Dr.

Günther, Daniel

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Now showing 1 - 9 of 9
  • Publication
    Sintering of 3D-printed aluminum specimens from the slurry-based binder jetting process
    ( 2024)
    Angenoorth, Jan Maximilian Golo
    ;
    Erhard, Patricia
    ;
    Wächter, Dennis
    ;
    Volk, Wolfram
    ;
    Günther, Daniel
    This work investigates a novel method of producing complex-shaped aluminum parts by slurry-based binder jetting and sintering. In this process, a green body is built up by layer-wise deposition of an aqueous aluminum suspension and selective powder bonding by ink-jet printing. The powder bulk generated from the suspension shows an increased density compared to powder-based binder jetting and, thus, a high initial density for the subsequent densification step. This allows for higher final densities and reduced shrinkage. Aluminum is of special interest as it is widely available and of low density but challenging to sinter due to an oxide skin surrounding every particle. The research in this paper investigates the effects of the sintering atmosphere and sintering additives on the microstructure of powder compacts produced by slurry-based binder jetting. The incorporation of magnesium as an additive during the sintering process of aluminum has been found to substantially improve densification during sintering in an argon atmosphere.
  • Publication
    Compound Casting of Aluminum with Sheet Steel in 3D Sand Casting Using an Inductive Heating System
    ( 2023)
    Locke, Christopher
    ;
    Guggemos, Martin
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    Gruber, Maximilian
    ;
    Maier, Lorenz
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    Mayr, Lukas
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    Weiß, Tony
    ;
    Volk, Wolfram
    ;
    Günther, Daniel
    Compound casting is a process in which a single component is made from two metallic materials, such as aluminum and steel. Solid-liquid bimetallic compounds can be produced by suitable process control. This technology can reduce the number of joining processes, and the specific properties of the respective metal component can be used for specifically designed product properties, for example, where lightweight and high strength are needed. This paper presents an experimental methodology for producing a purely material-bonded bimetallic joint from cast aluminum and zinc-coated sheet steel in 3D sand casting using an inductive heating system. The process-related temperature characterisation in the compound zone is described using a heating test rig and temperature measurements. It shows that inductive preheating can only produce a material bond between the aluminum casting and the coated steel sheet. Shear tensile tests showed strengths between 15 MPa and 22 MPa. Laser surface pre-treatment using laser ablation cutting on the coated steel sheet was carried out to investigate the benefit of possible microform-locking. The results show a strength-reducing influence on the tensile shear tests. Micrographs showed the formation of Al4.5FeSi and Al7Fe2Si, as well as the formation of other undefined intermetallic phases. The thickness of the compound zone is 10 µm.
  • Publication
    Modeling De-Coring Tools with Coupled Multibody Simulation and Finite Element Analysis
    ( 2023)
    Mariadass, Melvin
    ;
    Binder, Roman
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    Ettemeyer, Florian
    ;
    Volk, Wolfram
    ;
    Günther, Daniel
    De-coring is an essential process in the casting process chain, determining the quality and cost of production. In this study, a coupled multibody system (MBS) and finite element modeling (FEM) technique is presented to study the mechanical loads during the de-coring process. The removal of cast-in sand cores from the inner regions of the cast part by de-coring or knocking out is a complex process with dynamic loads. Currently, the process relies upon empirical knowledge and tests. Inorganic sand cores pose additional challenges in the success of the de-coring process. Increasing complexity in geometry and stringent environmental regulations compel a predictive process in the earlier stages of design. Predicting the process’ success is challenged by the dynamic non-linearities of the system. The dynamic characteristics and the interaction between hammer and casting were studied here for the first time using an industrial-based test rig, and a novel modeling approach was formulated. The results of the developed model are in good compliance with the experiments. The methodology presented in this study can be used to include a varying number of hammers and loads. The proposed approach presents the possibility to discretize the process and qualitatively assess the process parameters for optimization.
