Bremen, Germany
Bremen, Germany

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Schwenck D.,University of Bremen | Ellendt N.,IWT Bremen | Ellendt N.,University of Bremen | Fischer-Buhner J.,Indutherm Erwarmungsanlagen GmbH | And 2 more authors.
Powder Metallurgy | Year: 2017

Additive manufacturing processes such as selective laser melting and electron beam melting require small particle sizes. A widely used technique to produce suitable powders is close-coupled atomisation. To further decrease the achieved particle sizes, the annular geometry of the gas nozzle is changed to a convergent–divergent (CD) profile. This novel configuration is capable of operating stably at low pressures of 0.8 MPa and above. Beyond that, the unwanted effects of lick-back are avoided. Different nozzles with conventional and convergent–divergent annular geometry have been designed based on fluid-flow calculations. The aspiration pressure was measured to determine stable process windows. Powders from a CuSn alloy were produced using cold and hot gas atomisation to show the influence on the process stability, particle size and morphology. High-speed recordings are used to investigate the process conditions of the different nozzle configurations. © 2017 Institute of Materials, Minerals and Mining Published by Taylor & Francis on behalf of the Institute


Kuhfuss B.,University of Bremen | Moumi E.,University of Bremen | Clausen B.,IWT Bremen | Epp J.,IWT Bremen | Koehler B.,IWT Bremen
Key Engineering Materials | Year: 2015

Wires with 1 mm initial diameter have been reduced between 10 and 64 percent at different temperatures and strain rates by infeed rotary swaging, which is an incremental cold forming process mainly used for rods and pipes. The volume fraction of martensite in the deformed wires has been determined by X-Ray diffraction and by magnetic induction for different processing parameters. Measurements show that for already small percentage of reduction, martensite is present in the wires and its amount changes with the strain rate and temperature. While for smaller strain rates at room temperature the formation of martensite is promoted, it is restrained for higher strain rates and higher temperatures. Results also reveal that the martensite distribution in the sample is inhomogeneous. Further investigations have been made to analyze the microstructure by optical microscopy and to determine mechanical properties by tensile testing. © (2015) Trans Tech Publications, Switzerland.


Meierhofer F.,IWT Bremen | Hodapp M.,Regional University of Blumenau | Achelis L.,University of Bremen | Buss L.,IWT Bremen | And 5 more authors.
Materialwissenschaft und Werkstofftechnik | Year: 2014

Flame spray pyrolysis (FSP) is a versatile process for the production of inorganic nanoparticles featuring the advantage that the reagents are directly dissolved in the liquid fuel that is atomized to form the burning flame. A majority of previous studies on flame spray pyrolysis is focused on the formation and growth processes of the nanoparticles but neglect the preceding step of precursor atomization and spray formation. In this work an atomization concept for large-scale nanoparticle production by flame spray pyrolysis is presented. A pressure swirl nozzle is applied for creating a liquid hollow cone, and in a second step, different dispersion gas nozzles are utilized to enhance the atomization of the liquid phase and to influence the spray cone formation and geometry. The relevant parameters influencing the atomization process (dispersion gas feed rate, liquid feed rate) are investigated (for air, water) in non-burning (cold) spray conditions in order to access the utilization of the different atomizer concepts for the flame spray pyrolysis-process. Measurements are conducted by applying high speed camera imaging (HSC), particle image velocimetry (PIV) and laser diffraction spectroscopy (LDS). Computational fluid dynamics (CFD) revealed further insight into the gas entrainment and the trajectory of droplets within the spray. Results show that the liquid volume flow rate (and thus the productivity of the process) may be increased significantly while still maintaining an appropriate droplet size compared to the conventional atomization process conditions in flame spray pyrolysis reactors. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Bucquet T.,IWT Bremen | Fritsching U.,IWT Bremen
Materials Performance and Characterization | Year: 2014

Industrial gas quenching is a cost-effective, environmental-friendly alternative to conventional fluid-based quenching processes used for the heat treatmentof workpieces mainly in the automotive industry. The influence of the heat exchanger geometry in a novel gas quenching chamber on the gas flow wasinvestigated through measurement in parallel to CFD-simulations. With reduced quenching chamber dimensions, a flow guiding system utilizing aperforated plate placed between the heat exchanger and the batch has been found to play a significant role on the velocity and turbulence distribution ofthe gas flow. The use of various perforated plates in this gas quenching process focuses on the exploration of two main parameters: plate porosity andperforation hole diameters. By combining in situ flow and CFD-simulations of heat and fluid flow, optimized parameters have been determined indicatingimproved uniformity and intensity of the velocity distribution in the quenching chamber, thus obtaining the potential of an overall improvement of the gasquenching process. Geometric parameters of perforated plates introduced into the gas quenching chamber facility are investigated as, e.g., the distancebetween the plate and the batch. More generally, the use of a perforated plate system to optimize gas flows may be extended to other applications wheretube bundle heat exchangers in gas flow processes are involved. Copyright © 2014 by ASTM International.


