R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

96 Medical modelling
5.27 CNC machined foam model of the soft tissue of the hip.
Table 5.9 Advantages and disadvantages of CNC
Advantages Disadvantages
Very wide range of machine size and Pre-processing time consuming
cost
Very wide range of materials Set up time
Clean, safe materials Clamping the part during cutting
Good for large, thick, simple models Poor for thin walls and small features
Good accuracy possible Poor for internal detail, hollow parts or
undercuts
based on CAD data. Depending on the machine and material confi guration,
CNC allows complex forms to be machined rapidly and accurately.
The characteristics of machining make their use in medical modelling
particularly suitable to producing larger models of the external anatomical
topography. Typical applications may be for moulds and formers or custom
fi tting supports and wearable devices.
The artifi cial hip model shown in Fig. 5.27 was made to replicate the
human body in impact testing of hip protection devices for the elderly. The
model is made of dense, closed-cell foam and shaped using CNC machining
to replicate not only the external anatomical topography but also an internal
pocket in which an artifi cial femur can be located. The advantages and
disadvantages of CNC are summarised in Table 5.9.