Franzen, Daniel M.Sc.
Head of Investment Casting
Chair for comprehensive Foundry Science and Foundry Institute

Tel.: +49 (0) 241 80 - 98250

Precision Casting

For the further or new development of various investment casting processes, a wide range of plant technology is in use; including wax spraying, sanding and embedding equipment, a manually operated devesting plant, a multi-wave vacuum casting plant based on the Bridgman principle of the type VIM IC 5 S from ALD. Key data of this plant are casting weights from 1.5kg to 50kg, casting and heating temperatures of 1700°C and maximum mold shell dimensions of 600mm in diameter and 750mm in height. This new equipment provides improved analysis capabilities for the individual process steps, process parameters and solidification sequences, thus offering new possibilities for microstructure control. The increased process understanding and the high manufacturing flexibility allow a secured industrial suitability of the process. With this equipment, research can be carried out on state-of-the-art investment casting processes. Process development includes all process steps: Wax pattern production, molding material development, production of ceramic mold shells, alloy development and casting technology. Process development includes, for example, work on the latest fiber-reinforced materials as well as modern superalloys and other high-performance materials. In addition, process development can be accompanied by simulations at any time.

Ni based superalloys

The manufacturing process of complex single-crystal blades of modern gas turbines involves time-consuming, cost-intensive process steps and high material costs. A high reject rate of defective turbine blades due to the complex manufacturing process quickly leads to low value added. For this reason, cost-saving new processes, scrap-minimizing process optimization and alloy development to reduce expensive alloying elements are the focus of the following projects:

- Innovative process technology (DWDS) for directional solidification.

- Undercoolability of superalloys with the alloying elements Co, Re and Ru

- Mechanism of formation of the casting defect "Freckles”

- Scrap minimization by reduction of large angle grain boundaries at cross section changes during directional solidification

Properties of open-cell Al-alloy foams

Multiscale characterization of interactions between microstructure and geometry for tailoring the properties of open-cell Al alloy foams (DFG)

Duration: 01.02.2020 - 30.01.2023

Participating research institutions: Foundry Institute, TU Berlin

Different structural levels influence the mechanical properties of metallic foams, known as the structural hierarchy. On the smallest level, the microstructure as well as the arrangement of the phases, which are mainly influenced by the alloy and the heat treatment, are decisive for the mechanical properties. At the mesoscopic level, the design of structural struts and plates form edges and faces of cells. Finally, cell configuration and geometry design of cells influence foam properties.

In this project, the effects of various parameters at the above-mentioned levels on the mechanical properties of open-cell aluminum foams are investigated. These are produced via investment casting route. The parameters specifically considered include the influence of alloying elements and heat treatments, as well as the influence of different cell structures. In order to vary the cell geometry of the foams in a targeted manner, additive manufacturing technology is used, which allows different geometries to be investigated quickly and flexibly.

Stress and crack formation in investment casting shells

Investigation of stress and crack formation in investment casting shells during the melting process in a steam autoclave (AiF)

Duration: 01.08.19 - 31.07.21

Participating research institutions: Access e.V.

Foundry Institute started the project "Steam autoclave" together with Access e.V.. In this project, stress and crack formation in investment casting shell moulds during dewaxing process in a steam autoclave is investigated.

Investment casting is a versatile casting manufacturing process for high-precision and complex components. In several process steps, ceramic layers are applied to a disposable model material, this model material is later removed from the “green” ceramic shell mould, and the mould is subsequently sintered. A key process step here is the removal of model material from ceramic mould using a steam autoclave. Since waxes usually used as pattern materials have a higher coefficient of thermal expansion than ceramic shell moulds, heating a shell mould with a wax pattern inside it causes compressive stresses in the shell mould. This can lead to cracks and thus either to costly repair or directly to rejection of the shell mould. For this reason, a simulation model is being built in order to better understand stress and crack formation during such a dewaxing process, and to identify also avoid areas susceptible to cracking when designing model patterns and shell moulds.

MC Carbides

Multiphase solidification and polycrystalline microstructures in single crystal superalloys (DFG)

Duration: 01.03.18 - 31.08.20

The solidification behavior of nickel-based superalloys is very complex due to the multi-component systems with 6 to 10 alloying elements, and the solidification processes consist of a series of multiphase transitions. The low diffusivity of the alloying elements leads to significant segregation under non-equilibrium solidification, resulting in the formation of a eutectic microstructure at the dendrites and instability of the mechanical properties. In carbon-containing alloys, additional MC carbides form in the interdendritic residual melt. Eutectics can also nucleate on these carbides and thus have a different crystal orientation than the single crystal. To investigate these solidification mechanisms, quenching tests (see figure) are carried out in addition to casting tests in an industrial-scale Bridgman facility. Here, the alloying elements and the process parameters are varied in order to achieve an increase in performance and process optimization.