Characterisation of a prototype solar three-dimensional printer

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.