Numerical Simulation Of Gear Quenching Residual Stress And Its Influence On Gear Service Performance

Gear is an important part of the transmission system of mechanical equipment,in the process of gear processing,heat treatment technology is used to improve the hardness,wear resistance,bending strength,toughness and plasticity of gear and other mechanical properties.The residual stress formed after the heat treatment and quenching will affect the distribution of the force in the meshing process of the gear,and may even cause cracks in the gear due to coupling.so this topic in the quenching residual stress under the action of the service characteristics and fatigue life of gear.In this thesis,the distribution law of residual stress field of spur gear after quenching under different quenching medium is studied.On this basis,the distribution law of Mises stress,contact stress and bending stress in the gear meshing process under the action of quenching residual stress is analyzed,and the dangerous position is determined.The stress intensity factor at the crack tip was calculated and the fatigue life was evaluated.The conclusions are as follows:(1)The geometric model of spur gear was established,and the quenching residual stress of gear was numerically simulated and analyzed based on the heat conduction theory.It is found that the residual stress of the gear after quenching presents the distribution law of external pressure and internal tension.The maximum compressive stress is located at the root of the tooth and the maximum tensile stress is located at the center of the inner ring.By comparing the radial stress distribution of different cooling media,it is found that the faster the cooling rate is,the larger the temperature gradient is generated on the heat exchange surface,and the larger the thermal stress is.For spur gears,surface quenching with a relatively slow cooling rate should be selected to effectively control the distribution of residual stress.(2)The gear meshing process with or without quenching residual stress was contrastively analyzed.It can be concluded that the maximum bending stress is located at the tooth root,and the quenching residual compressive stress can offset the external load force,reduce the bending stress on the tooth surface,and enhance the bending fatigue resistance of the gear.The compressive stress of quenching residual stress and the external load acted on the tooth root,which promoted the increase of the compressive stress at the tooth root.The dangerous position of gear under the combined action of residual stress and external load is at the tooth root.(3)The stress intensity factor at the crack tip under quenching residual stress was solved.It can be seen that the fracture of the gear is mainly affected by ? type(open type)cracks during the meshing process.Quenching residual compressive stress can inhibit crack propagation.The Mises stress at the crack tip is the smallest when the crack Angle is about 30°.(4)In the fatigue life evaluation of spur gears with cracks,the smaller the stress ratio,the longer the fatigue life;The existence of quenching residual stress increases the service cycle of the gear by about 15%.