From tool to implant: Precision machining for medical devices done right!

Editor's Note: This article originally appeared in the September 2025 print edition of Today's Medical Developments under the headline “From tool to implant”.

When it comes to manufacturing medtech components, the tools used must not only meet close tolerance but also deliver flawless surface finishes, because these parts must be biocompatible with the body.

Precision is critical due to the sensitive nature of medical implant applications. Even minor imperfections such as rough edges or small burrs can lead to serious complications once the component is implanted. That’s why there’s no room for error.

“Everyone knows someone who’s had a hip replacement or a knee replacement, maybe a bone screw or a bone plate at some point in their life,” says Scott DeVinney, senior global product manager at Kennametal. “Unlike other industries, the medical one hits home.”

There’s a lot that goes into the planning of a part before it ever reaches the shop floor. Manufacturers must manage everything from tool pressure to fixturing strategies to maintain precise tolerances and ensure smooth surface finishes, especially on complex, curved components such as acetabular cups used in hip replacements.

“Kennametal’s expertise in CNC programming and process planning really pays a lot of dividends for our medical customers,” DeVinney says. “They don’t have a whole lot of process engineers. They’re busy working through new developments on implants and how they go into the human body. They benefit from machining strategies developed through collaboration with machining experts and that’s where Kennametal comes in.”

Advanced materials such as titanium, cobalt chrome, and stainless steel are essential but challenging to machine, which is something Kennametal engineers tackle daily. A significant insight from the team’s experience is the material’s purity is critical for reducing the risk of adverse reactions when implanted into a person. Leveraging their background in aerospace machining, the team has adapted and refined Kennametal cutting tools and processes to meet the stringent demands of the medtech sector.

“Kennametal has programming and application support teams located in-house (at Kennametal Labs) and in the field. These teams are capable of processing complete solutions for customers to help them get their medical projects off the ground,” says Chris Merlin, senior global product manager at Kennametal.

Kennametal also works closely with machine tool builders who set up turnkey systems for medical manufacturers. From the spindle out, the machine tool builders rely on Kennametal to ensure they have the right tools, workholding, and processes.

Machining acetabular cups and femoral heads

Machining complex medical components such as acetabular cups and femoral heads presents significant challenges due to their curved shapes, which complicate tool reach, risk deflection, and decrease the likelihood of achieving the most effective surface finish requirements. Achieving a high-quality surface is critical, especially for femoral heads, as it reduces the time needed for subsequent polishing operations.

To address these challenges, the A4 tooling system is designed to take on the complex geometries and precision demands of these components. Shaped like a double-ended ‘dog bone’ insert, the A4 allows for efficient machining by enabling a continuous tool path going back and forth, eliminating the need for retraction between passes. Its full nose radius insert is particularly effective for generating smooth outer diameters, while its long, slender shape provides the necessary reach for intricate features.

Additionally, the toolholder’s clamping system applies pressure to hold the insert securely in the pocket, creating a very stable and accurate connection. The pocket itself features a precision-ground V-groove, ensuring the tool is seated with high accuracy. The V-groove keeps everything precise.

The coolant and heat factor

Effective coolant delivery is essential and plays a key role in managing chip formation and preventing tool failure. Stainless steels, for example, tend to work harden, leading to issues such as depth of cut notching and a built-up edge. Directing coolant to the cutting edge helps reduce heat and improve chip control.

“High-pressure coolant can be applied in different places and the coolant from the A4 system comes out of the top and bottom to break up the chips better,” says Ron West, senior global product manager at Kennametal. “These materials are abrasive and at times can be difficult to break the chip. With top and bottom high-pressure coolant, you can maintain the chip much better along with controlling the heat on the insert.”

Holemaking with Drill Fix PRO

Another Kennametal tool designed to handle complex medical components is the Drill Fix PRO. The platform can be used for drilling and boring operations in one setup, making it ideal for machining complex internal curved surfaces. The robust design includes an oversized shank and a large flange, so the tool connection to the spindle is very strong.

Drill Fix PRO isn’t just a high-performance drill, it also functions as a boring tool, combining two operations in one. Beyond creating internal holes, the tool also machines a precise curved radius into the acetabular cup mirroring the shape of the mating femoral head. This feature is critical in medical applications, as it ensures the mating components seat properly with each other for minimal friction or interference, delivering mechanical strength and anatomical compatibility.

“Drill Fix PRO saves time and lets you start at the center like a traditional drill, then shift outward to make precision boring passes,” DeVinney explains. “This dual functionality simplifies the machining of complex shapes often required in orthopedic implants, and you have one tool to program, one tool to set up, and just one to maintain. It’s easier for everyone’s life in the process.”

Tool holding best practices

When precision is critical, you don’t want to rely on outdated tool holders such as endmill adapters, because they can’t keep the tool properly centered, leading to reduced tool life. Instead, use modern tooling solutions such as a HydroForce hydraulic chuck, ensuring concentric and low runout. This setup keeps the tool running true, allowing manufacturers to make accurate cuts in a single pass. With this level of precision, you can rough and finish using the same tool.

Milling in medical

Milling centers play a crucial role in producing complex, irregularly shaped components. They’re especially valuable in applications involving low production volumes and various part designs. For example, if you search for items such as bone plates or surgical instruments, you’ll find thousands of unique designs because every human body and application is slightly different.

Creating intricate surfaces requires extreme precision, especially given the small scale of the features involved. Since these components are implanted in the human body, reliability is critical and they must stay secure. Even the surgical tools used for installation are machined from tough materials like 316 or 17-4 stainless steel. For every implant, there are numerous tool configurations that also must be machined from solid stock.

Milling machines are incredibly versatile – they can transform a simple square piece of material into highly complex shapes. A common setup involves securing the part with a dovetail adapter helping minimize tool pressure. Despite titanium’s strength, once material is removed, the part can become delicate and prone to movement due to harmonics and cutting forces.

The HARVI IV 8-flute end mill with through coolant capability can produce smaller chips, reduce heat and tool wear, and apply less pressure to the part. It’s a high-speed, low-torque method increasing material removal rates while maintaining part integrity. As a result, the strategy is widely used for machining titanium and similar materials.

Precision isn’t just a benchmark in medtech, it’s a requirement. From the biocompatibility of materials to the immaculate surface finishes required for implants, every detail matters. Kennametal’s advanced tooling solutions, such as the A4 platform, Drill Fix PRO, or HARVI IV 8-flute end mill are engineered to meet the unique challenges of machining complex medical components.

By combining deep expertise in CNC programming, innovative tool design, and strategic partnerships with machine tool builders, Kennametal ensures manufacturers can deliver safe, reliable, and high-performance medical devices. The path from raw material to medical-grade implants not only becomes possible but lifesaving.

Kennametal
https://www.kennametal.com