Low-coherence interferometry in laser processing: a new sensor approach heading for industrial applications

Abstract

Since the moment when it was possible to achieve the necessary power density to start the process of deep penetration welding, accompanied by a keyhole, there is hope - and need - to measure the depth of this vapor channel. In the decades in which the technology of deep penetration welding has been used, various approaches have been developed that allow a message about the depth of the keyhole. All these approaches have one thing in common, the basics of determining the depth are based on secondary information, such as the dimension of the melt pool, or the strength of the emissions from the plasma or the metal vapor. Except by means of X-ray or destructive testing no method has been developed so far to determine the real keyhole depth. With the IDM system (In-Process Depth Meter) it is now possible to bring a system to market, which can measure the depth of the keyhole in industrial laser welding applications. It is important to bring up, that not only laser welding as a highly dynamic process, requiring a sensor with high temporal and spatial resolution can profit from this sensor technology. The use of this method in laser applications has risen in the last years. Since its first appearance in 2008 [1], application examples were shown for laser cutting [2], selective laser melting [3], laser micro machining [4], laser drilling [5] and laser welding [6]. For the latter, a huge potential is foreseen [8].