Preliminary study on residual stress in FDM parts

The Fused Deposition Modelling (FDM) is nowadays one of the most widespread techniques for 3D object rapid prototyping. In recent years, the FDM evolved from rapid prototyping technique towards a rapid manufacturing method, changing the main purpose in producing finished components ready for use. However, as the parts are built as a layer-bylayer deposition of a feedstock wire, the FDM technique shows, during the building process, distortion and de-layering problems. This issue influences the shape and the final dimensions of the parts or it can prevent the finalization of the objects due to unsticking problems from the bed. Several techniques can be employed in order to obtain parts of correct shape and dimensions. Many of these, such as depositing glue on the bed, aim to constrain the object. As a consequence, the FDM parts could show residual strain and residual stress that could influence their mechanical behaviour. The aim of this work is to measure, by ESPI technique, the displacements around a hole drilled into the material. This can be considered as a preliminary indication of the level of residual stress inside the FDM parts.