Building jet engines installed on modern aircraft involves thousands of manufacturing steps, including cutting through-holes that accommodate the fasteners required to complete assembly of an engine’s various units, components and sub-assemblies. To ensure a flawless fit and durability, it is vital that jet engine fastener through-holes are chamfered and free of metal burrs from the hole cutting process.
“A precise, smooth through-hole is a crucial requirement,” explains Gary Brown, vice president and general manager of Heule Tool of North America, a subsidiary of Heule Werkzeug AG. “In every jet engine you are going to have several components, either static or rotating parts that are assembled together. It is critical that the hole drilling and edge breaking processes be performed so that these parts stay together, which is particularly important with the rotating parts. So, we stress making good through-holes by drilling, milling or reaming – whatever process is called for.”
Brown adds that the top aircraft engine suppliers want a controlled hole-making and edge-breaking process, with the parts coming off their CNC machines finished and “to spec.” He explains that among the main goals for aircraft engine manufacturers is avoiding costly and time-consuming hand benching operations, where components are taken offline from the CNC operations so that holes – normally chamfered - can be deburred and finished by hand.
In combination with the Heule cutting tools, the Flex-Hone is used for final deburring of through-holse, which can be an expensive and time-consuming bench process.
Reducing bench work, and thereby increasing productivity, can be achieved if the proper tool is applied. However, the proper machining of the part is critical to the effectiveness of the deburring and chamfering tools. When cutting nickel and titanium alloys, drills and reamers quickly dull and can create large extruded burrs that will be difficult to machine. Burrs created from improper or poor machining conditions are difficult to remove because they tend to work-harden the exit burr. For optimal tool life, you must control the burr being created by using proper drilling procedures, not starving your tooling of coolant and changing tooling often as recommended.
“To avoid delays and keep tool costs to a minimum, the progressive shops are automating this process, incorporating our cutting, edge-breaking and deburring tools, plus a unique ball-style hone called the Flex-Hone that provides the final step in providing a flawless finish – without hand benchwork,” says Brown.
{INSERT (AM061610_Heule2.jpg )}A winning combination
Brown says that the major manufacturers of jet aviation engines are adopting advanced, hands-off hole drilling, edge-breaking, and deburring techniques and recommending or requiring that suppliers incorporate them, too.
Large burr formation in stainless, Inconel 718, or titanium alloys are difficult to deburr. The carbide radial COFA deburring tool will remove the burr, and is followed by the Flex-Hone to round out the transitions of the edge breaks.
To this end, a number of the builders are standardizing on Heule’s DEFA precision chamfering tool and COFA universal deburring tool, plus the miniature Flex-Hone tool supplied by Brush Research Manufacturing.
The DEFA tool, available is sizes from 0.157 in. to 1.750 in., is a double-bladed chamfering tools that creates pre-adjusted front and back chamfers in a single pass without stopping or reversing the spindle. Using this tool, exact chamfer diameters can be set without trial and error.
The COFA tool blade, available in sizes from 0.157 in. to 1.614 in., cuts a smooth tapered edge break from 0.005-0.020 in., based on the tool size. A cassette option is available for larger holes. The patented design incorporates a unique Tin- or TiAlN-coated carbide blade that allows for faster feeds and speeds, and provides exceptionally long tool life.
The Flex-Hone, available in standard sizes beginning at 4 mm (custom sizes and abrasives are available) is characterized by the small, abrasive globules that are permanently mounted to flexible filaments. A flexible, relatively low-cost tool, it is utilized in the manufacturing marketplace for ultra-fine surface finishing, de-burring, plateau finishing and edge-blending.
A major jet engine component manufacturer uses the Heule-BRM tool combination for finishing chamfered holes on rotating engine parts, not only because it is an efficient way to achieve the very stringent tolerances required, but also because there simply is not a another method of doing the work that is sufficiently stable and repeatable.
The finishing touch
The Flex-Hone is available in a variety of abrasive types and grit selections to provide the optimum surface finish on any base material. This patented, ball-style hone is commonly used to reduce Ra, Rk and Rpk values while maintaining Rvk and Vo volume for oil retention. Using this tool for surface finishing allows the sizing tools to do their jobs quickly and accurately without fighting surface finish.
In combination with the Heule cutting tools, the BRM Flex-Hone is used for final deburring of through-holes, which is often an expensive and time-consuming hand (bench) operation.
“Our tool cuts through the metal and puts the beveled edges on the front and back of the metal part,” explains Brown. “It produces the beveled edges on the front and back of the part as well as removes the drill burrs and drill caps that are created by the drill or reamer or end mill. Our tools also perform the edge-breaking step. But we also recommend the Flex-Hone to go in after we have created these beveled edges, and the flexible hone will round the transition between the beveled edge and the hole.”
Brown notes that workpieces of long-chipping material, such as stainless steel and titanium, can cause raised material around the drilled hole as you cut it. He says the Flex-Hone is very good for removing burrs up to 0.003 in. in size.
Although Flex-Hones are available in a wide variety of sizes and abrasive grit materials and sizes, Heule normally recommends that customers specify the BRM sizes with 180-240 silicon carbide abrasive grit and operating speeds of between 800 and 1,200 RPM and 40 to 60 IPM.
“You simply insert the tool for three strokes in both directions (in and out), and that will normally provide you with a smooth transition between the breakage and the finished hole,” he says.
Brown also recommends BRM’s Flex-Hone for use in other sectors served by Heule cutting tools, such as the automotive, semiconductor and medical sectors, wherever secondary burrs are created from a chamfer cutter.
“Anytime you drill a hole into nickel, Inconel, waspalloy (nickel-cobalt alloy), any type of titanium or stainless … when you drill a hole you will also create a burr,” he says. “We work with different manufacturers and suppliers in a wide range of industries to help them in their in-process hole cutting and edge breaking process. And we recommend the Flex-Hone as part of the process.”
The Flex-Hole tool is used to round the transitions of the edge breaks.
Customizing the solution
Brush Research has many years of experience customizing the Flex-Hone for demanding applications. Mike Miller, BRM’s vice president of global sales, relates their experience when contacted by the surface-finishing laboratory of a major jet engine manufacturer. The problem at hand was to provide an edge radius at the transition of the chamfer and through-hole. The application soon expanded to also remove the micro burr left on the surface at the major diameter of the countersink. This application became additionally complicated when BRM was asked to provide a tool that could also pass through the hole and perform the same deburring and radiusing on the backside of the hole.
To complicate matters further, the tool could only enter the front side of the part. A special Flex-Hone was developed to perform all the deburring and edge-radiusing required, simultaneously.
Heule cutting tools, together with the Flex-Hone, remove the drill burs and drill caps that are inevitably created when drilling a holes in nickel, Inconel, Waspalloy, titanium, and stainless steel. A precise, smooth through-hole is critical for manufacturing jet engine components.
Miller states the solution was to provide a tool much larger in diameter than would normally be used in the through-hole diameter. The major diameter of the Flex-Hone used is large enough to treat the breakout burr on the surface of the part. To ensure that the tool could enter the through-hole and perform the same on the backside of the part, lighter-diameter filaments and lighter gauge stem wire were used. “If we attempted to pass a standard tool thought the small through holes the balls would have been sheared completely off,” Miller states. “With our custom design we are able to handle combinations of through-holes with countersinks as large as .050 over the size of the hole. We also worked with the lab to develop operating parameters that maximize tool life.”
