Mechanical Aspect of Manufacturing of Metal Foil by Forging

Abstract

This study aims to give a mechanical explanation to manufacturing of metal (silver) foil in a traditional Japanese way in which the foils are put between Japanese papers and forged. It was clarified by forging tests carried out at various forging pressures that the forging pressure necessary for manufacturing silver foil is about 30 MPa, which is equal to one tenth of the yield stress in a 90 rolled specimen. The test also showed that the plastic elongation of foil is of the order of 0.1 per forging (pressure is 30 MPa). This result suggests that the foil is not stretched by forging pressure, but by frictional tensile stress applied to the foil by the Japanese paper. Another test to measure the elastic property of paper showed that the Japanese paper was elongated by 0.5～0.6 in the paper plane when it was compressed in the vertical direction at the pressure of 30 MPa. Considering the elastic strain of foil, the value of 0.5～0.6 agreed well with the plastic elongation of foil of 0.1. The forging tests also showed that the lower limit of foil thickness is dominated by the ability of paper not to adhere to the silver foil (removability); for example, it was 1 mm for some papers, but 0.4 mm for others. Keywords: forging, Japanese traditional way, silver foil, Japanese paper, deformation property, forming limit