Ask the Engineer

Spring Design in Product Development

By George E. Fournier
November 7, 2012


• Categories: 04-Product Design & Development, Ask the Engineer

Product development sees multiple iterations before the final product is introduced to the market place. With computer aided design and manufacturing, the time from initial concept, to prototype, to final product release to market has been reduced drastically.

Today, companies work with their vendors/suppliers in the development of the component specifications from initial concept to final tooling and production of the product. This is a valuable tool that uses the expertise and knowledge of the vendor/supplier for the most efficient manufacturing and robust product for the consumer in the marketplace.

Acme Monaco worked with a medical company in developing and designing two compression springs as part of an assembly to promote a near normal movement to the spine in lieu of the old method which fused the spine in the area of the spinal disc. This old method limits the normal body movements as far as the amount of normal spinal bending. After much iteration the final product specifications were completed and approved, clinical trials were performed, completed and approved by FDA.

The spring, if required in the product, is probably the least expensive component of the assembly. However, if it does not function as intended or fails, it can become a warranty issue which can be quite expensive as far as repair, loss of sales and product reputation. In designing the spring component, the following must be considered:

• Function (Spring Type);
• Material;
• Required forces to actuate;
• Safe stress levels;
• Cycle life (product life); and
• Efficient working area and atmosphere conditions.

This design information is through industry standards such as SAE HS‐795, DIN 2095 (Compression Springs), DIN 2097 (Extension Springs) and DIN 2194 (Torsion Springs), ISO 11070 (Medical). Another valuable source of information can be found at The Spring Manufacturers Institute, Inc. (SMI)

In many cases, engineers look only at the force side of the design and do not consider the stress side of the force values and only estimate the amount of room needed. They proceed to finalize the product design, build the necessary tooling and then design the spring based on the estimated working area only to discover the spring does not function or fails in the initial prototype assembly. This causes unnecessary delays and costs. To avoid this, the spring manufacturer should be contacted to aid in the initial and final design phases of the project to insure a smooth development to the production path.