Our “advantages” page on electron beam welding have told us what its outstanding advantages are. But how does it compare with other kinds of welding, and what are its prospects as a production welding technique? Westinghouse has made a thorough study of these questions at its Bettis Atomic Power Laboratory and has voted in favor of the new process, at least for certain applications.
“Chemical analyses, metallography, corrosion tests, and mechanical property evaluations have revealed satisfactory properties in the Zircaloy-2 welded by this process.” Of course, the main reason for its success in welding a reactive material like Zircaloy-2 is that the process operates in a high vacuum. At a pressure of only about 0.03 micron of mercury, there is practically no atmosphere left in the welding chamber to cause contamination. And, unless the high vacuum is maintained, the electrons will not travel from the cathode to bombard the work.
High depth-to-width ratio
A particular advantage of electron beam welding equipment is the high concentration of thermal energy at the work piece. Because of this feature, the machine can make welds with a depth-to-width ratio of 2:1 in Zircaloy-2, and a ratio of 3:1 has been achieved with special machine adjustments. But what does this mean in actual processing? Primarily, it means a narrow fusion zone and heat-affected zone, and it means less shrinkage and thermal distortion. The equipment also maintains “remarkably uniform weld penetration.”
The deep penetration of electron beam welds minimizes the amount of over-penetration and avoids the obliteration of adjacent seams. With the tungsten arc process, the seam adjacent to the last seam welded becomes covered by the fusion zone, and accurate tracking is difficult.
The lowered total energy input to the weld by the electron beam effectively reduces the shrinkage and thermal distortion to which the work piece is subjected. Total transverse shrinkage per weld seam has been 0.010 to 0.012 in. for tungsten arc welds and only 0.001 to 0.002 in. for electron beam welds. These benefits are possible only with high-voltage electron beam equipment.
How about costs?
But, with all its advantages, how does high-voltage electron beam welding stack up on costs? Andrews Hi-Tec Corp says the main factor here is the greatly reduced distortion because of lower energy input. Special spacers will be eliminated; post-weld match machining will be reduced; and special straightening operations will no longer be necessary. In addition, deep penetration will eliminate the need for multiple passes and filler wire additions. And the vacuum will permit fuel elements to be welded without removing the corrosion film left by previous corrosion tests and will permit elimination of subsequent corrosion testing of fuel assemblies.
Overall savings is huge
Taking all these savings together it appears that there is a potential cost reduction of 45 to 60% in direct labor costs of a typical assembly. Enough of a savings to justify choosing the electron beam welding expertise of Andrew Hi-Tec Corporation for your metal joining production applications.