Study On Forming Mechanism And Process Optimization Of Hot Power Spinning For Hard-to-deform Material Tubular Parts

The plastic forming process of hot power spinning is an ideal plastic forming method for large thin-walled tubular parts made by difficult-to-deform superalloy materials such as combustor of gas turbine because it can overcome the defects of poor ductility and strong deformation resistance of superalloy.Compared with the traditional manufacturing process of coiling and welding of sheet,it can eliminate the hidden dangers of cracks caused by the welding seam and improve the performance and reliability of the parts.But the harsh service environment of the combustor parts requires it has high dimensional accuracy and service performance,which brings new challenges to hot power spinning process.So how to set up the forming process and parameters,so as to solve the difficult problems of controlling the dimension accuracy of large size thin walled parts and the complicated changes to the microstructure of spun parts brought by hot flow spinning,has become an urgent research topic.The forming mechanism of hot flow spinning was deeply analyzed by combining theoretical research and experimental research in this article,so as to avoid forming defects,improve forming accuracy,improve its organization and service performance.Many technical details of the finite element model of hot power spinning heated by electromagnetic induction was studied in this paper.The boundary conditions and relative motion relations between the workpiece and the mandrel ere simplified by converting rotational motion of the workpiece to rotating motion of the rollers.The difficult to converge problem when the nonlinear problem was solved by implicit algorithm was overcome through the rational setting of boundary condition,iterative method and the time increment step.The servo induction heating was effectively simulated by adding a heat transfer torus.The problem of unloading of rollers at the end of the spinning was solved setting the rollers to evacuate the workpiece at regular time,simulation of multipass spinning in the same model was realized.The stress distribution of the material during hot power spinning was studied,the results show that the material data obtained by the plane compression test is more suitable for numerical simulation of hot power spinning.A more practical result were obtained by using the written user material files in the model.The finite element simulation of hot power spinning was studied based on the established finite element model.The characteristics of flow and deformation of material and forming mechanism of hot power spinning were revealed by analyzing the shape of deformation zone,velocity,strain rate,displacement of the material and stress and strain distribution of deformation zone.The reasons for easy appearance of cracks on the outer surface of spun parts and changes in the structure and properties of material in power spinning were explained.The results show that significant shear deformation occurred on the outer material of spun parts,the strain rate of material in the deformation zone is large.The non uniform deformation appear in the spun parts was analyzed.The reasons and the influencing factors for the larger shear strain of the external material were analyzed.The results show that the causes of larger strain in the outer layer is directly related to the shear plastic strain.The results show that the increase of thckness reduction is beneficial to improvement of the non uniform plastic deformation.The influencing factors and control methods of dimensional precision of spun parts were studied by finite element simulation.The causes of cracks in the inner wall were revealed through the analysis of fracture morphology and stress and strain distribution of material in the deformation zone.There is a directly relationship between the inner wall cracks and the tensile stress on the inner wall of the spun parts.The causes of defects such as ellipticity,pile up and end enlargement appear in spun parts were studied,the primary and secondary relations and rules of different process parameters on the above defects were analyzed,the degree and law of the influence of different process parameters on the above defects were analyzed.The results show that the thickness reduction has greatest influence on the dimensional accuracy of the spun parts,so a reasonable thickness reduction should be established.The above conclusion can provide a theoretical basis for setting up reasonable process parameters provide to improve the size accuracy of the spun parts and avoid the forming defects.The hot power spinning test of difficult-to-deform material of Haynes230 tubular parts was completed after the experimental platform was set up.On the basis of determining the range of processing parameters,the influence of main process parameters on the dimensional accuracy of spun parts was studied by orthogonal experimental design,range analysis and grey correlation analysis.Based on the orthogonal experimental results,regression analysis was made for wall thickness deviation and cylindricity of spun parts.The optimized combination of process parameters were obtained based on the established regression equation.The effect of the heating temperature of the workpiece on the microstructure of the spun parts was studied.The microstructure of the outer layer of the spun part was significantly recrystallized when the heating temperature is higher than 1100 degrees.According to the conclusions obtained from theoretical analysis and experimental analysis,process parameters were further optimized,high precision Hanynes230 superalloy thin-walled tubular parts manufactured by hot power spinning.