losses (energy losses caused by electric current passing through copper) are very minimal. The optimized winding paths (a symmetrical and identical shape to all turns) are responsible for this.
· Electric motors can produce more power with less energy, extending the range of the vehicle.
· Hairpins are easier to wind because of their symmetrical, solid form. This makes it much simpler than using round wires.
· Stitch cords are required to keep the round wires wound together. (This is known as stator lacing). Hairpins do not require this.
· Long-term, hairpin motors are less likely to fail. It is due to the fact that their conductors, which are larger and more solid, are less susceptible to vibrations.
· Round wires cannot carry as much current as hairpins. The motor and the windings are less heated due to the higher efficiency. It simplifies temperature control and increases the lifespan and reliability of the motor.
· Hairpins are much easier to position than round wires. This allows for a cleaner, more elegant design.
Copper hairpins also have a varnish that acts as insulating material. This prevents electric currents from flowing in any direction when the hairpins come into contact. Hairpin stator varnishes are usually one of:
· PEEK (Polyether ether-ketone)
· Polyamide-imides and polyimide foil
This video shows how a stator is manufactured, which is the defining component of a motor. You can watch the following steps:
· Insulation paper is placed between the hairpins of the stator and the laminations to protect them from abrasion.
· Hairpin manufacturing process
· Tolerances must be met through quality control
· Laser stripping the insulation layer
· Hairpin Laser Welding Process
· This process involves the impregnation of a part of the stator with a powder coat to cover exposed welds.
Hairpins are needed to complete the electrical circuit. While round wires, as used by stators form a path that is continuous in nature, they must be joined together to create a full-circuit. Laser paint stripping, and laser welding are the solutions.
To prevent contamination of the welds, the varnish on the hairpin end needs to be removed before welding.
Laser stripping can remove the insulation layer more precisely and consistently than mechanical abrasion. The rotating brushes need to be maintained regularly to avoid inconsistent results. The brushes also remove copper from the metal base underneath the insulation layer.
Three connector tabs (left) and a bridge (right) have been laser stripped to remove the epoxy before making the final electrical connections.
The exposed side of the stator has hairpin welds. This side needs protection from moisture, oxidation, and other conductive substances. To protect and insulate the welds, an epoxy powder is used. The process of impregnation is used.
This epoxy must be removed from the connector tabs before they can be attached to the other components of the motor during assembly.
Different parts of the stator may require laser stripping and welding, depending on its design. Hairpins, connectors tabs and stators bridges are examples.
Here is an example of laser peeling thick epoxy coatings.
The automotive industry is looking to use hairpin winding as a way of designing motors with greater efficiency.
The hairpin motors are able to keep up with bigger batteries. They also take less space and weigh less, reducing the overall weight of the car. These motors are a good step towards making electric cars more affordable and competitive.