Study On Radial Forging Process Of Barrel And Properties Of Forged Barrel

The radial forging process of an automatic rifle barrel is the research object of this dissertation.In allusion to the material properties, manufacturing process and formability involved in the forming process of barrel, the radial forging process of barrel, the material properties and the service performance of forged barrel are studied by theoretical analysis, numerical simulation and experimental research.Based on the characters of cold and hot radial forging process of barrel, the deformation region of barrel is divided into the sinking zone, the forging zone and the sizing zone. On the basis of considering the effects of strain, strain rate and temperature on flow stress of barrel blank and the effect of multi-inlet angle die on the forming, the analytical formulae of stress distribution and forging load in the cold and hot radial forging process of barrel are derived by using the slab method; then the accuracy of the analytical formulae is verified by comparing the die forging load calculated by the analytical formulae with the die forging load measured by the test.The axisymmetric model for cold radial forging process of an automatic rifle barrel is established by numerical simulation technology, the accuracy of the axisymmetric model is verified by comparing the die forging load predicted by the model with the die forging load measured by the test; based on the axisymmetric model, the simulations are arranged by the orthogonal experiment method, the relative effects of5process parameters, which are die inlet angle, reduction rate, die land length, axial feed velocity of barrel, champing pressure on the end of barrel, and3interactions between process parameters, which are the interaction between die inlet angle and reduction rate, interaction between die inlet angle and die land length, interaction between reduction rate and die land length, on the3forming indicators, which are die forging load, the load between barrel and mandrel, the deformation in-homogeneity of barrel, are obtained by performing analysis of variance on simulation results; the minimum die forging load, minimum load between barrel and mandrel and the corresponding process parameters values are predicted by the variance analysis results.Based on stress analysis on the barrel which deformed plastically under internal pressure, the test used to determine the tangential mechanical properties of barrel blank material and forged barrel material is designed, the tangential mechanical properties of barrel blank material and forged barrel material are obtained; then the axial mechanical properties of barrel blank material and forged barrel material are measured according to the national standard GB228-2002<Metallic materials——Tensile testing at ambient temperature>:The accuracy of the test used to determine the tangential mechanical properties is verified by comparing the tangential and axial mechanical properties of barrel blank material:by comparing the mechanical properties of barrel blank material and forged barrel material, the influence laws that increasing in strength, decreasing in plastic for forged barrel material by cold radial forging process are obtained, and the anisotropic of forged barrel material is verified.The axisymmetric model for predicting residual stresses distributions in forged barrel is established on the basis of the axisymmetric model for simulating the radial forging process of barrel, the distributions of the radial, axial and circumferential residual stresses along radial direction in forged barrel are obtained; the effects of the axial feed velocity of barrel, friction factors, reduction rate and die shape on residual stresses distributions are analyzed; the regression equations between residual stresses on inner, outer surface of forged barrel, in the middle of forged barrel and the main process parameters are built by the regression model method, then the maximum and minimum residual stresses and the corresponding process parameters values are derived through the regression equations; the validity of the regression equations are proved by comparing the predicted residual stresses with the FE simulated values.The theory of the blind-hole method used to measure surface residual stresses in plate is applied to measure surface residual stresses in forged barrel. The numerical method is used to calibrate the relaxation coefficients A, B values of the blind-hole, by comparing the relaxation coefficients of the blind-hole in the forged barrel and in the plate under the same material, the same force and the same drilling condition, the conclusion that when the ratio of barrel diameter to hold diameter D/a≥16, the blind-hole method can be used to measure the surface residual stresses in forged barrel is obtained; in this applicable range, the surface residual stresses on a forged barrel are determined by using the blind-hole method, and the off-center error is minimized by a method of modifying the relaxation coefficients directly; the accuracy of the numerical model predicted residual stresses distribution is confirmed by the test results.The numerical models used to calculate the dynamic strength of barrel and the axial and circumferential crack stress intensity factor on the inner surface of barrel under the explosive gas pressure are established respectively, the stresses distributions in the barrel calculated in dynamic strength and the relationship between the semi-elliptical crack stress intensity factor and the crack shape on the inner surface of barrel are received; based on the numerical models and combined with the prediction results of residual stresses in forged barrel, when the residual stresses values in forged barrel are extreme, the dynamic strength of barrel, axial crack stress intensity factor and circumferential crack stress intensity factor in the barrel are calculated respectively; so the qualitative influence laws of residual stresses in forged barrel on dynamic strength of barrel and crack stress intensity factor are obtained.