Development Of NC Assembly Machine And Research On Joining Technology For Assembled Camshaft

Assembled camshaft, where shaft tube and cam are separately produced and then assembled, has offered a range of remarkable advantages in cost reduction, weight saving, optimum combination of cam/shaft materials, design and manufacture flexibility and performance improvement over conventional camshafts made from one material. This technology is very important to reduce the automobile cost, lighten the engine weight and improve the engine performance. Assembled camshafts are attracted much attention as competitive products and technologies for camshaft manufacture because of its unique, composite design and special features compared to conventional camshaft. As a novel technology of camshaft manufacture, assembled camshaft has obvious advantages, it is the main developing object of camshaft manufacture.The key technology of assembled camshaft is the joining between the shaft tube and the cam lobe, or any other assembled component e.g. driving sprockets and journal bearings, which is depended on the assembly or joining method. The key supporting technology of assembled camshaft is the precision assembly machine with high efficiency. Nowadays, the most common industrially applied processes to build assembled camshaft include welded joint, sinter-bonding, expanding the tube by internal high pressure or inside mechanical pressure, knurling interference fit, etc. Based on the many problems and disadvantages existing in the connection methods of assembled camshaft at present, the current trend of the assembly or joining technology is towards cold-assembly and automatic production with high efficiency. It has much significance to prompt the research of connection technology and manufacture of its equipment by the knurling interference fit and expanding tube.In this dissertation, the FEM numerical simulation and experiments are used to analyze the connection technology of knurling interference fit and expanding tube by pushing through a ball. The various factors affecting the press fit load and joining strength are numerically simulated, the optimal factors are established. It illustrates that the numerical simulation and experiments results can provide the basis for the manufacture of assembled camshaft and the design of the assembly equipments. The major research is summarized as follows:(1) The expanding tube by pushing through a ball for assembled camshaft is proposed. The material performance of cam lobe and shaft tube is researched to base on the principle of expanding tube is analyzed. The process of expanding tube is numerically studied. As a result, the stress field and the distribution of wall thickness are given.Based on elasto-plastic theory, the effect of Young's modulus and Yield strength of cam and shaft tube on the expanding joining by pushing through a ball is analyzed in order to provide theoretical basis for structure design and materials mach of hollow assembled camshaft. The results shows that the core factors in expanding tube joining are Young's modulus and Yield strength of cam and shaft tube because of their crucial effects on elastic recovery of cam and shaft tube. The necessary condition for expanding joining is that Young's modulus of shaft tube should be higher than the one of cam, furthermore,Yield strength of cam has to be by far higher than the one of shaft tube if Young's modulus of cam should be higher than the one of shaft tube.The large deformation elasto-plastic FEM numerical simulation technique is first adopted to analyze the distribution of the equivalent stress, contact pressure and residual contact pressure in the process of expanding tube. The radial displacement distribution in the shaft is studied as well as the distribution of shaft wall thickness reduction during expanding tube process. It is concluded that, the internal surface of shaft tube subjects to the maximum equivalent stress,which results in the break of tube. The maximum contact pressure appears at the edge of the cam/tube joining, the radial displacement and wall thickness reduction of shaft tube is larger around contact zone of cam/shaft,(2) Based on elasto-plastic FEM numerical simulation and experiments of expanding tube by pushing through a ball, the factors to effect on assembly load and joining strength are analyzed, which provide the basis for the manufacture of assembled camshaft and the design of assembly equipments by expanding tube. The FEM numerical simulation technique is adopted to research on the factors influencing assembly load and joining strength. Assembly experiments and static torque strength of expanding tube are performed. The results show that the optimum combination of cam/shaft materials, fit clearance, magnitude of steel ball interference, wall thickness of shaft tube and cam lobe width influence the assembly load and joining strength significantly. The stability of the joining connection by expanding tube mainly depends on the optimal material matching of of cam and shaft, the proper choice of fit clearence, augment of magnitude of steel ball interference and cam width will enhance the joining strength of expanding tube. The results show that the assembled camshaft by by expanding tube can achieve the higher torsional strength and successfully guarantee engine performance.