Medical Machining Tightens Up

Medical Machining Tightens Up

Apr 7, 2016

Regulations, competition are causing part makers to tighten profit margins, part tolerances and cycle times

By Michael C. Anderson, Manufacturing Engineering

The medical device market finds ways to stay in the headlines in one way or another, whether it’s because of big mergers (such as Medtronic’s acquisition of Covidien) or tax-inversion moves (such as Medtronic’s subsequent relocation of its headquarters to Ireland). Medical device companies and their lobbyists continue to push back against the US medical device tax used to cover some of the costs of the Affordable Care Act. And recalls of medical products certainly get into the media. But away from the front page of the business section, manufacturers in the medical device field are feeling the effects of a shift in health care practices.

“The regulatory environment in North America and Europe has driven a shift to value-based healthcare solutions, which in turn has resulted in increased competition, changing business models, and innovative strategies to achieve sustainable growth,” medical market analyst Bryan Hughes of P&M Corporate Finance LLC (Chicago) said.

The ripple effects from all of these developments are reaching the medical device side of the machining business, resulting in a tightening of a number of parameters, from profit margins to part tolerances and more.

Tighter Margins

Scott Walker, president of Mitsui Seiki USA Inc. (Franklin Lakes, NJ), gives an example of the way hospitals do business has changed—and how that change affects medical manufacturers and their suppliers.

“Ten years ago, a hospital used to go in and buy the entire range of components,” Walker said. “For knee replacements, for example, a hospital would buy a box and in it would be, say, 15 sets of knees. They didn’t know until they cut your leg open what size would fit in there, so they were ready with a range of sizes that they had purchased.”

No longer, he said. “Today the way it works is, a knee-replacement salesman goes into the room with the surgical team, he brings in a box of knees, and the hospital only buys and uses what goes into the patient.”

That kind of practice means a lot fewer knees get sold, and so the manufacturers are hard-pressed to cut costs wherever they can. Walker recalled selling a dozen high-end five-axis machines to Johnson & Johnson for making knee replacements and eight more to Zimmer for making hip replacements some years ago. More recently, he said, the machines sold to Johnson & Johnson have been sent to Ireland and the Zimmer machines sent to Puerto Rico. “They went outside the US to reduce costs, and then started buying more commodity-based machine tools,” he said.

Other Mitsui Seiki customers—still in the US—are making smaller components, such as titanium intervertebral implants, as well as surgical tools and molds for plastic accessories. Walker said that their most popular machine with these customers is the Vertex line of five-axis vertical machining systems. The new Vertex 55X II model series, comprising six distinct models, was announced in February 2015. Linear axes strokes are 550 × 600 × 500 mm. “The line is designed for tight-tolerance work,” Walker said, and features XYZ positioning accuracy of 0.001 mm. Spindles are available in 15,000; 25,000; and 30,000-rpm speeds.

Tighter Tolerances

Even tighter than the profit margins in this business are the tolerances required for increasingly smaller, more detailed components.

“The medical industry is very innovative, and is coming to us with more and more complex components,” said George Bursac, general manager of Star CNC Machine Tool Corp. (Roslyn Heights, NY), a specialist in Swiss-style machining solutions. “Over 50% of our total business is in medical manufacturing. We work with a number of well-established medical companies and, you know, they always come back for more. Parts are becoming smaller and more intricate, with a lot more detail on them—and you can’t make them any other way than by using a Swiss-style machine.”

The type of parts Bursac is talking about include those from implants, surgical instruments, cardiovascular components, dental equipment and more, he said. “Some of the parts they’re manufacturing now are sometimes so tiny that you cannot see them with your eyes alone—you have to use a jeweler’s loupe to see certain details on these parts.”

Quality and repeatability are other requirements for machining these ever-smaller components, according to Bursac, which is a reason for automating more of the procedures.

“With smaller parts, a lot of people used to make different fixtures to hold them. Today, we don’t have to do this on our machines. We make parts out of bar stock from scratch,” Bursac said. “You put a rod in the machine and out will come a finished part. All details are added right in the machine. The part is picked up with a subspindle and finished on the back end as well.”

Bursac stresses the advantage of being able to start and finish a job on a single machine without human intervention. “Any handling of such precision parts by people, it introduces variables that could create problems. With the machine doing everything without a need to stop for fixturing and so on, it makes for a more accurate, repeatable process.”

