How Are Springs Made? Compression, Extension & Torsion Spring Manufacturing
Have you ever wondered how springs are made? Dozens of mechanical springs are employed in countless industrial applications, and it’s essential to understand how they are fabricated to fully appreciate their versatility and learn how to employ them within machine applications.
In short, a mechanical spring is a rigid wire material drawn into a coil shape designed to deform elastically under a mechanical load. The spring is a simple yet clever design that can store mechanical energy in small and large engineered applications.
Indeed, springs are used everywhere, from mattresses to clothespins, and their usefulness is impossible to understate. For example, you can find compression springs in many automotive assemblies, such as suspension systems. Furthermore, stainless steel springs are commonly used in medical devices such as surgical instrumentation, which require the spring to be chemically inert with surrounding environments and materials. Springs are also present in numerous electronic hardware assemblies, such as switches, relays, and motors.
How Are Springs Made? Understanding the Spring Manufacturing Process
Spring fabrication can be understood by looking at the three primary process steps involved. Modern manufacturing equipment makes the manufacturing process seamless once the tooling setup is complete to the exact dimensional requirements.
Spring Winding
The manufacturing process employed to wind the wire into the helical coil configuration is called the spring winding process.
In many instances, spring winding can be efficiently performed by traditional mechanical machine components such as gears and cams. The machines quickly perform spring winding operations by pulling the spring wire into the machine and straightening it from a wound coil into a straight wire configuration within the machine. Next, the machine forms the straight wire into a helical shape using one of the following machine processes.
When additional error-proofing and automated measurement of all critical spring dimensions during manufacture are needed, a CNC machine can wind springs by employing the same process.
Coiling: A coiling machine pulls the straight wire into rollers that draw the spring wire into tooling called guide sets, which gently shape the wire into a helical shape as it is pulled through the machine. Coiling can be used to make compression, extension, and torsion springs.
Forming: A forming machine contains multiple tooling slides configured in different axes and configurations. These tooling pieces form the wire into a helical coil using a series of forming operations that cold-work the wire in abrupt tool motions. Forming machines are commonly used to fabricate springs with unique end types, such as double torsion springs or extension springs with loop end configurations.
Heat Treating and Stress Relief
Before detailing the stress relief operations, it’s important to note that the coiling and winding processes detailed above are cold-forming (meaning no heat is applied) processes that introduce stress into the part because of large deformations performed at room temperature.
After forming, the spring undergoes stress relief at an elevated temperature, which is designed to relieve the stresses imparted during the winding process. Stress relief is performed on most springs fabricated from music wire and 302/316 stainless steel. However, other materials, such as 17-7 stainless steel springs, undergo a precipitation hardening (commonly called “aging”) heat treatment.
In general, for both aging and stress relief heat treatment, the springs are heated to an elevated temperature for a prescribed timeframe. Heat treatment is performed by a large conveyor belt that moves large quantities of springs into a large furnace. The conveyor speed is configured to allow the springs to hold the temperature for the specified time frame. Large stationary ovens with higher heating temperature capabilities are also commonly used to batch heat treat springs.
Secondary Operations and Finishing
Finally, depending on the spring type and geometry, additional operations are performed after heat treatment. These operations include bending, trimming, forming, tumbling, and buffing. Such additional secondary surface operations can significantly increase the spring's cost.
Grinding: The compression spring ends may be ground to allow them to stand flat and straight in the application. Grinding usually produces flat seats around 270° of the end coil circumference. However, customers can specify the exact amount of ground needed. These seats are nominally perpendicular to the spring axis and parallel to each other. In some cases, the thickness of the wire after the grind and the surface roughness of the grind are specified.
Surface Finishing Operations: Additional surface protection is sometimes desired to protect the spring in corrosive environments or high-load, high-vibration applications. Commonly specified secondary operations include shot peening, plating, and powder coating. Another important surface treatment worth mentioning is passivation, which is a non-electrolytic process used to create a protective oxide layer on the spring surface.
Presetting: Presetting is an important secondary operation that involves compressing the spring to its solid height or a given load point usually three times in succession to remove “the set” from the spring. This operation is performed when the spring is overstressed at its solid height or a given load point. This introduces “preset” stress into the spring, which increases its fatigue life and allowable stress limit. To learn more about the pre-set process please contact our experienced engineers.
Precision manufacturing is paramount in all these operations, from winding to final surface finishing, no matter the spring type.
