This technical information has been contributed by
Triangle Precision Industries, Inc.

Click on Company Name for a Detailed Profile

Medical Parts Are Machined in One Setup Using CAM Software Package

Precision CNC MachiningPrecision CNC Machining

A diversified, Ohio-based machine shop, named 2005 Supplier of the Year by a major medical/surgical manufacturer, avoids all manual handling while using a CAM mill/turn package to machine all sides of a part in a single setup.

Triangle Precision Industries, Inc. has achieved a long-sought milestone in manufacturing, true art-to-part production with one set-up. Triangle is doing this in medical implants where tight tolerances and the insistence by surgeons on delicate, flawless surfaces favors the maximizing of CAD-to-CAM automation in what, for want of a better term, could be called hands-off machining.

At Kettering, Ohio-based Triangle Precision, geometry sent in by medical supply companies, surgical hospitals, and research institutions is readied for machining with virtually no changes in a computer-aided machining (CAM) software package, EdgeCAM from Pathtrace Systems Inc. EdgeCAM is then used to program machining operations to avoid all manual handling—all sides of the part are machined in a single setup.

At Triangle, this is done by programmer Bryan Hunt on computer numerically controlled (CNC) machines with integrated milling and drilling capabilities on additional spindles. Known as mill-turn machines, they can be programmed as either 3-axis mills or 2- or 4-axis turning centers, or both.

EdgeCAM was chosen in part for its pioneering developments in programming mill-turns, which have up to nine axes to be coordinated, and for fully automated programming, otherwise known as machining from the solid. Together, they add up to hands-off machining.

Mill-turn machines are relatively costly, however, and hands-off machining is one good way to make them pay off—integrating turning and milling in a single setup. EdgeCAM handles this with its Mill/Turn package. Triangle's mill-turn machines are a Mori-Seiki SL253BMC and a Star Turn SR20.

Hunt said that most of his mill-turn jobs are programmed quickly, starting with the solid. "EdgeCAM Mill/Turn is very easy to use. Solid machining is strongest in round parts and it is very quick to set up the part, right on the centerline, oriented to the machine tool's axes," he added.

Tolerances on critical surfaces of surgical parts are 0.001-inch, which results in shiny finishes that surgeons insist on. For parts with staggered fits, tolerances get as tight as three-tenths or 0.0003 inch. Staggered fits are an error-prevention technique that is used to ensure parts can be assembled only one way. EdgeCAM programs those with no special effort.

Triangle Precision was named 2005 Supplier of the Year by its biggest medical / surgical customer, whose products include implants and instruments for hips, knees, shoulders, elbows, wrists, hands, and feet. Orders are often for a complete package of surgical hardware, assemblies, and instruments.

The medical business, along with machining of aerospace parts, is central to Triangle Precision's diversification. About a fourth of Triangle's business consists of implants, plus fittings such as screws and staples, cut guides, and cut-guide fixtures. At one time, a large portion of Triangle's business was machining special printing heads. Some of that work has gone overseas, triggering Triangle's diversification and search for new markets.

The transition to medical and aerospace has led in recent years to a substantial upgrade in capabilities for this 50-man shop that has been in business 25 years. Triangle's owners, Gerald Schriml and Paul Holzinger, are themselves highly experienced modelmakers.

PROBLEM: Taking Jobs Other Shops Turn Down
Hunt's biggest challenge stems from Triangle Precision's preference for jobs that other shops refuse to quote. In exchange for less price competition, Triangle takes on tougher technical challenges.

Most jobs are prismatic and relatively simple to program and machine. In contrast, most of the new medical and aerospace work has compound surfaces that are curved in two directions, like saddles, and organic surfaces, as in implants, that are entirely freeform. This work is common in the aerospace and medical industries.

A major challenge in medical work is the attainment of visually perfect surfaces. Because of the ever-present risk of infection, surgeons reject any implant or cut guide with any visible flaw, regardless of specifications and tolerances. "Because surgeons will reject anything that might harbor an infection, the aesthetics of the implants are life-and-death to us," Hunt said.

Many surface flaws are the result of rough handling between machining setups. At Triangle Precision, the avoidance of dings in delicate finishes was a major justification for the mill-turns. They can rough- and finish-machine every surface of a part in a single setup, eliminating most of the part handling previously required.

In aerospace work, inspectors won't accept even the smallest deviation from precisely defined surfaces. Many shops avoid these markets because they regard these rejections as arbitrary. "We have very tough quality-control people here who look for imperfections in machined surfaces," he noted. "This type of support is why we can do jobs that other shops won't quote."

