Ultrasonic Welding of Cables – Precise Joints for Copper, Aluminum, and High-Voltage Applications
Electrical conductors must be connected reliably and consistently in wiring harnesses, vehicles, battery systems, and numerous industrial applications. As demands on electrical performance, installation space, and process reliability continue to grow, ultrasonic cable welding is becoming increasingly important.
In ultrasonic metal welding, conductors are joined together under a defined force and high-frequency mechanical vibration. The process does not require solder or flux and, depending on the application, enables connections between copper, aluminum, and other suitable metallic components.
This process is particularly useful for cable-to-cable, cable-to-terminal, and other electrical connections that require a reproducible metallic connection within a small installation space.
How does ultrasonic cable welding work?
Ultrasonic welding of metals is a solid-state joining process. The conductors to be joined are first positioned between the sonotrode and the anvil.
A defined force is then applied. At the same time, the sonotrode transmits high-frequency mechanical vibrations to the joint area.
The relative motion of the joining partners under pressure mechanically activates the surfaces in the joint zone. This can break up or displace oxide layers and surface contaminants, allowing a metallic bond to form.
In this process, the parts to be joined are not completely melted. Rather, the joint is formed in the solid state through the interaction of pressure, vibration, relative motion, and proper process control.
The parameters required for a stable connection depend on the material, conductor cross-section, conductor structure, joint geometry, and tool design.
The Four-Step Process
1. Position the ladder
First, the conductors to be joined are positioned according to the intended joint geometry.
Precise and repeatable positioning is particularly important in automated manufacturing processes. Even small deviations in overlap, orientation, or clamping can affect the actual joint surface.
2. Apply welding force
The parts to be joined are clamped between the tool components with a specified force.
The required force is not the same for every application. It depends, among other things, on the material, conductor cross-section, conductor construction, joint surface, and tool geometry.
3. Initiate ultrasonic vibration
While the welding force is applied, the mechanical ultrasonic vibration is transmitted into the joint zone.
Depending on the welding system, the following parameters, among others, may be relevant for process control and monitoring:
- Welding force
- Amplitude
- Welding time
- Energy
- Power
- Path or Compaction
- Process Curves
The goal is to achieve a reproducible process condition in which a sufficient metallic bond is formed without placing unnecessary stress on the conductors.
4. End of the Process and Quality Assessment
Once the defined process conditions have been reached, the ultrasonic vibration is stopped and the joint is released.
Modern ultrasonic welding systems can store the data collected during the process and use it for process monitoring. Depending on the quality control strategy, mechanical, electrical, or metallographic tests may also be performed.
This allows for systematic monitoring of the process development from the first weld test through to mass production.
Which materials can be ultrasonically welded?
Ultrasonic welding is used in particular for electrical conductors made of copper and aluminum. Depending on the design, various conductor configurations, cross-sections, and connection combinations are possible.
Copper
Copper has excellent electrical conductivity and is therefore an important material for electrical wires and wiring harnesses.
Ultrasonic welding can be used, for example, on strands, conductor bundles, cables, and suitable terminals. The key factors here are not only the copper material but also the conductor cross-section, the strand structure, the joint surface, and the tool geometry.
Aluminum
Aluminum is also suitable for certain ultrasonic welding applications.
The natural oxide layer plays a particularly important role in aluminum. Process control must therefore be designed to achieve a stable metallic bond within the specified process window.
Depending on the application, aluminum conductors can be connected to other aluminum components or suitable terminals.
Joining Copper and Aluminum
Special requirements arise when joining different materials, such as copper and aluminum.
Differences in material properties, the oxide layer on aluminum, and the potential formation of intermetallic phases must be taken into account during process development. Fraunhofer IWM also describes these aspects as technical challenges associated with Cu-Al alloys.
Ultrasonic welding is an attractive joining technology for such applications. However, its specific suitability must always be evaluated based on the actual materials, geometry, and requirements.
Why is ultrasonic welding a good option for cable connections?
No additional solder or flux
The process does not require solder or flux for the actual metal joint. This allows the process to be carried out without additional joining materials.
