Machining Processes for High-Temperature Aerospace Alloys

CHRIS WADE: Thank you for joining us so early after the party last night. I know it was probably a struggle for some of you getting up. Thank you for joining our talk, which is on machining processes for high-temperature aerospace alloys. And hopefully we've got a really informative talk for you here today. We're going to start off with what I, personally, think is the best looking slide of the bunch.

So let me introduce myself. Oh yeah, just a note. Sorry, James didn't provide a picture in time so I had to make do. So let me introduce myself. I'm Chris. I work as part of Autodesk Advanced Consulting, which is a small subdivision within Autodesk. And I've been working as part of Autodesk on and off since 2012. So they first invited me in as a placement student while I was at university, and then I got invited back for a permanent job before moving into the advanced consulting team.

JAMES DONNELLY: And I'm James. I've worked for-- well, started Dalcom about three years ago in the [INAUDIBLE] machine and then moved into the Advanced Consulting team about five months ago.

CHRIS WADE: So just a little rundown of what we're going to be talking about today. So I know Autodesk Advanced Consulting isn't that widely known within Autodesk or even outside of it. So I'm going to give you a quick overview of who we are. Then I'm going to go through the types of materials that you might find in the aerospace industry and what the applications for those might be before going into some of their particular properties that make them useful in certain applications.

And then James is going to take over and go through some of the machining trials which we did in our advanced manufacturing facility in Birmingham in the UK, testing these materials and why you might want to machine them in certain ways. And then I'm going to go through two case studies, which we've got projects that we've done for a customer, going through, overall, the workflow of the project, and then takeaways that you can possibly use in your own related or maybe even unrelated projects. And then James has a project that he's working on at the moment, his little baby, so he's going to go through that in a little bit of detail with you.

So first of all, who are we? And I'm sure many of you after the party last night were lying awake thinking of this, but folks in specifically on Autodesk Advanced Consulting. We are, as I said, a small subdivision within Autodesk focused on completing work for customers and also research work internally in a variety of different industries and using a variety of different techniques. So from generative design, to factory automation, to what we focus on, which is subtractive manufacturing.

And without further ado, let's get underway. So materials in the aerospace industry-- I've broken this down into four sections. So first of all, I'm going to be going through why certain materials are used and two main groups of materials within the aerospace industry. Then I'm going to focus on a particular group that the materials which need to resist high forces and high temperatures. And I'm going to go through superalloys and why they might be used for that application and what makes them so super.

Then I'm going to go to them going to be going through their properties and what makes them difficult to machine or different to machine. So focusing, in particular, on commercial aircraft within the aerospace industry, because the aerospace industry encompasses commercial aircraft, military aircraft, and also spacecraft. And so we're focusing on commercial aircraft because we have a lot of experience with that and it's a little bit easier to talk about.

So I've broken down materials into two main groups as I see them. You've got parts and materials which have a focus on being lightweight to reduce the amount of lift required to get an aircraft into the air, reduce the amount of fuel. And this might be parts in the wing, parts in the fuselage, and there's been lots of good talks this week about weight reduction techniques, like through generative design or through different manufacturing techniques.

But today, we're going to be focusing on a different group of materials. And this is materials such as those in the engine that need to constantly withstand these high forces and keep their strength, keep their shape. And certain materials that are able to deal with this include high nickel-content steels and certain titanium alloys. So the nickel-content steels might be something like Inconel or Waspaloy, and titanium alloys, like titanium 6-4 is what we're going to be covering today.

And some of these alloys can be classified as superalloys. And a superalloy is just a generic term for an alloy, which excels in two or more criteria. So in this case, maybe it's incredibly strong and able to resist high forces and also able to resist incredibly high temperatures. And that would make it suitable for this application and a superalloy.

And within an alloy-- just going back to basics now-- within an alloy, you have an arrangement of the metal atoms. And these can form a crystalline structure, and it's the arrangement of this structure within the alloy that can give it its strength. So, for example, here, if you take a really close look at a cross-section of something like Inconel, you have a regular arrangement of nickel and aluminum atoms within it. And it's this regular arrangement within the crystals and the way that the crystals interact with each other that can give these high-strength and high temperature-resistant properties.

But this internal structure can change based on the way an alloy is formed. So rather than just machining a block of the material from scratch that can produce a lot of waste or whatever, sometimes it goes through a forming process first, like forging or casting. And this is just to get into the rough shape so that there's less machining work that needs to be done. And so forging is essentially-- it dates back ages, back to the dark-- maybe not quite as far as the dinosaurs-- medieval times.

