Characteristics of die spring
In recent years, with the development of die industry, the number and variety of die springs, especially special-shaped steel wire die springs, are increasing. Special section die spring has the characteristics of large stiffness, long service life and small volume. However, the development of its design theory is relatively slow.
At present, except that the design method of square section strong spring is relatively mature, the design method of other section strong spring is basically to find out the correction coefficient and obtain the empirical design formula of specific section according to the test of specific section. Now, a brief introduction is made to the characteristics and design problems of this kind of spring.
This problem is of great concern to those who use this spring and must be clarified. The following is a comparison between square section and circular section coil springs.
In the same space, the bearing capacity of square section steel wire spring is 43-48% higher than that of circular section spring. Obviously, the rectangular spring is more than 50%.
From the analysis that excessive service stress is the main cause of spring failure, under the same conditions, the service life of special-shaped section steel wire spring is 13-14% higher than that of circular section steel wire spring.
The steel wire spring with special-shaped section can produce large deformation.
The weight of special-shaped steel wire spring is large.
The linearity is better than that of circular section spring, that is, the stiffness tends to be constant. In particular, the long side is parallel to the axis of the spring.
The application scope is limited to a certain extent: it can be seen from the analysis that if the special-shaped section material spring can not make full use of its advantages, it will not produce economic benefits. Under what circumstances can it be used well?
(1) The design load cannot be reached with circular section material.
(2) Replace the circular section composite spring.
(3) When the required deformation can not be achieved with a round material spring.
(4) Where the spring installation space is small.
(5) Where spring characteristics are strictly required.
Design principle of die spring
1. Allowable stress of spring material[ τ] The selection of shall be mainly considered to ensure the fatigue life of the spring. The dynamic life of spring is generally divided into three categories:
Class I: the number of times of bearing alternating load is 106;
Class II: the number of times of bearing alternating load is 103-105;
Class III: the number of times of bearing alternating load is less than 103;
2. The width thickness ratio (A / b) of the material should not be too large, and the winding of the spring should not be too small.
3. When designing non rectangular special-shaped section spring, it must be deduced and drawn in different rotation ratio, different width thickness ratio and deformation correction coefficient（ τ) And shear stress correction factor（ β) Curve or calculation formula.
4. The design method with simple calculation and reasonable parameter selection shall be selected according to the given conditions and limiting conditions.
III. remaining issues
1. The low degree of standardization of die design limits the development speed of standardized die spring.
2. The standardization degree of die spring is low. At present, there is no officially used national standard or industry standard in China except qc7111-7113 standard formulated by our Institute for the automotive industry. The problem that die designers have no standard to choose is an urgent problem to be solved.
3. The design theory is not perfect. At present, the more mature is the rectangular section coil spring, but there is no final conclusion on its tolerance selection. The coil springs with special-shaped section are based on rectangular section and corrected by test.
4. There is no designated factory for the production of special-shaped section materials, especially the supplier of oil quenched and tempered steel wire without such materials. The material reformed by the spring manufacturer has unstable quality and high cost, which affects the popularization and application of this kind of spring.
5. There is no special coil spring equipment for producing such springs. The winding ratio of coil spring for die is generally less than 4, while domestic spring coiling machines are suitable for winding springs with a winding ratio of more than 4.