Determination of the temperature development in the cryogenic range for determination of heat transfer coefficient

Abstract

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. The accuracy of a thermomechanical simulation depends on thermal parameters and the description of the heat transfer. The presented data contains an experimental setup and the measured temperature development in the workpiece and tools for determining heat transfer coefficient. Here the workpiece is made of AA6014 and the tools are made of 1.7225. The workpiece is cooled in liquid nitrogen before the tests, while the tools remain at room temperature. The temperature is continuously measured, while different amounts of contact pressure starting at 0.1 MPa up to 50 MPa are applied. The heat transfer coefficient can then be calculated for the different contact pressure. The heat transfer coefficient between workpiece and tools can be determined from the experimentally determined temperature time series. The challenge here is the continuous change of the workpiece temperature and that no equilibrium is achieved. Therefore, a computation method was developed using least square fitting between the model output and the measured temperature curves, with the heat transfer coefficient as the parameter to optimize. The code for the parameter identification is published on GitHub: https://github.com/tud-if-ff/CryoHTC. A detailed description of the experimental setup and the used model for determining the heat transfer coefficient is published in the upcoming participation at the International Conference for Technological Plasticity 2023, with the working title: "Contact conditions and temperature distribution during cryogenic deep drawing with macro-structured tools".