Controlling root penetration in electron beam welding by a through-current feedback

Abstract

Electron beam (EB) welding is a keyhole welding process in which the kinetic energy of focused electrons is converted into the heat required for welding. When a full penetration weld is achieved in keyhole EB welding, a small part of the electrons from the electron beam pass through the workpiece via the open keyhole at the root side of the weld. These electrons provide a charge whose current value can be measured, namely, the through-current. The aim of this study was to develop and build a control system integrated in the EB welding machine that enables the maintenance of complete root penetration in EB welding by means of an adaptive control system. The adaptation was performed with closed-loop feedback equipment that simultaneously measures the electrons passing through the workpiece via the keyhole (transmitted through-current) and adjusts the required beam current parameter relative to the through-current measured during welding. The results of the welding tests demonstrated the functionality of the developed control system and the suitability of the concept itself. For example, in a welding test run in which the thickness of the test piece was linearly increased from 10 to 12 mm, the control system was able to react and regulate the welding power required for complete root penetration along the whole thickness range. In the above case, the test results showed that based on the measured through-current data, the control system instantaneously increased the amount of beam current required during welding linearly with increasing thickness of the plate to be welded.