Friction and Heat Transfer Models for Finite Element Simulation of Metal Forming

Computer simulation of metal deformation processes has become an essential part of process planning and tooling procurement. However, current computational approaches are known to be lacking in their treatment of friction and heat transfer. Most commonly, friction and heat transfer are restricted to constant values; a situation that does not accurately reflect real metal forming operations. Metal forging exemplifies a dynamic process where the surfaces roughness can increase or decrease with respect to time and location and the lubricant film can vary by an order of magnitude or more for a single, moderately sized part. The current representations of constant friction and heat transfer coefficients is a serious shortcoming of modern finite element codes and leads directly to their limited capability to serve as a predictive design tool. A new scheme for a friction and heat transfer module has been developed. This model accounts for the changing nature of roughness and lubrication to predict local friction and heat transfer coefficients for a metal/tool interface. The lubricant film thickness is analyzed through the Reynolds equation; heat transfer coefficients are obtained from a new model specifically derived for metal forming geometries and surfaces are allowed to roughen according to semi-empirical rules. The approach is implemented in a commercial code (DEFORM2D) through a user routine. Initial evaluations are based on forging examples.