Process window and strength of steels

Advanced high strength steels (AHSS) have been continuously developed and are increasingly adopted in car body manufacturing. The weldability of different steels is also different from each other resulting in changing process windows. With simulations and optimizations by SORPAS 2D.welding, it is possible to evaluate the process windows and splash limits of different steels for setting up or improving the real welding processes.

In this post, we present a case study on the relation between the strength of steel and the process window.

Material selection

Four types of steels were used in the simulations – DC06, HSLA340, DP600, and USIBOR1500. For direct comparisons of weldability between different steels, all sheets were welded with a thickness of 1.0 mm and GI coating.

Steel strength ductility diagram

Simulation setup

  • Welding machine & time- AC spot welding machine, 300ms
  • Simulation mode – Generation of weldability lobe with Current & force
  • Current range for weldability lobe – 4.5kA to 11.5kA with an increment 0.25kA
  • Force range for weldability lobe – 2kN to 5kN with increment 0.4kN

Weldability lobes

The general trend of splash limits for spot welding two steel sheets of thickness 1.0 mm:

  • The splash limit moves toward a higher current with a larger weld force.
  • The splash limit moves toward a lower current for steels with higher strength.
weldability lobe of DC06 2 sheets spot welding
Weldability lobe - DC06
weldability lobe of HSLA340 2 sheets spot welding
Weldability lobe - HSLA340
weldability lobe of DP600 2 sheets spot welding
Weldability lobe - DP600
weldability lobe of usibor 1500 2 sheets spot welding
Weldability lobe - usibor1500

For complex weld combinations of mixed materials, different sheet thickness and more than two sheets, please contact us.

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