Automated series production with robotic welding assistance systems

Various assistance systems for robotic welding are available, focusing on avoiding lost cycle times and ensuring perfect weld seam quality. Sensors play a key role in this: Lasers, cameras, and even touch sensors detect whether the component is in the correct position or if there are deviations. How the system should react can also be defined. However, this additional hardware entails not only high investment costs but also significant effort during installation and operation.

Many of these systems, in addition to improving weld seam quality, lengthen cycle times. Furthermore, their contours hinder component accessibility. To address these challenges, Fronius offers an excellent alternative: Thanks to high-precision welding wire control combined with fast data transmission from the TPS/i power source, the wire can be used not only as a filler material but also as a sensor, opening up new possibilities!

DETECTION OF EDGE POSITIONS AND UNWANTED GAPS WITH WIRESENSE
The patented WireSense technology, combined with the soldering system, enables the robot to detect the edge position and any gaps between sheets. To achieve this, the solder wire acts as a height sensor. During the scanning process, the robot first moves to the desired position. The solder wire, to which a low sensor voltage is applied, scans the component with wire recoils in the 100 Hz range. If the wire touches the component during this process, an imperceptible short circuit occurs, which is then interrupted by the wire lifting.

The TPS/i power source analyzes the change in solder wire position resulting from the short circuit and provides it to the robot as a height signal. In combination with position data from the robot controller and a reference point defined at the start, WireSense makes it possible to accurately record any geometric changes in the component. If we let the robot move indefinitely over the workpiece with WireSense and record each point, in theory, the complete contour of the component could be traced in 3D.

In practice, the most important application of this sensor system is edge and height detection, for example, in the case of overlap welds. A threshold value is previously determined slightly below the height of the sheet metal edge. If, during scanning, the power source detects values ​​above this threshold, this indicates that the sheet metal edge has been detected, and the TPS/i immediately outputs a digital tactile signal and the determined height value. This way, the robot knows where the sheet metal edge is and at what height.

EDGE DETECTION: ROBOT PATH CORRECTION
The robot controller can use this signal to store its current position data and then correct the robot path based on the nominal values. This way, component inaccuracies are detected and compensated for, and the robot welds in the correct location. Sheet metal thicknesses between 0.5 and 20 mm can be detected.

HEIGHT MEASUREMENT: RELIABLE WELDING DESPITE GAPS
Since the digital tactile signal also transmits the precise height of the sheet metal edge, WireSense is able to calculate the gaps between the sheets. Assuming these are precisely determined in advance, various welding programs, also known as “Jobs,” stored in the TPS/i are called up. This allows the robot to react appropriately and perform the weld with parameters perfectly adapted to the space dimension.

In this way, WireSense offers a solution for tolerance variations in the components to be welded and also counteracts tolerances in the clamping technology. The assistance system ensures reliable seam quality, reduces rework and component waste by up to 100%—without the need for additional sensor hardware! To ensure highly precise wire control, the Fronius welding system simply needs to be equipped with a CMT Ready system.

FASTER ROBOT PROGRAMMING WITH TEACHMODE
Before welding begins, the robot’s path must be manually programmed (known as the teach process). During this process, the welder or programmer controls the robot via a programming console or teach pendant, scans the component, and stores the corresponding position data. In terms of weld seam quality, it is important to maintain a constant distance between the component and the contact tip throughout the entire process, which is known as stick-out. Assistance systems can also be very helpful in this time-consuming manual process.

The Fronius TeachMode function prevents the welding wire from bending when it touches the workpiece during scanning by retracting the wire. As soon as the robot moves below the preset stick-out, the retracting process begins. At the same time, an optical-acoustic signal warns the user to move the welding torch away from the component, saving the operator from having to cut the deformed wire and remeasure the stick-out. This speeds up the programming process by up to 30%.

SEAMTRACKING: SEAL TRACKING DURING WELDING
The Fronius SeamTracking assistance system is particularly useful for rail vehicle and construction vehicle manufacturing. When welding thick sheets or long seams, the heat generated can cause deformation or incorrect positioning of components. To ensure that the robot continues welding in the correct position, a system that reliably detects the weld position during the process is required. With SeamTracking, this detection is guaranteed for prepared fillet and butt welds, without any additional sensor hardware.

To achieve this, the robot oscillates between the two sheets during the welding process. Based on the actual measured values ​​of each welding parameter, the robot detects the actual welding position and any deviations. The preprogrammed path is automatically corrected, and the weld is reliably performed in the correct position.

FILLET WELD POSITION DETECTION WITH TOUCHSENSE
To compensate for component and fixture tolerances, the robot can use TouchSense to automatically check the position of fillet welds before each weld. To do this, the robot touches the two sheets with the welding wire or gas nozzle, both with a low sensor voltage, at the start and end of the weld seam. Signals obtained during the short circuit can then be used to determine the optimal starting point.

COST SAVINGS WITH WIRE-BASED ASSISTANCE SYSTEMS
Ultimately, Fronius assistance systems make robotic welding processes more efficient and reliable. Component rework and the effort required for the subsequent reprogramming of robot paths can be significantly reduced, as the robot independently corrects the weld seam path, thereby reducing production costs. Fronius assistance systems use the welding wire as both a sensor and a filler material, saving users time and money on sensor hardware maintenance and eliminating component accessibility restrictions.

Author: Andreas Hummelbrunner, Product Manager MIG/MAG High-End Robotics, R&D Fronius International GmbH.

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