2010 年 51 巻 597 号 p. 953-957
A new extrusion process with bulge deformation type tribotest has been developed to investigate the frictional behavior of lubricant coatings on the surface of steel wire in cold forging. In the tribotest, the friction behavior in forward extrusion processing can be evaluated sensitively by adding bulge deformation. The sensitivity to the frictional shear factor was optimized by changing the land part shape and angle of the taper of the die entrance. The frictional shear factor of the lubricant coating can be obtained by plotting the measured forging load or the shape of the billet after forging on the calibration curve obtained by the finite element method. A series of experiments were carried out using two types of bonderized coating and a dry in-place lubricant coating. It was revealed that the variation in the frictional shear factor at processing temperatures from 20 to 200°C is less for the dry in-place lubricant coating than for the bonderized coating.