Efficient grinding of medical instruments
Medical technology saves lives and keeps people healthy - millions of times every day. But grinding medical instruments and implants presents some challenges. VSM explains what is important for machining.
Stringent requirements for medical instruments and implants
Medical devices and implants must meet the stringent requirements of the healthcare sector. Above all, they need to be highly reliable and as easy to clean as possible - and to withstand a great deal. The vast majority of medical instruments and many implants are therefore made of special steels. Grinding brings some material-specific and (end) product-specific challenges, including: precision, material hardness, heat development and surface quality.
To meet these challenges, grinding experts recommend the use of structured abrasives. With XELERION, VSM has developed a new product that perfectly meets the very stringent requirements for high-precision machining of medical instruments and implants.
Challenges involved when grinding medical instruments and implants
Precision
The tolerances of medical instruments with their often tight radii and contours are sometimes extremely tight. Even the smallest deviations could impair the function. High-precision machining is therefore necessary. The instruments also require burr-free, very sharp cutting edges.
Material hardness
Medical steel in particular is designed to ensure high strength or toughness and is therefore comparatively demanding in its machining. Among other things, this leads to increased heat development, vibrations, noise and also increased grain wear. Structured abrasives are ideal for this task because they produce a fine finish despite high stock removal rates.
Heat development
Heat is generated during (fine) grinding of medical and implant steels, and this can alter the material structure and even lead to deformation and discolouration. It is therefore desirable to have as cool a cut as possible.
Surface quality
Ultimately, it all comes down to ensuring a high-quality surface. Typically, a smooth, polished, high-gloss surface is desired to ensure sterility and prevent contamination or corrosion.
The solution: VSM XELERION
The finest surfaces, without any discolouration.
Medical instruments are demanding in terms of grinding: Narrow radii must be ground, heat development and discolouration should be avoided. The process should create a technically and visually flawless surface. For VSM XELERION, it’s easy: KK670F features a flexible backing which adapts perfectly to tight radii and complex contours. The random arrangement of XELERION dots ensures an optimised distribution of force and heat – and thus also cooler grinding, which helps prevent discolouration and deformation, for example. The result is a perfectly reproducible finish.
Stringent requirements for medical instruments and implants
Medical technology saves lives and keeps us all healthy, millions of times every day. There are over 500,000 different medical products - including medical devices and implants - in the EU alone, but they all have one thing in common: They have to meet the most stringent demands of the healthcare sector. Above all, they need to be highly reliable and as easy to clean as possible - and, as you will soon see, need to withstand a lot more. The vast majority of medical instruments and numerous implants under consideration here are therefore made of special steels. We show why a new VSM product range now plays an important role in the grinding of these devices during manufacture and reconditioning.
Materials and applications
Steel best meets the specific requirements of medical technology in many respects. Medical instruments made of steel are therefore used in almost all areas of healthcare. For example, in
Surgery: for scalpel blades, forceps, scissors, needle holders and staplers,
Orthopaedics: for implants such as bone plates, screws and pins for fracture repair, artificial joints,
Cardiology: for stents, replacement heart valves and other devices for cardiac procedures,
Endoscopy and diagnostics: for forceps, probes and clamps for various diagnostic procedures and, not least, in
Dentistry: for mirrors, pliers, probes and drills.
Steel is of course also used for external equipment and high-quality devices such as dialysis machines and ventilators.
Medical products are, by definition, intended for use on humans and act “primarily physically”. Medical steels need to be exceptionally durable and have special properties such as wear resistance (see below). Modern production facilities guarantee consistently high quality. Such steels meet the most important medical standards and are certified according to ISO and ASTM, for example.
Two types of medical steel
Basically, two types of special medical steel are used in medical technology: the first is medical steel, also known as surgical steel; the second is implant or prosthetic steel. These types differ in their manufacturing processes, compositions (alloys) and chemical and mechanical properties. Let’s first take a look at medical or surgical steel:
Medical steel - extremely hard and wear-resistant
Steel for medical instruments is mostly (around 80 percent) martensitic stainless steel, which is produced using a special production process called “martensitic transformation”. Put simply, very rapid cooling in the manufacturing process causes a structural change in the raw material austenite - the subsequent expansion of the austenite results in extremely hard steel. Other elements such as nitrogen, nickel, chromium and molybdenum are added, and these also affect the properties of the steel.
