• 2023-11-13
• 462
• 5 Comments

Method for improving the fatigue limit or fatigue strength of die materials

It is generally difficult to change the conditions of use of mold parts, and it is necessary to improve the design of mold parts as much as possible, such as starting from the surface effect. As long as the surface stress concentration of the structural materials and mechanical parts of the die is prevented, the slip accumulation of the dislocation is hindered, and the plastic deformation is suppressed, the fatigue crack of the die is not easy to nucleate or expand, which will increase the fatigue limit or fatigue strength.

1. Reduce stress concentration

2. Strengthen the surface layer

1. Measures to reduce stress concentration

In mold design, square holes and slots with sharp corners should be avoided.

Where the section size changes abruptly (such as the shoulder of the step shaft), a transition fillet with a sufficiently large radius is used to reduce stress concentration.

Because of the mold structure, when it is difficult to increase the radius of the transition fillet, a thinning slot or a cutting slot can be opened on the part of the shaft with a larger diameter.

There is an obvious stress concentration at the edge of the fit surface of the tightly fitted wheel hub and shaft. The stress concentration at the edge of the fitting surface can be improved if a load reduction slot is opened on the hub and the fitting part of the shaft is thickened to narrow the stiffness gap between the hub and the shaft.

In fillet welds, the stress concentration is improved more by using groove welding than by non-groove welding.

2. Strengthen the surface strength of the mold

Use mechanical method to strengthen the surface of the mold (such as rolling, shot peening, etc.), so that the surface of the mold component to form a pre-pressed stress layer, weaken the surface tensile stress that is easy to cause cracks, so as to improve the fatigue strength, or use heat treatment and chemical treatment, such as high-frequency quenching, carburizing, nitriding, etc.

The mold adopts a small steel ball with a diameter of 0.1-1mm to impact the surface of the sample at high speed to remove the surface acute Angle, rough edge and other easy stress concentration, and compress the surface to a depth of 1/4-1/2 of the diameter of the steel ball, so that the residual stress on the surface of the part is generated and the expansion of fatigue cracks is suppressed.