| The camshaft is one of the five key components of automobile engine and can directly control inlet and exhaust for valve system, affecting the engine fuel efficiency and power performance. As a kind of advanced manufacturing technology of camshaft, hollow assembled camshaft with the advantage of light quality, flexible structure design and high-usage of material, satisfies the current demand for energy saving and emission reduction and has been widely used in high performance car engine at home and abroad.In the preparation process of hollow assembled camshaft, because of mechanical interference fitted between cam and tube, the cam can be produced radial pressure. But in the running process of the and automobile engine,the surface of cam could withstand periodicity load and fast sliding contact. The cam should be good wear resistance and high hardness to ensure the dimensional precision and the service life. In order to keep high hardness, high wear resistance and low tensile stress of the surface of cam, Researchers for Grinm Advanced Material(Beijing) co., Ltd. supply a new methods for preparing cam, by using the principle of layered composite materials, the internal layer of cam can be used with high toughness of powder metallurgy materials, and the external layer of cam with high hardness, high density of sintered hardening materials, through high temperature liquid phase to form a metallurgical bonding between the internal and external layer of cam,which can realize internal surface hardness and toughness increase. During the mechanical interference fitted, internal layer of cam because of using high plastic and toughness Powder metallurgy materials, can well absorb the assembly stress, with weaken the stress concentration for the external layer of cam. However, the study of materials and structure for cam is less at present, especially the effect on assembly stress for material performance and layered structure of the powder metallurgy composite cam is not still reported.Therefore, with the cam interference assembly process analyzed, the stress of cam can be analyzed and the geometrical shape of cam was simplified. Three-dimensional finite element simulation method was applied to establish the model of interference assembling process between composite cam and tube. On the basis of the model, the equivalent stress distribution of composite cam in the assembling process was analyzed, and the effect of material of inner layer, thickness of inner layer and the model of inter layer binding on assembly stress of composite cam was discussed. Meanwhile, the experiment of assembly was performed to validate the effect.It could come to the conclusion that:(1)Three-dimensional finite element simulation method was applied to establish the model of composite cam for interference assembling process. Meanwhile, the experiment of assembly was performed and the different data between the experiment and simulation is in 5%. The results of numerical computation agree with the experimental data well and validated the mode.(2)When the inner layer of composite cam was used powder metallurgy(Fe-Cu-C)material and 45# steel, the model was analyzed. It could be concluded that when the magnitude of interference between the cam and tube is 0.08 mm, when the inner layer of composite cam was used powder metallurgy(Fe-Cu-C) material, the stress was changed in between 114 MPa and 372MPa; when the inner layer of composite cam was used 45# steel,the stress was changed in between 297 MPa and 380MPa; the surface stress of composite cam is 114 MPa and 297 MPa, the former is the 38% of the latter, inner layer with powder metallurgy(Fe-Cu-C) material can preferably ease stress in the assembly process and powder metallurgy(Fe-Cu-C) material would likely in layer material of composite cam.And when the inner layer of composite cam was used powder metallurgy(Fe-Cu-C)material, the internal layer can absorb stress gradually.(3)Based on the preparation technology of the layered composite cam, technological parameter was analyed. Then the characteristics of powder metallurgy materials(Fe-Cu-C)and the relationship between technological parameter and assembly stress was analyzed. It could be concluded that in order to fracture failure of composite cam, the yield strength of powder metallurgy materials(Fe-Cu-C) is more than 405 MPa. The effect eased stress in the assembly process is better, while the elastic modulus of powder metallurgy materials(Fe-Cu-C) is more small. According to the relationship between the material properties and the preparation, when the the compaction density of inner layer is 6.8g/cm3, inner layer can preferably ease stress in the assembly process. By using the model, optimization design of layer structure is processed on different thickness and the allowed thickness for in layer of composite cam is 1.75~2.25 mm, the optimal thickness is 2.05 mm. Compared between interference fit and metallurgical bonding, combining high temperature liquid phase metallurgy composite cam has better ease stress effect. |
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