Full Description

Since Nicoli Tesla first applied for patents on a light source based on electron beam bombardment heating of graphite in evacuated glass bulbs, electron beam technology has advanced wherein practical production joining by this method is gaining industry-wide acceptance. Men of importance who followed Tesla's concept of utilizing this energy source as a working tool were K. H. Steigerwald of the Carl Zeiss Foundation in West Germany and J.R. Pierce, author of a technical book on electron beam optics.

The first practical welding applications of this process were accomplished by J. A. Stohr, who announced the first electron beam welder at the Technical Symposium of Fuel Elements in Paris, France in 1957. W. L. Wyman of General Electric Hanford Laboratories is credited with developing the first electron beam welder in the United States at about this same time period.

Electron beam welding has gained rapid recognition in the materials joining field, particularly in the aerospace industry. More than 200 electron beam welding machines have been sold as of this writing and equipment manufacturers report an increasing activity and interest in this type of welding equipment.

The controversial subject of high vs. low voltage electron beam welding has faded into the background and this topic is no longer considered of prime importance in electron beam welding technology.

The basic components of an electron beam welding system are the vacuum chamber and pumps, electron beam gun, and high voltage controls. Electron beam welding machines have been classified into two groups, the low voltage type (up to 60,000 v) and the high voltage type (up to 150,000 Y). Also, there are two basic gun design concepts, the Steigerwald and Pierce type guns.

Unlike other more conventional fusion welding processes, the electron beam process is capable of producing very deeply penetrated welds with very narrow cross-sectional areas. The depth-to-width ratios of electron beam welds can be as great, or greater than, 20 to 1. This phenomenon is discussed and the effects of high depth-to-width ratios are explained.

Engineers who are planning and designing for electron beam welding must have a thorough understanding of the advantages and limitations of the process. Design concepts, joint configurations and other data pertinent to successful electron beam production of flight hardware are fully discussed.

Most metallurgical joining processes are highly dependent upon adequate tooling before metals can be joined. As in most fusion welding processes, electron beam welding must depend almost entirely upon tooling and fixturing before flight hardware can be produced to meet the stringent dimensional tolerances demanded of the aerospace industry. Problems associated with tooling when welding high temperature alloys such as columbium - 1 % zirconium, molybdenum and other refractory alloy configurations are discussed. Fixtures permitting high productivity of various aerospace hardware are illustrated. Weld joint designs and tolerances of abutting interfaces are described and illustrated to aid the design and development engineer.

Welding techniques and weld reproducibility are more a function of operator technique than in conventional welding. The electron beam welder is extremely sensitive to small variations in beam power and focus, thus requiring accurate controls and careful adjustments. The operator must be thoroughly familiar with the machine and its capabilities. In production applications, reproducibility of the process is extremely high. Repetitive weld operations have shown consistent weld penetration and width to less than 0.002 in. variation.

The electron beam welding process is easily adapted to weldments not feasible with conventional welding processes, the most important of which are welding foil material, thick to thin materials and dissimilar metals. Also, important applications of electron beam welding include complex structures where little distortion can be tolerated; structures where welding is required in deep holes, deep grooves and other relatively inaccessible areas; micro-electronics; and heavy sections where high-speed, single-pass electron beam welding offers significant economic advantage. Welding of reactive metals and ceramics has been successfully accomplished.

Quality control and inspection requirements are similar to those of conventional welding processes. Visual, magnetic particle, dye-penetrant, ultrasonic, and X-ray inspection procedures are all applicable to electron beam weldments.

While extensive cost analyses of electron beam weldments have yet to be compiled, typical examples predict a very favorable comparison with other automatic fusion welding techniques. Time losses due to chamber evacuation can be greatly compensated for by multiple fixturing.

At the present time the electron beam welding process is evolving from the laboratory to production and has become an integral part of the metals joining field. Future application of this process is virtually unlimited.

In addition to the conventional units having a chamber which contains the electron gun and traversing mechanisms and into which the workpiece is placed, custom units can be made whose chambers fit around the joint portion and the workpiece enters through seals. Development is well advanced on electron beam welders that will weld joints that are at atmospheric pressure.

The future of electron beam welding is dependent on man's ingenuity to apply it to his needs.

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Published: 1964 Number of Pages: 29 File Size: 1 file , 2.6 MB