Rapid prototyping, in its different forms, is now widely used for both aesthetic and functional assessments, and today’s 3D printers are sufficiently accurate and affordable that companies can justify having one (or more) in their design offices. But rapid manufacturing has been rather slower to become widely accepted, even though there were early adopters that made excellent use of the systems that were available, particularly for investment casting (also known as ‘lost wax’ casting).

In the last year or so, however, more and better rapid manufacturing equipment and materials have become available, and industrial users are increasingly taking advantage of the benefits available, including reduced time, simpler customisation, and lower costs.

BMW has adopted rapid manufacturing not for vehicle components but for jigs and fixtures used during assembly and test operations. Compared with traditional items machined from aluminium and polyamide, jigs and fixtures built from ABS using fused deposition modelling (FDM) are much lighter and can have ergonomically superior forms. Not only is the lower weight beneficial to the user, but it is easier for the designer to ensure that the jig or fixture has a centre of gravity that makes it easier to manipulate, and handles that are more comfortable to use.

The FDM technique enables parts to be built with an internal matrix and voids to save weight. Although this results in some loss of strength and stiffness compared with machined aluminium and polyamide, the end result is adequate for the part’s function.

Machining an ergonomic form – such as a handle – from solid can be costly and time-consuming. By using rapid manufacturing, however, virtually any shape can be built directly from the CAD model, with no additional expense associated with more complex three-dimensional forms. Rapid manufacturing can also create hollow parts – such as tubular components – that would be difficult or costly to machine from solid.

For this type of application, FDM provides the necessary accuracy (±0.1mm) and parts made this way can withstand the temperatures in the automotive assembly environment. Chemical resistance, strength and stiffness are also adequate, and the improved ergonomics of the jigs and fixtures delivers a direct benefit to the production line workers and, therefore, productivity. For this type of application, costs are comparable with traditional manufacturing techniques, so the main benefit remains the improved ergonomics.

Sand casting

Stratasys, which manufactures FDM machines such as that used by BMW, also reports that its machines are being used to create patterns for use in sand casting. Whereas a traditional sand casting would first require a pattern to be manufactured from wood or aluminium, it is possible to use FDM to create the pattern directly form the CAD model. Materials used in the FDM machines for this application include acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), an ABS-PC blend or polyphenolsulfone (PPSF/PPSU). It is said that using FDM can reduce lead times from weeks to days and can save hundreds of euros per pattern. Furthermore, because the rapid-manufactured pattern is then used in exactly the same sand casting process as a wood or aluminium pattern, any of the traditional materials can be used for the casting, including cast iron, steel, aluminium, brass or bronze.

In a similar approach to that above, Stratasys says its TitanFDM machines (Fig.1) are also being used to create patterns for vacuum forming components from a wide variety of plastic materials, including ABS, PC, polyethylene, acrylic and thermoplastic elastomers. For FDM tooling, ABS, PC and PPSF/PPSU can all be used, though tool life is inferior to that of tools machined from aluminium. Nevertheless, the FDM materials are adequate for short production runs of 100 to 1000 items.

Both time and cost can be saved in comparison with CNC machined aluminium tools, and it is possible to modify the build parameters to make the tool porous in defined areas, which eliminates the need to drill vent holes and gives a more uniform vacuum draw across the surface of the tool, thereby achieving better part quality.

Another company that produces equipment and materials suitable for rapid manufacturing is 3D Systems. Its Quickcast technique creates patters for use in investment casting and the company claims that lead times can be reduced by as much as 80 per cent compared with traditional investment casting processes. Instead of creating tooling to injection mould wax patterns, the Quickcast stereolithography method builds patterns directly from 3D CAD data. 3D Systems says Quickcast has been proven with parts cast from aluminium, stainless steel, tool steel, magnesium, titanium, and copper-, nickel- and cobalt-based alloys.

Unlike stereolithography models built for prototyping, which might have a shell and an internal supporting structure, Quickcast builds the models with an internal ‘honeycomb’ structure that minimises the mass and, therefore, the amount of material that has to be burnt out during casting.

Rapid convergence

Quickcast is effectively a special variation of 3D Systems’ stereolithography rapid prototyping technology, but the recent development of tougher materials means that rapid prototyping and rapid manufacturing are starting to converge. For example, 3D Systems’ Accura Xtreme Plastic material can either be used to create prototypes with improved functionality and durability, or it can be used to replace production components moulded from ABS and polypropylene (PP). To illustrate the way rapid prototyping and manufacturing are converging, in 2006 a survey showed that 42percent of Stratasys machine owners said they use rapid prototyping system for at least some manufacturing of end-use parts (Fig.2).

