The influence of coining force on spring-back reduction in V-die bending process

The spring-back phenomenon, an elastic recovery after sheet metalworking, will affect the accuracy of part geometry inevitably. The present paper is to explore the influence of coining force on the spring-back reduction in the V-die bending process.The highlight of this paper is that a basic approach, incorporating material properties and geometrical parameters, is developed to estimate the amount of spring-back reduction caused by coining force upon an elementary analysis. The approach is based on the assumption that the unloading moment (as a pure-moment bending under the punch nose) will be neutralized by the applied bending moment induced by the coining force in bottoming stage.A spring-back ratio SR is defined as a measure to predict the amount of spring-back reduction and derived as a function of normal anisotropy R, strain-hardening exponent n, thickness/punch radius ratio t/2ρ  , die width/thickness ratio w/tw/t, friction coefficient μ and half bent angle θ. And a loading factor α will be defined to measure the amount of coining force for trying to reduce the spring-back after unloading. In the meantime, a critical loading factor αc for completely eliminating the spring-back will be also discussed herein. As above, it will reflect the reliability of the spring-back reduction mechanism in the present model.It is thereby possible to better understand and control the spring-back reduction of V-die bending process in industry necessity.