Wave Spring vs. Coil Spring - Smalley

1. Can a wave spring replace a coil spring?

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   Wave springs can provide similar forces as a traditional coil spring at down to about half the height of a coil spring. Due to space and weight savings, a wave spring cannot be directly substituted for a coil spring in your existing application without reducing the size of the spring cavity. Wave springs must be designed into your application in order to realize all of the benefits. 

2. Does a wave spring provide the same function as a coil spring?

   Yes, a wave spring provides the same function as a coil spring. Both wave springs and coil springs apply force axially when compressed. A wave spring starts out at free height, which is the height without any load applied. The wave spring is then compressed until its work height, where a specified load is output. This is the same as a coil spring follows.

   The difference between a wave spring and a coil spring lies in the way they store and release energy. Wave springs rely on bending, similar to a simple beam, whereas coil springs are torsional. As a load is applied, the waves on the wave spring begin to flatten to provide an upward force, allowing for complete axial load transmission. Coil springs, on the other hand, twist as they compress, so not all the force is necessarily aligned with the axis.

3. Can a wave spring be made with the same or higher spring rate, compared to a helical coil spring? 

   In most cases, the spring rate can be matched or increased with various modifications such as the number of waves, material thickness, or number of turns. Please note that we tolerance load at a working height, unlike a coil spring that tolerances the spring rate.

4. Are wave springs cheaper than coil springs?

   Wave springs can save you money when considering the whole assembly. Crest-to-Crest wave springs allow for smaller assemblies with a reduced spring height, which results in a smaller spring cavity. This translates into considerable cost-savings for the surrounding assembly, resulting in a net saving that far outweighs the cost variance between the wave spring and coil spring.

   Bottom line? Wave springs may potentially have a higher piece price, but overall cost savings may be seen when designing a wave spring into your application. 

5. So you're telling me a wave spring can make my assemblies smaller and potentially save me money, why wouldn't I use this for everything?

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   Wave springs are the ideal compression spring to fit tight axial and radial spaces; however, they are not the ideal solution for applications with large travel and/or accompanied by a high load requirement. Let's take a pogo stick for example. A spring in a pogo stick must have a large travel and the load output to rebound the weight of a human, making it better suited for a traditional coil spring.

   Other applications where an alternative spring should be used is in cases where extension or torsion is required. Wave springs are designed for compression only.

6. I’m using a coil compression spring in my assembly and am ready to switch to a wave spring design to help with space savings. What do I need to know to find the wave spring best suited for my application?

   Since a wave spring is typically not a direct replacement for a coil spring, a good place to start is to provide us with the parameters in which the wave spring will be working. Please fill out our Spring Application Checklist and a Smalley Engineer will contact you shortly to discuss your application.

   Key Points​

Wave springs are versatile in their application

Customers of BAUMANN can choose from a wide range of different types of wave springs, for example for door opening systems in cars, valves and switches, as well as administering medication. “We support our customers in their product strategies with our application-specific expertise,” reports Martin Oschwald, Head of Research and Development at BAUMANN. “Our solutions for customers are precisely tailored to the design and purpose of the device in question. For example, our products enable defined compression and rebound in valve systems or ensure braking in powered liftgate systems.” Traditionally, customer requests were defined by specific geometric dimensions and usually an operating point on the force-displacement curve. Recently, however, performance requirements have increased, and designs have become more specific. “For us, this leads to higher challenges in the design of the springs and, moreover, we want to be prepared for future requirements,” explains Martin Oschwald. “We still see a lot of potential in the market for wave springs. But for reliable offers, numerous work steps are often still necessary. In addition, the cost pressure is considerable, so we want to tap into further optimization potential through digitization. Our goal is to reduce the lead time from customer inquiry to binding offer from weeks to days.”

Complex creation of prototypes

Previously, the design was carried out using a simple model approach, on the basis of which an initial offer was prepared with technical reservations. If the customer ordered a prototype, spring specialists at BAUMANN started manufacturing the first prototypes. Their design was based on an Excel-based layout environment, in which many empirical values were stored. With this method of working, an iterative approach was part of daily practice. Only when an acceptable solution was found in this way could sample production start to verify manufacturability. “Despite increasing requirements, the complexity in the design and production of wave springs should remain manageable for us,” explains Martin Oschwald. “That's why we have started a project together with Eastern Switzerland University of Applied Sciences to optimize our processes. The project was supported by Innosuisse and took two years. The aim of this project was to make our processes faster, more standardized and more digital.”

