Research On Forming Defects And Forgeability Of Sinking Section Of Precision Forging Pipe

In order to improve the coaxiality of barrel bore of chamber and reduce the processing procedures,the radial forging processes for both chamber and rifling is the best technology.Aiming at the problem of the cracking of the inner bore surface of the barrel in the sinking section during the forging process,this paper mainly uses the finite element simulation method and forging test combining the scanning electron microscope test to conduct the following research:The two-dimensional radial precision forging finite element model of the barrel was established by the finite element analysis software ABAQUS.Taking the 5.56 mm barrel as an example,the stress and strain of the sinking section during the forging process were extracted for detailed analysis.The analysis found that the barrel is subjected to periodically changing tensile and compressive stresses in the sinking section and the barrel’s stress state is poor,and there is a possibility of cracking on the surface of the inner bore in the sinking section during the forging process.Then use the ratio of hydrostatic pressure to equivalent stress as a characterization to study the stress state of the barrel in the sinking section,by changing the process parameters(the thickness of the blank,the forging angle of the hammer head,the inner diameter of the blank,and forging ratio of the forging section)during the forging process.Refer to the results of ABAQUS finite element simulation,an experimental research plan was designed for the influence of process parameters on the stress state of the sinking section.Through the forging test and the scanning electron microscope image,the stress state of the sinking section of the barrel was analyzed: the larger the inner diameter ratio of the blank,the thickness of the blank,and the forging angle of the hammer head,the worse the stress state of the sinking section.According to the research on the stress state of the sinking section of the barrel,three fracture criteria containing stress ratio components were selected to predict the cracking phenomenon of the sinking section of the barrel,combined with the results of the forging test,it was determined that the workability curve was used as the judgement of the barrel.Establish the cracking criterion in the sinking section helps to improve with the forging process parameters,and provides a theoretical basis for the evaluation criteria of material forgeability.Combining the results of finite element simulation and forging test,the influence of the forging ratio of the sinking section on the stress state of the sinking section was studied.The workability curve was used to obtain the maximum sinking section forging ratio that the barrel material can withstand.The forging ratio of the sinking section is used as the criterion of material forgeability to design a hollow tube diameter reduction evaluation method,which can accurately reflect the maximum forging ratio of sinking section that the material can withstand.This evaluation method can be used to determine whether the material can be used for the radial precision forging.