Stamped-bent parts used as springs are an essential part of many technical applications where an elastic restoring force is required. These parts are characterized by their ability to return to their original shape after deformation, storing and releasing mechanical energy in the process. Particularly in the automotive industry, medical technology and electronics, such springs often occur in the form of stamped-bent parts made of different materials. The selection of the right material and the right material thickness is decisive for the achievable spring force and the behavior of the spring under various loads.
Spring Properties of Stamped-Bent Parts
The spring property of a stamped-bent part is based on its ability to undergo elastic deformation and then return to its initial position as soon as the applied load is removed. This property is based on the elasticity of the material and is particularly influenced by the shaping and material choice of the stamped-bent parts. The spring travel, which describes the maximum deformation, as well as the material thickness are decisive for the applied spring force.
Frequently Used Materials
Stamped-bent parts that serve as springs are frequently made of spring steel strip, a specialized steel that is particularly suitable for spring applications due to its high elasticity and strength. The most frequently used materials are listed below:
- Spring steel strip 1.4310 (AISI 301): A high-alloy stainless steel known for its excellent corrosion resistance, which also offers good mechanical strength at higher temperatures. This steel is often used in applications where a high load is required with simultaneously good corrosion resistance.
- Spring steel strip 1.4301 (AISI 304): Another stainless steel known for its corrosion resistance and general strength. Compared to 1.4310, 1.4301 is somewhat less strong, but cheaper to produce and sufficient in many general applications.
- Spring steel strip C75S (unalloyed): An unalloyed carbon steel that offers higher strength than the stainless steels, but is less resistant to corrosion. This steel is particularly suitable for applications where high mechanical loads occur without special requirements for corrosion resistance.
- Copper alloy CuSn6 (F90): A copper alloy frequently used in electrical and electronic applications. It offers excellent electrical conductivity and corrosion resistance, but with somewhat lower strength compared to spring steel. The designation F90 indicates a tensile strength of generally 900 N/mm².
Material Thicknesses and Their Influence on the Spring Force
Material thicknesses of 0.2 mm to 1.0 mm are typical for stamped-bent parts used as springs. These material thicknesses make it possible to achieve a wide variety of spring forces tailored to the respective application. Thinner materials (e.g. 0.2 mm) offer a lower spring force, while thicker materials (e.g. 1.0 mm) enable a higher spring force.
Calculation of the Spring Force
The spring force of a stamped-bent part can be calculated using the spring stiffness (k) and the spring travel (x). The general formula (Hooke's law) for calculating the spring force is:
F = k · x
where:
- F is the spring force (in newtons),
- k is the spring stiffness (in N/mm), and
- x is the spring travel (in mm).
Spring Stiffness and Bending Stiffness
The spring stiffness k of a stamped-bent part can be calculated using the bending stiffness, which is derived from the second moment of area (I) of the cross-section and the modulus of elasticity (E) of the material. For a typical leaf spring clamped on one side (cantilever beam), the formula for calculating the spring stiffness is:
k = (3 · E · I) / L³
where:
- E is the modulus of elasticity of the material (in N/mm²),
- I is the second moment of area of the cross-section (in mm⁴),
- L is the free bending length of the part (in mm).
Second Moment of Area
The second moment of area I for a rectangular cross-section can be calculated with the following formula:
I = (b · h³) / 12
where:
- b is the width of the cross-section (in mm),
- h is the height of the cross-section or the material thickness in the bending direction (in mm).
Material Comparison at a Defined Spring Travel
At a defined spring travel, we can compare the spring force for the various materials using the calculations mentioned above. Assuming we have a spring travel of 2 mm and consider a stamped-bent part with a material thickness of 0.5 mm and a length of 50 mm:
- Spring steel strip 1.4310 has a modulus of elasticity of approximately 200,000 N/mm².
- Spring steel strip C75S has a modulus of elasticity of approximately 210,000 N/mm².
- Copper alloy CuSn6 (F90) has a modulus of elasticity of approximately 110,000 N/mm².
For the same geometry and the same spring travel, steel produces a higher spring force due to the higher modulus of elasticity. In the calculation of the spring force, copper alloys offer about half the value of steels, but score as excellent electrical conductors and with high corrosion resistance.
Conclusion
The choice of material and material thickness for stamped-bent parts used as springs is decisive for achieving the desired spring force and properties. Spring steel strip 1.4310 and 1.4301 are suitable for applications with increased requirements for corrosion resistance, while C75S offers higher mechanical strength but is less resistant to corrosion. Copper alloys such as CuSn6 are particularly suitable for applications where electrical properties and corrosion resistance are more important than maximum spring forces. The calculation of the spring force is carried out taking into account the material, the geometry of the stamped-bent part and the spring travel, with the modulus of elasticity and the second moment of area of the cross-section being the decisive factors for the spring stiffness.