AM IN Metals 1
The production of metallic objects directly through an additive process represents arguably one of the greatest revolutions in manufacturing since humans first began to deliberately manipulate metals around 8,000 years ago. Throughout human history civilisations have flourished as their understanding of metallurgy increased — and direct metals AM seems set to continue this trend.
From the earliest days metal was associated with value; from coins to elaborate jewellery the properties of metallic objects have transfixed us. Today the ubiquity of plastics in our daily lives has again strengthened perceptions of metal as something ‘premium’ — take for instance Apple’s switch from white plastic to glass and aluminium, or the use of ‘titanium’ to sell everything from sunglasses to oversized watches.
In the world of additive manufacturing the production of end-use parts, rather than the prototypes and models most closely associated with the technology in the past, has long been considered the Holy Grail. Industries as diverse as automotive, aerospace, jewellery, art, medicine and surgery, interior design, computing… and many many more all contain massive opportunities for the technologies. When this potential will be acted upon is dependent on the AM machine producers, materials suppliers, the standards commissions and the willingness of users of established technologies to take a risk on AM.
It must be noted that there are already many areas where the current abilities of direct metal AM machines are filling old niches, or creating entirely new ones. Dental applications have been some of the earliest commercial adopters of the technology because of the size and relative simplicity of the crowns and bridges that are routinely made through AM, and because of the expedited approval process. Non-critical components on commercial aircraft are believed to have been approved; AM generated medical implants are now certified for human use; jewellers and artists have made full use of the complex geometries available through AM — and can now build directly in precious metals.
As always, engagement with people who are willing to take risks and become early adopters — usually entrepreneurs and so-called intrapreneurs (entrepreneurs working within a large organisation) — is vital to the continued success of this relatively fledgling technology. As the AM sector enters into a acquisition-led growth phase, the IP surrounding the current systems is likely to continue moving up the ‘food chain’ as larger corporates and savvy investors realise the huge potential of current, and importantly future, processes and applications for direct metals AM.
History
It is important to contextualise the developments in direct metal AM by looking at the history of AM as a whole. Technically speaking, additive manufacturing can be traced back as far as the mid to late 1800s when contoured topological maps were made in a layer-wise manner. Other early developments include Francois Willème’s photosculpture experiments of the 1860s and the developments to remove the time-consuming carving process were made by C. Baese in 1904, who proposed exposing gelatin to a graduated light source and treating with water, whereby previous exposure would alter the level of expansion.
For the purpose of this article these early experiments are really little more than an interesting aside and many deal with a layer-wise approach, or a method that resembles modern AM, without being strictly additive. The experiments do help to demonstrate that although considered a modern technology, the earliest pioneers were excited by the possibilities over one hundred years ago.
The more modern history of AM started in the 1950s with a patent filing by Otto John Munz from 1956 entitled Photo-Glyph Recording. Munz’s filing shows significant similarities to many current photo-resin based systems, though through purely analogue manipulation techniques.
Pre-Direct Developments
The first patents that resemble modern AM equipment can be traced back to Pierre Ciraud in 1971. His application described a method of manufacturing objects of any geometry through the application of powdered material onto a substrate, followed by solidification through application of a focused energy beam. This patent explains that any meltable material could theoretically be used, including metals.
Ross Housholder’s 1979 patent clearly resembles a direct pre-cursor to current systems both in concept and in apllication — in this case selective laser sintering technology. Housholder describes “A molding process for forming a three-dimensional article in layers,” which by any interpretation sounds startlingly close to some of the ‘everyday’ AM equipment we now take for granted.
The first commercialised technology in the AM arena was Chuck Hull’s stereolithography system, with the first system being sold by 3D Systems in 1988. Although SL is a flexible technology in the plastics arena, it is not suitable for the direct processing of metals. It was selective laser sintering, pioneered by Dr Carl Deckard at the University of Texas, and commercialised first by DTM, that held the most promise for the direct metals AM world.
