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Processes and active zones in oxygen-free atmospheres for the development of sustainable production techniques and manufacturing processes
All technically used inert gas and vacuum atmospheres still contain sufficient oxygen molecules, which lead to the rapid oxidation of metal surfaces. This limits the possibilities of many processing and joining processes. The Collaborative Research Center 1368 "Oxygen-free production" is based on the idea of adding a small amount of silane (a few ppm) to the inert gas argon. The silane reacts with the residual oxygen and water in the atmosphere and reduces the partial pressure of the oxygen to less than 10-23 bar. This partial pressure is equivalent to extremely high vacuums (XHV-adequate atmosphere). The CRC is concerned with the development and research of specific production processes for forming, shaping, joining, cutting and coating in an oxygen-free environment.
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Sub-project T01 "DBD-assisted high-frequency welding"
Project leader: Prof. Dr. rer. nat. Wolfgang Maus-Friedrichs, Dr. Henning Wiche
Funding period: 01/2024 - 12/2026
Funding body: DFG
Researcher: M. Sc. Viktor Udachin (01/2024 - 12/2026)
Weld seam defects in the form of oxide inclusions are a major production problem in longitudinal high-frequency welding. This is where the present research project comes in. A plasma treatment unit, designed as a plasma jet, is to be integrated in the heating section with the additional introduction of reducing shielding gas mixtures such as argon/silane or argon/hydrogen to deoxidize the strip edges. The plasma activates the gases and thus enables effective deoxidation. The working gas flow provides a local XHV-adequate atmosphere during the welding process. The design of the plasma as a dielectric barrier discharge (DBD) prevents the additional introduction of thermal energy into the process. The basic principles for the use of DBDs for metal deoxidation in an oxygen-free atmosphere were successfully developed on a laboratory scale in sub-project C01 during the first funding period and are used there and in other sub-projects of the CRC for deoxidation. In addition to this objective, the effects on the welding process are also to be analyzed in detail. In high-frequency welding, for example, there are three characteristic welding gap shapes depending on the energy input, whereby a spatial separation can occur between the strip edge convergence point and the welding point. The processes in the resulting welding gap are complex. In particular, the stochastically occurring arc bridge formation at the convergence point and the molten pool ejection in the welding gap due to the electromagnetic fields acting as a function of the arc frequency at the strip edge convergence point pose challenges for process control. Any positive or negative influences of the plasma must be fully investigated. By implementing an oxygen-free production process, the application partner aims to improve the weld seam quality (characterized by the achievable notched impact strength), increase the process yield and expand the product portfolio. In addition, the findings on targeted process-integrated deoxidation using plasma jets, together with the experience from sub-project C01, can be used as a knowledge base for other sub-projects of the CRC.