R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

250 Medical modelling
This means that they are not recognised by current 3D Systems software
releases. A similar issue can be found when attempting to use SLI fi les
generated by CTM (a module of Mimics, Materialise NV), which are also
not recognised by Lightyear TM . This effectively renders the SLI export
option of CTM redundant unless the user is prepared to maintain and use
Maestro. This is an important point as the ability to move from CT or MR
data directly to the SLI format represents by far the most effi cient route to
a stereolithography build.
Given the fact that Maestro is old software, running on obsolete UNIX
hardware, the SLC fi les took an incredibly long time to prepare (approximately
three days). To reduce the fi le size requirement, four types of model
were prepared in a line that would fi t across the width of the SLA-250 build
platform. Once generated, this vector fi le was then copied four times at the
SLA machine. This method does not increase the size of the vector fi le but
offsets the whole set and repeats it. This enabled us to complete 16 models
without creating an unnecessarily large vector fi le. Even after taking these
steps, the vector fi le was large and the build took approximately 65 hours
using SL5220 resin. A second build was implemented along the same lines
to produce the remaining models of the 25 required.
An example of one of the models with its supporting crate is shown in
Fig. 6.96. Due to the extremely delicate nature of the models, they were
painstakingly hand fi nished using scalpels to remove the supporting structures
without causing damage. This was complicated by the inability to
familiarise the technicians with the models because it is not possible generate
three-dimensional rendered views of SLC data. One of the fi nished
models is shown in Fig. 6.97.
6.15.7 Conclusion
Issues caused by RP software made these items a particular challenge to
the application of stereolithography. The machine operators’ complete
dependence on the preparation software that is supplied with the machine
presents two main reasons behind the diffi culties.
Firstly, as RP develops and improves, the software is increasingly designed
to automate as many functions as possible. This is intended to improve the
ease and speed of use in the commercial environment. However, this
increasing level of automation reduces accessibility to variables and parameters,
removing many options from the expert user, particularly those in
the research community. In this case, typical semi-automated methods for
support generation would have proved utterly impractical for the nature of
these objects.
The second issue is the industry’s concentration on the STL fi le format
and complete neglect of 2 1 / 2D alternatives. As this case in particular shows,