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Medium-Frequency Inverter Technique (MFDC)


Resistance welding systems which are based on medium-frequency inverters are recently gaining in importance. All inverters have the principal design in common: first, the 3-phase input current is rectified and, in the downstream inverter unit, chopped by means of power semiconductors (IGBT) into higher-frequency alternating current of 1 kHz. This alternating current is then transformed by the welding transformer into quantities which are suitable for welding and, subsequently, rectified. Thus, direct current (DC) is applied at the welding point.

The price is higher than that of alternating current systems, but the multitude of advantages of the MFDC systems will certainly make up for the higher costs:

  • 3-phase balanced system load, no phase shift
  • low residual ripple of the welding current (2 kHz ripple)
  • smallest controllable unit of time ½ period = 0,5 milliseconds
  • also suitable for short welding times, starting from approx. 20 ms
  • uninterrupted energy input into the weld nugget
  • lighter and smaller transformers
  • low inductive losses, therefore the trafo size does not depend on the welding window.

These high-speed controllable MFDC power sources are, in sheet welding, also suitable for the application of the adaptive MASTER control method. Based on a reference welding, MASTER adapts the welding parameters optimally, also during disturbing influences such as shunts, sheet bulging, etc.

Our solutions:
Depending on the necessary welding power and the intended interface equipment, the medium frequency systems of the SPATZ+, SilverSPATZ and ServoSPATZ+ families are available.

Inverter Welding Current
SPATZ+M300
SPATZ+M400
ServoSPATZ+M400
up to 18 kA
SPATZ+M600
SPATZ+M800

SilverSPATZM600
SilverSPATZM800
ServoSPATZ+M600
ServoSPATZ+M800
up to 30 kA
SPATZ+M900 up to 45 kA
SPATZ+Tandem1600 up to 65 kA
SPATZ+MS2400 up to 100 kA