Research On The Defects Of Railway Vehicle Knuckle Coupler In The Extrusion-Closed Die Forging And Process Optimization

As an important land transportation method,railway transportation is widely used around the world for its advantages of strong anti-climate resistance,heavy load,low transportation cost,high safety and reliability.In order to meet the need for rail transport to develop toward high speeds and heavy loads,the coupler buffer system as a carriage connecting device needs to have good mechanical properties and a long service life.The knuckle is the most important part of the coupler buffer system and directly plays the role of connecting the carriages.Its working status directly affects the working state of the coupler buffer system.At present,casting knuckles and open-die forged knuckles are gradually unable to meet the needs of railway transportation development.Therefore,it is of great significance to study the closed process of knuckles die forging.The closed knuckle-die forging process is a novel method of manufacturing the knuckle with less application.Knuckle-molded parts produced by this process tend to have forming defects.The traditional solutions are empirical methods and trial-and-error methods,which greatly reduce the production efficiency and also cause a lot of waste of resources.In view of the drawbacks of the traditional methods,the finite element numerical simulation method was used to study the process and causes of defects in the closed knuckle-die forging forming parts.The influence of process parameters on the forming defects was explored.Then the process plan was optimized and finally verified by experiments: the reliability of numerical simulations.The main contents and conclusions of this paper are as follows:(1)The structural shape and material properties of the F51 AE type knuckle were studied.The working methods are introduced and the typical stress of the knuckle during the working process is analyzed.The structure and materials of the mold in the knuckle extrusion-closed die forging process was introduced.The characteristics of the mold were analyzed.The two defects of the knuckle-molded parts of the folding and filling lack were enumerated.In the process of numerical simulation,A novel method was designed to characterize the defects of folding and filling defects.The method can quantify two types of defects.(2)Based on the preliminary test data,two models of pre-forging and extrusion-closed final forging were established by using finite element numerical simulation software DEFORM-3D.The numerical simulation of two processes was completed.The changing law of the forming load,equivalent stress,equivalent strain during the forming process of the pre-forging and final forging were analyzed.The simulation results show that the pre-forged part does not have the same forming defect as the pre-forged part obtained in the test.The final-forging part has a folding defect at the connection of the hook head and the hook tail,and there is a defect of insufficient filling at the hook tail.The forming defects of the forged parts are almost the same.Combining the analysis function of the software and the finite element theory,the process of the production of the two major defects was analyzed,the types of defects were identified and the causes of defects were found.(3)The important process parameters affecting the forming quality of the final forged part are determined,namely the mold temperature,the forging speed,the pre-forging volume distribution and the pre-forging shape.The influences of these four process parameters on the defects of the formed parts were studied respectively,and four optimal process parameters were obtained.The optimized process plan was formulated using the optimized process parameters.The numerical simulation verified that the process plan could eliminate the defects of the formed parts.(4)According to the data of numerical simulation optimization process plan,the experiments were designed to verify the feasibility of the program.There was no folding defect on the surface of the final forged part obtained in the experiment,and the filling effect was good.The PRO CMM system three-dimensional scanner was used to measure the forming parts,the comparison of the forming errors of the experimental parts and the sample parts show that the molding parts have high forming accuracy and fully meet the actual production needs.