Surface Stress Measurements using Conical Oblique Pins on a Forging Die Mandrel

Abstract

Normal and friction stresses on a die mandrel were measured simultaneously using oblique pins when precision forging three different hollow shapes. The pins were conical to eliminate extrusion of the workpiece into the pin/bore clearance that occurs with previous designs. The variation of normal pressure and the direction of the friction force over the mandrel depends on the stage of die filling when a T-sectioned shape is forged. In general friction stresses approach the yield shear stress of the workpiece when the normal pressure becomes about twice the workpiece yield stress. Up to this value of contact pressure Amonton's friction law is applicable. Experimental results were found to be in good agreement with predicted ones.