| Assembly camshaft play an important part in the valve train of engine.Compared with one-piece camshaft,it has the characteristics of light weight,material split optimization,good performance and flexible structure design,and has been used in the manufacture of high-end automobile engine widely.For assembly camshaft,the design and manufacture of cam is one of the hot research directions in recent years.The cam profile requires high machining accuracy,the cam surface is subjected to severe friction under working conditions,and the core is subjected to periodic load.Therefore,for cam components,it is required to have high strength,wear resistance,core toughness and fatigue resistance.Now the manufacture method of assembly cam,mainly is made of low,medium carbon steel,alloy steel through precision plastic molding process,and then according to the requirements of use,taking some surface hardening treatment,including:Surface Induction Hardening,Carburizing,nitriding and so on.As powder forging,it combines the characteristics of powder metallurgy forming,and at the same time,with the help of hot forging,it reduces the porosity of powder metallurgy materials,greatly improves the density of materials and the mechanical properties.Easy to manufacture components with high precision and few steps,so it is a processing method which is very suitable for assembly cam.This paper focuses on the research and processing of the powder forging assembly cam,and makes the following research:1.Use numerical simulation technology to study the process of powder forging cams.With the help of material performance calculation software JMatPro,the thermal physical parameters and flow stress and strain curves of Fe-0.8C-2Cu materials are calculated and imported into the finite element software Deform as the model of the material.For one type of assembly cam,the design of die and preform is carried out,and then simulate the change of density field and stress field of the cam under four flow gap modes,and study the change of density field and velocity field of the cam with the stroke of top die at the both-sided flow gap model.The results show that the overall density of the cam is higher and uniform,the equivalent stress of the preform and die is lower under the both-sided flow gap model.So the both-sided flow gap model is the best model.After that,a simulation study was carried out on the size of the flow gap and the flow gap of 0.9 mm was finally determined.2.With the help of simulation technology,the effects of five forging process parameters on cam density and equivalent stress distribution were studied.The optimum forging process parameters were determined:forging speed:300 mm/s,initial relative density:0.9,preform heating temperature:1200℃,die preheating temperature:250℃,friction coefficient:0.3.Combined with the simulation results and the actual situation,produced some cam samples,and the material density,porosity,mechanical properties and microstructure before and after forging were studied.The tensile strength,yield strength,elongation and hardness of the cam were greatly increased from 470MPa,310MPa,2.5%and 50HB to 948MPa,663MPa,7%and 250HB.3.L9(34)orthogonal experiments were used to study the effect of temperature and time of quenching and tempering on the mechanical properties of cam,and then the effect of tempering temperature on friction and wear properties of the cam was studied.The results show that the tempering temperature has the greatest influence on the properties of the material,the tempering temperature rises,the martensite decomposes,the solid solution strengthening decreases and the strength of the material decreases.Because the Cu is insoluble in matrix structure,it is easy to segregation at grain boundary after low temperature tempering,so the tensile fracture morphology is mostly intergranular fracture.Among the friction samples at different tempering temperatures,200℃ tempered sample,under three loads,the friction coefficient is stable,the wear amount is small,and the wear form is mainly abrasive wear. |
