Method of metal transfer regulation during GMA welding

The main force that detaches a molten droplet from the electrode (wire) during arc welding is the interaction of the arc current with its own magnetic field. The magnitude of this force depends on the current distribution inside the droplet. A method to regulate the current distribution is proposed. The current redistribution is achieved by striking an additional arc with the droplet serving as a cathode of this arc. By the current redistribution it is possible (i) to decrease the threshold current of the globular to spray transition during GMA welding, (ii) to achieve this transition in different plasma gases, and (iii) to control the propelling direction of the detaching droplet. Some preliminary experiments confirm the proposed method

High-speed imaging investigation of transition phenomena in the pilot arc phase in Hf cathodes for plasma arc cutting

The behaviour of Hf cathodes has been investigated with high-speed camera (HSC) imaging techniques during the low-current pilot arc phase to highlight phenomena that take place during the transition from an insulating, non-emissive, cold phase to a conductive, emissive, hot phase for Hf-based materials used in electrodes for plasma arc cutting (PAC) of mild steel plates. The different behaviours during the start-up phases of new or used electrodes have been considered. Such phenomena have been partially described on physical bases in the past but can now be fully seen and analysed using diagnostics. Conclusions can be drawn concerning the particular conditions under which heat transfer transients in the cathode tip during the PAC pilot arc take place, giving additional useful information for future design-oriented simulation of such phenomena under different geometric and operating conditions, with the final aim of optimizing the cathode\u2019s expected service life

Advances in plasma arc cutting technology: the experimental part of an integrated approach

The experimental part of an integrated approach to design and optimization of plasma arc cutting devices will be presented; in particular results obtained through diagnostics based on high speed imaging and Schlieren photography and some evidences obtained through experimental procedures. High speed imaging enabled to investigate start-up transition phenomena in both pilot arc and transferred arc mode, anode attachment behaviour during piercing and cutting phases, cathode attachment behaviour during startup transient in PAC torches with both retract and high frequency pulse pilot arc ignition. Schlieren photography has been used to better understand the interaction between the plasma discharge and the kerf front. The behaviour of hafnium cathodes at high current levels at the beginning of their service life was experimentally investigated, with the final aim of characterizing phenomena that take place during those initial piercing and cutting phases and optimizing the initial shape of the surface of the emissive insert