Abstract:
Rapid prototyping techniques are quickly advancing to become market leading
manufacturing techniques in terms of: product availability, cost effectiveness and
environmental impact. In addition, they are also rendering many traditional
manufacturing techniques, still employed by small manufacturers or crafters, obsolete.
In an attempt to create an even more sustainable rapid prototyping technique, that is
cheaper and simpler to construct, the concept of a prototype three-dimensional (3D)
printer, that uses concentrated solar power to sinter a salt, which acts as calibrant, has
been developed. In order to test and calibrate this prototype, a thermodynamic model
was developed to predict thermal properties of mixtures of materials. These, and
conventional materials, were subsequently tested on a constructed prototype printer.
The thermodynamic model was found to be able to make reasonably accurate
predictions, with average errors of 12 % for the eutectic temperature and 30.6 % for
the latent heat of fusion. Based on these results a eutectic mixture of KNO3 and NaNO3
was selected for testing as this mixture has thermal properties very similar to those of
Nylon used in commercial SLS applications. Printing tests were conducted using a
mirror utilising two axis control to collimate sunlight and a Fresnel lens to concentrate
it. The printing process was analysed and, through application of a dimensional
analysis, a basic control philosophy for this process was developed. This control
scheme was able to control the sintered depth well, displaying an average error of only
2.4 %.
The current work established basic principles for the process of rapid prototyping using
concentrated solar power. The developed methods are able to predict the influence of
environmental effects on the process. However, a low resolution due to a large spot
size and warping of polymer parts currently limit its applicability. It is recommended
that further investigation into these aspects is conducted.
