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Binding Mechanisms in Selective Laser Sintering and Selective Laser Melting
Layer Manufacturing (LM) technologies like Selective Laser Sintering (SLS) were developed
in the late 80’s as techniques for Rapid Prototyping (RP). Today, SLS - as well as its derived
technology Selective Laser Melting (SLM) - is used as well for prototyping, tooling and
manufacturing purposes. This widening of applications is caused mainly by the possibility to
process a large variety of materials, resulting in a broad range of physical and mechanical
properties.
This paper presents a survey of the various binding mechanisms in SLS and SLM, which are
responsible for the broad range of materials and applications. Basic binding mechanisms involve
solid state sintering, chemically induced binding, liquid phase sintering, partial melting and full
melting. Many subcategories can be distinguished based on the type of structural or binder
powder composition: single component powder grains (single material or alloy), composite
powder grains, mixtures of different powder grains, distinct binder material (sacrificial or
permanent), etc. The paper will explain how these binding mechanisms apply for sintering
various types of materials: plastics, metal, ceramics and composites (e.g. glass reinforced
polymers, cermets, hardmetals, etc.). It gives a survey of research done at the University of
Leuven, Belgium, as well as at other European and non-European organizations.Mechanical Engineerin
Tailoring the thermal conductivity of the powder bed in Electron Beam Melting (EBM) Additive Manufacturing
Metallic powder bed additive manufacturing is capable of producing complex, functional parts by repeatedly depositing thin layers of powder particles atop of each other whilst selectively melting the corresponding part cross-section into each layer. A weakness with this approach arises when melting overhanging features, which have no prior melted material directly beneath them. This is due to the lower thermal conductivity of the powder relative to solid material, which as a result leads to an accumulation of heat and thus distortion. The Electron Beam Melting (EBM) process alleviates this to some extent as the powder must first be sintered (by the beam itself) before it is melted, which results in the added benefit of increasing the thermal conductivity. This study thus sought to investigate to what extent the thermal conductivity of local regions in a titanium Ti-6Al-4V powder bed could be varied by imparting more energy from the beam. Thermal diffusivity and density measurements were taken of the resulting sintered samples, which ranged from being loosely to very well consolidated. It was found that the calculated thermal conductivity at two temperatures, 40 and 730 °C, was more than doubled over the range of input energies explored
Investigating the melt pool properties and thermal effects of multi-laser diode area melting
Diode area melting (DAM) is a new additive manufacturing process that utilises customised architectural arrays of low-power
laser diode emitters for high-speed parallel processing of metallic feedstock. The laser diodes operate at shorter laser wavelengths
(808 nm) than conventional SLM fibre lasers (1064 nm) theoretically enabling more efficient energy absorption for specific
materials. This investigation presents the first work investigating the melt pool properties and thermal effects of the multi-laser
DAM process, modelling generated melt pools the unique thermal profiles created along a powder bed during processing. Using
this approach process, optimisation can be improved by analysing this thermal temperature distribution, targeting processing
conditions that induce full melting for variable powder layer thicknesses. In this work, the developed thermal model simulates the
DAM processing of 316L stainless steel and is validated with experimental trials. The simulation indicates that multi-laser DAM
methodology can reduce residual stress formation compared to the single point laser scanning methods used during selective laser
melting
Processing Parameter Effects on Residual Stress and Mechanical Properties of Selective Laser Melted Ti6Al4V
Selective laser melting (SLM) process is characterized by large temperature gradients resulting in high levels of residual stress within the additively manufactured metallic structure. SLM-processed Ti6Al4V yields a martensitic microstructure due to the rapid solidification and results in a ductility generally lower than a hot working equivalent. Post-process heat treatments can be applied to SLM components to remove in-built residual stress and improve ductility. Residual stress buildup and the mechanical properties of SLM parts can be controlled by varying the SLM process parameters. This investigation studies the effect of layer thickness on residual stress and mechanical properties of SLM Ti6Al4V parts. This is the first-of-its kind study on the effect of varying power and exposure in conjunction with keeping the energy density constant on residual stress and mechanical properties of SLM Ti6Al4V components. It was found that decreasing power and increasing exposure for the same energy density lowered the residual stress and improved the % elongation of SLM Ti6Al4V parts. Increasing layer thickness resulted in lowering the residual stress at the detriment of mechanical properties. The study is based on detailed experimental analysis along with finite element simulation of the process using ABAQUS to understand the underlying physics of the process
Post-intervention Status in Patients With Refractory Myasthenia Gravis Treated With Eculizumab During REGAIN and Its Open-Label Extension
OBJECTIVE: To evaluate whether eculizumab helps patients with anti-acetylcholine receptor-positive (AChR+) refractory generalized myasthenia gravis (gMG) achieve the Myasthenia Gravis Foundation of America (MGFA) post-intervention status of minimal manifestations (MM), we assessed patients' status throughout REGAIN (Safety and Efficacy of Eculizumab in AChR+ Refractory Generalized Myasthenia Gravis) and its open-label extension. METHODS: Patients who completed the REGAIN randomized controlled trial and continued into the open-label extension were included in this tertiary endpoint analysis. Patients were assessed for the MGFA post-intervention status of improved, unchanged, worse, MM, and pharmacologic remission at defined time points during REGAIN and through week 130 of the open-label study. RESULTS: A total of 117 patients completed REGAIN and continued into the open-label study (eculizumab/eculizumab: 56; placebo/eculizumab: 61). At week 26 of REGAIN, more eculizumab-treated patients than placebo-treated patients achieved a status of improved (60.7% vs 41.7%) or MM (25.0% vs 13.3%; common OR: 2.3; 95% CI: 1.1-4.5). After 130 weeks of eculizumab treatment, 88.0% of patients achieved improved status and 57.3% of patients achieved MM status. The safety profile of eculizumab was consistent with its known profile and no new safety signals were detected. CONCLUSION: Eculizumab led to rapid and sustained achievement of MM in patients with AChR+ refractory gMG. These findings support the use of eculizumab in this previously difficult-to-treat patient population. CLINICALTRIALSGOV IDENTIFIER: REGAIN, NCT01997229; REGAIN open-label extension, NCT02301624. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that, after 26 weeks of eculizumab treatment, 25.0% of adults with AChR+ refractory gMG achieved MM, compared with 13.3% who received placebo
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