So imagine a blacksmith hammering a piece of chest armor into shape from just a sheet of metal. That's forging. It's applying a force to a material in order to bend it into a certain shape. And nowadays it's not a guy with a hammer, it's a big hydraulic press and some dies. And casting is where you would take an alloy, turn into a molten material, pour it into a cast, and then let it set, break the cast away, and then you have the rough shape.

And each of these forming processes has their drawbacks. So, for example, forging can introduce new stresses into the material, areas of weakness, especially if there's sharp edges, sharp angles. And casting essentially re-arranges this entire crystalline structure I was talking about. So if you've got a regular structure that's been created as part of the alloy, it just breaks it all down and then when it sets again, you don't exactly know how it's going to reform. So there could be inherent weaknesses in the material there.

And these hot processes also have another problem. So forging can be done hot or cold and casting, obviously hot. So when it sets, you can get this oxidized layer on the surface of the material, which is incredibly rough and difficult to machine, and requires a lot of effort to remove. But focusing more on the materials in general again. So Seco Tools have done a lot of work regarding the properties of certain materials and what affects their machinability. And they've broken this down into five different factors, which you can see here on the screen. And the material shown here is a high-grade steel.

So all of these five factors might change, depending on whether something is incredibly ductile or something's incredibly thermally conductive. It changes the way that you might approach machining. And comparing this steel to Inconel 718, which is a high nickel-content steel, and titanium 64 on the right-hand side, you can see first of all, one thing that I like to point out, is that Inconel and titanium actually have a lower hardness than this steel.

And that might surprise a lot of you because these superalloys and these titanium alloys are known for being incredibly hard and incredibly difficult to cut through. But they have a lower hardness on this scale. And the reason why they have the reputation of being hard is because of this second property in the top right, which is strain hardening. They have a higher resistance to local force, or also known as work hardening.

So hardness is essentially a measure of if you apply a force to something, how much it's going to compress. But as it compresses, this crystalline structure that I was talking about can rearrange and it can resist this force. So as you're applying the force, it can become harder and harder. And it's this threshold for hardening that gives Inconel and titanium 6-4 their reputation.

And the last property I'd like to draw your attention to is the lower heat conductivity in the bottom right. And you might be wondering how does heat conductivity affect the way you might machine something? It's not got anything to do with it. And I've got two videos on the next slide of very similar titanium alloys. One is titanium 64 and the other is a burn-resistant titanium. So the only difference is the burn-resistant titanium has a much lower heat conductivity, so it's less able to conduct heat away from the cuttings there.

And these properties-- I mean these videos-- are courtesy of the University of Birmingham, and I'd like to thank them for providing them. And if you can see the video on the left playing, you can see it's a nice smooth cut. These aren't ideal cutting conditions, because there's no coolant and there's nothing to break up the chips, nothing to cut the swarf so it's got this nesting effect. You can see it's cutting nice and smoothly, no real chatter on the surface, no changes in color, and it's smooth.

Whereas immediately on the right-hand side, you can see an indication of the buildup of heat in the swarf and in the cuttings zone. And this heat can change the properties of the material. Not only the material, but the properties of the tool itself, which can eventually lead to failure of the tool, which you see there. So nothing has changed apart from the conductivity. But the focus is on if any of these properties change, depending on the material, you need to change the approach. You have two similar approaches there, similar materials, only one property changed, you would need to change the approach.

If you don't change your approach to cutting these materials, you can get tool breakage like you saw there, or maybe on the lower end of the threshold you can get something like a bad surface finish, chatter on the surface. Maybe it's just pushing material around then cutting, or maybe other parts of the system breaking. So in the center you've got a collet here holding a tool. And what actually happened was this collet failed. It sheared right at the bottom of this thread. And it had a little crack here in the slot.

But this is a top-down photo of the shear looking down on the collet And you can see a little crack in the top right. You can see the start of the thread. But you can also see a good indication of what I was talking about before with the crystalline structure and the changes in tone. All of the breaks were between the crystals, which would cause this jagged surface leftover. Or even just something simple like excessive tool wear, which would just increase the cost of a project.

Or maybe even something catastrophic like this can happen. And the interesting thing is, this isn't even an exotic material. This is just standard tool steel. This is a steel which people might be used to cutting day in and day out. But if the approach is wrong, something like this can happen. So again, the approach needs to change based on the material. And even if you do get something on the lower end of the threshold, maybe the tool has overworn.

