Research On Forming Quality And Microstructure And Properties Of Assembled Camshaft Hot Hydro-forging

With the rapid development of automobile industry,higher requirements are put forward for the technology and performance of automobile engine.Camshaft is the key part of valve train of automobile engine,and its performance affects whether the automobile can run normally.In recent years,the manufacturing technology of camshaft has been updated and iterated for many times.The integral camshaft manufactured by traditional technology can not meet the requirements of automobile lightweight.Compared with the traditional integral camshaft,the combined camshaft has greater technical advantages.Its shaft tube is hollow structure,so its weight is lighter.The cam and shaft tube can choose different materials according to the performance requirements,so it can better meet the high performance requirements of the engine camshaft.At present,the commonly used production process of combined camshaft includes welding,bonding and key connection.In this project,the hot expanding forging process is used to realize the production of combined camshaft,which has the advantages of simple connection process and low cost.However,the influence of forming complete camshaft and hot processing on the product structure,properties and connection strength is lack of in-depth research.The purpose of this paper is to optimize the structure of the hot expanding forging process,to form a complete combination camshaft,and to explore the influence of hot forming on the microstructure,properties and connection strength,so as to provide guidance for the industrial production of the process.This paper first optimizes the structure of the interference part between the insert and the axle tube to avoid the defect of biting mark on the axle tube after forming,and designs the specific structure of the insert according to the shape and size of the complete combined camshaft.Combined with theoretical analysis,finite element simulation and experimental verification,the influence of different experimental parameters on the forming quality is explored.The experimental parameters involved in this topic include:insert slope length,internal pressure,unilateral axial feeding amount,cam end slope and heating temperature.Then,the influence of different heating temperature on the microstructure,decarburization layer and hardness of camshaft at different positions is explored.Combined with the influence of various parameters on the forming quality and microstructure properties,the optimal process parameters are determined,and the complete camshaft connection experiment is carried out.The static torsional strength of the formed camshaft is tested and compared with the allowable static torsional strength of the camshaft.Then the thermal cycle experiment is carried out to explore the influence of high temperature conditions on the connection strength of the camshaft.In the process of hot expanding forging,the effective bonding length of the shaft tube and the cam is the joint of the shaft tube and the cam end face,which is also the main deformation area of the shaft tube.The shaft tube will fold under the axial push of the insert.With or without internal pressure,the axle tube can be well filled to the end face of the cam,and the folding is better without internal pressure;According to the requirements of cam spacing in the complete camshaft,the length of the inclined plane is3mm;Combined with the simulation and experimental results,the forming quality is the best when the feeding amount is 6mm;The larger the inclination of the cam end face is,the smaller the fitting length is;When the heating temperature is 950℃,the forming quality is the best.The microstructure of camshaft at different forming positions under different heating temperatures was prepared.With the increase of temperature,the room temperature microstructure of the joint between the shaft tube and the cam end changed from massive ferrite to acicular ferrite,and the room temperature microstructure of other positions changed little with heating temperature;There is no decarburization layer on the surface of the shaft tube at different heating temperatures,and the hardness of the shaft tube changes little with the increase of temperature.Compared with the target camshaft,the cam spacing and phase meet the requirements;Then the static torsional strength of each cam is measured,which is more than 450N·m,much greater than the allowable static torsional strength of 80N·m in the actual working condition of camshaft;The actual working temperature of the camshaft is 100℃.The static torsional strength of the camshaft can still exceed 400N·m after thermal cycling test at 400℃ for 12 hours.The test results show that the combined camshaft formed by hot air expanding forging process can meet the requirements.