Browsing by Author "Schulze, Volker"

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Open Access
Comparison of in-process laser drying with furnace and vacuum drying to reduce moisture of AlSi10Mg powder processed in Laser Powder Bed Fusion
(2024) Lubkowitz, Victor; Fayner, Leonie; Kramer, Steffen; Schulze, Volker; Zanger, Frederik
In most powder bed-based laser melting systems (PBF-LB), metal powders must be handled without inertization but in an air atmosphere for a short time, increasing the AlSi10Mg powder moisture and reducing the achievable component density. Consequently, different drying methods were investigated. Drying in a furnace with an inert atmosphere, using a vacuum to evaporate the water at low temperatures, and vaporizing moisture layerwise from the spreaded powder with a defocused, low-power laser beam as a further process step of the PBF-LB process. Therefore, four different moisturized powders, which were dried with different settings for the drying methods, are analyzed. All drying methods reduce the moisture content of the powder, with in-process drying being the most effective. Due to the oxide layer growth around the particles during furnace and vacuum drying, the achievable sample density after drying is worse. In-process drying with low energy density is the best option to reach a reduction of hydrogen pores and an increase of density.
Open Access
Evaluation of methods for measuring tool-chip contact length in wet machining using different approaches (microtextured tool, in-situ visualization and restricted contact tool)
(2022) Ellersiek, Lars; Menze, Christian; Sauer, Florian; Denkena, Berend; Möhring, Hans-Christian; Schulze, Volker
The contact length is one of the most important factors to evaluate the chip formation process and the mechanical loads in metal cutting. Over the years, several methods to identify the contact length were developed. However, especially for wet cutting processes the determination of the contact length is still challenging. In this paper, three methods to identify the contact length for dry and wet processes in cutting of Ti6Al4V and AISI4140 + QT are presented, discussed and analyzed. The first approach uses tools with a microtextured rake face. By evaluating the microstructures on the chip, a new method to identify the contact length is established. The second approach applies high speed recordings to identify the contact length. The challenge is thereby the application of high-speed recordings under wet conditions. In the third approach, tools with restricted contact length are used. It is shown that with all three methods the contact length is reduced using metal working fluid.
Open Access
Local laser heat treatment of AlSi10Mg as-built parts produced by Laser Powder Bed Fusion
(2024) Kramer, Steffen; Jarwitz, Michael; Schulze, Volker; Zanger, Frederik
Today, complex structural components for lightweight applications are frequently manufactured by laser powder bed fusion (PBF-LB), often using aluminum alloys such as AlSi10Mg. However, the application of cyclic load cases can be challenging as PBF-LB produced AlSi10Mg parts typically have low ductility and corresponding brittle failure behavior in the as-built condition. Therefore, this paper presents investigations on the feasibility of a laser heat treatment of PBF-LB produced AlSi10Mg parts to locally increase the ductility and decrease the hardness in critical areas. Potential heat treatment process parameters were derived theoretically based on the temperature fields in the material calculated assuming three-dimensional heat conduction and a moving heat source. PBF-LB produced specimens were then laser heat treated at varying laser power and scan speed. Hardness measurements on metallographic cross sections showed hardness reductions of over 35 % without inducing hydrogen pore growth.
Open Access
Potential of contactless support structures for improving the part quality of AlSi10Mg PBF-LB parts
(2023) Kramer, Steffen; Drechsel, Kai; Jarwitz, Michael; Schulze, Volker; Zanger, Frederik
Support structures are usually required to prevent thermally induced deformation of parts during the PBF-LB process, but also cause an increased effort for post-processing and an insufficient surface quality of the produced parts. An approach to overcome these limitations, suggested in the literature, is the use of contactless support structures (CSS), which should act as a heat sink to avoid thermally induced deformation. This approach was already successfully tested for electron beam melting (PBF-EB). Therefore, the aim of the present study is the experimental investigation of the application of CSS for the PBF-LB process. Different part and support geometries were built to investigate the potential of CSS to reduce thermally induced deformation during the PBF-LB process. Several use cases were covered, including increased overhang angles for thin features and maximized overhang thickness. The literature results for PBF-EB and Ti6Al4V could not be confirmed for PBF-LB using AlSi10Mg. The thermally induced deformation could not be reduced and the experimental results indicate that the use of CSS is accompanied by counterproductive process mechanisms.
Open Access
Stream finishing of additively manufactured AlSi10Mg PBF-LB parts: influence on surface quality and fatigue behaviour
(2024) Wexel, Helena; Kramer, Steffen; Schubert, Johannes; Schulze, Volker; Zanger, Frederik