Medical technology: the smallest cutters for the hardest materials
Nearly 200,000 artificial hip joints – and more than 150,000 knee joints – are implanted each year in Germany, according to data from the Federal Medical Technology Association. In order to permit the problem-free function of these devices and of others used in medical technology over the longest possible period, special materials such as titanium or stainless steel are often employed. Precision tools, some from LMT, permit the high-precision machining of these materials.
Corrosion-resistance, the lowest possible wear and, at the same time, the ability to withstand the compression and bending stresses to which they are exposed – the essential requirements of a prosthetic joint sound at first quite similar to other performance descriptions found in the machine construction field. In reality, however, in particular with what are known as endoprotheses, the situation is quite different. The reason for this is not hard to see: endoprotheses do their job inside the body. A new operation is needed after years – or decades – if the medical product loses its capacity to function as a result of wear. That means that these figures from the Bundesverbandes Medizintechnologie are particularly important: 95 per cent of endoprotheses are still working properly after 10 years, while 75 per cent of all prosthetic hip joints still do not need to be replaced even after 25 years.
It almost goes without saying that many technical medical products must demonstrate similar levels of quality. This has far-reaching consequences for the machining of these components, whether by chip-forming methods or otherwise – in respect, for instance, of their quality assurance guarantees in the broad sense.
Know-how for efficient machining strategies
The LMT Group has served medical technology for decades with ongoing new tool developments that improve the efficiency and the high-quality machining of many components – and, of course, not only in the field of endoprotheses. Prof. Diethard Thomas, Manager of the LMT Akademie, explains: “We understand the whole of the technology and the production conditions found in this sector – starting with the materials, through the conditions applying to their machining, and on to the preparation of the CAD/CAM programs without which an economical machining strategy would not be possible. This background knowledge has, of course, again and again borne fruit in new tool developments“.
Tools as drivers of innovation
This dynamic process is perfectly illustrated by the tools used in medical technology: it is now possible to mill even hardened steel with tools of minute diameters. These microcutters are designed in such a way that, in spite of their minimal dimensions, they are able to do their work reliably, even under heavy stress. LMT Fette offers microcutters with diameters starting at 0.2 mm. They are available with four different lengths, and, according to the application, may be uncoated or may have abrasion protection coatings of TiAlN, TiSiN or diamond. To machine titanium and stainless steels using tools with dimensions as low as 4 mm, LMT Fette has developed the DHC INOX range, which includes versions of various lengths and different cutting-edge geometries (DHC - Different Helix Cutter). The tools with 6 mm diameter and above are also even designed with internal cooling. DHC tools are available with diameters as low as 1 mm for machining normal steels.
Tiny tools at work
LMT Kieninger has developed tiny cutting tools with CBN cutter designs for machining miniature components of abrasive materials. These are available with diameters starting at 0.4 mm. LMT Belin completes the palette of microtools with ultra-small drills in polycrystalline diamond (PKD) cutting materials, and diameters that start at 0.5 mm. Cutting nonferrous metals and plastics are typical applications for these innovative tools.
Where exactly are these tiny tools used? "Microtools are, for instance, used in the manufacture of tooth implants and for bone screws.” But Thomas goes on to explain: "They are also, however, indispensable in the production of device components for minimally invasive interventions". Due to the high technical and hygienic standards, these applications place extreme challenges in terms of the required manufacturing tolerances and process reliability. Particularly when machining expensive materials such as titanium, the maximum performance of individual tools becomes less important than reliable, reproducible quality from all the tools throughout the whole process.
Micro Cutting