1990 Volume 8 Issue 4 Pages 475-481
In electron beam welding, it is very important to set focal position of beam on work piece appropriately. However, it is very difficult to set one accurately in case of complex joint geometry.
New beam focus detecting system have been developed as part of intelligent welding system for electron beam welding.
When electron beam is irradiated on work poece, backscattered electron, thermoelectron, secondary electron, ion or X-ray emitted from work piece are observed. Among these, thermoelectron is much affected with surface condition of a work piece. That is, as soon as the surface melted, thermoelectron increased rapidly.
The results obtained are as follows.
1. In case that the condition of beam convergency on work piece is shifted from out of focus to in focus, signal of thermoelectron shows peak value when beam focal position coincide with the surface of work piece.
2. It is possible to obtain high S/N ratio by employing positive collector bias by which thermoelectron gathered easily to the collector.
3. The detecting accuracy is within ±1% in the case that ab factor is 1.0.