Computer Numerical Controlled Grinding and Physical Vapor Deposition for Fused Deposition Modelled Workpieces

he use of additive manufacturing (AM) enables companies to directly produce complex end-use parts. Fused deposition modelling (FDM) is an AM technology based on an extrusion process of fabricating parts. This layer-by-layer method results in a poor surface finish, and as a result, manual finishing is often required, which consequentially reduces the definition of the geometrical features. This research proposes a novel way of achieving high surface finishing by using additive and finishing processes, followed by a physical vapor deposition (PVD) coating. Two test pieces were produced, the first one was subjected to computer numerical controlled (CNC) mechanical grinding with appropriate grades of grindstones; the second one was subjected to microsandblasting to remove excess material and the stair-stepping effect. Both test pieces were then subjected to a PVD coating process to provide a metal thin film. To benchmark the test pieces, the authors used a coordinate measure machine for dimensions and a roughness meter to verify the effectiveness of this postprocessing approach

Photogrammetric measurement of 3D freeform millimetre-sized objects with micro features: an experimental validation of the close-range camera calibration model for narrow angles of view

The measurement of millimetre and micro-scale features is performed by high-cost systems based on technologies with narrow working ranges to accurately control the position of the sensors. Photogrammetry would lower the costs of 3D inspection of micro-features and would be applicable to the inspection of non-removable micro parts of large objects too. Unfortunately, the behaviour of photogrammetry is not known when photogrammetry is applied to micro-features. In this paper, the authors address these issues towards the application of digital closerange photogrammetry (DCRP) to the micro-scale, taking into account that in literature there are research papers stating that an angle of view (AOV) around 10° is the lower limit to the application of the traditional pinhole close-range calibration model (CRCM), which is the basis of DCRP. At first a general calibration procedure is introduced, with the aid of an open-source software library, to calibrate narrow AOV cameras with the CRCM. Subsequently the procedure is validated using a reflex camera with a 60mm macro lens, equipped with extension tubes (20 and 32mm) achieving magnification of up to 2 times approximately, to verify literature findings with experimental photogrammetric 3D measurements of millimetresized objects with micro-features. The limitation experienced by the laser printing technology, used to produce the bi-dimensional pattern on common paper, has been overcome using an accurate pattern manufactured with a photolithographic process. The results of the experimental activity prove that the CRCM is valid for AOVs down to 3.4° and that DCRP results are comparable with the results of existing and more expensive commercial techniques.Percoco, G.; Sánchez Salmerón, AJ. (2015). Photogrammetric measurement of 3D freeform millimetre-sized objects with micro features: an experimental validation of the close-range camera calibration model for narrow angles of view. Measurement Science and Technology. 26(9):1-9. doi:10.1088/0957-0233/26/9/095203S19269Mitchell, H. L., Kniest, H. T., & Won‐Jin, O. (1999). Digital Photogrammetry and Microscope Photographs. The Photogrammetric Record, 16(94), 695-704. doi:10.1111/0031-868x.00148Chen, Z., Liao, H., & Zhang, X. (2014). Telecentric stereo micro-vision system: Calibration method and experiments. Optics and Lasers in Engineering, 57, 82-92. doi:10.1016/j.optlaseng.2014.01.021Stamatopoulos, C., & Fraser, C. S. (2011). Calibration of long focal length cameras in close range photogrammetry. The Photogrammetric Record, 26(135), 339-360. doi:10.1111/j.1477-9730.2011.00648.xYang, X., & Fang, S. (2014). Effect of field of view on the accuracy of camera calibration. Optik, 125(2), 844-849. doi:10.1016/j.ijleo.2013.07.089Strobl, K. H., Sepp, W., & Hirzinger, G. (2009). On the issue of camera calibration with narrow angular field of view. 2009 IEEE/RSJ International Conference on Intelligent Robots and Systems. doi:10.1109/iros.2009.5354776Ricolfe-Viala, C., & Sanchez-Salmeron, A.-J. (2010). Lens distortion models evaluation. Applied Optics, 49(30), 5914. doi:10.1364/ao.49.005914Ricolfe-Viala, C., Sanchez-Salmeron, A.-J., & Valera, A. (2013). Efficient Lens Distortion Correction for Decoupling in Calibration of Wide Angle Lens Cameras. IEEE Sensors Journal, 13(2), 854-863. doi:10.1109/jsen.2012.2229704Zhang, Z. (2000). A flexible new technique for camera calibration. IEEE Transactions on Pattern Analysis and Machine Intelligence, 22(11), 1330-1334. doi:10.1109/34.888718Percoco, G., Lavecchia, F., & Salmerón, A. J. S. (2015). Preliminary Study on the 3D Digitization of Millimeter Scale Products by Means of Photogrammetry. Procedia CIRP, 33, 257-262. doi:10.1016/j.procir.2015.06.046Ricolfe-Viala, C., & Sanchez-Salmeron, A.-J. (2011). Camera calibration under optimal conditions. Optics Express, 19(11), 10769. doi:10.1364/oe.19.010769Guidi, G. (2013). Metrological characterization of 3D imaging devices. Videometrics, Range Imaging, and Applications XII; and Automated Visual Inspection. doi:10.1117/12.2021037Herráez, J., Martínez-Llario, J., Coll, E., Rodríguez, J., & Martin, M. T. (2013). Design and calibration of a 3D modeling system by videogrammetry. Measurement Science and Technology, 24(3), 035001. doi:10.1088/0957-0233/24/3/03500

Analytical model to predict the extrusion force as a function of the layer height, in extrusion based 3D printing

Fused Filament Fabrication is the most widespread 3D printing process, and issues such as improving accuracy and speed are significant areas of research. To better understand and foresee the process, accurate models would be very useful. Several analytical models have been proposed in the literature; however, while the behavior inside the print core has been investigated, to the best of the authors’ knowledge, no studies are reported on the behavior of the melt filament downstream of the nozzle. This lack of research is very important, since the behavior downstream of the nozzle is influenced by the counterpressure generated by the deposited material. Qualitatively, the lower the layer height, the higher the counterpressure should be, while the higher the printing speed, the lower the counterpressure. No such models are available in the literature that take these phenomena into account, and such a model would help in managing the printing process when low layer height is required for improving the accuracy and roughness of the part. In the present study, a new analytical model was developed to compute the minimum force necessary to push the filament into the extruder according to given values of printing process parameters. The model considers both the contribution of the extrusion force and of the deposition force, allowing the prediction of the variation of the required pushing force when variations of the layer height occur and can be a useful tool in the design of process parameters when very accurate components are needed in the process of additive manufacturing (AM)

Left Ventricular aneurysm as very low complication of myocardial contusion in an athlete.

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