Electron Beam Welding, using advanced beam deflection techniques

As conventionally applied, the technique can make welds with very low heat inputs, at relatively high weld speeds, and it is this that the process is best known for. What is less well known is the potential for the control and manipulation of the electron beam (EB) heat source for other materials processing tasks, as well as advanced welding techniques.

Most people's (unknowing, in many cases) contact with manipulated electron beams comes with just about every conventional VDU that they look at. If you are sitting in front of a computer right now, looking at an ordinary monitor, you are looking at the results of a rapidly scanned electron beam, causing light to be generated on the inside of the screen wherever it contacts the phosphorescent material. In order to achieve this, the beam is scanned precisely at speeds of several kilometres per second. We can do this with a welding beam, too.

Effectively, this means that the beam can be in several places at once. This means that the EB heat source can be 'split' during welding so that a portion of the beam's energy can make the weld in the normal way, and the remainder can be 'timeshared' between locations elsewhere on the workpiece. The beam is cycled between the different locations many hundreds of times a second, so the weldpool does not 'know' the beam has gone. Elsewhere, the beam can heat the workpiece up, or make a second perhaps 'cosmetic' weld pass at the same time as the main weld pass is made.

Manipulating the electron beam so that it effectively becomes multiple heat sources can allow a radical change in the application of the welding process to materials that would be likely to suffer cracking or other welding difficulties when welded in a more conventional fashion.

The application of multiple heat sources to the welding process allows the solidification rate of the weld metal to be controlled, as well as some of the stresses around the solidifying and cooling weld metal. Welds made in this way are frequently made at lower weld speeds than would normally be the case for EB welds, and are made with a higher heat input per unit length. Despite this, levels of distortion in such welds are frequently relatively low.

At its simplest, the special welding procedure can consist of a simple 'travelling preheat' zone ahead of the weldpool. At its most complex, a large change in the stresses around the weld can also be achieved, and welds with microstructures not normally found in welds of low distortion are made.

The practical application of this family of welding strategies requires the fitment of additional equipment to an otherwise standard EB machine, and careful development and control of the welding procedures themselves for optimum results.

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