As such, Century Spring procures stock spring wire, which is procured to the most rigorous international standards, such as the American Society for Testing Materials (ASTM) and Aerospace Material Specifications (AMS).
Types of Springs and Their Manufacturing Differences
How Are Compression Springs Made?
Compression springs are designed to resist compressive forces. When the helical coils are compressed, they store compressive energy mechanically, and the coils do not touch each other when unloaded. Integrated springs in household items such as mattresses are excellent examples of how compression springs evenly absorb the compressive loading of a sleeping person.
As such, compression springs are usually manufactured using either a mechanical coiling machine or an automated CNC coiling machine. They typically undergo stress relief or heat treatment depending on the material of the spring. Then, after heat treatment, the ends of compression springs are typically ground flat so they can stand freely in all applications. Additionally, depending on the spring geometry, they can undergo pre-setting and/or shot peening. After this, additional surface cleaning or coating operations can be applied.
Check out our compression spring collection to see all available in-stock springs for same-day shipping.
How Are Torsion Springs Made?
Torsion Springs are engineered to resist twisting forces. They are tightly wound wire coils that elastically unwind as they absorb torsional loads. The torsion springs that hold recessed ceiling lighting within their fixtures are excellent examples of how torsion springs are used in practice. The spring legs hold the fixture in place by resisting torsional forces placed on the spring by the legs.
Torsion springs are most commonly fabricated from a CNC forming machine, which allows for quickly fabricating many different torsion spring end configurations via the forming tools.
Torsion springs also undergo heat treatment or stress relief via a furnace conveyor or ovens to relieve high stresses incurred during forming. After this, depending on the material and the application, additional surface treatments and coatings can be applied to increase corrosion resistance or better performance.
With a better understanding of the spring manufacturing process, you are ready to purchase torsion springs today!
How Are Extension Springs Made?
Extension Springs are designed to resist tension forces. They are similar to compression springs, except their coils are wound tight and designed to be extended during operation. As the coils separate, the spring absorbs mechanical energy. Extension springs found in consumer products such as trampolines illustrate this mechanical action extremely well.
Extension springs are most commonly fabricated from either a coiling or forming machine. Wire-forming machines are typically needed to efficiently manufacture the ends of extension springs. For example, a forming machine can quickly create loop and hook end configurations at the beginning and end of the coiling operation.
Extension springs also typically undergo heat treatment or stress relief, depending on the material, by means of a furnace conveyor or oven. After heat treatment, additional surface treatments are applied if needed.
When you are ready to move on to buying extension springs, Century Spring has thousands of extension springs available for immediate shipping.
Materials Used in Spring Manufacturing
A few key types of spring materials are worth noting as they are the most commonly specified materials for spring manufacture.
Steel Springs
High-carbon steel springs are an economical choice for applications with a wide range of loading requirements.
Stainless steel springs are commonly found in machine applications and require corrosion resistance.
Specialty Alloy Springs
Nickel-based alloy spring materials are used in the most demanding mechanical environments. They are high-strength and heat resistant.
Copper spring steel is specified as a spring material if an application requires the spring to possess unique properties such as electrical conductivity or non-magnetic. Copper springs also feature good corrosion and wear resistance.
The base material from which the spring is fabricated will impact the secondary processes performed on each spring. For example, carbon steel springs typically require additional surface coatings to add corrosion resistance; however, stainless steel springs do not require additional coatings. Additionally, specialty alloy spring materials may not need heat treatment because they already possess superior strength and fatigue properties.
Finally, you should note that non-metallic springs, such as urethane springs, are fabricated using entirely different manufacturing processes.
Century Spring’s Expertise in Custom Spring Solutions
Century Spring is a quality-first manufacturer specializing in stock and custom springs.
We are an ISO 9001 and AS9100 certified spring manufacturer employing the latest spring manufacturing technology to deliver custom spring designs in high product volumes as quickly as possible.
We are committed to always minimizing total development time on every project to pass the time savings on to you as reduced procurement lead times.
Our state-of-the-art manufacturing technologies feature CAD and CAM tools, allowing us to quickly create digital CAD designs and transfer them to our CNC spring coiling and forming machines for production runs. Our automated production machines and robotics can quickly perform complex multi-axis manufacturing techniques such as spring coiling and forming operations. These capabilities allow us to better serve industries that need large volumes of customized spring designs in accelerated development programs.
Don’t delay any longer; let us partner with you today to deliver your next custom spring solution! We also offer rapid turnaround, shipping, and delivery on over 40,000+ in-stock designs available to ship today! All springs are always made in the USA.