Getting real

Today it is not enough to have dimensionally accurate prototype alloy castings. They need to mechanically simulate production parts in every way. Charles Clarke reports

The modelling and prototyping market is one of those sectors that although constantly evolving, remains fundamentally the same. Today it is heavily influenced by events in the so-called additive fabrication business — which used to be called rapid prototyping (RP) before rapid manufacturing (RM) and rapid tooling (RT) came along.

The stereo-lithography (SL) resin suppliers continue to introduce new materials, and there are new machines and processes being developed — but the inescapable fact is that today some kind of RP technology is involved in almost every modelling or prototyping project.

During the past 15 years Hanman Advanced Casting of Gloucester has refined its process to achieve what it feels is excellent repeatability and accuracy in castings. This proved particularly important for the Dyson Airblade hand dryer project. Following trials with other processes, Dyson approached Hanman in an effort to meet its exacting needs.

Hanman’s process involves the production of an accurate SL model, which is then used to create a soft polymer tool. According to the company, this is the most important part of the process, as any deviation would mean additional post machining of the part. In this way, speed and process control helps to eliminate distortion from the part.

Once the tooling process is complete ceramic moulds are produced. This particular part of the project proved a real challenge for Hanman due to the size of the parts. However, the company overcame this by introducing an extended drying cycle so that once the moulds were dry the molten alloy was poured into them and left to cool. Dyson’s parts were then cleaned and powder coated.

Dyson is just one of many clients that now demand fully-functional prototypes. They must be as close to the production item as possible in terms of accuracy, density, strength and surface quality for the parts to be properly tested and used for field trials rather than just used for fit-and-function tests.

Hundreds of hours of performance tests were carried out to refine the Airblade and the prototypes were put through extensive durability trials. They were battered repeatedly, had cigarettes stubbed out all over them, stood on, sprayed with chemicals and then exposed to extreme temperature fluctuations.

RT technology comes into its own for components or models that are difficult to produce in any other way. Take, for instance, the wacky, curvy shapes used in modern architectural design. Imagine making the Beijing Olympic stadium out of balsa wood, string and sticky tape.

Hertfordshire company Ogle Models and Prototypes worked with the internationally renowned designer Zaha Hadid and her team when they needed high-quality models of futuristic designs for buildings in Dubai.

Developing these used to take weeks, if not months, to hand-craft every detail. But as technology has improved, so has the efficiency of model making. In fact, it has advanced so far now that an architectural model — even one incorporating the most complex shapes and materials — can now be made in a matter of days.

As time becomes more expensive architectural businesses, like other product design companies, need models produced quickly — but without sacrificing quality. Over the years, Ogle has created stunning models for companies, such as Bentley, Jaguar, Electrolux, Kraft, Virgin and many others.

To create the building models Ogle mainly used the SLA (resin) process, but for the very complex models that required a bit more strength, and where surface finish is not as important, Selective Laser Sintering (SLS) was used utilising powdered nylon 12. Because the process is fully self-supporting, it allows for parts to be built within other parts, with complex geometry that simply could not be made in any other way.

Ogle has a purpose-built paint and finishing department which hand finishes and refines all of the models. Hand finishing ensures 100 per cent accuracy and Ogle has a range of colour and textured finishes, which can be used to create the perfect model.

Using technology over traditional architectural model-making methods is cost-effective as the time taken is reduced. However, just because it’s fast, doesn’t make it any less impressive.

Accuracy and detail are increasingly important today — particularly to Hornby, owner of the Scalextric brand. This need for detail makes a 3D Systems Viper SLA machine — which builds to an accuracy of 0.05mm — ideal for creating such prototype parts. The accuracy of the Viper and the build style and geometry employed by AME Prototype Solutions of South Yorkshire enabled the production of several SLA models made to an extremely tight tolerance.

AME was the first in the UK (and probably in Europe) to adopt the higher-resolution Viper machine.

This allows the company to close the gap between prototype parts and the finished product, which reduces the level of risk for the client and provides tangible reassurance regarding product viability.

Time-to-market is always an issue in prototyping. To accommodate tight timescales the workshop at AME is run on a two-shift basis, with staff on-site from 6am through to 12 every day. This means that while it has its in-house plant permanently running at capacity (24 hours a day, 365 days a year), the post processing work is also handled in a similar manner.

Business manager Tim Wragg explained how he perceives the dual shift benefiting the customer. ‘The advantages of the shift-system we operate become particularly noticeable at times when we need to go the extra mile for a client’s project. The ability to be flexible is so important because it allows us to react to new information quicker than other prototyping specialists might be able to. Whether it’s an addition to a job, rectifying a problem, or simply an additional piece of new business.’

When the prototypers are busy, that means that the product designers are too, which usually means the economy is on the up — and long may it continue.