When it comes to part inspection, you'll realize the tool's worn too much more than you expected. It's geometrically out and it hasn't cut as deep as you thought it would. So you've got to go back. It increases the cost of the project. Or if you've got a bad surface finish, maybe arduous manual processes need to be used in order to smooth them up again, increasing the cost of the project.

And so I'd like to hand over to James now. He's going to go into a bit more detail about this. We've done some tests in our advanced manufacturing facility about just this very topic.

JAMES DONNELLY: OK, yeah. So I'm just going to show you a few slides with videos and some images. So we did some tests back in Birmingham with different materials to see how they acted under different cutting parameters. So these are the three main goals of our trials. So first, we wanted to see how the different materials acted in the different cutting parameters and what effect did the approach have on tool life and surface quality, as well as comparing the machinability of each material.

So the first of the three materials we used was EN24T steel. And this is a tempered steel with good machining characteristics. And its uses are found in aerospace and automotive parts as well as press tools for the tool and die industry. The second of the two material is titanium Ti6-4. Now, this is an aerospace alloy, which is harder to machine and that would be [INAUDIBLE] the EN34T steel. And its found in parts of the-- and prototypes of [INAUDIBLE] aerospace industry, as well as implants and prostheses. Now the third material is Inconel 718, and out of the three, this is probably the hardest to machine because of its work hardening characteristics as Chris showed in earlier slides.

And this material is also used in aerospace components as well as rocket and space application components. So the volume of material that we wanted to remove is shown there, so it's 100x25x18 mill. And what we're doing is using a 12 millimeter radius 1 end mill. This end mill has a Zeb Cob coat in which was supplied by SGX. It's a titanium alluminum nitride coating, and it's recommended for machining a varium range of materials with different hardness, so anything from cast irons to superalloys like Inconel 718. And this would be done on a Huron VX 12 milling machine, which is a flatbed three-axis milling machine.

So we tried two different methods of approach for machining that volume of material. The first onee's a traditional method. I call it a traditional method because it's that what would be used to machine a roughened area of material using [INAUDIBLE] cutter, adopting a large stepover and small stepdown, focusing a lot of the heat and the cutting forces on the tip of the tool. And the second method is one that would probably suit a high-temperature alloy. So this has a smaller stepover but a larger stepdown, utilizing the full flute of the cutter, spreading the heat from the tip to across the whole of the tool.

And it also takes less passes to remove the material, which is good for a material that work hardens, as the less times you have to cut it, the less chance you have of changing the properties of the material. Now as well as approach, we [INAUDIBLE] and the direction of cuts. Now on the screen you can say conventional and climb milling, both of which have their advantages in milling. But for this test, we chose climb milling. The reasons why were first, is bigger chips straightaway. So when climb milling, as soon as you're engaged with the cut, it's taking its biggest chip.

Now this helps for heat dispersion into the chip so you're getting the heat away from the cutting zone and into the chip and out of the way of the cut. And secondly, better sort of evacuation. So for when roughing, you're taking out a large amount material, you don't want the swarf to get in the way. You want to get it out of the cutting zone as fast as possible. OK, so the first of the three materials was EN24T steel. So you can see on the left-hand side of the screen are the parameters that we used. So we chose 4.8 millers of stepover, which is 40% of the tools' diameter, with a 1 millimeter step down.

Now, the reason we chose 40% of the tools' diametry is when choosing a stepover, you don't really want to go more than 50% of the tool because you run the risk of wrapping the tool and having a negative effect on the cutting. And the 1 millimeter stepdown would be similar to what would be used if you were using a Tipton [INAUDIBLE] cutter, because they don't have the luxury of having a long flute length so you're limited to how deep you can go with your cut.

And you can see the speeds and feeds here. These were taken out of SGS's catalog for this tool for this material. So this first video is the cutting tranche for the EN24T Steel. It's traversing nicely along the [INAUDIBLE] there's no visible signs of heat build up.

It's an easily machined surface with the right parameters. And this is shown, as well, in the after images of the tool. So on the left hand side, we have the nice, shiny new tool. And on the right, we have the tool after it and we shown the whole volume.

