Connect, no.146, January/February 2007, p.8

A cutting edge solution

For the first time in four decades of laser cutting, a serious contender to the CO ₂ laser may be on the horizon. It's the fibre laser.

In 2005, just over 35 000 production systems using laser beams for materials processing were installed worldwide. Some 24% of these systems were for laser cutting. Most of these systems still use carbon dioxide lasers. But that may be about to change.

Only very recently, an alternative laser source with real potential to replace the CO ₂ laser has become available. Fibre lasers are solid state lasers in which an optical fibre, doped with low levels of a rare earth element such as Ytterbium, is the lasing medium. The pumping mechanism is the laser diode, another solid state device.

So what are the potential advantages for this type of laser for cutting metal?

First, fibre lasers are; completely solid state, very compact kilowatt for kilowatt, and significantly smaller than the equivalent CO ₂ gas laser. Second, they are very efficient in energy usage, being some four times better than current CO ₂ lasers. Third, they have no recognised consumables. The laser diodes have projected lifetimes of about 100,000 hours and require essentially no maintenance. These advantages have particular significance when a laser is incorporated into a machine tooling operation.

TWI has recently conducted two series of laser cutting trials using fibre laser sources. The first was undertaken using the IPG YLR-7000, high power fibre laser, at the TWI Technology Centre in Yorkshire. For the cutting work, a standard industrial laser cutting head (with optics modified for the 1µm wavelengh of the fibre laser beam), was used.

In later trials, conducted in conjunction with Cambridge University, a second fibre laser was used, a YLR-2000, which could produce 2.2kW of output power, but at a significantly better beam quality (ie it could be focused to a very small spot).

The cutting speeds available on thin materials using a high beam quality fibre laser are high, with cuts made in 0.8mm thick steel at speeds of almost 60m per minute. It has also been shown that the other materials most commonly cut using CO ₂ lasers, such as stainless steel and aluminium, can also be cut effectively with the fibre laser. With more attention to the interaction between the assist gas flow from the cutting nozzle and the molten material ejected from the kerf, it may be possible to improve the quality and speed of fibre laser cutting over that presented here. In this context it should be remembered that by 2007, we will have been cutting with CO ₂ lasers for 40 years!

To learn more about this ground-breaking work using fibre lasers to perform cutting tasks contact Paul Hilton at TWI. E-mail: paul.hilton@twi.co.uk