TWI Industrial Member Report Summary 541/1996
F J Blunt and C N Ribton
Magnetic arc oscillation is a very efficient way of increasing weldbead width. The design of the electromagnet is important if costs are to be minimised.
Background
An experimental programme completed at TWI has shown that productivity of weld surfacing could be improved, in both the TIG and MIG processes, by magnetically deflecting the arc. The electromagnet used in the experimental programme was based on a design previously developed for the TIG welding of pipe joints. This magnet was adequate, but there was considerable scope to improve its efficiency. The solenoid required a current of several amps to achieve the magnetic fields required, and as a result needed a water jacket, to prevent its windings from overheating.
Since the fields required for arc oscillation were found to be of the order 15mT or less at the arc position, it was believed that the magnet could be redesigned to use a lower current density in the solenoid, so that the unit could be air-cooled. This would reduce the costs of manufacture, electricity and there would be no requirement to attach it to a water supply.
When surfacing a flat plate, access is virtually unlimited, and hence this allows a greater freedom in magnet design. Analytical solutions of magnetic field can only be achieved for relatively simple symmetrical shapes, hence, to assist the design process, a finite element program was used to predict the field at the project position of the arc. This allowed more complex geometries to be analysed. The program was also able to model the behaviour of non-linear magnetic materials.
Objectives
- To validate the software used to model the electromagnet
- To design an improved electromagnet, which could use a current density compatible with air-cooling the solenoid.