Joint project with Eastern Switzerland University of Applied Sciences

Together with the Institute for the Development of Mechatronic Systems (EMS) in Buchs, the wave spring as well as its forming process in production were analyzed and modeled in the Ansys simulation environment. The simulation of static-mechanical and dynamic systems is one of the core competences of the EMS Institute. Through such industry-oriented research questions, innovative technologies and acquired knowledge are transferred from the university of applied sciences to the local industry. Important questions during the project included which spring parameters have which influence for the design? How does the spring behave on the processing machine? How can digital and real processes be aligned to obtain reproducible settings for manufacturing? The new processes should be designed in such a way that employees can focus on the value-adding activities in the future. At the same time, the added value for the customer should be increased.

The optimizer keeps an eye on various targets

“One of the biggest challenges for us is finding an optimal solution for the various needs of the customer while not losing sight of our interests as a manufacturer,” explains Martin Oschwald. “Until now, we have followed a manual, iterative approach, which often takes a long time and does not always lead directly to the desired goal. That's why we have looked into new methods, including the Metamodel of Optimal Prognosis, which is included in Ansys optiSLang.” This allows product behavior to be improved in a targeted, fast and cost-efficient manner through variant studies. Sensitivity analyses enable the identification of the relevant parameters. Using response surfaces, the correlations between the design variations and the varying product properties can be determined and clarified in seconds instead of days. It is also possible to consider multiple optimization objectives simultaneously, using evolutionary algorithms to search the result space. In this way, solutions for wave springs can be found that achieve the values that BAUMANN was aiming for, both in terms of functionality and manufacturing costs. So far, this method has only been used in a few areas at BAUMANN, albeit with a high success rate. Therefore, its utilization will be expanded step by step.

Digital models for production processes

“The processes for production, specifically the forming operations in the manufacture of the springs, are also to be improved with simulation support. Here, the question of the required input parameters for the desired wave springs is the focus of interest. The spring diameter to be produced is calculated using simulations, with the position of the forming tools playing a decisive role, so that the position tolerance is kept as small as possible. Simulations are also used to analyze the generation of the desired wave in order to be able to further improve the excitation by machine parameters. Spring specialists are interested in which parameters have which influence on the expression of the wave geometry of the spring. So far, these simulations have mainly been carried out in the 2D range and provide a better understanding of the manufacturing processes. However, the long-term goal is to gain more insight into which specific input values are required to obtain the desired characteristics of the respective wave spring.

Continuous workflow developed

The goals achieved so far within the Innosuisse project, which BAUMANN has tackled together with OST, are very promising. The head of research and development at BAUMANN points to the general opportunities that have arisen as a result of the project: “It gave us broader access to the latest technologies and allowed us to test methods that were previously unknown to us. The innovative approaches from the university sector helped us to implement things that we would not have been able to do in our normal day-to-day work. The most important prerequisites for success were the time needed to deal intensively with the topic as well as the openness to change and innovation at all levels in order to jointly develop a company vision for integrating the new technologies.” With this in mind, the processes for the production of wave springs were comprehensively analyzed and the potential for redesign was identified. This required developing, building and implementing new types of workflows. Through standardization, optimization and digitalization, the spring specialists achieved greater process reliability and were able to accelerate the workflows. In addition, the ability to collaborate with external partners and universities was also improved. “The most important thing for us was to develop technologies that have the potential to significantly shorten the offer process, and that’s what we’ve achieved,” Martin Oschwald explains. “If we assume only one day of savings per offer, that already amounts to a time saving of 100 days for 100 offers per year. Furthermore, with the parameter analyses that we carry out with Ansys optiSLang, we are also able to keep the different optimization targets directly in view. Another important aspect of the continuous development is that the methodology and technologies we are now successfully using for the wave springs can be transferred to other types of springs. This means that in the future we will increasingly be able to do away with lengthy and inefficient design processes and focus on achieving our goals in a direct way.”