Comparative Analysis of Several Different Hairpin Forming Schemes

Hairpin forming is the first—and a critically important—step in the production of flat‑wire motor stators. As is well known, the processes involved in manufacturing flat‑wire stators are highly interdependent; therefore, ensuring a stable and reliable hairpin‑shaped winding geometry is essential for the efficient operation of the entire stator production line. The following discussion compares and analyzes several mainstream wire‑forming techniques currently available, helping to deepen your understanding of hairpin forming.

Hairpin forming is currently mainly divided into Fully stamped and formed and Full bend forming and also 2D bending + 3D stamping combined forming Three major categories;

All-pressed molding:

• Full‑stamping forming involves using a single die to first stamp the flat 2D shape, followed by stamping the 3D arcs, steps, and S‑bends, thereby completing the hairpin‑shaped part in two consecutive operations.

• The primary advantage of all‑stamping forming is its high line‑shape consistency, coupled with a rapid production rate—up to one part every 2 seconds.

• The drawback is that the mold is large and complex, basically… One piece of equipment can only be fitted with one set of molds. , Replacing the wire type requires changing the corresponding die, which is very cumbersome;

• Due to the inability to automatically generate The production line is all linear and cannot achieve automated wire insertion in a one-piece flow. ；

• The 2D portion of the stamping die cannot achieve inward tapering, so after pin‑line forming, “outward splay” is commonly observed due to springback.

• In addition, due to The copper wire is fully constrained in its degrees of freedom within the die; when transitioning from 2D to 3D, the head will inevitably stretch (depending on the hairpin’s curvature and span). Related to this, a minimum of 2–3 mm is required; otherwise, it can severely compromise the paint film, with 800 V copper wire—having an even thicker paint film—suffering greater damage.

Full bend forming:

• All‑bend forming requires no dies; it achieves the desired shape—whether circular arcs or stepped S‑bends—by precisely controlling the sequence and positioning of the forming guide rods, gradually bending the copper wire into the specified configuration.

• The advantages of all‑bend forming are Very flexible , simply switch the program to produce all line types—no hardware changes required;

• The motion accuracy of the forming guide rod is extremely demanding; even slight positioning errors will be magnified to the Hairpin dimensions.

• The bending speed should not be too fast; otherwise, excessive stress on the paint film at the bend—particularly at S‑bends—may cause insulation damage.

• Due to the large number and complexity of bending operations, the cycle time for full‑bend forming is very slow. At most, it can only achieve 4–5 seconds per strand. ；

2D bending + 3D stamping combined forming:

• First, the copper wire is bent into a flat 2D U‑shape, then fed into a 3D die for 3D stamping; both steps and the wire transfer are fully automated.

• The 2D bending section can produce all line types by simply switching bending parameters, eliminating the need for hardware tool changes.

• In the 3D embossing section, a vertical motion is used to form 3D arcs and stepped S‑curves.

• The mechanical property variations among different batches of copper wire can be compensated by adjusting the 2D bending parameters.

• 3D molds incorporate reserved shrinkage space for the wire legs to prevent end‑stretching issues.

• The advantage of this combined approach is that the 2D section can be entirely flexible, while the 3D mold can be designed to be very compact. A single machine can accommodate multiple molds and automatically switch between them to produce all product lines. , which can be directly connected to automated wire‑insertion equipment to enable single‑piece flow automatic wire insertion;

• The cycle time can be as short as 2 seconds per piece. Combines flexibility, efficiency, and molding stability. ；