How CNC Machining Is Changing the Medical IndustryHow CNC Machining Is Changing the Medical Industry
Digital motors, sophisticated software, and specialized cutting tools are yielding precision, repeatability, and scalability in CNC machining.
August 11, 2022
Products, devices, and accessories used in medicine are becoming ever more sophisticated as new technologies emerge to improve human health and patient outcomes. These products are found everywhere, from surgical wards to rehabilitation centers, from small town clinics to the family medicine cabinet.
Regardless of the type of product, they all share some common features.
Primarily they must be safe to use, and that degree of safety of course includes the raw materials from which they’re made.
They must be reliable, with close tolerances necessary for predictable and repeatable performance.
They are often highly customized, with unique designs that make them suitable for very specific applications related to human anatomy.
And it’s important that new product ideas can be prototyped, tested, approved, and brought to market quickly.
CNC machining is an ideal manufacturing solution to meet all these criteria and more.
The Current State of the Art in CNC Machining
Advances in CNC machine tool technology are being driven by the demands of the marketplace. Sophisticated designs for next-generation applications require higher levels of precision and repeatability. That, in turn, is expanding the envelope of what is physically possible in tool design.
Machine manufacturers are always searching for ways to optimize performance by controlling vibration, increasing machine speed, lowering maintenance costs, and providing flexible machining platforms that can perform multiple complex tasks in one machine set-up.
There are three advanced technical solutions that can help in all of these areas.
Multi-axis CNC machines travel on several independent axes. To do this, most machines use a rack-and-pinion guide or a linear screw and reciprocating ball drive system. Both types are subject to friction and wear and have limitations both in accuracy and in speed.
But linear drive systems work much like a Maglev train. Electrical current, interacting with powerful magnets, levitates the carriage off the guide rail while also driving its travel. This means no friction, no wear and tear, and no maintenance. And linear drive systems move much faster, with much higher degrees of accuracy and precision.
Another innovative drive solution, also calibrated to reduce friction, is the hydrostatic guide. These use precisely ground guideways that are cushioned with a thin film of oil. The oil is continuously pumped into and out of a carriage, and this carriage holds the workpiece. The oil flotation quells vibration and removes friction, thereby leading to excellent surface finishes on the part.
The buildup of heat is always a problem when machining at the very edge of performance. This is because the natural expansion of all materials when they heat up will definitely throw tolerances out of control—unless this heat is controlled with very serious central cooling. In addition, smart manufacturers have figured out how to calculate the rate of expansion for all critical components in their system and then counteract those movements accordingly.
More advanced machine tools allow for the manufacture of more advanced products, and that is certainly no exception when it comes to medical devices.
There is no other mass production process that is so reliable, precise, scalable, cost effective, and easily customized. Let’s take a closer look at how CNC machining can be used to improve the development of medical devices in certain key areas.
Every new product starts with a prototype. This is as true for medical technology as it is for any other industry. There are several advantages to using CNC machining for medical prototypes.
First, it’s fast. Once a design is approved, a finished part can be programmed and machined in as little as one day. This lets the product engineers get right to work testing for fit and function—critical steps in the prototyping process.
Physical prototypes help to identify any potential design flaws or areas that can be improved upon, and if minor changes need to be made, it’s a small endeavor to alter the machine program accordingly.
Precision and Repeatability of CNC Machining
Once a design has been dialed in, any properly functioning CNC mill or lathe can make duplicate parts, in any volume, with only the most minimal variation in tolerance part-to-part, typically 5 microns or less. In a previous era, achieving this degree of accuracy from a manually operated machine tool would have required the skills of a master machinist in controlled conditions, and it would have been much slower and much more expensive.
Now, digital motors, sophisticated software, and specialized cutting tools make this degree of perfection easily achievable and completely dependable. Therefore, medical product designers no longer need to ask—can it be done? Yes, it can.
Some mass production processes first depend on making dedicated molding or casting dies, such as with plastic injection molding or investment casting. These dies take considerably longer to make and require a large initial financial investment. The only way to recover the cost of this investment, from the point of view of the developer, is to commit to making a large number of finished products over time.
But many medical designs are highly customized and won’t be made in large volumes, so investing in tooling is not a viable option.
CNC machining does not require hard tooling, so a single part can be produced cost effectively, and the volumes slowly ramped up as demand increases.
CNC machining is also indifferent to the raw material being worked on, as long as it’s rigid enough to withstand the force of cutting tools. There may be some minor machine adjustments to account for different types of metal or plastic—speeds and feeds—but this versatility essentially means that designers, as well as medical technicians, have wide leeway to choose the material that is best for the intended application.
There are many independent certifications that might apply to various medical devices, the most important of which is ISO 13485. This stipulates that a manufacturer has demonstrated the necessary chain-of-custody protocols to safeguard all raw materials that pass through their facility as well as any finished or semi-finished goods. They must be kept clean and uncontaminated as well as sequestered from other non-conforming products, and the raw materials must be shown to contain no harmful chemicals.
It must be noted that when it comes to applying for FDA approval or clearance in the United States for a medical device, or the equivalent CE mark in Europe, it is the owner or licensee of the design who is responsible for making the necessary application—not the manufacturer. The product designer must demonstrate that the item in question has met all regulatory requirements at every stage in its production, so working with an ISO-registered business is one way to do that.
Because of its versatility, CNC machining lends itself to all manner of custom fabrication for medical products.
Examples might include stainless steel tools, forceps, and clamps; surgical implants for bone repair; orthotic and prosthetic components; high-temperature fittings for sterilization chambers; parts and components for test equipment; and many more. The list is truly endless. However, CNC machining is not best suited for large volumes of plastic parts, which should be injection molded instead.
The Future of CNC Machining
Already more than 160 hospitals in the United States have permanent 3D printing facilities on-site, to help make highly customized and complex shapes near the point of care. This demonstrates that there is an established and recognized need to fabricate physical objects on the spot to meet special requirements that can arise at any time and without the luxury of forecasting.
For this same reason, there may be a place for CNC machining in hospitals, clinics, and medical research centers. For many applications, CNC machining is faster than 3D printing, and the parts it can produce are much stronger and more accurate.
Small, portable, and largely self-contained multi-axis machining centers could easily be placed even in remote areas to provide fast, accurate, and inexpensive manufacturing solutions where other opportunities are limited.
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