Research On Fracture Prediction And Spinnability Of Deep Drawing Spinning For Conical-cylindrical Parts Of Ni-based Superalloy

Ni-based superalloy conical-cylindrical parts are one of the key components in the combustion chamber,and its forming quality directly affects the overall performance of engine and gas turbine.This type of parts is usually manufactured by multi-pass stamping and solution heat treatment,but there is a serious uneven wall thickness phenomenon,which can not meet the design requirements of the drawing.The accurate plastic forming of Ni-based superalloy conical-cylindrical parts can be effectively realized by using shear spinning to form the cone-shaped preform and multi-pass deep drawing spinning(DDS)to form the end cylindrical part.However,due to severe work hardening and limited formability at room temperature,Ni-based superalloys are prone to wrinkling,cracking and other defects.At present,there is no accurate method to predict the fracture defects of Ni-based superalloys during DDS,and its spinnability is not clear.Therefore,it is of great scientific significance to establish the ductile fracture criterion for DDS of Ni-based alloy conical-cylindrical parts,and to study its spinnability and forming quality,so as to fully tap the potential of material spinning and realize its high-precision manufacturing.In this paper,Haynes 230 Ni-based alloy conical-cylindrical parts are studied by theoretical analysis,finite element simulation and spinning test.By analyzing the stress-strain characteristics of DDS,it is pointed out that the tensile stress in the direction of generatrix and the alternating tangential tensile and compressive stress are the main reasons for the formation of tangential tensile crack in the wall and axial fracture in the mouth of the spun workpiece.Notched specimens with various stress states were designed,and the damage parameters of Oh,Oyane and Lou were calibrated by uniaxial tensile test combined with finite element simulation.Based on ABAQUS software,a finite element model for fracture prediction in DDS for Ni-based alloy conical-cylindrical parts was established.The simulation results show that because the oh criterion and Lou criterion only consider the influence of the maximum principal stress and the maximum shear stress respectively,the spun workpiece has a tangential fracture and premature axial fracture respectively,while the fracture form under the Oyane criterion is the tangential fracture of the middle and the mouth of the cylinder wall,and the prediction results are not consistent with the test results.By analyzing the mechanism of fracture formation in DDS,a modified Lou criterion considering tangential fracture and axial fracture in DDS is proposed,which can accurately predict the evolution of damage,and the time and location of crack formation are consistent with the experimental results.The limit drawing spinning coefficient m_??lim was used to characterize the spinnability of DDS of cone-shaped preform,and the toolings and dies of DDS were designed.The results show that the main defect of single pass DDS of Ni-based alloy is flange wrinkling due to the large deformation and low rigidity of flange,and the limit DDS coefficient is 0.875.The spinnability of the material can be effectively improved by multi-pass DDS,and the limit spinning coefficient is 0.77.When the feed rate,the roller roundness radius and the path gap are too small,the maximum equivalent plastic strain and the ductile damage along the axial direction of the material increase,and the fracture defects are easy to occur.Based on the finite element simulation,the influence of process parameters on the forming quality was studied,and the microstructure and mechanical properties of the spun workpiece were analyzed.The results show that feed rate,roller roundness radius and path gap have significant effects on the forming quality.When feed rate f=2.5?3.0mm/r,roller roundness radius r_?=15?18mm and path gap p=8?10mm,the spun workpiece with better forming quality can be obtained.The plastic deformation mechanism of Ni-based alloy during DDS is the coexistence of dislocation slip and twinning.The grains in the middle of the cylinder wall are elongated along the direction of material flow,and the grains in the mouth are accumulated,resulting in more deformation twins.After DDS,the strength of the spun workpiece is significantly increased,but the plasticity is decreased.