Numerical Studies On The Induction Quenching Process Of Crankshaft

Induction quenching is one of the widely used surface hardening methods of thecrankshaft. Some theoretical analyses, numerical simulations and experimental studiesabout the induction quenching process of the crankshaft were carried out under theprofoundly understanding of the principle of the electromagnetic induction quenching andthe practical quenching process. The main contents included:(1) The analytical solutions of the Electromagnetic Fields and the heat generation inthe induction quenching semi-infinite body were attained by the analytical method based onthe Maxwell Equations. Moreover, the effects of some parameters on the heat generation inthe semi-infinite body were studied. The results showed that the heat generation in thesemi-infinite body was in direct proportional to the square of the current density and thesquare of the width of the inductor coil. The heat generation rate followed the exponentialattenuation law with the increase of the air gap width. The current frequency had effects onboth the maximum heat generation rate and the heat generation rate distribution. When theeffect of the air gap was neglected, the maximum heat generation rate increased with thecurrent frequency. However, when the effect of the air gap was considered, the maximumheat generation rate increased with the augment of the frequency if the frequency was lessthan the critical frequency and decreased with the augment if the frequency was larger thanthe critical frequency. Moreover, the higher the current frequency, the heavier the heatgeneration rate attenuation in the workpiece.(2) The extended analytic kinetic model considering the effect of heating rates in theprocess of induction heating was fitted using dilatometric experiment data. Results showedthat fitted results of austenite reaction using the kinetic model met well with theexperimental data. The starting temperature of the austenitizing process and the heating ratefollowed a linear law. Moreover, the austenitizing time and the heating rate followed thedual logarithmic linear law. The starting temperature of the austenitizing process increasedwith the augment of the heating rate and the austenitizing time decreased with the augmentof the heating rate. Further, Austenite formulation of the induction heating crankshaft withcontinuous changing heating rates was predicted using the kinetic model and the additivity rule, which was the foundation of the subsequent quench cooling process.(3) Maynier’s model was used to predict the hardened layer distribution and thehardness. The effects of the material composition, the heat transfer coefficient and theheating time on the hardness of the induction quenched crankshaft were studied. Thesurface hardness decreased and the width of the hardened layer increased with the increaseof heating time if the heating time was long enough to ensure complete austenization at thesurface. The hardness of the upper material composition crankshaft after quenching waslarger than ones of the normal and the lower material compositions if other conditions werethe same. When the cooling medium was water, there was only a small difference in thesurface hardness when different heat transfer coefficients were used. However, the surfacehardness was larger than the design value. So, when the cooling medium was water, thesurface hardness didn’t meet the design value. The austenitizing process was predicted bythe traditional heating temperature method and the established extended analytic kineticmodel, then the difference of the predicted hardened layer distribution was studied. Resultsshowed that the hardened layer changed more smoothly at the fillet when the establishedextended analytic kinetic model was used to predict the austenitizing process. So, thekinetic model must be used to predict the austenitizing process exactly.(4)2D axisymmetric thermo-elasto-plastic model was established to predict theresidual stress of the crankshaft in the induction process. The residual stress at the journalsurface was compressive stress and the value decreased with the increase of the depth fromthe surface until the residual stress state changed into tensile stress state. Then, the tensilestress increased with the increase of the depth firstly and then decreased until the residualstress state changed into compressive stress state. And then the compressive stressincreased with the increase of the depth firstly and then decreased with the depth andtended to be0finally. The value of the residual stress at the journal surface almostdecreased with the prolonging of the heating time. X-ray diffraction results showed that theresidual stress at the surface of the fillet was compressive stress.(5) The FEM model to analyze the structure strength of the crankshaft was established.The nonhomogeneous material property was considered in the model. The distribution ofMises stress of the induction quenched crankshaft with the nonhomogeneous material properties under working state was attained. The effects of the nonhomogeneous materialproperty on the stress under working state were studied. The maximum Mises stressincreased with the augment of the ratio of elastic modulus of the surface layer and thematrix and the maximum Mises value and the ration nearly followed a linear law. Thedistribution pattern in the transition layer had little effect on the maximum Mises stress andelastic modulus in the transition layer could be set to equal the elastic modulus in thesurface layer or the matrix.