Study On Crack Of Cylindrical Surface During The Upsetting Of Heavy Forging

Heavy forgings in high quality are demanded to be furnished by manufacturing of heavy-duty machine as rapidly developing of metal processing industry in modern times. Heavy forgings are forged from steel ingots. It is inevitable that there are some defects such as segregation, porosity, microcracks in steel ingot. And the steel ingot is heavier, defects are more serious. These defects must be eliminated by forging to gain high quality forgings. Upsetting is the very important working procedure in manufacturing technology, and the main functions of it are enlarging forging ratio, closing up inner porosity flaw, increasing properties of the material. Because of friction during upsetting, grainsare crassitude in hard deformation area, centric puling stress give birth to flaw, and side surface flaws for asymmetric deformation, among which side surface flawing is usual and discard heavy forging as useless.The phenomena that cracks bring, grow and lead to macroscopical parting in plastic deformation process of metal is a complex process which is affected by structure of the metal, stress status, deformation velocity and so on. But the essential reason is cavities that engendered by defects such as inclusion in metal and the other phase. Cavities expand under certain outer condition, and then aggregate or connect, finally macroscopical crack is formed.The problem of estimating whether the side surface flaws or not is solved in this dissertation according to applying critical expanding ratio in upsetting technology. Asymmetric deformation leads to nucleation and expanding of cracks. So, in order to character asymmetric deformation in upsetting process, drum coefficient is defined. And the relation between drum coefficient during upsetting with stress on circumferential and axial directions is got according to simulation. Eventually the corresponding relation between drum coefficient with stress three-axial degree is certain. So evaluation of the expanding ratio will be simpler, and it will be possible to estimate whether the side surface flaws or not in practical manufacture according to critical expanding ratio.