Which is More Reliable: Laser Welding, Soldering, or Cold Crimping?

—A Comparison of Winding Wire Joining Processes

In the manufacturing of transformers and reactors, the choice of joining process directly impacts device efficiency, lifespan, and failure rates. Laser welding, soldering, and cold crimping exhibit significant differences in conductivity, mechanical strength, and thermal stability. Each method also carries potential failure risks that require careful evaluation. For example, the heat-affected zone (HAZ) in laser welding may cause uneven high-frequency current distribution, the low melting point of soldering can lead to secondary short circuits during overloads, and micro-voids in cold crimping may increase contact resistance over time. This article compares the core metrics and failure consequences of these processes, referencing international standards (IEC 60076, IEEE C57.12.00), to provide selection guidelines for high-reliability applications.

Content

1. Conductivity Comparison

● Laser Welding

The metallurgical bond in laser welding provides conductivity close to that of the base material. However, grain coarsening in the heat-affected zone (HAZ) can increase localized resistivity. In high-frequency transformers, this microscopic non-uniformity exacerbates the skin effect, causing localized overheating and accelerating insulation carbonization. For instance, a study (IEEE Transactions on Power Delivery) showed that resistance fluctuations in the HAZ can increase high-frequency losses by 5%-8%.

● Soldering

Soldering relies on alloy materials, which have an inherent resistivity about six times higher than copper. Worse yet, solder oxidation and thermal fatigue cracks can progressively increase contact resistance. In one case (EPRI report), a soldered joint in an oil-immersed transformer saw a 30% rise in contact resistance over three years due to solder creep at 120°C, ultimately leading to winding burnout.

● Cold Crimping

Cold crimping avoids thermal damage through mechanical compression, but micro-voids can generate micro-arcs under current flow, and oxidation may gradually increase contact resistance. NASA research found that unplated cold crimps in extreme space temperature cycles exhibited a 15%-20% resistance increase over a decade.

Table 1: Conductivity and Long-Term Risk Comparison

2. Mechanical Strength Comparison

● Laser Welding

While laser welds can achieve 90% of the base material’s strength, residual stress and HAZ embrittlement reduce fatigue life. A wind turbine transformer case (Wind Energy Journal) revealed fatigue cracks originating from the HAZ after eight years of vibration, leading to winding fracture.

● Soldering

Soldering offers the lowest mechanical strength (30-50 MPa), and thermal cycling stress can cause joint cracking. Automotive reactor data showed soldered joints failing after 2,000 temperature cycles (-40°C~125°C), whereas laser welds endured over 5,000 cycles.

● Cold Crimping

Cold crimp strength depends on compression rate, but over-crimping can sever wire fibers, weakening the joint. Industry statistics (ICEA S-97-682) indicate that 12% of field failures stem from insufficient compression due to die wear.

3. Thermal Stability Comparison

● Laser Welding

Laser welds share the base material’s melting point (copper: 1083°C), but rapid cooling may create brittle phases. A high-speed rail transformer failure analysis (EN 50329) attributed brittle fracture to excessive weld hardness under short-circuit forces.

● Soldering

Soldering’s critical flaw is its low melting point. In UL certification tests, lead-free solder (SAC305) softened at 217°C, causing inter-turn shorts during 150% overloads.

● Cold Crimping

While heat-resistant, stress relaxation reduces contact pressure over time. ASTM B542 tests showed an 18% crimp force decline in copper terminals after 1,000 hours at 150°C, necessitating elastic seals for compensation.

Process Selection Guidelines

In Summary

Laser welding, soldering, and cold crimping each have distinct advantages for winding wire joining. Laser welding excels in conductivity and mechanical strength, making it ideal for high-reliability applications like high-frequency or high-temperature environments, though HAZ control is critical. Soldering is cost-effective and easy to perform but is limited to low-frequency, low-power, or temporary repairs due to its low melting point and oxidation risks. Cold crimping offers the best balance of cost and stability for mass production, provided silver plating and die maintenance address micro-void and stress relaxation issues. Future advancements, such as IoT-based resistance monitoring and hybrid laser-assisted crimping, may further enhance reliability and adaptability in transformer manufacturing.

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