February 2007 Edition

MEDICAL MANUFACURING

A San Diego Medical Firm Prototypes With a ‘Personal’ CNC Machine

Just as the PC brought affordable computing to the individual level, a medical development company takes advantage of the “small” CNC machine on the market

Technological factors often converge that make advances inevitable. In the 1930s, six teams – each operating without the knowledge of the others – were developing concepts of the gas turbine engine: three in Germany, two in England and one in Hungary. Frank Whittle in England and Hans Von Ohain in Germany both brought aviation into the jet age. Technology followers often call it “railroad time.” When the time and technologies are right, advances like railroading will result whether George Stephenson is around to invent it or not.

In the same vein, the technological advances in small computers and software have had an effect on machine tools used for prototyping.

“We’re really talking about two different developments which have combined to bring useful 3D machining within reach of the average Joe,” Mike Ko, senior product development engineer, KFx Medical Corp., said.

“Both the hardware and the software have been dropping in price and rising in capability, ease-of-use, and quality. On the hardware side, development of the Tormach PCNC machine is one of the fi rst small capable and affordable CNC machines.”

Frayed Cuffs
Ko knows do-it-yourself production from recent experience. The San Diego-based KFx Medical is a venture-capital startup founded in 2003 to develop clinically relevant solutions to rotator cuff disease with a new approach for rotator cuff orthopedic surgery.

Torn rotator cuffs alone account for more than 500,000 surgeries a year and have traditionally required many weeks of rehabilitation.

Minimally-invasive surgical repair techniques provide patients with less pain and reduce time until range of motion is restored, but require surgeons to have advanced videoscopic skills.

KFx Medical is researching alternatives that provide less invasive systems for the surgeon, while at the same time provide a more anatomical-like repair for the patient that provide clinical outcomes. More than four million people seek medical advice each year due to shoulder pain. KFx Medical is a privately held company.

The company’s new surgical technique, SutureCross Knotless Anatomic Fixation, involves less complex and stronger tissue fasteners and does not require suture knots.

To realize the fixtures and application instruments from the virtual realm of CAD to real testable prototypes, Ko and the KFx development team, themselves, did the precision cutting. The company invested in a Tormach PCNC 1100, a lightweight mill simple enough to be operated by non-machinists for short runs.

In-house Prototyping
By keeping multiple iterations of the prototype designs in-house, KFx Medical avoided the costs and delays of outsourcing parts for CNC machining.

Ko said KFx Medical would have to spend at least three times as much money to get the quality and capability the firm got from creating prototypes in-house.

With the CNC machine tool from Tormach, Waunakee, WI, at its disposal, KFx Medical cuts its own prototype and preproduction components out of plastic, aluminum, and stainless steel. Even 420 stainless steel injection mold cavities were cut in-house in a matter of days rather than the weeks typically quoted by an outside vendor, without the need to hire an experienced CNC programmer or machinist.

“We were even able to use the 4thaxis rotary capability of the machine to fabricate prototype 316SS bone screws with a variety of tapering spiral thread designs,” Ko said.

In recent years, the price of CAD and 3D modeling software has brought the technology within reach of individual designers, entrepreneurs, and hobbyists. Last decade’s rapid prototyping and 3D printers permitted plastic replica fabricating in the design studio – rather than the shop floor – for testing the fit of parts and assemblies before actual prototypes begin. But, the final step of moving from idea to product – creating a physical prototype from actual materials – still belonged in the industrial realm.

CNC machining not only involved expensive equipment, it required expertise, including the knowledge of G-code and M-code, user-unfriendly machine languages. As the development of the “Personal CNC” follows the development history of the personal computer, the trend continues. What was once industrial now becomes individual.

All in the Code
“The software and hardware have become so capable, that a person can learn machine tool programming and then afford the tools necessary to go from the initial concept, to the virtual model, to the fabricated physical part,” Ko said, “without the need for a skilled CNC programmer or a skilled CNC operator.”

The term “Personal CNC” – coined by Tormach CEO Greg Jackson – describes the new Tormach mill used by KFx Medical. The term correlates to the first personal computers that shrunk in size and price to become practical tools for individuals. Jackson and the Tormach development team spent three years working with high-quality machine tool manufacturers to reach their goal. They created a small precision CNC machine that meets the needs of short-run production at the lowest possible cost.

