Medical Device Link.

MACHINING

As implantable medical devices continue to decrease in size, small batteries such as Greatbatch’s SVO GenV have been developed. Image courtesy of Greatbatch Inc.

Just how small have medical devices become in recent years?

So small that 10,000 pieces manufactured by Greatbatch Inc. (Clarence, NY) can fit in a sandwich bag.

Under tremendous pressure to control costs, the healthcare community is pushing the envelope for minimally invasive procedures because they are less expensive, shorten patient recovery time, and often can be done in an outpatient setting.

The growing demand for minimally invasive procedures puts medical device manufacturers to the challenge of having to produce instruments that are not only tiny but also are capable of multiple functions and can perform in the smallest of environments with incredible precision. And machining techniques are often what manufacturers turn to.

“What used to be major surgery is now microsurgery and, as device manufacturers, we are seeing everything being driven that way,” says Debra Van Sickle, vice president of Peridot Corp. (Pleasanton, CA), which manufactures precision components for medical and other industry categories.

Donatelle’s facility currently houses 44 Swiss CNC turning centers, two five-axis bar fed machining centers, and a multimachine, fully-automated wire EDM cell.

Dana Schramm, vice president of engineering for Donatelle (New Brighton, MN), a full-service supplier of molded, machined, and assembled products, says that size has become critical in the implants market in particular – which is 95% of what his company serves. “Everybody weighs sizes or devices by cubic centimeters, so if you can be just 1 cc smaller than your competitor, that’s an advantage. That’s what everyone is going to go after.”

Big Advances for Small Products

But these microsized designs present some challenges on the manufacturing end.

John Phillips, vice president of operations for Phillips Precision Inc. (Elmwood Park, NJ), a manufacturer of advanced orthopedic implants and instrumentation, says that little has changed in terms of the fixtures. “We’re still using high-tech software and hardware to produce these components,” he says.

Most of the advances, he says, have come on the design or navigation side.

This image shows various microcomponents for implantable medical devices. In the middle is a header used in micromolding. Image courtesy of Greatbatch Inc.

Greatbatch’s Drew Richardson points out that the physics are the same when manufacturing a ½-in. screw or one that is a tenth of that size. “We’re still focusing on standard processes, but making them smaller and smaller – smaller tooling, smaller holders. Some of our success comes from just taking it back to the basics but at a microscopic level,” says Richardson, who is the firm’s manager of microcomponents.

Phillips says the real challenge is having the ability to verify the elaborate 3-D geometric close tolerance schemes that are being applied to the designs. “Today, being able to inspect the part is as challenging as manufacturing the part,” he says.

Richardson agrees: “With smaller and smaller requirements, it gets to the point: Well, how do we measure that? Normal tools don’t work to measure it.”

In the past, a shadow box illuminator or a comparator would provide the measurements needed. Today, a lot of metrology has moved to industrial video, Richardson says. “A lot of the measuring has gone to video stereoscopes. You’re able to, with XY tables, measure accurately the various geometries on that part, but we’re doing it anywhere from 40 times to 200 times magnification to be able to really see what we’re doing.”

These days, Preferred Precision (Shelton, CT) is using optical measuring devices – laser and vision scopes – rather than computerized measuring machines (CMMs). “We are using optical measuring devices so we do not mark the parts as you would with a CMM probe,” says Andrew Shufelt, manufacturing manager. “Not only do the optical devices enable us to look at any surface imperfections at up to 200-power, but we also find they are much easier and safer. This way we’re not damaging the finish on the parts as we’re checking them.”

Advances in the raw materials also are enabling manufacturers to produce microsized devices, says Michael Howe, new technologies manager for Creganna Medical Devices (Galway, Ireland and Marlborough, MA). His firm specializes in metals, extrusions, and molding for catheter shafts and subassemblies.

Smaller stents demand ever smaller delivery catheters with thinner walls, but these catheters still must have the strength that will prevent them from kinking or buckling as the physician moves them through the body’s smallest vasculatures, Howe says.

“Through research and development, we have been able to improve the mechanical properties of existing materials and to find alternative materials for catheter shafts, so that we are able to provide customers with ever smaller shafts that do not compromise on functionality,” says Howe.

