Spring Design FAQs

What features need to be toleranced when developing a spring design?

While each application has its own unique needs, there are some general guidelines to follow. The various wire specifications typically include diameter tolerances. So, citing a wire type and specification along with a wire diameter tolerance can be either conflicting or redundant. The application may place some dimensional constraints (i.e. minimum or maximum free length, maximum solid height, maximum OD or minimum ID, etc.). Those significant to your application should be cited on the spring requirements. Spring force output at reference heights are often significant and can be toleranced. In general, spring rate and total coil count are referenced. Flexibility on these items provides the spring maker sufficient freedom to assure that the true key characteristics meet your needs.

What are acceptable design stress levels?

Appropriate stress limits on springs and other components depend on a number of factors. These include material type, operating environment, and whether the loading condition is static or cyclic. When you contact us with your application needs, our engineers are prepared to answer any questions you might have regarding spring design, material selection, or application. Let us help you develop the right spring for your product.

How do you analyze complex spring geometries?

In addition to handbook calculations, MW Components has developed a variety of proprietary models that enable us to accurately model complex geometries. These include variable wire diameter, spring diameter, and pitch.

Should spring ends be ground or unground?

The purpose of grinding spring ends is to distribute the force applied at the spring end across the largest possible surface area. This is typically done when the spring will be compressed between flat-end plates.

However, end grinding is one of the most expensive processes in spring manufacturing. If your assembly’s production volume is high enough, it may be more cost-effective to design components that mate with unground spring ends. This way, the load is still distributed across a large surface area without the high cost of end grinding. This is typically the case in automotive McPherson strut assemblies. Another case where grinding might be avoided is large index springs, particularly with very small wire diameter.

What is the difference between "cold winding" and "hot winding" and when is one chosen over the other?

The most common is cold winding. In this case, wire that has already been heat-treated or worked to its final strength level is coiled into a spring. Because the material is already at peak strength, large wire diameters and small indexes are difficult to achieve. The typical maximum wire diameter for this process is 0.625 inches.

The next process is less common, but still falls under cold winding. In this case, wire is coiled in a soft state and then heat-treated to its final strength condition after coiling. For a given piece of coiling equipment, larger wire diameter and/or smaller indexes can be coiled with this method. This process is used for wire sizes up to .875″ in diameter.

The final process is hot winding. In this case, bars are heated to approximately 1700°F and coiled. Usually, the red-hot spring is quenched in oil and tempered to complete the heat treatment. Coiling at such a high temperature enables spring manufacturers to work with far larger bar sizes than could be coiled at room temperature. This process is generally used for bars up to 1.75″ in diameter.

Which process to use is determined first by the size of wire that must be coiled. Once that is determined, the type of material, final wire strength level, and spring index will drive manufacturing toward a process that is most compatible with the available equipment.

How is square wire used to increase the force from torsion springs?

Often customers have a spring application that requires a lot of force in a little space — usually too little space. MW Components believes springs should be designed to fit your product and application, and not the other way around. One way of maximizing this force is to use square wire.

Where should load points be specified in a compression spring?

Load points should be specified between 15% and 85% of the possible deflection in a compression spring. Load points outside of these ranges are typically inconsistent with expected/calculated values. The values are not linear outside of this range and are often unpredictable. The illustration below represents calculated vs. measured values for a load specified outside of the 85% range. The values are as expected until we exceed 85% of the deflection.