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RoboSpin

Process technology – RoboSpin

What is RoboSpin?

RoboSpin is a further development, patented by KUKA, of the conventional, robot-guided resistance spot welding process (RSW). Unlike in the conventional technology, the robot can continue to move during welding. While the welding process is being executed, the weld gun is simultaneously rotated about the electrode axis. This transforms the traditional spot process into a continuous-path process with continuous robot motion. The RoboSpin process technology thus enables an optimized motion sequence to reduce repositioning times between the weld spots. Furthermore, the rotational motion of the welding electrodes on the workpiece also allows improvements to the welding process.

Repositioning times

The potential time saving was investigated on the basis of three significant example systems from projects that have already been implemented. In cooperation between the departments AK-D, AK-MP and AK-VP, the cells were simulated, and the motion sequence was digitally optimized and analyzed in the laboratory. The cycle-time-optimized rotational angles calculated for each weld spot ranged from 0.5° to 19°. The maximum time saving demonstrated for the three reference cases using RoboSpin was up to 12%.

Welding process

The effects of RoboSpin on the weld process were investigated by means of experiments in the laboratory. The rotational motion can be broken down into three main phases.
1. Rotation before the welding process
2. Rotation during the welding process
3. Rotation after the welding process

One effect of a large rotational angle before the actual welding process is that coatings, such as zinc, paint and oxides, are opened up. This results in significantly more constant contact between the electrodes and the base material. As a consequence, weld nugget diameters are less scattered and the required weld quality is more reproducible than conventional RSW.

A rotational motion performed in parallel with the welding process causes the geometry of the electrode tip to change. Depending on the number of weld spots, friction between the electrode contact surface and the workpiece causes both electrode tip material and also undesired alloy coatings, such as zinc, to be rubbed off. This corresponds to a continuous cleaning of the tip surface by RoboSpin. Under laboratory conditions, it was possible to achieve significantly increased electrode life compared with conventional RSW.

If a large rotational angle or a high rotational speed is applied shortly before the end of the welding process, the adhesive affinity of the electrode tip to the workpiece is significantly decreased. This is particularly noticeable in the case of special materials and coatings. These often have a high electrical interface resistance which, in the conventional process, welds the electrode tips to the workpiece. Here too, improvements can be achieved by using RoboSpin.

Summary

Compared with conventional RSW, use of RoboSpin offers advantages both in terms of cycle times and also for the welding process itself.
To achieve maximum time benefits, a cycle-time-optimized rotational angle must be calculated by means of simulation for each weld spot. In this way, time savings of up to 12% were realized.
To determine the ideal rotational angle for the process and to calculate all other weld parameters, welding tests must be carried out beforehand. An optimized process angle has a particularly positive effect on the service life of the electrodes. Under laboratory conditions, a significant improvement was achieved compared with conventional RSW.

A software package is currently being developed in cooperation with KUKA Belgium for user-friendly programming of the rotational motion. Further planned development steps are field trials during on-going production at customer plants.