Investigation On Springback Behavior Of Assembled Camshaft Under Hydraulic Expansion

As an important part of the automobile engine,the camshaft controls the opening and closing of the engine valve,and directly affects the working performance of the engine.Compared with the traditional integrated camshaft,the assembled camshaft has the advantages of optimized material,free cam arrangement,lightweight design and cost reduction.Hydraulic expansion connection technology is one of the effective connection process of assembled camshaft.The principle of expansion connection is that the core shaft shapes and deform due to the liquid pressure and causes the elastic deformation of the cam inner hole.After liquid pressure unloading,the two rebound to different degrees,thus interference fit is generated to achieve effective connection.The springback behavior of shaft and cam directly affects the connection quality of assembled camshaft.Therefore,it is of great significance to study the springback behavior of hydraulic expansion.The coordination interface of the assembled camshaft studied in this project is a isometric-trilateral inner profiles structure.Combined with the theory of swelling connection and springback,the finite element simulation and hydraulic expansion test,the springback behavior characteristics and rebound distribution rules of the cam and shaft under the coordination structure during the unloading stage are analyzed.This paper studies the influence of structural deviation,initial clearance and axial feed on the rebound behavior under different liquid pressure,and the optimization method of orthogonal test is used to find better process parameters combination to reasonably control and match the springback behavior of cam and shaft,so as to improve the connection strength of hydraulic expansion assembled camshaft.The results show that:(1)The isometric-trilateral inner profiles structure cam hydraulic expansion,the largest rebound occurs at the point of tangency position between the inner base circle,even the expansion after the separation of the core shaft and the cam,the rebound smaller position is mainly concentrated near the prominent position of the outer circle and the isometric-trilateral inner profiles point of tangency position,and the distance within the circle cut point 35°～45°.(2)When the inner base circle is the same,the change of the structural offset will affect the rebound distribution of the shaft and the cam.Within the offset of 1.0 mm,the overall rebound of the cam decreases with the increase of the offset,and with the increase of the liquid pressure,the greater the rebound rate is relatively smaller.(3)When the offset is the same,the change of the initial clearance will not affect the overall rebound distribution of the shaft and the cam.When the offset is 1.0mm,within the initial clearance is 0.2 mm,the rebound between the shaft and the cam will first decrease and then increase with the increase of the initial clearance.That is,the initial clearance is 0.15 mm,and the rebound between the shaft and the cam is the minimum.(4)The same structural parameter of cam hydraulic expansion,the axial feed will not affect the rebound distribution of the shaft and the cam.When the axial feed is more than 4%,the shaft will have obvious wrinkle phenomenon.In the range of 3% axial feed,the overall rebound rate of shaft and cam gradually decreases with the increase of axial feed.That is,when the axial feed is 3%,the cam rebound is the smallest,and the expansion mass is the best.(5)Through the optimized design method of orthogonal test,the best process parameters to reduce the cam return and improve the connection quality is liquid pressure80 MPa,offset 0.8 mm,initial gap 0.10 mm,axial feed 3%,and the order is axial feed>initial gap>offset>fluid pressure.