There's some slight build up of heat here in the tip of the tool. That's natural considering all the forces, and the heat is focused on that one area. But apart from that, there's hardly any wear, that tool is pretty much untouched. And the surface finishes well. This is a rough surface finish, but it's that with what we expected with a ruffian pass. If you were to finish that, all those marks would be removed. There's no visible signs of heat build up in the material, which is good. And then finally, the block after it had been machined. So it's a nice shiny surface, the whole volume is removed. There's no signs of chatter or anything like that.

Now the parameters I've just shown you will be applying to the titanium in the [INAUDIBLE] as sort of a benchmark parameter. So we'll be able to compare what those parameters look like to the correct ones and the correct approach. So here you can see the parameters we used for the Steel on the left side, and then the new parameters with that new approach. So it's a smaller step over which is now 1.2, just 10% of the total diameter. And a larger step down, which is 1 and 1/2 times the diameter of the tool.

These are a sort of standard for when you're doing this sort machining, and are using more of the flute length, and a bigger step down then step over. You usually use-- you don't want to go anymore than 10% of your tool's diameter in the step over. And we probably could've gone a little bit further with the step down, but it depends on how much flute length you've got on the top.

The spades and fades again were taken out of [INAUDIBLE] catalog and they have decreased quite dramatically. But one thing to notice is that there are approximate machining time has decreased. So because, as I mentioned earlier, it's taking less passes to machine the volume. Than that has a positive effect on the time taken. So here is just an image of the top of itself. With the large step over and the small step down. And again with the small step over and a large step down.

So this first video is using the Steel parameters on the titanium. So it's about half way-- about 60, 70% through the trials. And you can see the tool's struggling, there's sparks coming off it. The heat has built up too much, and it's no longer able to continue. This is because you can't remove the material at the rate required. It's a hard material to machine, and it's probably Chinese, it's probably a shit material that's burning the tool out.

And this is seen in the tool tip itself. So before on the steel we had very little wear, whereas now there is physical signs of heat build up around the tool. There's some of the materials welded itself to the tip and the tip is no longer there. And this also has a negative effect on your surface quality. So the image on the right is of the wall of the area that we have machined. And you can see here that some bits of material have welded itself back to what was already cut. Now this is because, as I mentioned, just the fact that it can't remove the material at the rate required. It's sort of pushing it out of the way and welding it back to itself.

Now the second of the two videos is using these correct parameters so that this new heartless method that would suit a high temperature alloy with the correct speeds and feeds. And you can say it's taken a nice uniform cut, the swarf a nice color if you can see it just here. There's no signs of heat build up as we saw in the last videos. And it got through the whole volume with no stress.

And that's shown in the tool finish a well. So if you can see on this image on the right, you see that this sort of light grey section. That's where the tool's been engaged with the cuts. There's no visible signs of burns or heat build. The tip's still intact. It's quite good wear. It's wear that you'd like to see from a tool cutting this material.

And this has had a positive effect on the surface finish as well. If we look back to the image before with the bits of welded material on it, that's no longer there. It's a nice surface finish. There's no signs of the tool has been struggling. And this is shown in the finished product as well. So on the right hand side, we have the correct parameters and it's been able to machine the whole volume of material. Whereas on the right side, we see that about 70% through with the marks on the wall, which is what was a microscopic image of the material being welded back to itself.

OK. So the last of the trials using Inconel 718, the hardest one of the three-- machine. Sorry. So we have the same parameters again, the ENT-- EN24T Steel. Sorry. With the improved parameters. Now all that shines here is the speeds and feeds which have decreased again. But this has had a negative effect on the approximate machining time. Because you need to treat it so carefully with this material, it slows everything down, it takes a long time to cut. But I can imagine that if we were to apply these speeds and feeds to the traditional method, it would take five times longer than what it does with this high temperature alloy method.

And again we see the pictures of the top of themselves. And this first video is of the inconel being cut using the steel parameters. Now it's about five passes through now, and the tool's already gave up. You can see it's glowing red, it can't continue. Where if you compare that to the steel, it got through, well there were no signs of this. I mean titanium got what? Half way through? Whereas this is four passes in and it's already given up.

And again, [INAUDIBLE] the titanium tested the tip has been burnt out. It's no longer there. There are visible signs of the material welding itself to the tool. And this tool was no longer able to continue. And this had a negative effect again, with the surface quality.

