Resistance brazing and soldering

With resistance brazing, divergent joining partners (in terms of geometry and material properties) and high connection cross-sections can be reliably connected. In general, brazing solder can be used in two forms:

• overlapping or in
• Butt welding process.

The butt-welded joint offers the following advantages:

• High savings in installation space (savings equal to the amount of the connector – max.height of the product corresponds to the strength of the terminal),
• strong reduction in compacting length (material savings),
• considerable reduction in the length of the contact part (material savings and advantages when punching),
• almost no heat input,
• almost no electrode wear,
• Tensile forces analogous to overlap welding or higher,
• very easy to monitor (analogous to overlapping welding),
• with the STRUNK process: no bulging at the joint (no reworking required),
• almost no contact resistance,
• all features of resistance welding are retained.

20 years of experience in resistance brazing

Process development with brazed welded joints has been part of the STRUNK portfolio for two decades. The starting point was an order from an OEM to develop an application with which oily stamped brass parts could be welded with a braid. The previously used connection methods led to a field failure and were therefore unusable.

Our consultig suggested that a resistor connection can be reliably mapped by adding a braze plate between the joining partners. In order to industrialize the feeding of the brazing alloy, we developed our first automated brazing alloy feeds for welding processes, which we have been continuously optimizing since then.

When the first intelligent battery sensors (IBS) appeared in the 12 V on-board network, the welding of the measuring shunt to the battery terminal, terminal or cable was already done with this process in manual to fully automatic production. Today almost all connections in the HV area (HV cabling and HV contacts), powertrain and power distribution (busbars and busbar electrical systems) are industrialized with this technology.

Resistance brazing is also useful if:

• the material thickness of the joining partners diverges so much that normal resistance welding cannot be carried out,
• the melting temperatures of the joining partners diverge significantly (e.g. copper to brass alloys),
• Large-area connections are to be implemented (BUS bars), where the connection by means of projection welding does not allow sufficient current carrying capacity to be achieved (connection only via projection -> HOT-SPOT = exclusion),
• Lines with large cross-sections are to be connected to terminals with extremely good conductivity (e.g. CuFe),
• the welding of the connection should be done with less machine power, ie concentration of the energy by the added solder, which increases the contact resistance before welding and then alloyed with both joining partners by melting.

In all cases mentioned, the resistance brazing results in an indestructible connection with a contact resistance of almost zero.

STRUNK Connect – your reliable partner for resistance welding under hard solder

Our current integrated servo solder feeders deliver a precise and reproducible amount of solder using servo technology and a multi-roll principle. This ensures:

• an exact, precise and reproducible position of the solder between the joining partners,
• a straight line support even over long distances through shaping measures,
• an integrated monitoring of the applied amount of solder between the joining partners as a countercheck to the conveyed amount.

  A punch cut to align the parameterization of the welding systems with the connection and not with the burning off of the solder.

Our control systems are fully integrated using independent software function modules, both in the welding current control and in the machine control. The feeds with a clamp system, which are suitable for right-hand and left-hand installation, sit on quick-change couplings with Harting plug connections, which enable a quick changeover to a different width. Flat materials with a cross-section of more than 0.05 mm² can be conveyed.

By supplying the hard solder, we achieve a current concentration at the desired point. By applying a short and strong welding current, the materials fuse to form a material bond that can only be separated in a destructive manner.

Our systems are not designed for pure soldering (melting of the brazing alloy) but, as with projection welding, are equipped with high power and high rigidity to produce the shortest possible welding time at very high welding currents.

In this way, we generate very high holding forces with the connection, whereby the contact resistance can be below the bulk resistance of the material (depending on the material). For example, with cables with a larger cross-section, pull-off forces of more than 10,000 Newtons can be achieved.

With this method, different materials with different cross-sections as well as BUS bars or busbars can be welded together. Contacts or busbars can also be provided with coatings.

We can use the method in the following variants. We are thus able to industrialize and automate a very high proportion of applications.

1. Direct application of hard solder between the parts to be joined using semiautomatic and automatic machines : using automatic STRUNK conveyor technology as well as manual workstations with manual feeds:
   • • between two BUS bars / busbars / components,
     • between a compacted strand and a terminal or BUS bar,
     • between an uncompacted stranded wire and a terminal or BUS bar (all-in-one shot)
2. Pre-soldering of joining partners using automatic STRUNK conveyor technology as well as manual workstations with manual feeds:
   • • Pre-soldering of BUS bars / busbars,
     • Pre-soldering during a compacting process (only possible semi or fully automatically due to the orientation (reference)). If the reference is lost, the orientation can be established manually in a second step using a marking).

With our practical solutions for resistance brazing, you can cope with the high technical requirements when joining workpieces and materials that are difficult to connect. Use our experience from more than 50 years of process technology to master your challenges in the area of resistance soldering and gain an edge over your competitors.