How do we...cut things up?
Posted on September 25, 2017 by Miriam Jesenik, Images by Robert Hack
Contact-free cutting using the CO2 laser
The laser travels in jerky movements across the sheet metal at speeds of over 100 meters per minute. Whatever shape is being cut out – rounded or with corners – the sparks fly, and the cutter moves on to the next piece. When it has finished, the sheet looks like a piece of dough after lots of differently shaped cookies have been cut out.
Around 180,000 components made from 22 different materials are cut out each year by the CO2 laser in mtu's Plant 2 in Friedrichshafen. The 7 kW laser is able to cut almost any material – at mtu, this is mainly carbon steel, nickelchromium steel and aluminum. “It is also able to cut greater sheet thicknesses than many other lasers. As we have to cut a very wide variety of thicknesses, mtu decided on a CO2 laser,” explains Werner Mogicato, Production Planner for welded sheet metals. The CO2 laser can cut carbon steel up to 25 mm thick, nickelchromium steel up to 30mm and aluminum up to 20mm.
Depending on the material involved, the mtu laser uses one of two types of cutting procedures: reactive laser cutting and meltand-blow laser cutting (a.k.a. fusion cutting). Reactive laser cutting is the process used to cut non-alloyed and low-alloy steel using oxygen. The material to be cut is heated to ignition temperature, and burned through by adding oxygen. In all other cases, the melt-and-blow laser cutting technique is used: the laser beam releases as much energy as it takes to make the metal melt, before nitrogen is blown into the cut at pressures of up to 22 bar, pushing the melted material out in such a way that it is unable to re-adhere.
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How does laser cutting work?
The CO2 laser used at mtu can cut a variety of parts – from simple sheet metal holders and complex component contours to large-scale gas turbine parts. Unlike other cutting processes, laser cutting is contact-free, ensuring that parts suffer no damage. The laser source creates a beam that is then concentrated and focused. This concentrated beam is then diverted by mirrors in such a way that it hits the sheet. The beam has to be concentrated in such a way that the width of the cut is between 0.1 and 0.8mm, depending on material and sheet thickness. One major benefit of the laser cutting system is that it is able to collate parts from different orders. The operator uses a piece of software to arrange for different parts to be cut from a single sheet in such a way that they are grouped together as closely as possible in order to minimize scrap levels.
This is called 'nesting'. To keep raw material wastage to a minimum, there are three standard sizes of sheet: small, medium and large. The correct size is chosen depending on how many parts are to be cut from a sheet. The data is then passed through to the laser cutter using a CNC program.
Cutting time depends on sheet thickness, the material involved and the way in which the parts have been 'nested'. Some jobs take seconds, while others take half an hour. To ensure components cannot tip over or fall through the grid during cutting, the laser beam leaves a small bridge. At the end of the procedure, the operator is then able to press the parts out of the sheet without damaging them.
“One major benefit is that the CO2 laser is highly flexible and able to process high volumes economically,” says Mogicato. “Laser cutting is also very flexible, and able to cut a wide variety of shapes, sizes and contours.”
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