Crankshaft Surface Induction Hardening Application Study

Surface quenching process can improve the comprehensive mechanical properties of the workpiece.In the engine crankshaft manufacturing field,surface induction quenching process is more and more used to improve the fatigue strength and wear resistance of the crankshaft.There are some problems in the crankshaft surface induction quenching process,such as low precision of process design,low process capability index,long adjustment time of process parameters,large workpiece deformation and so on.These problems are the key factors affecting the crankshaft processing quality and manufacturing cost.This paper will study these problems and work out solutions to improve the quenching quality of the crankshaft and reduce the manufacturing difficulty and cost.Firstly,in the early stage of the project,the process flow of induction quenching is designed,and the influence of the quenching process on the whole line process is analyzed.The quenching process is arranged after the oil drilling process in the rough machining stage and before the rolling groove process in the semi finishing stage,so as to improve the product quality and reduce the loss of tools and energy.Secondly,to he problem of the low accuracy of quenching process design,the distribution data of hardening layer depth and hardness are determined through experiments,and the depth distribution function and hardness distribution curve are established.During process design,the hardening layer width and hardness change of the subsequent process are determined through the distribution function and distribution curve,and the corresponding change is reserved for the subsequent process,it can improve the accuracy of the process design.Then,to the problems of low process capability index of hardening layer width and 100% martensite depth in the quenching process,based on the analysis of the quenching technical requirements of crankshaft and the rationality of induction coil design,it is found that the technical requirements of quenching process are too strict and the width design of induction coil is too large.By enlarging the width tolerance of the hardened layer,reducing the 100% martensite depth requirement,reducing the width of the induction coil,the process capability index is improved.After the change,the test results show that the fatigue life of the crankshaft,the torque and power of the engine can meet the design target,which effectively reduces the manufacturing difficulty and cost of the crankshaft.Fourthly,to the problem that the heating voltage adjustment time of quenching process is too long,based on the influence principle of heating voltage on the width of quenching layer,100% martensite depth and workpiece surface hardness,the numerical relationship between them is confirmed through experiments,and the mathematical model is established by the least square method to guide the adjustment of heating voltage and improve the accuracy and efficiency of adjustment.Finally,to the problem of large deformation of crankshaft caused by quenching process,based on the principle of crankshaft deformation caused by quenching process,the law of crankshaft length deformation is found through verification,and the influence of length deformation is offset by reserving length deformation to quenching process.For the deformation(bending deformation)in the diameter direction of the crankshaft,based on the analysis of the difference of quenching sequence between main journal and connecting rod journal,it is found that the process sequence of quenching the main journal first and then the connecting rod journal has less influence on the bending deformation of the crankshaft,which provides a strong basis for the design of the induction quenching process of the crankshaft.