Research On The Forming Limit Of The Precision Forging Of The Body Pipeline

The precision forging technology of barrel rifling is an advanced manufacturing process of barrel rifling.In actual production,there are three defects of radial forging of barrel,including the bore not touching the land,the rifling forming not full and rifling cracking.It is the key point of precision forging of barrel rifling to establish the forming limit of barrel material.In this paper,the research object is the precision forging of 5.8mm barrel rifling.The purpose is to get the forming limit of precision forging of barrel rifling.The research works are as follows:The two-dimensional plane stress model and three-dimensional finite element model of radial forging of barrel are established by using the finite element software ABAQUS.The contact status between bore and mandrel,contact normal force and variation of principal stress-strain of the internal bore during the forging process are analyzed in detail.From the perspective of plastic strain,the continuous forging model can replace multiple forging model.The results of the three-dimensional model are more realistic than the two-dimensional model.The contact normal force is first produced in the midpoint of the land.After fully forming,the mid principle plastic strain of the bore is circumferential along the mandrel surface.The mid principle plastic strain on the land and the groove is less than zero and the mid principle plastic strain on the cavity wall is more than zero.There are three defects of radial forging of barrel,including the bore not touching the land,the rifling forming not full and rifling cracking.In this paper,the characteristics and forms of the defects are studied from both experiment and theory.Establish criteria of the three defects.The contact normal force of the midpoint of the land is used as the criterion of the land touching and its threshold value is greater than zero.The mid principal plastic strain of a point from the edge of rifling is used as the criterion of rifling forging penetration and its threshold value is less than zero.The fracture criterion proposed by Atsuo Watanabe is used as the criterion of rifling cracking.The normal mechanical properties of material L were tested.Based on the test results and experimental simulation,the threshold value of the fracture criterion is obtained.According to the two-dimensional planar stress model and three-dimensional finite element model of barrel radial forging,combined with the three defect criteria,the forming limit is characterized by blank diameter ratio with radius reduction and blank diameter ratio with forging ratio.The forming limit diagram is established and the range of blank diameter ratio is from 3 to 6.The veracity of the forming limit diagram is validated by the forging test.