Pressure down

As a general rule, SSLs are therefore the preferred option for thin sheet applications, while CO2 lasers are considered to be the superior choice for sheet thicknesses greater than four millimetres. Welding applications in certain fields such as gear manufacturing, in which the weld depth is far in excess of 10 millimetres, are completely out of reach for solid state lasers. Regardless, industry demand for SSLs continues to grow, largely in response to economic considerations, in particular the wish to boost energy efficiency and manufacturing flexibility.

Joining forces
In contrast, electron beam welding enables greater penetration depths and produces high-quality weld seams, but has the disadvantage of requiring a much lower working pressure of approximately 10-4 millibar. In many cases, however, this technique does not actually present a viable alternative. Part sizes are restricted because of the required vacuum chamber, and cycle times are higher due to the use of a vacuum pump and the need to move components in and out of the chamber. Further disadvantages include the X-rays generated by the process and the fact that capital costs typically tend to be higher. This prompts the question of whether it might be possible to merge the advantages of both electron beam welding and solid state laser welding by bringing together aspects of both processes in a combined method. As part of a joint research project with TRUMPF Laser- und Systemtechnik GmbH and pro-beam AG & Co. KgaA - one of the leading German manufacturers of electron beam technology, the Institute of Joining and Welding (ifs) at Technische Universit?t Braunschweig is currently attempting to develop a novel combined technology of this kind, investigate its feasibility, and make it commercially available.

Pressure: a pivotal factor
One of the key advantages is the way in which SSLs can be flexibly integrated into production systems. Multiple processing stations and/or vacuum chambers can have access to a single laser beam source and use it for what is, in many cases, a broad range of different welding applications. One of the most significant results of reduced ambient pressure is that it changes the metal vapor plume that is typically seen in solid state laser welding. Even a slight drop in pressure leads to a visibly narrower plume and a substantial reduction in the amount of weld spatter. A further drop in pressure to 100 millibar shrinks the metal vapor plume still further, reducing it exclusively to the joining zone
and producing only isolated spatter. The plume and spatter formation disappear entirely once a pressure of 10 millibar is reached. The reduced pressure also yields weld seams that, in terms of quality, are on a par with seams produced by electron beam welding.

Striking quality
Using a laser power of six kilowatts to weld 10-millimetre-thick mild steel at a feed rate of two metres a minute, the researchers were able to produce remarkably high quality penetration welds without any irregularities. Under atmospheric pressure, this level of quality could not be achieved even with a CO2 laser.

What's next?
As a result, this process represents an opportunity to achieve significant efficiency growth in efficiency in existing markets and opens up multiple new fields of application. For applications where high-weld seam quality is particularly important, such as powertrain manufacturing in the auto industry, this new process could very well be a viable option.

In fact, researchers have still only scratched the surface of the potential offered by this new process: For example, it is conceivable that the process could have an equally positive effect on the formation of process pores in laser beam welding.

Contact
Christian B?rner
ch.boerner@tu-braunschweiNike Air Max Plus TN