Laser cutting

Laser cutting is a technology that uses a laser to cut materials, and is usually used in industrial manufacturing. 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,^[1] 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. Some 6-axis lasers can perform cutting operations on parts that have been pre-formed by casting or machining.

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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 may include the high energy required.

Types

Both gaseous CO₂ and solid-state Nd:YAG lasers are used for cutting, in addition to welding, drilling, surface treatment, and marking applications.^[2]

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 now 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.

Process

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.

Machine configurations

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 less lost power 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.^{[citation needed]}   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.

Pulsing

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.

See also

• Laser engraving
• Laser ablation
• Laser-microjet
• Laser converting

Citations

1. ^ Machinery's Handbook 27th Edition, p.1447.
2. ^ Machinery's Handbook 27th Edition, p.1445.

References

Oberg, Erik; Franklin D. Jones, Holbrook L. Horton, Henry H. Ryffel (2004). Machinery’s Handbook. New York, NY: Industrial Press Inc.. Machinerys27. ISBN 978-0831127008. 

External links