More, too, is being made from nitinol, a combination of nickel and titanium. It is a `smart’ alloy in that it remembers its shape. “Nitinol is an excellent material because it has super elastic properties, but unfortunately it is quite expensive,” Howe says. Researchers at Creganna have delivered a hybrid nitinol and stainless steel welding solution for tubular components that is helping to drive down this cost.

Tighter tolerances

As parts are getting smaller, tolerances are getting tighter as well.

“Thanks to improvements in CNC [computer numerical control] technology and in lasers, we are able to hold tolerances today that five years ago we couldn’t have dreamed of,” says Peridot’s Van Sickle.

In the past, a standard tolerance was ± .005 in., Richardson says. “On today’s microsized parts, if we did ± .005, we’d have the entire geometry wipe out the part,” he says. “We’re down to .0005, even .0003.”

Designed for instruments requiring fluid-handling assemblies, the VFP17 precision dispense pump allows easy integration with valves, manifolds and other components. The machined pump head is available in various polymers, including Acrylic, Ultem, and PEEK. Photo courtesy of IDEX Health & Science.

Frank Molgano attributes the ability to hold tighter tolerances in part to advances in machine tool controls technology. He is engineering manager for new product and process development at Eastern Plastics Inc. (Bristol, CT), a unit of IDEX Corp. that specializes in precision plastic machining.

He explains that positioning drives have become more accurate. “So now we’re able to position within .0002 in., which is extremely precise. A human hair is .003 [in.], so we’re down to about 1/15th the thickness of a human hair, and there are optical machining centers that are keeping much closer tolerances than that.”

Preferred Precision just recently upgraded its equipment to hold tighter tolerances, better finish requirements, and faster turnaround times to meet today’s customer demands, Shufelt says.

Molgano says that the higher precision is a result of improvements in the structure and design of the CNC machining centers as well. Machines have become much lighter in weight, which means they can move faster and more accurately. Reducing the weight of the spindles provides greater control. “When you had a 100-lb. weight that you had to move very quickly and then stop very quickly, it required a lot of power in the motor system and rigidity in frame of the machine tool,” says Molgano. “The task is a lot easier if you can design the structure that is moving your spindle to be more efficient with less material. If you have a 10-lb. spindle, you can move and position it much quicker and stop it much faster. You still need to assure that the rigidity of your machine isn’t compromised and your whole spindle system is very accurate and precise.”

The software that controls the positioning of the spindles also has become more advanced. “If I have to accelerate something very quickly, and I have to go from 0 to 300 ft per minute, for example, I’m ramping up to that speed and I need to have sensors that tell me how quickly I am moving up to my desired speed,” says Molgano. “Then when I get there, I need to be able to stop quickly without overshooting my position. As a result, a lot of the software requirements have become more demanding, but you are able to process a lot more data in a faster period of time. The computers and electronics have become more advanced as well.”

Shufelt, of Preferred Precision, says he has found that customers are not only demanding tighter tolerances but also placing a greater emphasis on the look of the product.

“Cosmetics also have become really important to customers and surgeons today,” Shufelt says. “They want a good-looking part that still meets the specified requirements.”

Today’s customers, he says, are demanding very high mirror finishes, almost as if the parts have been chrome plated. For example, Preferred Precision is machining a part for the spinal industry where it is required to hold a tolerance of ± .0002 in. and a surface finish of 6 µin. “It looks like a mirror,” Shufelt says.

To meet the surface finishing requirements, Preferred Precision is doing 3-D contour surfacing on high-speed milling machines. “Our surfacing on our machines can go to 24,000 rpm, our feed rate is 350 in./min, and our stepover is 0.0002 to provide a better quality surface finish,” Shufelt says.

Multifunctioning parts

Eastern Plastics regularly machines long, straight, burr-free fluid channels with aspect ratios in excess of 50:1 in some materials, even 100:1. From IDEX Health & Science.

Not only are machined medical devices getting smaller, but they also are required to do more.

“There’s always a desire to put more functionality into devices,” says Howe, of Creganna.

