Welding Large Cable Cross-Sections Welded By Ultrasound

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TELSONIC AG

FAULHABER Drive Systems

SIMTOS (Seoul International Machine Tool Show)

Ultrasonically welding cables to cables is now widespread in low-voltage applications and for cables with small cross-sections. However, applications in the high-voltage sector with individual cable cross-sections of 0.02 to 0.15 in² could also benefit from this technology. The Swiss Telsonic Group has now developed a system capable of welding cable cross-sections totaling up to 0.43 in².

The applications where ultrasonic welding of large cable cross-sections is required are diverse. The automotive sector, for example, could greatly benefit from this, both in passenger cars and in vans and trucks. So-called splices can, for instance, help save expensive connectors.

Today, electric vehicles typically have a charging socket on either the left or right side. The length of the charging cables determines how correctly the vehicle must be positioned at the charging station so that the cable can reach from the station to the car's charging port. A charging socket on each side of the car would be a significant convenience. However, until now, this would require a cable for each side inside the car, with a plug at each end—one for the connection to the charging socket and one for the connection to the battery.

If the cables coming from the charging sockets on the left and right were instead ultrasonically welded together in the middle of the vehicle and then routed to the battery with a single cable, one plug and a section of cable could be saved. The same applies to power distribution from the battery to the drive systems with multiple motors. Here too, a splice could save plugs and cables. However, for ultrasonic welding of thicker cables to work reliably, several challenges need to be overcome.

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Challenges in Ultrasonic Welding of Large Cross-Sections

In typical applications, three to five wires are welded together during strand welding. One challenge lies in reliably welding the connections. In the node, the wires must always be positioned identically in the longitudinal and transverse directions. Additionally, "side splices" must be avoided, meaning wires that shift and are welded side by side instead of on top of each other. The optimal alignment of wires into the node for vertically positioned wires is also relevant.

Another challenge is the high power required for thick wires to fully penetrate the weld node and create a consistently high-quality connection. At the same time, heat spots must be avoided to prevent damage to individual strands. For very different wire cross-sections coming together in a node, determining the optimal welding parameters is not trivial. Additionally, the insulation of wires should be protected from heat and spreading in the entry zone to prevent cracks from forming.

In general, we can currently ultrasonically weld any mixture with up to five different copper cables and a total cross-section of 0.43 in². Soon, we will also be able to weld aluminum cables of this size as splices. And even with cross-sections, the limit of what is achievable is far from reached.

Dr.-Ing. Shimaalsadat Mostafavi

Up to five cables and a total cross-section of 0.43 in² spliced using ultrasound

The list of challenges is indeed long. Telsonic has the solution: the ultrasonic experts have developed a system for their ultrasonic welding machine TelsoTerminal TT7, which can weld various combinations of large wire cross-sections. Realized projects include welding four wires with a cross-section of 0.11 in² each (totaling 0.43 in²), four wires of 0.08 in² each (totaling 0.31 in²), and one 0.12 in² wire combined with three 0.04 in² wires (totaling 0.23 in²). "These are just a few concrete examples," reports Dr.-Ing. Shimaalsadat Mostafavi, Head of Metal Lab & Application Architect at Telsonic. "In general, we can currently ultrasonically weld any mix of up to five different copper wires with a total cross-section of 0.43 in². Soon, we will also be able to weld aluminum wires of this size as splices. And when it comes to cross-sections, we are far from reaching the limits of what is possible."

Technology Introduces Amplitudes And Force Centrally into the Middle of the Splices

This success was achieved by the Swiss team through a combination of various technologies. A key factor is the use of the PowerWheel technology, which introduces amplitudes and force centrally into the middle of the splices. Welding is performed using a rocking rolling motion directly over the joining area. This ensures that the maximum amplitude is always in the center of the welding surface, and the energy is applied precisely within the welding zone. This not only provides ideal penetration of different wire cross-sections but also protects the wire insulation. An integrated displacement and force measurement system also monitors the precision of the joining process. To ensure that the process is completed quickly, even with high wire cross-sections, a generator power of 14.4 kW enables short welding and cycle times. The ultrasonic welding machine allows cables to be fed into the welding area from both left and right, significantly easing handling, particularly with large diameters. To prevent cable slippage, they are held in position with special tools and masks. The entire process is made easier for the user by a user-friendly interface and various digital process support features. Furthermore, since the process data is relevant for its optimization and the quality of the respective products, this data is not only stored in the machine but also transmitted via a standardized data interface to the MES or automation systems.

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