How to create spring specifications for manufacturing

Developing accurate spring specifications is essential to ensure that a spring performs reliably within its intended application. A well-prepared spring specification guide will typically define the core performance requirements, including load, deflection, and fatigue life, alongside dimensional and material details. These parameters provide manufacturers with the technical blueprint needed to achieve both functionality and cost efficiency.

When creating specifications for spring manufacture, engineers usually begin with the application environment. Factors such as operating temperature, corrosive exposure, required cycle life and available installation space all influence material selection and coil geometry. For instance, aerospace springs may require high-performance alloys such as Inconel to withstand extreme heat, while medical springs often demand biocompatible stainless steels to ensure regulatory compliance.

A typical spring specification will include:

Dimensional data — wire diameter, coil diameter, number of active coils, free length, and end configuration.

Performance requirements — spring rate, maximum load, working deflection, and expected fatigue cycles.

Material and finish — choice of alloy, protective coating, or passivation treatment to ensure durability.

Tolerance and testing standards — defined according to ISO or sector-specific standards such as AS9100 or NADCAP.

By developing a clear spring specification guide at the design stage, procurement teams and engineers can avoid costly redesigns, accelerate prototyping, and ensure a smoother transition into volume production. William Hughes’ design engineers regularly collaborate with customers during this process, using simultaneous engineering and early prototyping to refine specifications before committing to high-volume manufacture.

 

Popular Spring Types

The most popular spring types are compression, tension and torsion. Depending on the characteristics required, these can be manufactured in a wide range of materials including stainless steel, brass, phosphor bronze beryllium copper and nickel-chrome alloys.

Compression springs are usually round but can also be made as conical, concave (hourglass) and convex (barrel). Their many applications include automotive, aerospace, electronic and electrical equipment. To engineer a compression spring, basic dimensional characteristics are needed as well as the spring rate, which is the load required to give a stated deflection.

Tension or extension springs work in the opposite way to compression springs and are usually used to provide a resistance to a pulling force. Typical applications include return springs on automobile carburettors and brakes, trampolines, toys, medical equipment and office machinery.

The third type of spring, torsion, is designed to exert a torque or rotary force. These are typically used for hinges and lever return applications. Examples include clipboards, swing-down vehicle tailgates and garage doors. In addition to the dimensions, the designer will also need to know the torque required for a given arm deflection.

Quality and consistency is important for users of all types of spring and William Hughes employs the latest optical and computer based measurement systems to ensure specifications are being met. The company’s quality systems have been accredited to ISO 9001:2008, ISO/TS 16949:2009 and AS 9100 to ensure consistency and accuracy of supply.

 

Torsion spring application example

Double torsion springs can sometimes be better than single ones as a manufacturer of car interior parts discovered when specifying springs for the door handles of a popular small car. The spring needed to meet the exacting specification of the car manufacturer, whilst ensuring that it could be manufactured using CNC machinery to minimise cost.

The spring is used inside the car to return the handle to its normal position. By making the spring in two fully automated stages, the difficult central section is easily formed to produce a spring that is compact, cost effective and which encompasses the right performance characteristics and durability. The final process is to finish and protect the springs by using an organic and environmentally-friendly anti-corrosion paint containing zinc flake.

 

Meeting the special needs of the Aerospace Industry

Springs for the aerospace industry are often used in critical applications such as oxygen systems, access hatches, and the solenoid valves used to control the hydraulic and cabin pressure systems.

To meet the demanding specifications for high temperature performance, springs can be manufactured in exotic materials such as Nimonic, Inconel and Ni-span. These expensive materials are more difficult to work with than conventional materials and require special machinery and expertise to ensure high accuracy and minimum wastage.

Suppliers need to be accredited to AS9100, now widely adopted as the quality management system for the industry. In addition, the NADCAP (National Aerospace and Defense Contractors Accreditation Program) is an industry-managed approach to conformity assessment of 'special processes'. As a measure of the difficulty of achieving NADCAP accreditation, William Hughes is one of only a handful of UK companies offering this standard for its heat treatment, room temperature tensile testing and passivation plant.

So if you are struggling to source a spring, William Hughes has the knowledge and experience to design and engineer a cost effective solution - taking the stress out of spring specification.