2020 年 61 巻 2 号 p. 289-294
The effect of production rate on the lubrication performance of an environmentally-friendly lubricant in the cold forging of aluminum alloy was investigated using the tribological test of combined forward-can and backward-can extrusion proposed by one of the present authors. In this test, the lubrication performance was examined by both finite element analysis and experimentally. A double-layer-type environmentally-friendly solid lubricant was used. The undercoat plays the role of mitigating pick up, whereas the overcoat reduces friction. Using finite element analysis, a calibration diagram of the relationship between the extruded geometry of the workpiece and the punch stroke was prepared at the production rate of 1 and 20 stroke per minutes. The Coulomb friction coefficient between the workpiece and the outer die was identified by plotting the punch stroke and the extruded height of the workpiece on the calibration diagram. Three different surfaces of annealed aluminum alloy A4032 formed by different treatment conditions were used. The first is a surface roughened by a lathe, the second is a surface roughened by a lathe and then alkali-etched, and the third is a surface roughened by a lathe and then shot blasted. The tests were performed by varying the punch stroke between the two production rates. As a result, the dependency of the friction coefficient on the production rate was reasonably clarified, and the friction coefficient value estimated was higher when the production rate was smaller. A significant influence of the surface treatment on the friction coefficient was not observed due to the moderate deformation resistance of workpiece material.
