Developments in Laser Systems, materials and processes. As with all manufacturing processes, opportunities arise through developments in the equipment and materials used. Some lead to a reduction in cost, while others provide a step-change in quality. The functionality of laser systems is constantly being improved. From the user’s point of view, the time and expertise needed for operation and servicing are being reduced, which enables extended warranties to be offered.
Developments in Laser Systems, Materials and Processes
Smaller laser footprints mean that processing can be carried out in smaller premises. Improvements to laser efficiency, for example through the use of diode pumping in solid state lasers, and diffusion cooling in CO2 ‘slab’ lasers, lead to lower operating costs. New designs, such as slab, tube, fibre and disc geometries in solid state lasers, also provide improvements to running efficiency, which offset the high initial cost of a laser system.
Laser manufacturers seek means to reduce manufacturing costs and improve performance. As the popularity of laser-based manufacturing grows, so opportunities to implement techniques of mass production arise. Lasers can then be built on production lines, using techniques found in the automotive industry for large volumes, or methods favoured by the aerospace industry for niche products. The unit cost of lasers will then fall significantly, which will feed expansion of the market.
The use of lasers in the manufacture of other lasers is just one example of this trend. Significant improvements can be made through developments in optical components. Lenses capable of focusing the low quality beam from diode lasers provide opportunities for penetration processing. Novel designs, such as twin focus optics, lead to improvements in cutting. Work is being done in the field of diffractive optics, which enable a low quality beam to be transformed into an appropriate tool for a variety of processing mechanisms. Adaptive optics compensate for irregularities in beam propagation, improving processing performance.
Light is easily transmitted over large distances in air. Workstations can therefore be located remote from the laser. The beam can be switched between workstations quickly, or divided to serve many workstations simultaneously. This aspect of remote processing provides advantages in terms of productivity, flexibility and production engineering.
Individual production cells can then be constructed, in which process monitoring and adaptive control enable manufacturing to continue with little human intervention. Systems are becoming more user friendly, thanks to advances in software and control systems. Components for fabrication are now routinely created as digital files, which can be transferred via the Internet to the processing site – another meaning of the term ‘remote processing’.
Light, compact lasers are ideal tools for autonomous, flexible, robotic systems for material processing, which enable small batches of tailored components to be fabricated quickly. Discerning customers expect customized products. Manufacturers endeavour to reduce the lead time from concept to manufacturing. Current dedicated automatic processes are unable to respond with sufficient agility.
Robot-mounted lasers provide solutions to such problems, and can be expected to be found in an increasing number of manufacturing sites in the future. Industrial micromachining was revolutionized when ultrashort (femtosecond) pulsed lasers became commercially available in highly automated systems.
Infrared diode lasers are used to write information on CDs and DVDs; now shorter wavelength blue–violet diode lasers enable optical discs to store larger amounts of data. Such applications represent two extremes of the laser processing industry: the technology push of ultrashort pulse lasers into systems into micromachining (after a few years); and the industry pull that drove the development of blue–violet gallium nitride diode lasers for high density optical disc storage.
‘Technology push’ and ‘industry pull’ will continue to present opportunities for new applications of existing lasers, and the development of new devices.
Laser-based processes that exploit the mechanism of melting are used widely in surface engineering. Rapid, highly controllable thermal profiles are used to create surfaces with properties tailored to particular applications. Rapid solidification can be induced, resulting in alloys that possess enhanced solid solubility compared with the equilibrium phase diagram. The amorphous structure of the liquid phase can be retained at room temperature, resulting in the production of metallic glasses.
Not only do such microstructures enhance surface properties, but when processed in an appropriate manner they can be used as materials in their own right. Laser beams may thus be used to synthesize new materials as well as to process existing materials. A good example is the in-situ production of functional materials containing gradients in properties. Variations can be produced by constantly changing processing parameters for a given material in a controlled manner, or by introducing new materials during processing.
The opportunities for producing multipurpose components that incorporate materials whose function depends on their location in the component provide means of reducing assembly times, discussed below. Biomaterials in particular require specific properties at discrete locations; the formation of in-situ composite surface structures by laser deposition provides a means of attaching prostheses to bone via an intermediate biocompatible layer. Further processing of this layer, e.g. by drilling microscopic bulbous holes in the surface, may aid in the growth of bone and improve the integrity of the joint.
The relative importance of processes changes, sometimes dramatically: demands for fine microstructuring in the microelectronics sector drives exponential growth in the area of scribing and optical lithography, for example. However, progress continues to be made in all areas of processing; some involve process refinement, while others involve the introduction of novel processes.
Current trends help to identify future opportunities. Although laser cladding continues to be an efficient means of surfacing discrete parts of components, the basic processing geometry has undergone modifications to create an industry in which parts can be manufactured rapidly and flexibly. Other processes have joined the family of rapid manufacturing: laminated object manufacturing, selective laser sintering, stereolithography, to name just three.
All are based on innovative applications of a basic process. In the field of ‘traditional’ laser thermal processing, more such developments can be expected, driven by the availability of even smaller, cheaper lasers. As an example of the development of traditional thermal laser processing, welding is normally thought of as a through-thickness method of joining.
However, the optical nature of the laser beam provides possibilities for novel welding geometries and techniques. The beam may be directed into a highly absorptive opening between plates (a kissing joint) to join thick section materials rapidly at their surface. It can also be used when access to a joint is available from only one side (a stake weld), which provides the designer with a greater range of joint types.
Hybrid welding processes combine the characteristics of their constituent techniques: a laser beam is highly penetrating, but intolerant to variations along the joint line; these can be accommodated by more forgiving arc fusion processes. Hybrid processing enables technical problems to be overcome as well as reducing the requirements placed on the laser, leading to a reduction in capital investment.
This type of reasoning can be applied to most thermal mechanisms of laser processing, presenting opportunities for novel application of an existing technology. Novel applications can also arise as a result of the introduction of a new laser system. Photorefractive surgery and other cosmetic procedures have been revolutionized as user-friendly turnkey excimer laser systems found their way into consulting rooms.
Similarly, femtosecond pulsed lasers in user-friendly workstations caused a revolution in athermal micromachining. The search for sources of even shorter wavelength laser light continues in order to meet increasing industry demands.