Wiegel bonds with UAM to make a better busbar, faster, with a lower cost

The Challenge
In 2018, an electric vehicle (EV) manufacturer approached Wiegel Tool Works with a new battery pack design. The design required a busbar that weighs less, retains stiffness, and provides pre-installed battery fuses/connections while maintaining high levels of electrical conductivity. Maximum conductivity is a crucial requirement for a battery busbar in an EV. The efficient use of battery energy is critical in electric vehicle design, and keeping the vehicle as light as possible is important for minimizing energy use and extending battery life. The busbars needed to fulfill three main criteria: (1) be strong enough to maintain their form in a high-vibration operational environment, (2) be as light as possible, and (3) have the highest possible electrical conductivity. The busbar geometry was complex, requiring precision handling and processing. Unwilling to settle for the status quo, Wiegel’s team partnered with Fabrisonic and their Ultrasonic Additive Manufacturing (UAM) capability to produce the busbar, providing the EV manufacturer with a distinct advantage. The Wiegel-Fabrisonic team developed a novel manufacturing process that leveraged Wiegel’s expertise in high-volume stamping and Fabrisonic’s unique welding technology, which effortlessly welds dissimilar metals at high speed and low temperature.

The Solution
The battery busbar needed to be optimized for Size, Weight, and Performance (SWaP). The ideal busbar composition would be bimetallic, highly reproducible, and produced at high volumes rapidly. Combining two metal alloys would reduce the weight of the busbar while retaining sufficient rigidity. Several metal joining processes were evaluated, and one process emerged as ideally suited for joining dissimilar metals and highly adaptable to a high-volume progressive stamping machine while meeting Wiegel’s high-quality standards. Ultrasonic Additive Manufacturing (UAM) is a unique and proprietary process owned and developed by Fabrisonic. Although UAM is part of the Additive Manufacturing (AM) family, it is fundamentally a welding process. Unlike most welding processes, ultrasonic welding does not melt the material. Instead, ultrasonic (acoustic) energy is used to scrub the two metals against each other, oscillating only a few microns, to create a fully dense, high-conductivity joint. This process creates a full metallurgical bond with very limited heating, allowing operation adjacent to sensitive electronics. Wiegel and Fabrisonic employed UAM in a seam welding application, which worked perfectly to create a bimetallic busbar with high-quality welds between two material thicknesses with takt times measured in seconds.

Traditional pack manufacturing involves stamping individual bus bars and then welding thin strips of metal to connect the busbar to each individual battery. Both laser welding and ultrasonic wire bonding have been used to make these individual strip connections. However, each weld requires several seconds, and complex fixturing must be built to ensure intimate contact between the foil and busbar/battery.



Wiegel’s novel solution was to make the busbar-to-foil connection using a continuous foil that is welded at high speed. Both the busbar and foil are stamped with high-volume progressive stamping dies. The newly stamped foil is placed on the busbar and then welded at high-speed using Fabrisonic’s ultrasonic weld heads. After welding the entire length of the busbar-foil interface, a secondary stamping operation forms the three-dimensional tabs. Later in the manufacturing process, the tabs are welded to each individual battery. This elegant approach allows:
• A more robust design with continuous welded surfaces instead of single points of failure. One continuous weld covers the entire surface of the busbar, ensuring full conductivity. The continuous welds also make the joints more robust, reducing the chances of fatigue failures during operation.
• The ability to make all the busbar foil welds at once greatly reduces overall manufacturing time. Instead of individual robot heads making thousands of individual connections, a continuous ultrasonic roller creates welds at speeds up to 200 in/min.
• Opportunities for engineers to create geometric features for electrical control. For instance, the final stamped tabs can be shaped to act as individual fuses. Similarly, stamping allows complex mating shapes for the final connection to individual batteries.

This unique design hinges on Wiegel’s ability to make continuous welds between dissimilar metal foils. After numerous welding vendors turned them away, Wiegel approached Fabrisonic, whose ultrasonic additive technology regularly joins dissimilar metals, including different aluminum alloys, aluminum to copper, copper and/or aluminum to nickel, aluminum to stainless steel, and numerous other metal combinations. Wiegel worked with Fabrisonic to build custom automation that used Fabrisonic’s SonicLayer welding technology. Because ultrasonic welding does not melt the material, the team was able to create high-quality welds between metals of different alloys and thicknesses. Wiegel’s expertise in stamping was leveraged to create both busbars and individual foil connections. A series of SonicLayer welding heads were combined on a series of continuous conveyors to reach the required takt time. After welding, an additional stamping process produces the final geometry of the interconnect.

Using Fabrisonic’s SonicLayer welding technology and Wiegel’s unique expertise in stamping systems, the team developed a new busbar architecture, reducing potential failure points and greatly reducing manufacturing time [insert metrics here]. Production automation incorporated a series of SonicLayer welding heads coupled with high-speed stamping equipment to reach the required takt time. The result was a system that exceeded the customer’s production and part quality requirements.



Results
Today, the system designed and built for the EV manufacturer has resulted in Wiegel reaching production rates of over 23 million parts annually. The combination of stamping with the SonicLayer welding technique allowed Wiegel to design and build a progressive stamping system that produced bimetallic busbar systems meeting all the stiffness, weight, and electrical conductivity requirements. The busbars contributed to driving higher SWaP and resulted in an optimized busbar architecture for an EV. The ability to uniquely employ the UAM seal welding application in a progressive stamping machine resulted in an astounding increase in manufacturing speed by 200% with a corresponding reduction of manufacturing costs by 45%.