Electron Beam Machining
5.3.1 Introduction
The earliest work of material removal utilizing an electron beam wasattributed to Steigerwald who designed a prototype machine in 1947.Electron beam machining (EBM) has been used in industry since the1960s, initially in nuclear and aerospace welding applications. Drilling small holes, cutting, engraving, and heat treatment are a set of modernapplications used in semiconductor manufacturing as well as micro-machining areas.Basic equipment and removal mechanism
The main components of EBM installation, shown in Fig. 5.43 arehoused in a vacuum chamber, evacuated to about 10–4torr. The tungstenfilament cathode is heated to about 2500 to 3000°C in order to emitelectrons. Ameasure of this effect is the emission current, the magni-tude of which varies between 20 and 100 mA. Corresponding currentdensities lie between 5 and 15 A/cm2. Emission current depends on thecathode material, temperature, and the high voltage that is usuallyabout 150 kV. Such a high voltage accelerates a stream of electrons inthe direction of the workpiece. After acceleration, electrons, focused bythe field, travel through a hole in the anode. The electron beam isthen refocused by a magnetic or electronic lens system so that thebeam is directed under control toward the workpiece. The electronsmaintain the velocity (228 × 103km/s) imparted by the accelerationvoltage until they strike the workpiece, over a well-defined area, typ-ically 0.25 mm in diameter.