Preforming Operation And Optimization For Near-net-shape Forming Process Of Complex Coupler Knuckle

As an important traction part of railway vehicles,the performance of coupler knuckle has a significant impact on the carrying capacity and safety of vehicles.In recent years,with the increasing shortage of railway transportation resources,its development focus has gradually shifted to high-speed and heavy-load,and the requirements for the production technology and forming quality of coupler knuckle parts have also increased.The traditional casting and open-die forging processes have been unable to meet the development needs.Therefore,it is of great significance to explore a new forming method of complex coupler knuckle.The near-net-shape forming based on closed-die forging can effectively overcome many defects in the traditional manufacturing process of coupler knuckle and realize the precise forming of complex parts.However,its technical difficulty is relatively high,and the systematic research is urgently needed.In this paper,a near-net-shape forming process for coupler knuckle based on closed-die forging without flash is proposed,and the preliminary design of the preforging is completed.In addition,the response surface method is introduced to optimize the preforging shape,the key technical proplem of the preforging design is solved,and the near-net-shape forming of complex forgings is realized.The specific contents and conclusions are as follows:1.The structure of the coupler knuckle and the feasibility of near-net-shape forming are analyzed,the final forging and its die are designed,and the near-net-shape forging process based on closed-die forging is developed.The preliminary design of coupler knuckle is studied systematically,the methods to establish the preform design basis and to design the shape and size of preforging are given.On this basis,the preliminary preform design method based on the metal flow characteristics and structure features of final forgings is proposed.2.The material model of 25 Mn Cr Ni Mo A is presented,and the finite element model for shaping forged knuckle using near-net-shape forging process is built based on the preliminary preforging.The defect forms,metal flow and related field distributions in the near-net-shape forming process of forged knuckle are studied by numerical simulation,and the rationality of the preliminary preforging is analyzed.The results show that the final forging has the defects of under-filling and longitudinal burr,the forming quality is not ideal,and the shape parameters of preforging need to be adjusted.3.The shape parameters of the preforging are selected as design variables,and the objective functions including filling capacity,deformation homogeneity,and damage degree of forgings are established.The CCD method is used for experimental design,the real values of the test points are obtained by numerical simulation.Response surface analysis is carried out and the optimal shape of the preforging is determined by two-step optimization.The results show that the preform optimization can make the final forging fully fill the mold cavity,improve the deformation uniformity of the final forging,and reduce the damage degree of the final forging.4.According to the above research,the near-net-shape forming scheme of coupler knuckle is obtained,the numerical simulation of the optimized preforging is carried out,and the feasibility of the near-net-shape forging process for forming complex forged knuckle is verified.The coupler knuckle forging is obtained by the forming process experiment,the shape of forging is extract by PRO CMM,and the forming accuracy and error are analyzed.The results show that the shape of coupler knuckle forging has high forming accuracy,the overall error distribution is reasonable and the surface quality is good.Based on the designed preforging,near-net-shape forming process is capable of producing coupler knuckle of high quality and without forming defect,which can meet the actual production requirements.