Crack predicting in multi-way loading forming process of AISI-5140 tee-joint valve

Multi-way loading forming process of a tee-joint valve is a complicated hot forming process under coupled effects of multi-parameter, multi-step and multi-die constraint. The crack is prone to occur due to the complex stress state, material flow behavior and severe inhomogeneous deformation in the forming process. Firstly the Cockcroft-Latham criterion was determined as the reasonable criterion to predict crack during multi-way loading forming process of AISI-5140 tee-joint valve, then the critical damage value of AISI-5140 is derived as 0.881. Taking the peak value of damage as examination index, the crack initiation trends and zones in the forming process were analyzed and predicted by combining orthogonal experimental design method with finite element (FE) simulation. The results show that in the last stage of forming process the crack may appear in the upside of tee-joint valve shoulder where damage value reaches the peak. The cracking trend increases with the increase of the radius of die and decrease of the friction. The larger the loading speed is, the less cracking trend will be. Crack may occur at the tee-joint valve when value of loading speed is less than 15 mm/s. For the given billet, the peak value of damage increases with the increase of the inner diameter of tee-joint valves, i.e. the cracking trend increases. For the tee-joint valves with the same inner-outer ratio, the peak value of damage decreases with the increasing of the outer diameter of tee-joint valves and the cracking trend decreases.