Product Code: ICA10_507

Laser Power Modulation at the Threshold from Heat Conduction to Deep-Penetration Welding
Authors:
Peter Stritt, GSaME Graduate School of Excellence advanced Manufacturing Engineering; Stuttgart Germany
Rudolf Weber, Ifsw Institut Fuer Strahlwerkzeuge; Stuttgart Germany
Thomas Graf, Ifsw Institut Fuer Strahlwerkzeuge; Stuttgart Germany
Steffen Mueller, Audi AG; Neckarsulm Germany
Christian Ebert, Audi AG; Neckarsulm Germany
Presented at ICALEO 2010

Today, lasers are operated either in pulsed or cw (continuous wave) mode for laser welding applications. While the cw mode is common for larger structural welds, pulsed welding is mainly used for smaller components, as it allows precise matching of the pulse properties with the desired melting and solidification conditions.
In this paper a different approach is used, modulating a cw laser source with a sine wave power signal at the deep penetration threshold. Thereby the lower laser power levels lead to heat conduction welding whereas the higher levels result in deep penetration welding. A complex welding process is generated where the variation of modulation parameters such as frequency or amplitude leads to significant changes in welding depth and welding efficiency.
Experiments were performed with a 5 kW disk laser on aluminum. The process was monitored using a high speed camera and coaxial back-reflection measurement.
The experiments clearly show that the resulting changes are caused by opening and closing mechanisms of the keyhole. Both, the time constant of the power modulation and the energy input determine the characteristics of the process.
The obtained results are used to analyze keyhole dynamics such as opening and closing time constants of the keyhole.