NOVEL WELDING STRATEGY IN HIGH DEPOSITION RATE LASER-ASSISTED DOUBLE-WIRE WELDING PROCESS WITH NONTRANSFERRED ARC

Laser-assisted double wire welding with nontransferred arc melts material using an arc between two conveyed wires. Driven by gravity the molten metal drops onto the substrate. A laser beam is oscillated on the melt pool to bond the weld beads to the substrate without undercuts. Claddings at high deposition rates (11.6 kg/h) were performed with 316L on mild steel. The first welding strategy (AAA) is to weld adjacent beads (A) with a varied track spacing of 7 to 9 mm. The second strategy (ABA) consists of beads (A) welded at a distance of 14 to 18 mm from each other, so that a third bead (B) can be deposited in the space between. Claddings with the determined track spacing for AAA of 9 mm and ABA 18 mm were created in order to compare the resulting surface properties. The ABA cladding did not achieve a more uniform surface and less waviness than the AAA cladding.Mechanical Engineerin

Micro- vs. macro-phase separation in binary blends of poly(styrene)-poly(isoprene) and poly(isoprene)-poly(ethylene oxide) diblock copolymers

In this paper we present an experimentally determined phase diagram of binary blends of the diblock copolymers poly(styrene)-poly(isoprene) and poly(isoprene)-poly(ethylene oxide). At high temperatures, the blends form an isotropic mixture. Upon lowering the temperature, the blend macro-phase separates before micro-phase separation occurs. The observed phase diagram is compared to theoretical predictions based on experimental parameters. In the low-temperature phase the crystallisation of the poly(ethylene oxide) block influences the spacing of the ordered phase

A small volume, local shielding gas chamber with low gas consumption for Laser Wire Additive Manufacturing of bigger titanium parts

This paper shows how additive manufacturing of large size titanium parts can be achieved by means of a mobile shielding gas chamber, without the consumption of excessive amounts of shielding gas. While welding, the oversized cover of the chamber can be slid to the sides without opening it. The laser head is only partly inserted into the chamber through the cover. This enables a small sized chamber and allows a quick filling with argon. Since the chamber has a low leakage, only small amounts of argon (5 l/min) are needed to maintain a sufficient welding atmosphere with less than 300 ppm oxygen. For large sized parts, the chamber can be repositioned on the substrate. It has flexible parts which can be fit to the already welded structures that otherwise would prevent the chamber from being put flat on the substrate. The limited build space inside the chamber requires a new welding strategy, which is suggested.Mechanical Engineerin

PROCESS-INTEGRATED ALLOY ADJUSTMENT IN LASER DEPOSITION WELDING WITH TWO WIRES

For Direct Energy Deposition (DED) with wire as filler material, the material selection is mostly limited to commercially available welding wires. This limits the achievable material properties for cladding and Additive Manufacturing purposes. Using a coaxial deposition welding head, in which two different wires can be fed and controlled individually, the alloy composition can be adjusted in the common process zone in-situ. In this study, the two wire materials AISI 316L and ER 70S-6 are used in different mixing ratios to fabricate single weld seams. The different mixing ratios are achieved by varying the wire feed rates. The material content in the weld is varied between 0% and 100% in 20% steps. The weld seams are examined with regard to the distribution of alloying elements, hardness and microstructure. Homogeneous mixing of the two materials was achieved at all mixing ratios. At a content of 40% or more of ER 70S-6 in the weld seam, there was a drastic change in the microstructure and a significant increase in hardness. The microstructure changed from austenitic to ferritic-pearlitic, which was accompanied by an increase in hardness from 170 HV0.1 to 428 HV0.1.Mechanical Engineerin

Influence of Silane-doped Argon Processing Atmosphere on Powder Recycling and Part Properties in L-PBF of Ti-6Al-4V

In the additive manufacturing of metal powders, the residual oxygen in the processing atmosphere plays a crucial role, especially in highly reactive materials like titanium alloys. Besides oxidation of the built parts, it leads to oxygen pick-up into the unmolten powder. Since oxidized particles cannot be removed during recycling, the powder properties deteriorate after multiple uses. In this work, Ti-6Al-4V powder was processed under conventional argon atmosphere (residual oxygen content < 0.01 vol%) as well as silane-doped argon atmosphere (< 0.001 vol% silane in argon). The silane-doping leads to a residual oxygen content of < 10-20 vol%. The powder was sieved and used 5 times for each atmosphere. The powder properties morphology, chemical composition and flowability were analyzed for virgin as well as reused powder. Furthermore, the roughness and relative density of the built parts were evaluated. It was hypothesized that oxygen-free production improves recyclability and thus resource efficiency.Mechanical Engineerin

Towards experimental process parameter development for Ti-6Al-4V TPMS lattice structures with application to small scale dental implants using micrographs

