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What’s So Hard about Making Orthopedic Parts?

Meeting customer specifications and verifying features are the most challenging parts of manufacturing metal orthopedic components.

Bob Michaels

 
The feature dimensions of such orthopedic devices as this critical-fit bone plate with bone-screw interface from Autocam Medical are verified using a variety of different measurement machines.

Everyone knows that as the U.S. population ages, healthcare interventions will become more and more common—not least in the area of orthopedics. Hence, it is hardly surprising that by 2017, the global market for orthopedic devices and materials will reach $57.2 billion while the market for joint repairs and replacements will reach $40.2 billion, according to a 2015 Research and Markets report.

What does this mean for manufacturers of orthopedic devices and components? It means that they will face heightening demand for high-quality machined products. But it also means that they will be under increasing pressure to meet stringent quality standards so that their products not only fit right but also look right.

Measure for Measure

“Our big concern is not necessarily focused on the actual metal working itself,” remarks Joel Diemer, manufacturing engineer at Kentwood, MI–based Autocam Medical. “Being able to accurately measure parts is often a bigger concern. The customer puts certain specifications on a print, some of which may or may not be readily measureable without special gauging in order to verify features. Thus, one of our biggest challenges is having measurement methods in place that can prove that our parts have been manufactured to customer specs.”

Typical tolerances for noncritical or nonmating features are commonly around 0.005 in., although some tolerances can be as low 0.0002 in. in certain applications “That’s about as tight as we go for standard manufactured orthopedic parts,” Diemer says. “Most medical device applications don’t go beyond that tolerance. By the same token, because it is challenging to maintain critical dimensions with such small tolerances, process validation becomes critical, often requiring that manufacturers use specialized process and measurement equipment.

Standard tried-and-true measurement methods include optical comparators and micrometers, and calipers, according to Diemer. Every supplier that produces components for the orthopedic market has at least these instruments. In addition, coordinate measuring machines and vision machines with tactile probes are used to measure diameters, lengths, and geometric tolerances. Some of these instruments can measure threads, and some can measure more than one feature at a time, rapidly generating large volumes of dimensional information.

As you branch off from there, high-end computer-driven digital microscopes are employed to recognize minuscule features, Diemer notes. Such instruments must be programmed, and how well the operator programs the equipment plays into how well it will measure an orthopedic part.

“All part features must be dimensionally correct,” Diemer emphasizes. “Proving this has always been one of the hard parts of manufacturing orthopedic components. Utilizing such tools as gauge repeatability and reproducibility studies, as well as statistical process control, adds extra certainty that the components being manufactured will always meet customer specifications.”

A Day in the Life of an Ortho Parts Maker

An acetabular cup with an Asymmatrix coating from Orchid Orthopedic Solutions is manufactured based on detailed product quality planning procedures.

What steps does a manufacturer take to produce a typical orthopedic component? “When an order is received, we first go through a detailed order start process,” explains Ken Altman, director of advanced manufacturing, Machining Div., at Bridgeport, MI–based Orchid Orthopedic Solutions. “During this process all necessary specifications, including material choices and necessary processing sequences, are reviewed.”

The company then goes into great detail to develop suitable advanced product quality planning procedures in order to meet the customer's quality expectations. While the quality plans are being built, manufacturing engineers review the customer’s drawings, compile a tooling list, order the necessary tooling, create set-up sheets, and review the manufacturing programs for each stage of the process. In addition, routers and bills of materials are established based on the customer’s print, ensuring that the orthopedic part is processed to specification.

“After the machining steps have been completed, the part is cleaned according to standard procedures,” Altman says. “Then, it is electropolished, laser etched, passivated using a nitric or citric process, and reviewed for final acceptance. If required, the part is packaged and labeled in a certified cleanroom and sterilized.”

Importantly, every part has to be burr-free, according to Diemer. “We can’t compromise making a part faster if doing so creates more burrs, since no orthopedic component can be shipped if it has flakes of metal on it.” To ensure that parts are burr-free, manufacturers crack out their microscopes and visually inspect the parts for any type of debris—especially burrs—that might remain from the manufacturing process.

Hey Good Lookin’

Spinal screws (pedicles) from Autocam Medical are manufactured to meet customers' cosmetic requirements.

Especially in the medical device field, customers are very particular about the cosmetics of their parts. “Once they’ve been around for while, engineers have a good idea about how to manufacture a part,” Diemer states, “but every customer wants the part to have a specific visual look. One customer’s specification for a part with a satin finish is not necessarily the same as another’s. Thus, ensuring that we can meet each customer’s cosmetic expectations is one of our larger challenges.”

Many customers require that a portion of a component have a satin bead-blast finish and a coating on the same part. Transitioning from the one to the other can be difficult because there must be a smooth, accurate interface between the two types of surfaces. “The cosmetic appearance of a component can also depend on the cleanliness of the water in the facility,” Diemer adds. “Manufacturers must ensure that parts do not exhibit water stains because everything has to look clean and sharp.”

Bob Michaels is senior technical editor at UBM Canon. Reach him at [email protected].

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