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Comparison of I-pin, Hairpin, and X-pin

Honest| 2023-12-20|Return

What is hairpin winding?

Hairpin wrapping involves the use of preformed "hairpins" made from flat copper strips bent into a U-shape, similar to how hairpins work. They are then inserted into the slots in the motor's stator. Compared with traditional round wire winding, hairpin winding has the following advantages:


Hairpin winding’s advantages:

1. High power density. Compared with the traditional circular winding method, the motor with flat wire winding has a larger cross-sectional area and higher current carrying capacity, making the motor more compact and powerful. And the slot fill factor is higher, which can save space. Under the same volume, flat wire winding can output higher power than circular wire winding.

2. Lower loss. Since copper has a rectangular shape, it has less resistance, which reduces energy losses and increases efficiency.

3. Simplified structure. The hairpins are inserted directly without soldering or welding connections, simplifying the assembly process.

4. Enhanced cooling. The increased surface area of the flat bar improves heat dissipation and contributes to better thermal management.

5. Design flexibility. Different hairpin shapes and sizes can be used to optimize motor performance for specific applications.


Hairpin winding’s disadvantages:

Flat wire winding is more expensive to manufacture. Since flat wire winding requires special coil winding processes and equipment, the manufacturing cost is high. In addition, the irregular shape of the coil cross-section of the flat wire winding requires special insulation treatment and protection measures, which increases the manufacturing difficulty and cost. 


The methods of hairpin winding:

According to the manufacturing process, the winding methods of flat wire motors mainly include I-pin, hairpin and X-pin.

1. I-pin

Introduction: I-pin winding is an axial embedded winding. It uses I-shaped flat wire conductors for winding. After directly embedding the flat wire conductors axially into the core slot, the two ends are twisted and welded.



(1)Higher slot fill factor. The slot fill factor of I-pin winding can reach about 74%, which is 4% higher than hairpin winding.

(2)Smaller welding end size: The I-pin winding has a smaller welding end size, which can reduce the copper losses of the motor.

(3)Lower winding cost: The winding cost of I-pin winding is lower, mainly due to the reduced cost of the welding process.



(1)Slightly less reliable: I-pin winding is slightly more complex and has a greater number of welding points.

(2)slight low efficiency: I-pin takes up additional radial dimensions, has a long tail, and consumes a lot of copper. As the temperature increases, the efficiency will also decrease.


2. Hairpin

Introduction: Hairpin winding requires pre-formed the flat copper wire into a hairpin shape, and the other end is a welding end, making the manufacturing process difficult. However, due to the reduction of welding at one end, the overall copper consumption is lower than that of the I-pin winding, and the motor efficiency is also improved to a certain extent.


Features: The manufacturing process of hairpin winding is relatively more complicated than that of I-pin winding. There is an additional pre-forming step in the manufacturing process, and the shape is similar to a hairpin.

 hairpin wire


(1)High slot fill factor. Hairpin winding can effectively utilize the space of the stator core, and the slot fill factor can reach about 70%.

(2)High reliability: The hairpin winding has a simple structure and high reliability.



(1)Larger solder end size. The larger solder end size of the hairpin winding will increase the copper losses in the motor.

(2)Higher winding cost. The winding cost of hairpin winding is higher, mainly due to the cost of the welding process.

hairpin stator assembly

3. X-pin

Introduction: X-pin winding is a flat wire winding technology that uses wavy flat wire conductors for winding. Flat wire conductors have greater flexibility, which reduces motor noise and vibration.



(1)Lower copper loss. The copper loss of X-pin winding can be reduced by about 10%.

(2)Lower winding cost. The winding cost of X-pin winding is lower, mainly due to the reduced cost of the welding process.

 x pin stator winding


(1)Complex manufacturing process. The manufacturing process of X-pin winding is relatively complex, requiring double-sided welding and specialized equipment to form flat wires.

(2)Slightly lower reliability. The structure of X-pin winding is slightly complex and the reliability is slightly lower than hairpin winding.


Comparison of I-pin, hairpin, and X-pin


The same point:

All the above three winding methods have the advantages of high power density, high efficiency, and good heat dissipation performance, which can meet the needs of high-power applications such as electric vehicles. And they are widely used in electric vehicles, aerospace, and industry applications and other fields.



In manufacturing process aspect:

The manufacturing process of hairpin winding and X-pin winding are relatively complex and require special equipment to bend and shape the flat wire.

Instead, I-pin winding is a relatively simple manufacturing process and has no welding requirements.

motor winding section diagram

In reliability aspect:

Hairpin winding: The highest reliability, but also the highest cost.

I-pin winding: higher reliability and lower cost.

X-pin winding: lower reliability and lower cost.



Hairpin winding, I-pin winding and X-pin winding are all types of flat wire winding with high power density and efficiency. Hairpin winding has the highest reliability, but the manufacturing process is complex. The manufacturing process of I-pin winding is relatively simple, but the reliability is slightly lower than that of hairpin winding. X-pin winding has similar properties to I-pin winding, but the manufacturing process is more complex. The selection of the specific winding methods needs to be determined based on product design and actual application needs.


HONEST has successful cases in I-pin, hairpin, and X-pin motor winding and assembly equipment, and has achieved mass production for leading companies in the automotive industry. We have very professional and experienced R&D teams and design teams that can provide customers with customized automation equipment solutions, including manual, semi-automatic and fully automatic.

X-pin Motor Production Line

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