After stress peening, the residual stress layer is firmly attached to the surface of the wire, especially for the key parts of the spring (maximum circle and small end ring 1.7 turns), and these two are often minibloc springs. Stress concentration point. 2 The residual stress of these two key parts is described as the distribution of preload force between different layer thicknesses. The maximum residual stress value appears at approximately 0.15 mm deep below the surface layer. The residual stress value at a depth of 0.35 mm is almost close to a fixed value. This is because the spring is pre-pressed to the specified height before shot peening. Gradually increasing the preload before shot peening will reveal that the residual stress value will also increase. Some data show that the maximum can be 50% of the original stress value. However, after the pressure exceeds 60% of the free height (convert the preload into Spring height), this value will not continue to increase. In addition, the small end ring is 1.7 turns, because the circle is nested in a larger circle diameter, resulting in a measured residual stress value of 10% less than the original.
The distribution of residual stress between different layer thicknesses (1.7 turns at both ends of the spring) is another type of post-processing of shot peening in a specific high temperature environment. From the perspective of organizational structure, the residual stress formed after shot peening is distributed between different layer thicknesses (in the middle of the spring). There is a very high density of dislocations in the surface strengthening layer. Under the influence of subsequent variable stress and thermal temperature, After the error, the rules are gradually rearranged to form a residual stress layer. Thermal spraying makes it easier to achieve the required dislocations on the surface of the steel material, resulting in higher energy. However, thermal spraying is more suitable for cold coil springs, because the cold rolled spring has the characteristics of high surface hardness and less decarburization relative to the hot coil spring. The thermal spray has the advantages of small pellet loss and obvious shot peening effect, and the shot peening method combined with the stress shot peening can be selected to improve the fatigue strength.
If the S-type spring is placed at a higher temperature for stress peening, a higher residual stress can also be detected in the test. The object of this test is the surface of the wire where the outer diameter of the middle of the spring is the largest. When the temperature reached 180%, no significant difference was found in the results, but when the temperature was raised to 240%, the higher residual stress value required to increase the fatigue strength was measured.
Conclusion Automotive spiral springs will directly affect the driving feel and the comfort of the rear seat passengers. As the vehicle moves, the spring will continuously reciprocate, so its fatigue strength will become a key assessment indicator. (1) After stress shot peening, the fatigue strength will be greatly improved. (2) When the temperature is high enough, the thermal spray will also effectively enhance the performance of the shot peening, helping to improve the fatigue strength of the part. (3) For components with high design stress, thermal spray and stress peening can be combined, and the problem of uneven coverage in stress peening can be effectively improved to further improve the fatigue strength of the component.
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