Material extrusion based additive manufacturing is used to make three dimensional parts by means of layer-upon-layer deposition. There is a growing variety of polymers that can be processed with material extrusion. Thermoplastic polyurethanes allow manufacturing flexible parts that can be used in soft robotics, wearables and flexible electronics applications. Moreover, these flexible materials also present a certain degree of viscoelasticity. One of the main drawbacks of material extrusion is that decisions related to specific manufacturing configurations, such as the inner-structure design, shall affect the final mechanical behaviour of the flexible part. In this study, the influence of inner-structure design factors upon the viscoelastic relaxation modulus, E(t), of polyurethane parts is firstly analysed. The obtained results indicate that wall thickness has a higher influence upon E(t) than other inner-design factors. Moreover, an inadequate combination of those factors could reduce E(t) to a small fraction of that expected for an equivalent moulded part. Next, a viscoelastic material model is proposed and implemented using finite element modelling. This model is based on a generalized Maxwell model and contemplates the inner-structure design. The results show the viability of this approach to model the mechanical behaviour of parts manufactured with material extrusion additive manufacturing.

Industrial adoption of additive manufacturing (AM) processes demands improvement in the geometrical accuracy of manufactured parts. One key achievement would be to ensure that manufactured layer contours match the correspondent theoretical profiles, which would require integration of on-machine measurement devices capable of digitizing individual layers. Flatbed scanners should be considered as serious candidates, since they can achieve high scanning speeds at low prices. Nevertheless, image deformation phenomena reduce their suitability as two-dimensional verification devices. In this work, the possibilities of using flatbed scanners for AM contour verification are investigated. Image distortion errors are characterized and discussed and special attention is paid to the plication effect caused by contact imaging sensor (CIS) scanners. To compensate this phenomena, a new local distortion adjustment (LDA) method is proposed and its distortion correction capabilities are evaluated upon actual layer contours manufactured on a fused filament fabrication (FFF) machine. This proposed method is also compared to conventional global distortion adjustment (GDA). Results reveal quasi-systematic deformations of the images which could be minimized by means of distortion correction. Nevertheless, the irregular nature of such a distortion and the superposition of different errors penalize the use of GDA, to the point that it should not be used with CIS scanners. Conclusions indicate that LDA-based correction would enable the use of flatbed scanners in AM for on-machine verification tasks.

Laser triangulation systems (LTS) are one of the most popular non-contact inspection techniques. These systems are widely used in reverse engineering tasks as they allow for a fast acquisition of thousands of points that represent the geometry of the part in a virtual 3D model. The accuracy and repeatability of these systems are lower than the traditional contact inspection techniques, as they depend on the surface properties, the illumination conditions and the LTS configuration. Present work deals with the influence of surface material on the quality of the virtual model. The objective is to evaluate the behaviour of different materials and their suitability for being digitized.

Accessibility analysis represents one of the most critical tasks in inspection planning. This analysis determines those probe orientations that can touch an inspection point without collision. This paper presents a methodology based on part discretization and the application of space partitioning techniques (kd-tree) in order to reduce the number of intersection tests between probe and part. A STL model has been used for discretizing the inspection part in a set of triangles, which permits the application of the developed system to any type of part, regardless of its shape and its complexity. Likewise, a recursive ray traversal algorithm has been used in order to speed up the traversal of the kd-tree hierarchical structure and to calculate exclusively the intersection of each probe orientation with those part triangles that can potentially interfere with it. In a further step of the analysis, the real geometry of the probe has been considered. Hence, a simplified model has been developed for each probe component (column, head, touch probe, stylus and tip) using different basic geometrical shapes. Finally, collision-free probe orientations are clustered for minimizing the orientation changes during the inspection process. Furthermore, the applied algorithm allows for determining different valid combinations of clusters. The developed system was applied to two example parts in order to prove that this methodology is adequate for the solution of real cases.