Martensitic steel has to meet special requirements in medical technology. Its exceptional hardness is particularly worth mentioning here. It has extremely high strength and does not abrade even under demanding conditions. The greatest possible rigidity is also important so that blades, for example, remain sharp for a long time, even during intensive use. This enables precise cutting.
High resistance to heat and acids is necessary to withstand daily sterilisation after use, for example in operating rooms. And of course, instruments must be rust-proof, because the human body is made almost entirely of water. So it is good that stainless steel does not corrode and, depending on the alloy, even has an antibacterial effect to ensure maximum hygiene.
About hygiene: Most medical instruments are chromium plated. And not just because this looks better. Rather, because chrome ensures a scratch-resistant surface that always remains hygienic. Otherwise, even the smallest scratches could become a breeding ground for bacteria.
Implant steel - resistant and (bio)compatible
Implants are mostly made of stainless steels that undergo a special austenitic manufacturing process, such as the electro-slag remelting process. These steels are particularly pure, free of metallic contaminants and are characterised by high corrosion resistance and biocompatibility, making them ideal for sensitive use in humans.
Implant materials must meet a wide range of requirements to withstand the special properties of the human body. The main requirements are excellent mechanical properties such as strength and the best possible integration into biological tissues, which is known as bioadhesion. In addition to the corrosion resistance already mentioned, which is absolutely necessary in the "wetness" of the human body, implant steel must also be acid-resistant, for example. Acids are continuously produced in the body, and although they are usually neutralised directly by bases, they could still attack the material. For this reason, implants are often coated with a layer of antibacterial agents to prevent immune reactions. The same applies with regard to biological compatibility: Prosthetic steel must not cause any foreign body reactions; it must be able to be integrated into the metabolism. Thanks to the steel’s excellent biocompatibility, this is not a problem.
Another prominent material for implants is titanium. Certain alloys of this light metal have very high strength and score highly in terms of bioadhesion, i.e.: after a certain period of time, the body can actually incorporate the material completely into the bone structure. However, titanium is also significantly more expensive than implant steel products and very demanding in the machining process, see more below.
The properties and test methods for cold formable, stainless metallic materials that may be used in the production of surgical implants have been defined by the EU in the ISO 5832 series of standards “Implants for surgery — Metallic materials”.
The market for medical instruments and implants
The market for medical devices and implants is an extremely attractive global growth market. This is mainly due to ageing populations, technological advances and an increasing demand for cosmetic procedures.
Global sales of almost half a trillion euros (471.10 billion) are expected for 2024, according to Germany's Federal Statistical Office. Experts forecast an annual market growth of 5.9 percent to 628 billion euros by 2029. According to other sources, the implant market generated sales of 111.33 billion euros in 2023. The USA/North America are leaders both in the overall market and in implants.
Germany is also an important player in the development and production of medical devices. Germany is considered the third largest market for medical devices worldwide, after the USA and China. Germany also ranks third as a production location. Around 210,000 people are employed in this industry, which is heavily dominated by small and medium-sized enterprises. Clusters have formed in certain regions, probably the most well-known being Tuttlingen in Baden-Württemberg, a small town with just 38,000 inhabitants but 300 medical technology companies.
Other focus regions in Europe include Northern France, the Czech Republic and Hungary. Original Equipment Manufacturers (OEMs) often manufacture to the highest possible quality and manufacturing standards in countries such as Pakistan and China.
Grinding challenges
Grinding medical instruments and implants presents some material-specific and (end)product-specific challenges, including:
Precision: The tolerances for medical devices, with their often tight radii and contours, are sometimes extremely tight. Even the smallest deviations could impair the function or, in the worst case, endanger patient safety. High-precision machining is therefore necessary. The instruments also require burr-free, very sharp cutting edges.
Material hardness: Medical steel in particular is designed to ensure high strength or toughness and is therefore comparatively demanding in its machining. Among other things, this leads to increased heat development, vibrations, noise and also increased grain wear. Medical instruments, as well as implants, are therefore often ground using structured abrasives. Because: These produce the desired fine finish despite high stock removal rates.
Heat development: (Fine) grinding of medical and implant steel generates heat that can alter the material structure, resulting in deformation and discolouration. As cool a cut as possible is therefore desirable.
Surface quality: Ultimately, grinding medical instruments and implants is all about achieving an extremely good, high-quality surface: as smooth as possible, without any scratches, grooves or material displacement. Typically, a smooth, polished, high-gloss surface is desired to ensure sterility and prevent contamination and corrosion. The goal is always a flawless, uniform and reproducible scratch pattern despite high stock removal.
