INPRO Innovationsgesellschaft mbH Berlin

Spot welding has remained the dominant joining technique in chassis construction. Welding arm drives have therefore remained traditionally wedded to pneumatic techniques. Electric-motor-driven arms, however, offer significant advantages in relation to control and regulation equipment. Their use makes it possible to achieve a clear improvement in process safety and quality – especially all in the processing of innovative lightweight construction steels.
INPRO partners recognized this potential and decided to test together the benefits and drawbacks of the new technologies, in order to determine the technological and commercial advantages as compared with conventional pneumatic drives in a systematic manner.

It has been demonstrated that servo motor-driven welding arms significantly improve welding quality. It facilitates a controlled movement of the electrodes to the sheet metal and ensures an accurate position determination at all times. The shock-free placement of electrodes improves electrode life and reduces noise emission during operation. Top benefits include the ability to set power profiles and the behaviour after setting, i.e. the sinking of the welding caps during the welding process, in a controlled fashion. Electric-drive welding arms guarantee faster availability of full power levels, which result in a measurable increase in cycle times.

Based on INPRO's findings, KUKA decided to include the control of electrical welding arms as the seventh axis in robot controls. As a result of this development, two very successful products have been positioned in the market: torque regulation over the motor current of the arm drive, and power regulation using a power sensor on the electric motor.

Today, over 5,000 units are used in industry, whereby vehicle production has profited from increased reliability and quality.

Modern high-strength steels are an important foundation for the production of chassis with high stability and low weight. From the viewpoint of welding technology, this is a major challenge. The use of electric-drive servo arms has shown itself to be highly beneficial. Therefore, this innovative technology is seen as a key to vehicle safety and lightweight construction.