Knight Carbide–MEDICAL CARBIDE

Making the Tools to Make Medical Parts

In the high-precision world of CNC machining, there is no field more stringent in its demands for accuracy than in the machining of medical parts and instruments. With surgical implants becoming more and more commonplace, the need for close-tolerance machining of surgical screws and other parts is also increasing. The minute scale, intricate forms, and complex geometries of these parts, in addition to the materials they are made from, make them extremely challenging to machine. Success depends not only on the skill and experience of the machinist, but also on the quality of the cutting tools they use to do the job. 

Success Is in the Details

Achieving the precision and repeatability required in parts for medical implants would be impossible without specialized tooling. At Knight Carbide, we produce the cutting tools used to manufacture highly precise parts for use in, for example, hip arthroplasty (hip replacement). 

In this increasingly common procedure, the surgeon removes a worn or damaged hip joint and replaces it with artificial parts, including a ball (femur head) at the top of the thigh bone, and a concave “cup” (acetabulum) attached to the pelvis. Often, the artificial acetabulum will require additional stability, in which case, the surgeon will secure it to the pelvic bone with a small titanium screw threaded into a plastic liner, which is inserted into the pelvic bone itself. Both the screws and the liners are made of materials that are highly difficult to machine. Their miniscule size and tight tolerances only add to the challenge of producing them.  

Machining the Screws and Molding the Liners

Acetabular screws are typically machined out of titanium, while the acetabular liners are made from a high-performance polymer like ultra-high-molecular-weight polyethylene (UHMWPE). These materials are used because they offer the critical properties of high durability, wear resistance, and biocompatibility. Production of these parts presents significant challenges that can only be overcome with cutting tools made from precision-ground carbide with the proper edge prep and coating.  

Acetabular screws are created by extracting material from a titanium ingot. Their highly precise threads are created by a high-speed, close-tolerance CNC thread whirling operation in which the custom carbide cutting tool can shear the material in a single pass. 

Likewise, the design and machining of the mold tools used to produce the plastic acetabular sockets are critical for achieving the correct shape, fit, and finish of the final part. To meet stringent medical standards, these mold tools must be precisely machined, often using multi-axis CNC machining or electrical discharge machining (EDM). These methods allow for tight tolerances and intricate surface details that ensure the plastic socket will align perfectly with the metal components of the hip implant.           

Tool Material Selection

The tools required for producing these parts must be extremely hard and resistant to wear. Carbide cutting tools can withstand repeated high pressures and temperatures during the molding and machining processes. However, carbide itself is even more difficult to machine than titanium, so making carbide tools requires high-precision, high-durability tooling equipment, in addition to considerable expertise.

Special Coatings

To extend tool life and maintain the cleanliness and performance of the tooling, specialized coatings like titanium aluminum nitride (TiAlN) or diamond-like carbon (DLC) may be applied. These coatings help to reduce friction during the machining and molding processes, minimize sticking of the plastic material to the mold, and provide corrosion resistance, all of which contribute to tool longevity and help minimize downtime.

Maintenance and Re-Sharpening

Due to the high wear and tear of the cutting edge, and from molding polymers, these tools often require routine maintenance and re-sharpening to maintain precision. Knight Carbide recommends a preventive maintenance schedule that includes regular inspection, cleaning, and potential re-coating of the tools, ensuring that each part meets medical-grade quality standards every time while reducing the waste of time and materials that inevitably occurs when tool performance begins to degrade over time.

Look to the Experts

The extreme challenges of medical tooling are commensurate with the critical nature of their application. The margin for error is, effectively, nil, and the repercussions of failure can be catastrophic. For those reasons, it is vital to entrust your medical tooling to expert firms like Knight Carbide. Find out more about us here.