Machining parts with complex geometries and fine surface finishes is common in the aerospace and automotive markets, but medical implant manufacturing takes it to a whole other level. A common saying in manufacturing for space applications is, “there is no repair shop in space.” The quality, precision and reliability of each part must be perfect because once it leaves this world, it just has to work since millions of dollars are on the line. Arguably, the same holds true in medical machining. If an orthopaedic implant doesn’t work correctly, the health and well-being of a patient is affected. When the surgery is complete, it just has to work.

Global demographic trends indicate that the need for medical implants will grow, and so will competition in the market. According to Seco Tools, approximately five major suppliers claim 85 percent of the orthopaedic component manufacturing market, with more than 200 companies fighting for the remaining 15 percent share.

Materials

Knee and hip implants are typically made of cobalt-chrome alloy or titanium. (Image courtesy of Seco Tools.)

Just like in any other engineering discipline, material is a critical consideration for medical implants. The two characteristics of material performance are biofunctionality and biocompatibility. Biofunctionality is more of a consideration for things such as plastic materials—the functionality of bone and joint implants is well-served by most metals. With metals, biocompatibility is the main consideration—examining corrosion properties of the metal and interaction of the corrosion reaction and the body’s tissues.

According to a recent article co-authored by Jan-Willem van Iperen and Ruud Zanders, engineers at SECO tools, the most common materials for knee and hip implants are cobalt-chrome alloy, such as CoCr28Mo6, and titanium, such as Ti6Al4V. Titanium is less popular but growing. Stainless steel also is used for temporary implants, as it is less corrosion resistant than cobalt-chrome or titanium.

Bar stock, forgings or castings are typically the starting point for machining operations, which are followed by grinding and polishing. Machining these materials can be challenging due to the same characteristics that make them functional in the body—their high strength and stiffness.

For example, cobalt-chrome is hard, abrasive and highly elastic. This can cause intense tool wear, compounded by the material’s low heat conductivity. Titanium, on the other hand, has the lovely property of work-hardening, as well as poor heat conductivity. During machining, heat builds up at the cutting edge and tool face.

The usual response to these types of materials is to dump plenty of coolant into the cut. However, traditional coolants can contaminate medical implants, requiring expensive and time-consuming cleaning processes. For this reason, Fusion Coolant Systems developed a coolant system using supercritical carbon dioxide. For more information about scCO2 dry-cutting technology, visit Fusion Cooling Systems.

Machining Operations

Like other manufactured parts, orthopaedic implants can involve several machines or computer numerical control (CNC) cutting operations, including grinding and even potentially metal 3D printing. On the machining center, operations for a typical knee implant can include roughing, tray base roughing, tray base finishing, chamfer milling, T-slot undercut machining, wall finishing/chamfering and undercut deburring. The goal is to achieve the required surface finish on the machine, reducing the need for time-consuming manual finishing.

Five-axis milling and grinding machines provide advantages to working with the complex shapes and contours of orthopaedic implants.

Cutting Tools

Jabro medical cutting tools maximize machine performance for medical components. (Image courtesy of Seco Tools.)

Seco Tools has introduced a line of cutting tools designed to shorten knee implant cycle times through high-speed machining and other aggressive milling strategies.

The Jabro medical range includes nine geometries and 39 tools, most of which are part of the Jabro Tornado high-speed cutting family. Each geometry is designed for particular applications in the machining of tibial tray and femoral knee implant components. Additionally, because these new dedicated tools are targeted for the machining of CoCr (cobalt-chrome) and 3-D printed Ti6Al4V ISO-S12 parts, they can be used for other medical implant components as well, including parts used in hip replacements and bone plates.

Should You Get into the Medical Machining Market?

If your machine shop already does high-precision or 5-axis machining for aerospace, it could be worthwhile to look into this lucrative, albeit highly competitive, manufacturing market. If your shop is eying the medical implant market, consider the following factors:

· What is your capability for small-scale or micromachining? Some medical devices require very small components.

· What is your capability to machine titanium and other challenging materials?

· Can you efficiently manufacture small-batch or custom one-off complex parts?

· Can your shop meet FDA certification standards for your machining processes?

· Can your equipment handle the complex geometries required?

For more information on the equipment required for medical machining, check out this article from Mazak about its 5-axis machines’ applicability in this market.