LETTERS TO THE EDITOR

Worldwide EB Welding Technology

Dear Editor: A long review paper entitled "Electron

Beam and Laser Beam Materials Processing in japan," by T. W. Eagar, was published in the ~uly 1986 issue of the Welding Journal. It is

of interest to learn what is going on over there, and to make comparisons with the status of this technology here. The paper does this by means of remarks and cross-refer- ences. While one would not expect a total review of the developments in the U. 5. in a paper on japan's developments, I am afraid that the American reader, be he a technical executive or a student, may come away with a distorted view of the developments, and the leading role of the engineers in American industry (not the universities!), if he gets exposed to electron beam technology for the first time through this presumably authoritative artide in a technical society journal.

Historically, EB welding as an industrial man- ufacturing method began with the nuclear industry in France, where J. A. Stohr, in 1954, used the method to close fuel elements. This was first published in 1958. Much more needed to be said to give an adequate, correct account of VEB, or EB welding in vacuum. For reasons of space, I want to comment mainly on AEB. or atmosoheric EB weldine falso called . ~ ,~ - . non-vacuum EB welding), which is curiously misrepresented byMr. Eagar. Yet, it is present- ly the one welding method with the greatest untouched potential. It started not 15, but over 30 years ago, and not in Japan.

In 1952, at the T. H. Stuttgart, Stuttgart, Germany, the writer developed, independent- ly of any other group, a system to transfer a focused high-power density beam into the atmosphere, through free apertures of about 1 mm in diameter, utilizing gas dynamic effects, not just differential pumping [OPTIK 10:116-131; U. S. Patent 28995561. By 1954, Heraeus GmbH offered a commercial 4-kW, 150-kV atmospheric EB gun based on this design. Surface treatment, chemical reactions, melting, welding, cutting and thermal blasting, generation of sound, even isotope separation by the focused beam in the atmosphere, were mentioned at this time, as were ion beam plating and ion implementation. Beam plasma generation attaining nuclear fusion was also suggested [Can. I. Phys. 35239, 19571. Updated design procedures for the dynamic vacuum system for beam transfer were pub- lished at the 2nd International Vacuum Con- gress, Washington, D. C., 1961, with EB weld- '"8 once more explicitly mentioned. A machine based on another design principle [U. 5. Patent 3162749, 3444350, and others] was devel- oped by United Technologies, a type still sold

by Leybold-Heraeus Vacuum Systems. ^e machines built in-house by A. 0. Smith [Welding journal, ~ugust 19741 utilize yet another principle. The writer demonstrated that an electron beam can also be fired into the atmosphere coaxially with an aspirator jet Of air, steam, or water [Contract DAA 02-

73-C-0158, U. S. Army Mob. Equip. R&D Ctr.].

At Westinghouse Research, Pittsburgh, the writer built the prototypes for the later com- mercial 12-kW, 24-kW and 60-kW atmospher- ic electron beam guns (1965 to 1976), some of which are still on the production lines today [Welding Journal, ~ a y 1973; 1. Appl. P&. 47:95-106, 19761,

Much misinformation about the behavior of the electron beam in air is still circulating, and in the day when lasers are mentioned for com- parison, people are never told that the elec- tron beam can have 1000X the radiance (in W c m 2 srl! of the best oossible carbon dioxide laser and be g.enerated witn 99% efficiency In his article, Mr Eagar makes light of atmospher- ic AEB welding with the remark 'Although there was some research on out-of-vacuum electron beam welding in the United States and Japan 15 years ago, very deep penetration welding must be performed in vacuum." This begs the question: Who says we want to make only very deep welds? The 60-kW atmospher- ic electron beam can make single pass butt welds in 38-mm-thick steel and make a melt cut (not oxygen cut) through 120 mm of steel or aiuminum. Presently, the chief application of the AEB process is high-speed welding of thinner material, at up to 360+ ipm for steel, 800 ipm for aiuminum. Welds are often not wider than those made in partial vacuum. The cost per kW beam power is %to X o of that of the laser, and enough beam power is readily available to fill gaps with sacrificial metal from the edge of the part, or from filler wire. Some 90 million catalytic converters have by now been made with this process, similar numbers of car frame blanks. and close to a million ~. ~ ~~ ~~~- ~- ~

die-cast aluminum intake manifolds. And this in spite of the fact that the research funds for AEB technology have been a minute fraction of that going into laser applications. Sugges- tions [U. S. Patent 42517091 to use liquid metal jets as filler for thick-section welding or badly fitting parts have never been supported. Another application for the AEB process, with great advantages over the laser, Is surface hardening. Certain "problems" with EB tech- noloey mentioned bv Mr. Eaaar. such as ioint tracking, non-uniform penetration, and lack of beam stability, drp not generic and have largely been solved. The AEB process needs no large, expensive vacuum chambers, nor does it Gf- fer from the cost and the complexity of sliding seal machines.

I hope that these comments will wake some people up and uproot some deep-seated misunderstandings about EB technology, which have prevented many potentially good applications. I also hope this letter will cause some readers to aooreciate the contributions U. 5. industrial scientists and engineers have made to EB technology and its applications to industrial productivity.

Berthod W. Schumacher Dearborn, Mich.

-continued on page 8

8 1 JANUARY 1987

The author o f the artide, "Electron Beam and Laser Beam Materials Processing in Japan," replies as follows:

From the tone of Dr. Schumacher's letter, he wds piqued by my article. His two major complaints arise from my failure to discuss the history of electron beam welding in France, Germany and the United States, and my omis- sion of a lengthy section on atmospheric electron beam (AEB) welding. To these omis- sions, I plead guilty. However, given the facts that my article is titled ". ..in Japan" and that these references to western technology and AEB welding are irrelevant to an already lengthy article on Japanese technology, I plead not guilty.

In his closing, Dr. Schumacher indicates that he hooes to "uoroot some deed-seated mis- understandings about EB technology8' and to recognize "the contr:butfons of U. S. industrial scientists." I applaud the former, as this was one of the ourooses of mv article. As for the latter, I alsorecognize the contributions. In my article, on page 25, I note that "Most of this low-power beam technology [in Japan] has been licensed from the United States, France or West Germany." Perhaps Dr. Schumacher could write an article on electron beam materials processing in the United States and Europe to supplement my review of Japan.

Finally, it is easy to understand the hub which Dr. Schumacher displays toward A@ given that he has spent 35 years studying tlj process. Nonetheless, the Japanese do not u~ this technology commercially, and one mb question why so few people around the wort have adopted AEB for critical components.

Thomas W. Eaex u-

Associate Professor Materials Engineeriu

Mi Cambridge, Mass

WELDING JOURNAL 1 7