Laser cutting uses a high-power laser which is directed through optics and computer numerical control (CNC) to direct the beam or material. Typically, the process uses a motion control system to follow a CNC or G-code of the pattern that is to be cut onto the material. The focused laser beam burns, melts, vaporises or is blown away by a jet of gas to leave a high-quality surface finished edge.
The laser beam is created by the stimulation of lasing materials through electrical discharges or lamps inside a closed container. The lasing material is amplified by being reflected internally via a partial mirror until its energy is enough for it to escape as a stream of coherent monochromatic light. This light is focused at the work area by mirrors or fibre optics that direct the beam through a lens which intensifies it.
At its narrowest point, a laser beam is typically under 0.0125 inches (0.32 mm) in diameter, but kerf widths as small as 0.004 inches (0.10mm) are possible depending on material thickness.
Where the laser cutting process needs to start anywhere other than the edge of the material, a piercing process is used, whereby a high power pulsed laser makes a hole in the material, for example taking 5-15 seconds to burn through a 0.5-inch-thick (13 mm) stainless steel sheet.
Types of Laser Cutting
This process can be broken down into three main techniques - CO2 laser (for cutting, boring, and engraving), and neodymium (Nd) and neodymium yttrium-aluminium-garnet (Nd:YAG), which are identical in style, with Nd being used for high energy, low repetition boring and Nd:YAG used for very high-power boring and engraving.
All types of lasers can be used for welding.
CO2 lasers involve the passing of a current through a gas mix (DC-excited) or, more popularly these days, using the newer technique of radio frequency energy (RF-excited). The RF method has external electrodes and thereby avoids problems related to electrode erosion and plating of the electrode material on glassware and optics that can occur with DC, which uses an electrode inside the cavity.
Another factor that can affect laser performance is the type of gas flow. Common variants of CO2 laser include fast axial flow, slow axial flow, transverse flow, and slab. Fast axial flow uses a mixture of carbon dioxide, helium and nitrogen circulated at a high velocity by a turbine or blower. Transverse flow lasers use a simple blower to circulate the gas mix at a lower velocity, while slab or diffusion resonators use a static gas field which requires no pressurisation or glassware.
Different techniques are also used to cool the laser generator and external optics, depending on the system size and configuration. Waste heat can be transferred directly to the air, but a coolant is commonly used. Water is a frequently used coolant, often circulated through a heat transfer or chiller system.
One example of water cooled laser processing is a laser microjet system, which couples a pulsed laser beam with a low-pressure water jet to guide the beam in the same manner as an optical fibre. The water also offers the advantage of removing debris and cooling the material, while other advantages over ‘dry’ laser cutting include high dicing speeds, parallel kerf, and omnidirectional cutting.
Fibre lasers are also gaining popularity in the metal cutting industry. This technology uses a solid gain medium rather than a liquid or gas. The laser is amplified in a glass fibre to produce a far smaller spot size than that achieved with CO2 techniques, making it ideal for cutting reflective metals.
This technology can be used for a variety of applications, including cutting and scribing metals such as aluminium, stainless steel, mild steel and titanium. However, the process can also be used for the industrial cutting of plastic, wood, ceramics, wax, fabrics, and paper.
Laser cutting technologies are used across a range of industries, including aerospace and automotive applications as well as for cutting in hazardous environments, such as with nuclear decommissioning
Cutting metal is one of the most common applications of laser cutting and is used on materials including stainless and mild steel, tungsten, nickel, brass and aluminium. Lasers are ideal for cutting metal as they provide clean cuts with a smooth finish.
Laser cut metal can be widely found for components and structural shapes including car bodies, mobile phone cases, engine frames or panel beams.
This cutting process can be used with wood, with MDF and birch plywood among the most common substances chosen as they can be manufactured in large sheets. The harder the wood, the greater the laser power required, with dense hardwoods needing more power than softer woods like balsa.
Wood is a favoured material as it provides strength without the cost of metals however, on the downside, wood can warp or bend over time, especially if placed under high strain or used in a damp environment. Aside from cutting, lasers are also frequently used to engrave wood, with CAD programs being used to create precise yet complex designs.
Laser cutting offers a number of advantages over other processes, such as reduced contamination and easier workholding. Precision can also see improvements with lasers as the beam does not wear down during the cutting process, while materials are also less prone to warping with laser cutting. Lasers allow for the cutting of materials that may be difficult to cut using other methods.
Laser processes also provide consistently high levels of precision and accuracy with little room for human error, creating less wastage, lower energy use and subsequently lower costs.
Laser cutting can be used to etch complex designs on smaller parts while still leaving metal free of burrs and with a clean cut. There is also less workpiece contamination with laser cutting than with other processes.
While there are plenty of advantages, the process is also synonymous with high power consumption. Furthermore, laser cutting of plastics creates toxic fumes which need to be ventilated – in itself an expensive task.
Effective laser cutting is also dependant on the thickness of the workpiece, the material being cut and the type of laser being used. Without proper care the materials to be cut can be burnt while some metals can discolour unless the correct laser intensity is used. While plasma cutting still allows for the cutting of thicker sheets than laser cutting, advances in laser technology mean that the gap is closing, although the machinery costs can still be prohibitive.
Finally, while being an automated process, test runs and repairs require human involvement which leads to a risk of serious burns should an operator come into contact with the laser.