Study on the problem of filling the cavity derived from crack removal in hydroelectric turbine runners in out of position pulsed GMAW welding: bead geometry prediction for deposition planning

José Luis Lázaro Plata¹; Edison Andres Arteaga López¹; Guilherme Caribé de Carvalho¹

¹ Universidade de Brasília

doi:10.20906/CPS/COB-2015-1187

Resumo

Fatigue crack removal and cavitation erosion phenomena promote the loss of mass in hydroelectric turbine runner blades. Generally, the blade geometry recovery is carried out by means of depositing weld metal to fill the cavities followed by a gridding process to recover the original geometry. Such work is normally carried out manually, thus requiring several hours of highly skilled welders. In the last few years, some attempts have been made to automatizing such repair work, mainly in recovering cavitation erosion cavities. In the case of fatigue crack recovery, manual welding is still the main process of depositing the metal. This work presents a study on the bead deposition planning strategy in order to allow the use of robotic welding on the task of filling the crack removal cavity. Considering that a crack normally develops from the external surface of the blade towards its inner volume, after its removal the cavity will not be totally surrounded by blade material. Sometimes, the crack partially goes through the blade thickness which implies that, after its removal, the resulting cavity will need a backing plate on one of its sides in order to provide support to the filling weld beads. When thinking about defining the necessary sequence and the distribution of weld beads to fill the cavity with metal such that the deposition process can be robotized, some problems arise related to the bead section geometry dependence on the welding parameters and on welding position. Such geometry will strongly influence the number of layers of weld beads needed, considering that the filling process is carried out in layers. In this case, the first problem to be faced is the definition of the distance between parallel beads necessary for the deposition of a maximally flat weld layer. The second problem is the layer thickness that results from the selected distance between parallel beads within a layer. This paper, therefore, addresses the two previously cited problems by developing statistical models that can map the bead sec

Palavras-chave: Pulsed GMAW; bead geometry modeling; out of position welding