Back in 1985 Mr Ferdinand Piech, the then chairman of Audi, tore up the automotive manufacturer’s rulebook when he set out to develop and market the first completely hot-galvanised car body.
Achieving this goal involved creating a floor panel whose dimensions lay outside the maximum rolling width for steel.
Thyssen FÃ¼getechnik developed a technology to create the necessary size sheet by laying two panels together and welding the edges with a laser. Tailored blank welding was born.
Sixteen years later Corus AutoLaser Technologies is celebrating the first anniversary of production at it’s Nd:YAG (Neodymium-Yttrium Aluminium Garnet) two-dimensional welding facility. The facility, based in the West Midlands, has already won contracts from Jaguar and BMW and production rates of 600,000 advanced tailored blanks have already been achieved.
Tailored blanks are constructed from two or more blank pieces typically different properties of steel gages, different metallurgical grades or different coatings.
These are welded along linear paths, often using carbon dioxide laser welding systems. One of the advantages of using laser-welded blanks has been the reduction in component weight, helping to reduce vehicle fuel consumption and emissions. The benefits of the Nd:YAG laser over conventional carbon dioxide systems is said to come from several sources.
The Nd:YAG laser uses a man-made crystal as its active medium and produces light with a 1.06µ wavelength compared to the 10.6µ wavelength in Co2 welding. Fibre optic cables deliver the 4kW laser beam down to the weld site, which simplifies the problem of controlling beam direction when it has to follow a complex path.
‘As you start to get more complicated shapes your ability to take two different blanks and pull them together with a small gap gets more difficult, which makes Nd:YAG more sympathetic to that type of crowding,’ says Trevor Day, general manager at the facility.
‘What Nd:YAG does is address a fundamental question in welding: getting the blanks in nice and tightly together,’ he adds. ‘Once they’re tightly together, as long as the beam picks up the seam it (YAG) will weld.’
The cross-section of the Nd:YAG beam signature also differs from a carbon dioxide laser. While a carbon dioxide beam has an energy distribution with a pronounced peak at the centre of the beam that requires pinpoint accuracy, the Nd:YAG beam has a broader ‘top hat’ profile, which distributes the power of the beam more uniformly across a larger area of the weld.
‘The YAG, with its wider beam, allows for slightly wider gaps that can be welded successfully that on CO2 would either be rejected-out to be recrowded again or it would produce a poorer weld,’ says Trevor Day.
The system is controlled by a ‘real time’ seam tracking process. Trevor Day explains: ‘We use ‘fuzzy logic control’, which essentially monitors the gaps between the blanks. What that does is either speed up or slow down the welding process or it adjusts the beam height of the laser to account for bigger or smaller gaps.’
Key personnel are then alerted to any welding anomalies by email in the event of a problem.