The ST-38 model from Star CNC is popular with the company’s medical customers, according to Bursac. It features the company’s multiturret technology and has the capacity to machine components ranging in size to 38 mm. The machine’s triple-turret design capitalizes on simultaneous capabilities to reduce overall machining time, which is beneficial given the medical industry’s tight margins.

The machine also offers deep-hole drilling on both the front and rear ends of components, as well as high speed and universal control. To further improve accuracy and productivity, the machine is equipped with the company’s custom “Motion Control” feature. A flexible toolpost design enables the incorporation of additional tools to increase functionality.

Tighter Cycle Times

The tight margins in medical manufacturing demand the fastest cycle times possible while maintaining quality, affirms Mazak Corp. (Florence, KY) VP Rick Ware. For medical shops making a range of precision parts, that calls for a five-axis system with speed, accuracy and flexibility, he said.

To illustrate, Ware shared the example of Mazak customer OneSource Manufacturing Technology (Leander, TX). OneSource manufactures primarily medical implants—knees, hips and a variety of spinal components—along with some associated supportive instrumentation. Parts range in size from 3.2 mm2 up to 457 mm2. Typical tolerances are ±0.227 mm and as tight as ±0.0127 mm, and materials include stainless steels, titanium, cobalt chrome, PEEK and others.

When the company first moved into medical work a few years ago, they did their five-axis machining with three-axis VMCs outfitted with fourth and fifth-axis trunnion units. They soon discovered that such an approach hindered their part processing speed and cost-effectiveness. The communication between the trunnion units and the VMCs on which they were mounted caused lags in positioning; the units’ additional mounted weight restricted how fast the machine tables could rapid traverse; and the extra inertia involved with moving the added weight also accelerated machine wear and tear as well as generated vibration that affected part surface finishes. But what really hindered operations was the amount of time and effort it took to achieve required levels of machining accuracy.

OneSource purchased a Mazak VCU 400A 5X VMC that features an integrated tilt/rotary trunnion table with roller gear cam technology. The machine has as 40-taper 12,000-rpm spindle, automatic toolchanger and 30-tool storage capacity. With an X-axis stroke of 505 mm, the VCU 400A 5X handles parts up to 400 mm in diameter and 304 mm in height.

According to Ware, for every job the shop has moved to the VCU 400A 5X, it has immediately reduced cost per part by at least 15% through shorter cycle times. In some instances, cycle times were reduced by more than 25%.

“The small-footprint VCU VMCs feature trunnion-style rotary/tilt tables that make it possible for shops like OneSource to cost-effectively add full-axis machining to their operations, especially for producing medical components,” Ware said.

‘That’s the Priority’

At toolmaker Iscar Metals (Arlington, TX), the focus is also on reducing cycle times—a more important concern than increasing tool life, according to Grip Systems Product Manager Clay East.

“Tool life is important, East said, “But what Swiss-style machining shops and medical shops realize is that if we can extend their tool life by 20%, that’s great—but if we can extend their productivity by 20%, well, they’re jumping over buildings at that. That is going to allow the customer to get 20% more usage out of their machines. It frees up their machines—by 20%!—for other jobs.

“That’s the priority,” East said. “You want to squeeze every penny out of every machine you’ve got when you’re in the medical industry.”

East offered two examples of recent innovations at Iscar that are helping to increase productivity for their medical customers. The first is an update to a decade-old product called Swisscut. In its original design, a user would have to completely remove a screw in order to index the tool insert or remove the insert completely.

“It sounds like a small thing,” East says, “but I used to work in a Swiss machine shop and I can tell you firsthand that when you drop a screw, it’s very frustrating” as your work comes to a halt while you search for it. “And if it happens several times a day, and 52 weeks a year, that adds up to real loss in productivity.” So about two years ago the Swisscut was redesigned so that the user need not completely remove this screw in order to index or remove the insert.

“About three turns and you can take the insert off,” East said. “It’s accessible from either side of the tool. This allows you to change that insert without removing the tool from the machine, saving time.”

His second example involves precision boring an inner diameter with solid carbide tools such as boring bars or grooving bars. Iscar has developed a secondary bar holding solution for use with their Pico line of tools, he said. “By going from what used to be the industry standard of two-screw clamping of the tool to three-point-contact clamping,” East said, “we were able to take our repeatability on this ID boring operation from 50 to 5 µm, both radially and axially.”

To put that into perspective, a human hair is about 100-µm thick.

