The system for sheet forming design

In the paper the modern sheet metal forming process design technique and diagnostic system is described. The system incorporates the forming limit stress diagrams and the wrinkling stress diagrams as the limit conditions of forming into the commercial finite element method programme MARC. The constitutive equations and boundary conditions, good describing the materials reaction on the complex deformation conditions are also included. To build such system for the sheet metal forming design the following partial tasks had to be solved: development of the theoretical calculation of forming limit stress diagram by using different yield criterion and its experimental verification, elaboration of wrinkling stress criterion and its experimental verification, elaboration of the model describing boundary conditions between sheet metal and tools in plastic deformation processes, development of constitutive equations more precisely describe behaviour of used sheet metals, creation of mathematical model of selected deep drawing processes for laboratory and industrial applications. The forming limit stress diagrams was created on the base of theoretical calculation and experimental research. The original and modificated M-K theories and perturbation analysis in theoretical calculation of the forming limit stress diagram were used. The choice of yield criterion has a great effect on the predicted strain and stress limit. As a basic yield criterion the Hill' s new anisotropy function was used. The wrinkling criterion was build on the base of shell theory. The sheet metal buckling during forming operation was considered as the bifurcation type buckling of the shell in elastic-plastic range. On the base of FEM analysis the critical condition of wrinkling onset for each element at successive time increment are found. The material models and friction conditions were established in the forms of equations on the base of the experimental researches. The forming analysis was performed with MARC K7.2 finite element software package using rigid-plasgic flow method. The tooling shape for analysis was converted from Pro/Engineer system into IGES formats and meshed pre-processing MENTAT 3.2 program. Application of the system for sheet metal forming design (SSMFD) creates the possibility to design the sheet metal forming processes without expensive and time consuming trail and error techniques so that the necessity of investigation of metal forming processes by using of the rea tools may be reduced or eliminated. The system will able to predict the forming loads, to create the geometry of the deformed sheet and tools, to distribute the strain and stress and to determine the process conditions. The SSMFD uses the final shape and size of formed parts, material properties, rate of deformation (punch velocity) and boundary condition as input parameters, and a discretized mesh to represent the sheet blank dimensions. Application of the SSMFD in industry will make the production of sheet parts more competitive and cheaper.