Strain behaviour of aluminum 99.5 in micro‐forming conditions of the coining process

Abstract

The coining process can be identified as a shallow die forging. By using this process, it is possible to produce very fine surface geometries. This leads to dimension scaling into micro dimensions and causes the specific material behavior. In the micro area, continuum laws are not strictly followed anymore. The leading role in determining the deformation and strain level is taken by the fine surface geometry dimension and the size of the crystalline grain of the workpiece material. This is known as the size effect and defines all micro‐forming processes. In order to provide monitoring of the filling of the smallest die dimensions, additional supporting procedures should be used. In this case, radiography testing procedures for observing the specific points of the workpiece geometry are applied, characterized with very small dimensions (less than 0.5 mm). Testing aluminum samples are formed using two techniques – open and closed die coining, with identical surface geometry. Their crystalline structures are in two‐grain sizes of 34 μm and 80 μm. Scanning results show different material behaviour and different surface deformation for the same level of forming force in all four testing cases.