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Citation link: https://doi.org/10.26092/elib/156
DMFOAJ_6_2020_128-165_Reichardt.pdf
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Tribological system for cold sheet metal forming based on volatile lubricants and laser structured surfaces


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Authors: Reichardt, Gerd 
Wörz, Christoph 
Singer, Markus 
Liewald, Mathias 
Henn, Manuel  
Förster, Daniel J. 
Zahedi, Ehsan  
Boley, Steffen 
Feuer, Anne  
Onuseit, Volkher  
Umlauf, Georg  
Reichle, Paul 
Barz, Jakob Philipp  
Tovar, Günter  
Hirth, Thomas 
Editors: Vollertsen, Frank  
Abstract: 
A novel tribological system has been developed, in which volatile lubricants (carbon dioxide - CO2 or nitrogen- N2) are used as a substitute for mineral oil-based lubricants in deep drawing processes. This process enables the introduction of an intermediate medium under high pressure through flow-optimized, laser-drilled micro holes into the contact surfaces. This eliminates the need for subsequent, cost-intensive cleaning processes, as the volatile lubricants evaporate without leaving any residue during expansion to ambient pressure.
The design of initial micro hole geometries was based on simulations of the flow behaviour of the lubricants passing through, which in turn were validated using pressure reactor tests. In addition, the wetting behaviour of CO2 on relevant surfaces (tool surface and sheet material surface) was investigated experimentally using the captive-bubble-method. Thus, the optimal design of the micro holes (diameter, hole geometry and number of micro holes) could be determined using flat strip drawing tests. The optimal micro hole geometry determined in this way is suited for the use of both CO2 and N2 as volatile lubricant. Furthermore, extensive investigations for the production of the required micro hole geometry by laser drilling were carried out. The fundamentals for drilling micro holes in steel with high aspect ratios could be developed using an ultrashort pulsed research laser with very high pulse energy. Further experiments were conducted using an ultrashort pulsed prototype laser of the kW-class specially developed to increase productivity when drilling a multitude of micro holes with higher average laser power. The novel tribological system has been characterised by means of strip drawing tests and stretch bending tests. For both, CO2 (liquid) and N2 (gaseous), relatively low friction values could be achieved compared to conventional lubricants. It could be shown that deep drawing with both CO2 and N2 as dry lubricants is possible. Here, usage of the volatile lubricants not only allows the replacement of mineral oil based lubricants, but even improves the tribological system with regard to frictional forces in sheet metal forming. The feasibility of the new tribological system has been proven by performing deep drawing tests of rectangular cups. These tests showed a significantly enlarged process window of the forming process, which emphasise the tremendous potential of this new tribological system.
Keywords: Dry Metal Forming; Deep drawing; Ultrashort pulsed laser drilling; Volatile Lubricant
Issue Date: 12-Jun-2020
Project: SPP1676 
Journal/Edited collection: Dry Metal Forming Open Access Journal 
Start page: 128
End page: 165
Type: Artikel/Aufsatz
DOI: 10.26092/elib/156
URN: urn:nbn:de:gbv:46-elib43711
Institution: Universität Bremen 
Faculty: Zentrale Wissenschaftliche Einrichtungen und Kooperationen 
Institute: BIAS - Bremer Institut für angewandte Strahltechnik GmbH 
Appears in Collections:Forschungsdokumente

  

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