Laser-based ultrasonic measurement of the influence of PBF-LB/M-typical thermal cycles on sheet metal components of hybrid parts

Abstract

In order to cope with the upcoming challenges from industrial trends, such as mass customization, hybrid parts made out of sheet metal and additively manufactured components offer a possible approach. Hybrid parts can be used for instance in the field of medical and aerospace industries. The combination of the two technologies forming and additive manufacturing allows to use the advantages of each while at the same time avoiding the disadvantages. During the additive manufacturing process, however, the sheet metal substrates, which are a component of the later part, are subjected to heat input such as substrate heating and laser radiation. Each heat input has a different temperature and duration, which are simulated to detect changes in the material properties. Experiments are performed for 316L and Ti-6Al-4 V, which are both commonly used in additive manufacturing. The investigations aim at proving that the substrate heating has no influence on either material. To investigate the influence of substrate heating during additive manufacturing, tensile tests in heat-treated state as well as laser-based ultrasonic measurements are used to detect changes in mechanical or microstructural properties. However, the heat input of the laser is expected to lead to a phase transformation for the titanium alloy due to the high cooling rate. Therefore, the feasibility of using a laser based ultrasonic measurement system to detect microstructural changes during heat input similar to the laser radiation during laser-based powder bed fusion processes is tested. Based on the results, the substrate heating does not influence the sheet material, despite long holding times. However, the short laser beam-like heat inputs lead to phase transformations for the titanium alloy, which can be detected temperature and time dependent via laser-based ultrasonic measurements.