06 Feb 2007
A team of researchers from Russia, Italy and Germany says that a combined light-and-laser welding system based on powerful polychromatic energy sources addresses several shortcomings of conventional laser welding.
The first experimental version of the lamp-laser combination involves two energy sources: an Nd:YAG laser, which performs the spot weld itself, and a special light module with an adjustable spectrum. The system also features standard welding components and software to enable automatic welding with a pre-set program.
The lamp-laser system is being developed by scientists from NPO Lavochkin, Russia and the All-Russia Research Institute of Experimental Physics (VNIIEF) in Sarov, as well as Antonio Lapucci from the Institute of Applied Optics in Florence, Italy, and Ulrich Delthey, who is director of the Welding Institute in Aachen, Germany. Financial support for the project is coming from Russia's International Science and Technology Centre (ISTC).
The crux of this new technique, which is currently being tested at the ISTC, lies in the use of the second light source. Its power and attributes are such that it quickly and effectively heats the weld area and surrounding space to at least 1000 °C. This reduces the number of defects that typically form under the welding of non-heated parts, while also eliminating the need to anneal finished products.
Welders have long known that the quality of a weld is better if the parts are pre-heated, and cases have even been known when large metal parts are welded before they have cooled after smelting.
One problem with conventional welding has been how to pre-heat parts quickly and effectively if they are made from different material. For example, one part could be made from invar (an iron-nickel alloy), which hardly alters its dimensions when heated, while the other could made from a problematic material such as glass. How should such a combination be heated to high temperatures without damage?
To resolve this problem, Valentin Sysoev and his colleagues use of a powerful lamp to pre-heat the materials to the required temperature. The weld laser beam is then directed into the center of the heating beam. With this approach, the drop in temperature between the point of the weld and the area around it is much smoother, which helps in the formation of a high quality weld.
"If we take account of the fact that a combined approach of this kind can function on weaker lasers than those that are traditionally applied, it transpires that the new method is not only more effective, but also more economical as the price of lasers is proportionate to their power," says Sysoev. "So it can be hoped that in the near future the process of laser welding of car chassis and other such items will become better and cheaper."