With this in mind, he immediately recognized the advantages of the Ophir BeamWatch system from MKS. After a successful presentation of the technology at Volkswagen in Wolfsburg, it was decided to make the instrument an essential part of the research project.
The principle behind multi-focal welding is that several laser beams are generated simultaneously by a laser beam optic. The innovative process technology joins hot-dip galvanized sheets in a zero-gap configuration. In a beam setup with two highly focused, forward laser beams and one main welding spot, twoand three-sheet metal joints are produced with high seam quality. The trick to it, among other things, is keeping the geometry of the laser beams in exact relation to one another – but in order to do this, you first have to measure them.
With conventional instruments, it takes a lot of effort to meet this challenge. This is different with the Ophir Beam- Watch system. Here the beam to be measured is deflected through the measuring device without ever touching it. The Rayleigh scattering of the laser beam is measured by a camera in the X and Y directions. What was ideal for Volkswagen was that the BeamWatch system also allows the observation of multiple beams that are directed simultaneously through the system. The measurement is done in less than 100 milliseconds; and in another 300 milliseconds, BeamWatch displays all the relevant measurement results. For Alexander Franz, this was an enormous advantage: “We took measurements with the BeamWatch system every time we changed the development system. In this way, we were able to make the effects directly visible. Even the thermal focus shift – that is, when the focus position changes over time – is detected by the system.”
Overall, the laser experts at Volkswagen are interested in numerous parameters related to the beam caustics: With each measurement, the beam parameter product, the Rayleigh length and the beam divergence are all determined in real time. Alexander Franz sees great benefit in measuring the focus position with the Ophir BeamWatch system: In contrast to other measuring instruments, the operator can freely select the reference plane and thus obtain greater flexibility in the process. “Many measured values – excepting the thermal focus shift – can also be determined via other measuring technologies. But the effort involved is disproportionately higher,” he explains, adding: “Ophir‘s non-contact technology has completely changed the way the team views measuring. Their willingness to measure, and thus the quality of our results, have together contributed to significant improvements overall.” Whereas previously, because of the effort, the colleagues might have thought twice about whether a measurement was actually necessary, now they just do it. Instead of taking more than five minutes, a measurement is now complete in less than 1 second, and the prep time is also short. A power connection and possibly a network connection are all thatare required to run the instrument. Operation of the measuring device is made even simpler by integrating it into the robot-guided welding cell that the development department uses in their offices for testing. The Ophir BeamWatch system is directly connected to the PLC, so all readings can be directly processed and stored as required.