Beginning to add up

For metalcutters, the two most interesting additive manufacturing processes are laser sintering/melting of metal powders to produce small parts or small features on large parts, and traditional welding for laying down large volumes of material to generate large parts, such as aero engine casings. The former is more common, the latter being a minority process, but it is still of great importance to companies such as Rolls-Royce, which is involved with the development of the process at the Advanced Manufacturing Research Centre with Boeing, located close to Sheffield. On the laser sintering front, material and machine developments are regular news. Most recently, for example, German firm EOS unveiled a new version of its EOSINT M 270 machine, which has particular advantages when processing titanium (EOS UK, 01926 623107); of interest to the aerospace industry, of course. Until now, the high reactivity of titanium has hampered sintering progress, but the new version of its M 270 can process pure titanium, as well as Ti64 alloy (6 per cent aluminium/4 per cent vanadium). In so-called Installation Mode Xtended mode, the build chamber is filled with argon, but, importantly, condensate is removed. Older M270s can be upgraded. TITANIUM SPEC MACHINE The Department of Engineering and Technology within the University of Wolverhampton is one of the first academic institutions to have the latest titanium-specification EOSINT systems. Other users include Airbus in the UK, rapid prototyping and manufacturing bureau 3T RPD in Newbury, Berkshire, and many other companies around the world, it is said. Image: The University of Wolverhampton is one of the first academic institutions to have the latest titanium-specification EOSINT systems Dr Mark Stanford, Reader in Engineering at the University of Wolverhampton, is responsible for R&D using the newly modified laser-sintering machine, which sits alongside an EOSINT M 250 Xtended, installed in 2005. His intention, he says, is to conduct further research into the properties of sintered metals; not just titanium, but also other metals and alloys, most of which can be processed in the argon atmosphere. The university has already qualified EOS CobaltChrome MP1, which is especially useful for high temperature applications and components that require high wear resistance; EOS MaragingSteel MS1 is currently being evaluated for tooling intended for series production applications; Argentium silver powder for mass customisation of jewellery is also being investigated. It is titanium, however, that is the main focus of attention. Most EOS metal powders for laser-sintering are processed using a layer thickness of either 20 microns or 40 microns, the former achieving high resolution surfaces, while the latter is capable of faster build speeds. Titanium powder is processed in 30-micron layers. While the university's EOSINT M 270 already had titanium-processing capability, its performance was limited by the gradual generation of condensate (vaporised particulates) in the argon-filled build chamber. This tended to defocus the laser and cause variation in the density of the sintered metal as the component build progressed, layer-by-layer. Recent upgrading of the argon filtration system has resulted in a significant improvement in quality and part integrity, while the latest version of EOS's PSW process software has also enhanced system operation. Quantifying the upgrade: surface finish is now two to three times better, typically 4 to 5 Ra, instead of 10 to 12 Ra; scanning speed is three to four times faster, up from 350 to around 1,200 mm/s, resulting in much faster build speeds. Significantly, components produced are homogeneous and fully dense throughout, regardless of the length of the build cycle. The University of Wolverhampton is seeking collaboration partners to further its research into laser-sintering, with links already forged with the Advanced Manufacturing Research Centre, Sheffield, the University of Waikato in New Zealand, and Kyungpook University in South Korea. Dr Stanford and his research team are also working on the development of new, laser sinterable powders, including metal/ceramic mixtures and wear resistant alloys. News of a recent breakthrough on ceramic metal mixes has come from America, in fact. Researcher Dr Ming Leu at Missouri University of Science and Technology is leading a team that is involved in developing metal/ceramic mixes for the production of "functionally graded" material components that could be used for hypersonic aircraft or as parts of ultra-high temperature engines and rocket boosters. Metal and ceramic materials are extruded together in a precise fashion to create a blended material that combines the toughness of the metal with the heat resistance of the ceramic. But there is a problem with additive manufacturing, and that's one of standardisation and material performance. A part cut from a solid material will have well understood and consistent mechanical properties, but additive manufactured parts will have properties that vary, depending on the type of process, the material and direction of applied force. STANDARDISATION MOVE ASTM International, headquartered in America and which develops international standards for materials, products, systems and services used in construction, manufacturing and transportation, has, together with the Society of Manufacturing Engineers, established a new committee (F42) to look at standardisation aspects of additive processes and equipment. Richard Hague, professor of Innovative Manufacturing /head, Rapid Manufacturing Research Group, at the Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, is involved. The establishment of this committee is heralded as a turning point in the industry. Standardisation under a number of headings is being pursued. One of these is 'Test Methods', described thus: "Because the industry builds pieces layer-by-layer, properties of a material can be different in different directions. Task groups will be studying how standard test methods, such as for tensile testing, can be applied to additive manufacturing processes." Yet another States-side initiative is the Additive Manufacturing Consortium (AMC). The new body will establish a US centre of excellence, which engages a national technology network to provide unbiased advice, development, performance testing and qualification of additive processes. Consortium members will consist of industrial end users, universities, research centres, equipment suppliers and their technology partners. Set up by EWI – the leading engineering and technology organisation in North America, dedicated to the research and development of materials joining and welding – AMC's core studies programme will "work to advance the current state of the technology by seeking higher speeds, larger sizes, real-time quality control, better properties, and greater ranges of materials". Box item Materials development Late last year, Concept Laser unveiled an expanded range of materials for use with its LaserCUSING process, which first appeared in 2000 (ES Technology, 01865 821818). New developments in materials mean that the range has been expanded to include a finer quality variant of stainless CL20 ES (1.4404), providing additional improvements in component surface finish. The original titanium powder CL40 TI, based upon the alloy Ti6A14V, is complemented by a high purity version CL41 TI, which meets the strict requirements of ASTM standard F136 for surgical implants and further expands the potential for direct components made from titanium. Also, part of the ongoing development in the materials field is the introduction of a new class of cobalt-chrome based alloys. Developed as part of a (working relationship between Concept Laser and Dentaurum, alloys CL110 CoCr and remanium star CL open up a host of potential applications within the dental, medical and prototype fields, it is said. Image: Parts like this are targets for additive manufacturing First published in Machinery, April 2010