Sourcing the right mechanical components for your medical device can have a dramatic effect on the quality of the final product. As you try to find the right balance between cost and quality, you will likely find yourself trying to decide between custom and stock springs. Although this may seem like a minute decision at first glance, it can often prove to be a differentiator between meeting customer expectations and not. So, evaluating the pros and cons of each choice is important.

How to Choose a Spring for a Medical Device
As you are sourcing your springs, it is helpful to have clear goals and expectations about what your chosen component will be able to provide. Many factors can influence your priorities. However, four elements are important for almost all medical equipment designers: quality, use, environment, and cost.

Quality: Unsurprisingly, finding a sufficiently high-quality part is essential. In medical devices, this is especially important because part failure could have significant consequences for the end user. Spring material will have an influence on the quality. For both stock and custom springs, quality usually impacts durability and performance for your medical device.

Use: Different device applications call for different types of springs. Your device may require compression, torsion, power or spiral torsion springs, or some combination. Furthermore, the application of the device may have an impact on the quality requirements. For example, a spring-loaded dust cover is likely less critical than a vibration isolator on an imaging device.

Environment: Also consider the environment in which the device will be used. For many medical devices, the environment is relatively sterile. However, factors such as temperature, exposure, humidity, and corrosiveness can impact the spring you may require.

Cost: Finally, the cost is always an important consideration when designing a component. It often relates closely to the above factors (high-quality, robust, specialty springs are typically expensive). Costs for components can often be brought down by buying in bulk.

Plus, an expensive but effective device is usually preferable to the alternative in medical device manufacturing. Nonetheless, this is an essential factor to consider.

Keeping these considerations in mind, you can begin to evaluate the specific pros and cons of stock vs. custom springs. The right choice can help you to design a better device.

Benefits of Stock Springs
For medical equipment designers, ordering from stock can offer some substantial advantages. These are especially significant for non-critical components. However, in many cases, even critical elements of the device can be designed to use stock parts.

Cost-Effective: In a lot of cases, stock components benefit from economies of scale. Since they are already produced in bulk, the cost per unit is usually relatively low. If you can find one that satisfies your requirements, this may be the right choice.

Readily Available: By the same token, these springs are already being produced; therefore, they are available almost immediately. There is no lead time necessary for design or tooling. Instead, they can be shipped and delivered exactly as needed. This is ideal for designers on a tight production timeline.

May Be Easier to Use in Design: In some cases, it is easier to design around a component that already exists. You can get specifications from the manufacturer on tolerances and load capacity. Additionally, you can know the exact size in advance.

Drawbacks of Stock Springs
Of course, there are a few significant drawbacks to using stock.

The most significant issue is the part may not meet the exact specifications necessary for the device, especially if it’s proprietary or hasn’t gone to market. It is often better to order a custom part than to try to work around an imperfect stock spring. It may actually save you time and money.

Additionally, the quality may not always be up to par. If you need very specific tolerances, it may be better to work directly with a manufacturer to ensure ideal production quality. You also risk sourcing components from several sources, all of which may have different quality standards.

Benefits of Custom Springs
Custom springs and assemblies can offer a solution made specifically for your device. For medical equipment designers, using custom-designed springs may be ideal for critical applications. Following are several benefits.

More Design Options: You don’t have to settle for a spring from the parts bin. Instead, custom designing your spring(s) along with the manufacturer gives you a chance to set your own specifications. For medical devices, this can sometimes be the difference between achieving the desired functionality and having to redesign.

Higher Quality Standards: If you work with a custom spring manufacturer, you can set your own quality specifications and tolerances. For any device that needs perfectly machined parts, this may be the preferable option.

Perfect Fit: Many medical devices require precision and intricate mechanical functions. The right fit can be important in these cases. Custom springs are designed to fit and mount to your device, leading to minimal prototype revisions.

Drawbacks of Custom Springs
Although the custom manufacturing route has many benefits, it isn’t always the right choice. It is typically more expensive than using stock springs on a per-unit basis. Although, ordering in bulk can achieve near-parity in terms of cost.

Additionally, any custom part will take more time to produce. It needs to be designed, prototyped, and tested before tooling can even begin for production. Therefore, if the need is urgent, it may make more sense to opt for a stock alternative.

Considerations for Medical Equipment Designers
Overall, if a stock spring meets your requirements, it may be a better solution for your device. However, there is no guarantee that stock components will meet your needs. Consider other factors besides cost. The upfront cost may be more expensive with custom solutions, but you may save more money in the long run.

As you make your decision, balance the aforementioned consideration factors. If you are sourcing for a critical or intricate application, ask for quotes from custom spring manufacturers. This information can help you to make a better-informed decision.

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Edward Jones is the marketing manager of John Evans’ Sons, the international designer and manufacturer of constant force springs, spring reels, spring sub-assemblies, and other mechanical components for a number of industries, including medical devices. John Evans’ Sons is ISO 13485 and ISO 9001 certified.