Interchangeable metal transfer phenomenon in GMA welding: Features, mechanisms, classification

Metal transfer modes in arc welding processes have previously been classified as Natural or Controlled Metal Transfer. Modern laboratory techniques have helped to establish a new transfer classification mode in GMAW of carbon steels, which has been termed Interchangeable Metal Transfer. In order to characterize the new mode, a series of specimens was welded at different combinations of welding current (wire feed speed), arc voltage and gas composition. Laser backlighting techniques and high speed filming were employed to study metal transfer. The video was synchronized with the welding current and arc voltage signals to aid the understanding of the transfer behaviour. The results showed that this new interchangeable metal transfer class is distinguished from the Natural or Controlled Metal Transfer class because of its unique characteristic of periodical changes in the transfer mode induced by changes in welding parameters (a self-sustained behaviour). The characteristic feature of the interchangeable metal transfer class was shown to comprise of two or more natural transfer modes occurring in a regular repetitive sequence. The metal transfer sequence occurs without interference from the operator or the adaptive control system of the power source. Phenomenological explanations based on arc physics are given to justify the main governing factors for the particular metal transfer characteristics.