Dr.

Günther, Daniel

Filters

9 6
Reset filters

Settings
Now showing 1 - 10 of 15
  • Publication
    On the mechanism of binder migration in furan binder jetting of sand molds and cores
    ( 2024-03-05)
    Hartmann, Christoph
    ;
    Silberhorn, Jonas
    ;
    Erhard, Patricia
    ;
    Günther, Daniel
    Binder Jetting is a layer-based additive manufacturing process in which a printhead deposits droplets onto a preprepared layer of particles. Upon droplet impact, the binder begins to migrate and infiltrate adjacent areas away from its originally intended location. The purpose of this study is to investigate the mechanism of furan binder migration. Observing in-situ binder spreading is challenging, especially for the furan binder used in this work. The strong discoloration of the surrounding sand makes it difficult to distinguish between the printed pattern and the surrounding loose sand. For this reason, a fluorescent dye is added to the binder. A wavelength-matched laser in the binder jetting machine provides the excitation energy, and in-situ observation of binder migration becomes feasible. The results show an unexpected behavior where the actual microscopic fluid redistribution of the binder does not match the observed macroscopic measurements of other reports. It becomes clear that the migration mechanism of furan binder in sand binder jetting is strongly influenced by gaseous mass transport. To support this theory, a phenomenon called boundary zone is studied by micrographic and computed tomographic analysis. This outer shell region surrounds samples with higher binder contents and extends over a thickness of approximately 400 µm. The binder content here is significantly higher than that of the core of the specimen and its target value, demonstrating that liquid concentration equalization is not feasible. A plausible explanation is evaporation and condensation of binder, resulting in localized binder accumulation in areas of high catalyst to binder ratios. Since binder evaporation is an overlooked issue in furan binder jetting, additional experiments are performed to demonstrate the extent of evaporation. For this, particle layers are deposited on a scale, the printhead deposits binder, and the resulting mass loss is recorded. With a better understanding of binder migration, new strategies can be developed to reduce geometric deviation, improve geometric precision, and possibly allow for higher layer thicknesses in furan sand binder jetting.
  • 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
    Hybrid Joining of Cast Aluminum and Sheet Steel Through Compound Sand Casting and Induction Heating To Enable Thin-Walled Lightweight Structures
    ( 2024)
    Locke, Christopher
    ;
    Guggemos, Martin
    ;
    Maier, Lorenz
    ;
    Hartmann, Christoph
    ;
    Volk, Wolfram
    ;
    Günther, Daniel
    Combining different joining processes to form a hybrid process offers new manufacturing possibilities. Adding induction heating to compound sand casting with additively manufactured lost sand moulds to preheat a metallic solid insert increases the degree of the metallic bond between sheet metal and casting metal. In this study, the manufacturability of thin-walled sheet steel/cast aluminum structures with reduced cast wall thickness in sand casting is characterized for the first time. Enabling lower wall thicknesses of sheet metal/cast metal structures in sand casting shifts the current limits and offers more significant lightweight construction potential. Shear tensile, compression shear, and pullout tests characterize the mechanical properties of the joints. Light microscopic imaging of metallographic samples quantifies the compound zone intermetallic (IMC) thickness. The shear tensile test specimens fail at wall thicknesses below 10 mm in the cast material, so metallurgical bond strength characterization does not occur. Therefore, the compression shear test is used to evaluate the metallurgical bond. Sound metallic bonding with smaller cast wall thicknesses of 8, 6 and 4 mm is achieved. Pullout specimens with 3 mm cast wall thickness further investigate the force-transmitting mechanisms of metallic bond, force-fit and form-locking. It is shown that metallic bonding is the predominant mechanism for force transmission when the compound sand casting process is enhanced by induction heating.
  • Publication
    Production of inorganic hollow cores using sacrificial ice cores
    ( 2024)
    Locke, Christopher
    ;
    Polzin, Hartmut
    ;
    Bissels, Joshua
    ;
    Günther, Daniel
    The production of hollow cores using 3D sand printing is state-of-the-art. Hollow cores are advantageous in decoring, gas permeability and material consumption. The methodology for producing hollow cores, as in 3D sand printing, is not transferable to core shooting. However, using sacrificial ice cores (SaIC) as a tool to produce hollow cores in a core shooting process enable complex hollow structures, as in 3D sand printing. Recently there has been an effort towards more environmentally friendly production. In this regard, water glass binders are in the focus of the metal casting industry and research institutions. This work presents a new method for producing water glass-bonded hollow cores using SaIC in a core shooting process. The manufacturing principle is detailed using a bending test bar and a near-series prototype core. The bending strength of the hollow bending test bars reaches up to 300 N/cm2. Due to the hollow structure, the decoring behaviour is significantly improved compared to solid cores.
  • Publication
    Predicting and Evaluating Decoring Behavior of Inorganically Bound Sand Cores, Using XGBoost and Artificial Neural Networks
    ( 2023-07-06)
    Dobmeier, Fabian
    ;
    Li, Rui
    ;
    Ettemeyer, Florian
    ;
    Mariadass, Melvin
    ;
    Lechner, Philipp
    ;
    Volk, Wolfram
    ;
    Günther, Daniel
    Complex casting parts rely on sand cores that are both high-strength and can be easily decored after casting. Previous works have shown the need to understand the influences on the decoring behavior of inorganically bound sand cores. This work uses black box and explainable machine learning methods to determine the significant influences on the decoring behavior of inorganically bound sand cores based on experimental data. The methods comprise artificial neural networks (ANN), extreme gradient boosting (XGBoost), and SHapley Additive exPlanations (SHAP). The work formulates five hypotheses, for which the available data were split and preprocessed accordingly. The hypotheses were evaluated by comparing the model scores of the various subdatasets and the overall model performance. One sand-binder system was chosen as a validation system, which was not included in the training. Robust models were successfully trained to predict the decoring behavior for the given sand-binder systems of the test system but only partially for the validation system. Conclusions on which parameters are the main influences on the model behavior were drawn and compared to phenomenological-heuristical models of previous works.
  • Publication
    Compound Casting of Aluminum with Sheet Steel in 3D Sand Casting Using an Inductive Heating System
    ( 2023)
    Locke, Christopher
    ;
    Guggemos, Martin
    ;
    Gruber, Maximilian
    ;
    Maier, Lorenz
    ;
    Mayr, Lukas
    ;
    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
    ;
    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.