Setup for electrical resistance measurement for laser material deposition with coaxial wire feed and use for process control

Abstract

Within laser additive manufacturing (directed energy deposition with laser beam), processes are further distinguished by the form of the filler material. In terms of availability, storage, safety, and cost, wire is commonly the preferred filler material in comparison to powder. Despite these advantages, due to the different material transfer modes, a greater process control is required. Within this work, an experimental setup for electrical-resistance-measurement within the laser material deposition process with a coaxial wire feed and its possible use for an automated process control is investigated. The measurement is performed between a wire, a substrate, and over the melt pool. One main influencing factor on process stability is derived from the timing of the trigger sequence of the laser power, process feed, and wire feed at the start and end points of every track. Consequently, inaccurate settings of the trigger sequence can, e.g., lead to deviations in track length and part geometry. Additionally, a smooth transfer of the wire into the melt pool is imperative during part build-up to ensure a stable deposition process. Variation in laser power, wire feed, process feed, or wire transfer mode can lead to process instabilities. This can result in imperfections, bonding defects, or pores in the tracks and layers that will add up in built components and must be avoided for defectfree three-dimensional geometries. Within the experiments, it is investigated whether the resistance-measurement provides consistent results under varying conditions and potentially can be utilized to automate the trigger sequence of deposition. Furthermore, it is investigated whether different wire transfer modes can be linked to the measured resistance values during welding of single tracks.