The Precision of Machining Medical Parts

Micro Precision Parts Manufacturing (MPPM) is a small but busy machine shop on bucolic Vancouver Island. The majority of the parts the company makes are medical related. “Last year and this year so far, we’re probably about 65–70 per cent [medical parts],” says owner/president Steve Cotton.

MPPM has made an array of surgical and dental items, including brain biopsy tools and an aneurysm clamp. Much of their work centers on medical device prototypes.

“We’re [currently] doing a very small tool used for surgical processes on children. It’s still in development stages…a lot of the projects we get are what I call finicky and really delicate parts,” says Cotton.

Cotton has a background in the excruciatingly minute and complex world of making and repairing watches and clocks, which puts him in good form for doing tiny medical parts.

“When you’re handling small parts, if you’re not used to them, the average machinist would probably struggle picking up a part that’s 60 thou, whereas with clock and watch parts you are picking up part sizes like that all day,” notes Cotton.

Challenges of Machining Medical Parts

In addition to minute size, tough medical part materials present an additional challenge. “We do lots of titanium. We’re machining titanium all the time, all the different grades…and stainless steel. The last three medical components were all done in stainless steel…medical grade stainless,” says Cotton.

The company has also worked extensively with ceramic material.

Cotton has considered buying new machine tools for medical parts, but is waiting to see how the training process works out for three potential new machinists.

“We’ve discussed it…I probably wouldn’t be doing any expansion until I see how my [trainees] do…I’m not going to jump into an expansion or a new tool until I can see I have it running 80 per cent of the time,” he states.

Fortunately for Cotton, if he does decide to purchase a new machine tool for the finicky, delicate world of medical parts, he has a wide selection to choose from. Of course, any machine tool he purchases will almost certainly be customized to suit the special needs of the medical market.

His company currently relies on two well-seasoned OM-2A Office Mills and one OL-1 Office Lathe from Haas Automation of Oxnard, California for much of its work. MPPM also has a small benchtop prototyping four-axis mill and small CNC lathe from Sherline of Vista, California.

Medical Precision Machining

MPPM’s Haas mills are equipped with spindles capable of 30,000 rpm and 20-tool changer carousels. Both mills have sub-spindles that can hit 200,000 rpm for high speed machining and automatic laser tool setting systems from Renishaw for accuracy and repeatability. The OM-2A Office Mills offer x, y and z axis travels of 12, 10 and 12 inches, respectively, and a table 20 inches long by 10 inches wide.

The OL-1 lathe has x axis of 12 inches, z axis of eight inches, 6,000 rpm spindle and maximum cutting diameter of 4.95 inches (varies with turret). MPPM has added an axial sub-spindle to the C-axis equipped lathe capable of 60,000 rpm and a radial sub-spindle that can do 40,000 rpm.

Cotton’s son, Matthew, does most of the programming for MPPM, utilizing a Mastercam CAM system from CNC Software of Tolland, Connecticut, for this purpose.

The company likes to use carbide cutting tools when doing medical parts, primarily from two firms, Drill Bit City of Prospect Heights, IL and Harvey Tool of Rowley, MA.

Should Cotton seek out a new machine tool, he might want to look at the Integrex i-150 multi-tasking machine from Mazak.

“We developed the Integrex i-150 specifically for the medical industry,” says Ray Buxton, general manager of Mazak Canada in Cambridge, ON. “The Integrex machine is geared towards doing items like hip joints and knee replacement components. One of the criteria for the [medical parts] industry is to be able to put as many machine tools in as small a space as possible, because for the companies that do this type of work, part cycle times can be long. So, the more machines a shop can have running parts, the more it can increase production. And several Integrex i-150s will take up very little space.”

The Integrex i-150 has full five-axis machining capability, 5,000 rpm spindle speed, 36 tool capacity (72 tool optional) and offers a maximum machining diameter of 15.75 inches (400 mm), maximum work bar capacity of 2.6 inches (65 mm) and maximum machining length of 15.160 inches (385 mm).

The Integrex i-150 can be ordered with SmoothX CNC, which should result in “a very significant improvement to the productivity of that particular machine in the medical industry,” says Buxton.

Introduced at IMTS 2014 in Chicago, “the SmoothX control is geared pretty much for every aspect of the machine. SmoothX, in different forms when we roll it out, eventually will replace all of our controls, primarily on our high-end five-axis machines, because the major benefit is in five-axis contouring and ease of use in complex machining…we’ve seen increases in productivity anywhere from 10 to 15 per cent all the way up to a couple hundred per cent,” he explains.

Mitcham Machine Tools of Toronto is distributing an updated Traub TNL18 sliding/fixed headstock automatic lathe with seven linear axes. Made by Germany’s Index Group, this lathe is now available with an extra axis on the upper turret which expands its ability to handle the kind of challenging machining typical of the medical parts field.

The TNL18-7 can be equipped with a B-axis tool carrier which is able to pivot 100 degrees. Complex parts and complicated contour elements that require additional operations such as milling, drilling, lateral drilling or threading can be machined at any angular position.

The same company also produces a TNL32 lathe.

“The Traub TNL18 and TNL32 lathes were designed with productivity and flexibility in mind. They are convertible from fixed headstock to sliding headstock, so parts that require Swiss-style machining can be processed. This makes possible a wide variety of applications, medical or otherwise,” says Randy Carlisle, proposal engineer at Index. “We have these machines making bone screws, dental implants and anchors for steel and titanium bone stabilizing rods.”

While neither are new, the N2 and N2-5XA CNC horizontal machining centers from Makino are “designed specifically for small medical components, including knee, hip, spine, dental and other implants,” says Mark Rentschler, marketing manager at Makino’s North American headquarters in Mason, Ohio.

“The four-axis N2 provides a cylindrical work envelope measuring 400 mm high by 400 mm in diameter. The five-axis N2-5XA accommodates 300 mm diameter workpieces that are up to 270 mm high. These work zone measurements are appropriately sized for the vast majority of components produced within the medical market, preventing medical manufacturers from over-investing in unnecessary work zone space and eliminating excess rapid movements that lead to in-cycle, non-cut time. Additionally, floor space is often at a premium in medical manufacturing facilities, so the N2 and N2-5XA’s appropriately sized work zone enables a highly productive solution that consumes less than 26 square feet of floor space,” he explains.

The two machining centers have rigid base casting and “C-frame structure and three point leveling system. Together, these design elements provide exceptional rigidity for long hours of continuous machining in hard and exotic materials,” says Rentschler.

Medical Precision Machining's Future

Industry experts ponder the future of machine tools that make medical parts.

“The reduction of machine tool footprints is important to a number of industries, but this is especially true for medical manufacturers. We expect that machine tools for the medical market will continue to become increasingly compact, while simultaneously packing in more advanced technologies for improved rigidity, power and speed. In the near-term, medical manufacturers are likely to begin introducing more automation into their manufacturing processes,” says Rentschler.

“I think we will soon start to see more specialized machining processes such as 3D printers become more common for prototyping,” adds Carlisle.

This is an area where Cotton agrees.

“The 3D printing is interesting…the machines are getting better and better,” he states.

More than anything, Cotton expects 3D printing to have an impact in terms of making models or prototypes of medical parts.

“I think [3D printing] has its place, for sure. When you’re talking models, if they can put in a program and 3D print something…they can touch, feel and look at the size of it,”

says Cotton.