In the early 1990s DTM developed a process for indirect manufacture of metal parts for the tooling market. The process used selective laser sintering of polymer coated metal powders in which the powder would be sintered together through melting of the polymer coating. The resulting green parts could then be post-processed in a furnace to burn away the polymer and sinter the remaining metal powder. The now porous part could then be infiltrated with bronze to make it fully solid. This approach was a stepping-stone to direct technologies, and this sort of indirect process is still used. Likewise ProMetal (www.prometal.com) employs a selectively dispensed binder to hold powdered metal together before thermal processing sinters the metal part to solidity.
These indirect techniques were useful in generating interest in the possibility of direct metal AM, though they had at that time limited applications away from the tooling arena, but not the solution that industry was waiting for.
First Steps in Direct Metals AM
There are a number of players in the industry who all claim to be the first to produce direct metals AM machines because of the relatively malleable definition of the terminology. This issue is further clouded by the fragmentation of the same basic technology across so many companies, and the fact that there is significant overlap in the research and development projects of competitive companies.
Although the idea of direct metal AM and some of the related patents date from the 1970s and ‘80s, the first company to commercialise a direct metal AM machine was Electro Optical Systems (EOS), founded in 1989. The EOSINT ‘M 250’ system had its commercial release in 1994 with the first system shipped to a client in 1995. Using the same 200 W CO2 lasers employed in plastics sintering devices, the EOSINT M 250 processed a pre-alloyed copper-rich material. This first direct metal machine caused a flurry of interest in the industry as it proved that the direct metal technology could be made to work, and opened up possibilities for developers who were not interested in plastics-based technology.
However, the EOSINT M 250 caused a relatively short-lived spike in interest as Vice President Technology at EOS GmbH, Mike Shellabear, explained: “The release of the first EOSINT M machine raised a lot of interest in direct metals AM but was followed by a relative plateau of interest. The market was interested but the technology was not able to process they types of metal they were interested in at that time.”
By around 2000 the research of Dr. Matthias Fockele and Dr. Dieter Schwartz (F&S), Trumpf and the Fraunhofer Institute was bearing fruit for MCP Group, who had commercialised a direct ‘pure metal’ F&S Realizer machine. It is this research and commercialisation that has led to the seeming over-abundance of players in such a small market. MCP became the separate entities of MTT Technologies and ReaLizer in 2004. MTT subsequently split again into MTT Technologies based in Stone, UK and SLM Solutions based in Lübeck, Germany in 2011. MTT Technologies (UK) has recently been acquired by Renishaw PLC and will in time become a Renishaw-branded division. (I hope you’re keeping up! — Ed).
The Current Crop
By 2004/2005 EOS had made the switch from the CO2 laser used in plastics selective laser sintering, to a fibre laser. Fibre lasers are better suited to processing of metals because they exhibit a higher beam quality allowing a higher intensity of power transfer. The wavelength is also around 10 times shorter than CO2 lasers and is in a range that is much more effective at melting metal. Also around 2004 the MTT/ReaLizer technology was capable of processing reactive Aluminium powders.
Phenix Systems, based in Riom, France, was established in 2000 as a spin out from work at École Nationale Supérieure de Création industrielle (ENSCI). From 1992 onwards ENSCI began to develop AM processes designed to manufacture ceramic parts using laser sintering without a binder. In 2003 Phenix employed this know-how to direct metals AM. The company currently has machines processing powders of ~8 µm in dental, automotive, aerospace, watch and jewellery making, energy and universities.
From 2004 onwards therefore there have been a choice of commercialised powder-bed systems that can process aluminium, inconels, stainless steels, cobalt chromes, maraging steels, titanium, tool steels and super alloys.
Because of the technological challenges associated with creating machines that matched industries expectations, the installed base of metals AM machines is still much smaller than that of plastics, but is growing at an much faster rate, as Stuart Jackson, EOS Regional Manager commented: “When I began with EOS in 2002 metals machines were around 20% of our total output, compared to around 50% now. This growth has stabilised and we anticipate that technological innovations in both metals and plastics — for example the recent introduction of PEEK to the material line-up on the plastics machines — will increase the total number of systems sold without altering the plastics to metals ratio in the short-term.”
Overall there is agreement that the medium- to long-term outlook for direct metals AM over shadows that of the plastics machines by an order of magnitude. As ever there are dissenting voices, however, and some companies believe that the era of direct metals AM is much further in the future.
