Development of an Automatic Beam Focal Detection System for Electron Beam Welding

概要

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In electron beam welding, it is very important to set the beam's focal position on a workpiece properly. However, it is very difficult to position one accurately in the case of workpieces having complex joint geometry. A new beam focal detection system has been developed as part of an intelligent wedling system for electron bearn welding. When electrons are irradiated on a workpiece, backscattered electrons, thermoelectrons, secondary electrons, ions or X-rays are emitted from the workpiece. Among these, thermoelectrons are greatly affected by the surface conditions of the work piece: When the surface melts, thermoelectron emissions increase rapidly. The new system has the following features : 1.When a beam converging on a workpiece changes from out of focus to in focus, the signal from the thermoelectrons shows a peak value when the beam's focal position coincides with the surface of the workpiece. 2. A high S/N ratio is obtained by employing a positive collector bias which causes thermoelectrons to be drawn to the collector. 3. Detection accuracy is within ±1% when the a_b factor is 1.0.
社団法人溶接学会の論文
1992-04-01