Now on the left hand image you can say chattering, and that's vibration so that the tool can't remove the material as quick as it needs to. It's damaged the tool, and then it's just rubbing itself along the surface. This is vibrating. Which, if you look closer, it's got some signs of heat build up in the material, which has probably changed the properties. So it's made the material a little bit harder and it's harder to cut. Instead of cutting the material it's sort of pushing the swarf out the and you'll re-cut in that swarf on the next pass, which will have a negative effect on your tool.

Now the second video is that using the correct parameters. We have the high temperature alloy approach. And like the titanium, it's really slow, but it's not a nice uniform cut. There's no signs of it struggling. There's no heat build up. And at the very end of the machine, the whole area, there's very little wear on the tool. Similar to that of the titanium trials, there's a little bit of wear, which is very even, across the whole of the tool where we've been engaged in the cut. Comparing that to the incorrect parameters, the steel parameters, where there is no longer any tool tip there. It was a great improvement.

And again this is shown in the surface finish. On the right hand image we see the same image is what was before, where we had chattering marks, where that's all been removed. It's a nice finished surface. There's no signs of heat build up or anything like that. That's what you'd like to see and you can see the differences there. So the left hand image is obviously used in steel parameters and it was only able to go through those five passes before it was burnt out. And on the right is a whole volume removed nicely, and there's nice surface finish. It's what you would want to see from trials like these.

So I'm going to hand you back over to Chris to talk about some projects that we're doing. The advance consulting team.

CHRIS: Thank You, James. So essentially just the idea that we want to get across is whatever the material, make sure you're cutting with the correct settings. There's a lot of research done by various academic's and tooling suppliers about specific materials. So just look it up if you're ever in doubt.

So I want to take a step back now and look at two projects that we've done in recent years for Rolls-Royce. They've allowed us to show you these projects today, and these projects are very different. What I want to do is go through, essentially, the work flow for each project. And then I want to highlight some key points that you can hopefully take away and use within your own projects.

So this first one is to do with the Advance3 Blisk. And here is a nice cross section of it here. So Rolls-Royce, within the aerospace industry, are well-known for their trench series of engines. And the Advance3 is their idea of a step forward from that. It's essentially a concept, an intermediary stage between what they hope the ultra fan will be. So in 2025 they hope to bring out the ultra fan, and that should lead to a reduction in fuel burn of 25%, which is a hell of a lot. I think you'll agree.

So this Advance3 is a proof of concept for that. And for those that aren't really familiar with the workings of an aircraft engine, I'll just give you a layman's version. So the air comes in the front through this bypass fan, and it's got two routes from there. It can go outside or through the combustion part of the engine. And within the combustion part of the engine you have a series of blisks. You've got this intermediate pressure part here and then high pressure bit at the back where the combustion occurs. And what we're focusing on is one of these intermediate pressure compressor blisks. And that took a lot of practice to say.

So we were asked to machine the one to the left. And for those that aren't aware of what a blisk is. They're also known as IRB in other parts of the world. A blisk is essentially a combination of the words bladed and disk. So we were asked to machine this IP4, which is on the left hand side. And Rolls-Royce asked us to machine two of these out of titanium 64. And what we decided to do was also machine one out of steel, a smaller scale version, just to check our processes to make sure everything was correct.

So I'm going to go through a series of images of the steel process with you, that the same would apply to the titanium as well. The reason we chose to do it out of steel rather than titanium is just because it's a lot cheaper, mainly. So we created this very precise fixture to go on our tool. And here we're using [INAUDIBLE] C50 within our advanced manufacturing facility again. And the first thing we need to do is just check that the table, the bed of the machine can actually rotate the amount we wanted it to with this fixture on top.

So after that check's done what we got was a forging, and as opposed to the forgings with the oxidized layer that I was speaking about before, this is a bright forging. So all of that layer has been removed, saved us a lot of work. So the steel forging was put onto the fixture, and then it went through two turning processes. One, machining from one side, then we flipped it over and machined from the other side just to get the rough shape.

And the cool thing about this C50 is that, essentially, it's capable of milling and turning. So you can place the part on the bed and mill it, and then you can actually have a static tool as well and just spin the table. So here you can see the tool engaging with the part. And the other cool thing is that as well as this turning capability, you can get continuous a-axis movement of the table. So as the tool's engaged, in order to keep the load consistent on the tool, the bed can just rotate and allow you to cut down the length of the hub.

So after we've done those two turning processes, it was time to cut out the blades so we cut slots between each of the blades and then roughed out their geometry. And then each blade, in turn, was machined one after the other doing a semi finishing and a finishing process back to back for each individual blade. And here you can see a video, an indication of why we might have wanted to check that the table could rotate enough, because we want a machine around the back of the blades. It's very upright at the moment.