  • Publication
    Advanced Procedures for Series Production with 3D-Printed Core Packages
    ( 2023)
    Erhard, Patricia
    ;
    Hartmann, Christoph
    ;
    Li, Rui
    ;
    Volk, Wolfram
    ;
    Günther, Daniel
    The application of additive-manufactured cores and molds is of great interest for complex cast components. Nevertheless, several challenges still exist in utilizing binder jetting in the multi-step additive manufacturing process for foundry applications to its fullest extent. This contribution shows methods that facilitate the use of 3D-printed sand molds and cores in casting series applications. The binder jetting process itself is assessed from an overall process chain perspective to highlight the benefits of its application in series production. The challenges associated with automating mold cleaning for highly complex casting contours are depicted. In particular, employing the method of cleanable mold partitioning is shown to enhance the automation level of the overall process. Mold design tailored to 3D printing is demonstrated to contribute to overall cost and time savings in enhanced core packages. Topology-optimized, lightweight part designs involving complex freeform surfaces may require mold partitioning associated with laborious burr removal processes. A new approach in answer to the shortage of skilled workers in the harsh and hazardous foundry environment is shown. Implementing motion tracking technology is demonstrated to enable economical automated burr removal for minor quantities or high variant diversity in the future foundry. All the methods shown are of great importance for introducing printed core packages into series production.
  • Publication
    Influence of the Resin System and Sand Type on the Infiltration of 3D-Printed Sand Tools
    ( 2023)
    Erhard, Patricia
    ;
    Taha, Iman
    ;
    Günther, Daniel
    Binder jetting is a highly productive additive manufacturing (AM) method for porous parts. Due to its cost-effectiveness, it is used for large components and quantities ranging from prototyping to series production. Post-processing steps like sintering or infiltration are common in several applications to achieve high density and strength. This work investigates how 3D-printed sand molds can be infiltrated with epoxy resins without vacuum assistance to produce high-strength molds for thermoforming applications. Specimens 3D-printed from different sand types are infiltrated with resins of different viscosity and analyzed for infiltration velocity and depth. The infiltration velocities corresponded well with the correlation described in Washburn’s equation: The resins’ viscosities and the saturation level were decisive. Amongst the investigated sand types commonly used in foundries, sand type GS19 was found most suitable for infiltration. However, the sand type proved to be a less relevant influencing factor than the resins’ viscosities and quantities applied. Infiltration of topology-optimized 3D-printed sand tools up to a wall thickness of 20 mm for thermoforming applications was found to be feasible.
  • Publication
    Simulation of Binder Infiltration in Additive Manufacturing of Sand Molds
    ( 2023)
    Erhard, Patricia
    ;
    Tanjavooru, Vivek Teja
    ;
    Hartmann, Christoph
    ;
    Bosch, Lucas Valentin van den
    ;
    Seidel, Alexander
    ;
    Volk, Wolfram
    ;
    Günther, Daniel
    This article proposes a computational fluid dynamics approach to simulate binder infiltration in 3D printing of sand molds using OpenFOAM facilitating the identification of suitable levers for application-specific material and process developments. A method for randomly generating powder bulks of designated powder size distributions (PSD) and procedures for automated analysis of the infiltration profile and volume are introduced. Simulation is utilized to investigate binder infiltration using different droplet spacings, representing different printheads’ resolutions. The apparent particle size at the exact location of the droplets’ impact, the droplets’ landing position in relation to the respective surface topography, and thus the statistical appearance of particle formations appear to be influencing the infiltration profile. High-speed camera observations show the plausibility of the predicted infiltration kinetics. An exemplary use case compares the predicted infiltration profiles to the compressive strength of specimens printed from silica sand with low binder contents. Simulation predicts an average infiltration of 250 μm that presumably achieves reliable bonding for layer thicknesses up to 365 μm. A decrease in strength with increasing layer thickness at constant binder contents can be found in the experiment – at layer thicknesses above 350 μm, only minor strengths are achieved.
