Four Decades of Electron Beam Development at TWI

Abstract

EBW equipment was first installed at TWI in the early 1960s. Although of limited performance, the deep narrow, single pass welds made in 12 mm steel created a great deal of excitement and spawned an extensive, higher power, research and development programme. This led, by the early 1970s, to an advanced, high vacuum, 75 kW, 150 kV machine capable of 300 mm penetration in steel, 450 mm in aluminium alloy and 125 mm in copper alloy. The work set the trend for subsequent decades and notable further developments took place in both electron gun and power source design to meet the demands of industrial thick section applications. Electron sources were improved to achieve longer cathode life, even higher performance and greater beam stability. Flashless, intelligent, switch mode inverters replaced conventional power sources. Differentially pumped systems were devised to permit operation at pressures up to several millibar to offset the limitations of vacuum operation and both external and internal chamber guns were designed for a wide range of large applications. Significant advances were also made in Non-Vacuum EBW, with the establishment of a large 300 kV, 150 kW facility and in recent times a special high frequency beam pulsing device was used to increase the penetration depth and reduce the width of welds made at atmospheric pressure. In addition, special high intensity guns were designed for material surface processing. These are capable of producing innumerable macro and micro effects, offering a whole new range of possibilities for metal bonding for aerospace, automobile and medical applications. EBW equipment and application highlights are described with particular emphasis on work carried out in the last few years.