Additive manufacturing

One recent major development in the world of manufacturing is additive manufacturing, or 3D printing. The Manufacturing Technology Centre in Coventry has a team at the cutting edge, and David Wimpenny - the technology manager - spoke to Chris Smith about how additive manufacturing is a real game changer...

David - It's so different than conventional manufacturing methods. As Mike already said, we’re used to making parts by injection moulding, where the shape of a part is controlled by tooling, or by taking a block of material machining away to form the shape. Both those techniques have drawbacks in terms of the waste of material that's formed, the geometrical flexibility, and the need to have fixed tooling. 

Additive is quite a simple technique. You're just making objects by depositing layer upon layer of material on top of another. It allows unlimited flexibility in terms of the part geometry. And of course another advantage, you can print parts on demand, you don’t need to have the lead time and time to separate a mould tool, for example, so it's really a game changer. You can imagine a part that's being formed where across each layer can be different distribution of materials, and layer by layer that distribution can change. There is no process that I can think of that allows that flexibility and the potential that brings with it.

Chris - I was going to pick up on the point you made about making these things to order. Of course, when we engineered or made things in the past, it was so expensive to make prototypes that actually often things were very very slow to develop but if you can 3D print things you can try lots of different ideas very very cheaply.

David - Absolutely, your lead time between thinking of an idea and be able to bring it into production is very short. Now we have a whole raft of new companies where you got an entrepreneur that's maybe even sat in his bedroom designing something and the next day could potentially be asking your company to print it, and doesn't even have the printing equipment itself. The printing equipment can be based anywhere in the world. So this is flexibility we've never seen in manufacturing before. And, of course, another advantage is that we can print things that are customized to individual people. printing things like customized implants for surgery for hip surgery and also many people who've got dental work will have implants made for them especially by 3D printing that match specifically what they need. So it's that flexibility we dont get with conventional manufacturing.

Chris - People are often familiar with 3D printers using plastic, and things like that, but actually Rolls Royce hit the headlines a couple of years ago when they flew apart in an engine which was the biggest flying 3D printed part. They printed a whole chunk of jet engine and they used obviously metal for that so tell us a bit about how we can use different materials in a 3D printing environment to make very specialist components.

David - Some of these materials, particularly in the aerospace industry, titanium alloy components, are very commonly used. But it’s quite a difficult material to process, it’s hard to machine and it’s also very expensive. If you’re using these more exotic materials, you don’t really want to waste that material and so additive manufacturing offers the potential. It’s not just complex shapes but also not to waste the material, you can add and also print the material exactly where you want it.

Chris - So how does it actually work? If I wanted to make a very complicated bit of engine out of a very costly material, how do I do it?

David - Yeah, that’s a good question. So normally we take a powder a fine powder, we lay it down in the very thin layer and then we use a laser or an electron beam to selectively melt that powder to form a slice through the object. And then this process is repeated layer upon layer upon layer to effectively form the entire component. It starts as a powder and ends up as a solid metal object.

Chris - Structurally, has it got good integrity? My reason for asking this is that I have been fortunate to go to Rolls-Royce precision casting facility up in Derby, and they grow parts for their jet engines out of single crystals of the metal. So when they make the cast they pour it into a very hot mold and then they start this little crystallization process at one end of the object and it spreads through the entire thing they’re making. And that gives it enormous strength. If youre just fusing tiny little bits on each time you get the same single crystal, same strength that you would get?

David - We’re struggling with the crystal at the moment, that's one area where this still some work to do. But one thing we do get, compared to conventional forgings, is that we can get really fine microstructure. The material itself has better properties than you get with some of the conventional manufacturing techniques and certainly better than castings where we're used to quite large defects, in some cases for certain complex parts.

You are getting a better, what we call, metallurgy from the materials you're using but we're still struggling to get the quality you get from a single crystal but, of course, in the future it may not be utilising metals at all.  We might be using ceramics advanced ceramics for for these high temperature, high corrosion, areas of a gas turbine. As we increase the temperature, we get more efficient engines.  Ceramics are very hard to form conventionally so additive is yet another method to form these difficult to manufacture materials.

Chris - I've not heard anyone talking about 3D printing ceramic materials before. So if you say they're hard to work with, why are they hard to work with, and how will we do this?

David - Typically, they're very brittle, they're difficult to shape. And with additive manufacturing, we can take apart materials in the form of powders, and shape them. It also makes them less sensitive to cracking during processing. So I've got colleagues working at the moment on using machines where we lay down a layer of fine ceramic material, and we print a binder using an inkjet print head. That forms what we call a green component, effectively a loosely bonded ceramic component. That can get be heated and fired in a furnace to make a fully dense component. That revolutionises the shape of parts that can be made by ceramics. There's also potential to mix ceramics that are very hard to mix using conventional bulk processes. It could potentially revolutionise the ceramics industry, but ceramics is still lagging behind the plastics and metalic additive manufacturing processes because they've been around longer and more money has been dedicated to them. But ceramics is the next thing coming through and we're starting to see really important developments. 

Chris - So what kind of industries would you be talking to then? I can imagine medical - implant makers might find a use for ceramics because people are worried about the wear parts of metals from say a hip replacement, but what else?

David - Anything where you've got high temperatures and a corrosive environment, ceramics are a big bonus. There are applications at very high temperatures, again in aero engines, particularly space applications. The rockets used in sending space craft into space require very very high temperature materials, and often the current materials we've got can't reliably last long enough but with ceramics you have that extra heat resistance.