In the catheterization lab, for example, there’s a tremendous advantage to using one device to diagnose as well as treat. “If you used one device that senses, and you have to pull it back and insert another device that treats, the patient needs to be on the table longer,” Howe says. “If you combine the sensors with treatment devices, you’re reducing the time in the cath lab for the patient.”

Another example, says Richardson of Greatbatch, is neurological devices that in the past might have had one or two leads. Now they are being built with as many as seven or eight.

The need for smaller devices with tighter tolerances and multiple capabilities has resulted in manufacturers assembling parts in one operation as opposed to multiple operations. When a process can’t be done in one operation, it is done in as few steps as possible.

Shufelt says that Preferred Precision’s turning side is using 9-axis mill-turn twin spindles. “On those machines, we’re capable of holding within ± .0001 in. and surface finish of better than 8 µin. Those machines, being twin spindle, enable us to machine parts complete to the exact customer specifications.”

Another way manufacturers have been able to increase machining throughput is to utilize multipart work-holding fixtures, rotary fixtures, pallet changers, and pallet pools. The fixtures and pallets allow for higher efficiencies by automating the loading of parts and presenting different parts to the machine. “Today, we can put multiple parts into the machine instead of working one part at a time,” says Molgano. “With multipart work-holding fixtures I can line up five, 10, [or] 15 parts in my machine. I call my first drill, and I drill all 15 parts before changing to the next tool. Then I use a rotary work-holding fixture that spins that part around automatically so that I can machine multiple sides without having to take the part out of the machine to flip it around.”

To avoid material stress, burrs, and cracking during the machining process, Eastern Plastics engineers offer design for manufacturing assistance as a crucial component of successful precision machining.

Molgano says pallet pools with automatic pallet changers permit a queue of perhaps 10 pallets of parts to be loaded. This way, an operator can walk away from the machine for hours at a time or overnight and know that the parts will be automatically presented to the machine in the proper order. When completed, the parts will be offloaded onto another pallet pool device, and the next parts are then moved forward to be machined.

“It has become much more affordable to use the pallet changers, and the work-holding devices have become much easier to incorporate as well,” Molgano says.

Schramm, of Donatelle, says manufacturers are always looking for ways to reduce costs, including labor, and automating production is a step in that direction. He says automation also helps solve another industry quandary: a shortage of qualified machinists.

Assuming compatibility of materials, a variety of components can be bonded into multilayer machined manifolds such as conductive metal elements, mixing elements, heaters, and films. From IDEX Health & Science.

The demand for multiple functioning parts is also requiring their designers to have more knowledge of different engineering sciences. In the past, medical device design engineers needed only a background in mechanical engineering. “Today, they might have to design a device that treats cardiac arrhythmias, and so they might have to put an electronics sensor in that device and thus need an electronics background,” says Howe. If they are making implants that deliver drugs, they may need to know pharmacology as well.

Engineering advances

Molgano also says that advances in CAD are helping medical device manufacturers to meet the demand for smaller, multi-functioning parts with tighter tolerances.

Design engineers are taking advantage of finite element analysis (FEA) software, a very popular tool that has become a lot more affordable and is more easily integrated into standard CAD or drawing packages, Molgano says. In the past, such analysis would require separate computer programs that necessitated a specialist’s knowledge and a strong materials background to be able to use them. These days, he says, the programs produce 3-D objects that can be easily rotated on the computer screen and tested to see what the best materials for the device would be.

Design of experiment (DOE) software is also helping to optimize part design for functions, Molgano says. “What this does is it takes in multiple variables and looks at their different outcomes in a part’s performance and helps optimize what the best characteristics are. It will tell me whether I might need a very thick wall with a low-strength plastic or a much thinner wall with a higher strength plastic, and what would be the advantages or disadvantages to such a tradeoff.

“Using DOE software, I can look at multiple design input variables and evaluate their outputs and then optimize my design by picking the proper materials for features and size,” Molgano says. “Like FEA software, DOE software has become much easier to use and has a much friendlier interface.”

Beth W. Orenstein is a freelance writer based in Northampton, PA.