(3) Using FEM numerical simulation technique, the press fit process and static torque strength of knurling interference fit are analyzed. The influences of material, magnitude of interference, knurling width, knurling form and its tooth spacing on press fit load and joining strength are foundBased on the principle of joining by knurling interference fit, the assembly process by knurling joining and torque deformation of assembled camshaft are numerically studied and the various influencing factors on the press fit load and joining strength are deeply explored by comparing simulated results with experiment study. The results show that the following conclusions can be drawn:1) The optimum combination of cam/shaft materials has an important influence on joining strength.The low hardness cam has easy ductility,so it is assured that the tight press fit joining between cam and shaft is formed.As a result,under the guaranteed production performance condition,the cam material of low hardness is first choosen.However,as the production requirement is the high hardness cam,the surface of the bore in the cam lobes can be profiled in axial direction to provide a frictional and positive bond with the tube.2) As the material is defined,the magnitude of interference enlarged or knurling width extended can obviously enhance the joining strength.The extending knurling width or enlarging magnitude of interference can expand the contact area of knurling joining,in addition the elastic recovery causes tight press fit with the shaft,therefore the higher torsional load can be worked.3) The triangle tooth can reduce not only the pressure fit load in course of the assembly but also enhance the joining strength. Furthermore, the sparse knurling tooth in the assembly process leads to the severe metal plastic flow and expands the contact area, thereby the joining strength is increased.4) Compared with the experimental results, the numerical results agree well with the ones. It illustrates that the numerical results can provide the basis for the manufacture of assembled camshaft and the design of the NC assembly machine by knurling interference fit.(4) Aiming at the joining by knurling interference fit, the experiments including to the press fit, the torsional static and fatigue strength of lobe/tube joining are adopted to research on the factors influencing press fit load and joining strength by choosing different parameters.According to the joining technology by knurling interference fit, the experiments including to the press fit, torsional static and fatigue strength of lobe/tube joining are performed at various maiterial, mangitude of interference fit, knurling pattern(axially and hoop) and its tooth spacing. The torsional static and fatigue strength by joining of knurling interference fit are studied as well as press fit load . The results show that the assembled camshaft by knurling interence fit can achieve the higher torsional fatigue strength and successfully guarantee engine performance. At the same time, the experimental results are in agreement with the numerical simulation results. It illustrates that the numerical simulation results can provide the basis for the manufacture of assembled camshaft and the design of assembly equipments by knurling joining.(5) The research and developement of NC assembly machine for assembled camshaft by knurling interference fit.According to the process flow of cam lobe mounted by knurling interference fit, the integrated design concept of NC assembly machine is proposed. The mechanical system, hydraulic system and numerical control system in combination with the technology parameters of assembled camshaft by knurling joining are specially designed and manufactured, which the mechanical system is composed of an array of parts such as the driving system at Z axis, the system of shaft tube by clamped and rotated, the outfit of roll and extrude knurling forming, the feed outfit of cam elements. The NC assembly machine for assembled camshaft by knurling joining is manufactured first at home. Based on improving the production efficiency and automatic level of assembled camshaft, additional the cost reductions and weight savings, the cantilever assembly machine for assembled camshaft by knurling joining is designed first by optimum design of mechanical structure.(6) Research on the technology test of automatic assembly for assembled camshaft by knurling interference fitThe NC assembly machine is adopted to researche on the automatic assembly technology of V348 intake/exhaust camshaft. The angle and axial position of the camlobes mounted are measured, which meets the technical requiments of the V348 assembly camshaft. The measured results indicate that assembly machine can realize the high precision process with the high flexibility performance. At the same time, a small batch of V348 camshaft is assembled to study the mehanical strength and camlobes axial and angular position of the camshaft, it is the basis for the industrialized production of assembled camshaft by knurling interence fit.