Aim

Within the railway industry, the rigidity of sidepanels and roof structures is achieved with bracing members that are spot welded horizontally and vertically. Due to the dimensions of up to approx. 20m in length and 3,5m in width fixed arm welding guns are very difficult to position, resulting in a time consuming welding process.

Alternatively, resistance spot welding machines with two independently controlled electrodes find application. The exact position of the braces needs to be known in order to allow the accurate positioning of the two electrodes relative to the material and to each other.

Challenges

The solution to be developed was to allow the control of two welding stations at the same time, to reduce the processing time by 50%. In order to further reduce the welding time, the measuring of the exact position of the braces was to be performed while moving the electrodes from one spot to the next.

Solution

The solution is based on one Sinumerik 840D sl control system for 16 axis and 4 channels. Each of the four channels has an active 4 axis transformation, to allow porgramming within the workpiece coordinate system. A multi-TCP structure and two synchronous functions ensure synchronization. The positioning of the upper and lower electrodes is handled by a tandem function.

The exact position of the braces is evaluated with the CNC-integrated function measure in motion and several point sensors.

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