Welding downtimes

After explaining the DIN profile of a welding programme sequence in resistance welding, the importance of the welding auxillary times is pointed out today.

Welding idle times are all times in the programme sequence during which no current flows. But that does not make them any less important. The most important auxiliary times are the pre-holding or pre-pressing time, the pause time and the holding or post-pressing time. Often underestimated in practice is the importance of the lead time.  It must be set long enough for the electrodes to close and build up the desired pressure. If it is too short, initial spraying will occur because the necessary strength has not yet been built up. If it is too long, this is at the expense of the cycle time.

Especially with modern materials such as high-strength steels or with large sheet thicknesses, the setter works with several welding pulses. The time between the individual impulses is the pause time.  In it, heat is distributed in the vicinity of the welding point without complete re-cooling of the electrodes. This usually results in pause times in the range of 1 to 2 periods or 10 to 50 ms depending on the application.

The holding time runs in after the last current-carrying time. It is used for rapid cooling of the spot weld under pressure so that the weld can transmit forces.

As with the lead time, the duration is also important here. The motto: as short as possible and as long as necessary. If the holding time is too long, the material can harden due to the more intensive cooling; if it is too short, there is a risk that the weld spots cannot yet absorb the forces and crack.