Schimanski K.,IWT Bremen | Schumacher J.,IWT Bremen | Lang A.,Faserinstitut Bremen E V | Von Hehl A.,IWT Bremen | Bomas H.,IWT Bremen
Materials Science Forum | Year: 2011

Modern lightweight structures containing hybrid materials allow an improvement of the weight-specific properties. In this regard, the great potential of FRP-Al (fibre reinforced plastic - aluminium) structures is far from being exhausted. As an alternative to bulky riveted joints the development of integral joint concepts with good corrosion resistance has currently a high priority for aerospace industry. The DFG researcher group 'Schwarz-Silber' (FOR 1224) at the University of Bremen set itself the goal to explore and develop interface structures for advanced FRP-Al compounds. Considering textile, welding and casting techniques, novel joint concepts will be designed, dimensioned and produced within five interdisciplinary projects. Experimental and numerical investigations support the validation and enhancements of the developed solutions. Regarding the joint concept combining textile and welding techniques, basic investigations were done. This concept envisages the coupling of FRP with Al sheets by using Ti wire loops at the materials interface. It is intended to join the wire loops by textile techniques on the FRP side and on the Al side by laser beam welding. The results showed a correlation between the microstructure and the fracture behaviour of the Ti-FRP joint under static loading. Based on these results, first design principles for advanced FRP-Al compounds with Ti interface structures are derived. © (2011) Trans Tech Publications.


Grohmann O.,IWT Bremen | Meyer C.,IWT Bremen | Schulz A.,IWT Bremen | Uhlenwinkel V.,IWT Bremen | And 2 more authors.
HTM - Journal of Heat Treatment and Materials | Year: 2014

In the industrial manufacturing chain of roller bearings the hot bars are subsequently sheared into billets and these are automatically transported to the first forming stage of the press. Normally the cobalt-based hard-facing alloys for the blades are deposited by manual metal arc or plasma transfer arc welding. In the research work presented here, the hard-facing alloys are produced by spray forming to increase the life time of the tool. Long life time is expected because of the advantages of spray forming: homogeneity of the microstructure, a low segregation and absence of a heat affected welding zone. For this purpose a bi-metal composite is deposited in a co-spray process to combine the hard-facing alloy layer with a hot working steel to insert the blade into a carrier. The interface between the two different materials was analyzed in terms of porosity, hardness, adhesive strength and machinability to describe the new composite material.© Carl Hanser Verlag GmbH & Co. KG.


Bucquet T.,IWT Bremen | Fritsching U.,IWT Bremen | Gulpak M.,IWT Bremen | Wagner A.,IWT Bremen
ASM International - 28th Heat Treating Society Conference, HEAT TREATING 2015 | Year: 2015

The bainitizing potential for new forging steels and heat treatment gas quenching have both gained a growing interest in the automotive industry. The bainitizing process, particularly within the lower bainite range, aims at providing an improved ductility with strength above martensite level. Previous investigations demonstrated the ability of controlled gas quenching for bainitizing of a stepped shaft from the forging heat. In the present work, quenching and machining process steps have been combined to investigate the bainitizing potential of the specimen during machining at elevated temperatures (hot machining). Therefore, gas jet quenching has been experimentally evaluated and the derived heat transfer coefficient distributions have been implemented into heat treatment simulations. Bainitizing strategies featuring various quenching field configurations can be operated based on simulations and time-temperature-transformation diagrams for high-strength ductile bainite (HDB) steel grade. Selected strategies have been tested within a turning machine adapted for controlled heat treatment using a gas quenching field. © 2015 ASM International®.


Bucquet T.,IWT Bremen | Fritsching U.,IWT Bremen
International Journal of Microstructure and Materials Properties | Year: 2016

Since its initial industrial applications, heat treatment gas quenching has undergone several technical improvements and a growing acceptance among conventional and innovative quenching techniques, however limited by the quenching medium to high-hardenable quenched parts. When assessing quenching processes to determine the ideal quenchant, knowing the proper process parameters is essential for given process and load dimensions. The present work aims at providing the necessary background to support the technical evolution and classification of heat treatment gas quenching. A combination of experimental and numerical methods, presented in this work, has helped understanding the mechanisms of heat transfer enhancement owing to flow conditioning around complex metal specimen geometries from the automotive industry. Flow conditioning strategies, at batch and single part scales, are presented in the conclusion of this paper. © 2016 Inderscience Enterprises Ltd.

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