Low thermal load
Since the parts to be joined are not completely melted, this process differs fundamentally from traditional fusion welding processes. This can be particularly advantageous for electrical conductors and temperature-sensitive components.
Compact Metallic Joint
The connection is formed directly in the designated joining zone. This makes it possible to create compact electrical connections, such as in cable-to-cable or cable-to-terminal applications.
Suitable for various conductor materials
Depending on the machine configuration and tooling, copper and aluminum conductors, as well as various connection combinations, can be processed.
Process data can be monitored
In industrial ultrasonic welding systems, relevant process parameters can be measured and documented. This allows the welding process to be designed and monitored in a reproducible manner for mass production.
What factors determine weld quality?
A stable ultrasonic bond is not achieved by a single parameter. The key factor is the interaction between the material, geometry, tool, and process control.
The most important factors include:
- Material and Material Combination
- Conductor cross-sectional area
- Conductor Construction and Strand Geometry
- Joint Surface
- Sonotrode and Anvil Geometry
- Welding force
- Amplitude
- Welding time
- Energy or Power
- Compaction and Path
- Process Monitoring
- Testing and Quality Concept
For this reason, welding parameters should not simply be transferred from one existing cable design to another.
For new combinations of materials or cross-sections, it makes sense to first determine a suitable process window based on actual components and then validate it using defined tests.
From the first welding test to mass production
A successful ultrasonic application doesn't begin with the selection of a machine. The first crucial step is to accurately describe the intended joint.
1. Determine the material and conductor geometry
What materials are being connected? What is the conductor cross-sectional area? Are they single conductors, strands, conductor bundles, braided conductors, or terminals?
2. Define the joint geometry
How should the conductors be connected to each other? Is a cable-to-cable, cable-to-terminal, or terminal connection intended?
The geometry plays a key role in determining the selection of the sonotrode, anvil, and fixture.
3. Determine the process window
Appropriate values for amplitude, force, energy, and time are determined based on actual components.
In this context, one should not focus solely on a single target value. What is crucial is a stable process range in which the required joint quality is achieved consistently.
4. Check the connection and document the process
Depending on the application, tensile tests, electrical resistance measurements, metallographic examinations, or other customer-specific tests may be required.
At the same time, process data can be documented to support traceability in mass production.
Typical Applications of Ultrasonic Welding
Ultrasonic welding can be used for various electrical connection applications, such as:
- Wiring Harness and Conductor Connections
- Cable-to-Cable Connections
- Cable-to-Terminal Connections
- Braided Conductor Connections
- Busbar and Terminal Connections
- Connections in Electric Mobility
- Applications in Battery Systems
- Power Electronics
- FPC and Other Metallic Compounds
In the fields of electric mobility and high-voltage applications in particular, the importance of reliable connections for large conductor cross-sections and various material combinations is on the rise.
However, the specific technical suitability always depends on the particular application.
Which ultrasonic cable welding machine is right for my application?
With its KS series, Magntek offers a variety of ultrasonic cable welding machines for different conductor cross-sections and connection methods.
KSK – for small conductors and terminal connections
The KSK was developed for precise connections between small-gauge conductors and terminals. It is suitable for copper and aluminum conductors as well as various standard terminal types.
The copper conductor cross-sectional area is up to 25 mm². The machine operates at 20 kHz and supports both time and energy modes. Manual or automated feeding is possible.
KSM – Compact Connections
The KSM is designed for compact cable connections in fields such as electronics, the automotive industry, and electrical engineering.
Depending on the application, connections such as copper-to-copper and copper-to-aluminum, as well as single-wire-to-multi-wire, braided conductor, and tinned conductor connections are possible.
KSS – for medium-sized conductor cross-sections
The KSS is designed for the mass production welding of cable harnesses with medium cross-sections and terminals.
Among other things, it supports connections between copper and aluminum conductors and terminals, braided conductor connections, and busbar tabs. The specified range for copper conductors is 16–70 mm². Automatic cable and terminal feeders can be integrated.
