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Lightweight materials such as aluminum alloys have an important role to play in weight reduction. However, their limited formability at room temperature poses a major challenge and restricts their use. Significant improvements in formability can be achieved by heat-assisted forming processes. However, this improvement in formability is generally associated with a change in microstructure that leads to a reduction in strength. Alternatively, improved ductility and formability can be achieved at cryogenic temperatures without the disadvantages of warm forming processes. In this project, the focus is on developing a new process for forming aluminum alloys at cryogenic temperatures without active cooling. For this purpose, macro-structured tools are used to reduce the contact area between the tool and the blank. The aim is to minimize the heat flux to the blank to maintain low temperatures during forming. This is to take advantage of the improved formability of aluminum alloys at cryogenic temperatures and thus extend the process window for deep drawing of aluminum alloys. This data collection contains material characterization data required for numerical process modelling. The focus is on the characterization of thermal and mechanical properties at blank temperatures.
High-speed processes can lead to significant technological advantages like an increased formability, reduced springback or an improved quality of cutting edges. For conventional forming processes, quasi-static conditions are a good approximation and numerical process optimisation is state of the art. However, there is still a need for research in the field of material characterisation for high speed forming and cutting processes. Production technologies with high velocities leads to high strain rates and the dependency of strain hardening and failure behaviour on the forming velocity cannot be neglected. Therefore, the data of the material behaviour at high strain rates is required for modelling high velocity processes. The challenge here is the measurement of relevant process quantities due to short process time that requires a very high sampling rate and the limited size and accessibility of the specimen. In this context, an inverse method for determining material characteristics at high strain rates was developed. The approach here is the measurement of auxiliary test parameters, which are easier to measure and then used as input data for an inverse numerical simulation. Two devices were implemented for different ranges of strain rates: a pneumatically driven device for strain rates up to 1.000 1/s and an electromagnetically driven accelerator for strain rates up to 100.000 1/s. The method developed by Psyk et al. is presented in detail in the contribution "Determination of Material and Failure Characteristics for High-Speed Forming via High-Speed Testing and Inverse Numerical Simulation". https://doi.org/10.3390/jmmp4020031. In order to test and comprehend the inverse method for material characterisation the experimental data and the FE-model (LS-Dyna) are presented in case of the electromagnetically accelerated unit. The experimental data are the displacement curve of the flyer and the recorded elastic strain curve of the solid rod for determining the force. The FE-model contains the whole test setup (flyer, specimen, measurement rod) and the determined flow curves as well as the data for the damage behaviour.
In high strain rate forming processes two superposing and opposing effects influence the flow stress of the material: strain rate hardening and thermal softening due to adiabatic heating. The presented FE-model and experimental results are based on https://doi.org/10.3390/app12052299 where uniaxial tensile tests at different high strain rates are analyzed experimentally and numerically to understand the influence of adiabatic heating of the workpiece during deformation under high-speed loading. A thermal camera and a pyrometer were used for temperature measurement in the fracture region in addition to the measurement of force and elongation. The numerical simulations are carried out in LS-Dyna using the GISSMO model for modeling damage and failure.
Based on the material properties determined in "Forming and cutting at high strain rates Part 1" and "Part 2", the applicability of the methodology and the material characteristics are verified using a high-spped blanking process of DC06. This data collection includes the numerical model of the Butzen as well as the experimental data of the high-speed shear cutting process and figures of the resulting slugs. A detailed description of the experimental setup and the method is published in https://doi.org/10.21741/9781644902417-4.
Based on the material properties determined in "Forming and cutting at high strain rates Part 1" and "Part 2", the applicability of the methodology and the material characteristics are verified using a deep drawing process with strain rates up to 100 1/s. This data collection includes the material and failure characteristics of the deep drawing steel DC06 at high strain rates and a FE-model for deep drawing at high velocities. The numerical model as well as experimental and numerical results are first presented in doi.org/10.1088/1757-899X/1238/1/012047.