GB1331113A - Control apparatus for an electron beam welding machine - Google Patents

Abstract

1331113 Welding by fusion DEFENCE SECRETARY OF STATE FOR 5 Nov 1970 52643/70 Heading B3R [Also in Division G1] In an electron beam welding apparatus, a photo-electric device, energized through a variable mark/space ratio pulse generator, is used to control switching on and off of the electron beam at sufficient speed to avoid steplike changes in temperature of the workpiece as it is heated or cooled, which would result in cracking thereof. The electron welding equipment comprises gun 10 and workpiece 14 enclosed in vacuum chamber 12. The high voltage (160 Kv) switch 18 for the gun is immersed in a tank of oil 16. The photo-electric cell for controlling switch 18 is located adjacent thereto and receives light pulses via optical fibre guide 42 from a gallium arsenide lamp 40 which is supplied by the pulse generator 38. The pulse generator control circuit, Fig. 3, includes integrating amplifier 26 whose output voltage, on starting of a welding operation, by a START order to control circuit 20, gradually increases in amplitude, causing a control on line 36 to pulse generator 38, which produces pulses of gradually increasing duration. This results in heating of the workpiece. When the voltage, which is also fed to amplifier 32, reaches the value set by resistor 34, the logic circuit 20 switches over, opening 24, and closing 43. The output of amplifier 26 now decreases until the voltage drops below the value set by 34, to cause switching of logic circuit 20 once more. The total effect is for the voltage to hunt around the level set by 34, resulting in a constant duration of pulses from 38. This continues until the welding cycle is virtually complete. The logic circuit 20 is then signalled from 14 to switch over and allow amplifier 39 to be effective as the voltage from 26 decreases until it reaches the value set by 48 and switch down of the system occurs.