Enhancements to power beam welding processes for land transport

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Enhancements to power beam welding processes for land transport

Shi, Gongqi / Hilton, Paul / Booth, Geoff / Punshon, Chris

The applicability of electron beam and laser beam welding is limited by specific process characteristics. For example electron beam welding is traditionally carried out in vacuum and laser welding requires an accurate part fit-up. Recent work has been directed to overcome these limitations. Work is carried out to perform electron beam welding in non-vacuum and reduced pressure environments. An example is described where non-vacuum electron beam welding (NVEB) was used to produce edge welds of a structural beam in 2.5 mm thick AlMg3 aluminium alloy for the VW/Audi group. The high welding speed (12m/min) was achieved by high power output available from the electron beam generator (19.3kw). Current research at TWI is examining the performance of an NVEB welding system with a maximum power of 150kW. Reduced pressure EBW is equally effective for aluminium and titanium alloys where welds have been produced with a marked absence of porosity and obvious contamination in thicknesses in excess of 16mm. It is expected, that the ability to employ local sealing and the reduction in pump down time to near insignificant levels afforded by Reduced Pressure Operation will lead to the adoption in the automotive industry. In a second part, the need for good fit-up when laser welding is addressed. Gaps must generally be small enough to ensure that the focussed beam (typically 0.3mm diameter or less for CO2 laser welding) does not pass directly through the joint without achieving a weld. The objective was to establish the gap bridging capability of autogenous laser welding and then compare this with results obtained using hybrid CO2 laser/MAG welding. Welding parameters were first obtained to produce fully penetrating welds on close fitting butt joints in 8mm thick structural C-Mn steel complying with BS EN 10025 S275 which is of immediate interest for shipbuilding and off highway vehicle industries. These conditions were then used on specimens with constant joint gaps to establish limits. The increased tolerance to joint gaps in the hybrid-laser process is believed to be largely the result of an interaction of laser and arc processes that prevents the laser beam simply passing through the joint when the gap is larger than the beam diameter. Secondly, the addition of filler from the consumable means that material is available to fill the gap joint, reducing joint underfill. In future the capabilities of the hybrid process are expected to be enhanced by increasing wire feed speed or reducing travel speed and by incorporating an adaptive control approach to sense joint gap and process parameters.