Monitoring through the optical combiner in fiber laser welding

In the last years the introduction of the fiber laser (FL) technology has upset the whole scenery of laser processing. Unlimited laser powers, high beam quality and high reliability are only some of the key features of this new family of laser sources that are defining new edges to the process performances in laser welding and cutting. The increasing interest in this new technology has focused the attention on many scientific topics; among them a renewed role is nowadays played by the laser welding monitoring, required mainly in the industrial fields where quality is a must. In this paper we present a new monitoring technique openly designed for FL systems. Referring to a classical architecture, the central part of a FL source is the optical combiner in which the power of the different laser modules is summed and then convoyed to the laser head through the delivering optical fiber. Besides its “hub” feature for the laser power, the optical combiner can play also a prime role in process monitoring because it can be used like a check window from which optical signals coming directly from the keyhole plasma can be drawn. A slightly new design of the optical combiner is needed for the application of this monitoring technique and former tests are being performed on an IPG Photonics YLR1000 laser source. As a benchmark, the paper presents the monitoring results obtained on the case study of the laser welding of sheets of Ti6Al4V Titanium alloy.