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Laser Resources outline the need for extra power for high-power laser yield

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article image Extra power for beam product with laser gas

Laser Resources  relate views on the necessity of increased power in production through laser technology.

In the past decade, the market for laser technology for industrial material processing has reached double-digit growth rates.

With improved beam sources and expansion of scope and optimisation of system concepts, lasers have become efficient, reliable manufacturing tools in a variety of sectors.

The automotive industry and general mechanical engineering have been driving forces for further development of laser technology and subsequent improvements.

In these industrial sectors, beam sources with higher output powers and improved beam qualities have expanded the range of laser applications.

From the beginning, CO2 lasers have been among the workhorses of the laser industry, with their high power, beam quality, easy handling, and ability to integrate into existing plant setups. An estimated 60% of all CO2 lasers are used for cutting applications. Earlier most flatbed processing systems were equipped with 1- to 2-kilowatt lasers. Today, most systems’ lasers have power higher than 2 kW.

Demand for more power

Higher power does not always accelerate the speed, however, because many laser operators are unable to use the full power their processing systems can deliver.

If the material is from 1 to 6 millimeters thick, for example, it is not always possible to apply the full laser power to the workpiece—whether it is mild steel, stainless steel or aluminium.

Increasing the power during thermal cutting beyond this value may expand the size of the material’s heat affected zones and place higher demands on the motion system, thus limiting cutting speeds.

Therefore, when laser cutting metal sheets up to 4 mm thick, operators reduce the power to far less than 2 kW. Even on sheet metal thickness range of 4 to 6 mm, they operate 5-kW laser at noticeably reduced power—usually not exceeding 2 kW.

When cutting thicker sheet metal, they find that increasing output power does not increase cutting speed substantially.

Diffusion-cooled CO2 slab lasers

With a new process called diffusion-cooled CO2 slab lasers, improved beam quality and smaller focus diameters may be realised under comparable conditions. The optical resonator is formed by the front and rear mirrors and two parallel RF-electrodes.

Excitation of the laser gas takes place in the RF field between the water-cooled electrodes. The heat generated in the gas is dissipated by the water-cooled electrodes (diffusion-cooled).

The conventional gas circulation systems involving roots blowers or turbines are not required. A beam shaping telescope is integrated into the laser head and produces a high quality round symmetrical beam. The resonator design produces a 45° linearly polarised beam.

These characteristics allow narrower cuts, which in turn enhance cutting speeds because there is less material to be cut. As a result, diffusion-cooled CO2 slab lasers are especially suitable for thin sheet metal processing.

Cutting speeds on mild steel attained with a 2.5-kW CO2 slab laser are comparable to the results obtained with a conventional fast-axial-flow CO2 laser with 4-kW output power. It is only when sheet metal is thicker than 10 mm that the differences in speed become significant.

In laser fusion cutting of aluminium, the effect of the higher beam quality becomes more evident. In the thickness range below 2mm, slab laser speeds exceed comparative values obtained with flow lasers. Up to a thickness of 4 mm, both beam sources achieve similar results. When cutting thicker metal sheets, however, the higher wattage flow laser beam source has an apparent advantage.

Similar effects are observed when cutting stainless steel. In this case, however, higher-power lasers show benefits at sheet metal thicknesses of more than 2mm.

At sheet metal thickness range around 1mm, the lasers with maximum beam quality attain higher speeds compared to conventional beam sources, provided that the system periphery is adjusted accordingly.

Savings in operation

Another important factor to be considered in conjunction with the operating expenses is the laser design. For instance, diffusion-cooled CO2 slab lasers have a simple layout involving only two metallic mirrors. The diffusion cooling principle eliminates the need for turbines and blowers for gas circulation, giving rise to an almost wear-resistant laser.

Owing to the negligible gas consumption of diffusion-cooled CO2 slab lasers, the premix gas bottle integrated into the laser head allows more than a year of continuous operation. After this period, the bottle is exchanged for a new one. Thus, no external laser gas supply is needed.

Power where power is needed

Since increasing power increases cost, doing so makes sense only if there is an economic advantage. Sheet metal up to 4-6mm thick, which account for most sheet metal processing applications today, may be processed using lasers with beam sources of 2.5-kW output power at high speeds, provided the beam quality is at its optimum.

On the other hand, high-powered beam sources can cut thicker workpieces at higher speeds. But the advantages of higher speed must be critically weighed in view of the higher investment costs and increased operating expenses associated with these lasers. In specific cases, high-power lasers yield an economic advantage. Those applications that require them could hardly be done without the extra power.

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