Axisymmetric Deep Drawing-bulging Forming Based On Direct Integral Solution And Analysis Of Winkle And Crack

Bending,axisymmetric deep drawing,bulging and round hole flanging are the four basic deformation methods for sheet metal forming,and the deformation of other complex shaped parts generally consists of two or more of these deformation methods.Using theoretical methods to calculate the stress and strain distribution is the basis for further research on the prediction of critical blank holder force and forming limit,wrinkle and fracture of parts during the forming process.Taking axisymmetric drawing and bulging composite forming as the research object,the direct integral method is extended to solve the entire deformation area of general curved surface forming,which provides a new method for the analytical solution of sheet axisymmetric forming.The direct integral method is used to study the drawing bulging composite forming.The main contents include: for axisymmetric forming,when smooth flat punch is used,the deformation area at the bottom of punch is proved to be in an equibiaxial tensile stress and strain state by theoretical method;The stress and strain distribution in the whole region of axisymmetric drawing bulging composite forming part was given by direct integral method.Combined with the direct integral method and the conditions of wrinkle and fracture,the formulas of critical BHF of wrinkle and fracture of conical parts is given,and the influence of different parameters on critical BHF of conical parts is analyzed.Firstly,in view of the complex forming problems of axisymmetric drawing and bulging,the calculation formulas of axisymmetric forming are given by introducing parameter method under the condition of proportional loading and film assumption.For the axisymmetric forming problem,it is proved mathematically by the Taylor series and the method of finding the limit that the bottom region of the cylinder is in an equibiaxial tensile stress-strain state when the smooth flat punch is used for forming.Taking conical and cylindrical parts as examples,the stress and strain distribution of the whole region is calculated,and the influence of the blank holder force and the diameter of the sheet on the position of the stress boundary circle of the conical parts is analyzed.Secondly,according to the stress and strain solution obtained by the direct integral method,combined with the wrinkle instability condition given by the energy method,the calculation formula of wrinkle critical BHF is derived.The calculation formula of critical BHF is given according to the cracking instability criterion,and the influence of the properties of sheet metal,such as strength coefficient B,hardening index n and anisotropy coefficient R,on wrinkling and cracking critical BHF is further analyzed.The curves of wrinkling and critical BHF are drawn.When the other calculation conditions are the same and the material with R value greater than 1 is selected: the increase of B value will lead to the increase of both the critical BHF for wrinkling and cracking,and the wrinkling trend of the part in the forming process will increase and the cracking trend will decrease.With the increase of N value,the critical BHF of wrinkling decreases,and the critical BHF of cracking increases,and the trends of wrinkling instability and cracking instability decrease.When the value of R increases,the critical BHF of the conical is increased,the critical BHF of wrinkling is almost unchanged,and the fracture trend of the conical is reduced in the process of forming.Finally,Dynaform software was used to compare the results of theoretical calculation and finite element strain distribution under the condition of changing several parameters,and the applicable conditions of theoretical calculation and the accuracy of the results were verified.Tensile experiment was carried out with 08 Al material to obtain its performance parameters,and two conical parts with drawing height of 24 mm and 27 mm were obtained by using the material to carry out the stamping experiment.The strain distribution of the forming parts was obtained by using the Vialux Auto Grid strain scanning system.Three methods of direct integral solution,finite element calculation and experiment are used to obtain the strain distribution of the conical parts.The strain data of the three methods are compared.The results show that the error between theoretical calculation and experimental data is less than 10%,and the reliability of the algorithm is verified.The finite element and experimental results show that the direct integral method based on parameters is accurate and effective in calculating the strain distribution of axisymmetric deep drawing bulging composite forming.