ASK THE EXPERT: Walter USA’s Ashton Cherry on the new challenges for aerospace manufacturing

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Tomorrow’s aircraft will be required to rise above the net zero emissions initiatives increasingly coming to the fore. Doing so will require changes in both component design and materials used. In a two-part interview, Ashton Cherry, industry driver – aerospace solution specialist with Walter USA, details how this will change the design and makeup of aerospace parts and the tools required to manufacture them.

SHOP: Tomorrow’s aircraft will be required to fly in a more sustainable manner from an emissions standpoint. How do you see that affecting airplane component design?

CHERRY: The lightweighting aspect has an effect on the materials used. We are seeing more aluminum, more titanium, and more composites. But components are also being designed in a way that makes them more efficient, not just lighter weight.

The complexity of components, however, is making them harder to machine, not just from a tooling standpoint but the machine capabilities required as well. There is a big push towards single-aisle planes with smaller engines. The smaller engines are definitely more complex to machine because you lose rigidity due to the size requirements of the tool. We see a lot of friction welding in the industry now. Where  there were two parts before, now they are friction welding them together. You would have had easier access to machine such parts in the past and now that they are friction welded together you must rough them separately and then have complex tools to  access their features and  finish them. The smaller more complex parts definitely present issues with the tooling and the process rigidity that we see.

Additive manufacturing is a big focus because with additive manufacturing you can make more complex components, and you can make them more efficient also.

SHOP: We are already seeing increasing use of nickel-based heat resistant super alloys (HRSAs) and advanced ceramic matrix composites (CMCs) in aero engine components because they’re capable of withstanding higher temperatures. What challenges do these materials present at the machining stage?

CHERRY: They are extremely difficult to machine so we look at using harder carbide substrates. The harder carbide substrates are more brittle, so there is really an emphasis on proper programming technique to make sure that you are making in-tolerance parts consistently. As a result of being difficult to machine, there is a long cycle time, so we see shops that must order new machines to meet their rate requirements. Even though there are cost savings efforts and efforts to reduce the machining time,  the cycles are still quite long and require additional equipment. There  is shorter tool life with a lot of the nickel-based alloys, so we are looking at higher tool consumption, larger machine magazines, and larger tool rooms to accommodate all that.

We see a lot of ceramic and CBN that we use to improve cycle times. Ceramics are very cost effective but on the flip side, CBN is expensive to produce so you are always weighing the cost versus the improvement in time. Tool pressure is extremely high with nickel materials so the tools need to be rigid and that plays into the smaller components that we are seeing and having to provide unique and special solutions. Once the tool starts to wear there is an increase in tool pressure and concerns over surface finish, microstructure and  overall part quality.

SHOP: The much higher temperatures that we are running at, what kind of challenges does that pose for the tooling? Is that heat going into the tool and is it deforming the tool?

CHERRY: The biggest factor in terms of how much heat is going to be produced at the cutting edge is the surface footage the tool is run at.  A good generic number is 200 surface feet with carbide. Once you start to get into 250 sfm, 300 sfm, you start pushing that envelope, and the tool life is exponentially dropping off. You have to be really careful and dial in the surface footage, that is going to play the biggest part on what your tool life is going be. If we are looking at a carbide finishing insert, you might see 15 minutes of run time, once the cutting edge starts to break down you are introducing a whole host of other problems. The tool needs to stay sharp, which means you must run it slow, and because you have to run it slow you end up with a long cycle time. We work on developing new grades and new coatings to help deal with the heat and extend tool life but there is a limit. CBN is capable of withstanding significantly more heat but it’s brittle.. CBN has limited applications because the insert geometry has to be strong. We see it a lot in round profiling inserts but it can be hard to get it to work well with a traditional 80-degre diamond or 55- or 35-degre diamond, like you see a lot of customers using.

In Part II of our interview with Ashton Cherry we dive into the tooling solutions that can best meet the new challenges of manufacturing for aerospace.

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