  • Publication
    Innovative Salzkerne für komplexe Geometrien
    ( 2022-08)
    Erhard, Patricia
    ;
    Günther, Daniel
    Das Fraunhofer IGCV und die K+S Aktiengesellschaft haben in einem gemeinsamen F&E-Projekt eine übergreifende nachhaltige Prozesskette für das Schießen von Salzkernen zur Darstellung innen liegender Kavitäten im Aluminiumguss entwickelt. Im Vergleich zu konventionellen Sandkernen nutzt das vorgestellte alternative Verfahren ein Salzgemisch zur Herstellung binderfreier Salzkerne, welches mit Wasser rückstandsfrei ausgespült werden kann. Die dabei entstehende wertstoffhaltige Salzlösung kann, so das erarbeitete Konzept, von der K+S Aktiengesellschaft recycelt werden. Die neue Technologie überzeugt durch hohe Geometriefreiheit und besonders durch die erleichterte Entkernbarkeit der Bauteile.
  • Publication
    Removal of Stair-Step Effects in Binder Jetting Additive Manufacturing Using Grayscale and Dithering-Based Droplet Distribution
    ( 2022)
    Hartmann, Christoph
    ;
    Bosch, Lucas Valentin van den
    ;
    Spiegel, Johannes
    ;
    Rumschöttel, Dominik
    ;
    Günther, Daniel
    Binder jetting is a layer-based additive manufacturing process for three-dimensional parts in which a print head selectively deposits binder onto a thin layer of powder. After the deposition of the binder, a new layer of powder is applied. This process repeats to create three-dimensional parts. The binder jetting principle can be adapted to many different materials. Its advantages are the high productivity and the high degree of freedom of design without the need for support structures. In this work, the combination of binder jetting and casting is utilized to fabricate metal parts. However, the achieved properties of binder jetting parts limit the potential of this technology, specifically regarding surface quality. The most apparent surface phenomenon is the so-called stair-step effect. It is considered an inherent feature of the process and only treatable by post-processing. This paper presents a method to remove the stair-step effect entirely in a binder jetting process. The result is achieved by controlling the binder saturation of the individual voxel volumes by either over or underfilling them. The saturation is controlled by droplet size variation as well as dithering, creating a controlled migration of the binder between powder particles. This work applies the approach to silica sand particle material with an organic binder for casting molds and cores. The results prove the effectiveness of this approach and outline a field of research not identified previously.
  • Publication
    Characterization of Slurry-Cast Layer Compounds for 3D Printing of High Strength Casting Cores
    ( 2021)
    Erhard, Patricia
    ;
    Angenoorth, Jan
    ;
    Vogt, Joachim
    ;
    Spiegel, Johannes
    ;
    Ettemeyer, Florian
    ;
    Volk, Wolfram
    ;
    Günther, Daniel
    Additive manufacturing of casting cores and molds is state of the art in industrial application today. However, improving the properties of chemically bonded casting cores regarding temperature stability, bending strength, and surface quality is still a major challenge. The process of slurry-based 3D printing allows the fabrication of dense structures and therefore sinterable casting cores. This paper presents a study of the slurry-based fabrication of ceramic layer compounds focusing on the drying process and the achievable properties in slurry-based 3D printing of casting cores. This study aims at contributing to a better understanding of the interrelations between the drying conditions in the 3D printing process and the properties of sintered specimens relating thereto. The drying intensity influenced by an IR heater as well as the drying periods are varied for layer thicknesses of 50, 75, and 100 µm. Within this study, a process window applicable for 3D printing of sinterable casting cores is identified and further indications are given for optimization potentials. At layer heights of 75 µm, bending strengths between ~8 and 11 MPa as well as densities of around 50% of the theoretical density were achieved. Since the mean roughness depth Rz is determined to be <30 µm in plane, an application of slurry-based 3D printing in investment casting is conceivable.