Published on 21 January 2013
Framatome Technical Centre at Le Creusot, France has taken advantage of TWI's electron beam digital deflection system for use with its 100kW electron beam welding gun. The system allows a beam deflection pattern for welding to be designed by the machine operator.
Programming a pattern for the beam to follow can dramatically improve welding performance and extend the range of potential applications of a single EB machine. The unit even includes a facility for engraving a part number on a processed workpiece.
The digital deflection system can be tailored to fit into any EB machine and the means of controlling frequency, amplitude, and pattern can be fully automatic (by CNC), manual or via an RS 232 serial link.
The system operator can design a simple pattern consisting of just a few points, or one which is very complex with up to 255 individually positioned points. The electron beam can then be deflected from point to point to reproduce the pattern on the workpiece surface. The cycle is repeated at a programmed frequency - its deflections may range from less than 0.5mm amplitude up to several tens of millimetres.
For welding applications, distribution of the beam power within the pattern can be used to improve the depth-to-width ratio, to control the cooling rate of the weld (which can avoid defects caused by rapid self-quenching of the fusion zone), and to provide control of the top and bottom bead appearance. Specialised high amplitude patterns are also being investigated for use in EB surface modification.
The patterns are designed on a PC and can be stored on disc for later use. The final pattern may consist of several parts: a welding oscillation, a cooling rate control raster, and a post weld 'cosmetic' raster. Each part can be designed separately and then merged into the final deflection pattern which can be downloaded to the deflection unit. Once the pattern is in the unit it is stored until it is overwritten by a new design. Up to 32 patterns can be stored by the unit for selection by the operator.
As an optional extra the unit interfaces to the EBW machine CNC system, this is in fact how TWI configured Framatome's 100kW machine where the horizontal size and frequency of the deflection can then be programmed as axes. These will smoothly interpolate with the other axes of the system including the table and gun mechanical movement, the beam current, and focus coil values.
Interest in this technique is being expressed by a large number of manufacturers who use EB, for applications which range from engraving and surface treatment at beam powers less than a few kilowatts to deep section welding at powers up to 100kW.
For information about TWI's capabilities please contact us.