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Product category: Fast prototyping equipment, pattern-making and services
News Release from: Unimatic Engineers | Subject: Rapid prototyping
Edited by the Manufacturingtalk Editorial Team on 30 August 2006

Looking at the future with rapid
prototyping

The phrase 'rapid prototyping' means different things to different people and has moved away from confusing jargon to well understood definitions and martin Stevens provides an overview.

Rapid prototyping includes many related technologies that are used to create parts or models directly from CAD files Thus once a designer has completed a CAD drawing, a prototype is but a few mouse clicks away

The time saving over traditional prototyping procedures can be huge, especially when the project requires a series of design modification each taking its own time envelope.

Rapid prototyping can reduce 'time to market' of a finished design so much that it provides a competitive advantage for users over non-users.

Legend has it that the technique was developed at NASA.

Desperately short of time and facing a belligerent sub-contract model maker engineers tried filling an inkjet printer with molten wax and driving it with a CAD file.

The idea was that layers of wax would fuse together and build up a solid model.

This story may be apocryphal, but it does illustrate nicely the additive form of rapid prototyping.

There are also subtractive or reductive procedures referred to as rapid prototyping based on CAD and CNC technologies, but most of the growth in the field is with the former.

Currently the global market for rapid prototyping is valued at around $1bn, and it is growing at between 10 and 40% a year.

It should be noted that there are other forms of rapid prototyping, such as stereolithography, selective laser sintering (SLS), fused deposition modelling (FDM), laminated object manufacturing (LOM); but inkjet-based systems and three dimensional printing (3DP) are by far the most popular and the fastest growing.

* More complex models - over the years advances have been made in the techniques and technology of rapid prototyping, so that ever more complex models and prototypes can be produced.

In fact the science is now so well developed that it has spawned 'rapid manufacturing' for production of a range of items direct from CAD data.

These include medical and dental implants, hearing aids and many other solid items of relatively complex shape, such as casings and housing, jewellery and artworks, inserts and spacers that would traditionally be made by cutting or moulding metal or other material.

One of the key developments, brought to market 12 years ago, was the use of a multiple jet printer.

This is capable of laying down two or more different materials.

Often one of the materials is soluble and is laid down in the voids of the model to support the primary material where required, and is dissolved away once the 3D printing stage has been completed.

This technique has made it possible to print very complex and delicate shapes and opened up rapid prototyping to a far wide range of applications.

Ultimately, the materials used in rapid prototyping are limited.

However, the range and properties available are growing and currently include various plastics, waxes, resins, ceramics, metals, and papers.

These are usually adequate for prototyping, but may be limiting in rapid manufacturing, in which case secondary processes will be needed to convert patterns to finished goods.

There are many advantages to rapid prototyping, such as the ease of forming models of great geometric complexity without the need for elaborate machine setup or final assembly.

Inevitably rapid prototyping reduces the construction of complex objects to a manageable, straightforward, and relatively fast process; and the cost is often far lower than using conventional techniques.

But it should also be noted that the dimensional accuracy available with 3D printing (although in the low microns) can be less than is required for precision items, which still have to be made by techniques such as metal cutting, spark erosion and moulding.

As well as reducing the time required to develop a final design, engineers (and other users of rapid prototyping, such as surgeons, architects and artists) have found that it aids communications with others involved in the project, so reduces time spent on aspects such as tooling development, marketing, packaging etc The result is very much faster project completion, which can represent the difference between success and failure in competitive markets.

* Development time reduced - a supreme example of this is that Adidas has slashed its training shoe development time to 30 days from 90, by adopting rapid prototyping on a global scale.

It has implemented a complete digital process that shares 3D data in real time between all its global corporate bases and its contract factories in Asia.

The final piece of this jigsaw was the adoption of Object Geometries PolyJet rapid prototyping technology, which is available in the UK through Unimatic.

The machine adopted by Adidas has a print head consisting of over 1500 nozzles which builds the model-master in a series of micron-thick layers of a special photopolymer resin.

For Adidas, sharing RP models between global design studios is the equivalent of 3D fax.

In fact Adidas has always pioneered rapid prototyping.

Initially this was for design verification, but the quality of PolyJet models has reduced time to market and saved considerable costs because Adidas use them as the masters when vacuum casting parts for production tooling.

Jewellery school Holts of Hatton Garden in London has invested in a Unimatic Solidscape rapid prototyping machine for modelling and rendering students' designs in 3D in wax.

Holts chose the Solidscape for its fantastic surface finish and resolution which give wonderfully detailed results, the defining issue for jewellery.

It can be used to produce wax patterns for prototypes, moulds and even finished items.

The ultra-high resolution of up to 0.0127mm and the fine surface finish eliminate the need for cleaning and polishing prior to casting and enabling the most intricate and delicate of designs to be realised.

Solidscape uses a dual material deposition to produce complex designs with the assurance of results that are geometrically perfect and, in many cases, unable to be produced by hand crafting or machine milling.

Undercuts, overhangs and cavities are no problem because of the dissolvable support material structure.

Design features can be as small as 0.254mm, while the maximum size envelope is 150mm x 150mm x 150mm (6in x 6in x 6in), enabling students to model trophies and ornaments as well as jewellery.

The medical professions have become increasingly reliant upon rapid prototyping.

In one of the most dramatic cases surgeons used the techniques in their preparations for separating conjoined twins.

The twins, Guatemalan girls, were joined at the head, but had separate and complete brains.

However, many of the associated veins were interwoven and connected into each others' circulatory system.

Surgeons at the University of California's Mattel Children's Hospital determined that separation was possible; they had to separate the skulls, reroute the blood supply and plan skin grafts.

In the build up to the operation the team used many, many models produced by Objet's three-dimensional rapid prototyping systems to plan and practice their procedures.

With such comprehensive preparation, the operation was successfully completed in 22h - a marathon for both patients and medics, but a fraction of the 97h that would have been expected had the 3D modelling not be available.

* About the author - Martin Stevens is managing director of Unimatic Engineers. Request a free brochure from Unimatic Engineers ...

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