Numerical Simulation Study On Void Defects For Heavy Forgings

As basic components of national core equipment,heavy forgings have played an important role in many fields.Its production quality level reflects the country's industrial development in a certain extent.Heavy forgings with the characteristic of large investment, small batch, more variety, manufacturing cycle is long,etc, which restricts the rapidly development of heavy forging industry. Our country's develop- pment of heavy forging industry have a certain gap with developed countries, especially in high-quality, high weight of heavy forging production can not meet the needs of the development of related industries.Some core technology need weight and size of forgings are gradually increased, so that such as the segregation, porosity, residual shrinkage holes, voids and other defects in the ingot are more obvious, it will largely reduce the pass rate of heavy forgings.Therefore, the forging process of heavy forgings is not only the forming process of the forging, but also is the process of repairing the defects and improving the structure.Large size,large weight and high production cost are the characteristic of heavy forgings,which determines directly used heavy forgings for upsetting test is diffcult.Firstly, based on the basic theory of plastic finite element, this paper analyzes and derives the evolution model of the internal void defect and the criterion of the closure of heavy forgings. Then analysis 45# steel cylinder under different parameters is carried out by using the Deform-3D numerical simulation software. The internal stress and strain distribution,void closure process as well as the influence of the parameters such as the ratio of height to diameter,the position of the void, the friction coefficient and the temperature on the influence of void closure are obtained, and demonstrate the conclusion is reasonable by citing.The results of the study show that the height to diameter ratio of cylinder model is 1.6 for non void cylinder, each point from the center to the surface of transverse, axial and diagonal, the same axis point equivalent strain nearby the point decreases gradually with distance from the center to the surface become large,while for the same point equivalent strain is increased gradually with increase of the reduction rate, approximate to a certain linear relationship.Forging upsetting, at both ends of the forgings will appear difficult deformation area, the deformation of this area is very nonhomogeneous, when the reduction rate is about 25%, the warping phenomenon will appear, warping phenomenon more obvious with increase of the reduction rate, forgings easy to crack when the reduction rate is more than 50%.Void shape changes can be see from upsetting simulation process that is spherical, ellipsoidal, crack, tiny cracks, closed and the void is basically fit slowly from the vicinity of the center of the void and gradually extended to the two sides of the void, when the reduction rate to the critical value of void closure,the void will close completely.Through analysis the magnitude and distribution characteristics of stress and strain near the void.We can see that at the time of void closing, near the void the stress and strain will dramatic changes,then the void closed, but is not crystal structure of welding.When the height to diameter ratio of forgings is near 1, is the best condition for void closure, voids are easiest to closed.The ratio of height to diameter and reduction rate of large forgings are the main factor that affect the void defcts closure.Friction coefficient, temperature and the size of void have little effect on void closure.The position of void has relatively large effect on the void closure, but because the voids are mostly concentrated in the center of the heavy forgings, we can research the voids which only at the center of the forgings.