Are you welding large wires you should be soldering ?


Historically, robotic soldering has been limited to small electrical joints. Yet, a growing number of companies are requesting that we solder large wires to lugs. Our initial reaction was to refer them to companies that make resistance welding systems, however the customers told us welding would not work. So, we soldered some sample parts for them and were rather astonished by their excitement with the results. We had to ask, “Why wouldn’t welding work, and why is soldering better?” We got several answers that are worth sharing.

What we learned about welding large wires

The most common answer was also the most interesting. Welding causes the wire to break over time. To be clear, this is not a common problem. Breaking seems to be limited to stranded wires that are subjected to movement or vibration. Resistance and ultrasonic welding compress the strands and fuse them at the joint. This abrupt transition from large, round, stranded wire to a thinner, flat, solid block creates a stress point. Vibration and movement focus near the joint, and the individual strands tend to break at the joint over time. By contrast, soldering is an additive process that does not compress the stranded wire, and solder wicks into the strands providing a more gradual transition from joint to wire.

Another issue with welding is, as the wires become larger, clamping forces required by ultrasonic and resistance welding also increases. These higher clamping forces can damage delicate wire strands or the terminal. This is not an issue with soldering because soldering does not clamp the wire.

Also, clamping forces can exceed the capability of the machines manufactures currently use, so new equipment must be larger and they are priced accordingly. Soldering machines are typically a fraction of the price of welding machines.

We found this information be very interesting because requirements for high-amperage wires is increasing dramatically – especially in electric vehicles. Many of those stranded wires experience vibration, so it is reasonable for us to ask a broader audience, “Are you welding large wires you should be soldering?” Don’t worry, we are prepared to help you answer this question.

Example of medium solder joint

Our experience soldering large wires

Contrary to common belief, welding is not the only way to join large wires. In fact, Unitechnologies has always been able to solder large joints. We designed our induction soldering system specifically for this. The photo above is an example that closely resembles some medium joints we have provided to actual customers. In this example, we are soldering a 10-AWG stranded wire to a 1/2″ brass hex in about 15 seconds. We have successfully soldered much larger wires with cross sections up to 60mm2 to EV battery connectors. Furthermore, larger wires should be possible; we simply have not tested larger wires yet.

Moving forward

We are prepared to help you research the answer as it specifically applies to your product. If you are experiencing strands breaking, or if you have a new product and this is a potential concern, or if there is another reason welding does not work for you; let us know.  We can schedule a Teams meeting to overview your process. If it looks like something we can solder, we will solder some of your parts in our lab and return them to you for detailed evaluation.