Tribological Behaviour of Lubricants in Hot Stamping of AA6016

Abstract:

The increasing demand for fuel-efficient vehicles has led automotive industry to introduce new alloys in car manufacturing, characterized by a high stiffness and strength-to-weight ratio. Due to their mechanical and chemical properties, aluminium alloys appear potential candidates to replace traditional steels for several parts of the car-body-in-white, even if the limited formability at room temperature, the marked springback and the severe tribological behaviour have often represented important drawbacks in traditional properties. Recently, the use of temperature-assisted processes, such as hot stamping, allows overcoming such limits thanks to substantial increase of the formability and, at the same time, a drastic reduction of springback. However, the choice of proper process parameters, in terms of lubrication at the interfaces between the dies and the blank, and thermal parameters of the dies materials still represent critical points for the feasibility of the process. Recent investigations have proved the limits of assuming constant friction for all the areas of the dies and the steps of the deformations, especially with variable pressures and non-constant temperatures at the interfaces. Such factors, together with the lubricants and the lubricant deposition on the blank, the blank and dies coatings, the surface roughness, the stamping speed are not always considered, despite their considerable influence on the process tribology. In this paper the friction behaviour of commercially available automotive aluminium (AA6016 alloy) is studied. The friction coefficient is measured by means of a new machine for strip draw test at different levels of pressure, temperature, sliding speed and type of lubricant. The results report the investigation of the surface topography of the metal sheets, investigated by Energy-Dispersive X-ray spectroscopy and optical profilometry.

• Periodical: Key Engineering Materials (Volume 639)
• Pages: 221-226
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.639.221
• Online since: March 2015
• Authors: Francesco Medea, Andrea Ghiotti, Stefania Bruschi
• Keywords: Aluminium, Hot Stamping, Lubricant

References

[1] Mohamed S. Mohamed, Alistair D. Foster, Jianguo Lin, Daniel S. Balint, Trevor A. Dean, Investigation of deformation and failure features in hot stamping of AA6082: Experimentation and modeling, International Journal of Machine Tools & Manufacture 53 (2012).

DOI: 10.1016/j.ijmachtools.2011.07.005

[2] I. N. Fridlyander, V. G. Sister, O. E. Grushko, V. Berstenev, L. M. Sheveleva, L. A. Ivanova, Aluminium alloys promising materials in the automotive industry, Metal Science and Heat Treatment, Vol. 44, Nos. 9 – 10, (2002).

DOI: 10.1023/a:1021901715578

[3] R.P. Garrett, J. Lin , T.A. Dean, An investigation of the effects of solution heat treatment on mechanical properties for AA 6xxx alloys: experimentation and modeling, International Journal of Plasticity 21 (2005) 1640–1657.

DOI: 10.1016/j.ijplas.2004.11.002

[4] W.S. Miller, L. Zhuang, J. Bottema, A.J. Wittebrood, P. DeSmet, A. Haszler, A. Vieregge, Recent development in aluminium alloys for the automotive industry, Materials Science and Engineering A 280 (2000) 37–49.

DOI: 10.1016/s0921-5093(99)00653-x

[5] Paolo F. Bariani, Stefania Bruschi, Andrea Ghiotti, Francesco Michieletto, Hot stamping of AA5083 aluminium alloy sheets, CIRP Annals - Manufacturing Technology 62 (2013) 251–254.

DOI: 10.1016/j.cirp.2013.03.050

[6] N. Mori, (Ed. ), Digital Die Design System—Final Report, (2005).

[7] Hyunok Kim, Edison Welding Institute Nimet Kardes, The Ohio State University, Friction and Lubrication, Chapter 7, (2012).

[8] I.G. Masters, D. K. Williams, R. Roy, Friction behaviour in strip draw test of pre-stretched high strength automotive aluminium alloys, International Journal of Machine Tools & Manufacture73 (2013) 17–24.

DOI: 10.1016/j.ijmachtools.2013.05.002

[9] Datasheet by Acheson, product Pulve® MoS2 D18 A, molybdenum disulphide in aerosol.

[10] Ghiotti A, Sgarabotto F, Bruschi S, Medea F, Novel wear testing apparatus to investigate the reciprocating sliding wear in sheet metal forming at elevated temperatures, Metal Forming 2014, Palermo Italy, 21-24 September 2014, pp.1158-1166.

DOI: 10.4028/www.scientific.net/kem.622-623.1158

[11] Giovanni Straffelini, Attrito e usura Metodologie di progettazione e controllo, first ed., Tecniche Nuove, Milano, (2005).