by Mary Scianna
Meeting the cutting demands for aerospace machining
Serving the needs of the aerospace manufacturing industry can be a formidable challenge for a machine shop. The demand for consistent tight tolerances with tough-to-machine super alloys means manufacturers have to continually assess and invest in technologies to meet the demands of this marketplace.
Cutting tools play a critical role and cutting tool suppliers are also continually investing in new technologies and concepts. Shop Metalworking Technology asked some suppliers about key tooling technology changes in cutting tools for aerospace.
Remove the metal
Aerospace manufacturers strive to achieve high metal removal rates, but that can be a challenge with aluminum and titanium, two materials typically used for aerospace component manufacturing.
“When you look at aerospace, manufacturers want the most secure metal removal rate they can achieve. Titanium adds a challenge because they want high metal removal rates in a very difficult heat-resistant material,” says Brian MacNeil, milling product specialis with Sandvik Coromant in Canada.
Tooling suppliers have developed high feed cutters able to reduce heat and increase feed rate at the same time, in some cases manufacturers can increase the feed rate by as much as six times over a standard 90°.
Walter Tools, for example, has developed three new tools specific to rough machining of titanium: the Blaxx M3255 porcupine milling cutter, a tangential mounted insert with four cutting edges and positive chipbreaker for increased metal removal rates; Prototyp Ti40 solid carbide tool for roughing and semi finishing with five cutting edges; and Prototyp Ti45 an insert for finishing titanium to achieve near net shape.
According to Bill Radtke, engineering coordinator for the Americas for Walter Tools, the M3255 cutter is based on a high strength, rigid core and mono-bloc design with optimized flute design for rapid metal removal via a 27° helix. The Ti series of cutters are designed for thin wall deep pocket finishing and are available with “anti” pull-out shanks for a variety of matching spindle adaptors.
Some suppliers advise that the best cutting tools for high feed milling of titanium are PVD coated inserts with ground edges.
Sandvik Coromant’s new Zertivo PVD coating is one example of how the company has addressed this concern, says MacNeil.
“Thinner coatings are often a problem because they can flake and increase tool wear. The key is to produce a coating that adheres well to the insert and keeps the edges sharp, and Zertivo does this. We’ve seen up to a 40 per cent increase over our older generation PVD grade. The technology is being introduced into our super alloy grades.”
What Sandvik Coromant has done with its PVD coating, Walter Tools has done with a new CVD coating, WSM45X, designed for titanium machining. “Customers want to increase speed in titanium to get high metal removal rates,” explains Radtke. “We’ve always had PVD coatings for titanium machining but PVD coatings are typically thinner and not as resistant to heat as a CVD coating so our challenge has been to develop a CVD coating that keeps the edges of the insert sharp and combat the heat and that’s what our new WSM45X insert does.”
Lead the way
Inserts that provide low lead angles are best, adds Todd Miller, milling product manager for Seco Tools. “Trigon-style inserts provide the lowest possible lead angle over round or square inserts. Low lead angles produce a much thinner chip, which in turn requires higher feed rates to maintain proper chip thickness for the insert geometry. The lower lead angle also directs the cutting forces in the axial direction, pushing up into the spindle, which is more stable and easier on the machine. Higher lead angles produce more radial force, causing vibration and stress on spindle bearings.”
One of Seco’s solutions is its series of high feed milling cutters including Highfeed 2 and 4 indexable insert milling cutters. The company recently expanded the lineup to include a new Highfeed 2 small diameter cutter and a Highfeed 4 cutter with double sided inserts. Both cutters incorporate new insert designs combined with more teeth per diameter.
In deep grooving or rough turning applications, inserts typically experience notch wear at the depth of cut and the common solution is to use a 45° lead angle insert.
“This spreads the load and the heat to eliminate notch wear for a time, but this type of insert can’t produce a shoulder,” explains Kevin Burton, turning product manager with Sandvik Coromant in Canada.
Sandvik Coromant has come up with an insert called Xcel that has a 45° nose like a CNMG insert, but unlike typical CNMG, inserts it eliminates notch wear and is able to produce a shoulder, “so it provides the benefits of a CNMG insert with added performance.”
Stop the movement
High feed and high speed machining can help improve machining cycle times but harmonics generated from such processes create problems for tooling, says Matt Tegelman, product manager for BIG Kaiser.
“Vibration can occur from part instability, high speed machining or in long reach applications. You may have a large part that’s hollow and that’s when harmonics occur and can impact tool life and machining quality.”
The answer to the problem is a damping mechanism that can absorb vibrations caused by the cutting action, reduce tool wear and improve cutting performance.
BIG Kaiser’s solution is the Smart Damper. The toolholder body is constructed of a steel tool equipped with a carbide clamping mechanism. The Smart Damper series is available in diameters from 41 mm up to 100 mm.
Sandvik Coromant’s Silent Tools series of toolholders are another example.
“By using dampened Silent Tools you can increase the cutting parameters and at the same time get a more secure and vibration free process with close tolerances, good surface and much higher metal removal rate, which gives you a lower cost per component,” explains Burton. As a general rule of thumb, Burton says Sandvik Coromant advises that Silent Tools are your best options for overhangs between four times diameter to 14 times diameter.
High speed machining of aluminum aerospace frames is common and one of the concerns is security issues with tooling, says MacNeil. “Security in tooling is paramount. You can’t go with high metal removal rates if the process breaks a tool.” To address this, Sandvik Coromant has developed a new indexable carbide router, the RAL90, which provides stability in high speed milling of aluminum. Two versions are available, one for machines running up to 24,000 rpm and another for machines running up to 33,000 rpm. The router features a high chip removal rate of up to 0.3 mm/tooth and is designed with a secure, high precision interface between the tip seat and the insert.
MacNeil says the router was a result of a request by one of its aerospace OEM customers because it’s a more economical solution to high speed machining of aluminum frames.
“The router is starting to become more widely approved by a lot of machine tool builders because they’re concerned about the tools being put on their spindles and want to ensure their customers achieve the performance and the security they need in aerospace machining.”
Ensuring tooling is secure during high speed machining is critical and it applies equally to inserts and toolholders. “Materials being cut in the aerospace industry are sometimes difficult to cut,” says Tegelman. “You either have to cut very deep with high feed rates or take light cuts at high speeds and lot of traditional holders for milling tools have a hard time gripping the tools properly to ensure they don’t pull away from the toolholder.”
BIG Kaiser’s solution is its Mega Perfect Grip milling chuck that is designed with a high clamping force and low runout of less than .0004 in. at 4 xD. A unique lock mechanism using what the company calls a Key Grip prevents the slip and pullout of the tool during heavy cutting. By using straight shank cutters with a Weldon flat milling cutter, no special cutter is required. The Key Grip grooves provide channels for high volume coolant to the cutter, which dissipates heat generated during high speed machining and removes chips. SMT