One important lesson learned from the economic crisis was that a country’s economy could not solely survive on the financial services sector. In fact, the countries that were least affected by the financial downturn were the ones that relied upon the manufacturing sector to pull them out of the crisis. This was put into action following the financial crisis in the UK, where first the Labour then the current coalition government attempted to revive the manufacturing sector, focusing on what is called ‘high-value manufacturing’ (HVM), where advanced technical knowledge is utilised to develop products and manufacturing processes that can bring sustainable growth and high economic value.
HVM addresses a number of manufacturing challenges including
• the development of high throughput technologies.
• decreasing the lead time from design to market.
• the adoption of resource-efficient manufacturing due to the limited availability of resources (e.g. energy, raw materials, etc…) and growing demand.
• the need to minimise the carbon footprint, through the re-use, recycle, and re-manufacture (repair) of the existing products.
• improving product performance through the use of high performance materials.
These points illustrate clearly the potential of HVM as an economic driver. It helps ensure that the UK has a vibrant manufacturing sector, but one were our competitive advantage is in the techniques and skills we use rather than the volume.
Birmingham is making a number of key contributions to this field. The research conducted in the advanced materials and processing group (AMPLab) considers the ethos of HVM through assessing a number of manufacturing techniques, commonly referred to as net-shape manufacturing (NSM). NSM or near-NSM refers to the manufacturing of a product in its final shape or near to its final shape, to minimise the energy and material waste in the finishing operations, which are known to contribute up to two-thirds of the manufacturing cost of a product. Our work in Birmingham focuses on the use of powders as a feedstock for manufacturing, through a number of technologies including net-shape powder hot isostatic pressing (commonly referred to as powder metallurgy), where powders get consolidated into solid products through the application of temperature and pressure. In addition, we combine the use of powders with lasers to melt the powders to create complex shapes, which is referred to as additive manufacture (AM) or sometimes 3D metal printing. AM specifically has become one of the fastest growing technologies in the 21st century, especially as it liberates the designers from the constraints imposed by the manufacturing methods, enabling them to design the product based on its functional requirements rather than on how to make it. Additive manufacture (AM), is now believed to be the new game changing technology that will revolutionise the high-value manufacturing sector. It is estimated that this business approached £1.2 bn in 2011, including the AM systems sales, and its associated materials and services. The Technology Strategy Board (TSB) estimates that by 2020 the net worth of this field will approach £4.5 bn, and as such it is important to understand the range of technologies and applications that can arise from AM . This TSB report has recently published a document on the national competency in AM highlighted the potential applications of AM in the aerospace, healthcare, and other industries. The report also highlighted the key advantages of AM, especially the design flexibility, product customisation, and minimisation of material waste via subtractive manufacturing. The TSB report highlighted that the aerospace sector, with its civil and defence applications, is the strongest supporter for AM technologies, with an approximate R&D investment of ~£13 M in the period 2007-2016, in addition to a further £20.5 M of public funds. In 2011, the aerospace sector brought a total revenue of £24.2bn, increasing by 4.7% from 2010. Furthermore, the growth of civil and defence aerospace exports increased from 2010 by 13% and 5%, respectively , making them a potential venue for the application of AM technologies.
The concept of AM is simple. A computer geometrical (CAD) model is used to generate a numerically-controlled path to add a material layer-by-layer, building a structure bottom-upwards. For metals, the process generally comes in a number of variants, one of which is what is commonly referred to as a powder bed method, whereby thin layers of powders (~20-100 microns) of the material to be ‘printed’ are spread using a recoater blade from a powder reservoir to a neighbouring substrate. A heat source (e.g. laser or electron beam) is used to selectively melt or sinter the powders on the substrate, only in the regions that correspond to the 2D section of the component being built. By repeating this process, the entire structure can be grown, and then extracted from the powder bed, with the surrounding un-sintered powder being recycled. The other more common variant is direct laser deposition, where a laser, electric arc, or electron beam is used to melt a wire or powders being sprayed through a nozzle to melt and deposit in ‘free-form’. The process can be used for repair applications, or hybrid additive manufacturing where structural features (e.g. bosses or lugs) can be deposited on structures to simplify the manufacturing process and to avoid whenever possible excessive machining operations. The Following picture shows the complex geometry manufactured using AM in University of Birmingham.
