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There are usually many ways of machining a part, but nothing beats using precisely the right machine tool for a job. And for most of the same reasons, nothing beats having precisely the right programming software for that machine tool. That's the lesson that Turbine Fuel Technologies (West Des Moines, Iowa), a division of Goodrich Corp.'s Engine and Safety Systems Group, learned when it began adding CNC multitasking machines to its collection of conventional CNC lathes and machining centers.
Turbine Fuel Technologies (TFT) makes fuel nozzles and other fuel system-related components for turbofan, turboprop, turboshaft and stationary turbine engines. It made the jet fuel nozzles for the engines of the turboprop commuter plane that took this editor to and from TFT's headquarters and prototype development facility in West Des Moines for the information for this article.
The word nozzle prompts images of the familiar two-piece brass nozzle usually found at the business end of a garden hose. Nozzles for aircraft engines are a bit more complicated. "There are six to 20 parts in a jet fuel nozzle," explains Greg Helton, advanced development programmer/machinist. "And up to 24 nozzles in a given engine, so there are a lot of piece parts to be made. The parts range from 0.1 pound to 1 pound and from 1 to 4 inches in length, and are made of Inconel, Hastelloy, Stellites and other exotic metals capable of withstanding the operating temperatures in excess of 1,000° F ."
Nozzles are designed for specific applications, and they require unusually close collaboration between TFT and its customers—companies such as Alstom, General Electric, Honeywell, Kawasaki Heavy Industries, Pratt & Whitney, Rolls Royce and other jet engine builders. The process begins with a CAD solid model containing the starting part geometry from TFT's engineering department. The solid model is imported into GibbsCAM as the basis for machining programs for initial prototypes. Parts undergo testing on equipment at TFT, designs are modified based on the results, and revised parts are made for further testing.
"Parts can go through many iterations, involving changes in hole/slot location, hole/slot angles, offset changes . . . even actual burner rig tests as we get close to a final design," explains Joel Sheldon, manager, engineering laboratory. "The purpose of all that testing is to find the optimal nozzle design—in terms of reliability, fuel economy and other critical criteria—for the customer's application."
Until recently, every time a design change was made to a prototype nozzle part, the shop would make a new batch of revised parts (20 or so pieces) for further testing. Making the parts involved machining them in multiple operations on three or four conventional CNC lathes and machining centers. The process was wasteful (frequently the design changed before the latest batch was used up), created opportunities for error because of the numerous setups and handlings for the various machining operations, and perhaps most serious, was time-consuming.
A Big Change
All of that changed when Goodrich Corp. approved a request from TFT to purchase a Model G200 turn/mill center from Index Corp. (Noblesville, Indiana). The G200 (shown at left) is a twin-spindle, twin-turret CNC machine. Its main spindle and counter-spindle are directly opposed and identical. A top turret is located above and between the two spindles and is mounted on an inclined bed. It holds up to 14 tools, which can be any combination of turning and rotary tools. The turret moves in an additional Y axis and a B axis to provide inclined, off-center drilling and milling capabilities. Also, the tools mounted on the top turret can be used to machine the part held in the counter-spindle simply by rotating the main turret 180 degrees.
An additional heavy milling spindle at the back of the main turret accommodates large milling cutters for heavy-duty milling operations. It is served by a six-tool toolchanger.
A bottom turret is located between and below the main spindle and counter-spindle. It also holds 14 turning or rotary tools in any combination and can be used to machine parts in the main spindle and counter spindle.
TFT purchased one G200 for the prototyping facility in West Des Moines and four more for its production plant located approximately 100 miles away in Carroll, Iowa. The initial strategy was that the West Des Moines machine would be used to develop prototypes. Once the design was finalized, the most efficient machining program for the part would be developed (by TFT's Mr. Helton) for use on the production machines at Carroll.
Since 1994, TFT had been using GibbsCAM computer-aided manufacturing software, made by Gibbs and Associates (Moorpark, California), to program the prototyping facility's conventional CNC lathe and machining centers. The software was more than adequate for the shop's more conventional two- and three-axis lathes and four-axis mills—even for one of the shop's newer acquisitions, a five-axis machining center. However, it did not meet the programming needs of the shop's newly acquired multitasking machines.
Mr. Helton was reluctant to abandon GibbsCAM for another programming software, so he looked for ways to build on his existing platform. He went to an outside source, who wrote five separate custom post processors for the Index G200 to cover the movements of the top turret and main spindle, the top turret and counter-spindle, the bottom turret and main spindle, the bottom turret and counter-spindle, and the B axis.
"We ordered a custom post for every conceivable machine combination," Mr. Helton explains. "That enabled us to use our existing programming software with the five post processors as needed for a particular job."
The arrangement was far from perfect, however, particularly when it came to balancing the operations assigned to the main spindle and counter-spindle: "We would write the program, then have to go out on the plant floor to view a dry run in order to find all of the non-machining times. Then we would go back and start editing the program with the five different posts to balance the machining operations."
