Compression springs are one of the most widely used mechanical components in various industries. They are designed to withstand compressive forces and provide resistance when compressed. A constant force compression spring is a type of compression spring that is specially designed to maintain a constant force over a wide range of deflection. In this article, we will discuss the design and analysis of a constant force compression spring.
Design
The design of a constant force compression spring starts with determining the required force and deflection range. The spring rate, which is the force required to compress the spring by a unit distance, is calculated by dividing the required force by the deflection range. The spring rate is expressed in units of force per unit length, such as pounds per inch (lb/in) or Newtons per millimeter (N/mm).
The next step is to determine the wire diameter, mean diameter, and number of coils based on the spring rate and available space. The wire diameter is the diameter of the wire used to make the spring, while the mean diameter is the average diameter of the coils. The number of coils is the total number of turns in the spring. The formulas for calculating these parameters are:
Wire diameter = (8 * F * L) / (pi * G * d^3)
Mean diameter = d + (L / pi)
Number of coils = (L / d) + 2
Where F is the required force, L is the deflection range, G is the shear modulus of the material, d is the wire diameter, and pi is the mathematical constant pi (3.14159).
The free length of the spring, which is the length of the spring when it is not compressed, is calculated by adding the deflection range to the solid length of the spring. The solid length is the length of the spring when it is fully compressed.
Analysis
After the spring is designed and manufactured, it needs to be tested to ensure that it meets the design requirements. The parameters that need to be tested include the force-deflection characteristic, free length, solid length, and spring rate.
The force-deflection characteristic is the relationship between the force applied to the spring and the corresponding deflection. This characteristic is measured by applying a force to the spring and measuring the deflection using a load cell and a displacement sensor. The free length and solid length are measured using a caliper. The spring rate is calculated by dividing the force by the deflection.
If the spring does not meet the design requirements, adjustments need to be made to the design or manufacturing process. For example, if the spring rate is too high, the wire diameter can be decreased or the number of coils can be increased.
Conclusion
Constant force compression springs are important mechanical components that are used in various industries. They are designed to maintain a constant force over a wide range of deflection and require careful design and analysis. By following the design and analysis procedures outlined in this article, engineers can ensure that the constant force compression spring they design and manufacture meets the requirements and functions correctly.
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