Preventive measures for grinding cracks of automobile steering shaft teeth

The stress released in the grinding process of gears generally comes from two aspects: one is the residual stress formed in the carburizing and quenching process of the workpiece itself; On the other hand, it is the thermal stress produced in the grinding process and the microstructure stress produced by material phase transformation. The improvement measures and schemes are put forward from two aspects: heat treatment and grinding process; Based on the meshing principle of gears, the design idea of gear machining to avoid grinding cracks is put forward.

(1) for 20CrMnTi steel shaft teeth, direct quenching after carburizing at 930 ℃ can be considered, and the quenching temperature can be appropriately reduced to avoid the formation of excessive residual austenite and coarse martensite; On the premise of ensuring relevant technical indexes, increase the tempering temperature or prolong the tempering time to fully eliminate the residual tensile stress in the process of carburizing and quenching.

(2) adjusting grinding process parameters during grinding process, appropriately reducing the feed rate of single pass grinding or changing from 1 grinding to 2 grinding to avoid the quenching of martensite and tempered structure of quench in two times. Reduce the hardness index of the grinding tool and trim the cutting surface of the grinding wheel with the help of the diamond trimming pen to form a new sharp edge; On the premise of ensuring the surface roughness and accuracy of the gear, improve the rotating speed of the workpiece and the linear speed of the grinding wheel; Use the coolant with good fluidity and cooling property to strengthen the cooling effect in the grinding process, so as to reduce the generation of grinding heat in the grinding process.

By improving the heat treatment process and grinding process, there is no grinding crack in the later machining process of this type of shaft tooth, and the fatigue and other performance indexes in the bench test meet the relevant technical requirements. The tooth root of the gear rack of the hydraulic power steering system does not participate in meshing in the process of transmitting power. Therefore, the design idea of no grinding of the tooth root can be considered in the gear machining design. Non grinding of tooth root can improve the bearing capacity of gear, avoid grinding damage and improve grinding quality, but it is necessary to consider using pre grinding hob for tooth profile pre machining in advance in the process of gear machining.

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