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Additive layer manufacturing

Additive manufacturing technologies are now finding ready acceptance in a range of industries, and for a range of reasons.

In the late 1970s, Fiat ran an advertising campaign with the tag 'hand-built by robots'. Today, the tag 'hand-built by lasers' could be applied to products made using rapid manufacturing techniques.

For any manufacturer who needs to get products to market faster, rapid manufacturing sounds like the perfect solution. However, once you start looking deeper you may be faced with a baffling array of machines, processes and technologies, such as 3D printing, stereo-lithography, selective laser sintering, and fused deposition modelling.

Otherwise known as additive layer manufacturing (ALM) or direct freeform manufacturing, rapid manufacturing grows parts from elements like minute Lego bricks – or triangles, to be precise – unlike a subtractive manufacturing technique such as CNC machining.

ALM allows a manufacturer to make something with a hole – or even a matrix or latticework – in it without using separate castings. It does this by taking CAD models and transforming them into a language that a machine will understand, in the form of industry-standard stereo-lithography (STL) format files. An STL file is a triangular representation of a three-dimensional surface geometry.

The surface is tessellated or broken down logically into a series of small triangles (facets). Each facet is described by a perpendicular direction and three points representing the vertices (corners) of the triangle. These data are used by a slicing algorithm to determine the cross-sections of the 3D shape to be built by the fabricator.

Time to market isn't the only advantage of additive manufacturing, however. It can also be a much more economical production method where one-offs or short runs are required, and as some niche manufacturers are discovering, the way that the additive processes work can give the resulting components unusual or even unique physical properties.


One area which has seen an increase in the use of rapid manufacturing is bioengineering. The growth is driven by an increase in the number of rapidly manufactured implants, particularly acetabular cups, or hip replacements.

The number of people undergoing joint replacement surgeries such as total hip and knee replacement is steadily increasing as people live longer. Higher expectations for quality of life also produce an increasing number of younger patients.

One key requirement for orthopaedic implants is the implant's ability to fix itself to the hosting bone, by enabling the bone to grow into it and make the implant almost an integral part of the body: osseointegration.

Porous scaffolds that resemble the natural bone structure have been developed, such as Zimmer Holdings' Trabecular Metal, a tantalum biomaterial, formed by vapour deposition of metal onto a carburised organic bone sponge structure.

However, as Dr Gregory Gibbons of the Rapid Prototyping & Manufacturing group at Warwick University's WMG (Warwick Manufacturing Group) explains: 'The structure simulates trabecular bone but is not formed by ALM, so you cannot control the structure.'

WMG is therefore working with additive electron beam melting (EBM) technology, which additively manufactures parts by melting thin layers of metal powder. As the name implies, the energy source is an electron beam gun, and the process takes place in a vacuum chamber.

Other conventional methods to improve bone ingrowth by adding a porous coating of titanium beads or hydroxyapatite to the implant's surface work well, but still do not provide the optimum conditions for osseointegration, argues EBM's developer Arcam AB of Sweden. Arcam claims EBM technology can be used to build orthopaedic implants with full material properties and an integrated trabecular structure for improved osseointegration.

The vacuum environment makes the EBM'process especially well suited to manufacturing parts from reactive materials with a high affinity for oxygen. An example is titanium, the most widely used material for implants because of its biocompatibility, but whose material properties alter when the oxygen content increases.

In November 2009 Arcam introduced the Arcam A1, a new EBM system specifically developed for Additive Manufacturing of orthopaedic implants. Arcam's A1 features advanced trabecular structures and replaces the Arcam EBM S12 system – as used by WMG, and claimed to be the de facto industry standard for additive manufacturing in the orthopaedic implant industry.

In June 2010, Arcam received an award at the 15th European Forum on Rapid Prototyping & Manufacturing in the category Meilleure Application de Fabrication Directe for how the EBM technology is used for series production of CE-certified implants with integrated, engineered porous structures for improved bone ingrowth.

Gibbons adds: 'We are also working with Birmingham and Leeds to additively manufacture structures with different porosities, like macroporosity for bone growth, for example, or microporosity to enhance the bioactivity of synthetic bone graft substitutes, or even nanoporosity to interact with cell material to encourage cells to grow. Birmingham has done some trials to bond soft tissue tendon to hard bone.'

This work too is additive, but he says that rather than EBM it uses a ZCorp 310+ 3D printer, printing in biocements.

Fighting scepticism

Gibbons is also involved in laser melting of high temperature alloys for aerospace structures, but finds that the aerospace industry remains sceptical about ALM. He explains: 'You still have companies saying that it comes as a powder and is therefore not a wrought material. 

