Study on crack formation mechanism of a motor gear in cold extrusion
Aiming at the crack defects on the teeth top surface of the inner teeth of a motor gear with 20Cr during cold extrusion,the cold extrusion process was simulated to study the crack formation mechanism based on DEFORM-3D.The finite element results show that the metal flow velocity of the inner teeth is smaller than that of the middle and lower outer teeth,the metal flow velocity at the teeth root on the teeth top surface of the inner teeth is the smallest,where the flow is the most uneven and the stress concentration is easy to occur.The maximum principal stress and damage distribution of the teeth surface were analyzed,it is concluded that the stress concentration is the most obvious at the middle and the position about 1 mm from the lower end surface on the teeth top surface of the inner tooth.The tensile stress is larger than the tensile strength of the material,and damage value is also larger than the critical damage value,and cracks can be generated,which is consistent with the actual situation.The forming defects were controlled by changing the die entry angle.When the die entry angle is 23°,the tensile stress at the teeth root decreases,the damage value decreases,and the defective rate is reduced from 50%to 1%after production.
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