Ultrafast cooling and lubrication during hot die forging (T02#)

• Subject Area: Fluid Mechanics ; Mechanics
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 84292822

A power hammer or die used for metal forging must to be cooled after each working cycle to prevent its thermo-mechanical fatigue. Moreover, to reduce the friction between the die and the metal workpiece, the die has to be coated by a thin, uniform layer of lubricant, normally supplied in the cooling liquid. The simultaneous cooling and lubrication are often realized using a spray or a jet impingement process. The forging industry demands are to choose the most suitable spray system and operational parameters, which satisfy the required cooling requirements of the die and at the same time reduce environmental waste water with lubricant particles. A prerequisite to achieving this aim is a reliable predictive model for the evolution of the die temperature during spray cooling for pure water and for lubricants, in order to determine the allowed minimum duration of the working cycle and to optimize the amount of lubricant and the correct size and form of the lubricating particles/droplets, depending on the specific operating conditions. In this project a predictive tool is proposed, based on the validated theoretical model for pure water developed in the framework of the project C4 of the collaborative research centre SFB-TRR 75. Nevertheless, the addition of lubricants, in the form of solid particles of the size 1 to 100 micrometers, can potentially lead to significant changes in the regime maps of drop impact onto heated surfaces. For instance, these particles serve as nucleation sites, thus enhancing vapour bubble formation and evaporation, or larger inertial particles can potentially penetrate a vapour layer formed in the Leidenfrost regime. The accreted particles can then lead to pinning of the initial contact line. It is simply not yet known how colloidal drops with lubricant particles effect the cooling process. The main goal of this project is to provide the industry with a reliable model for spray cooling and for die lubrication based on a basic understanding of the main physical processes. The project will be performed by a consortium of academic and complementary industrial partners, each providing a significant and unique contribution. The specific tasks of the TU Darmstadt team include (i) laboratory investigation of the thermodynamic and hydrodynamic phenomena of single drop impact onto a very hot smooth or coated substrate at different lubricant concentrations, including description of heat transfer and residual shape of the lubricant layer; (ii) experimental study and modelling of heat flux during spray impact onto a hot substrate and characterization of the residual particulate layer after wall film evaporation. Further important tasks of the application partners: (iii) design and preparation of generic and optimal industrial lubricant mixtures; (iv) development of an industrial 3D code able to describe the wall cooling process by a lubricant spray, and its (v) validation and transfer an industrial environment.

• DFG Programme: CRC/Transregios (Transfer Project)
• Subproject of: TRR 75: Droplet Dynamics Under Extreme Ambient Conditions
• International Connection: France
• Applicant Institution: Universität Stuttgart
• Co-Applicant Institution: Technische Universität Darmstadt
• Business and Industry: Fuchs Lubritech GmbH ; Dr. Thomas Miekisch, Head of Lubrodal Division; Hammerwerk Fridingen GmbH; Umform- und Bearbeitungstechnik; Transvalor S.A. ; Dr. Etienne Perchat, Head of Development
• Project Heads: Professor Dr.-Ing. Ilia Roisman; Professor Dr.-Ing. Cameron Tropea