'They will not accept ALM for critical applications, believing that the structure is not integral enough. The structure is nevertheless the same because the material is fully melted and therefore you have crystal regrowth across all the layers.

'If you look at the structure under a microscope, you will not see multiple layers but a new, reformed structure, which is just the same as an original machined structure. Fortunately the ASTM Committee F42 on Additive Manufacturing Technologies was formed in 2009. If you can standardise the manufacturing, testing and validation then you have effectively a validated process.'

Another key candidate for additive manufacturing is the motor industry. Koenigsegg Automotive AB was launched in 1994 by Christian von Koenigsegg, who had the dream of creating the perfect sports car. With headquarters in a former fighter jet facility in southern Sweden, Koenigsegg can now assemble up to 15 high-spec vehicles per year and up to seven at one time with the help of a Stratasys Dimension 3D printer.

Manufacturing and assembling each component of a Koenigsegg is very labour intensive, as more than 300 carbon fibre parts make up each high-tech supercar. The best method of designing a new car is to test the parts virtually and as true-to-life prototypes. By testing throughout the development cycle, designers can determine which designs yield the best possible results.

The team of six starts the development process by designing each individual part via CAD. They then 'print' a high-density plastic model of each component to carry out physical tests. If changes are required, they can be made manually and then scanned from the altered model component. This scan is then used to make a new CAD model, which can be printed again for further testing.

Previously, Koenigsegg outsourced the 3D printing of its prototypes to a service bureau. This proved disruptive to the process, and typically added days to the cycle. The company needed to speed up its prototyping in order to evaluate different versions of a design faster and more effectively.

After evaluating all printers available on the market and judging each one on performance, available materials, price and size, Koenigsegg purchased a Dimension SST 1200es printer. The printer can be used for tooling, fixtures and studies on component mountability and serviceability. Prototype parts produced can also be used as working parts in the end product.

'Dimension was an obvious choice for us, as it not only allows us to modify and print prototypes quickly but also provides us with the option to use them as parts in our cars,' says Koenigsegg.

'The process of printing prototypes on site and testing each component has speeded up the development of the car design by an estimated 20 per cent. The turnaround time for getting a component right in terms of design has decreased enormously – it now only takes a few days instead of a number of weeks. Our designers and engineers can quickly establish a part's suitability for the supercar without stifling their creative flow.'

The 3D printer has aided in the design of Koenigsegg's latest model, the Agera. Printing and testing prototypes for the air inlets assisted Koenigsegg's engineers in developing a supercar with a staggering torque of 920Nm at 5,000rpm.

Bridging to high-volume production

Additive manufacturing can be economical for small volumes, but a related discipline – rapid prototyping – can also be deployed to bridge manufacturers over to larger volume runs where traditional techniques would normally be more competitive. For instance, polymer specialist Igus has developed a new tooling method for injection moulding which can get custom-designed bearing parts delivered in under 24 hours.

As there are no minimum order quantities, 'Speedigus' is suitable for one-offs, prototyping, low volumes and bridge tooling, argues Matt Aldridge of igus UK. 'Standard tool manufacture can take four to eight weeks and is normally only available for minimum orders of around 5,000 pieces but with Speedigus you can get a single part in just one day,' he says.

The majority of Speedigus parts manufactured to date are custom-design components that have a bearing function, such as a small roller in a photocopier, for example. For orders up to a few thousand parts, prototypes or one-offs, speedigus can accommodate parts that fit into an envelope up to 475 x 750 x 200mm, with wall thicknesses down to 0.5mm. All that is required for a quotation is a 3D CAD file (preferably a STEP file), and the required quantity.

Standard Speedigus tooling lead time is 15 days from placement of order, but parts can be produced in as little as 24 hours. If production should move to high volumes, then Igus manufactures a standard production tool, and unit costs reduce considerably.

'Polymer bearings would not go into car engines, but could be used in a throttle linkage or exhaust manifold control for example, at temperatures up to 250°C,' explains Aldridge.

'From a 3D CAD file we manufacture an aluminium tool for prototyping and small volume production in as little as one day, so we are moulding a part cheaply when compared with normal tools. With additive manufacturing, you are making products that look the same but with a material that may functionally be quite different from that used in volume production.

'With Speedigus you get a prototype part made out of the same material and the same process as the production part, so testing is more reliable. In terms of volume, we offer machined parts as well. We would machine anything up to 50 pieces because it is quicker and cheaper. Between 50 and 5,000 pieces we offer speedigus, and for anything above, it is worth investing in a standard moulding tool, which we can also provide.

'In terms of turnover, Speedigus is a small but growing part of our business but the point is that because of Speedigus, we have managed to secure high volume orders where we make a standard Igus moulding tool.'

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