March 2010 / Volume 62 / Issue 3|
By Bill Kennedy
| Custom tools tackle complex aerospace applications.
As machined parts become more complex, require tighter tolerances and have higher value, the tools and processes to make them must become more sophisticated.
Aerospace components are a good example. Requirements for reliability, efficiency and performance drive aerospace part manufacturers to make them stronger, lighter and more precise, while employing advanced workpiece materials. In addition, aerospace parts are typically produced in small volumes, often from proprietary designs. Accordingly, the processes and the tools to make the parts are, in many cases, customized to their applications. According to various estimates, 75 percent or more of the tools used in certain aerospace manufacturing operations are specials.
Courtesy of B. Kennedy
What exactly determines if a tool is a special is a matter for discussion. A custom tool can be an endmill with minimally altered geometries or a one-of-a-kind, massive milling cutter that starts as a blank CAD screen. Andrew Gilpin, business development manager for toolmaker Amamco Tool, Duncan, S.C., said his basic definition of a custom tool is “anything other than a traditional standard endmill or jobber length drill. You take a regular 4-flute endmill, put a 15.5mm radius on the corner, and that becomes a custom.” However, that simple definition can change.
An example would be the compression routers Amamco produces for trimming the edges of the carbon fiber-reinforced plastics applied in aerospace parts. The tools have separate sets of left- and right-hand flutes that overlap to push and then cut the composite layers cleanly.
When developing compression routers for aerospace manufacturers, Gilpin said, “The tools are definitely custom designs all the way through the R&D and the tweaking phase of the part manufacturing process. But when the aircraft goes into production, and the manufacturer starts buying the tools in mass quantities, then it’s no longer a custom tool to us; it’s a ‘standard custom tool,’ if you will.”
Even when produced in large quantities, custom tools lack the economy of scale characteristic of standard tools. John Aiello, a business development specialist and aerospace industry veteran with experience in both cutting tool manufacturing and distribution, said a part maker’s willingness to pay a premium and take advantage of specials depends largely on the shop culture.
“Standard tooling is cheaper, but there is value in the more expensive custom tools; they offer more capability,” he said. “If a shop uses the custom tools properly, their productivity can go way up and their profits can go way up too.” With many operations reluctant to make large capital purchases, a custom tool may enable a shop to increase productivity without purchasing new equipment.Convenient vs. Custom
Convenience or complacency may also affect a shop’s decision to employ specials. Peter Diamantis, Amamco plant manager, said some shops try to make do with tools that are not customized, or optimized, for a particular operation. “They will have headaches with them, but the tools are readily available and they don’t have to wait 4 to 5 weeks to get them.”
Courtesy of Greenleaf
He pointed out that large aerospace manufacturers regularly use custom drills because they generally provide longer tool life and better hole quality, and the cost of reworking out-of-spec holes can easily exceed the custom tools’ cost. Those manufacturers plan months ahead in most cases.
However, according to Diamantis, other shops serving the aerospace industry are not as proactive with inventory. A shop may deplete its supply of a certain diameter custom drill and then rush to find a standard drill in that diameter. “They will put it out there and let the machine operator fight it because it’s convenient.”
Planning ahead can produce multiple benefits. Diamantis cited a shop that was machining a stainless steel missile component, which included drilling, reaming, counterboring and chamfering a hole with four different tools. Amamco designed and made a multifunction tool to handle all four steps in one pass. “Cycle time went from 5 minutes down to about 1½ minutes, and they don’t have to keep four different tools in inventory,” Diamantis said. The trade-off is that the shop now has to order the tools 4 weeks in advance.
While specials do require longer lead times, they help shops avoid production problems, according to Don Hughes, applications and project development engineer for toolmaker Greenleaf Corp., Saegertown, Pa. “We have witnessed instances where, due to time constraints, customers have had to dramatically alter a standard tool on their own to begin prototype production,” he said.
Courtesy of AMEC
While the modified tool may be able to machine the prototype parts, it may not work the best, and may result in an unstable condition with a longer cycle time. In many of those cases, Hughes said, Greenleaf can analyze the application and engineer a special with the rigidity necessary for increased metal-removal rates and reliability, often utilizing Greenleaf’s WG300 or WG600 ceramic inserts or one of the company’s high-performance coated carbide grades. “We can focus on the problem features, or we can be called in at the very earliest stages of process planning,” he said. “In general, we like to be called in early so we can develop a tool layout.”
