Kazuhito Asai

Evaluation of Tribological Performance of Lubricants and Nitrided Die for Hot Forming of Steel Using Tapered-Plug Penetration Test

High performances of tool materials and lubricants have been necessarily developed to extend die life for hot forming of steel. To promote the developments, economical and simple evaluation testing methods have been required. Tribological performances of tool materials, surface treatments, and lubricants are examined by this test. In this paper, a tapered-plug penetration test has been devised for hot forming of steel. It was found that the combination of an appropriate non-graphite lubricant and a nitride die was effective in reducing in galling and friction between a die and a work by the tapered-plug penetration test.

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

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.