Frictional characteristics of steel sheets used in automotive industry

Abstract

In this paper the results of experimental tests aimed to determine the friction coefficient in sheet metal forming operations for various sheet metal materials and at different operative conditions are presented. The research has considered the frictional characterization of three kinds of drawing quality steels that are commonly used in automotive industry. These are a drawing quality steel (DQ), a deep drawing quality steel (DDQ), and extra deep drawing quality steel (EDDQ). For measurement of the sheet surface topography, a 3D stylus instrument Alicona InfiniteFocus was used. To determine the friction coefficient three tribological tests, i.e. a strip drawing test, a draw bead test and a pin-on-disc tribometer, have been conducted. The experimental results have ascertained several relationships showing the effect of sheet metal surface roughness, lubricant conditions and sheet orientation on the value of friction coefficient in sheet metal forming processes. The results further showed that the surface topography and sample orientation in the rolling direction of the sheet are significant factors that influence the friction coefficient. It was found that the tested steel sheets, selected from automotive industry applications, exhibit anisotropic resistance to the friction corresponding to the measured orientation in relation to the rolling direction of the sheet.

Evaluation of friction coefficient of an auto-body steel sheet

“…In consequence the coefficient of friction value changes with the change of load. This relationship is also observed in other recent studies [2].…”

“…The phenomenon of flattening causes an increase in the real contact area. The increase in the real contact area occurs gradually from the initial peak surface roughness contact to full contact after balancing normal force and the force required to deform roughness [2].…”

“…The role and effects of the occurrence of frictional resistance are difficult to define. The unfavourable effects of the presence of frictional resistance include, among others [1][2][3]: non-heterogeneity of drawpiece deformation, an increase of the pressure exerted by the punch causing a danger of crack occurrence, as well as the worsening of the surface quality of a drawpiece. Beneficial effects of the frictional resistance on the forming process may include friction existing between the sheet metal and the punch because it increases the permissible value for the maximum force in deep-drawing.…”

Experimental Evaluation of Draw Bead Coefficient of Friction

“…The effectiveness of friction reduction by resin is highest in the case of testing a specimen width of 7 mm: a twofold decrease of friction coefficient is observed. As observed by Trzepieciński et al [1], in sheet metal forming, the real contact area plays an important role in determining the frictional resistance. The character of sheet deformation during the passing of the sheet strip on the drawbead depends on sheet width and is manifested by a change of the shape of the rectangular cross-section into a convex cross-section (Fig.…”

“…The friction conditions are dependent on the tribology system, i.e. the applied pressure load, surface roughness -both of sheet metal and tool and process conditions (static or dynamic loads, forming temperature, sliding speed) [1][2][3][4]. The friction mechanism also depends on the material of the tool and the relative hardness of the surface of the specimens to the tool materials [5,6].…”