Designing Constant Force Springs

Constant force springs are mechanical devices that provide a constant force throughout their deflection. They are used in a wide range of industries, including automotive, aerospace, medical, and consumer goods. These springs are designed to provide linear force, and their design is critical to their functionality. In this article, we will discuss the factors that go into designing constant force springs.

Material Selection

Material selection is an essential aspect of designing constant force springs. The material used in the spring must have the necessary strength and durability to withstand the forces applied to it. The most common materials used for these springs include stainless steel, high-carbon steel, and titanium. Stainless steel is an excellent choice for most applications due to its high strength, corrosion resistance, and ease of fabrication.

Wire Diameter

The wire diameter of a constant force spring is another critical factor in its design. The wire diameter determines the amount of force the spring can produce and its deflection characteristics. The larger the wire diameter, the stronger the spring, and the less deflection it will experience. Similarly, increasing the wire diameter will also increase the spring’s size, weight, and cost.

Number of Coils

The number of coils in a constant force spring affects its deflection and the amount of force it produces. The number of coils needed for a spring depends on its required deflection and the desired force produced. A higher number of coils will result in a smaller spring size, but it will also have less deflection and force. A lower number of coils will result in a larger spring size, but it will also have more deflection and force.

Spring Length

The spring’s length is another critical factor in its design. The length of the spring affects its deflection and the amount of force it produces. A longer spring will have more deflection and produce more force, while a shorter spring will have less deflection and produce less force.

Spring Rate

The spring rate is the amount of force required to deflect the spring a unit distance. It is determined by dividing the force produced by the spring by its deflection. The spring rate is essential in determining the spring’s overall performance and is typically specified by the manufacturer.

Coil Pitch

The coil pitch is the distance between each coil in the spring. It affects the spring’s deflection characteristics. A tighter coil pitch will provide more deflection, while a wider coil pitch will produce less deflection. The coil pitch is typically specified by the manufacturer and should be chosen based on the desired deflection of the spring.

Conclusion

Designing constant force springs requires careful consideration of several factors, including material selection, wire diameter, number of coils, spring length, spring rate, and coil pitch. These factors all affect the spring’s performance and its ability to provide a constant force throughout its deflection. By properly considering these factors, engineers can design constant force springs that meet the requirements of their applications.