Research On The Microstructure And Carburizing-quenching Process Of The Fine-blanked Gear

Gear transmission is widely used in the mechanical industry,and its working performance will directly affect that of the whole equipment,so there are strict requirements for its cut surface quality as well as dimensional precision.Fine blanking process has been increasingly adopted to fabricate gears recently,while gears used to be manufactured by casting,forging or machining process.As compared with these conventional methods mentioned above,fine-blanking is such a metal forming process in which can not only ensure the geometric accuracy of formed parts,but also obtain the cut surface with good quality.In this paper,an investigation has been made on the microstructure of the fine-blanked gear(including spur gear and helical-spur gear).The method in which combine metallographic experiment and finite element simulation has been adopted to discuss the relationship between the macro rule and the micro rule during the forming process.Since the carburizing-quenching process plays an important role during heat treatment procedure of the gear,and the previous investigation shows that the microstructure of the gear has actually changed,therefore,an investigation has been made to explore the similarities and differences between the deformation area and the non-deformation area of the fine-blanked spur gear during its subsequent carburizing-quenching process,and also the reasons which lead to these similarities and differences have been explained.Through a series of metallographic experiments,the distributions of the phases,grains and microhardness of the fine-blanked gears(including spur gear and helical-spur gear)have been obtained;With the help of finite element simulation,the distributions of temperature,strain and metal flow velocity have been obtained;based on its respective forming principle,as well as the results from both of metallographic experiment and finite element simulation,the relationship between the macro rule and the micro rule during the fine blanking process has been obtained,including the relationship between the macro forces,flown line,deformation degree,microhardness and equivalent strain,and so on.In addition,the formation mechanism of the die-roll of the fine-blanked spur gear was discussed in this paper,and it was found that thedirect reason of the die-roll formation is the non-uniformed metal flow velocity distribution within the workpiece,while the essential reason of the die-roll formation is the non-uniformed stress distribution within the workpiece.The higher the stress gradient of the area is,the smaller the die-roll is.Through studying the carburizing-quenching process of the fine-blanked spur gear,it was found that the dislocations,grain boundaries and sub-grain boundaries,which existed in the deformation area of the gear,provided a faster access for the active carbon atoms to diffuse during the carburizing process,accelerating the diffusion process and finally acquiring a greater amount of diffusion.As a result,martensite with high carbon content was obtained during the subsequent quenching process.Therefore,under the same carburizing-quenching process,when compared to the non-deformation area,the deformation area will have a wider carburizing layer,a smoother microhardness gradient distribution,and a higher average microhardness value within the carburized layer.Moreover,the wider the fine blanking deformation area is,the better the carburizing-quenching effect is.The conclusions obtained in this paper can provide credible theoretical basis to make fine blanking technology perform better in manufacturing gears,and also make the heat treatment plan more reasonable.