R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

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developing complementary technologies and acquiring competitors. This
led the US Justice Department to declare that 3D Systems was effectively
in a monopoly situation and they forced the licensing of stereolithography
patents to Sony, who had been producing stereolithography machines for
the domestic Japanese market for many years. It is yet to be seen what
effect this will have on the US RP market.
Meanwhile Stratasys has steadily developed a single technology, fused
deposition modelling, to produce a comprehensive and reliable range of
machines from the cheapest desktop modelling machines to large capacity
functional prototyping machines. Concentration on a single technology and
the ability to sell cheaper machines has sustained the company through the
economic downturn of recent years.
Recent newcomers to the market include Z-Corp (USA), EnvisionTEC
(Germany) and Objet (Israel). Z-Corp produces a range of threedimensional
printing machines using technology licensed from MIT. These
machines are fast and cheap to operate. However, the models are comparatively
less accurate and physically weaker, although newer materials are
being developed to address these issues. The EnvisionTEC machines selectively
cure cross sections of photopolymer utilising digital micro-mirror
devices to project visible light. The Objet machines aim to deliver the cost
effi ciencies of printing technology with the functionality and accuracy of
stereolithography.
Due to the technology-driven nature of RP companies and their products,
the industry is awash with trade names, abbreviations and acronyms
for the various processes, software, hardware and materials. Many of these
are registered or recognised trademarks and these have been indicated
where possible. A glossary of terms can be found in Chapter 8.
The most common RP processes are described later in this chapter. Each
major RP process type is covered in principle and in some detail. Whilst it
is not practical to describe every single aspect of every machine available,
the sections should provide a good overview of the technologies, their pros
and cons and their appropriateness for various medical applications. Further
reading and a list of contact details for the major RP manufacturers and
material suppliers is provided in Chapter 9.
5.1.3 Layer manufacturing
RP systems work by creating models as a series of contours or slices built
in sequence, often referred to as layer manufacturing. The different RP
systems vary in how they create the layers and in what material. By convention,
the axes X and Y represent the plane in which the layers are formed
and the Z-axis is the build direction, usually referred to as the height.
Consequently, the number of layers required for a given object is a function