Figure 2. The laser cutting process illustrated diagramatically.
Figure 3. Three-dimensional laser cutting of catalytic converter shell.
Figure 4. Cross section of laser-drilled hole: 1 mm diameter and 12 mm deep. Image: CSIR
gas is employed to shield oxygen and prevent spontaneous burning. The process is common for cutting plastics, textiles and non-melting materials like wood, cardboard or foam. ■ Microjet cutting, which is an option when the use of shielding gas is not favoured. The laser energy is transferred to the substrate in exactly the same way that light is transported along an optic fibre. The laser beam is contained inside a water jet of 20 to 150 micrometer diameter. The water not only carries the laser energy, it also washes away any debris at the cutting surface and cools the surface. Excess water forms a film around the work area, preventing the formation of spatter (molten metal droplets that re-attach to the surface). The final result is a smoothly cut, high-quality surface. Laser drilling Drilling small holes into tough or brittle materials used to be a cumbersome experience that often ruined the part – laser drilling now provides the solution. The process does not depend on the hardness of the material. Paper, polymers, metals,
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Figure 5. Laser-drilled cooling channels in turbine blades.
ceramics and even precious stones have become regular candidates for laser drilling. An added advantage is the fact that no mechanical stresses are introduced into the material. The laser doesn’t blunt and all holes can be finished to the same quality and dimensional accuracy. Along with this, the relative ease of moving light beams around the work area has enabled considerable improvements in production speeds. Laser drilling requires intensely focused laser beams that allow instant melting and gas formation. The high intensities are created by setting up lasers to deliver radiation in short, intermittent pulses of high energy. Four machining strategies are used: ■ Single shot drilling exposes the work area to a single high energy laser pulse of short duration. This approach is suited to drilling small holes in thin materials. A large number of holes can be created in an extremely short time. A popular application is the creation of micropores in paper layers for filter applications. ■ Percussion drilling employs a series of successive low-energy pulses at the same positon to produce
deeper, more precise holes. Smaller diameters are possible with this strategy. The process is well suited for drilling deep holes in small nozzle components. ■ Trepanning drilling starts off with a single percussion drilled hole which is then enlarged by the application of repetitive pulses delivered in circular patterns that gradually move outwards from the centre. Relatively large holes are machined that can typically serve as lubrication holes in mechanical transmission systems. ■ Helical drilling does not remove all material. Percussion drilling in a helical spiral configuration is done to move gradually from the top to the bottom of the material. The unaffected core is then removed to expose the hole. High-quality holes that are relatively large and deep can be created. Cooling channels in aerospace turbine blades is a popular application for this technique. Laser structuring and ablation Laser ablation is similar to mechanical milling where parts are produced by removing material layer by layer from a workpiece. The cutting tool is replaced in this case by a finely