“Like a personal computer, the first rule is that it must be affordable,” Jackson said.

The Tormach PCNC 1100 retails around $6,800, and comes with a standard 34"×9.5" table and 17" vertical clearance. It cuts iron, steel, titanium, and chromium alloys, such as 300 or 400 series stainless.

To make the Tormach affordable, the design concedes spindle power and speed. It takes a few minutes longer to cut a precise part on the Tormach machine than larger industrial machines. But, it also makes the machines suitable for short production runs, research and development prototyping, business start-ups, machining instruction, and hobby applications, rather than high volume manufacturing.

Large Volume Ludicrousness
“A 1.5 hp CNC mill with 65 ipm rapids is ludicrous in a large volume production environment where minutes per piece are crucial,” Jackson said. “However, in a prototype environment, where run time is a tiny fraction of setup time, those extra minutes per part aren’t relevant. What is relevant is the cost savings.”

The design leverages the mass of the machine against the surface cutting speed, creating a careful trade-off between speed and weight. The PCNC 1100 used by KFx weighs in at just more than 1,000 lb – lightweight compared to the normal 5,000 lb or more for a CNC machine.

“If you only have a thousand pounds of iron to work with, it does not make sense to put a lot of it in a supporting base,” Jackson said.

Like the personal computer, as compared to its room-sized predecessors, a personal CNC needs to be easy to move, easy to learn, and easy to maintain, according to Jackson.

The PCNC 1100 uses open architecture. The PC and Windows control computer, G-codes and M-code commands, drawing and image file support, spindle taper, machine dimensions, and the electrical interferences are all industry standard.

One of the most challenging research and development tasks for KFx Medical’s new suture system was the ergonomics of the tool’s plastic handle.

Proper Instruments
“Like all hand instruments, the device had to have the proper feel in the surgeon’s hands,” Ko said. “To find this elusive feel, numerous full-size handle prototype variations needed to be made and put into the hands of the surgical advisory board members.

“The design variants were comprised of blended compound curves and surfaces, to create an functional and comfortable handle. The current pallet of high-tech rapid prototyping methods could accurately reproduce the required shapes of the handles, but not in materials that would stand up to the rigors required of an orthopedic device. Contract machine shops could machine the handles out of suitably robust materials, but usually required a four to five-week lead time for delivery.”

KFx Medical’s solution was to fabricate the handle models in-house. According to Ko, it would be difficult for a machinist to create the compound shapes on a manual-milling machine. In-house production with standard CNC machines would be costly.

“Most entry-level machines cost $30,000, plus the wage of a skilled CNC programmer and machinist,” Ko said.

Such an investment was out of the reach of a small company such as KFx.

“With the Tormach and the current suite of 3D solid modeling and CAM software, we are able to go from a 3D CAD solid model to a machined handle component in one day, and to a completed, fully-functional handle assembly in one week,” Ko said.

Iteration Control
“Using the personal CNC machine did not require a highly-trained CNC operator. The time and costs were even less for the fabrication of the second, third, and tertiary iterations of the same handle design, since all of the previous work was stored in a readily recallable Computer Aided Machining – CAM – program,” Ko said.

The confluence of the “individual” CNC machine hardware at the same time advances in design and manufacturing software made do-it-yourself machining a practical option for KFx; it was “railroading” time. CAM converts CAD files to G-code, instructions recognized by the CNC equipment.

“The new CAM software makes it unnecessary for the machinist to have significant experience with G-code in order to cut a sculpted 3-D part,” Ko said. “It actually creates the G-code.”

He uses FlashCut, Visual Mill, and DeskProto for G-code generation. “These CAM programs are powerful, and simple,” he said.

KFx used the high-end SolidWorks 2006 software for its 3D MCAD, but Ko said that the same design and prototype project could be easily done with the same quality in the less expensive Alibre Design software suite.

“I use Alibre Design Professional for my personal consulting business, which is much, much cheaper than Solidworks, and is fully capable solid modeler,” he said.

Other convergences in technology promise advancements in the small shop and prototyping environments.

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