Modelling of friction for high temperature extrusion of aluminium alloys

Modelling of friction for high temperature extrusion of aluminium alloys

Wang, L.

Katgerman, L. (promotor)

Mechanical, Maritime and Materials Engineering

Materials Science & Engineering

2012-02-06

In recent years, finite-element (FE) simulations have been extensively used in scientific research and industrial practice to analyse the extrusion process. A basic issue of FE simulations is the accuracy of the results, which is mainly determined by the viscoplastic material behaviour of aluminium alloys at elevated temperatures and the determination of boundary conditions, especially the friction boundary condition. In this thesis, the determination of friction boundary conditions for hot aluminium extrusion process was done by using the short sliding distance ball-on-disc test at elevated temperatures. A mathematical model for high-temperature ball-on-disc tests was developed. This model is capable of discriminating the individual contributions of ploughing and shearing friction to the apparent friction. It was found that during high-temperature ball-on-disc tests, the friction coefficients obtained from ball-on-disc tests alone were insufficient to represent the frictional interaction between deforming aluminium and steel at elevated temperatures. Based on the ball-on-disc test results, a novel physically based friction model (adhesive strength friction model: ASFM) was developed for the bearing channel of an aluminium extrusion die. To verify this friction model, a novel extrusion testing method, double action extrusion (DAE), to highlight the effect of friction at the die bearing in aluminium extrusion was developed. The ASFM was implemented into the FE simulation of DAE tests, and good agreements between the FE predictions and experiments were obtained, indicating that ball-on-disc test is an effective way of characterizing the friction for the bearing channel of extrusion dies. For a further understanding of the DAE, a theoretical model was developed, and a good agreement between the modelling results and experiments was obtained. The theoretical modelling results revealed that the length difference of the extrudates was caused by the combined effects of friction and material rate dependency at elevated temperatures.

extrusion
friction
aluminium alloys

http://resolver.tudelft.nl/uuid:6f76d5c3-5cc2-4cdf-a2af-d6cb1323e289

9789461820785

Institutional Repository

doctoral thesis

(c) 2012 Wang, L.