| Gear has the function of transmitting torque and power,and is the basic transmission parts of aerospace,automobile,machinery and other industries.Performance improvement and lightweight is the development trend of gear.The steel/aluminum bimetal gear can combine the advantages of high strength of steel and low density of aluminum to achieve the overall weight reduction of the gear,and achieve the optimization matching of the performance of the two kinds of billets in the component by integral forging.However,the significant differences between steel and aluminum in thermal physical and mechanical properties will lead to many problems in the bonding of metal interfaces,which brings challenges to the hot forging process of steel/aluminum bimetal gears.On the basis of theoretical calculation,a new method was proposed for the size design of steel/aluminum bimetal gear billet in this paper.Through finite element analysis and process test,the forming process and interface bonding characteristics of bimetal gear hot precision forging are systematically studied.The main research contents are as follows:In this paper,a mechanical model of steel/aluminum bimetal gear was established.Based on strength theory,the influence of billet distribution at dangerous section on mechanical properties of gear was analyzed.The results show that the thickness of billet at the tooth root should be higher than the theoretical lower limit in order to avoid the aluminum alloy at the dangerous section breaks before the gear steel,causing the mechanical properties of the bimetal gear to decline.Based on the principle of equal volume,the dimension design formulas of steel ring and aluminum core were put forward.The 45 steel and the 1060 pure aluminum are selected as bimetal gear billets.Based on the dimension design formula of steel ring and aluminum core,the minimum dimension requirement of steel ring thickness is calculated.The forming characteristics and metal flow law of bimetal gear with different thickness of steel ring are analyzed by finite element simulation.Considering the gear forming effect and the degree of lightness,4.2mm was selected as the thickness of steel ring in the process experiment.The influence of preheating temperature of steel ring on billet temperature and interface temperature is analyzed.It is found that the temperature difference of aluminum billet after forging can be reduced if the aluminum core is set at room temperature of 20 ° C and the steel ring is preheated to 900 ° C,and the melting of aluminum billet can be prevented during forming.The effect of billet extrusion velocity on gear equivalent stress field and interface temperature was analyzed,and5mm/s was selected as the suitable billet extrusion velocity.Finally,on the basis of finite element numerical simulation,the billet preparation and forging die design were completed,the bimetal gear forming process scheme was set up,and the gear hot precision forging forming process experiment was completed.Three bimetal gear samples with different deformation degrees were wire cut,and the gear interface was polished.Optical microscope,scanning electron microscope and energy spectrum were used to observe the microscopic morphology of the gear interface and determine the elemental composition.The results show that when the deformation degree of bimetal gear is 50% and 70%,the connection mode between steel and aluminum interface is mechanical connection.When the deformation degree of gear is 90%,mutual diffusion of Al and Fe occurs in the interface connection area,and intermetallic compound layer is formed,and local metallurgical connection appears between steel and aluminum interface. |
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