Cause study to the occurrence of unmelted wire pieces during wire arc spraying

摘要

The occurrence of process instabilities like separation of unmelted wire pieces (cold shots) or wire sticking during spraying is investigated for three different wire arc spraying equipments: An experimental spray gun, a large scale production and a small scale production equipment. Particular designed mobile diagnostics are used to record high sampling rate waveforms of quantities like arc voltage and current, voltage drop at the wire contact sleeves and finally the wire feed velocity at the feeder and just in front of the contact sleeves for push systems. A spectrum analysis based strategy is developed to predict the occurrence of process instabilities with a view to quality assurance. In addition a competitive visual inspection system of a camera and a pulsed LED illumination is designed as a tool for manual inspection of droplet detachment and spray jet generation. For each of the investigated spraying equipments, the applied diagnostics are presented and the results are interpreted with respect to the physical cause of instabilities and how to potentially avoid them.