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3567 |
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Monday, September 16, 2013, Hall Europa 10:30 AM Opening |
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Portevin lecture:
Automation in electron beam welding is the key to quality and productivity |
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Dietrich von Dobeneck* / pro-beam AG & Co. KGaA, Germany |
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Automation means that a machine does a number of chained production processes by itself without manual interference of an operator. The purpose of automation is to increase productivity, at the same time to reduce scrap rates and / or eliminate boring or tiring labour. As the subject automation is too diversified, I will, besides a few standard solutions for the equipment, concentrate on the intelligence for automation of an electron beam. The peculiar properties and capabilities inherent only in electron beam technology are rapid and nearly inertialess direct controllability by computers. A further physical property which has been disturbing in earlier years, has now become an important carrier of automation: back scattered electrons, resulting when the beam hits material and, here in special, the weld joint. The first step of automation is to make sure that the tool electron beam is constant and always the same in its geometrical and optical parameters. This adjustment requires skilled operators or an automated adjustment routine. The beam calibrates itself. A typical application for automation is to weld many identical parts. It was a tiring procedure to position each part with optics and a reticule. Therefore SPS and CNC control were introduced which however needed precise tools and positioning equipment and from time to time manual input as the systems warm up and expand. During the time there were many improvements on this conventional kind of automation. However the big innovation came from introducing the information on the weld joint by back scattered electrons. The new system needs no precise tools and even drifting of the beam is no problem, as the measuring beam is at the same time the welding beam. A number of examples for this big step in technology for automation in welding will be given. For mass production today one piece flow is preferred. Parts may arrive at the welding station in varying positions or upside down. It is no longer necessary to rotate the part into a uniform location; the beam scans the actual position and welds accordingly with a cycle time of 6 sec. There are numerous applications where a quality control is required before welding in order to prevent welding of misassembled or misaligned parts and thus producing scrap. The back scattered electrons signal to the CNC control whether the parts may be welded with an additional beam deflection or be rejected before welding. Another category of work pieces carry a large number of joints, e.g. turbine vane rings with more than 100 welds on the circumference. Symmetric heat input and shrinkage from each weld has to be taken into account. This requires an online seam tracking together with a weld sequence plan. As the weld joints are 3 dimensional in space, scanning and welding have to follow the profile. With conventional semiautomatic EB welding 2 operators need 8 hours to finish 1 ring of vanes. Automated it takes 4 hours and produces much fewer defects. Finally back scattered electrons can be used for inspection of the weld quality before the part is removed from its weld fixture and tooling. This capability allows eventual repair welding without losing a lot of additional time. |