In recent years, with the development of the mold industry, the number and variety of mold springs, especially special-shaped cross-section steel wire mold springs, are increasing. The special-shaped cross-section die spring has the characteristics of high rigidity, long life, and small size. But the development of its design theory is relatively slow. At present, in addition to the more mature design methods of square section strong springs, the design methods of other section strong springs are basically based on the specific section through the test, find the correction coefficient to obtain the empirical design formula of the specific section, now the characteristics of this type of spring Give an introduction to the design problem.
This problem is a problem that people who use this kind of spring care about and must figure out. The following is a comparison between a square section and a round section coil spring.
In the same space, the load-bearing capacity of the square section wire spring is 43-48% higher than that of the round section spring. Obviously, the rectangular spring should be more than 50%.
From the analysis that excessive use stress is the main reason for spring damage, under the same conditions, the service life of the special-shaped section wire spring is 13-14% longer than that of the round section wire spring.
The special-shaped cross-section wire spring can produce a large amount of deformation.
Special-shaped wire springs are heavy.
The linearity is better than that of the circular section spring, that is, the stiffness tends to be more constant. Especially springs with long sides wound parallel to the axis.
The scope of application is limited: It can be seen from the analysis that if the special-shaped cross-section material spring cannot fully utilize its advantages, it will not produce economic benefits. Under what circumstances should it be used?
(1) The design load cannot be achieved with circular cross-section materials.
(2) Replace the circular cross-section compound spring.
(3) When the required deformation cannot be achieved with the round material spring.
(4) Where the spring installation space is small.
(5) Places requiring strict spring characteristics.
2. Design principles of mold spring
1. The selection of allowable stress [τ] of the spring material should be mainly considered to ensure the fatigue life of the spring. The dynamic life of springs is generally divided into three categories:
Class I: The number of alternating loads is 106;
Class Ⅱ: The number of alternating loads is 103-105;
Class Ⅲ: The number of alternating loads is less than 103;
2. The material width-to-thickness ratio (a/b) should not be too large, and the winding of the spring should not be too small.
3. When designing non-rectangular shaped cross-section springs, it is necessary to derive and draw curves or calculation formulas in different rotation ratios, different width to thickness ratios, deformation correction coefficients (τ) and shear stress correction coefficients (β).
4. According to the given conditions and constraints, choose a design method that is simple to calculate and select reasonable parameters.
Three remaining problems
1. The low standardization of mold design limits the development speed of standardized mold springs.
2. The degree of standardization of mold springs is low. At present, apart from the QC7111-7113 standard formulated by our institute for the automotive industry, there is no official national standard or industry standard in China. The lack of standard selection by mold designers is an urgent problem to be solved.
3. The design theory is not perfect. At present, the rectangular cross-section spiral spring is more mature, but the selection of its tolerance is still inconclusive. The spiral springs with special-shaped cross-sections are all based on rectangular cross-sections, which have been modified by experiments.
4. There are no designated factories producing special-shaped cross-section materials, especially oil-quenched and tempered steel wire suppliers that do not have such materials. However, the materials reformed by the spring manufacturer itself have unstable quality and high cost, which affects the popularization and application of this type of spring.
5. There is no special coil spring equipment for producing such springs. The spiral spring winding ratio for molds is generally less than 4, while the domestic spring coiling machine is suitable for springs with a winding ratio above 4.