Tools for special threads

For internal thread whirling, the tool must be guided at an angle (swivel angle = angle of the thread). The compensated whirling tools from Louis Bélet, on the other hand, move parallel to the bore axis and can therefore plunge deeper into the workpiece. © Louis Bélet

"In certain areas of application, ISO threads are not even used. There are also numerous other standards, tapers and multi-start threads," adds Arnaud Maître. This applies not only to medical technology, but also to the watchmaking industry and certain areas of application in the automotive industry. For the production of the corresponding special tools, this means that suitable tool shapes, machining strategies and application parameters must be found. One example of this is angled multi-start threaded bushes with a conical base for bone implants, which enables the surgeon to center the screw easily when inserting it. For such cases, the tool, machining strategy and recommended application parameters must be developed together as a complete package. The customer is supported in such projects by specialists, who also become active on site if necessary. Trials are carried out in Vendlincourt using our own test facilities. The customer therefore receives a tried and tested tool that can be used immediately. This is supplemented by on-site support should any problems arise.

Numerous materials, coatings and geometry variants

Whirling of a five-point conical thread. © Louis Bélet

"As our customers often use materials that are difficult to machine, such as stainless steel, titanium or lead-free brass alloys, we also have a great deal of expertise in the area of materials for milling cutters," reveals Falbriard. Optimization for a specific application begins with the selection of the most suitable carbide variant and the corresponding coating; alternatively, tools made of PCD diamond or boron nitride are also manufactured.

Quality control is carried out using computer-aided optical measuring systems. © Klaus Vollrath

One of Louis Bélet's specialties is the production of forming and stepped tools on machines specially designed for this purpose. In addition, there are specially adapted cutting edge geometries, for example to prevent the formation of long chips, as well as progressive flutes for optimum chip removal. The result is often a service life that is several times longer than can be achieved with conventional tools. The results with ceramic tools are particularly remarkable, where the durability when machining non-ferrous metals is sometimes 30 times better, while the machining quality of the workpieces remains consistently high.

The tools are designed using high-performance CAD/CAM software. © Klaus Vollrath

"Another example of our innovative capacity are slim micro-milling cutters with load-optimized geometry for Torx recesses in bone screws," explains Maître. The Torx profile in the head must be very precise and also deeply recessed. Due to the geometric specifications of the Torx profile, this requires milling cutters with a very small diameter and long lateral cutting edges to enable the deepest possible penetration into the material. In addition, bone screws are difficult to machine materials such as titanium, stainless steel or chrome-cobalt, which is why adapted cutting geometries had to be developed for the various materials. In addition, the milling cutters must be able to withstand high forces in order to minimize geometric deviations due to lateral displacement. For this reason, and to avoid vibrations, the shank of the milling cutter must be designed to be as rigid as possible. For this reason, a special shank geometry has been developed for this category of milling cutter, which ensures maximum rigidity even when plunging deep into the workpiece. Cutting edge lengths of up to 5 × Ø are possible. For a milling cutter with a diameter of 0.2 mm, the lateral cutting edges are therefore 1 mm long. By using these milling cutters, the final use of a cutting punch can be omitted when manufacturing the screws.

Standard tools for difficult materials

Production system with robot-supported workpiece handling. © Klaus Vollrath

"For standard applications with difficult-to-machine materials, we have developed tool lines that are precisely optimized for the material," reveals Pierre Falbriard. These "Expert" tools are available in standard size gradations and a wide variety of designs such as drills, milling cutters, taps, saws or gravers. Depending on the design and application, variants in terms of material (carbide or PCD) or coating are also possible, and form cutters are also available on request. Expert tools are available for stainless steel, brass, titanium, aluminum and composite materials. Specific versions for sub-categories are also available for the individual materials. In the case of fiber composites, for example, a distinction is made between carbon or glass fibers, thermoplastic or thermoset matrix and honeycomb structure. An important advantage for the user is availability: in the interests of high supply availability, around 650,000 tools in more than 7,000 different designs are constantly kept in stock in Vendlincourt.

Klaus Vollrath, freelance journalist / ag