Numerical Analysis of Hot Deep Drawing Process of Thick Steel Sheet without Using Blank Holder with Tractrix and Pseudo Tractrix Dies

Deep drawing is a process that is usually performed in cold conditions, but there are also cases of using this process in hot conditions to reduce the forming force. The use of a blank holder in the forming process leads to an increase in the forming force and changes the thickness of the sheet, especially in the hot state, due to the increase in friction. On the other hand, omition of blank holder will cause wrinkling of the sheet due to development of periferal stresses, and this problem is aggravated by increasing the depth of drawing. In this research, the finite element analysis for forming a hemispherical head from a high strength steel sheet in the hot deep drawing process without using a blank holder is studied. Simulations are done for two types of tractrix and pseudo tractrix dies and for sheets with different thicknesses and diameters, and the results are compared with each other. The results of the analyzes show that with the increase in the thickness and diameter of the sheet, the force required by the mandrel for forming increases. In general, less forming force is required in the tractrix die and at the same time it brings less thickness changes. Furthermore, the formation of hemispherical objects lacking cylindrical tiles in thicknesses higher than one centimeter will be healthy and free of wrinkles.