The powder bed method has traditionally been used to build orthopaedic and dental implants from titanium alloy, cobalt-chrome and stainless steels, but current research being undertaken at the University of Birmingham is looking into using it to build aerospace and defence titanium, aluminium, and nickel superalloy structures. For medical implants, the process offers the advantage of creating customised medical implants, that can be tailored for uncommon injuries (typically in the battlefield). This is done by manipulating MRI or CT scan data to create the geometry for an implant that will ‘fill’ the injury place (e.g. in a skull). Additionally, the process enables designing for functionality rather than manufacturability. AM liberates the designers from the constraints imposed by the manufacturing methods, enabling them to design the product based on its functional requirements rather than on how to make it. For instance, surface functionality for prosthetic implants can be ‘engineered’ to enable better bonding between the bone and implant structures, through the creation of a ‘trabecular’ structure that makes the implant surface more bio-compatible. Unfortunately, this advantage is occasionally overlooked by manufacturers when they undertake research programmes to assess the utility of additive manufacture to make a part that is usually fabricated by conventional manufacturing methods (e.g. casting or forging), as it is conceivably possible to re-design the part to add a functionality into it (e.g. creating cooling channels, surface texturing, etc). AM also provides a resource-efficient approach to produce complex netshape structures, with a potentially low buy-to-fly ratio and considerable reduction in materials waste compared to other manufacturing process for high-value materials (Ti-alloys and Ni-superalloys) especially in the aerospace structures (structural sections, landing gear, and engine parts).
Both variants of AM for metallic materials face a number of challenges to address. First, the structures built using both techniques are prone to structural integrity issues, since AM is more like a mixture of joining and casting. In fact, it is generally known that the weldability of a certain material can be used to assess its processability using AM. As such, issues like the development of structural defects (pores and cracks), distortion/residual stresses, and microstructural anisotropy (which leads to a directionality in the mechanical properties). These issues combined can be resolved or avoided through the introduction of new alloys variants that are suitable for AM, which is yet to be developed, in addition to the development of advanced metallurgical and structural assessment techniques, such as X-ray tomography. Equally, to maintain the structural and geometrical integrity of the component during deposition, the development of on-the-fly non-destructive evaluation (NDE) of the structure for detection of porosity is required to ensure the repeatability of the process.
We try always to make it clear that we are materials scientists, supporting the manufacturing sector, through developing new materials, or assessing the suitability of new materials for those advanced manufacturing processes. As such, our main experimental tools, including electron microscopy, X-ray and neutron diffraction, and mechanical characterisation, help us tailor and probe the material structure.
Over the years, AMPLab has collaborated with a number of major UK aerospace manufacturers, especially Rolls-Royce plc, which has a University Technology Centre hosted by the School of Metallurgy and Materials to train the future generations of materials and manufacturing engineers. Current project at AMPLab approach in value £ 4.5 millions (2013), from the EU (FP7 programme), TSB, EPSRC and a number of industrial contracts. The group works closely with the Catapult’s Manufacturing Technology Centre (MTC), providing the academic leadership for the netshape and additive manufacturing theme. AMPLab at the University of Birmingham has been working closely with a number of aerospace manufacturers to develop the AM technologies, with funding from the TSB, Engineering and Physical Sciences Research Council (EPSRC), Defence Science and Technology Laboratory (Dstl) and the European Framework 7 programme (FP7). These technologies are exciting, innovative and provide opportunities for business to create products more efficiently and to a higher specification. Our contribution to the development of these technologies is achieved through developing new materials, or assessing the suitability of new materials for those advanced manufacturing processes
These relationships are symbiotic as they help businesses to innovate but they provide our lab with ideas to help shape our research and teaching. Although there are many good examples of these relationships between academics and business we would like to see more being done to recognise the important role they play in driving innovation in the economy. Keeping this the objective, AMPLab now hosts the Second Research Day in University of Birmingham on 17th October, 2013 www.birmingham.ac.uk/research/activity/irc-materials-processing/themes/AMPLab/AMPLab-events.aspx