KSG – for large conductor cross-sections and high-voltage cables
The KSG is designed for large-cross-section wiring harnesses and demanding high-voltage applications.
Possible applications include cable-to-cable, cable-to-terminal, and terminal-to-terminal connections, as well as large-area welds on copper and aluminum components. Magntek specifies a range of 95/120 mm² for copper conductors and up to 160 mm² for aluminum conductors.
The KS series thus meets a variety of requirements—from small terminal connections to large-cross-section high-voltage conductors.
Not sure which machine is right for your application?
Magntek can assist with the selection process based on material, conductor cross-section, connection geometry, and production requirements.
Magntek Ultrasonic Cable Welding Machines
FAQ: Frequently Asked Questions About Ultrasonic Cable Welding
Can copper cables be welded using ultrasound?
Yes. Copper is one of the most important materials used in ultrasonic metal welding applications. Depending on the conductor cross-section, conductor construction, and connection type, various cable and terminal geometries can be implemented.
Can aluminum cables be ultrasonically welded?
Yes. Aluminum can be used for suitable ultrasonic welding applications. The process parameters and tools must be adapted to the material, cross-section, and geometry.
Can copper and aluminum be joined together?
Yes, certain Cu-Al compounds can be produced using ultrasonic welding. Due to the varying material properties and long-term stability requirements, each specific material combination should be validated separately.
Does ultrasonic welding produce a molten pool?
In ultrasonic metal welding, the parts to be joined are not completely melted. The joint is formed in the solid state under a defined force and mechanical ultrasonic vibration.
Do you need solder or flux?
No additional solder or flux is generally required for the actual ultrasonic bonding process.
What parameters are important in ultrasonic welding?
Depending on the machine and application, welding force, amplitude, time, energy, power, and travel may be particularly relevant. The key factor is the interaction of these variables within an appropriate process window.
Is ultrasonic welding suitable for mass production?
Yes. Ultrasonic welding can be integrated into automated production processes. To do so, the machine, tooling, process parameters, feeding system, process monitoring, and quality control system must be coordinated with one another.
What conductor cross-sections can be welded?
The possible cross-sectional area depends on the material, conductor construction, connection, and machine design. The Magntek KS Series covers a wide range—from small conductors to large-cross-sectional-area copper and aluminum conductors.
Conclusion: Ultrasonic Welding as a Precise Joining Technology
Ultrasonic welding enables the reproducible joining of electrical conductors using a defined force and mechanical ultrasonic vibrations. This process offers a wide range of possibilities, particularly for copper and aluminum conductors—from small terminal connections to large-cross-section cables and high-voltage applications.
However, the material alone is not the only factor crucial to a reliable connection. The conductor cross-section, conductor structure, joint geometry, tooling, process parameters, and quality requirements must all be considered together.
With its KS series, Magntek offers a variety of machine designs for small, medium, and large conductor cross-sections. From the initial welding test through process development to automated mass production, the appropriate ultrasonic solution can be tailored to the specific application.
Are you planning a new cable connection or looking to switch an existing application to ultrasonic welding?
Sources and Further Information
[1] Fraunhofer IWM: Information on technical challenges associated with Cu-Al compounds, particularly oxide layers, intermetallic phases, and differing coefficients of thermal expansion.
[2] Fraunhofer IFAM: Studies on aluminum-copper joints and the use of ultrasonic welding for electrical connections.
[3] Fraunhofer ISE: Report on Battery Wiring – including, among other things, materials, oxide layers, and requirements for electrical connections in battery systems.
[4] Magntek Electronics GmbH: Ultrasonic Cable Welding Machine – Product overview and applications of the KS Series.
[5] Magntek Electronics GmbH: Ultrasonic wire welding – Applications and Machine Overview.
[6] Magntek Electronics GmbH: KSK Ultrasonic Cable Welding Machine – Technical Specifications and Scope of Application.
[7] Magntek Electronics GmbH: KSS Ultrasonic Cable Welding Machine – Technical Specifications and Scope of Application.
[8] Magntek Electronics GmbH: KSG Ultrasonic Cable Welding Machine – Technical Specifications and Scope of Application.