Knee Joint Manufacturing à La Mikron Tool

Just crazy Knee Joint Manufacturing à La Mikron Tool

2025-12-17 From Matthias Böhm | Translated by AI 4 min Reading Time

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The Mikron Tool developers have developed a complete manufacturing process—including CAM programs—for knee joint manufacturing. For the two knee joint components (upper and lower leg), the manufacturing specialists need only a total of 50 minutes, including the pre-finishing (CNC brushing) of the surfaces— simply crazy.

Perfectionist machining of the upper knee joint component at the Mikron Tool development center with one of the newly developed milling tools.(Image: Thomas Entzeroth) — Perfectionist machining of the upper knee joint component at the Mikron Tool development center with one of the newly developed milling tools.
(Image: Thomas Entzeroth)

With 250 employees, Mikron Tool specializes in the production and development of high-performance tools and processes for machining difficult materials (titanium, stainless steel, Inconel, and cobalt-chrome alloys—CoCr). Recently, the machining specialists from Mikron Tool presented the SMM editorial team with a sophisticated manufacturing strategy for producing the two knee joint components (femoral—thigh / tibial—lower leg) from CoCr.

Tangible Enthusiasm in the Development Team

When Alberto Gotti (Head of Development) and his development team present the newly developed milling tools and the manufactured knee joint prototypes to the editorial team at the company's own development center, you can feel their enthusiasm for the new tools and manufacturing processes.

Gallery

In the middle of the image are the raw parts and the finished knee joint components with a mirrored surface. On the left is the toolset for the upper knee joint implant. On the top right are four tools for the lower knee joint implant as well as additional medical milling tools.(Image: Thomas Entzeroth)

The specialists at Mikron Tool are highly professionally equipped. The knee joint cast components are also from a supplier in the medical technology industry.(Image: Thomas Entzeroth)

Antonio develops the CAM strategy. This is an extremely demanding process, not only because of the CoCr material being processed but also because of the required very high surface quality of Ra = 0.4.(Image: Thomas Entzeroth)

Antonio inspects the surfaces and transitions of the upper knee joint component.(Image: Thomas Entzeroth)

No wonder, as the demands from implant manufacturers are enormous. The material is a machining challenge. And neither chatter marks nor other transitions may be visible or noticeable.

A. Gotti: “The raw parts are CoCr precision cast components, produced using the near-net-shape process. Particularly challenging is the casting skin in terms of tool wear. It has a thickness of about 0.016 inches and is highly abrasive.

Here, we experience the highest wear rates on the cutting edges of the tools. It is absolutely crucial to efficiently remove the casting skin. The gating systems are also highly challenging and repeatedly caused us machinists headaches."

Smooth Cutting Delivers Outstanding Surfaces

Everything perfect? Measuring the surface quality, which at Ra = 0.285 is below the tolerance limit of Ra = 0.4.(Image: Thomas Entzeroth) — Everything perfect? Measuring the surface quality, which at Ra = 0.285 is below the tolerance limit of Ra = 0.4.
(Image: Thomas Entzeroth)

Alberto Gotti comments on the machining challenge: "Due to the material properties, chatter marks can occur very quickly during the machining process. The tools must have perfectly tailored micro- and macro-geometries for the material and the workpiece shape. If all additional manufacturing parameters are in place—a highly rigid and dynamic machine, excellent workpiece and tool clamping, efficient cooling—then we achieve a smooth cut with outstanding surfaces. The surface quality of the finished implant must ultimately be below Ra 0.4. And this with a material that is optimized for everything but machining."

Thigh Knee Joint Component: Most Complex Freeform Surfaces

The manufacturing of the thigh knee joint component is particularly complex. It predominantly features freeform surfaces, semi-deep pockets, and narrow ribs. What makes it truly challenging is the combination of the material to be machined and the required surface quality of the CoCr alloy from which the knee joints are made.

Grinding Process Could Be Substituted

A. Gotti: "The required high surface quality could previously only be achieved through subsequent 5-axis simultaneous grinding processes. Thanks to our newly developed tool program for knee joint prostheses, the coordinated milling strategies, and an integrated CNC brushing process, we achieve the required surface quality within a single CNC process. This allows us to replace the previously necessary external grinding process."

Marco Cirfeta (Global Head of Sales & Marketing): "The substitution of the grinding process means that the manufacturing process is significantly simplified for manufacturers—including logistically. Until now, it was not possible to produce surfaces with grinding quality on knee joint components in the machining center. With our process, the knee joints can be directly transferred from the machining center to the drag finishing process."

To achieve this result, the Mikron Tool specialists developed four coordinated milling tools each for the thigh and lower leg components.

For the complete thigh component, a conical full radius cutter (Z = 4), corner radius end mill (Z = 5), and full radius cutters (Z = 5 and Z = 8) are used for fine finishing the surface.

A. Gotti: "With subsequent CNC brushing using diamond filaments, we can achieve a surface roughness of Ra = 0.1. The total manufacturing time for the femoral component is currently just under 40 minutes. I must say, we haven’t yet fully optimized the process. At present, we achieve up to double the tool life compared to our competitors' tools. So there is still potential to further reduce the process time."

Manufacturing of the Lower Knee Joint Component (Tibia)

The tibia component is simpler in terms of complexity (no freeform surfaces), but equally demanding in terms of material. After a pocket about 6 mm deep is milled into the tibia component, it must be deburred inside. Additionally, it receives an undercut. This is necessary to securely clamp the plastic sliding component (polyspacer).

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Date: 08.12.2025

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Mikron Tool Specialists Achieve A Surface Quality of Less Than Ra 0.2

As with the femoral component, exactly four milling tools are required for the tibial component: a radius end mill, a chamfer geometry mill, a form mill, and a finishing form mill for undercuts. After finishing, the Mikron Tool specialists achieve a surface quality of less than Ra 0.2, thus remaining below the required tolerance range. This is a significant factor, as mirror-smooth surface structures are required for various medical reasons. The tibial component is fully milled in just under seven minutes.

Knee Joint Manufacturers Receive A Highly Process-Reliable Procedure

M. Cirfeta: "With the manufacturing strategy developed by Mikron Tool, based on the newly designed knee joint tools, knee joint manufacturers gain a highly process-reliable method that is also incredibly expedient. Once again, we are setting a benchmark and—if we may say so—we are not done with the development yet. There is still more to come. But already now, we have developed a manufacturing strategy that is among the fastest in knee joint production worldwide. That is simply crazy—but that's just how we are."