TPT November 2010

C utting , S awing & P rofiling

Laser cutting with the right beam source CO 2 or solid-state laser? Many users ask this question when they consider doing cutting work with a laser. “The application decides which beam source is best to use,” explained Dr Arnd Szelagowski of Trumpf Laser und Systemtechnik, Ditzingen/ Germany who recently spoke at the congress of the German Welding Society (DVS) in Nuremberg/Germany. In his presentation – Laser beam cutting today and tomorrow – current developments and trends in laser cutting technology, Dr Szelagowski said, depending on material and sheet thickness, the CO 2 laser is a better choice for one application, while the solid-state laser is a better choice for another. If users want a flexible way to cut across all sheet thicknesses and obtain good cutting quality, the CO 2 laser is the beam source of choice – despite its lower efficiency compared to the solid-state laser. If the users focus is on thin sheet cutting, the solid-state laser has real advantages. Dr Szelagowski explained the reason for this by describing the absorption ranges of both laser beam technologies for iron. With a wavelength of 1µm, the solid- state laser produces a very broad, almost constant absorption level across an angle of incidence varying from 0 to 60 degrees. In the range of about 78 degrees, a distinct level with a subsequently steep drop is

noticeable. With a wavelength of 10µm, on the other hand, the CO 2 laser shows a significant increase in the absorption level with an increasingly steeper angle of incidence (greater than 80 degrees), and thereby an improved coupling of the laser output into the material. These effects directly impact the laser beam fusion cutting – but not the flame cutting. “In this case, the laser plays only a subordinate role. That is why the cutting quality and speed in flame cutting for mild steel do not vary between CO 2 and solid-state lasers,” he added. The situation is different for thin sheet metal, which is processed at a generally higher feed rate and develops a flat cutting front. This favours the solid-state laser and therefore leads to improved coupling conditions. “But with increasing sheet thickness, the maximum achievable cutting speed drops, resulting in a steeper cutting front,” explained Dr Szelagowski. Conversely, this cutting front feature, in conjunction with the high melting temperature, produces a constant high absorption rate in the CO 2 laser beam in thick sheet metal. The molten material is homogenously low-viscosity across the sheet to the bottom edge and – despite its high volume – it can be driven out of the groove, improving the cutting quality. This explains the different areas of application for these two laser technologies. “Solid-state lasers show considerable advantages for stainless steel sheet thicknesses up to 4mm. Compared to the CO 2 laser, they cut faster and are therefore more efficient and productive with the same high cutting quality,” concluded Mr Szelagowski. With the CO 2 laser, in contrast, a broad

material and sheet thickness range can be processed with high quality cutting results. In order to obtain optimum benefit from the high productivity of the solid-state laser, the machine dynamics have to be in line with the laser’s performance capacity. “On top of that, users should be aware that a 700 hp engine does not turn a compact car into a Formula 1 race car,” said Dr Szelagowski. The new TruLaser Cell 7040 fibre provides a system for 3D sheet processing with a TruDisk disk laser. The TruLaser Cell 7040 fibre with a working range of 4 x 1.5m is the largest model in the TruLaser Cell Series 7000. Trumpf GmbH + Co KG – Germany Fax: +49 7156 303 936115 Email: holger.kapp@de.trumpf.com Website: www.trumpf.com

If users want a flexible way to cut across all sheet thicknesses with very good cutting quality, the CO 2

laser is the

beam source of choice, says Dr Szelagowski

97

www.read-tpt.com

N ovember 2010

›