Development of a programmable pattern generator for electron beam welding
has led to the investigation of a range of oscillation patterns, some of which have extremely beneficial effects on the depth-to-width ratio, bead appearance, and consistency of welding performance.
Most electron beam welding machines are fitted with a low frequency (50Hz) deflection system, used to produce a circular movement of 0.5-2mm to 'stir' the weld pool. This new system allows any shape of beam deflection to be designed by the operator, and this is executed at a frequency in the range 1Hz to over 100kHz. The pattern generator unit will also allow development of specialised surface heat treatment patterns and control of weld cooling rate.
Electron beam deflection during welding has a dramatic effect on fusion zone shape, and top and bottom bead appearance. The frequency and amplitude of deflection are important weld parameters.
In this device, patterns are designed on a personal computer and then downloaded into the deflection unit where they are stored in a battery-backed memory. Modifications to the pattern or even completely new deflection patterns can be designed and tested on the welding machine in just a few minutes. Each pattern consists of up to 16,000 discrete dots which are used to produce a heat distribution over the workpiece surface.
The full extent of applications for programmable deflection are not yet complete. However, thick section welding in the nuclear and power industries has benefited enormously by the increased depth-to-width ratios possible.
Work in thin section material has also shown that particular patterns control keyhole stability, weld spatter, top and bottom bead appearance and can enable welding of crack susceptible alloys.
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