Investigations in instable process conditions during laser beam microwelding of copper
Final Report Abstract
The objective of this project was to investigate the reasons and find possible countermeasures for the process instabilities in laser micro-welding of copper when using near-infrared lasers. Simulations with literature data confirmed an expected mutual amplification between the disadvantageous effects of the temperature-dependent absorptance and thermal conductivity. They further showed that the temperature-dependent function of the absorptance is the key reason for the low process reproducibility. These simulations still required a correction factor of 1.7 for agreement with experiments. Measurements of the temperature-dependent reflectance in nitrogen atmosphere were conducted in an integrating sphere setup developed by us. We further corrected the measurements regarding a reflectance drift and the timedependance of redox reactions. With these new input data, a correction factor was no longer needed in the simulations. Experiments and simulations with the corrected reflectance data showed that a thermal reduction of oxides on the sample surface leads to smaller process windows during the production of laser micro-spot melts, while elevated initial temperatures and a ramp-up pulse shape increase the process window and thus stabilize the process on reduced and untreated samples.
Publications
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Simulation of the influence of temperature-dependent material parameters on the temperature evolution in laser micro-spot welding of copper. International Congress on Applications of Lasers & Electro-Optics, M604.
Mattern, Manuel & Ostendorf, Andreas
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Temporal temperature evolution in laser micro-spot welding of copper considering temperature-dependent material parameters. Materials Research Express, 5(6), 066545.
Mattern, Manuel; Weigel, Thomas & Ostendorf, Andreas
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Temperature-dependent reflectivity of unpolished rolled copper for near infrared lasers. OA in: Proceedings of Lasers in Manufacturing Conference
Mattern M. & Ostendorf A.
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Combined experimental and theoretical approach to improve measurement accuracy of temperature-dependent reflectance of copper.
Mattern, Manuel; Kukreja, Lalit Mohan & Ostendorf, Andreas
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Temperature-dependent reflectance of copper with different surface conditions measured at 1064 nm.
Mattern, Manuel; Kukreja, Lalit Mohan & Ostendorf, Andreas
