Research On Warm Forming And Anticorrosive Process Of Large Curvature Spring

Spring is an important basic part of the machinery industry.It is used in various types of high speed rail,automotive,aerospace and other fields.It is an important industry to promote the development of China’s industry and national economy.It is used to control mechanical movement,store and release energy,buffer balance,automatic control and safety insurance.Spring is an essential part of mechanical equipment.It is the trend of spring industry reform to develop new technology and new method of spring forming,which conforms to the development concept of social economy,low carbon and non-pollution.In this paper,the large curvature structure spring was put forward using an electromagnetic induction heating warm forming.The optimum processing parameters of warm forming were determined by the compression test.Secondly,the microstructure and properties of warm forming large curvature structure spring were researched,which to verify the feasibility of the warm forming process.Finally,the spring surface used the manganese series phosphating method.The optimized process parameters were carried out by salt spray and electrochemical corrosion tests.And the corrosion resistance of the spring surface was improved.The compressive flow stress and strain of oil-quenching 65Mn spring steel were studied with a thermomechanical simulator.A strain-compensated Arrhenius-type constitutive model was established.The experimental values were compared with the predicted values of the model.The absolute value of relative error(AARE)and correlation coefficient(R)is 6.98%and 0.981,respectively,which indicates that the model has good predictability of the flow stress for the 65Mn spring steel.The established model can be applied to the finite element simulation of the spring forming process.The working diagram of 65Mn spring steel was established according to the dynamic material model(DMM).The optimum hot working range of hot deformation was determined as deformation temperature 630 ℃-671℃ and strain rate 1～2.718 s-1.In order to obtain the temperature field in 65Mn tape-steel.The electromagnetic thermal coupling finite element model was established to analyze the influence of different alternating current on the electromagnetic field and temperature field of 65Mn tape-steel.The simulation results show that the magnetic field intensity,magnetic flux density,current density and temperature field of the tape-steel increase with the increase of the current frequency and alternating current of the electromagnetic induction coil under the same coil turns and electromagnetic induction coil current frequency.The magnetic field intensity,magnetic flux density and current density of the upper and lower parts of the tape-steel are larger than the middle part.The microstructure evolution of the tape-steel heating area and the influence law of process parameters on its performance are studied by the high frequency electromagnetic induction heating equipment.The results show that cementite exists in different forms under different alternating current,tensile strength and yield strength decrease,but brittleness increase and elongation decrease after heating and water cooling.The maximum relative error between the measured temperature curve and the finite element simulation results is about 3.13%,which verifies the rationality of the simulated data.It provides a reasonable temperature field for forming a large curvature structure spring.Take the flat spiral spring products as an example.The main forming structure models of tape-steel,coiling wheel and guide groove are established.The forming of large curvature flat spiral spring is simulated and analyzed by finite element method.It can be seen that the large curvature structure parts of the Mises stress and forming resistance decreases.When forming temperature is 650℃,the forming dimension accuracy of a flat spiral spring is high,and residual stress low.The microstructure is composed of ferrite and a few of pearlite in the bending position,and ferrite is stretched in the direction of bending.The relationship between rotation angle and torque at different forming temperatures was tested by spring torsion testing machine.The results show that the torque of spring changes linearly with the increase of rotation angle,which verifies the feasibility of electromagnetic induction heating forming large curvature flat spiral spring technology,and provides theoretical and technical support for spring factory flat spiral spring forming.The anticorrosion technology was carried out on the surface of the formed flat spiral spring.The effects of phosphating process parameters(acid ratio,phosphating temperature and phosphating time)on the surface macromorphology,film weight and copper sulfate corrosion resistance time of the spring were studied by the orthogonal test of three factors and four levels.The phase composition and microstructure evolution of the phosphate coating with different process parameters were analyzed by X-ray diffractometer and scanning electron microscope with energy spectrum.The results show that the macroscopic morphology of the phosphate coating was black,gray and gray black.The phosphate coating was mainly composed of Mn52+(PO4)2(PO3(OH))2·4H2O and MnHOP4·2.25H2O phase.When the ratio of phosphating acid is 10,the phosphating temperature is 85 ℃,and the phosphating time is 5 min,the spring substrate has a large area of yellow rust by salt spray test.The electrochemical corrosion potential of the phosphate coating is higher than that of the 65Mn spring substrate,and the current density is one order of magnitude smaller.