Development of design tools for coining process using FEM

Coining is a forging process in which a metallic disk, characterized by a low volume-surface ratio, is deformed with the aim to impress 3D images on its three surfaces. Due to the large production volumes and the high quality standards required for the final products in terms of final dimensions, tolerances and surface finishing, such cold forging process requires a careful evaluation and choice of the proper operation parameters. To facilitate the design process and understand the mechanism and metal flow during the minting process of a silver coin, a study was undertaken to develop the design tools for coining process.;Using the material properties and frictional parameters obtained, a two-dimensional axisymmetric coining process was simulated with a FEM code, ABAQUS. The model consists of a blank, dies and collar that form the blank into a coin. The compression force, deformation pattern and stress, strain contours were predicted, which illustrates how the material flows as the deformation progresses. Through the FEM simulations, three major coining design parameters were investigated: die curvature, rim height and surface relief. By changing one of them at a time, coining loads, material flow, stress and strain developments were obtained. The effects of these parameters were analyzed and discussed.;A series of three-dimensional FEM models were developed using the input models and the numerical approach established. A simplified three-dimensional FEM simulation was performed for the axisymmetric model to compare with the results of the two-dimensional axisymmetric coining simulation. Three-dimensional coining with the reduced features of industrial design and serrations were then simulated. The effects of three-dimensional serrations and reduced relief were analyzed and discussed. Through the simulations, the material flow, loading patterns, die cavity filling and other conditions like stress and strain in the coin can be obtained. Through this work, it is established that the detailed 2D and 3D finite element simulations can be used to predict the mint coining process reliably. These simulations can be used as design tools for the silver dollar coin manufacturing process.;The finite element method is found to be an effective tool to simulate the coining process. The FEM approach was validated by investigating the effects of some key numerical parameters through FEM simulation. The typical coining material properties and the coining interface friction conditions were investigated. The fine silver material properties and a two-parameter non-classical bilinear friction model were successfully obtained through experimental and numerical methods.