All of the technologies offered by the aforementioned companies are essentially identical, with relatively minor variations in scanning, recoating and atmospheric control that confer benefits to certain applications. Only Arcam offers a significant variation on the theme by using an electron beam as the power source (EBM), which can deliver up to 4000 W of energy for melting the powder, deployed in a vacuum.
The EBM technology was developed by Arcam and the Chalmers University of Technology in Gothenburg, resulting in the founding of Arcam AB as sole developer and commercialiser in 1997. The initial patent describing the principle behind EBM was filed in 1993. The EBM process operates at between 700°C and 1000°C, which removes residual stress in the created parts, and removed the need for post-processing, and brings the powder much closer to its melting point. This high-temperature, combined with the ability to ‘split’ the electron beam means that Arcam machines generally exhibit shorter build times than their laser counterparts.
Laser-based powder-bed systems purge oxygen from the build chamber to allow the processing of reactive metals and alloys such as Titanium; for example the MTT systems employ high-purity argon to reduce the build-chamber oxygen content and maintain an inert environment.
One of the important trends from this sector is the diversification of offerings based on the needs of certain niches. There will always be a need for a machine that can cover a number of process bases for customers who regularly need to process different metals, for different purposes, but don’t build enormous numbers of parts, and also in a research setting where flexibility is key. Once a manufacturer has ‘bought in’ to the idea of direct AM in metals however, it makes sense to provide them with a machine tailored to their specific requirements — be it in jewellery, medical applications, aerospace or elsewhere.
Concept laser recently launched the Mlab aimed specifically at the jewellery, bracelet and watch-making markets, that offers a compact system capable of processing precious metals. ReaLizer markets the SLM 50, also aimed at the jewellery and dental sectors. EOS already supplies machines tailored to specific metals, though the changes are predominantly in the embedded software rather than the hardware.
Rob Weston of MTT commented: “I believe that it is likely that we will see more variants of a central theme offered in the world of direct metals AM. The nature of AM metals processing technology is inherently more complex than traditional subtractive techniques, and preparing to build in a new material is not yet as easy as choosing a new tool and spindle speed.
“With this in mind, and considering the diverse applications of this technology, there are likely to be a number of users who want to run only one material, or need only a very small build bed. Likewise some customers will be demanding larger builds, or the ability to process multiple materials on the same machine.”
Energy consumption of direct metal AM is generally high when compared to traditional manufacturing techniques, though not necessarily because of the process itself. The production of the gas-atomised powders for these systems requires a high energy input, and the power source of the furnace in this process dictates a large percentage of the total impact.
It is generally accepted that EBM technology requires a higher energy consumption because of the elevated temperatures involved. The pay-off here is that no post-processing is required, but it is also accepted that the additional heat-processing needed for SLM-type systems is more efficient than EBM’s one-stop strategy.
The green credentials of direct metals AM parts come not in their manufacture but in their use. The weight-saving geometries created, including lattice structures and organic optimised forms, can substantially reduce weight in transport applications such as aerospace. Every kilogram shaved from the weight of a modern airliner results in significant fuel savings over a lifetime — saving both money in the face of rising fuel prices, and carbon dioxide emissions.
An interesting current development is in the field of micro manufacturing using direct metals AM. The micro manufacturing industry has grown exponentially in the last couple of years, and many AM processes are well-suited to development in this area (see page 47 of this issue for part two of an article on micro stereolithography). Micro parts produced through AM in metal will be of particular interest to the watch, medical, electronics and dental sectors, but their appeal will undoubtedly spread much further once the process is refined. Figure 1 shows some micro metal AM parts produced by EOS.
Future Challenges
Uptake of the technology will likely progress at different rates across different industries, with the lead continuing to be taken by non-critical applications. To this end, one of the biggest hurdles for direct metals AM in sectors such as aerospace remains the long validation procedures that are needed for any new process or material. Not only must direct metals AM machine manufacturers prove beyond any doubt that the process is stable within the build of a part (i.e., the same output is measurable in the first layer or deposit to the last) but also between parts across several years (i.e., put in material X, run part Y and obtain identical parts today and on 2021, 2031 and so on).
