Making implants from tough-to-machine titanium

Machining medical components cost-effectively and reliably requires high-precision tools that have been tested in practice to meet specifications that often reaches the micron level.

Inovatools, the tool manufacturer from Haunstetten near Kinding in Germany, offers the Inomed range of tools for this application. According to the company, the tool’s optimized geometries, quality documented with test reports and service life make the Inomed tools ideal for processing the kinds of materials required in medical engineering, which include stainless steels, zirconium oxides, titanium, and cobalt/chrome.

One example is the production of bone compression plates for osteosynthesis in jaw surgery. For these types of implants, the material most often used by surgeons, orthopedic technicians and dentists are specially alloyed surgical steels or highly bio-compatible titanium alloys. But, these materials are difficult to machine cost-effectively and in-line with the relevant directives such as high elasticity and low-thermal conductivity.

This is because the cutting edge can reach high temperatures due to low heat dissipation through the chips and workpiece. This can result in thermally induced stress in the tool. In addition, the high threshold load due to the lamellar chips combined with the high, localized pressure loads on the cutting edges due to the material hardness mean that conventional tools quickly reach their limits.

Nilüfer Cebic, head of product management and marketing at Inovatools, said, “Miniaturization, precision and compliance with the most stringent of standards are decisive in medical engineering, which is something that tool manufacturers have to take into account and reflect in their product ranges.”

To cope with these hard-to-machine materials, Cebric said the development of the cutting-edge geometries requires a sharp awareness of these factors coupled with the right combination of coatings and surface and edge preparation.

“After all,” she said, “only implant manufacturers that can rely on the quality of the very best tools available can perform machining processes cost-effectively and with maximum precision.”

Express shipment of special tools

Due to the difficult-to-access geometries of bone compression plates for fractures in the jaw area, machining tools are often narrow and usually designed with a long reach. To avoid vibrations caused by the long projection lengths, Inovatools matches the helix angle and cutter pitch of the tools to these special machining situations.

Norbert Geyer, head of the special tools department at Inovatools, said, “The range of Inovatools INOMED mills … opens up new options for high-precision milling in the micro range for diameters of between 0.1 mm and 20.0 mm.”

According to Geyer, the company also develops and produces  special tools for complex drilling and milling tasks with extreme precision and accuracy in the micron range. The company offers a Special Tool Express Service so that a manufacturer receives a quotation specially tailored to its requirements within 24 hours. The solid carbide (SC) special mills and drills in dimensions from 0.1 mm to 32 mm, which are custom-made for individual requirements including edge preparation and PVD coating, can then be shipped within just one week.”

Bone compression plates used in jaw surgery are titanium implants and they are available in different thicknesses and designs. Due to the stringent requirements imposed on the material, application-optimized tools are absolutely essential for machining. The tendency toward sudden strain hardening, for example, can instantly increase the friction on the cutting edge, causing the tool to become blunt. The combination of carefully selected, ultra-fine-grain carbide, the perfect geometry and chip control, prepared cutting edges and high-performance coatings is the key to commercial success and consistently high quality.

During the machining of bone compression plates to create frictional connections, the Inovatools tools can be used in a range of representative applications compared with conventional tools.

SC standard fiber end mill 132

The SC tool’s geometry offers a high machining rate during the milling of titanium alloys. Taking the jaw plate as an example, the challenge was to increase throughput without compromising process reliability. The tool was optimized with special surface treatment, edge preparation and internal cooling. The resulting special mill 998049223_HB100100326 makes the milling process 40 percent faster with V_c = 70 m/min; F = 700 mm/min.

With a second special fiber end mill (998051524_HB100100455), the upper and lower outer edges of the jaw plate are chamfered simultaneously (V_c = 60 m/min; F = 225 mm/min), reducing the machining time by 50 percent. With a Inovatools combination tool for drilling and chamfering (998044881_HB100100166), implant manufacturers can achieve time savings of more than 60 percent compared with conventional production using two tools.

“Where every micron of precision counts, our micro-tools offer outstanding surface quality, the narrowest of tolerances and long service lives,” said Cebic. “Thanks to Inomed, we can supply our customers with ‘high-end powerhouses’ almost instantly. And if customers need to perform even trickier tasks, our developers can deliver the perfect solution with smart special tools.”