Discussion on stress accumulation of pressing die on gear shaft

A large stress concentration occurs at the edge of the top end of the insert. Since the blank is temporarily stored and is stressed for a short time during operation, the structure is inverted to 2x45. Beveled and rounded at the turning point. The large stress zone at the top selects the most suitable transition angle under the premise of satisfying the material strength and the optimum metal flow. The optimized transition angle from 25 to 24 is the cone angle 90. The larger the taper angle is, the worse the metal fluidity is, the lubrication is difficult, and the stress concentration is easy to occur; the taper angle is too small, although the deformation of the extrusion is uniform, the unit pressing force is also reduced, but the length of the deformed region of the forming portion is increased, and the friction is increased. When the lubrication condition is worse, the lubrication condition becomes worse, the forming pressure becomes larger, and the phenomenon of metal adhesion die is generated. Therefore, in order to achieve the best transition angle, it is necessary to try many times in the design process and adjust it with the analysis results to obtain the optimal design.
The stress concentration at the 3mm press-fit of the bottom surface of the two inserts is a negative effect brought about by the best press-fit effect, which is unavoidable. However, according to the magnitude of the pressing force, the optimum turning angle can be selected within 0-30 to reduce the stress concentration.
Generally, a larger turning force selects a smaller turning angle, and a smaller pressing force selects a larger turning angle. Therefore, for the cold extrusion, the shape is as simple as possible under the premise of the size of the part, which can bring convenience to the mold design, and does not cause excessive stress area of ​​the concave mold during the working process, and the mold is improved. life.

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