The current technology across all manufacturers is certainly good enough to meet the requirements of most applications, providing the machine is correctly set up for the task. It is the ability to prove the stability of the process that is holding direct metals AM back. Where traditional subtractive manufacturing techniques act upon the starting material to produce a part, they are not considered to be integral to the final part — AM parts are much more dependent on the variables with the process for their accuracy and strength and are thus likely to be regarded as more a combination of process and material when being assessed.
Another potential hurdle is one of material supply. For direct metals AM to truly be accepted across the whole gamut of potential industries that could use it, it must become another machine tool in the engineers armoury. To become just another tool the AM machine manufacturers must start to behave like tool manufacturers and sell tools, which is to say sell machines.
If an engineer specifies a new 5-axis CNC machine they’re not likely to entertain any company that tells them: “You can have our CNC machine, but we want to become you sole materials and service provider too.” Any savvy company knows that having single suppliers in at part of the chain is a disaster waiting to happen. To rely on one supplier of injection moulded PET parts would be understandable — ship the mould to one of the thousands of injection moulding companies on every continent and resume production overnight.
Things become a little more complicated when trying to source powdered metal of a specific grade for an AM machine. Metal powders that are nominally identical in terms of chemical analysis and grain size can create parts with differing properties if the correct qualification process is not first undertaken. This involves a major R&D step and is not embarked on lightly. With this in mind, many users will stick with pre-qualified supplies from the machine manufacturer or undertake their own qualification procedures on materials from one or more suppiers, depedent on their internal procedures.
Materials must also be developed from the bottom up for these systems to truly fit into the engineers toolbox. With the exception of a couple of materials, including EOS’s cobalt-chrome for dental applications, all materials currently used in bed-based AM systems are used because it is what industry is asking for, rather than because they have been developed to work with the processes concerned.
It is likely that in future we will also see direct metals AM used to create bespoke parts for the general public through the ‘consumer bureau’ model of Shapeways and others. Sterling silver jewellery created directly from a consumer’s design has already created a flurry of media interest, and as initial purchase and long-term running costs are further driven down, more service providers will be able to economically enter this arena.
It is not unimaginable that we will see a consumer focused metal ‘3D printer’ in the not-too-distant future either. There are already a number of projects in place that aim to do for metals AM what Makerbot et al have done for plastics AM. Indeed it may well be a company such as Makerbot that produces this technology first. Belgium-based Layerwise already runs a successful metal-only bureau catering to prototyping, parts, tooling and arts communities.
Larger platforms are sure to emerge in parallel with faster scanning systems and more powerful lasers. MTT is already pursuing a 500 mm x 500 mm build chamber, which is loaded with 1 metric tonne of powder. The powder deposition systems (to be covered in the next issue) are already considerably large than their powder-bed counterparts and where the deposition head is on a multi-axis robotic arm the scope for larger size is very real.
It would be remiss to believe that this status quo will last for long — larger companies are already getting involved in the technology directly and there are rumours aplenty of existing AM companies expanding into direct metals technology in the near future. With size comes money, and with money comes the ability ot develop the processes at a previously unattainable rate. As ever in the world of AM, “watch this space.”
Conclusions
Metals AM has seen a surge of development in the last five years, spurred on by developments in the laser and scanning systems available, and by uptake of large OEMs acting as development partners for the relatively small machine manufacturers. Although some of the barriers to uptake have been removed or overcome, many still exist for certain applications.
Robin Weston, MTT Technologies Group, explained the situation: “Uptake is dependent on trust — how much trust can an engineer place in these systems? Until process control can be shown to be at least equal to existing mainstream technologies engineers are unlikely to place much faith in the technology — and at the moment no direct metals AM machinery manufacturer can legitimately demonstrate this level of process control, but we are improving all the time, and are working hard to realise this as soon as possible.”
Currently direct metals AM is of most use in areas where either there is no other way of making the same part, where the quality of the part cannot be achieved by other means, or where the specific materials properties imparted by AM is required.
It would be remiss to believe that this status quo will last for long — larger companies are already getting involved in the technology directly and there are rumours aplenty of existing AM companies expanding into direct metals technology in the near future. With size comes money, and with money comes the ability ot develop the processes at a previously unattainable rate. As ever in the world of AM, “watch this space.”