So here you can see a nice finished blade in the center, rough blades either side. And after finishing all of the blades, we went back and we did two further turning processes, just finishing off the shape of the hub. And then it'll be sent for inspection, check it's all geometrically correct. And then possible further processes to improve a surface finish like polishing or anything like that. Manual processes. And then it will be packaged and sent to the customer for final testing and inspection.

So this is all well and good. We did all of this. Thank you, us. But what can you learn from it? So I've isolated four main points that I'd like to focus on. The first one is the idea of hoop stress. So within a cylindrical part you have what's called hoop stress, which is keeping the shape of this cylindrical part intact. And as soon as you cut a slot into the part you break this hoop stress. And the bulk of material that hasn't been cut pulls away at the slot and can widen it, and it can distort it. And this is isn't ideal if you want to be geometrically precise, as you do in the aerospace industry.

So what we decided to do was, after cutting the first lot, we cut them in a very particular way. So you can see here we've got three slots already cut. Essentially a fourth one about to be cut quartering this cylinder. And the reason why we did this is essentially, if you cut the slots one after the other, you don't do anything about this bulk of material around the bottom of the cylinder. You still got that there pulling away at each and every slot that you cut, distorting every slot. Whereas, if you cut first by halving, and then maybe quartering, then maybe turning into eights, the cylinder as many slots as you need, you're essentially halving this hoop stress each time. Which will reduce the amount of force pulling on the sides of the slots, reducing the amount of distortion.

So this can be done for any cylindrical part, anything with a circular cross-section. The second point I'd like to focus on is the use of blade monoliths. Now I'm using blade here in context of the blisk, but again this can be applied to any thin part that you've got to machine. So I mentioned that after roughing the blades we did a semi finishing and then a finishing process back to back. If we semi-finished the whole blade, and then finished the whole blade after that, once we apply a tool to the top on the finishing process the blades so thin it's going to deflect rather than cut. The force applied by the tool can just push the blade. There's no material left after the semi finishing process to withstand that force. And this is where the idea of blade monoliths comes in.

So by cutting the blade splitting the blade into sections and then semi finishing and finishing the blade in those sections you can leave material on in what we refer to as a monolith. So now when you have that tool cutting the tip of the blade in the finishing process, that force is withstood. Some of the deflection is withstood by this monolith. And so here I've got some images from a different project that we did, which is just a really good indication of these monoliths in action.

So you've got the roughed blades here, just the rough geometry intact. And then you've got all the monoliths for all of the blades, and then for this individual blade you can see the finishing process has been completed for the top section. It's been semi-finished here. And then you still have the monolith at the bottom. And then this is the blade complete. This is exactly the sort finish we were looking for. And then this will be repeated for each blade [INAUDIBLE].

The third thing is the use of test blocks. So I mentioned that we cut our test piece of steel because it's cheaper. But everything we've gone through before that is to do with making sure that you've got the cutting approach correct for certain materials. We needed to make sure that the steel tool parts that we use could also cut titanium. So rather than machining an entire blisk out of titanium, we machined just specific spans of four-five blade spans.

So we cut the hub into the correct shape to make sure we would get any of that deflection correct. And then used our processes on the blades. And this can cause certain issues that you might not have expected to be indicated, like some chattering here to do with the blades being long and thin. And then here again. And this might not be something that you can really do anything about in the final process, but at least you can be aware of it, and you can plan for future finishing processes. And yeah, some of this might be relieved by using enough blade monoliths. But going back to the idea of that, you could split the blade into 20-30 monoliths, but you've also got the idea of cutting time and economy. So you've got to find the balance between them.

The last thing I'd like to do, I'm sure you're all aware, safe panhandling. Just focusing on when we were flipping the part, making sure it was free, able to move maybe but not going to collide with anything, custom made boxes, things like that. We're going to focus on that too much, because I'm sure you're all, if you're manufacturers, aware of that. So the second project I'd like to go through is completely different. So it's another part of an aircraft engine called an outlet guide vane. Rather than a rotating part like a blisk, this is a static part within the engine.

