Method for high accuracy measurements of energy coupling and melting efficiency under welding conditions

The demands on production processes vastly increased in the last decade. Besides the fulfillment of the fabrication task, a process has to be energy efficient and resource saving to be in line for mass production. For the evaluation of competing technologies or for the optimization of a process regarding these requests, the knowledge about the specific process efficiency is crucial. However, the value strongly depends on the chosen process parameters and the environmental conditions, wherefore documented values in the literature are inapplicable. Hence, an experimental determination for each individual case is inevitable. Existing methods for the estimation of the process efficiency are either inaccurate or time and cost intensive. Therefore, a new method for determining process efficiencies for almost arbitrary materials and process conditions is presented. The method is based on process observation using thermographic imaging and a subsequent adjusted numerical computation of temperature fields. The result of the numerical calculation in combination with the evaluation of the weld seam cross section is the value for the energy coupling efficiency, melting efficiency as well as the overall thermal efficiency. The features of the proposed method are evaluated with a Design of Experiments approach. The technique is applied to a conventional laser and plasma welding process as well as to laser-assisted plasma arc welding. In comparison to the individual processes, the laser-assisted plasma arc welding shows a more than doubled overall thermal efficiency, which can be ascribed to a drastic increase in melting efficiency and a moderate increase in energy coupling efficiency