Research On Forming Defects Of Barrel Precision Forging

Radial precision forging of rifling and chamber simultaneously is the main method of manufacturing the barrel.The forming of barrel's chamber is the key and difficult point in the radial forging process.The forming quality of the inner wall of chamber is directly related to the accuracy and service life of barrel.This article mainly uses the finite element method to study the possibility of ringing defects and cracks on the inner wall of the chamber.Based on the actual forging process of the barrel,a finite element model is established for simulation.The force characteristics and flow conditions of the inner wall of chamber during the radial forging process are analyzed.Combining finite element analysis and experimental study,the cause of generating ring pattern defeact is obtained and the relevant judgment criteria for ring pattern are established.Through comparing the simulation stress analysis curve and experimental results,it is found that the generation of ring pattern is related to compression buckling.When the tangential stress component of the inner wall exceeds the critical value,the wrinkles appear.Further research found that when the forging ratio of the forging section of chamber reaches the critical value,the ring pattern on the inner wall will be re-flattened in the subsequent forging process,and the defect of the chamber can be eliminated.The results show that when forging a 5.56 mm caliber barrel,the tangential compressive stress of the inner wall is more than 2150 MPa during the forging process,which leads to compression buckling of the inner wall.When the forging ratio of the forging section exceeds 28.5%,the ring pattern on the inner wall can be flattened.The effects of plunger force decrease position,the hammer lift position,the axial feed speed,chuckforce and friction coefficient between blank and mandrel on ring pattern defects are analyzed from two aspects:tangential compressive stress and forging ratio of forging section.A fracture criterion with stress triaxiality as an influencing factor is used as a criterion for judging the cracking of chamber's inner wall.Theoretically,the fracture strain of metallic materials approaches infinity when the triaxiality of stress approaches-1/3,and the material will not fracture.Through ABAQUS simulation of barrel forging,the stress triaxiality of chamber's inner wall during forging is far less than-1/3,which predicts that the material inside the bomb chamber will not crack due to stress concentration.Through the radial forging test of the barrel,the influence of the process parameters on the ring pattern is discussed using the control variable method,and the conclusions obtained by the finite element analysis are verified.The ring pattern defect criterion is applied to the forged test piece,and the applicability and feasibility of the criterion are verified.