Robot Welding Guns Made Easy

2023 Author: Hannah Pearcy | [email protected]. Last modified: 2023-11-26 11:39

The assembly of automobile bodies is 90% automated. For the shell of the VW Golf, for example, around 1,500 robots move tools with masses of sometimes more than 100 kg. Most of these robots have welding guns on their arms and use hundreds of spot welds to join the preformed sheet metal parts into bodies. The cycle times, i.e. the time interval between two welds, is currently approximately 2.5 seconds. "But that's not a constant of nature," says welding technology specialist Prof. Dr.-Ing. Peter Puschner, "There is still room for improvement." Like Puschner, manufacturing technology specialists all over the world are working on optimizing robot-based manufacturing technology. The first step is to increase the speed of the robot movements. However, this leads to higher energy consumption and premature wear of the mechanics due to the moments of inertia of the moving masses. A promising way is to consistently use lightweight tools with new design features, which makes it possible to use smaller robots with lighter arms. Because the masses to be accelerated are smaller, the robots can move faster to their point of use, and the cycle times are noticeably reduced.the robots can move faster to their point of use and the cycle times are noticeably reduced.the robots can move faster to their point of use and the cycle times are noticeably reduced.

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Lighter thanks to the 10 kHz frequency

Another approach also comes from a completely different corner. So far, the transformers of the robot welding guns were fed from 1000 Hz inverters. The switch to a supply voltage with a 10 kHz frequency also promotes the trend towards lightweight technology. The greatest benefit of this technology can be seen in the transformers. With a 10 kHz supply these can turn out to be more than 50% smaller and lighter. Intelligent process control can also reduce the cross-section of the supply lines. But there is no really significant weight saving for free. When switching to the so-called 10 kHz inverter technology, all partners involved in the system are required to make their contribution.

The new technological features result in considerable weight savings, which leads to modern lightweight welding guns. Where previously up to 110 kg had to be accepted as a tool weight, today the same or even better results can be achieved with tools weighing 45 kg. Every gram of weight saved contributes to the 'speed' account and reduces the energy consumption of the robot. This can be seen very well in the hose packages, which could also be slimmed down. Lightweight pliers, for example, manage with an operating pressure of 6 bar for the pneumatic actuators. This results in hoses of smaller dimensions.

Cable cross section significantly reduced

Weight can also be saved with the power cables. If cable cross-sections of 25 mm² were necessary for conventional welding technology, 16 mm² would be sufficient for the 10 kHz technology. However, a different cable structure is required, since a noticeable skin effect already occurs at 10 kHz. This ensures that the current density in the cable is not evenly distributed, but pushes the charge carriers to the outside. This is remedied by special HF cables, the overall cross-section of which is divided into individually isolated strands.

The hose package contains all the lines that are required to operate a welding gun. In addition to the air line and water lines, it contains the cables for the electrical power supply, control and process voltages and light guides. Due to the permanent movement of the robots, the hose package is exposed to enormous mechanical stress. There are connectors in several places. They make it possible to replace the primary circuit supply on the robot arm in the shortest possible time without interrupting operation for an impermissibly long time.

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