Transformers for resistance welding

Transformers for resistance welding are designed for overload operation in a specified range. In this context, different technologies also have different requirements for the design of the transformers. The dominant method today is the use of medium-frequency rectifier units (MFDC). In addition, AC systems or single-phase or three-phase rectifier systems are still used for simple requirements.

The following is a list of welding processes with typical requirements. Products for the different processes can be found here.

All information given in the following is exemplary.

Spot welding

The main application is robot and manual gun welding in the automotive industry for body welding.

Typical parameters are

Steel applications:

- Welding current 5 ... 15 kA
- Welding times 300 ... 1000 ms

Aluminium spot welding

- Welding current 20 ... 60kA
- Welding times 50 ... 150ms.

Corresponding products you find here.

Projection welding and capacitor discharge welding

Projection welding is characterised by the fact that projections are incorporated on the component side, which are melted by a short current pulse.

The necessary currents depend on the material, projection geometry and number of projections. The currents can range from a few kA to several 100 kA. The current times range from a few milliseconds to 150-200 ms.

In recent years, the demands on projection welding have increased greatly due to changes in materials. Extremely short pulses with very short current rises of a few milliseconds can achieve very good results here. Technical implementations are achieved with medium frequency systems and capacitor charge welding. For the short current rises, higher voltages are required on the secondary side.

You can find corresponding products here.

Capacitor discharge welding is used as a special form of projection welding. Further information can be found here.

Butt welding

Butt welding is used when relatively large flat surfaces are to be butt welded together. This process is used, for example, for

Rims
Radiators
Round steels
Chains
Knives
...

Butt welding usually requires relatively long current times. In automated operation, high duty cycles can also occur. The transformers must be designed accordingly.

We offer transformers in the known technologies with mains frequency, 3 phase rectifier or medium frequency systems. The latter allow significant energy savings.

You can find corresponding products here.

Flash butt welding

Flash butt welding is an extension of butt welding. Here, non-planar and contaminated surfaces can be welded together. Before the actual welding process, the surfaces are 'burnt off' with the help of voltage flashovers. For this purpose, the distance of the surface to be welded is varied at a defined current flow. Due to the current interruption, strong voltage flashovers occur which 'burn off' the surface.

Depending on the surface to be welded, very high currents (several 100kA) are sometimes required. Classically, 3 phase rectifiers are used for this process. In the last 10 years, medium frequency systems have also become established here. The main reason is the significantly reduced use of material, better quality of the welds and significant energy savings (in some cases up to 70% compared to AC solutions).

Flash butt welding is used in the following applications:

Rail welding
Rim welding
Chain welding
Turbine rings in aircraft construction
...

You can find corresponding products here.

Seam welding

Seam welding is based on the use of rollers as electrodes between which the workpiece is continuously moved. A pulsed or continuous current flows between the contact points of the rollers and the workpiece. Areas of application include

Joining coils in the sheet metal industry
Production of vehicle tanks
White goods (ovens, dishwashers, ...)
Grid welding
Door frames
...

The welding currents are generally relatively low due to the small sheet thicknesses. However, continuous or pulsed current flow is a special requirement for the welding transformer. Here, there are correspondingly adapted variants for the AC and also MFDC range. Special attention must be paid to the diode load in pulsed applications. The time between two pulses is a decisive factor when considering service life.

You can find corresponding products here.

Norm based transformers

In the past, standards for the area of transformers for resistance welding were defined by various national and international committees. Based on these, a number of OEM-specific standards have also been developed. A small list is given below: