R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

Physical reproduction 85
In medical modelling terms, LS models prove useful but perhaps not
ideal. LS models offer reasonable accuracy and surface fi nish and would be
comparable to FDM TM models. The strength and toughness of the models
is a defi nite advantage, but the powder nature of the material leads to a
rough surface, which can trap dirt and grease in handling. This, together
with the porosity of the models, poses some concerns for sterilisation, especially
if patient contact is being considered. Unused material remains as
loose powder so it can be removed from internal spaces and voids, although
this may sometimes be diffi cult. The advantages and disadvantages of LS
are summarised in Table 5.4.
5.5.3 Selective Laser Melting (SLM TM ) and Direct Metal
Laser Sintering (DMLS ® )
SLM TM , the technology behind the MCP Realizer SLM machine (HEK
GmbH, SLM Tech Center Paderborn, Hauptstrasse 35, 33178 Borchen,
Germany), and DMLS ® (EOS GMBH Electro Optical Systems, Robert-
Stirling-Ring 1, D-82152 Krailling/Munich, Germany) are similar in principle
to LS except that high power solid-state lasers are used to melt very
fi ne metal powders in inert gas atmospheres. The full melting enables the
production of solid, dense metal parts in a single process (i.e. not using
binders or post-process furnace operations that have been previously used
to make metal parts via LS). A variety of metals can be used, including
stainless steels, cobalt-chrome and titanium. These processes are relatively
new and, whilst they are not suited to the production of models of human
anatomy, their potential for producing custom fi tting implants and prostheses
is already evident. Fig. 5.19 shows a mandible made using SLM TM whilst
Fig. 5.20 shows a partial removable denture framework (described in detail
in Section 6.14 Rehabilitation applications case study 7). They also lend
themselves well to the manufacture of custom surgical guides, templates
and instruments, as described in Section 6.6 Surgical application case study
4. The similar Arcam CAD to Metal ® process (Arcam AB (publ.), Krokslätts
Fabriker 30, SE-431 37 Mölndal, Sweden) utilises an electron beam to melt
Table 5.4 Advantages and disadvantages of LS
Advantages Disadvantages
Strong, tough models High cost of machine and materials
Reasonably accurate Large machine, nitrogen supply, water cooling
Wide range of materials Heat up and cool down time
Poor surface fi nish
Materials not suited to sterilisation