Adding up the benefits

No one is arguing that additive manufacturing of metal parts – basically the selective melting of metal powders to form 3D shapes, although there are variations – has become mainstream technology just yet. But it will happen, of that there is little doubt, because additive techniques make sense: there is no waste; only the material required is used. Furthermore, there are no fixed costs, due to the elimination of tooling, meaning that time-to-market is reduced. It is also easier to realise true design potential, as complex shapes are more easily created using additive techniques. Parts currently manufactured by additive manufacturing take in mould tools (where conformal cooling holes can be produced), medical parts (patient-specific hip implants, volume production of dental crowns [see box item], and orthopaedic implants featuring hybrid structures), small aerospace parts (impellers, swirlers), and fashion items (pendants, shoe heels). Additive manufacturing sees parts built up layer by layer, with a minimum layer thickness today being 20 microns and a maximum thickness up to 100 micron. According to EOS Direct Metal Laser Sintering (DLMS) technology user 3T RPD (01635 580284), the process produces metal components directly from 3D CAD data that are 99.99 per cent dense. It adds that the parts produced are comparable to a good investment cast part, with the advantage of the process being that the more complex or feature-rich the component, the more economical the process becomes. 3T RPD was one of the speakers at a recent Association of Laser Users (AILU – www.ailu.org.uk) event, where several presentations outlined the path to greater take-up, particularly for metal component fabrication. The event intended to highlight some of the current technical barriers to successful commercialisation. EXPLODING MYTHS Kicking off proceedings was Rob Scudamore, technology group manager at TWI, who wanted to explode some of the myths surrounding additive manufacturing. Among his conclusions: there is not unlimited design freedom, but there is great design freedom; it is not 'rapid', but it is very agile; it does not yet have 100 per cent material usage, but it is getting close; and it will not be suitable for all applications, but it is currently especially good for small batches of complex and/or personalised parts. According to the TWI, the current global market for additive manufacturing technology stands at $1.4 billion per year and is growing at an approximate annual rate of 15 per cent. Focusing on one of the main barriers – cost – Mr Scudamore says that processing speeds need to be increased, in tandem with reductions in the cost of capital equipment and materials, while a reduction in post-processing would also be welcome. Among required improvements in process capability are support for larger parts and improved surface finish, while "platform-to-platform capability" (eg EOS to MTT) would provide a boost. Of course, people are working to improve these areas, largely because the potential rewards are so vast. The TWI says that existing casting and forging markets are worth around £200 billion per annum globally. In the aerospace sector alone, there will be 24,300 new aircraft built in the next 20 years – these programmes will use 20 million tonnes of billet, yet only 2 million tonnes will actually make it on to the aircraft after machining. Indeed, while additive manufacturing activity in the UK is still at an early stage, 3T RPD highlights that there is significant market potential. The company estimates that the current UK market is worth around £5 million a year, but sees potential aerospace component work worth £5 billion in the UK, while UK medical device potential is put even higher, at £8 billion. MORE MACHINES, PLEASE But just hitting the £1 billion mark in the UK would require around 3,000 machines at current productivity (presently, there are fewer than 20 at UK bureaux). It would also require around 600 maintenance/support engineers, where there is presently only a handful. Other consequences would be the need for 30,000 tons of powder per year (less than 1,000 tons used at present), while OEMs will need perhaps £10-50 million of materials testing work over the next 5-10 years to prove the components are fit for purpose. So, while 3T RPD says the market is very attractive and that this technology will eventually prove a significant substitute for conventional manufacturing techniques, its introduction has barely begun. Assessing some of the latest technology developments in the field was the aim of a recent seminar staged at the University of Warwick's International Digital Laboratory. The event was hosted by rapid manufacturing specialist Materialise (01142 541 249), which markets the Magics e-Solution software suite. Efficiency, lead-time and quality are among the main challenges of additive manufacturing and, according to Materialise, software can play a major part in overcoming these hurdles. For instance, Magics e-RP enables users to streamline and automate the entire additive manufacturing process, from order follow-up and data preparation, through platform scheduling and machine monitoring, to production planning and part tracking. Meanwhile, e-Tools is a modular framework of server-based automated operations that can be integrated