Much progress has been made in laser application technology since the invention of the laser in the 1960s. Over the next decade industrial laser applications harnessed relatively low power, compared to today’s standards, where carbon dioxide (CO2) lasers of around 1 kW were used for cutting wooden die boards with air and for cutting steel with oxygen. Nitrogen cutting was possible, achieving an unoxidised edge, but laser power was simply too low to make this a commercially attractive option.
The advent of high powered CO2 lasers and the development of reliable laser cutting machines created an entirely new market segment of laser cutting job shops, delivering custom-cut components from one-offs to thousands of parts, at very short delivery times.
The recovery period after the global economic downturn in 2008 witnessed a step-change in laser technology for laser cutting and welding: the fibre- and fibre-delivered laser. It had become clear that the laser and fibre technology originally developed for telecom applications was able to handle the extremely high power needed for cutting and welding operations. The advance of these lasers for metal fabrication was driven by the development of cost-effective, reliable high power diode lasers necessary to "pump" fibre lasers.
Today most new laser welding machines are powered by a fibre-delivered lasers, which have a much shorter wavelength than CO2 lasers and, in addition to the big advantage that this wavelength can be transmitted by optical fibre, there is also a significant difference, based on wavelength, in how these two types of laser interact with metal, for cutting and welding.
Afrox has recognised the importance of fibre-delivered lasers for cutting and has introduced a number of improved or alternative supply options in addition to nitrogen cylinders and bulk tanks to accommodate the needs of every customer. For example, a global investment programme by Linde over the last three years has seen the introduction of 300 bar nitrogen cylinder bundles which will be available in South Africa in due course. Compared to a 200 bar bundle, this cylinder holds 50% more nitrogen, but for the laser operator, the benefit is even better. Conventionally, when the bundle has reached a pressure of 40 bar it must be replaced by a full one, leaving 20% of the nitrogen unused. In a 300 bar bundle containing approximately 190 m3 of useable nitrogen gas, the remaining unused nitrogen is only 13%.
The availability of high power lasers was also an enabler for another important laser application — welding. As the beam quality requirement for welding is not as stringent as for cutting, even higher power lasers, up to 15 kW, were produced. For the first time in decades, a completely new technology was able to produce the weld geometries impossible with arc- and plasma techniques, such as deep-penetration butt-welds in automotive gears, which require a narrow, low heat input welding process. To avoid oxidation and plasma plume formation, most welding applications required pure helium as a welding process gas. Since helium is difficult to liquefy, it is always supplied as a compressed gas in cylinders or tube tanks.
While the use of pure helium is often essential to suppress a plasma plume during welding with very high power CO2 lasers, Linde technologists have long recognised that welding process efficiency could be improved by the substitution of a mix of helium with lower cost inert gases such as argon, together with the addition of active ingredients such CO2 or oxygen and an optimisation of the welding process gas nozzle geometry.
Since fibre delivered lasers do not generate the plasma plume associated with CO2 lasers and therefore don’t always require helium, there is a greater scope to vary the gas composition to optimise weld productivity.
Hennie van Rhyn