Automated preheating and welding in one clamping

For (load-bearing) steel components made of fine-grained steels to be welded without cracking, they have to be preheated. This is usually carried out manually, but with batch sizes of over 1,000 units – and due to a skilled worker shortage – an automated solution was the only option for Finsterle GmbH, a company located in Dürmentingen, Germany. As the metal construction company had already had positive experiences with manual welding machines from EWM, it only made sense to commission the Mündersbach-based manufacturer of welding solutions for the construction of a robot system as well.

As a contract manufacturer, flexibility is of major importance to Finsterle GmbH with regard to both applications and components. “We don’t know what kinds of orders customers will approach us with, but we want to be able to complete them all,” said Thomas Finsterle, technical managing director of Finsterle GmbH, summarising his day-to-day challenges. That’s why a robot system was commissioned to provide precisely the flexibility required.

Automatic preheating unit

Preheating is carried out with an oxyacetylene torch. A protective pipe with an optical sensor is mounted parallel to the torch pipe. This is aligned directly with the torch flame and checks whether it ignites if needed. The robot arm is outfitted with a pneumatically operated tool changer which traverses to the parking position of the oxyacetylene torch and picks it up. It then traverses to an external ignition station. The control starts the flow of gas and ignites the torch flame, monitored by the sensor. The preheating process can now begin, whereby the robot guides the oxyacetylene torch flame over the component.

From preheating to welding

Following preheating, the system control cuts off the gas flow and the torch flame is extinguished. The robot traverses the oxyacetylene torch to its parking position and sets it down there. It then switches to the opposite side of the system, where the welding torch is located in its parking position. This arrangement prevents the hoses of the various torches interfering with one another during operation. The welding torch is equipped with the same pneumatically operated coupling, which makes swapping very easy. Once coupling has been carried out, the welding process can begin.

Compensating for thermal distortion

Most components can be reliably welded using teachin paths and correspondingly wide weld seams. When it comes to thin-walled components for attachment, though, thermal distortion may be too much for teaching in alone. In this case, the exact position of the component must be determined. This occurs with the help of the filler metal in the welding torch. The filler wire of the welding torch is shortened to exactly 15 mm at a torch cleaning station. The welding wire then functions as a sensor. It’s guided to the component from above, and a short circuit occurs as soon as contact is made. In this way, the program is able to deduce the exact component position based on the position of the robot. To determine the lateral orientation of the component, the welding wire has to contact the component laterally at any point. Six of these tactile-measurement points are sufficient for precise positioning and orientation of the component and reliable welding results.