Case study: strengthen wave spring performance with CuBe material

By Fernando Gonzalez

RPK Group embarked on an investigation to improve the performance of wave springs by exploring the use of CuBe (Copper Beryllium) material for a long-time client who asked us for a stainless steel + nickel coated wave spring with loading function and electrical conductivity.

Why CuBe material for springs?

Copper beryllium alloys are frequently selected for springs due to their high strength and excellent thermal and electrical conductivity. This material is used for its ductility, weldability in metalworking, and machining properties. CuBe alloys are used in specialized applications across various sectors, including hazardous environment tools, musical instruments, precision measurement devices, and aerospace—a field in which RPK has also applied this material.

The goal was to optimize the spring´s reliability while boosting its electrical conductivity, ensuring it met both mechanical and electrical specifications. This case study details the journey through testing, material optimization, and successful production trials.

Challenge

The customer required a wave spring with specific conductivity and impedance characteristics, originally intended to be met using stainless steel and nickel coating. Our engineers sought to push the boundaries of wave spring technology by investigating the use of CuBe material. The challenge was to meet strict dimensional and load requirements while improving the spring´s conductivity and impedance performance, which are critical for applications where electrical flow is a key factor.

Though RPK Group had experience using CuBe for compression springs, this was the first time we tested it for wave springs. The main challenges were:

• Shaping the round wire into rectangular form
• Managing tensile strength differences between CuBe and stainless steel
• Ensuring proper stress relief after forming
• Meeting precise drawing specifications for both mechanical and electrical performance

Investigation and process development

1. Wire lamination

The round CuBe wire needs to be rolled into a rectangular shape to meet the load-length requirements before forming. Due to CuBe's lower tensile strength compared to stainless steel, the required thickness had to be slightly increased from 0.24 mm to 0.27 mm to ensure that the spring could withstand the necessary loads.

2. Stress relief optimization

Previous research indicated that stress relief at 340ºC for 1 hour was effective for compression springs. However, applying this method to wave springs led to a loss of coil tension and the risk of tangling. After further investigation, we optimized the stress relief process, achieving the desired mechanical properties while maintaining dimensional accuracy.

3. Conductivity testing

Our engineers performed two key tests to verify the spring´s electrical conductivity:

DC conductivity verification

The spring was placed in a jig, compressed to 2.8 mm., and connected to a micro-ohmimeter. The CuBe wave spring achieved a maximum impedance of 0.050 Ohms, meeting the specified electrical requirements and performing comparably to a stainless steel + nickel-coated version.

Frequency conductivity testing

Using BODE 100 equipment, the spring was tested at different frequencies (10 kHz, 100 kHz, 1 MHz, and 10 MHz). The CuBe spring performed well at frequencies up to 100 kH<, with slightly higher impedance values at 1MHz and 10 MHz, though still within acceptable limits for the application.

4. Mechanical performance testing

The CuBe wave spring was measured dimensionally and for its load-length requirements using adequate equipment. The result showed that the CuBe spring performed well and fully complied with the drawing's required specifications.

Conclusion

Through a focused investigation, RPK Group successfully optimized the use of CuBe material for wave springs, achieving superior electrical conductivity and meeting all mechanical specifications. The CuBe springs performed at par with, and in some cases exceeded, the capabilities of stainless steel + nickel-coated versions. Given CuBe´s excellent electrical properties and adequate mechanical strength, this material proved a viable alternative for producing high-performance wave springs.