Laser cutting: Difference between revisions
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'''Laser cutting''' is a technology that uses a [[
'''Laser cutting''' is a technology that uses a [] to materials, and is typically used for industrial manufacturing applications. Laser cutting works by directing the output of a high power laser, by computer, at the material to be cut. The material then either melts, burns, vaporizes away, or is blown away by a jet of gas,<ref>Oberg, p. 1447.</ref> leaving an edge with a high quality surface finish. Industrial laser cutters are used to cut flat-sheet material as well as structural and piping materials.
==Comparison to mechanical cutting==
==Comparison to mechanical cutting==
Revision as of 15:57, 30 October 2008
Laser cutting is a gay technology that uses a penis to stick materials in the rear, and is typically used for industrial manufacturing applications. Laser cutting works by directing the output of a high power laser, by computer, at the material to be cut. The material then either melts, burns, vaporizes away, or is blown away by a jet of gas, leaving an edge with a high quality surface finish. Industrial laser cutters are used to cut flat-sheet material as well as structural and piping materials.
Comparison to mechanical cutting
Advantages of laser cutting over mechanical cutting vary according to the situation, but two important factors are the lack of physical contact (since there is no cutting edge which can become contaminated by the material or contaminate the material), and to some extent precision (since there is no wear on the laser). There is also a reduced chance of warping the material that is being cut, as laser systems have a small heat-affected zone. Some materials are also very difficult or impossible to cut by more traditional means. One of the disadvantages of laser cutting includes the high energy required.
Common variants of CO2 lasers include fast axial flow, slow axial flow, transverse flow, and slab.
CO2 lasers are commonly "pumped" by passing a current through the gas mix (DC Excited) or using radio frequency energy (RF excited). The RF method is newer and has become more popular. Since DC designs require electrodes inside the cavity, they can encounter electrode erosion and plating of electrode material on glassware and optics. Since RF resonators have external electrodes they are not prone to those problems.
In addition to the power source, the type of gas flow can affect performance as well. In a fast axial flow resonator, the mixture of carbon dioxide, helium and nitrogen is circulated at high velocity by a turbine or blower. Transverse flow lasers circulate the gas mix at a lower velocity, requiring a simpler blower. Slab or diffusion cooled resonators have a static gas field that requires no pressurization or glassware, leading to savings on replacement turbines and glassware.
Laser cutters usually work much like a milling machine would for working a sheet in that the laser (equivalent to the mill) enters through the side of the sheet and cuts it through the axis of the beam. In order to be able to start cutting from somewhere else than the edge, a pierce is done before every cut. Piercing usually involves a high power pulsed laser beam which slowly (taking around 5-15 seconds for half-inch thick stainless steel, for example) makes a hole in the material.
There are many different methods in cutting using lasers, with different types used to cut different material. Some of the methods are vaporization, melt and blow, melt blow and burn, thermal stress cracking, scribing, cold cutting and burning stabilized laser cutting.
In vaporization cutting the focused beam heats the surface of the material to boiling point and generates a keyhole. the keyhole leads to a sudden increase in absorptivity quickly deepening the hole. As the hole deepens and the material boils, vapor generated erodes the molten walls blowing ejecta out and further enlarging the hole. Non melting material such as wood, carbon and thermoset plastics are usually cut by this method.
Melt and blow
Melt and blow or fusion cutting uses high pressure gas to blow molten material from the cutting area, greatly decreasing the power requirement. First the material is heated to melting point then a gas jet blows the molten material out of the kerf avoiding the need to raise the temperature of the material any further. Materials cut with this process are usually metals.
Thermal stress cracking
Brittle materials are particularly sensitive to thermal fracture, a feature exploited in thermal stress cracking. A beam is focused on the surface causing localized heating and thermal expansion. This results in a crack that can then be guided by moving the beam. The crack can be moved in order of m/s. It is usually used in cutting of glass.
Burning stabilized laser gas cutting
Burning stabilized laser cutting is essentially oxygen cutting but with a laser beam as the ignition source. This process can be used to cut very thick steel plates with relatively little laser power.
There are generally three different configurations of industrial laser cutting machines: Moving material, Hybrid, and Flying Optics systems. These refer to way that the laser beam is moved over the material to be cut or processed. For all of these, the axes of motion are typically designated X and Y. axis. If the cutting head may be controlled, it is designated as the Z-axis.
Moving material lasers have a stationary cutting head and move the material under it. This method provides a constant distance from the laser generator to the workpiece and a single point from which to remove cutting effluent. It requires fewer optics, but requires moving the workpiece.
Hybrid lasers provide a table which moves in one axis (usually the X-axis) and move the head along the shorter (Y) axis. This results in a more constant beam delivery path length than a flying optic machine and may permit a simpler beam delivery system. This can result in reduced power loss in the delivery system and more capacity per watt than flying optics machines.
Flying optics lasers feature a stationary table and a cutting head (with laser beam) that moves over the work piece in both of the horizontal dimensions. Flying-optics cutters keep the workpiece stationary during processing, and often don't require material clamping. The moving mass is constant, so dynamics aren't affected by varying size and thickness of workpiece. Flying optics machines are the fastest class of machines, with higher accelerations and peak velocities than hybrid or moving material systems.
Flying optic machines must use some method to take into account the changing beam length from near field (close to resonator) cutting to far field (far away from resonator) cutting. Common methods for controlling this include collimation, adaptive optics or the use of a constant beam length axis.
The above is written about X-Y systems for cutting flat materials. The same discussion applies to five and six-axis machines, which permit cutting formed workpieces. In addition, there are various methods of orienting the laser beam to a shaped workpiece, maintaining a proper focus distance and nozzle standoff, etc.
Pulsed lasers which provide a high power burst of energy for a short period are very effective in some laser cutting processes, particularly for piercing, or when very small holes or very low cutting speeds are required, since if a constant laser beam were used, the heat could reach the point of melting the whole piece being cut.
Most industrial lasers have the ability to pulse or cut CW (Continuous Wave) under NC program control.
- Oberg, p. 1447.
- Oberg, p. 1445.
- Oberg, Erik (2004). Machinery’s Handbook (27th edition ed.). New York, NY: Industrial Press Inc. ISBN 978-0831127008. Unknown parameter
- Steen, Wlliam M. (1998). Laser Material Processing (2nd edition ed.). Great Britain: Springer-Verlag. ISBN 3-540-76174-8.
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