What Happens to Your Weld When Welding with High Power Over Long Periods of Time?

Nowadays, it is quite common to weld with a laser. But some welding applications still require expert skills and customized solutions. A customer of ours in the shipyard market owns a powerful 12KW fiber laser. Most of the time, they weld small metals pieces. But for a new application, it required a new process.

Author:

Nicolas Chaise, Regional Sales Manager, Ophir Spiricon Europe

Welding Large Parts of a Boat

This company wanted to weld large parts of the boat itself. This kind of welding can last up to 20 minutes over several meters. This generates new challenges.

During 20 minutes, the focal head and especially the focal lens are overheated. This causes the focal plane to shift and, consequently, the weld itself is affected. For that reason, we put one of our new products to work, BeamWatch.

Figure 1. BeamWatch, non-‐contact laser beam measurement system.

BeamWatch’s technology allows users to measure many laser parameters instantaneously, without coming in contact with the beam. This is disruptive technology that provides significantly more accurate measurements than existing systems.

BeamWatch was plugged into the customer’s computer via a GigE cable. This allowed us to work outside of the safety cabin. We also connected an Ophir 10KW thermal head to measure power and to block the beam.

The Measurements

In only a minute, we were able to align the power meter and the BeamWatch system with the laser. By shooting inside the 12mm hole, we were able to measure many important laser parameters: M2, Focal Shift, Waist Location, Divergence and Diameter in real time during an unlimited period.

Figures 2a and 2b. Beam waist measurement at 1 minute into the weld and at 7 minutes into the weld.

The first weld measurement lasted 10 minutes at 8 kW. After only 7 minutes, the most impressive result was seen…the focal plan shifted by 8mm.

At the end of the test period, all numerical data was saved and the user was able to create graphs for each parameter over the time of the weld, for each different focal lens they own, at different powers.

Figures 3. F300 focal lens @ 8 kW.

Conclusion

Laser welding during a long time period generates a real effect on the focal plan. This is fully amplified by the laser power. The more power you use, the more focal shift you get. Depending on your application, it could be critical.

Theoretically and according to laser manufacturers, this effect should be much lower. In fact, with dirt optics and robot movement, we easily observed a focal shift above 10 mm after 10 minutes.

BeamWatch reveals the need for monitoring the focal shift in high power applications. Our customer is now able to characterize all focus heads and optimize processes during a very short production timeout.