So here are some images of Trent 1000 engines which is one of four variants that we were machining this for. And here is a cross-section of that Trent 1000 and circled is the outlet guide vane, the static part holding the outside together. And also there to direct the airflow. So these parts are mass produced rather than the Advance3 Blisk, which is just a two off we were asked to do. These are mass produced on a production to sell. So slightly different method of approach. So here's the part itself, and rather than machining the entire part, we were asked to just machine the top edge of the part. because the parts are actually made geometrically through another forming process which you haven't gone through, and this is super plastic forming. So in super plastic forming, it's very different to forging or casting. Essentially, an inert gas is blown into a material, and it expands in order to fit a mold. And that's how the rough shape is taken up.

So we were asked to machine the top edge, but in this super plastic forming process there is an inherent inaccuracy in it. You can have parts that maybe distort by a couple of millimeters each time, a couple of millimeters out from each other. So if we were using the same two paths again and again along the top edge, maybe for one part it would cut fine, and the other part it would cut maybe two millimeters deep on one side and not even touch the other side, which isn't the aerodynamic effect that Rolls-Royce will be looking for.

So we got this part. We made a fixture for it very different again to the Advance3. Vacuum fixture here. And it was located for a series of points just placed on. And then put into a machine, just a couple of tool pass to machine the top edge. Again, going back to the idea of just a single direction cut that James was talking about, and the benefits of that. Only cutting in one direction, repeatedly along the top edge. And then this is exactly the finish we were looking for. So you've got the darker unmachined material and the shiny machined edge. And the bottom image shows a good idea of the blend that we're looking for between the machine and unmachined material.

Again this is all well and good, but what does it matter to you? So I haven't really touched on the adaptive process part of the title here. So with the geometry changing we wanted to make sure that we cut the same region of the part each time no matter its geometry. And this was accomplished through a series of inspection routines. So here you can see an image of [INAUDIBLE], an Autodesk piece of software mainly used for inspection and checking geometric accuracy.

Here we were using it to determine where exactly certain points were on the blade, so we were probing two points on each side of the blade at certain cross-sections. And then these two points we used to find the top edge of the blade. And then here you can see another routine probing that top edge after it's been calculated. And these five points go into the creation of curves. And here you can see these of power shape which is Autodesk's modeling software from manufacturing. And the software we use in Birmingham.

These curves went into the creation of a surface. And this surface went in to the creation of some tool parts. And these two parts were made using Autodesk PowerMill. So that's essentially how the adaptive process was completed for each and every part. And this can be applied to any number of things. So maybe if you've additively produced a part that can be some inaccuracies with some processes still, you might want to get rid of, maybe, supports. And so you might want to see where those supports are exactly and machine them away so you don't cut into the part. Things like that.

And while we're on this slide, I want to go through the idea of cutting correctly with tools, especially round tip tools, ball nose tools and spherical tools, things like that. So when you're cutting you want to make sure you use the correct part of the tool. Which is towards the top of the radius and the flank rather than the bottom. There's a couple of reasons for this. The first one is effective speed at that point. So spindle speeds, cutting speeds are set for a reason.

And if you're cutting using the center of the tool, you're essentially minimizing the circumference of that tool at the cutting point. So you might have the same revolutions per minute. But you've got a much lower millimeters per minute. So the cutting speed is going to be lower. It's not going to be as effectively. As opposed to if you're using the entire circumference of the tool. The other thing is, a lot of tools the teeth don't actually go all the way to the bottom. So you've got a nice silhouette here, which shows that the tooth actually stops there. So if you're cutting with the bottom part of the tool you're not actually cutting you're rubbing, which isn't good for the tool or the part or probably your job.

So even a little bit further up where there is a tooth. You can see it's very thin it's not going to be able to cut as effectively. It's not going to be able to get rid of that swarf out of the cutting zone. So you want to cut further up with this deeper tooth where you can evacuate the swarf, the cut material all the way up and out of the cutting site through the tool. And the reason why I'm focusing on this is because it goes hand in hand with machine tool selection.

We chose a three plus two axis machine tool to start this project. But because of the geometry of the vein, we weren't always cutting with the best part of the tool, and that was having an effect on the results that we could get. So you need to think carefully about the machine tool that you use beforehand. For those that aren't aware of the difference between three plus two and five axis, I'm just going to go through that quickly. Back in the day when I was at university, I was like three plus two is five. They're the same. It's not the same.

So three plus two axis is essentially you can change the tool axis but not while it's in cut. So if you want to cut a part you keep a consistent tool axis, maybe you want to cut a different region. Change the tool axis, go back into cut, and then you have to cut the whole thing again.