with Magics e-RP to enhance the efficiency of additive manufacturing processes (3T RPD is a materialise software user, in fact – see extended web article). But it is in hardware development where most activity is to be seen. One of the most common additive manufacturing technologies is SLM or SLS (selective laser melting/sintering), and the UK's MTT Technologies (01785 815651) is currently engaged in the development of a large machine having a working volume of 500 by 500 by 500 mm, its SLM 500. The company's current machines are 125 mm3 and 250 mm3 (SLM125 and SLM250). The new machine, expected to be available this year, has a translation speed of 3 m/sec and will also sport a 1 kW laser, although a 400 W unit is being used in testing, it is reported. Image: An example of one of MTT's SLM units COMMERCIALLY AVAILABLE SLM is described as using a high powered laser to fuse fine metal powders together, layer by layer, direct from CAD data, creating functional metal parts. After each layer, a powder re-coater system deposits a fresh layer of powder, in thicknesses ranging from 20 to 100 micron. The system uses commercially available gas-atomised metallic powders to produce dense metal parts in materials such as titanium, stainless steel, cobalt chrome and tool steel (other companies, notably EOS, develop materials for use with their machines). German company EOS range of EOSINT machines (01926 623107) seem to have the widest penetration, with over 900 now sold (it also makes a large machine, P700 – 700 by 388 by 580 mm). EOS offers a number of metal materials suitable for its EOSINT 'M' range of machines, such as high strength steels for injection mould tooling, stainless steels for medical applications, cobalt chromes for dental work, and nickel alloys and titaniums for aerospace and motorsport customers. EOS has, in fact, recently announced a new breakthrough regarding the laser sintering of titanium, which beforehand had been hampered by the material's high reactivity. Performance was limited by the gradual generation of condensate (vaporised particulates) in the argon-filled build chamber. This tended to de-focus the laser and cause variation in sintered metal density as component build progressed. Image: Titanium test pieces be sintered in an EOS machines Users of older models can have their machine upgraded by EOS to the new specification, which is what the Department of Engineering and Technology within the University of Wolverhampton has chosen to do. The university says that surface finish is now two to three times better, typically 4 to 5 Ra, instead of 10 to 12 Ra, while scanning speed is three to four times faster, up from 350 to around 1,200 mm/s, resulting in much faster build speeds. Perhaps most importantly, components produced are homogeneous and fully dense throughout. Image: Warwick University has upgraded its EOS machine for better titanium part manufacture There is UK research ongoing. For instance, metal additive layer manufacture using arc and wire is the subject of scrutiny and development at Cranfield University, under the tutorship of Professor Stewart Williams. Elsewhere, the University of Warwick is partnering with the University of Wolverhampton on the assessment of laser sintered titanium for hydraulic components such as manifolds, many of which contain complex fluid flow channels. And Laser Optical Engineering (01509 228733), a company based at Loughborough University's Innovation Centre, is focusing on novel beam shaping for improving metallurgical quality in additive manufacture. Laser Optical has developed the use of diffractive (holographic) optical elements to reconstruct the laser beam to reflect any custom designed shape, intensity and focus. Box item Dental parts laser sintering factory Renishaw has just opened a new facility that will allow the manufacture of low cost CAD/CAM frameworks using pure, certified medical-grade Cobalt Chrome metal. Image: Renishaw will make dental copings and frameworks at its new facility The new copings and frameworks will be produced using EOS Direct Metal Laser Sintering (DMLS) and allow dental laboratories to offer a high quality, lower cost alternative to ceramic restorations, which Renishaw is calling Laser PFM. The new DMLS process fuses together successive thin layers of powdered metal, just 0.02 mm thick. The frameworks are created from powdered cobalt chrome and, when every layer has been built up, the solid copings and bridge frameworks are then removed from the machine, sand blasted, polished, inspected and ultrasonically cleaned. The DMLS machine can create hundreds of units at a time, meaning that cost per unit is kept low. Box item Additive manufacturing report Wohlers Associates (www.wohlersassociates.com) has released its Wohlers Report 2010, a 250-page analysis of the newest developments and trends in additive manufacturing (AM) worldwide. "Using AM for part production is considered the next frontier, with opportunities beyond measure," said Terry Wohlers, principal author of Wohlers Report 2010 and president of Wohlers Associates. "Corporations, entrepreneurs, investors and researchers are considering ways in which AM can be used to manufacture an exciting array of products in quantities of one to several thousands," he states. Image: Wohlers report First published in Machinery, June 2010