Rapid progress

Once the preserve of design visualisation and simulation, rapid prototyping techniques could soon be used for desktop manufacturing. Charles Clarke explains.

Rapid prototyping techniques were once used for only design visualisation, ergonomic studies, basic design simulation and testing. With the introduction of new metallic materials, rapid manufacturing and desktop manufacturing is now a real possibility.

German factory and process automation supplier Festo, for example, has been using rapid prototyping (RP) technology for a number of years. The company’s prototyping department relied on a technique called laser melting to produce a series of mechanical stops for its rodless slide-drive DGC pneumatic linear actuator.

With this method, a laser beam melts a fine powder of stainless steel or hot work tool steel layer-by-layer until the finished component is left on the material substrate.

The prototypes of the stops, which transmit the kinetic energy of the piston to the shock absorber, performed 30 million dynamic load cycles in continuous operation. This corresponds to an operating distance of around 18,000km. To put it another way, this is equivalent to the parts receiving an impact of 400N every 1.25 seconds for a year and a half over a distance stretching between Germany and New Zealand.

Not a single stop failed during the continuous loading. Initial sampling using conventional methods would have taken a number of months, but advanced prototyping in the form of laser melting reduced the construction time to 3.5 to 4.5 hours/item. Furthermore, it cut the time to market of the whole DGC project by 25 per cent.

By providing visual and functional samples as well as testing new bench-scale manufacturing methods, advanced prototyping is not only driving research and development at Festo.

The samples are also used for marketing at trade fairs, in sales training courses and market studies, while advanced prototyping also provides support in production planning. From a customer perspective, the rapidly created samples help to visualise possible solutions and act as a selection aid.

RP in metals is what CRDM, the UK’s leading direct metal laser sintering (DMLS) service provider, does best. It has just taken delivery of its second EOSINT M 270 system. As well as operating with the standard nickel-bronze and mild steel, the M 270 gives CRDM the capability of offering two new materials; stainless steel and the nickel-free Cobalt Chrome MP1.

These new 100 per cent dense materials are both corrosive resistant and sterilisable. The MP1 fully meets the requirements for cast cobalt-chromium-molybdenum (CoCrMo) implant alloys, as well as the requirements for wrought CoCrMo implants, and manufactured components typically come within +/-0.05mm tolerance.

Like Festo the DMLS process has been successfully used by CRDM for the manufacture of injection-moulding and pressure die-cast tooling where traditional tool-making methods would be too costly and time-consuming to achieve the desired geometry.

This is also important outside the manufacturing industry. Now that 3D CAD is breaking through into architecture, architects and building designers are beginning to use RP techniques to validate their designs and to help produce architectural models.

At the recent SmartGeometry 2008 Conference sponsored by Bentley Systems there was an EOS laser sintering system producing building geometry that would be almost impossible to produce by hand. And why would anyone want to when there is a perfectly useable 3D solid model available and a 3D hard copy just a couple of mouse clicks away?

The 3D models were developed using Bentley Systems’ GenerativeComponents software, which enables architects and engineers to achieve detailed design of free building forms that were only ever previously conceived in science fiction renderings. GenerativeComponents is a unique parametric design tool that links to advanced manufacturing technology allowing new forms of architectural and structural expression which are changing the world of the built environment radically.

The software is integrated with building information modelling, analysis and simulation software, providing feedback on building materials, assemblies, systems performance and environmental conditions. This integration also ensures that intent becomes reality by enabling designs to accurately and efficiently flow through to detailed production and fabrication.

Ogle Models and Prototypes has a more traditional approach to modelling and prototyping. It was asked recently by Nissan, to produce a new concept hardtop convertible based on the Micra for the Frankfurt motor show.

The creation involved new front and rear bumpers and sills, plus re-trimming and painting of existing parts. For the creation of the new parts Ogle was given the full surface data by Nissan. Nissan Design Europe (NDE) supplied Ogle with a donor vehicle, along with new mirrored glass and lamp parts and Ogle worked on the interior and exterior.

It had to shape new sill parts and produce new front and rear bumpers, and the exterior was painted in a high-quality show-car finish as specified by the NDE colour studio. Ogle re-finished unassembled production parts for the headlamps and tail-lamps and made two alternative sets of wheels. One set was for the show for static viewing only, while the other set was made robust enough for tyres to be fitted and for the car to be driven safely at speeds up to 30mph.

To complete the interior Ogle had to re-trim the instrument panel front pad, door-trims, steering-wheel and seats. It also fitted new fully-functional seat belts, and various miscellaneous vents, buttons, gearshift-knob and handbrake were re-finished to match.

In contrast Paragon Rapid Technologies was approached by London-based TV and special effects modelmaker, Asylum, to produce vacuum castings of a small fully poseable character for the recent Sony Ericsson advertising campaign. The model was first built as a stereo-lithography model from supplied CAD data, before producing silicone tools and pigmented polyurethane (PU) castings.

The benefits of silicone prototypes are that the material is not just similar to production materials, but in many cases it is exactly like them.

In most cases the mechanical properties of silicone are far superior to PU rubber, having greater elasticity, tear strength and thermal stability, but in addition many of the grades available are suitable for medical applications.

Paragon has developed a variety of tooling and moulding procedures, which can be tailored to each specific project allowing the manufacture of complex geometries as one-offs or for low-volume applications.

The company is able to create multi-shot rubber parts in multiple colours and also two-shot moulding of rigid components with silicone overmoulded elements. Recent projects have included gloves for prosthetic hands, complex silicone seals for the food industry, overmoulded baby soothers, respirator masks, silicone gaskets and an innovative bath mat.