Over the past years, some efforts have been implemented to increase understanding of the role of friction in sheet metal forming. Many methods for determining the coefficient of friction (COF) have been studied and the most widely used is the method of bending under tension test. This method consists of pull a sheet through a pin of radius R with a specific angle, and makes it slide to measure the force acting on the sheet. The bending under tension test (BUT) is used to simulate the deformation of the material in the die radius where tensions are greatest. Through this test, it is possible to obtain, for example, information about the frictional forces, the lubrication effect, the die finishing and the material of the sheet. The aim of this paper is to describe the test and show the equations used to calculate the friction coefficient. There are several mathematical models to calculate the friction in the same test and there is no correlation between them.

bending under tension test, friction coefficient, sheet metal forming process.