Online monitoring of additive manufacturing processes using ultrasound

Additive manufacturing processes have been investigated and some of them developed commercially since the late 1980s. With Selective Laser Melting (SLM), components can be produced by localized melting of successive layers of metal powder. In comparison with todays conventional techniques, this way of manufacturing allows for considerably more freedom in designing and has a tremendous economic potential. Thus, it is particularly interesting for the production of geometrically complex aero engine components. By local melting with a laser beam such engine components have already been manufactured from the heat-resistant nickel alloy Inconel 718. To ensure the quality, the starting powder and the manufacturing parameters are supervised; also, the built-up components are inspected nondest ructively. In order to be able to describe and to understand the complex dynamics of the SLM processes more accurately, online ultrasonic measurements have been performed for the first time. In this contribution, we report on the integration of the measurement technique into the manufacturing facility. We present first results based on generalized B-scans which illustrate the build-up of test specimens based on single layers of 40 µm thickness. The analysis of the ultrasonic signals allows to infer information about the fusion of the single layers and about the temporal formation of material defects. We also discuss the further potential of ultrasonic measurements