Simulation Study On Connection Strength And Fatigue Life Of Shrinkage Fitting/Knurling Assembled Camshaft

Compared with the traditional one-piece camshaft, the assembled camshaft hasthe remarkable advantages such as light weight, high production efficiency andprecision, low cost and pollution, and choice flexibility of materials according to theproperties of different parts, which makes the assembled camshaft become the mainprocessing technic of camshaft gradually. This kind of camshaft is assembled byconnecting separate parts, and the connection between the cam and shaft is thetechnology kernel. The camshaft is subjected to high speed periodical torque when theengine works, so the research on the connection method and strength of assembledcamshaft and its service life is of great importance and attracts attention in theindustry increasingly.The safety and reliability of the camshaft to transmit torque and the service lifeof the camshaft depend on the connection strength between the cam and shaft.Shrinkage fitting and knurling connection are two kinds of common mechanicalconnection methods of assembled camshaft, and both belong to interferenceconnection essentially. Using these methods, the connection strength and fatigue lifeof the assembled camshaft is affected by interference amount, material and geometryof connection surface. The camshaft in engine CA488was taken as a typical examplein this paper. Making use of ABAQUS and nCode Design-life, the assembly process,static torsional strength and fatigue life of shrinkage fitting and knurling interferenceconnection assembled camshaft were analyzed with numerical simulation andcompared, and the effects of materials and technological parameter were studied toprovide the basis for practical production.The main research work and achievements of this paper are as follows:1)As for shrinkage fitting, the connection process and the static torsion wereresearched with numerical simulation. Firstly, according to thick cylinder interferenceconnection, the minimum interference amount to meet the work requirements wasfigured out, which was used to calculate the shrinkage fitting temperature. Then, thestress field of shrinkage fitting and torsion and torque curve were numericallyanalyzed. As last, the effects of interference amount and materials on static torsionalstrength were researched. The results show that with the interference amount of0.05mm, the static torsional strength of the group shaft45-cam20can reach three times as much as the practical operation torque of camshaft, followed by the groupshaft20Cr-cam45which can reach more than two times.2)After building the numerical model and boundary conditions of axial knurlinginterference assembly, the assembly process was numerical simulated, and the stressdistribution and pressure assembling force of separate parts after pressure assemblywere calculated. The stress field after pressure assembly was taken as the initial fieldto simulate the static torsion and analyze the effects of interference amount, toothform, materials on assembly process, pressure assembling force and static torsionalstrength. The results show that as for the knurling connection, high torque can beachieved by selecting tooth number, tooth height and interference amount. Thematerial group which meets the requirements of separate parts and has large yieldintensity difference can result in higher static torsional strength.3)The fatigue life of shrinkage fitting and axial knurling connection camshaft wasanalyzed. The calculation of fatigue life was completed by loading a cyclic load. Theeffects of interference amount, materials and tooth form on fatigue life of the twomethods were studied. The results show that the proper choice of tooth number, toothheight and interference amount can ensure the reliability of connection and improvethe fatigue life obviously.4)The results of comparison of static torsional strength and fatigue life betweenshrinkage fitting and axial knurling interference connection show that the fatigue lifeof axial knurling interference connection outclass that of shrinkage fitting, and thestatic torsional strength is close to each other only if the interference amount is same.Restricted to the conditions of materials and heating temperature, it is hard for theconnection strength of shrinkage fitting to be improved further. By contrast, theknurling connection method not only has high connection strength and fatigue life, butalso provides more choice for materials.