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JUL/AUG 2013  

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Carbon dioxide snow-jet cleaning for laser machining, precision cutting

Editor's Note: Advanced Clean Production GmbH, Wiernsheim, Germany, provided the following information.

To remove micron-range residues from highly filigree shapes, a leading manufacturer of laser processing machines has integrated the CO2 snow-jet technology into its systems.

Sauer GmbH | Lasertec, a Deckel Maho Gildemeister company based in Kempten, Germany, develops and manufactures machines for laser machining, laser precision cutting and laser drilling. Sauer also supplies 3-D laser machining systems, which is capable of producing the tiny, highly-filigree cavities and shapes that are in growing demand by the computer, medical, automotive and aerospace industries.

The use of 3-D laser machining makes it possible to produce extremely small, filigree forms and cavities. If certain materials are used, CO2 snow-jet cleaning even enables sheer walls up to 90° with a depth of 2mm to be manufactured.

Components might include injection molds, electronic and semiconductor molds, mold inserts, indexable inserts, extrusion dies and prototypes. As well as featuring shorter processing times and reduced staff time involvement, the technique also possesses a significant number of economical advantages over conventional methods. The main customers of the high-tech company include companies concerned with mold construction, tool manufacture and rapid tooling.

In the case of highly filigree shapes, tiny particles of residue may settle on the surface and impair the effect of the laser beam (right), resulting in defective goods. The CO2 snow-jet cleaning is able to remove these residues (left).

“Unlike milling or die sinking, the idea of using 3-D laser machining to manufacture molds isn’t very widespread,” said Michael Kuhl, manager of laser technology development at Sauer. “As a result, our customers want to see how the technology works and what a finished part looks like. In order to be able to demonstrate the process, we operate a range of machines at our test center.”

Residues in the micron-range can lead to defective goods

The laser beam can be used to process a wide range of materials such as steel, aluminium, brass, carbide, ceramic, graphite and boron carbide. Extremely fine residues such as cinder and scale are generated during the machining process thta are then removed by suction. In the case of highly filigree shapes, especially those with sheer walls, tiny particles of residue may settle on the surface and impair the effect of the laser beam, resulting in defective goods.

“Therefore, it is essential that they are removed completely,” explained Kuhl, who about 6 years ago began searching for a suitable solution for his machines and stumbled across the CO2 snow-jet technology from acp—advanced clean production GmbH, Esslingen, Germany. Because the carbon dioxide cleaning technique is a dry process and also because the system made by acp requires a minimum of space and is easy to integrate, it was ideal for incorporating into laser-processing machines.

“Back then, I also talked to other manufacturers of CO2 snow-jet cleaning systems, but the one made by acp is by far the best,” Kuhl said. “The fact that the company is locally based also played a role in our decision because it is essential for people to cooperate closely on such a project—things are working out fine with acp.”

Cleaning tests confirm suitability

Cleaning tests carried out on various components in acp's technical center formed the basis of the decision. The tests confirmed that residues could be removed effectively. With this technique, liquid CO2—which is fed from cylinders at Sauer—is utilized as a jet medium. Through a combination of mechanical, chemical and thermal actions, the non-toxic, non-combustible CO2 snow removes solid and filmy contamination using a dry, residue-free process. On impact, the snow crystals liquefy and then sublimate. The sublimation impulse detaches and removes the tiny particles of contamination adhering to a workpiece. In the liquid phase, the environmentally safe CO2 functions like a solvent and removes filmy coatings or contamination. The low degree of hardness of the tiny snow crystals ensures that the surfaces of the filigree workpieces do not become damaged.

For the cleaning intervals, the guidance machine of the 3-D laser system positions the component in front of the cleaning head in accordance with a program specific for each part.

The main reason behind the effectiveness of the snow crystals is the patented acp cleaning head that is equipped with a supersonic, two-component ring nozzle. Liquid CO2 expands when exiting the nozzle to create a mixture of snow and gas that forms the core jet. Compressed air also is fed to the nozzle as a jacketed jet, and this accelerates the CO2 snow crystals to supersonic speed. The acceleration with compressed air results in a significantly higher degree of cleaning efficiency than that attained with single-component nozzle systems—it also considerably reduces CO2 consumption.

“To achieve good cleaning results, it is imperative that the quantities of CO2 and compressed air are optimally matched,” said Kuhl.

Interval cleaning using a system integrated into the laser machine

The laser-machining process takes up to several hours to complete. In order to be able to carry out the necessary cleaning steps during the process, Sauer integrated the CO2 cleaning system into its laser machines. Workpieces are processed on a guidance machine equipped with an X- and Y-axis as well as a turntable. For the cleaning intervals, which take about 10 minutes each time, the guidance machine positions the component in front of the cleaning head in accordance with a program specific for each part. As a result of integrating the CO2 snow-jet cleaning system, our customers are now able to manufacture extremely filigree parts with maximum precision, even with sheer walls up to 90° with a depth of up to 2mm—provided certain materials are used.