When developing advanced tools for machining aerospace components, sometimes all it takes is a simple microscope to understand how a material interacts with the cutting tool.
Advances in the aerospace industry are often tied to advances in materials, especially the strength-to-weight ratio and temperature resistance of new materials.
The materials of choice today for aerospace engines are heat resistant superalloys, or HRSA, a complex cocktail of specialty metals – nickel, cobalt, iron and certain TiAl (titanium aluminide) based alloys – which provide crucial advantages such as the possibility of high working temperatures. Many of these components have complex shapes and can be 3D printed. This in turn creates new manufacturing opportunities and new challenges for machine tool manufacturers such as Sandvik Coromant.
Tip in tool design
Since the beginning of manned flight with wooden and fabric planes, the watchword of manufacturers has been to reduce the weight of the plane. Over the years, aluminum and titanium alloy constructions replaced wood and fabric, and eventually carbon fiber and composites entered the mix.
Compared to standard materials such as iron, today’s HRSA materials, in all their chemical and physical permutations, have unstable properties. More advanced tools are needed to cut and finish aerospace components in batches that make financial and technical sense to manufacturers.
“The trick in cutting tool design has always been to increase tool life by decreasing wear, while achieving higher cutting speeds,” says Stina Odelros, senior R&D engineer at Sandvik Coromant. “But the aerospace industry requires extremely high component tolerances, and sometimes there is no tool change capability in a process, so we are constantly developing new, better performing tools. We need to know what our customers are struggling with, and then we try to solve their problems. »
Constant adjustment of materials
Odelros explains that aircraft manufacturers and suppliers are constantly modifying materials such as HRSA and other alloy blends to achieve these goals. In addition to weight constraints, an engine component must also be able to withstand outside air temperatures as low as minus 60 degrees Celsius as well as internal engine temperatures of around 2,000 degrees Celsius.
Developing tools for this demanding industry is tricky. The only way to see how a tool works is to look at the used inserts under a microscope to see how they wear. “We don’t have access to all of these materials on the market, so we depend on collaborations with key customers to tell us how our inserts are doing.“, explains Odelros.
Core of R&D work
As Odelros explains, a 3D printed, forged, or cast aircraft component cannot be turned, milled, finished, or drilled with a previously used tool. Sometimes machining a large and expensive engine component can take a week or two, and each machining pass must be continuous to avoid structural defects. A tool failure midway through this process is not acceptable as it could result in part failure. And a part failure in an engine could be catastrophic if it happened in flight.
What Odelros then looks for under the microscope, besides controlled wear, is the size of the wear and whether more unpredictable types of wear such as chipping or fracturing are present, which at worst cases, could lead to costly production failures.
This is the core of R&D work. Although a carbide insert is no larger than an average fingernail, the permutations of its construction – angles, substrates, coatings, material constitution, crystal structure, and treatments such as chemical deposition or vapor phase physics – are almost infinite. The right combination and mix can yield results tailored to specific customer uses.
For more information: www.sandvik.com
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