“It was the move to three-point clamping that allows us to get to that level of precision,” East said. “To this day I have yet to see any of our competitors publish anywhere near the 5-µm repeatability axially and radially. The closest any have gotten that I’ve seen is 50-µm axially and 20-µm radially.”

Model-Based Definition

The connection between part designers and manufacturers has also become much tighter with the advent of software-aided designing for manufacturability. “One big change the industry has seen is the move toward MBD, or model-based definition,” said Keith Goodrich, a product specialist at CNC Software Inc. (Tolland, CT), the makers of Mastercam software.

“Although not specific to the medical industry, the effects are felt strongly in this corner of manufacturing,” Goodrich said. “Designers and their customers weigh aesthetics heavily in the medical industry, smooth transitions from one feature to the next are increasingly more important and always difficult to define on 2D blueprints. Using MBD, a profile tolerance to a supplied model or individual feature of a supplied model is extremely simple to convey from the designer to the manufacturing engineer.”

This move to MBD has a further impact on the task of machining medical components, Goodrich explained: It has streamlined the process from manufacturing to inspection.

“Instead of a machine operator requiring custom gaging to check 2D blueprint callouts—which is cumbersome, time consuming, and often unnecessary with respect to a part’s design intent—a first-article inspection using a CMM or optical scanner can quickly confirm a MBD profile tolerance has been met,” he said.

According to Goodrich, the latest iterations of Mastercam are further addressing the productivity concerns of the medical market through an ongoing project the company calls “Rest Machining—a quick way for manufacturing engineers or programmers to target material left behind in a machining operation.”

He explained that Mastercam’s Stock Model feature can calculate the shape of the stock—the material from which a part is being machined—anywhere in the process the programmer desires. So, when referencing a Stock Model and a finished part model, Mastercam’s toolpaths can be set to only machine areas where material protrudes from the finished part model.

“Taking this approach saves our customers time and money by efficiently targeting only the stock left on the part, and not having to waste machine time ‘air-cutting’ over already finished areas,” Goodrich said.

Further clarifying the condition of the in-process stock relative to the finished part profile is Mastercam’s Compare feature, Goodrich said. “This feature compares the machined material to the finished part model with user-specified tolerances and clearly displays any material remaining as well as any over-cut, gouged features.” The result is a better use of machine time as well as of stock.

Tight Simulations

Multiaxis machining equipment and the tools and automation needed to meet customer demand are a big investment for medical manufacturers and the thought of the cost of downtime and repairs if a program goes wrong can bring night sweats to the most hardened of executives. For this reason, a growing number of companies are first trying out their machining programs on virtual machines by way of simulation software.

“The trend in medical device manufacturing is going toward more and more use of complex multitasking machines,” said Silvère Proisy, general manager of Spring Technologies Inc. (Boston, MA, and Paris), a developer of NC simulation and verification software for optimizing CNC machines. “Machines that are complex enough to do everything, and this is where simulation can have a crucial impact on a company’s return on investment.”

Proisy offered the example of a major medical-device OEM that recently invested in some five-axis machining centers that feature dynamic offsets to allow the completion of a complex part in a single operation as well as in robotic loading/unloading equipment.

The company “needed to make sure that when they set up a new program, its going to execute correctly without any crashes or any part issue,” Proisy said. “We have to take into account all of the parameters that reside in the real machine. When we set up the simulation, we ask the customer to give us all of the knowledge about the subroutine macros from the machine—we extract these from the real machine and put it into the simulation.”

The more abilities a machine and its CNC software have, the more parameters need to be reflected in the simulation’s virtual machine, according to Proisy.

“It can be very complicated,” he said. “It took us a couple of months to set the virtual machine up properly” in the case of this project. In the end, however, the customer was able to avoid a lot of risk and save time by working with the simulation to optimize their new machining cells.

While that customer’s machines used FANUC controls, Proisy pointed out that this simulation system can work with machining programs from any software package.

“Another medical client asked us in 2012 if we could simulate and optimize an operation that used a legacy program that was written with software that doesn’t exist anymore or programmed manually,” he said. “We said yes because ultimately we are reading G code. As long as a program comes down to G code moves, we can simulate it no matter what the software was.

“People at that company told us later on that just by putting that operation into our software, they were able to significantly cut machining time,” he said. “After a year they had saved half a million dollars just through time saved.”


This article was first published in the March 2016 edition of Manufacturing Engineering magazine. Read “Medical Machining Tightens Up” as a PDF.


Leave a Reply

Your email address will not be published. Required fields are marked *