Investigation on Occurrence of Elevated Edges in Selective Laser Melting

Selective laser melting (SLM) is a layer-wise material additive process for the direct fabrication of functional metallic parts. During the process, successive layers of metal powder are fully molten and consolidated on top of each other by the energy of a high intensity laser beam. The process is capable of producing almost fully dense three-dimensional parts having mechanical properties comparable to those of bulk materials. However, one of the problems encountered in SLM process is the occurrence of elevated ridges of the solidified material at the edges of the successive layers. Those ridges reduce the dimensional accuracy and topology of the top surface. The edge-effect problem is encountered not only in SLM, but also in other production techniques applying melting processes such as LENS® (The Laser Engineered Net Shaping) and EBM (Electron Beam Melting). In this study, the reasons for elevated edges and solutions to this problem are investigated and reported. Different scan strategies as well as different hatching and contour parameters are tested to reduce the edge-effect problem. Besides, the influence of applying laser re-melting in combination to selective laser melting has been investigated. It turns out that re-melting layers deposited by SLM improves the part density and surface roughness, but creates on its own elevated edges.Mechanical Engineerin

Multiscale fatigue modelling of additively manufactured metallic components

Additively manufactured metallic components have been used in medical and aerospace applications. In these components, surface roughness and porosity are integral features that might significantly reduce their fatigue lives, especially in the high cycle fatigue regime. Thus, to precisely estimate the fatigue life of an additively manufactured component, these defective features are incorporated into our proposed fatigue model. To capture the local plasticity caused by the defects, a nonlinear isotropic-kinematic hardening elasto-plasticity model is employed in our finite element (FE) models. Additionally, the gas-entrapped pores are modeled as circles whilst the surface topography, which was measured using stylus-based profilometer, is explicitly mo deled in the FE models. The finite element results are post-processed by our in-house software to extract the Smith-Watson-Topper (SWT) fatigue indicator parameter. This parameter is calculated at each element centroid of the FE mesh, i.e., the local indicator. Afterward, an average value of the SWT parameter over a so-called critical area whose center is located at the considered centroid is also calculated, i.e., the nonlocal indicator. The results show that the local SWT indicator is too conservative in predicting the fatigue life of the componentwhile the nonlocal SWT one can provide good results

Review of in-situ process monitoring and in-situ metrology for metal additive manufacturing

Lack of assurance of quality with additively manufactured (AM) parts is a key technological barrier that prevents manufacturers from adopting AM technologies, especially for high-value applications where component failure cannot be tolerated. Developments in process control have allowed significant enhancement of AM techniques and marked improvements in surface roughness and material properties, along with a reduction in inter-build variation and the occurrence of embedded material discontinuities. As a result, the exploitation of AM processes continues to accelerate. Unlike established subtractive processes, where in-process monitoring is now commonplace, factory-ready AM processes have not yet incorporated monitoring technologies that allow discontinuities to be detected in process. Researchers have investigated new forms of instrumentation and adaptive approaches which, when integrated, will allow further enhancement to the assurance that can be offered when producing AM components. The state-of-the-art with respect to inspection methodologies compatible with AM processes is explored here. Their suitability for the inspection and identification of typical material discontinuities and failure modes is discussed with the intention of identifying new avenues for research and proposing approaches to integration into future generations of AM systems

Cross-Border Dissemination of Methicillin-Resistant Staphylococcus aureus, Euregio Meuse-Rhin Region

MRSA clones were associated with hospital-associated clonal complexes and with Panton-Valentine leukocidin–positive community-associated MRSA

Het Vlaamse politieke gebeuren in 1996

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A Monitoring System for On-line Control of Selective Laser MeltingA Monitoring System for On-line Control of Selective Laser Melting (Eenmonitoring systeem voor on-line controle van Selectief Laser Smelten)

Selective Laser Melting (SLM) is an Additive Manufacturing (AM) processwhich allows to produce complex metallic parts in a layer by layer fashion.The use of SLM is advantageous in industries as for instance aerospace or medical industries, since SLM allows a larger design freedom than possible with conventional material removal processes such as milling, cutting or drilling. For medical industries SLM is advantageous to produce custom designed parts and for aerospace the technique allows to produce lightweight parts.In recent years the SLM technology has made an enormous progress in machine construction, production speed and part quality. However, for a large breakthrough of SLM in industries with high quality demands, an issueto be addressed is online quality control of the process. The target ofthis research is to develop a system which allows to monitor during theprocess (i.e. on-line) whether the SLM process runs according to the desired behavior, which leads to the desired part quality. This monitoringsystem can then be used for applying corrective actions during the build, in case the quality deviates from the desired quality.This work first describes the necessary hardware and software developments, including optimisation of the melt pool monitoring system for SLM, development of a machine control system for the in-house build SLM machine of KU Leuven (the LM-Q machine) and development of a visual inspection system for inspection of powder deposition. Also a novel method has been developed for visualisation of the melt pool data. This use of this so called `mapping method' significantly facilitates the interpretation of the melt pool data, and has therefore been patented in 2012.With the developed monitoring tools, the behaviour of the melt pool in SLM in various circumstances has been studied. Also its use in detectionof processing errors, i.e. deviation from the optimal behaviour, has been proven. It has been shown that the system is a powerfull tool in enabling a better understanding of the physics of the SLM process. Also occuring disturbances during the process, such as overheating of the melt pool, can be monitored and detected.Besides melt pool monitoring, hardware and software algorithms have been developed for inspection of powder deposition. Three occurring errors can be succesfully detected with the system: deformation of the part dueto thermal stresses, short of feed powder and defects in the coater blade. The power of using a separate system besides melt pool monitoring isto allow to correct for occuring errors during the deposition phase, before the scanning of the powder layer.The combination of melt pool and deposition monitoring allows to detecta wide range of typical process disturbances and allows to assess the quality of the building process during the actual build. The system as a whole will facilitate the introduction of Selective Laser Melting in industries with high quality demands.status: publishe