Driving industry from the university laboratory
In advance of his plenary presentation at ILAS 2019, Professor Duncan Hand discusses the results of CIM-Laser, a collaboration between five UK universities that has supported the country’s uptake of laser-based manufacturing over the past five years
The EPSRC Centre for Innovative Manufacturing in Laser-based Production Processes (CIM-Laser) is a five-university centre that has played a key role in supporting an increased uptake of laser-based manufacturing in the UK over the past five years. The academic partners (Heriot-Watt, Cranfield, Liverpool, Manchester and Cambridge Universities) have worked with more than 30 companies in a wide-ranging programme of coordinated industrially-focused research and network-building activities. Together with the Association of Industrial Laser Users (AILU), we have developed a national strategy for increased use of industrial lasers in the UK: Lasers for Productivity: a UK Strategy, which was launched at the Houses of Parliament in March last year.
In the past five years we have delivered a significant volume of industry-focused manufacturing research, much of which is either being transferred to industry, or being further developed in follow-on EPSRC-, EU- and Innovate UK-funded projects. We have also contributed to the development of many highly skilled people, with more than 60 researchers directly involved in CIM-Laser: 19 academic staff, 26 research associates, 12 PhD and five EngD students. In addition, we have funded four innovation projects at universities outside of CIM-Laser.
CIM-Laser has supported a total of 40 separate projects, co-funded with our industrial partners. Our strategy throughout has been to combine laser material interaction fundamentals with advanced materials science, to underpin the development and optimisation of laser-based manufacturing processes. We developed, initiated and delivered projects across a wide range of laser interaction timescales – from picosecond pulses to continuous lasers – to characterise basic laser-material interactions at a fundamental level, while solving specific manufacturing challenges. For example, we undertook fundamental research to understand the underlying physics and hence significantly improve the yield of a novel picosecond laser welding process for direct bonding of highly dissimilar materials, such as glass and metal. A selection of key research outcomes have been highlighted in this article.
Ultrashort pulsed laser welding of glass to metal
We have developed a robust process to weld optical materials directly to mechanical support materials, such as metals (see Figure 1). This is dependent on creating the right mix of rapid absorption of the high peak power laser light leading to plasma generation, and thermal accumulation, to create a suitable melt volume. Following the CIM-Laser research, Heriot-Watt, Oxford Lasers and other partners developed an Innovate UK project, UltraWELD, for industrial translation of this process. It involves the development of a prototype ultra-short pulse laser welding machine by Oxford Lasers. End-users Leonardo and Gooch & Housego, are also involved.
Figure 1: Ultrashort pulse laser welding of glass to metal (a) welding arrangement and (b) example weld (Al6082 to fused silica glass, viewed through the fused silica)
Tamper-proof holographic markings for high-value metal goods
By carefully controlling the pulse energy from a nanosecond-pulsed UV laser, it is possible to create optically-smooth craters, a few microns wide and a fraction of a micron deep, with a high degree of dimensional control. These craters have been used as the basis of holographic structures, by creating a suitably patterned array of craters on a smooth metal surface (see Figure 2). When illuminated with a visible laser beam, light reflected from these craters interferes with that reflected from the unprocessed metal surface, creating a diffractive image that can be viewed on some kind of screen, e.g. a piece of paper or card, placed a short distance away. This work is now being translated to industry via further support from an EPSRC Impact Acceleration Account. A patent was filed in 2017 on techniques to hide additional information in the holograms, and we are now working with Sisma, in Italy, to incorporate the process into their laser marking machines for applications in the jewellery industry.
Figure 2: Holographic marking on watch back cover. Inserts: Laser-written craters viewed under optical microscope (left) and diffractive image obtained by laser illumination (right)
Holographic diagnostics of laser-based processes
Laser manufacturing processes have, in general, been developed empirically, that is, based on observation and experience, rather than derived from theory. Whilst this approach has been very successful, the large number of variables involved means that large regions of potential parameter space remain unexplored, and many processes are likely not optimised.
To address this, in CIM-Laser a gigahertz frame rate holographic camera has been developed to provide a proper link to process and material fundamentals. This has now been commercialised by Cambridge Techworks (see Figure 3), with a ready market in laser processing research laboratories.
Figure 3: Falcon gigahertz frame rate holographic camera. (Image: Cambridge Techworks)
Wire and laser additive manufacturing (WLAM)
A fundamental study of this process was made within CIM-Laser, including a study of the critical parameters underpinning the process, resulting in development of a well-controlled deposition system, and demonstration of high build rate and net shape deposition.
This led to additional major EPSRC and industry funding – £8.7 million – for the NEWAM Programme Grant, led by Cranfield University, to transform large-area metal additive manufacturing, by pioneering new high build-rate wire-based processes with greater precision of shape and microstructure. A key focus is to guarantee as-built structural integrity with process-independent physics-based quality control and assurance, enabling low-cost industrial qualification.
Multi-laser powder bed fusion
Powder bed additive manufacturing has enjoyed great commercial success in recent years, however it remains slow, with builds taking many hours or days to complete. The process is also plagued by problems with residual stress, which can warp parts, lead to catastrophic failure during manufacture and premature fatigue failure during operation. In CIM-Laser we have developed equipment and processes to measure the effectiveness of a multi-laser powder bed process, and instigated the development of new high-throughput melting strategies that also minimise residual stress. This has contributed to the development of a new AM platform by Renishaw (see Figure 4). The University of Liverpool is continuing to work closely with Renishaw to ensure that developments are transferred rapidly into products.
Figure 4: A project at CIM-Laser contributed to the development of Renishaw’s quad laser AM machine. (Image: Renishaw)
Refractory material for laser powder bed fusion
Refractory metals such as tungsten and niobium are extraordinarily resistant to wear and high temperature, so they are important high-value materials.
However, their high temperature properties mean that they are very difficult to process using AM. By carrying out detailed process development supported by fundamental knowledge, we have defined suitable parameters with which these materials can be processed effectively. We have designed and modified production equipment to enable use of these parameters, and have identified stable processing regimes to facilitate this effective production.
A further two-year project has been secured to transfer the developed process knowledge to a commercial platform – Renishaw’s RenAM 500M – and the industrial partners have reported that they are adapting the technology to replace conventional and expensive manufacturing routes.
Professor Hand is the director of CIM-Laser and deputy head of the School of Engineering and Physical Sciences at Heriot-Watt University in Edinburgh, Scotland.