3D Systems has also targeted a niche market where the need is to build truly customised components. Working in partnership with Dreve Otoplastik, 3D Systems has developed a compact, fast, low-cost hearing aid manufacturing system based on its new Film Transfer Imaging (FTI) technology. Known as the V-FlashHA230 Desktop Manufacturing System, the equipment builds high-quality, three-dimensional hearing aid shells within hours, enabling hearing aid manufacturers to build products that perfectly match patients’ ears.

Powder sintering is another technology where rapid prototyping and manufacturing are converging. 3D Systems’ Sinterstation Pro and Sinterstation HiQ machines, for example, use selective laser sintering to build prototypes and production parts in Duraform plastics and Laserform metals. Duraform materials suitable for rapid manufacturing include grades PA (polyamide), GF (glass-filled polyamide), EX (offering the toughness of injection-moulded polypropylene and ABS), Flex Plastic (thermoplastic elastomer) and AF (polyamide with an aluminium filler). Laserform metals are available in three grades, A6 (steel), ST-200 (stainless steel with properties similar to P20 grade tool steel) and ST-100 (stainless steel with properties similar to C35 grade tool steel). These three steels are all aimed primarily at the production of injection mould tools and tooling inserts.

Directtool is the name used by EOS for its Direct Metal Laser-Sintering (DMLS) process when applied to tooling, and Directpart the name used for end products manufactured this way. One example of the type of parts manufactured this way is prostheses sintered from a biocompatible alloy.

EOS has also successfully applied laser sintering technology to the direct production of sand cores and moulds for casting parts in aluminium and magnesium – and potentially cast iron and steel too. Specially optimised sands are used in the laser sintering machine to produce cores and moulds in what EOS calls the Directcast process. The company says this is suitable for building highly complex, detailed sand cores and moulds for premium castings in series quality, with a building speed of up to 2500 cm3/h.

Aerospace application

Of course, EOS also has machines and materials capable of building production parts from plastics. One interesting recent development has been the release of PA2210FR, a material that is certified and accredited by independent laboratories complying with regulations relating to flammability, smoke generation and smoke toxicity. As a result, the material is suitable even for aerospace applications. Paramount PDS, a product development and rapid manufacturing company in the USA, has used this material to manufacture flight hardware components for commercial luxury aircraft, enabling the aircraft company to slash production lead times and eliminated tooling costs (Fig.3). Furthermore, applying rapid manufacturing techniques gave the designers the freedom to create components with more complex forms than would have been possible had traditional production methods been used.

As proof of its rapid manufacturing capability, EOS has incorporated 23 laser-sintered parts in the FormigaP100 machine that it presented at the 2007 Hannover Messe, including the filling hopper for the plastic powder, the switch cover and several pyrometer elements.

Swedish company Arcam has recently introduced a larger machine for rapid manufacturing in metal, based on its electron beam melting (EBM) technology. With a choice of two build tanks (200x200x350mm or 300mm diameter by 200mm high), the new ArcamA2 is capable of building parts 75percent larger than the previous EBMS12 machine.

Many of the EBM S12 machines are being used to manufacture medical implants, but it is hoped that the Arcam A2 will enable the company to penetrate the aerospace, motorsport and general engineering industries. Arcam currently offers Ti6Al4V, Ti6Al4V ELI and ASTMF75CoCr materials, and the fast EBM process creates parts with material properties that are comparable to wrought parts. Moreover, the company says that its machines can produce titanium components with material properties that are better than cast titanium, making the ArcamA2 a viable proposition for manufacturing aircraft components.

At the International Rapid Manufacturing Conference, held at Loughborough University, UK, in July 2007, CRP Technology presented a case study ‘Turning point in the creation of racing engines: structural parts made by laser sintering’. The paper explained how Ilmor and CRP Technology are implementing rapid manufacturing in four-stroke MotoGP engine development. Besides the numerous non-structural parts manufactured by selective laser sintering that can be found in the Ilmor engine, the major innovation is the camshaft cover. This is a structural part that supports the camshaft bearings (spinning at 19,000rpm) and that is mounted directly on the cylinder head of the four-stroke 800cc engine, whose average working temperature is about 130-140°C (Fig.4). The aim is to use selective laser sintering to reduce the weight of the camshaft cover and increase its reliability. In addition, rapid manufacturing will enable modifications to be completed faster – so that some features can even be changed mid-season.

Given some of the current applications for rapid manufacturing – such as surgical implants, aerospace components, and structural parts for motorsport applications – it can be seen that rapid manufacturing has now matured. Whereas designers tended in the past to view it as ‘someone else’s technology’, it is now something that should be considered far more widely.