Ti-6Al-4V is a widely used alloy in implant engineering and lattice structures can be applied to locally match the stiffness of the implant to the stiffness of bone. Triply periodic minimal surface (TPMS) structures are popular due to their curved surface, which supports a good manufacturability and osseointegration of the implant. Tests with different TPMS structures showed a strong interaction between design factors and manufacturing parameters resulting in the need for individual parameter development. However, to the best of our knowledge, the most work in the current literature focusses on mechanical and biological examinations of TPMS structures manufactured with standard parameters. As process parameters influence the structural properties, the optimum values for further analysis may not have been investigated (e.g., their influence on microstructure and mechanical properties). In this work, a design of experiments approach is used to develop process parameters. As computer tomography scans are resource intensive for large scale parameter development, a sparser approach using micrographs for porosity analysis is introduced. Small structures with unit cell size as small as 1.0 mm are fabricated on a laser powder bed fusion industrial machine. Our initial studies show that the design factor pore size is negligible in comparison to wall thickness when optimizing internal porosity.Mechanical Engineerin

Neuropsychiatric phenotype of post COVID-19 syndrome in non-hospitalized patients

The post COVID-19 syndrome (PCS) is an emerging phenomenon worldwide with enormous socioeconomic impact. While many patients describe neuropsychiatric deficits, the symptoms are yet to be assessed and defined systematically. In this prospective cohort study, we report on the results of a neuropsychiatric consultation implemented in May 2021. A cohort of 105 consecutive patients with merely mild acute course of disease was identified by its high symptom load 6 months post infection using a standardized neurocognitive and psychiatric-psychosomatic assessment. In this cohort, we found a strong correlation between higher scores in questionnaires for fatigue (MFI-20), somatization (PHQ15) and depression (PHQ9) and worse functional outcome as measured by the post COVID functional scale (PCFS). In contrast, neurocognitive scales correlated with age, but not with PCFS. Standard laboratory and cardiopulmonary biomarkers did not differ between the group of patients with predominant neuropsychiatric symptoms and a control group of neuropsychiatrically unaffected PCS patients. Our study delineates a phenotype of PCS dominated by symptoms of fatigue, somatisation and depression. The strong association of psychiatric and psychosomatic symptoms with the PCFS warrants a systematic evaluation of psychosocial side effects of the pandemic itself and psychiatric comorbidities on the long-term outcome of patients with SARS-CoV-2 infection

Structural and functional evolution of the P2Y12-like receptor group

Metabotropic pyrimidine and purine nucleotide receptors (P2Y receptors) belong to the superfamily of G protein-coupled receptors (GPCR). They are distinguishable from adenosine receptors (P1) as they bind adenine and/or uracil nucleotide triphosphates or diphosphates depending on the subtype. Over the past decade, P2Y receptors have been cloned from a variety of tissues and species, and as many as eight functional subtypes have been characterized. Most recently, several members of the P2Y12-like receptor group, which includes the clopidogrel-sensitive ADP receptor P2Y12, have been deorphanized. The P2Y12-like receptor group comprises several structurally related GPCR which, however, display heterogeneous agonist specificity including nucleotides, their derivatives, and lipids. Besides the established function of P2Y12 in platelet activation, expression in macrophages, neuronal and glial cells as well as recent results from functional studies implicate that several members of this group may have specific functions in neurotransmission, inflammation, chemotaxis, and response to tissue injury. This review focuses specifically on the structure-function relation and shortly summarizes some aspects of the physiological relevance of P2Y12-like receptor members

Optimierung eines FE-Modells auf Grundlage einer Experimentellen Modalanalyse

Knowledge about the dynamic behaviour is a basic condition for a secure operation of modern machine tools. Hence numerical methods predicting the dynamic properties are gaining in importance. Usually for complex and coupled structures, the results of dynamic property calculation are yet insufficient. Therefore Finite Element model updating is a tool to improve the hypothetical factor of the analysis. Within the present thesis Finite Element modelling is performed using the example of the „Scherenkinematik”, a machine tool based on hybrid-kinematics. Initially the results of an Experimental Modal Analysis are evaluated by identifying Modal parameters and deriving possible structural modifications. In the second part of the thesis, the machines Finite Element model is created using the FEA-Software ANSYS. Afterwards the Finite Element model updating is performed by coupling ANSYS and the CAE-Software FEMtools. Therefore two approaches are formulated and tracked. It turns out, that there is no improvement of the analytical and experimental models correlation, neighter with nor without a steady reduction of the search domain needed for mode coupling. It is reasoned, that the characteristics and the results of an Finite Element updating process are affected by the quality of the model at start time and the approach as well as the technique chosen for model updating and parameter modification. Therefore the CAE-Software FEMtools is suitable to only a limited extent for Finite Element updating of strongly coupled mechanical structures as a result of the sensitivity analysis used for parameter modification