The newly developed method improves the monitoring and control process for beam welding. In contrast to most commonly used methods, the new monitoring process is root sided, i. e. it takes place on the back part of the workpiece. Furthermore, the invention describes a monitoring device optimized for beam welding. Beam welding using the invention avoids incomplete fusion at the weld interface and increases the stability of the weld joint.

Macro material processing via beam welding puts high demands on the alignment and positioning accuracy of the system. Typically the welding process is monitored at the upper side of the workpiece where the optical analysis of the keyhole provides a measurement for the quality of the weld. However, incomplete fusion cannot be excluded by only monitoring the upside of the workpiece. It is, for example, not possible to register a tilt between the beam and the joining gap. Already small angles lead to incomplete fusion if the material is thick. But not only a tilted beam can lead to incomplete fusion - also the geometry of the workpiece might introduce an angle between the beam axis and the joining gap. Such an angle results in incomplete fusion at the root area even if the process is monitored on the upper side of the workpiece. The error can only be detected by monitoring the welding from the root side. Some workpieces do not allow for a perpendicular alignment between workpiece and beam axis, in this case monitoring the upside of the workpiece is equally insufficient. Finally, besides the need to adjust the alignment of the beam it is also often necessary to adjust the power of the laser beam in order to maintain the necessary welding depth. Figure: Construction model (left) and realization (right) of the root sided process monitoring system. (Image Source: Stefan Kaierle, LZH)


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