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Hairpin Welding in Electric Motors


The boom in e-mobility is generating an increasing demand for electric motors which are manufactured with solid copper pluggable shape windings (called hairpins) in the stator which generate a magnetic field that creates the motion. These copper wires need advanced production methods and strategies including ablation and welding before being ready to use, we discuss these processes below.

Laser Power Demand Focus Beam Ø Linear Speed of spiraling beam Welding Time
 redPOWER QUBE  2kW 1.1  35µm (1/e²)  1m/sec 0.5sec

What is the need for hairpins?

Many electric vehicle manufacturers are moving to copper hairpin technology in place of copper winding in the production of vehicle stators. The hairpin is inserted into the stator and the hairpin/stator are welded together through the use of a laser beam.

Many hairpins are used, typically up to 220 are a common number to be present. Hairpin technology has the advantage of improving the vehicle performance substantially whilst also reducing the overall size of the stator too.

How are hairpins coated?

Copper hairpin wires are typically lacquered or coated with an organic layer (often polyamide-imide (PAI) or polyether ether ketone (PEEK)) to give them electrical isolation and may also have a thin layer of enamel and/or glue too. This layer needs to be removed from the welding zone prior to joining – this can be done by one of our ns pulsed fiber lasers. These wires can take many forms, from straight bar, would coil and small round wire < 3mm to square sections that can be up to 6mm in width. Traditionally this stripping was achieved mechanically, but this doesn’t scale up very well. This is a standard ablation task, which is just one of the many applications for which our range of fiber lasers can be used.

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Welding of hairpins - an e-mobility solution.

Fiber laser welding of hairpins – a solution from SPI Lasers

The challenge when welding hairpins is to produce a high-quality bond with minimized heat input and with minimal spatter. Excessive heating can lead to unwanted burning of the electrically isolating coating and spatter can cause unwanted deposits on the stator with the risk of electrical shorts in the assembly. Hairpins need to provide high process speeds whilst also having ultra-high reliability when used within an electric vehicle.

Our redPOWER 2kW QUBE single mode fiber lasers are ideally suited to this task, they are contact-free and can effectively join the copper wires with low heat input and minimal spatter. Using a scanner-based optical delivery system the small spot size generated by the high beam quality is moved rapidly in a spiral motion using very high linear speeds. This technique helps to control the weld pool and its stability giving rise to deep penetration, low heat input welds with minimal spatter. The spiralling technique gives a lot of flexibility in tailoring the joint for the shape and size of the wires to be joined. This process delivers two major requirements of hairpin welding, namely:

    1. Alignment – the weld must create perfect hairpin alignment. Fiber lasers are absolutely precise and ensure hairpin alignment is 100% perfect, which helps to deliver maximum efficiency of the electric motor
    2. Defect elimination – due again to the levels of absolute precision, no defects are produced. It is important that defects are avoided as they increase the level of resistance and reduce the efficiency of the electric motor operation

Meeting the demand from manufacturers

The surge in the popularity of electric vehicles means that manufacturers face the challenge of needing to deliver high-quality electric motors in volume. SPI fiber lasers are ideal to meet this challenge, as they can be integrated into manufacturing processes seamlessly, enabling the delivery of high-quality batteries in volume.

Welding and ablation solutions and much more from SPI Lasers

Hairpins are just one type of welding, which are made available for users of our fiber lasers. If you are interested in ablation or welding or wider e-mobility and automotive applications then contact SPI Lasers today. Our Continuous Wave and Pulsed fiber lasers can be configured to deliver a variety of applications and solutions, which our experts can discuss with you today. To receive future content updates, click this link.


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