Greenleaf develops the layouts by gathering machine, part and fixturing information from the customer. Greenleaf’s design engineering department then reviews the company’s database of proven concepts for industry- similar features. Tool layouts often include multiple sheets to illustrate all the standard and special tool bodies and inserts necessary to machine various part features. “Tool layouts are a great way to communicate and brainstorm ideas back and forth between Greenleaf and our customers,” Hughes said.Custom Timeline
Time pressures involved in the development of custom tools generally depend on when the toolmaker gets involved, according to Rob Brown, product manager at toolmaker Allied Machine & Engineering Corp., Dover, Ohio. “If you are working with the manufacturer’s R&D lab in developing the process itself, you have more time because that process has not yet been released to the floor,” he said. “But once the process has been released to the floor, they have parts to make.”
After that, the time availability “goes the other way—if they have a problem, they need a quick answer,” he said. “Then you are rushing because they have to stop production until they get the tools they need to move forward.” In problem- solving cases where tooling from another company may be involved, a toolmaker must adapt its tools to established setups, Brown noted. As for introducing custom tools for productivity improvements, he said, “Quite honestly, if they are not having problems, we can preach that we can make the hole faster but they are probably not real interested because of the issues involved in approving process changes.” After a process is approved and running, it’s locked in and manufacturers are reluctant to experiment with new tools.
Courtesy of Kennametal
Custom tool design may involve an amalgamation of several different standard products. Brown said AMEC has produced custom variations of its Gen2-TA and Gen3sys tools for the aerospace industry, involving coating and substrate changes as well as advanced geometry.
In some cases, a custom tool may be the only way to produce a complex aerospace part, according to Mark Huston, vice president, engineered solutions for toolmaker Kennametal Inc., Latrobe, Pa. For example, an aerospace manufacturer required an extended-shank milling cutter to reach around a flange and mill underneath it. The initial design’s long tool length and high forces in the cut combined to produce uncontrolled vibration. Kennametal was tasked with producing a “tunable” milling cutter assembly. In a tunable tool, a mass on the assembly’s front end is suspended between two elastomers, which can be adjusted to provide different dampening levels.
“You put the tool at the extension at which it will operate and tune it at that length-to-diameter ratio to make it dynamically stable,” Huston said. Tuning consists of striking the tool assembly with a special instrumented hammer and adjusting the dampening until unwanted vibrations are eliminated. “It works whether you are an inch into the part or 13 ' into the part because you tune the dynamics of the overhanging mass,” he said. The tunable tool solved the vibration problem.Customs Standardized
Aerospace manufacturers can also benefit from a new approach to the idea of custom tools, according to Chris Mills, U.S. senior project manager of aerospace development for toolmaker Sandvik Coromant Co., Fair Lawn, N.J. “Our goal has been to shrink the requirement for specials in aerospace,” he said. “Because special tools are more expensive than standards and have longer lead times, customers don’t like specials.” There’s also the pioneer factor to consider: a special, by its nature, hasn’t been subject to the extensive field development of a standard, so the user is the first one to test it.
Courtesy of Sandvik Coromant
One solution is a group of products Mills calls “industry-specific” standards. Sandvik Coromant analyzed typical aerospace components and created a list of common machining features. “The same feature may appear on different parts, so we pulled out dedicated concepts for aerospace,” Mills said. He used the company’s SL70 system as an example. “We found there was a very high requirement for specials in profile turning of large diameters with deep pockets. The SL70 system’s modular blades accept ceramic, round carbide and CoroCut grooving tools and “all these blades fit on the same adapter, and they have clearance for face grooving and internal machining, so they can go in any orientation. With a relatively small program, we’ve covered a wide range of applications; the grade and the geometry are dedicated standards for aerospace,” he said. The inserts, toolholders and adapters are standard items, available for next-day delivery compared to a 10-week lead time for a special. Industry-specific standards are also free of the exclusivity restrictions common with tools customized for one manufacturer.
