Machining aerospace materials is a challenging task. Not only are machining operations tightly controlled, a wide variety of workpiece materials are employed, including aluminum, titanium, and carbon-fiber reinforced plastics (CFRPs). The following is a brief guide to cutting tool options for successful machining of airframe components. All of the tools referenced are manufactured by Mitsubishi Materials.
The Challenges of CFRP
When drilling CFRP for airframe components, a special point angle is recommended to reduce thrust when drilling to prevent delamination and improve hole tolerance. The Mitsubishi MCS drill, for example, can accomplish this while achieving 1.6 times longer life than conventional tools. When drilling CFRP-Al (which includes layers of CFRP and aluminum), the same MCS drill, with its unique flute design and low resistance wavy cutting edge reduces delamination and burrs when drilling CFRP and CFRP/aluminum, CFRP/titanium stacks. This will also prevent aluminum chips from damaging the finish of the CFRP section, thus reducing the gap in hole size between the aluminum and CFRP sections.
When trimming CFRP with end mills, cutting tool life is usually extremely short because of the high strength of the carbon fiber. Also, delamination and burring frequently occur during cutting. As a result, a coated tool with high wear resistance is effective. For example, DFC solid-carbide end mills reduce burrs and delamination due to their CVD diamond coating and optimized tool geometry.
Milling Aluminum Alloys
When face milling and pocket milling aluminum alloys for airframe components, high-efficiency machining at high speed is required to reduce cost since rib-type components require removal of large material volumes—typically more than 90% of the workpiece. As an example, the AXD series indexable end mills employs a helical flank and optimized relief angle to achieve low cutting resistance without lowering the insert edge strength. For example, a 50-mm diameter cutter can achieve a metal removal rate (MRR) of 10,000 cm3/min. when using the XDGX227040PDFR-GL TF15 insert. Also, the tool produces superior surface finishes because it can interpolate corners of the pocket and prevent vibration.
When milling aluminum-lithium airframe components, tools such as the AXD series of indexable end mills are recommended. In an application, a GM breaker, in combination with MP9120 inserts, reduced chipping and promoted stable machining in aluminum-lithium.
When face milling and pocket milling aluminum airframe materials, end mills can be effective. For example, the ALIMASTER series of solid-carbide end mills achieves good chip removal due to the cross-sectional shape of the tool’s flute geometry. In an application, MRR of 5000 cm3/min. was achieved with a machine tool with sufficient power.
When side milling and rough pocket milling titanium for airframe components, problems such as chipping and abnormal damage of the cutting edge occurs if low-rigidity tools are used. Using high-rigidity tools and low-cutting-resistance inserts, such as the VFX series indexable insert milling tools, is recommended. VFX mills have an insert geometry with a convex cutting edge and a V-formation on the clamping face that resist chipping and cutting edge damage.
When roughing titanium airframe components at high speeds, there is typically concern about chipping and fracture because cutting resistance varies in the process of generating saw-toothed chips. The combination of the MP9130 grade of indexable inserts and the AJX series of indexable face mills produces excellent wear resistance due to multi-layering of the coating and JL breaker with low cutting resistance, enabling stable high-speed roughing.
There are other airframe component recommendations for titanium as well as for machining precipitation hardening stainless steel that we do not have space to cover here. These and recommendations for machining other aircraft components, such as landing gear and engine components, are available in the Aerospace applications area of the Mitsubishi Materials website: http://www.mitsubishicarbide.com/en/solution#industry.