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Ball bearing for upper extremity orthotic braceWhen cost containment, regulatory compliance, and the ability to respond quickly to new opportunities are of critical importance, it’s easy to select a standard bearing from a catalog and move to the next step in production.

But what does that simple decision really cost?

Surprisingly, a greater sacrifice to the development process than a design engineer might realize. Specifying a standard bearing for a medical device only takes into consideration basic, functional requirements such as load and speed. What many don’t realize are the limitations and design constraints that are associated with the use of a standard bearing.

Standard bearings are made to standard sizes and require the medical device design to fit those sizes. In reality, to make sure the bearing meets the speed and load requirements plus safety considerations, the next larger standard size is chosen. That decision alone increases the size and cost of every other component in a design. This is the first expensive sacrifice to a product’s design.

Standard bearings are made from standard materials. Chrome steel bearings are subject to corrosion and the design will be complicated by the necessity of protecting the bearing from contamination. Stainless steel bearings are made from 440C stainless, making them corrosion resistant but also magnetic, limiting usefulness in sensitive applications. Ceramic bearings are clean and nonmagnetic, but will inflate the budget due to high cost. Material limitations represent the next expensive sacrifice to a design.

Standard bearings are “off the shelf,” ubiquitous, and readily available as long as only a few are needed. The vast majority of standard bearings are made offshore. When large production quantities are required, with extensive quality documentation and traceability such as for a medical device, the lead times for standard bearings will be measured in months and minimum quantities will become enormous. So marks the last expensive sacrifice to a design.

In worst case scenarios, the easy decision of selecting a standard bearing results in costly production delays, inefficient assembly processes, expensive redesigns, and, worst of all, in-field failures.

It unfortunately happens, but there is a better way. A custom bearing for a medical device can offer four distinct advantages.

  • Dramatically improved design freedom
  • A final device that is smaller or more compact
  • A device that is feature rich
  • Reduced production issues, lower costs, and faster time to market

Custom ball thrust retainers1. Set the Design Free
Design freedom begins with collaboration and the custom bearing design process reflects that. The design engineer and bearing engineer (yes, there is such a thing) work together to create the best bearing for the overall application. The design engineer can share the full vision for the product, allowing the bearing engineer to recommend a solution that meets all the performance parameters and more.

It’s important to note that this process does not automatically translate to greater expense or increased production timeframes. In fact, the opposite is true, enabling design innovations such as smaller overall size, simplified design, and improved assembly. Using the right material, achieving proper sizing, eliminating components, and including additional features sets the designer free to develop the best medical device instead of settling for a less than ideal solution.

2. Smaller, More Compact
Many design engineers don’t realize the enormous and negative impact a standard bearing can have on the size and complexity of a device.

Custom bearings can be properly sized to fit the demands of an application. Dependent on load and speed of the application, bearings can be designed with just the right number of rolling elements, or using races that have unique diameters or widths. That means a housing or mount can be designed for the bearing that is smaller and less expensive. It also means that an adapter does not need to be added to fit a shaft or spindle to a standard bearing bore.

Custom bearings can be made from the appropriate materials that are lighter, non-magnetic, or resistant to contamination. Engineering grade plastics, non-magnetic metals, and ceramics can be used so that the design is more focused on the application and less on protection of the bearing.

Custom bearing can be made to fit the lifecycle of the design. Not all applications need to perform millions of cycles, spin at thousands of rpm, or last for decades of use. Particularly in disposable or limited-use applications, a bearing that is designed to match the performance requirements of the device can be much more cost effective.

Custom stainless steel angular contact retainer for a medical device caster3. Feature Rich
Standard bearings are just that — standard. The sole function of the bearing is to reduce friction during movement. To mount the bearing, a component must be added. To limit motion, a component must be added. To add an aesthetic feature, a component must be added. Each additional component increases cost and complexity in the design, in the manufacturing process, and in the supply chain.

Custom bearings can be designed to include necessary and desirable features while reducing cost and complexity. A mounting stud or bracket can easily be integrated; a ratcheting mechanism can be added to limit direction or give an audible indication of movement.

4. Reduced Production Issues, Lower Costs, Faster Time to Market
Custom bearings can’t solve every issue but they can certainly address some of the most vexing problems. Using a custom bearing that integrates a mounting method or allows for some adjustment during assembly can simplify the assembly process.

Designing a custom bearing that only includes the bearing components necessary for the application (e.g., using only a thrust retainer rather than a full thrust bearing) can speed up assembly while reducing the size and cost of the medical device.

Developing a custom packaging solution that presents the bearings to assembly personnel, ready to install, in the right quantities and properly sized for the assembly area, can dramatically improve productivity. Reusable and recyclable packaging can also be developed to reduce costs and waste.

There are other ways in which a custom bearing can impact cost and time to market while reducing production issues without negatively impacting medical device quality. A bearing engineer can help identify these benefits early in the design process.

Getting Started
An experienced bearing engineer who is oriented around elevating the performance of the medical device while simultaneously helping to manage cost and production timelines will be able to:

  • Review the design and make recommendations not only for the bearing itself but for related components
  • Understand the relationship between the bearing, its components, and the complexity of the subassembly process
  • Provide assistance in remedying devices that are in production or the field and failing

If cost containment, time to market, and product quality are key considerations, consider a custom bearing.

For more information, visit www.nationalbearings.com.

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