Both kinds of surfaces put tough technical demands on tooling, fixtures, and programming. Those demands are compounded by the business necessity of keeping machine tools running flat out and the predominance of short runs and prototypes. Most "production" orders are five to 80 pieces, said Hunt, while orders for prototypes are usually half a dozen pieces. "Some prototype jobs have more pieces than production jobs," he added. Very few job orders reach three figures at Triangle.

Deadlines are tight and engineering changes are frequent. Hunt praises EdgeCAM for handling changes in a matter of minutes. "We are able to reprogram so quickly and so accurately that there is no need to treat prototype and production jobs differently," he said.

SOLUTION: Zeroing in on Geometry
The big differentiator between print heads and the medical and aerospace businesses is curves. Print heads had few if any curves, but the new work often seems to be nothing but. To deal with this, Triangle has six EdgeCAM seats. Four are networked and drive the three mill-turn machines, plus 14 machining centers, a laser cutter, and seven EDMs. The other two EdgeCAM seats are dedicated to the tool- and die-makers.

Also packed into Triangle's 24,000-square-foot shop are 18 Bridgeport milling machines, four surface grinders, welders, riveters, saws, a blast-cleaner, and a deburrer. In addition, the company uses presses, shears, and press brakes for sheet metal fabrication. Triangle also has a well-equipped inspection department with coordinate measuring machines (CMMs). The company's expertise with a variety of manufacturing technology has helped put Triangle Precision in the enviable position of being able to provide complete parts-making services. See Triangle Precision Industries, Inc.

In his multi-axis mill-turn work, Hunt opens EdgeCAM from within SolidWorks from Dassault Systemes. This eliminates "importing" and "exporting" of product geometry and the (small) risk of a translator error. As he gets ready to machine medical parts, Hunt opens EdgeCAM from within SolidWorks using the SolidWorks toolbar. Then, working in EdgeCAM, he lays toolpaths over the solid model, and finally post-processes the job to the specific machine tool.

RESULTS: Mill-Turns and Simulation
Simulations with EdgeCAM help Hunt determine whether a job can be run on one of the mill-turn machines rather than on a machining center. For starters, the mill-turn jobs must be done with no more than 10 tools (not a limit for mill-turn machines in general), the most that can be mounted in the particular machines that Triangle uses. That means parts like implant cap screws, rods, pins, and fasteners with special threads. Many have special head configurations with buttons and knurled knobs that mill-turn machines handle well. Triangle's mill-turns also produce surgical drive wrenches that have one end turned and the other milled.

Hunt machines small surgical staples on a Star Swiss-turn because the specified material, a low vacuum melt (LVM) grade of stainless steel, is available only in round stock. It made more sense to use one of the mill-turns since they are equipped with bar feeders. Producing the staples on a machining center would have meant sawing the LVM stainless into blanks, wasting much of the steel.

The geometrically more complex parts, like surgical cut guides and most implants, go to one of the 14 machining centers.

BENFITS: More Business in a Competitive Market
To Hunt, the overall benefit of using EdgeCAM is more business in a market that grows more competitive every year. "We get a lot more work now because EdgeCAM helps us cut costs and be more competitive,"said Hunt, adding that "short-run machining and prototyping are very competitive."

At Triangle Precision, the benefits include enhancing and accelerating the diversification away from the printing / graphics business, and doing a better job of serving other, longtime customers such as with high-precision, short-run, fast-turnaround work. Another benefit is supporting the ongoing business transformation to "single-sourcing." At Triangle, that means almost any conceivable metalworking operation can be done in-house. The benefit is that customers no longer have to worry about what is happening to their parts as they are moved from one specialized shop to another.

Following the success of Triangle Precision, other shops are attempting to master the intricacies of medical / surgical and aerospace markets, or hire the skills needed. They're also looking to invest, as Triangle has, in machining innovations like mill-turn and trunnions that save time, lower costs, and boost quality. And while that adds challenges for innovation leaders like Triangle, it helps keep high-paying manufacturing jobs in Ohio and surrounding Midwestern states that are undergoing their own diversifications and reducing their dependence on the Big Three Automakers.

For more information on EdgeCAM software from Pathtrace Systems, visit www.edgecam.com.

This technical information has been contributed by
Triangle Precision Industries, Inc.

Click on Company Name for a Detailed Profile

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