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EB-welding-tipson less known practical details.SOLUTIONS with Effective, Practical Advice
EB-welding-tips are additional bits of information. They may help in specific situations to solve hard questions and overcome hindrances. We already introduced Electron Beam Welding in the We reviewed Here we address a few practical EB-welding-tips and hints that may come handy to those who operate an electron beam welding machine for the first time. Before closing the door and starting pump down, all the chamber space should be dry. Any moving table or fixture bearings should be lubricated by dry lubricant (graphite or molybdenum disulfide). Any small oil drop would interfere with the vacuum process by unduly prolonging the pump down time. Steel parts must be thoroughly demagnetized, lest they interfere with the electron beam by throwing it out of position.
One can study if simple fixtures and mechanical manipulators would allow processing more than one part in any vacuum cycle. If the parts were already in the chamber, one could do so by bringing the parts, one by one in sequence, to the welding position without breaking the vacuum. The pumping down time saved can easily pay for mechanical or automatic manipulators, especially if many simple identical parts can be welded this way in any one cycle. One of the most useful EB-welding-tips refers to parts too long to be accommodated in a given chamber. One can sometimes install suitable extensions to be bolted in place of a regular chamber window. The extensions, in the form of flanged tubes, should be obviously leak proof both to air and to X radiation (dangerous unavoidable by-product). Such a solution can avoid the need to procure a larger chamber for long parts, while improving the usage of existing equipment. Whenever in need of testing the electron beam characteristics and after each filament change (filaments are expendable parts) one should remember this one from the collection of EB-welding-tips. The electron beam can be operated and tested without fear of damaging the chamber or its accessories. One needs only to place a massive copper block under the electron beam gun to absorb and dissipate the heat. The live beam falling on the copper block can be manipulated and focused with different parameters. Typically the joint configurations should be adapted to the electron beam technology, and meet the welding purpose while being easy to perform and to inspect.
Square groove welds are used but also T-joints, lap joints, edge and corner welds. See further down the ASM publication: "Design considerations..." EB-welding-tips suggest that parts to be welded be positioned right in front of the beam at a suitable distance. Generally there is no need of filler metal whatsoever. Sometimes however a shim or foil of suitable material may be used either to help in degassing (titanium) or to avoid cracking. If the weld starts and ends on the edge of the part, one uses starting and runoff weld tabs, additional material extending beyond the joint, to provide smooth transitions. If circular welds are used one has to develop suitable energy ramp up at the start and ramp down at the end after covering the initial, incomplete penetration portion of the weld. A complete circular weld is therefore longer than 360 degrees. One proceeds to perform shallow tack welds at reduced intensity to check the weld path all along its length. After performing geometric corrections if needed one is ready to start the full energy pass. One of the most important EB-welding-tips is to center the joint, otherwise the weld operation is faulty and the part is not acceptable. Therefore it is recommended to use the seam tracking facility, if available. It is an electronic device that scans the area ahead of the welding beam and finds the geometric position of the joint providing automatic correction if necessary. Once the penetration weld is finished it is customary to perform an additional cosmetic pass at lower intensity and penetration to provide a visually improved and smoother surface, if requested. The development of electron beam welding schedules is performed on test pieces to be examined by non destructive tests (themselves to be developed) but also by sectioning, to confirm the exact positioning of the weld, its shape and dimensions. These trials are necessary to develop the needed confidence in one's ability to operate the machine and to obtain acceptable results. It is hoped that the above EB-welding-tips may help new operators in their initial learning stages to gain the proper experience, obtainable only by thorough and thoughtful work, in the operation of any given electron beam welding machine. An Article on Additive Manufacturing was published (7) in Issue 144 of Practical Welding Letter for August 2015. On Electron Beam Welding, interested readers may find useful information in Chapter 13 of:
and also at page 254 of: Design Considerations for Electron Beam Welding ANSI/AWS C7.1/C7.1M:2004
See Table of Contents for the above at ANSI/AWS C7.3:1999
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