Simulation Analysis On Tube Expanding Processing And Fatigue Life Prediction Of The Assembled Camshaft

Through split manufacturing and high accurate connection technology, the assembled camshaft possesses a variety of properties, such as material matching, weight saving design, the flexible structure design and manufacturing, which extremely improve the entire performance and production efficiency of camshaft, and appear to the trend of modern engine development. Now there are various connection techniques of assembled camshaft, such as knurling connection, tube expanding, power sintering and welding, As the important characteristics of assembled camshaft, torsional strength and fatigue life affect the engine performance and get noticed widely.At present, the research of assembled camshaft mainly focuses on the assembly parameters, assembly load and connection strength, for example the assembly load and torsional strength in knurling connection, the in-depth and comprehensive study is still necessary. Because of accurate positioning, high efficiency, easy operation, the tube expanding method has become the main stream connection technique. Based on the National Science and Technology Major Project, this paper conducted the analysis on tube expanding technology and fatigue life prediction, combining with the experiments, the whole tube expanding connection was researched systematically. Based on the design requirements of assembled camshaft, the processes of tube expanding connection, torsion analysis and fatigue life prediction were systematically. Two typical connection surface of camshaft were discussed about connection process and static torsional strength, fatigue life prediction of assembled camshaft relied on the modern CAE fatigue analysis, and the influencing factors of the assembled camshaft connecting strength were discussed and optimized. In turn, provides reference for the early stage of the assembled camshaft design.The major research work of this dissertation is summarized as follows.1. Analysis on the theory of fatigue life predictionBased on the basic theory of fatigue life prediction, the method of fatigue analysis, the fatigue damage accumulation theory and the general flow of fatigue finite element analysis were researched, and the main factors influencing fatigue life of materials or components were analyzed,which provided basement for the later fatigue analysis.2. The establishment of finite element modeling of tube expanding connection and the numerical simulation of the process of connection.Combining with the connection theory and the torsion experiments, the finite element models of tube expanding and torsion process were established, other technical issues such as constraint, friction and loading technology of boundary. The tube expanding processes for two kind of assembled camshaft were numerical simulated, the stress distribution,contact stress and the thickness reduction were obtained,then the influencing factors on the process of connection were studied.3. The establishment of finite element modeling of torsion process and the impact analysis of the key process parameters on the static torsional strength.and the finite element models of torsion processes were established. The torsional value and the state of connection surface were discussed under 10 degree angular displacement load, Then many factors that have significant influence on connection strength were discussed deeply including the material match, fit interference, initial clearance between cam and shaft. Finally verify the simulation analysis with the. torsional and connection.4. Fatigue life predict and the analysis on influencing factorsThe process of tube expanding connection, torsion analysis and fatigue life prediction were systematically numerical simulated in this paper. The deformable model and residual stress were regarded as the initial state, based on the modern CAE fatigue analysis, the fatigue life and dangerous nodes were predicted. Then many factors that have significant influence on fatigue life were discussed deeply including the material match, fit interference, initial clearance between cam and shaft, and compared with the influencing rule of static torsional strength, then provided the reference for the camshaft design. At last, the concept on fretting fatigue of assembled camshaft was proposed. Depending on the definition of fretting and location of the fatigue crack, the possibility of fretting fatigue on assembled camshaft was studied.