Lasers are, at the most basic level, a heat source. Their advantage lies in their flexibility and, in particular, the ability to change where and when that heat is deposited onto a surface to induce modification.
Variables ranging from the speed at which you scan a laser across a surface and the spot size to whether it is pulsed shape the way this heat is deposited onto the material. To attempt similar process modifications with machine tooling requires new machinery and, for many high value applications, is less likely to achieve the same levels of precision as lasers. Conversely, with lasers, by changing the optics and using feedback measurements, it is possible to optimise a manufacturing process that is ideally suited for purpose.
Historically used in car manufacturing and other macro scale areas, laser manufacturing has developed significantly in recent years, and there are a number of current, developing, and cutting-edge applications to consider.
Laser cleaning uses a beam in an elongated sheet to illuminate the surface. Photon absorption is determined according to the surface material, and can remove particles such as dirt, oil or rust which absorb strongly. A self-selective process, laser cleaning does not damage the surface and requires less pinpoint accuracy, as other materials will not be affected. It is a particularly advantageous technique to use in big-scale engineering in marine environments and with other outdoor machinery.
With surface processing technologies, lasers are used to melt or modify a thin layer of the surface to change its shape or properties. For example, this technology can be used to change the friction coefficient of an engine or induce hydrophobicity.
Laser sculpting uses the surface tension of a laser-melted surface to manipulate the shape of the material by encouraging it to flow, either towards the laser or away from it. One application is to create metal replicas of grating structures made out of glass, to make them easier to transport when made over a large scale, for example, long fragile encoders used in up-scale manufacturing plants.
A further developing application for laser sculpting is polishing. This is particularly attractive for additive manufacturing. Three-dimensional metal parts produced by 3D printing have rough surfaces, and laser polishing can overcome this issue, and can do so selectively if desired. An advantage of additive manufacturing is the ability to make bespoke parts and, as a result, it is often used in medical device/implant manufacture. Consequently, selective laser polishing is expected to have a vital role to play alongside additive manufacturing in medical applications in the future.
3D beam shaping
Current research is developing 3D beams whose shape can be manipulated to meet exact manufacturing requirements. The standard laser beam shape, a Gaussian, limits the capacity to tailor the process of melting or ablation, which decreases efficiency and thus limits what can be made. The beam-shaping techniques under exploration will improve the level of precision with which techniques are carried out, enable new techniques, and reduce the cost of high precision manufacturing.
Laser beam shaping can be applied to almost any process but includes applications in drilling holes for sensors and cameras on smartphone screens, and in increasing the density of information on semiconductor chips, meeting the ever-increasing demand for more memory in devices.
Avoiding a melt zone
Using ultrashort pulse lasers reduces, indeed almost eliminates, incidental thermal damage. This has key applications for processing materials which are otherwise difficult, for example, flammable or brittle. The biggest current application for this technique is cutting chemically toughened glass, such as touchscreens for mobile phones and tablets.
The focused energy of ultrashort pulse lasers also makes it possible to change properties within transparent materials and thus effectively manufacture something within glass. One application of this is writing optical circuits inside the material which is already in mass production for telecoms.
Welding glass to metal
A recent breakthrough in laser research has seen glass and metal successfully welded together. This previously hasn’t worked, owing to the different thermal properties of the materials. Traditional adhesives are not ideal for instruments that need to remain effective and contaminant-free for long periods of time, and therefore the potential applications for this technique are huge, extending to space, defence, optical technology and healthcare. This cutting-edge research is on the cusp of becoming an industrial process.
Laser manufacturing in the UK
The potential for the UK to adopt more laser manufacturing processes is significant. However, more information needs to be shared about the scale of flexibility that lasers can offer and, furthermore, the ease with which they can be deployed in manufacturing. Most laser systems are now turnkey machines with no need for a dedicated laser engineer to operate them.
By pivoting to high value manufacturing and adopting technologies such as those coming from application-led research, the UK has the potential to carve a niche and to position itself at the forefront of advanced manufacturing.
Richard Carter, Assistant Professor at Heriot-Watt University and academic lead for High Precision Manufacturing at the National Robotarium