167 research outputs found
Porosity testing methods for the quality assessment of selective laser melted parts
Get PDFThis study focuses on the comparison of porosity testing methods for the quality assessment of selective laser melted parts. Porosity is regarded as important quality indicator in metal additive manufacturing. Various destructive and non-destructive testing methods are compared, ranging from global to local observation techniques and from quick low-cost to expensive time-consuming analyses. Forty test specimens were produced using five varying control factors. The experimental results show that Archimedes and CT methods compare well, Archimedes can be deployed to inspect parts in small series and CT pre- and post-cut analysis show that post-cut porosity results are systematically highe
Pulsed mode selective laser melting of porous structures: Structural and thermophysical characterization
Get PDFIn this paper, the potential of selective laser melting (SLM) of stainless steel CL 20ES powder was investigated with a focus on controlled fabrication of porous structures with strongly reduced pore sizes, i.e. feature sizes significantly below conventional minimum SLM feature sizes. By controlling laser scan properties interacting with the powder bed directly, porous structures can be generated by selectively sintering powder particles. A wide range of porous samples was manufactured following this strategy, aiming to increase porosity while keeping pore sizes low. The effect of process parameters, including laser power and focal point positioning, was evaluated for a fibre laser operated in pulsed wave (PW) emission mode. The first part of this study focuses on characterization of key porous structure properties, i.e., porosity, average mass density, average pore sizes and structures at microscopic scales. The second part deals with the influence of porosity and pore sizes on thermal and fluid properties, i.e., the effective thermal conductivity (ETC) and wettability. We have quantified the directional dependence (build direction plane and scan direction plane) off the structural and thermophysical properties of porous structures. For a range of porosities and pore sizes, we have observed that porosity and surface morphology influence the thermal properties and contact angle of droplets on the printed surface. Thermal conductivity was measured and the associated analysis was compared with available models and correlations in literature. The average thermal conductivity of fabricated porous structures was determined between 6−14 W/m K and found to be a function of porosity. Furthermore, the capillary wicking performance of additively manufactured stainless steel porous structures having an average pore radius from 9 to 23 μm was determined
Investigation on the Accuracy of CT Porosity Analysis of Additive Manufactured Metallic Parts
Get PDFAdditive manufacturing (AM) is emerging as an important manufacturing sector, due to its almost unlimited design freedom, the capability to produce personalized parts and the efficient material use. A reliable knowledge about material porosity of manufactured parts is crucial for optimizing AM process parameters. Indeed, internal pores can be sometimes desirable, e.g. for biomedical implants and thus obtained intentionally by an appropriate selection of such parameters. However, pores are mostly unwanted defects (e.g. in automotive and aerospace sectors) which appear due to process irregularities. X-ray computed tomography (CT) has become a promising method in the field of porosity analysis. Although metrological CT systems are available today and are used as coordinate measuring systems for performing dimensional measurements, their capability of accurately quantifying pores volume and local distribution is still to be proven. The current work aims at investigating the accuracy of CT porosity analysis of AM metallic parts by means of comparisons with other techniques, including Archimedes method and microscopic analysis of cross-sections. Experiments were conducted on Ti6Al4V tensile specimens produced by selective laser melting (SLM), for which the correlation of internal porosity with mechanical properties is of high interest (e.g. for optimizing AM process parameters). In particular, specific cross sections were selected to compare porosity analyses by CT and by microscopic optical measurements after destructive sectioning. Optical measurements were found to provide systematically larger dimensions of pores in comparison to CT measurements. The same samples were CT scanned before and after the cutting procedure: a significant enlargement of pores diameters was confirmed only for pores in the cut section. Possible causes were identified in the cutting procedure itself and the outflow of entrapped powder. Reference measurements for diameters of pores were obtained by means of a high-accuracy CMM equipped with image processing sensor (MPE = (1.8+L/250) µm, with L in mm). In addition, an aluminum reference object with calibrated hemispherical defects was manufactured by micro-milling at the University of Padova and then used for evaluating the accuracy of CT 3D defect detection
Design for Additive Manufacturing: Automated Build Orientation Selection and Optimization
Get PDFAbstractAdditive manufacturing, or 3D printing, is an emerging type of production technology that is seen as the core technology for future high-value engineered products. Due to the additive nature of stacking and unifying individual layers, the part and process design is substantially different from conventional production methods. This paper addresses one of the challenging design aspects for additive manufacturing, namely the determination of the build orientation. The build orientation has a large impact on the final part quality and must therefore be chosen wisely. This paper presents an approach to support the build orientation selection by a feature-based design algorithm. After automated part tessellation and the detection of outer part surfaces, the algorithm determines candidate build orientations through a ray-tracing and convex hull method. Candidate solutions are ranked based on minimizing overhang structures, as this also minimizes the need for additional support structures
Experimental Performance of a 3D-Printed Hybrid Heat Pipe-Thermosyphon for Cooling of Power Electronics
Get PDFThis paper presents an innovative metal 3D-printed hybrid heat pipe-thermosyphon for cooling of power electronics. This hybrid device has an evaporator design based on heat pipe technology, while the condenser design is based on a thermosyphon. An array of cubic fins is 3D printed on the inner surface of the evaporator bottom plate to enhance capillarity and evaporation rates. The thermal performance of the additively manufactured heat pipe-thermosyphon, fabricated from aluminium alloy, was examined under vertical orientation using acetone as the working fluid. Experiments were conducted to determine thermal resistances of the device by instrumenting thermocouples along the wall. The effects of liquid filling ratio and heat flux were examined. The results show that for a heat flux of 35 W/cm 2 a liquid filling ratio of 30% gave the best performance with a minimum evaporation, condensation and total thermal resistance of 0.086, 0.17 and 0.26 K/W, respectively
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