The Frictional Force between Slug and Die in Shear Cutting after Material Separation

Abstract:

Frictional forces in sheet metal blanking are central in different aspects, e.g. in wear prediction, validation of simulation models or in so called slug pulling. The latter is a phenomenon where the slug is pulled out of the die by the punch after the sheet metal is separated. This leads to process disturbances reaching from a blocked belt feeder up to severe tool damage caused by the simultaneous cutting of the slug and the sheet metal strip. A sufficiently high frictional force between the slug and the die prevents this effect. Despite its importance, this force and its causes have not yet been investigated in detail. A method was developed in this paper to measure the frictional force between slug and die. A shear cutting tool with an integrated piezoelectric load cell and an inductive position sensor was used on a stamping press to cut sheet metal made of CuSn6 (R350, thickness 1 mm). The die clearance, the punch edge radii and the lubrication conditions were varied. A larger die clearance resulted in a lower frictional force while a larger punch edge radius increased it significantly. Lubrication reduced the frictional force, especially for small die clearances. Finally, the cause of the frictional force was investigated by identifying the relevant springback modes of the slugs. This was carried out by correlating the slugs' deflection, oversize, and clean cut height with the frictional force. Especially the slug oversize, i.e. the difference between the slug's diameter and the die's inner diameter, revealed a strong correlation. Calculations showed that the deformation in radial direction is the main cause of the frictional force between slug and die. It suggests that the slug oversize is a good measure for the magnitude of the frictional force.

• Periodical: Key Engineering Materials (Volume 883)
• Pages: 285-293
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.883.285
• Online since: April 2021
• Authors: Jens Stahl*, Isabella Pätzold, Lucas van den Bosch, Alexander Kindsmüller, Roland Golle, Wolfram Volk
• Keywords: Blanking, Friction, Slug Pulling

References

[1] V. Tittel, L. Bernadič, A review of methods and precautions against slug pulling, International Journal of Pure and Applied Sciences and Technology 12(1), 7-15 (2012).

[2] V. Tittel, L. Bernadič, Comparison of methods controlling slug pulling by using an indirect method in automotive industry, International Journal of Mechanical Engineering 2(10) (2012).

[3] R.A. Schmidt, M. Hellmann, R. Burkhard, P. Rademacher, P. Höfel, F. Birzer, H. Hoffmann, Cold Forming and Fineblanking, 2nd edn. Carl Hanser Verlag, München Wien (2007).

[4] H. Gürün, M. Göktaş. A. Güldaş, Experimental examination of effects of punch angle and clearance on shearing force and estimation of shearing force using fuzzy logic, Transactions of Famena 40(3), 19-28 (2016),.

DOI: 10.21278/tof.40302

[5] T. Kopp, J. Stahl, P. Demmel, P. Tröber, R. Golle, H. Hoffmann, W. Volk, Experimental investigation of the lateral forces during shear cutting with an open cutting line, Journal of Materials Processing Technology 238, 49-54 (2016),.

DOI: 10.1016/j.jmatprotec.2016.07.003

[6] E. Gustafsson, L. Karlsson, M. Oldenburg, Experimental study of strain fields during shearing of medium and high-strength steel sheet, International Journal of Mechanical and Materials Engineering 11(1), 14 (2016),.

DOI: 10.1186/s40712-016-0067-x

[7] J. Ramaekers, J. Kals, Strain, stresses and forces in blanking, Proceedings of the IMC Conference Galway, pp.126-138 (1986).

[8] E. Doege, T. Liesener, Schneidkraftbedarfsermittlung beim Scherschneiden von Feinblechen, EFB-Forschungsbericht, Hannover (1999).

[9] M. Sasada, K. Shimura, I. Aoki, Coefficient of friction between tool and material in shearing, JSME International Journal Series C Mechanical Systems, Machine Elements and Manufacturing 49(4), 1171-1178 (2006).

DOI: 10.1299/jsmec.49.1171

[10] C. Husson, J.P.M. Correia, L. Daridon, S. Ahzi, Finite elements simulations of thin copper sheets blanking: study of blanking parameters on sheared edge quality, Journal of Materials Processing Technology 199(1-3), 74-83 (2008),.

DOI: 10.1016/j.jmatprotec.2007.08.034

[11] R.Q. Hsu, J.R. Chang, D.L. Liang, Prediction of slug carry-up by the punch in blanking by air-blow of the slug. Journal of Materials Processing Technology 201(1), 252-255 (2008), 10th International Conference on Advances in Materials and Processing Technologies.

DOI: 10.1016/j.jmatprotec.2007.11.297

[12] P. Sachnik, Methodik für gratfreie Schnittflächen beim Scherschneiden, Dissertation, Technische Universität München, München (2017).

[13] KME Germany GmbH & Co. KG: C51900 CuSn6 Industrial Rolled, (2017) accessed 13.10.(2020).

[14] T. Mang, W. Dresel, Lubricants and Lubrication, Wiley-VCH, Weinheim (2017).

[15] H. Kuchling, Taschenbuch der Physik. Fachbuchverlag Leipzig im Carl-Hanser-Verlag, München (2011).

[16] U. Gamer, Elastic-plastic deformation of the rotating solid disk, Ingenieur-Archiv 54(5), 345-354 (1984).

DOI: 10.1007/bf00532817