Abrasives for machining
First choice: Structured abrasives
To meet the challenges described here, grinding experts recommend the use of structured abrasives. With XELERION, VSM has developed a new product that perfectly meets the very stringent requirements for high-precision machining of medical instruments and implants.
The structured abrasive has a newly developed backing structure and grain structure: The abrasive grains are applied in several layers and are not arranged strictly symmetrically on the backing, but randomly. This innovative manufacturing process ensures a cooler cut, less heat development and therefore also less discolouration and deformation. Users find working with XELERION to be a much more pleasant experience, since it is significantly quieter and generates less odour and dust.
High flexibility and pliability for perfectly reproducible high-gloss surfaces
The random distribution of the abrasive dots on the backing material results in outstanding adaptability to the geometry of the workpieces - XELERION is significantly more flexible, regardless of the backing type, than comparable conventional abrasives. Especially on very flexible fabric backings, a belt flexibility is achieved that other scattered abrasives could never aspire to: The narrow radii and complex contours of medical instruments can be machined precisely and accurately. The special “pliability” of XELERION allows extremely even stock removal from the fine, even surface. A perfectly reproducible finish is achieved - or even a flawless scratch pattern for high-gloss surfaces.
Fewer grit size steps - more productivity
The stock removal rate is high right from the start, even with fine grit sizes, which means that XELERION can also be used for rough pre-grinding without problems. Common grit steps can be skipped to achieve the desired surface finish in fewer grinding passes. Compared to competitor products, the number of workpieces per belt can be doubled in the medical instrument production process.
VSM XELERION is available as
- KK670F in roll or belt form on a very flexible cotton fabric backing (F) in grit sizes 240, 320, 400, 600, 1200 and 2500. Ideal for finish grinding with low to medium pressure.
- KK670J series as rolls, belts and discs on a flexible fabric backing (J) in grit sizes 240, 320, 400, 600, 1200 and 2500. Ideal for finish grinding with low to medium pressure.
Other VSM abrasives for machining medical instruments and implants:
VSM SILICON CARBIDE: Although not quite as abrasive as ceramic grain, its excellent cutting ability can deliver very good results when machining medical steel: VSM silicon carbide produces an extremely fine scratch pattern and particularly brilliant gloss levels, which is why it is also popular for machining titanium.
VSM ALUMINIUM OXIDE: VSM ALUMINIUM OXIDE is ideal for contour machining and edge grinding. As a simply coated abrasive on a flexible backing material, it also performs very well in the surface processing of medical instruments thanks to its excellent adaptability to the workpieces.
VSM COMPACTGRAIN: VSM has more than 20 different products in this series - the long-term abrasive is a permanent favourite in the VSM portfolio. When grinding medical instruments, the compact grain on a flexible or very flexible fabric backing excels thanks to its optimal self-sharpening and constant, reproducible surface values. It guarantees a long service life - and ensures a uniform scratch pattern with consistent surface roughness and high gloss levels.
Grinding processes and use of machines
Medical instruments and implants are usually processed by hand grinding, i.e. either on the backstand/grinding block and on the offhand grinding belt or using a hand-held power tool. XELERION has been specially developed and optimised for these types of grinding process.
In slack-belt production, large manufacturers increasingly rely on robot grinding to achieve the most consistent results possible. Due to its unique behaviour in grinding, XELERION is predestined for such automated use because: It delivers consistently high stock removal over the entire service life - while competitor products whose abrasive grains have a pyramid structure, for example, blunt quite quickly, generate more heat and then decline in performance.
Different manufacturing and repair requirements
In the production and reprocessing of medical instruments and implants, abrasives have to meet quite similar requirements overall.
Manufacturing focuses on the highest precision and quality. The requirements are stringent, since any irregularity could affect the function of the instrument. This requires state-of-the-art tools and careful control to achieve exactly the required specifications and standards. At the same time, a reproducible finish of the highest surface quality with low roughness must be achieved as efficiently as possible - a particular challenge with sometimes small, tight radii. The structured, particularly flexible VSM XELERION abrasive is the first choice here.
In the reprocessing of instruments, the focus is on restoring functionality and implementing hygiene measures. It is about cleaning, disinfecting and sharpening used equipment, as necessary. It is important to repair damage and wear without affecting the original quality of the device, for example if too much material is removed by accident. For repairs and reprocessing, machining therefore usually starts with finer grit sizes than for new production. The work tends to be more manual - but otherwise the processing steps are very similar and the requirements for the end product are basically the same as for production.