Estimation of Frictional Coefficient between Punch and Billet at Back-Stroke in Backward Can Extrusion Test of Steel

Abstract

A backward can extrusion test provides severe tribological conditions because high pressure, high temperature, and large surface expansion ratio affect the lubricant. During the forward stroke these conditions intensify with increasing cup depth of the extruded workpiece; additionally, the back-stroke force during retraction of the punch rises to a significant level under a poor-lubricated condition. This study estimates the coefficient of friction μp between punch and workpiece during the back-stroke by combining experiments using conventional soap-phosphate coated steel and numerical analysis by FEM. The values of μp were estimated to be 0.09 and 0.03 in case of small and large workpiece depth, respectively. Friction decreased with elevating temperature.

Effect of pretreatment by shotblasting prior to lubrication for cold forging

“…Furthermore, it is large when using a punch with a large nose radius. For example, the report has shown experimentally that the surface expansion is larger than 180 when h0 = 36 mm, rp = 4 mm (Danno et al, 1983;Asai and Kitamura, 2021) and more sever condition when h0 = 36 mm, rp = 8 mm (Nonoyama et al, 1993a(Nonoyama et al, , 1993b. Each test measures a punch pushing load at the forward stroke and the punch pulling force at the backstroke to estimate the maximum pushing load and the maximum pulling force.…”