Mr. Helton's programming woes eased considerably about a year ago, when Gibbs and Associates announced a new programming module called MTM (for Multi-Task Machining), developed expressly for multitasking machines. "Controlling multiple tools across one or more spindles at one time introduces a whole new level of complexity to programming, especially if you want to create efficient programs," explains Bill Gibbs, president of Gibbs and Associates. Most CAM software can handle only one process flow (sequence of machining operations) at a time, for example, turning a cylindrical blank in a chuck or drilling and tapping a prismatic workpiece on a machining center. Because of its process modeling orientation, extending GibbsCAM to support multiple flows was fairly straightforward, Mr. Gibbs adds.
The MTM module addresses synchronizing multiple tools through its Sync Manager, a new interface added to GibbsCAM's graphical user-interface environment. The Sync Manager allows multiple process flows to be displayed alongside of and relative to each other (photo on page 42) to facilitate setting synchronization points. It also takes into account dominant tooling and automatically adjusts operation durations based on which tooling controls the spindle speed—yet another level of detail programmers would normally have to contend with.
The Sync Manager handles the time-dependent aspects of the program, all of the details that are introduced when multiple tool groups are cutting simultaneously. Using the multitask machine programming module, operations can be moved around in the overall flow to minimize non-cutting time. At any point in time while developing the machining program, the machining process can be graphically simulated and visually reviewed. The programmed machining operations can be simulated using GibbsCAM's cut part rendering capabilities, as shown in the sequence of screen images in the sidebar at right.
Before, TFT's Mr. Helton had to wrestle with a handful of custom posts to balance and optimize machining programs for the Index machine. The MTM programming module that he currently uses has made programming considerably easier since it is set up specifically for his machine, from the exact machine configuration to the machine-specific post processor used to generate the (edit-free) machine-specific NC code.
"With the MTM software, I can balance the part with Sync Manager without having to go out to the machine," Mr. Helton explains. "It generates the code and inserts waits in the appropriate places to avoid collisions. I don't have to worry about the top turret colliding with the bottom turret because they're both trying to do something on the same spindle at the same time."
By producing parts in one setup on the Index multitasking machines, TFT has cut machining time in half on a number of parts. Work-in-process, represented by queues of parts at various conventional CNC machine tools, has been eliminated. Part quality has improved since the multiple setups and handlings that characterized production in the past have been eliminated. Also, there are fewer disruptions to the production schedule because of problems with one of the machines needed for production.
A New Role
One of the responsibilities of TFT's West Des Moines facility is to provide support for the Carroll production plant. When the Index machines were installed at Carroll about 3 years ago, the support included doing all of the programming. About 18 months ago, however, Carroll began to program parts on its own, allowing the West Des Moines facility to devote more attention to improving its prototyping activities.
"Shifting some of the part programming to Carroll has enabled us to focus more on development work," Mr. Helton stresses. "We're becoming more of a prototype development shop, primarily involved in working with design engineers and performance engineers instead of simply providing support for a production facility.
"We're using our Index machine and the MTM programming software as development tools for the new products that we design and fabricate here in the prototype shop," Mr. Helton continues. "Instead of making a batch of prototypes in three or four operations on as many different machines as we did before, we can machine them completely on the Index. If an engineer makes a design change to the part, we can quickly make the necessary changes in the program using the MTM software and provide revised parts much faster than before. Our new tools also have enabled us to eliminate the trays of prototype parts made by the former method that we scrapped with every design change."
Another advantage of the prototype facility's new hardware and software is being able to produce virtually any design from bar stock. Many of MTM's production parts are machined from castings or forgings. However, the prototype shop machines its parts from bar stock exclusively.
At Carroll, production parts can also be machined from bar stock. Doing so eliminates the delay associated with ordering the castings as well as such problems as fluctuating price and uncertain delivery. By making the parts from bar stock, TFT maintains better control of the process. It also increases the company's production flexibility. TFT can get into production with parts machined from bar stock long before cast or forged blanks start flowing from the supplier.
Case in point is the part shown in the accompanying photos and depicted in the sequence of screen images shown in the accompanying sidebar. The prototype facility machines a length of 4-inch-diameter, 347-alloy stainless steel bar into a shape that approximates the forging from which the production part will be machined. In the process, an 18-pound length of bar stock will be reduced to the angular part shown, which weighs just over ½ pound.
The mock forging, which TFT refers to as a hog-out, is not a nozzle part, but it is representative of some of the milling intensive parts that go across the prototype facility's Index multitasking machine. "We have jobs that require 28 or 29 tools, of which only two will be turning tools—the rest are live tools for drilling, tapping, milling and so forth," Mr. Helton explains.
A Seat For Carroll
TFT is pleased with the advantages that its multitasking machines have provided to both its prototyping and production facilities. The company was able to justify their purchase on the basis that it would be able to halve the cycle time of any part previously produced on its conventional CNC lathes and machining centers. Adding the MTM software provided a way to optimize the part programming for those machines as a way of ensuring their performance. TFT needed programming software that would enable it to exploit the full capabilities of its multitasking machines, and proof that the GibbsCAM MTM module filled the bill can be seen from the fact that the company will soon be ordering another seat of MTM for the Carroll production facility.