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Considering a simple test part as shown in Fig 3.9, which is a typical thin shell type
part, the curvature of the shell is considered as a geometrical parameter. This is
significant in influencing strength and surface quality of parts, a varying slope of the
surface results in different levels of stair-step effects and continuous fibres, as in the
case of curved layer deposition and might lead to significant improvements over the
flat layer counter parts. The speed of deposition is a process parameter, and could
have significant influence on the part characteristics, as the material processing
scheme in FDM is a thermo-mechanical process. Any new road, immediately after
exiting from the nozzle would be at a relatively high temperature, and as it is
deposited, the temperature drops [33]. Subsequent mechanical behaviour of the
road and its ability to fuse into adjacent roads will depend on the thermal conditions.
The higher the speed of deposition, the better is the sintering process between
adjacent roads, considering a better thermal situation. Normal FDM machines would
have a heated chamber in which the actual deposition takes place, and the envelope
temperature is maintained at above the glass transition temperature. However, in the
present case, the test bed does not support a controlled envelop temperature, and
hence, the speed of deposition becomes a significant parameter. Deposition style,
whether flat or curved any way is the main aspect of interest in the current research,
and is implemented through a proper control of the test bed.
It is finally conceived to analyse the influence of these three fused deposition
modelling parameters with the help of L8 orthogonal array as suggested by Taguchi.
It was also assumed that there is no interaction between the factors considered in
experiments. The final input parameters for the fused deposition modelling with the
test bed are as follows:
Curvature
Speed of deposition
Deposition Style
A brief introduction to Taguchi methods follows next, before presenting the actual
experimental design
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