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Determination of coefficient of friction under conditions of deep-drawing and stretch forming

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DOI: 10.1016/0043-1648(73)90070-7


Abstract Lubrication plays an important role in deep-drawing and stretch forming processes. It effects the boundary frictional (shear) stresses and modifies the strain distribution across the product quite considerably. The location of plastic instability and fracture, and the magnitude of the instability or fracture strains in stretch forming and deep-drawing depends largely on the lubrication conditions between sheet metal and the tools. The effectiveness of boundary lubricants can be determined by finding the operatuve coefficient of friction between sheet metal and the tool. For this purpose, two different methods for the determination of coefficient of friction were developed. The first method is applicable to the radial drawing region (between sheet metal and die) in deep-drawing. The second method is applicable by finding the operative coefficient of friction between sheet metal and the tool, experimentally measured quantities such as loads and strain distributions, the coefficients of friction can be calculated using analytical equations. The results indicated that the coefficient of friction varied as a function of the plastic deformation. Coefficients of friction in stretch forming were found to be much higher than those in radial drawing. Experimental results indicated that plastic films could be more effective in reducing friction than grease type lubricants. The methods developed can be used in the evaluation of the lubricants in such processes. They can also be used to provide the necessary coefficients of friction to be used in metal forming theories.

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