How is welding quality ensured for ultrasonic metal welding in new energy vehicle (NEV) motors?

I. Hardware-based assurance (preventing welding defects at the source)
1. Stable ultrasonic system output
• Automatic frequency-tracking generator: Delivers stable, constant-amplitude output at 20 kHz; amplitude remains steady despite fluctuations in copper wire thickness or layer count, preventing localized over-welding (insulation burn-off) or under-welding (delamination);
• High-strength titanium alloy sonotrode + hardened steel anvil: Wear-resistant with uniform hardness; maintains shape and integrity during long-term mass production, ensuring consistent weld-point patterning; periodic flaw detection checks for sonotrode cracks to prevent batches of defective welds (cold joints) from reaching the next stage;
• Closed-loop pressure servo cylinder: Precisely controls welding pressure (adjustable from 2000–8000 N for hairpin motors) with real-time feedback; eliminates issues such as poor bonding due to insufficient pressure or increased internal resistance caused by excessive pressure flattening the copper wire and enlarging its cross-sectional area.

2. Positioning and error-proof tooling
• High-precision visual positioning (±0.02 mm): Ensures precise alignment of hairpin flat wire ends and multi-layer copper foil busbars, preventing off-center welding or one-sided bonding;
• Specialized insulation protection tooling: Isolates and protects stator insulation film, coil formers, and sealing rings outside the weld zone; prevents the sonotrode from scraping the insulation layer, thereby eliminating risks of future electrical leakage or short circuits;
• Layered clamping fixtures: Securely clamps and aligns multi-layer copper foils or wires, eliminating inter-layer gaps and preventing fusion failure between layers.

3. Temperature Control and Dust Removal Systems
• Circulating water cooling for the welding head: Prevents temperature rise during prolonged continuous welding, avoiding heat conduction that could melt the insulation of enameled wires.
• Negative-pressure dust removal at the welding station: Extracts metal micro-particles to prevent residual copper dust from causing inter-turn short circuits in the motor.

II. Closed-Loop Control of Standardized Process Parameters (Core process controls to prevent under-welding and over-welding)
The four core ultrasonic welding parameters are linked to the work order, and equipment settings are locked to prevent unauthorized modification: amplitude, hold time, weld time, and weld pressure.
1. Establishing standard process windows by product type
Hairpin flat wire terminals: Medium amplitude, high pressure, and short weld time; ensures bonding of copper atoms across layers without collapsing the conductor cross-section.
Fine enameled wire bundle terminals: Low amplitude to minimize damage to the enamel coating.
Dissimilar copper-aluminum busbars: Extended hold time to fully break through the oxide layer and prevent the formation of a brittle, high-resistance interface layer.

2. Real-time process curve monitoring and data acquisition
The system records energy, displacement, and pressure curves every second; alarms trigger and workpieces are rejected immediately if the following anomalies occur:
Total ultrasonic energy too low → Under-welding; insufficient bond strength.
Sudden energy spike or excessive copper wire compression → Over-welding; reduced copper wire cross-sectional area and increased internal resistance.
Excessive displacement fluctuation → Copper wire misalignment or inter-layer gaps.

3. Process window validation via tiered trial production
Process boundary testing: Testing maximum/minimum wire diameters and maximum/minimum layer counts to identify the acceptable operating range; mass production is set within the safe middle range so that minor fluctuations in incoming materials do not result in defective products.

III. Incoming Material Pre-treatment and Control (Eliminating welding failures caused by oxidation and oil contamination)
Oxidation of motor copper components, drawing oil residues, and residual insulating varnish are primary causes of cold joints; therefore, the following pre-treatment controls are implemented:
1. Enameled copper wire: Precise stripping of insulation in the welding zone-ensuring no residual varnish and no damage to the copper substrate due to over-stripping.
2. Copper busbars/foils: Degreasing to ensure surfaces are free of oil; sealed storage to prevent oxidation; prohibition of using components with severe oxidation in production.
3. Copper-aluminum transition components: Removal of the aluminum layer's anodic oxide film via grinding prior to processing; otherwise, a metallurgical bond cannot be formed at the interface.
4. Incoming material thickness: 100% inspection; materials falling outside thickness tolerances are prohibited from entering the welding station.