Foil-based flexible electrical connectors are widely used in industry for applications where relative motion exists between two surfaces. Often times, customers come to Fabrisonic with a multitude of flexible electrical welding problems. This blog will delve into the traditionally-used joining techniques for foil-based welding and explains how our Ultrasonic Additive Manufacturing (UAM) process provides several benefits for welding foil-based electrical connections.
A common example in welding is a resistance welder where the charged electrode moves up and down and is connected to the chassis of the machine via a curved copper ‘shunt’. In the battery industry, foils are routinely used to connect individual cells onto busbars and thus, into a larger battery pack.
Foil-based electrical connectors are manufactured through a variety of joining techniques. In each case, individual foils are cut out using a die or shear and then are stacked. The stacks are then joined at each end, while leaving the center of the foils loose to allow relative motion.
Many joining techniques can be found in production including:
- Mechanical fasters – Foils are stamped to shape and then joined into a larger bar using bolts or rivets. Although mechanical fasteners are simple to implement, fasteners can lead to inconsistent electrical contact through thickness-reducing performance. Also, the dissimilar metal stack-ups lead to galvanic corrosion at the fastener.
- Mechanical crimps – Stacks of foils are crimped in a hydraulic die, sometimes at elevated temperatures. A crimp can provide high quality joints, but dies are prone to wear. Small changes in die shape can result in large variations in-process quality.
- Resistance welding – Stacks of foil are pressed together under high currents to weld individual layers into a plate. The stack-up for a resistance weld requires great care and planning. Current variations due to material and geometry result in weld zones that vary in shape.
- Brazing – Alternating layers of copper and braze foil are stacked and then heated under pressure to create a brazed end. While the braze creates good electrical contact, the dissimilar metals and cleaning fluxes can lead to corrosion in the joint over time.
Fabrisonic’s Ultrasonic Additive Manufacturing process welds stacks of individual foils to print a part near net shape. Our sample parts, shown at left looks a lot like one half of a flexible shunt. Naturally, customers have approached Fabrisonic with a wide variety of flexible electrical welding problems.
UAM provides numerous benefits for welding foil-based electrical connections:
- Low temperature – The solid-state nature of the UAM bond keeps temperature near room temperature. For sensitive electronic components, UAM can produce a high-quality weld just adjacent to the component without any deleterious effects.
- Geometric freedom – For most shunt manufacturing methods, fixturing limits the shape of the final part. With UAM, the weld head is a roller that can be positioned many times per layer. This allows much more complicated geometries to be realized. In fact, it allows for multiple ‘solid’ zones for mounting. Everywhere a designer wants a solid portion for mounting, the UAM weld head will come in and make a weld. This enables larger ‘spider web’ like designs with multiple flexible zones.
- High quality – Joining techniques like mechanical fasteners and mechanical crimps are prone to failure, especially in fatigue. UAM produces a fully dense, metallurgically bonded part that lasts under the most demanding of applications.
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