EXPERIMENTAL DETERMINATION OF THE DRAW BEAD COEFFICIENT OF FRICTION OF CuZn SHEETS IN SHEET METAL FORMING PROCESSES

In sheet metal forming, draw beads are used to limit the flow of sheet metal in specific areas of the stamping die. The value of the coefficient of friction at the draw bead determines achievement of the desired resistance to sheet displacement. This article presents the results of experimental tests for determining the coefficient of friction on a draw bead using a specially developed tribotester. The test material consisted of CuZn37, CuZn30 and CuZn10 brass sheets in various states of hardening. Investigations were carried out with different roughness of the countersamples and sliding speeds. In addition, the tests were carried out under conditions of dry friction and lubrication of the sheet surface with LAN-46 machine oil. The relationships between the process parameters and the value of the coefficient of friction were analysed using the analysis of variance. It was found that the coefficient of friction decreases with increasing mean roughness of the countersamples. Lubrication reduced friction by about 6.2-29.8% depending on the grade of the tested sheet and the sliding speed.