Streamlining Hairpin Stator Production: What Are the Key Processes and Challenges?

Flat wire motor stators deliver superior power density and efficiency, but their manufacturing involves precise, multi-stage processes. Here's a breakdown of the core production steps and current industry challenges:

1. Slot Liner Insertion: 

Insulation between conductors and the stator core is critical. This involves forming O, C, B, or S-shaped slot liners (typically O-type; B/S offer better insulation but lower copper fill and complexity), cutting, and inserting them into the stator slots. A major automation hurdle arises when two separate liners are required between phases, reducing power density and complicating robotic insertion. Advancements focus on integrated liner designs to overcome this.

2. Hairpin Coil Fabrication:

Straight copper strands undergo straightening, insulation stripping (laser stripping is precise but costly; traditional methods risk copper damage), cutting, and forming into hairpin shapes (I-PIN, Hairpin, Wave Winding). Forming techniques include stamping and gentler, higher-cost CNC spring forming, which minimizes conductor stress.

3. Automated Coil Insertion: Pre-formed hairpins are loaded into a fixture and inserted as a complete set into the stator core slots, pressed to their final position. Significant progress has been made in automated insertion complexity, moving from 2/4 layers to advanced 6/8-layer systems, now achievable by leading manufacturers.

4. Expanding, Twisting & Welding:

Expanding: Fixtures position the stator. A tool grips and radially expands the ends of all but the innermost hairpin layers.

Twisting (Transposing): Tools align the innermost layer ends. A twisting mechanism rotates inner and outer dies in opposite directions to bend the hairpin legs into position for welding. This repeats layer by layer.

Welding: Laser or TIG welding are common, using localized high heat to melt copper and form electrical connections. Alternatives like CMT (Cold Metal Transfer) exist. Key drawbacks of laser/TIG include potential insulation damage from heat, compromising reliability, and slow point-by-point welding, hindering throughput for stators requiring hundreds of joints. Faster, cooler welding methods are a critical industry need.

5. Insulation Coating & Impregnation:

This seals the winding. Processes typically involve:
Coating: Stator preheating, applying powder or liquid insulation, then curing.
Impregnation (Varnishing): Preheating, applying varnish via traditional dipping, Vacuum Pressure Impregnation (VPI), or drip methods, followed by gelation and full curing. VPI is often preferred for superior penetration and void elimination. Post-impregnation checks like weight comparison ensure quality.

Key Industry Drivers:

Automation is paramount, especially for complex slot liners and high-layer insertion. Enhancing welding speed and reliability while protecting insulation remains a top priority. Optimizing impregnation techniques ensures long-term dielectric strength and thermal performance in demanding electric vehicle and industrial applications. Continuous refinement of these processes is essential for scaling high-performance hairpin stator production efficiently.

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