Laser cutting

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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 high power laser, by computer, at the material to be cut. The material then either melts, burns or vaporizes away leaving an edge with a high quality surface finish.

Advantages of laser cutting over mechanical cutting vary according to the situation, but important factors are: 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[1]. Disadvantages of laser cutting may include the high energy required.

The most popular lasers for cutting materials are CO₂ and Nd:YAG, though semiconductor lasers are gaining prominence due to higher efficiency. Typically there is a choice between a DC (Direct Current) and RF (Radio Frequency) powered resonator (laser generator). The fundamental choice of beam generation method can have significant impact on productivity and life cycle costs.

DC resonators have internal electrodes situated within glassware. The main benefit is that DC resonators are thought to be about 30% more power efficient than RF. As the electrodes are encapsulated, they are also safer and more robust during maintenance. Drawbacks compared to RF are 30% more use of gas and a need to replace glassware between 20,000-25,000 hours, costing about £30,000. The saving on power is greater than the cost of additional gas, but not much.

The alternative, RF resonators, have external electrodes. Electrode wear is less and glassware is uncontaminated by what is considered to be a cleaner process of laser generation. Some argue that this gives a better quality of beam, but profiling performance is not noticeably improved. On the downside, RF resonators are less easy to work on and may need returning to the manufacturer for repair, potentially causing downtime. Servicing costs include replacing end stop valves for approximately £4000 every 2,000 hrs. The life of the RF generator is finite and may require replacement at some point after 30,000 hrs at an approximate cost of £20,000.

Fast Axial Flow Resonators generate a laser beam using power emitted from electrodes in an atmosphere of exited lasing gas. The mixture of Carbon Dioxide, Helium and Nitrogen is forced to circulate the glassware by a turbine. Turbine bearing wear is an issue to be considered. Non contact bearings may outlast the machine whereas contact bearing wear may require turbine exchange at a cost of between £10-15, 000 at uncertain intervals.

There has been a recent surge in interest in Slab Resonators the alternative to Fast Axial Flow featuring RF resonator technology. Slab laser profilers have a static gas field that requires no pressurisation or glassware hence savings on replacement turbines and glassware. Drawbacks of slab laser profilers are reduced performance with stainless steel and aluminium plate; although they will cut, productivity is less.

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.

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 pulsating 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 generally three different types of industrial laser cutting machines. Flying Optics lasers usually feature a stationary X and Y axis table where the cutting laser moves over the work piece in both of the horizontal dimensions. Flying Optics is popular due to the low cost of stationary tables, and their higher cutting speed limits, since the mass of the optics is much smaller than the mass of the table. 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 controling this include - Collumnators, Adpative Optics or Constant Beam Length Axis. A constant beam length axis is provides the most consistent beam quality over the entire table.

Both Hybrid and Pivot-Beam lasers usually involve a table which has the capability of X axis travel. Because of this, the head has to move only in two directions (usually the ones with the shortest runs), thus improving its efficiency, as the path traveled is shorter. Pivot-Beam lasers offer the highest performance per watt and the most reliable cut consistency of the three styles. Hybrid style lasers typically can cut thicker material per watt than other types of laser cutting machines. This is due to the fact that fewer mirrors are required to deliver the laser beam to the cutting head. Each time the laser beam gets reflected by an optic a certain amount of power is lost in the reflective optic.

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.

[edit] See also

Laser engraving (aka laser etching) is a similar process in which the laser does not cut fully through the material
Plasma cutting
Water jet cutter
Laser converting