Mills said an increase in the number of standard tools available for aerospace applications will benefit manufacturers. “For too long the aerospace industry has not demanded standard tools. It is a huge industry and the more they can standardize, the better they can cope with the increased volumes anticipated for the future.” CTE
About the Author: Bill Kennedy, based in Latrobe, Pa., is contributing editor for Cutting Tool Engineering. He has an extensive background as a technical writer. Contact him at (724) 537-6182 or by e-mail at email@example.com.
Courtesy of Janicki
One and done holemaking
Sedro-Woolley, Wash., began as a developer and producer of large, 5-axis machine tools and applied them to manufacture large tooling for boat hulls. It then began providing machining services for other industries, including aerospace. Its machining capability includes 5-axis milling that can hold 0.003 " tolerances over the entire length of its 100 ' work envelope.
Today, Janicki Industries develops and manufactures tooling for manufacturing composite parts for projects that include NASA spacecraft, the Boeing 787 and the Lockheed Martin F-35 Lightning II. Janicki has also delved into part production in support of similar programs.
“Right now, working with Amamco Tools, we are tackling drilling and trimming composite panels for the F-35,” said Eric Friesen, program manager. “The autoclaved, cured, high-performance carbon fiber laminates are strong and difficult to cut. Lockheed Martin, Amamco and Janicki have worked closely to optimize the tooling.”
Holemaking gets special emphasis because Janicki drills thousands of holes in composites daily. Diameters range from about 0.125 " to 0.500 ", with tolerances of a few thousandths of an inch. Considering the high volume, Friesen said, “If we have to touch each hole twice, that’s huge. We have been reluctant to use piloting or drill/ream, even in the case of countersunk holes.”
To minimize tool changes, Amamco develops unique multifunction holemaking tools for Janicki. Friesen described a drill-countersink for an application where “we have to control the diameter of the hole, the angle and depth of the countersink and the concentricity of all of the above to tight tolerances.” The drill-countersink Amamco engineered for the application enables Janicki to “drill a countersunk hole in one shot, where every aspect of it is controlled to within less than 0.002 ". It’s what we’ve got to have. Drilling a thousand holes a day, one shot has been a pretty firm mandate from the beginning, and we have been able to hold to it.”
Courtesy of OSG
Getting to the point
is always changing, the need for precise holemaking remains the same. “Everything in an airplane—the wings, fuselage, tail sections—has holes for fasteners, which, of course, must be drilled,” said Drew Strauchen, vice president of engineering and marketing for toolmaker OSG Tap & Die Inc., Glendale Heights, Ill. For holemaking in carbon fiber-reinforced plastics (CFRP), OSG typically provides tools in diameters ranging from about 0.050 " to 0.500 ", coated with OSG’s CVD diamond to maximize tool life in the abrasive materials. The coatings vary in thickness from about 8µm to 12µm, depending on the application and the tool size.
OSG fine-tunes geometries to the material being drilled. “Generally, we work with the end user to figure out their modes of failure and their criteria for a particular hole,” Strauchen said. “It really depends on what kind of CFRP it is, the directionality of the layered fibers and how the resin has been applied.” If the CFRP is backed with another material, such as titanium or aluminum, a compromise between geometries best suited for each material may be required.
According to Strauchen, the most common problems when drilling CFRP are oversizing or undersizing of the hole and delamination. Delamination can occur at the hole entry, exit or both, and manufacturers have different specifications for and ways of measuring its severity.
“Sometimes the material can flake away, making craters around the edge of the hole, and the manufacturer will measure the crater depth to determine if it is within standards,” Strauchen said. Other materials will roll outward at the hole exit or entrance. The combination of drill penetration force and heat separates the layers, causing the layer closest to drill entry or exit to protrude outward. “Based on the height of the protrusion, the hole will pass or fail inspection,” Strauchen said.
If the application specifies a chamfer for the entry side of the hole, there will typically be a delamination specification for only the exit side. “In those cases, we typically use a variation on a double-angle drill,” Strauchen said. “Basically, it cuts twice. The drill has a very sharp initial point angle to cut one direction of fibers; the second point angle is more gradual and is designed to shear opposing directional fibers, thereby creating a clean hole with no delamination.” When delamination specifications exist for both sides of the hole, Strauchen said, “we’ll use a triple-angle drill with specific angles designed to achieve zero delamination on both the entry and the exit of the hole.”
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