Spring strengthening process
Suspension spring reinforcement
Thanks to the high stress lightweight design, the weight of suspension spring has been greatly reduced in recent years. It is very common for the stress of suspension spring of new models to be > 1000MPa. The service of spring under such high stress has exceeded the limit that the material can bear, so it must be supplemented by other strengthening means (such as shot blasting).
The main engine manufacturer adopts very strict test standards for automobile suspension springs. The longest test cycle is up to 70 days (10 weeks). It should be that the suspension springs working under high stress conditions will produce corrosion fatigue failure once the surface is subjected to stress corrosion. If the broken spring port pierces the tire, it may cause major safety and personal accidents.
Shot blasting is the most effective strengthening means of suspension spring. After proper shot blasting, the fatigue life of high stress spring can be increased by more than 5 times. At present, steel wire shot cutting is mostly used for shot blasting of suspension spring, and multiple shot blasting (different shot diameters) is widely used in technology. The strength and depth of spring surface compressive stress are important indexes to measure the effect of shot peening. The surface stress of good shot peening shall be at least – 600MPa, up to – 800MPa at 50um from the surface, and the surface compressive stress of stress shot peening spring shall be more than – 800MPa, up to – 1200Mpa at 50um from the surface
Leaf spring strengthening
A continuous through shot blasting strengthening equipment can be used to strengthen the leaf spring one by one, so that the geometric concave surface of the leaf spring can be exposed to the high-speed shot flow. The typical model includes a throwing head for throwing the top of the leaf spring, a throwing head is installed on the side, and the left and right sides of the leaf spring are sprayed at the same time.
The passing speed of this standard leaf spring strengthening equipment is 10 ft / min. if higher production speed is required, the number of throwing heads can be increased and the motor frequency can be adjusted. Under working conditions, the leaf spring will be repeatedly affected by unidirectional bending stress, so it is sometimes strengthened by stress. In the strengthening process, simulate the situation that the leaf spring will be “stress strengthened” in the later use process, and let it apply a “static stress” in the direction of bearing the load, and shot peen it at the same time. After strengthening, release the applied static stress. Experiments show that stress strengthening can further prolong the service life of leaf spring than conventional strengthening.
Round spring strengthening
Because of its spiral geometry, the strengthening of circular spring is more difficult than that of flat surface leaf spring. In addition, the strengthening effect of the cross section of the round spring must be strictly evaluated, so as to fully understand the resistance of the round spring to fatigue fracture.
The round springs are individually sent to the shot blasting room through a continuous conveying chain system. A group of parallel roller tables are installed in the shot blasting room. While strengthening, the roller table keeps rolling, driving the round spring to move forward while rotating. In this way, the high-speed shot flow can pass through each ring of the round spring and hit the metal surface of the inner ring, which is exactly the place where the stress of the round spring is most concentrated.
For applications requiring high production capacity, a strengthening equipment that can spray two round springs at the same time can be selected. The latest R & D result is to combine multiple nozzles on the basis of the original shot blasting strengthening equipment for more targeted and fire concentrated shot blasting in specific areas of the round spring (stress concentration to please).
