Investigation about dimensional accuracy, shrinkage and distortion in Selective Laser Sintering

Selective Laser Sintering is one of the many technologies that can be applied when is wanted to print something in 3D. This additive manufacturing process is not only used for rapid prototyping but as well for final goods, so the quality of the piece is very important. The aim is to analyze the dimensional tolerances of different prototypes printed using the selective laser sintering technology, employing a benchmark process, comparing the dimensions of the geometries as well as their measures, by means of the IT Grades and the ISO basic sizes. Many geometries were studied: cylinders, cones, planes, tilted planes, angular planes, polygons, etc. in order to get for each of them, the best position, horizontally or vertically, and if it is better to be in the bottom, in the middle or in the top of the building volume of the Formiga velocis P110. On top of that, by using the software “MiniMagics”, is obtained the final triangulation of the CAD, called the STL file, that is downloaded into the printer, so the final tolerances given by the printed sample, will need the subtraction of the possible errors present already in the triangulation. Overall, horizontally printed samples show a better behavior for all vertical features, and vertically printed ones are better for horizontal geometries. The found differences in the same height of the building volume are due to a non-constant heat distribution, so the scale factor, actually, should not be constant neither. The non-homogeneous heat diffusion is then, a key factor to get better tolerances and less shrinkage.