Friction stir welding for vacuum chambers

Traditionally, aluminum vacuum chambers were either machined out of solid or welded together using MIG or TIG welding. With traditional welded joints, great care in preparation and skilled welding techniques are required to create a leak proof, crack free join. Even using robotic welding or employing highly experienced tradesmen, perfect welds can be hard to achieve. With a chamber unable to be properly vacuum tested until finished, a lot of work is involved before the join can be leak checked. If a leak is subsequently discovered in a finished product, extensive rework is often required.

Friction stir welding is the ideal solution to many of the problems associated with arc welding. Using a blunt, rotating tool forced along the join line, the materials either side of the seam are plastically deformed together before they solidify behind the tool. Advantages over conventional welding include, guaranteed full weld penetration, no shielding gas requirement and low distortion due to the solid-state nature of the process. However, the greatest advantage of friction stir welding is that the weld has very low porosity and can be machined afterwards without the risk of incurring a vacuum leak. When machined and polished, the weld zone is almost indistinguishable from the material on either side. Buckley Systems has been a pioneer in friction stir welding and we have developed tooling, fixtures and techniques to optimize the process. Our engineering team are experienced in designing seams that selflocate, offer maximum stability and provide zones for tool insertion and extraction.

Friction stir welds are so homogenous with the parent material that they can be machined without the danger of causing leaks and can even cross O-ring surfaces without affecting the seal. The technique has opened up new ways of fabricating chambers that would be impossible to create any other way.

The D-Pace Mini-PET beam tube is fabricated from two machined halves that are friction stir welded together before the end flanges are friction stir welded on to each end. The result is an extremely accurate tube with no visible welding.

Another example is large, 2000 mm x 815 mm x 800 mm analyzer beam manifolds that are fabricated from 60 mm thick 6061-T6 aluminum plate. Fabricating each box takes over 3.2 meters of welding and the welds cross over O-ring grooves 8 times. Over 220 of these boxes have been produced so far with zero inservice failures reported.

This piece was reprinted by D-Pace, Inc. from the Buckley Systems Fall 2017 technical bulletin with permission from Buckley Systems Ltd. It may not be reproduced in any form without permission or license from the source.

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