Universität Stuttgart

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Institute: search.filters.UBSInstitut.Institut für StrahlwerkzeugeAuthor: search.filters.author.Tovar, Günter E. M.

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    ItemOpen Access
    Friction and wear behavior of deep drawing tools using volatile lubricants injected through laser-drilled micro-holes
    (2021) Reichardt, Gerd; Henn, Manuel; Reichle, Paul; Umlauf, Georg; Riedmüller, Kim; Weber, Rudolf; Barz, Jakob; Liewald, Mathias; Graf, Thomas; Tovar, Günter E. M.
    In deep drawing processes, the use of lubricants is mandatory in order to prevent wear on tools and surface damage to the formed sheet metal components. Here, frequently used lubricants are synthetic and mineral oils, emulsions, and waxes. However, these conventional lubricants have to be applied to the sheet material prior to the forming operation and removed afterwards by cleaning processes. Additionally, the lubricants often contain substances that are harmful to the environment and to human health. To counteract these economic and ecological disadvantages, research is currently being conducted on a novel tribological system. For this, volatile media such as liquid carbon dioxide and gaseous nitrogen are being used, and are introduced directly into the friction zones between the tool and the sheet metal material during deep drawing under high pressure through special laser-drilled micro-holes. This paper covers the latest investigations and findings regarding the design of flow-optimized micro-holes, the laser drilling process, the friction characterization on tool radii, and the tool wear to be expected when using the lubrication medium CO2.
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    ItemOpen Access
    Volatile lubricants injected through laser drilled micro holes enable efficiently hydrocarbon-free lubrication for deep drawing processes
    (2023) Reichle, Paul; Reichardt, Gerd; Henn, Manuel; Umlauf, Georg; Barz, Jakob; Riedmüller, Kim Rouven; Liewald, Mathias; Tovar, Günter E. M.
    In order to reduce the use of classic lubricants such as synthetic or mineral oils, emulsions or waxes in the deep drawing process, a new tribological system based on volatile lubricants was investigated. In this system, a volatile medium is injected under high pressure through laser drilled micro holes directly into the contact zone between the tool and the sheet metal and serves as a temporary lubricant. In order to investigate this tribological system under realistic conditions, strip drawing experiments with different volatile lubricants (air, nitrogen, carbon dioxide and argon) were performed on galvanized sheets. Therefore, a new generation of strip drawing tools was designed and numerically calculated for low elastic deformations to ensure a uniform contact pressure distribution over the entire friction contact area. To obtain a homogeneous distribution of the volatile lubricants, a number of micro holes with a depth of several millimeters were drilled into the hardened strip drawing jaws using ultrashort pulsed laser radiation. Taking into account the capabilities of this laser drilling technique in terms of size and shape of the micro holes, computational fluid dynamics simulations were performed to predict the flow behavior of the lubricant within the micro hole as well as the contact zone and were compared with observable effects in outflow tests. The chemical composition of the acting tribological layers was characterized by means of X-ray photoelectron spectroscopy and their changes during the deep drawing process were correlated with the lubricants used as well as the measured wear and friction values.