| Sintered composite powder metallurgy hollow camshaft is a lightweight,high-performance new camshaft.Under the trend of vigorously promoting energy saving and environmental protection,the development trend of sintered composite powder metallurgy hollow camshaft is very broad,because of its light weight,good wear resistance,flexible design and so on.It is well known that the powder metallurgy green material has a low strength and a high brittleness,so that the cam pieces in the transport and assembly process prone to damage or even rupture.At present,the sintered combined powder metallurgy hollow camshafts need to pre-sintering the cams in advance,which increases the pre-sintering process,increases the equipment input,and increases the energy consumption,thus increasing the production cost.Therefore,the green assembly of the cam is a difficult problem to be solved.In this paper,a binder with high intrinsic mechanical properties was added to the powder by the binder treatment technology to improve the process performance and the mechanical properties of the green body,and finally the automatic assembly process of the camshaft green body was realized.In this paper,a variety of binder resin were compared and modified to determine the type and amount of binder and compared the performance of the powder after the binder treatment.Through the research on the powder pressing process and the blanking performance,the green curing process was optimized,and the cam green body with higher strength and toughness was obtained.The roughening parameters in the assembly process are optimized to realize the automatic assembly of the green camshaft of the powder metallurgy and the sintering experiment is carried out.Get the following conclusions:1)The effect of the binder type on the mechanical properties of the green was studied.25 wt.%of the thermoplastic resin TP was mixed with 75 wt.%of the thermosetting resin W6 by the blending reaction to obtain the excellent mechanical properties WT25 binder.Adding 1.0 wt.%of the modified binder powder green strength reached 36.1MPa,tensile strength reached 8.7MPa,breaking deformation rate of 2.6‰.2)The effect of the binder content(0?3.0 wt.%)on the performance of the powder was studied.When the binder content was 1.0 wt.%,The flowrate of the binder powder was 30 s/50 g,the bulk density was 2.7 g/cm3,and the adhesion ratio increased from 25%to 96%.The coefficient of variation of the graphite was reduced from 8.6%to 1.2%.At this point the bonded powder has the best comprehensive process performance.3)The effect of curing process on the mechanical properties of the green was studied.With the increase of curing temperature and curing time,the comprehensive mechanical properties of green body increased,more than 210? will lead to binder failure.The optimum curing process was 150? for 150min,the green strength was 39.3MPa,the tensile strength was 9.6MPa,and the tensile deformation rate was 2.8‰.4)The effects of knurling,tooth length and tooth pitch on the surface strain of the cam during the cam assembly were studied by,orthogonal test.When the tooth height was 0.04mm,the tooth length was 8mm and the tooth pitch was 0.6mm,the minimum strain at assembly was 120?m/mm.In this condition,the cam was not easy to crack and the product was more stable.5)The cam was assembled with the camshaft automatic assembly machine under the optimum assembly parameters.After the assembly of the camshaft cam angle and axial position pass rate of 100%,while the cam surface cracking probability of only 1.3%.Therefore,the automatic assembly of the cam green body was realized.6)The camshaft prepared by the green assembly was sintered,the cam density was 7.6 g/cm3,the cam hardness was above 55 HRC,and the welding torque between the cam and the shaft was about 1000 N·m. |
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