Magazine Articles
The articles below are from the Summer 2011 Issue of the AILU Magazine
Adaptive control in high brightness laser-arc welding
Precise workpiece fit-up and accurate alignment of the laser beam with the resulting joint line, pre-requisites for high quality welds, remain barriers to the wider take-up of laser welding. These requirements put restraints on welding fixtures and edge preparation methods, and impose tolerances that can prove difficult to meet in industrial practice. This can be particularly the case when welding large components or fabrications, where the assembly of a number of subcomponents, or a build up of distortion, results in cumulative errors in joint fit-up, even with the best edge preparation. The ongoing emergence of high brightness, fibre-delivered, lasers, with their highly focusable beams, promising ever faster, lower heat input welds, but makes attention to such requirements even more critical.
Robotic hybrid welding trials were carried out using a Kawasaki FS-060L robot with a D+ controller, an IPG YLS-5000 Yb fibre laser and ESAB synergic MAG arc welding equipment. Suitable shielding gas/wire combinations of Ar/1.2 mm A18 (for steel) or Ar-2%O2/1.2 mm 308LSi (for stainless) were used.
Our conclusions are
• The tolerance of high brightness hybrid laserarc butt welding to joint gap and mismatch in 6-8mm plate, whilst still producing the most stringent class of welds to ISO 13919-1:1997, is ~0.3-0.5mm and ~0.5-0.6mm, respectively, if fixed conditions are used.
• Off-line trials can identify those parameters which, if changed, can increase these tolerances.
• A laser vision sensor can then successfully relay the fit-up details to process controllers, pre-programmed to respond with these changes, to maintain weld quality over a wider range of gaps and mismatches. Using this approach, in this work, these tolerances have been doubled for the production of Class B welds.
Chris Allen, Steve Shi and Paul Hilton TWI Ltd, Gt. Abington, Cambridge, UK
Image: A laser vision sensor mounted ahead of a hybrid welding process..
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Hazard potential and cleanup cost of fume created during the laser welding and soldering of steel
In a typical automated laser welding or soldering process a filter system is integrated into the process chain to capture both the emitted gases and fumes from the process zone. Databases of process emissions can be used in principle to predict emissions for an industrial process. However, many of these were established more than 10 years ago and are often incomplete. In addition, there have been developments in laser technology and new trends in the field of semi-finished products, such as multi-metal material mixes.
In recent studies at Laser Zentrum Hannover, measurements were made of gaseous and particulate emissions during laser processes for sheet metal (mostly steel) of various grades, with or without surface coating, at four different industrial facilities.
Four categories have been defined in order to rank the expense of environmental protection, but the laser joining processes investigated here were all assigned to categories 1 (No filtering measures for the exhaust air are necessary since all emissions comply with the TLVs) and 2 (State-of-the-art particle filters are required if specific aerosol TLVs are exceeded). Yet even with these assignments the cost of meeting environmental standards represented up to 14% of total running costs though figures of around 8 % were more typical, which is comparable to laser cutting of polymers with a typical cost fraction of about 10 % for handling and filtration of the exhaust air. The interactive database "Laser Safety" has been revised. It provides details of laser process emissions and has been available in the internet for several years as an aid to the planning and selection of suitable exhaust systems for laser welding and soldering.
Jürgen Walter, Michael Hustedt, Volker Wesling and Stephan Barcikowski, Laser Zentrum Hannover e.V. (LZH), Hollerithallee 8, D-30419 Hannover, Germany
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