Innovative solutions for the reliable joining of aluminum strands and copper sleeves with our resistance welding technology

While resistance welding has been used successfully for copper-copper connections in the automotive wiring system for decades, joining aluminum and copper in the cable harness was previously considered difficult. This was due to the fact that there is aluminum oxide on the individual strands of the cables and on the surface of the busbars. In order to produce an optimum connection in terms of conductivity (contact resistance) and long-term mechanical stability, the following challenge arises: the aluminum oxide must be broken and then uncontrolled melting of the aluminum must be ruled out. To achieve this, intermetallic phases and brittleness must be avoided.

We have successfully created an aluminum-copper connection with extreme durability and minimal contact resistance. This can now be used in the following parts of cable harnesses and high-voltage applications:

1. in aluminium busbar systems with copper connectors or flex busbars to make the systems more flexible and
2. in aluminum conductors (also with very high cross-sections) to copper connectors or HV connectors in sleeve form.

With our innovative processes, it is now possible to combine the advantages of aluminum (weight savings, cost reduction compared to copper) with the known properties of copper in the contact and connection area. Below, we explain the properties and advantages of our methods.

Connecting copper to aluminum busbars – S2R Method

Aluminum is increasingly being used in the busbar network of the electrical system in vehicles due to cost and weight savings. This particularly affects long paths such as the charging path. For these applications, we offer a butt welding process that connects copper screw-on pieces (terminals) precisely and reliably to the ends of the aluminum busbars.

The advantage of butt welding in this context is the space-saving contacting, especially for tightly laid busbars such as in the charging path at the socket. In addition, by increasing the contact area, a low contact resistance (a few µOhm) can be achieved together with a high holding force (depending on the cross-section and material; approx. 10,000 newtons for 100 mm² cross-section of the aluminum busbar). In addition, material savings are achieved compared to overlap welding, which leads to further cost reductions.

The connection is made without additional materials such as solder. A very fast STRUNK control system is used to break up the oxide layer to ensure that the materials are joined with long-term stability and without aluminum spraying. This welding process for busbars is also suitable for making connections with copper strands or copper braids to make busbar sets more flexible.

Connecting aluminum stranded wires to (HV) round connectors – STRUNK HC-L Process:

In order to reliably connect aluminum cables to round contacts using the resistance welding process, we have developed a new method. It enables both the metallic connection to the round connector (inner area) and the metallic connection of the individual strands (cores) to each other. We now have resistance welding machines specially adapted for this application and the associated “ALUMINIUM” application software on offer.

Our systems and software ensure a controllable and stable welding process between the strands. The cable brackets or round connectors used for this are coated in order to avoid intermetallic phases and to achieve long-term stability. The necessary connection to the connector is achieved via a brazed joint of the respective coating.

This connection is also characterized by high holding forces and excellent conductivity from the aluminum wire to the copper connector. The breaking of the oxides and the exact melting temperature of the strands are achieved via a special application of our welding current control.

Our STRUNK HC-L process is suitable for cross-sections of up to 160 mm². It creates stable connections both between the individual strands and between the strands and the sleeve material (see Fig. 1). The advantages of this process also include a high load-bearing capacity with very good mechanical properties and excellent conductivity of the aluminum-copper connection (see Fig. 2).