Keeping a cool head
Sometimes lasers get very hot under the collar, especially when processing thick steel. CoolLine is deal for chilling with a water fog.
Although they look very robust, they can get quite touchy when a laser sets to work. Parts made of thick mild steel are full of surprises that can upset the cutting process. Uneven chemical composition and surface quality are the main culprits. In the past, mild steel that was not of a laser-cutting grade could not be processed at all or only with great difficulty.
And the results, even materials amenable to laser cutting, were not always convincing. The thicker the sheet metal component, the lower the cutting speed — and the more laser energy required to cut the metal. This becomes especially noticeable when thickness exceeds fifteen millimeters. The material around the cutting point gets hotter and hotter, causing a significant temperature difference compared to the rest of the metal, with an unpleasant out-come: the so-called self-burning effect.
The kerf in the hot sheet metal becomes irregular; the material in the kerf no longer flows away in a controlled fashion and starts to burn. This leads to an unsightly build-up of excess slag on the back of the workpiece.
A sure cut in spite of difficult conditions
To ensure that everything stays cool in the kerf, TRUMPF has developed a solution for localized workpiece cooling. The centerpiece of the CoolLine option is a separate cutting head with special nozzles that spray a fine fog of water. The cold fog is sprayed onto the material through holes in the nozzle, coaxial to the laser beam. It then settles on the workpiece and evaporates.
That’s a simple measure with great effect. Thirty milliliters of water evaporating each minute represent about one kilowatt of cooling power. That cools the metal by approximately twenty percent with a five kilowatt laser. Temperatures in the processing zone are thus reduced significantly. The laser beam hits material of a uniform temperature and can even process mild steel that is not laser-cutting grade at complete stability.
An efficiency bonus for high-grade material
The fine water fog is also beneficial when processing laser-grade sheet metal. With more precise cutting quality, thick components can be nested closer together, reducing waste. The same factor provides more latitude with complex contours. In pre-tempered material, the laser cuts thinner strips and diameters, quickly and reliably. It is possible to cut diameters less than half of the sheet metal gauge without sacrificing feed rate.
And there are very few changes for the operator, who programs and controls the work with TruTops Laser. All the necessary tubing for the water supply is integrated into the CoolLine cutting head. The job can get started immediately after the standard cutting head has been replaced by the CoolLine head — no matter what surprises the sheet metal might have in store.
Contact us: MastersofSheetMetal@trumpf.com
This article was first published in autumn 2011.