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Is it possible to 3D print an axial turbine 2 - 4 inches (50 - 100 mm) in radius, capable withstanding temperatures about 800 - 1000°C and rotation speeds of 100 - 120 x 103 rpm?

How expensive is that? Is it cheaper to mill such a turbine from a whole piece of alloy?

What technologies and materials should be used?

Are Inconel alloys suitable for 3D printing?

Are there any titanium alloys suitable for this task? I've read titanium is rarely used in rapidly rotating parts due to its ability to ignite if mechanical failure occurs and rotating blades touch the casing. Do titanium alloys still have this drawback?

Is it possible to make disk of titanium and blades of Inconel, and have them welded (considering heat expansion)?

How blades or blisks can be ceramically coated?

Thank you!

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    $\begingroup$ Welcome to 3D Printing SE, this is a great topic that hasn't come up too much here on 3D Printing SE! However, there are too many questions in a single question here. Please consider breaking this up into other question posts to avoid having this post closed due to "unclear what the user is asking" issues. $\endgroup$ – tbm0115 Dec 6 '16 at 17:26
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You ask some very interesting questions! Firstly, when researching topics such as this, you will have far more luck using 'additive manufacturing' as a search term rather than '3D printing'. In the professional industrial environment, '3D printing' is not a term that is really used to describe the manufacturing you are talking about.

Selective laser melting is the additive manufacturing process most suited to metallic aerospace parts. Inconel alloys can be processed (e.g. IN718 being one of the easiest) along with titanium (almost exclusively Ti6Al4V). As for manufacturing turbine blades and similar parts, you might find this interesting: Additive Manufacturing - Breakthrough with 3D printed Gas Turbine Blades.

Titanium is not typically used in high-temperature sections of gas turbines, but will be used in larger, cooler components such as fan blades, where it's strength to weigh ratio is a benefit (less mass to rotate = better fuel efficiency).

Coating of high-temperature nickel superalloy components is usually performed with electron beam physical vapor deposition (EBPVD) or thermal spray such as high-velocity oxy-fuel (HVOF); each process has certain characteristics that dictate when/where is it used.

This is only really a surface depth answer to your questions, but it would be impossible to answer fully here!

(My experience: PhD student using selective laser melting with aerospace alloys)

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  • $\begingroup$ Thank you for your answer! Still there is one important thing I'd like to know: how expensive is additive manufacturing next to milling this kind of product? $\endgroup$ – Eugene Feb 16 '17 at 0:03
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    $\begingroup$ That's very difficult to evaluate. Overall, the cost of manufacturing a turbine blade via additive manufacturing (AM) will be higher than via casting (the conventional manufacturing method). However, AM can add value through complexity, e.g. internal cooling channels or lattice structures to minimise weight. So really, it is a cost-benefit analysis rather than a straight costing. (Rough example) machining the outer form of a turbine blade via CNC milling may cost 10% of that of an AM part. However, even a 1% fuel efficiency increase over the component life blows this cost out of the water. $\endgroup$ – samcs640 Feb 16 '17 at 0:23
  • $\begingroup$ The overall answer - it is almost always cheaper to stick to conventional manufacturing (e.g. milling), but the aim is to leverage the advantages of AM to improve (add value to) your component. Taking an existing CAD file and simply printing it is pointless - use the principles of 'design for additive manufacturing' to really make use of the technology. $\endgroup$ – samcs640 Feb 16 '17 at 0:32
  • $\begingroup$ What's the difference in designing for AM? What special features this needs? Or it is about thinking how to improve component design using newly available manufacturing methods? $\endgroup$ – Eugene Feb 16 '17 at 1:08
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    $\begingroup$ DfAM covers a huge range of topics, enough to do a whole degree on. I'm struggling to find an open-access source for you but the wikipedia entry gives a good basis (en.wikipedia.org/wiki/Design_for_Additive_Manufacturing). For mini-turbines, it is likely you would keep combustion temperatures low enough to prevent the need for excessive cooling channels (i.e. well within the material's operating temperature). Increasing temperature is chasing better efficiency, this is something you would probably need to sacrifice. $\endgroup$ – samcs640 Feb 16 '17 at 10:05
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This depends primarily on economics and on desired lifetime. Rather obviously you need a material whose strengths and melting points exceed the operational specs. Determining the various break strengths (shear, bending, etc) is an engineering problem, not a manufacturing problem per se.
Next, consider the production time and cost of 3D-printing vs. some typical assembly line process. Nearly always the 3D approach loses for large quantity builds.
Designing and operating devices like this can be extremely dangerous. Very tight tolerances are required. This site describes the difficulties, starting with material choice, moving on to tolerances, and so on. I don't think you want to go at this in your basement.

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I would think it's definitely possible, steel 3D printers are most likely capable of printing with the kind of precision you need (I've had experience designing and printing barrels for handguns as part of a forensic science research project), but be aware that with most processes I'm aware of, you'll need to go in post-production and do some polishing or surface refinement, specially for a turbine application where those temperatures are already high and any surface flaws won't help durability.

Otherwise, I would just make sure you use a material with a track record of meeting your specifications. Likely easier finding extremely reliable and robust materials to mill but 3D printing would be possible in theory.

Financially speaking, though I don't have any experience comparing the costs on that specific kind of a component, milling is likely going to be cheaper as long as you can find someone who will do single unit production runs.

Personal opinion: I would go with milling. I've had a lot of experience with 3D printing and am a die-hard proponent of its merits, but given the lack of personal knowledge about how a 3D printed turbine would perform long-run, and the consequences of failure of something rotating at those speeds, I would be inclined to go the traditional manufacturing route.

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    $\begingroup$ I don't know, but I suspect that the only justification for commercial 3D printing of this sort of structure is to achieve internal details - for ventilation/cooling, and the level of precision in the process control makes small quantities impractical. $\endgroup$ – Sean Houlihane Dec 5 '16 at 8:28
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Some companies are already on the move with this idea. I think I remember hearing that Pratt and Whitney and Boeing are 3D printing some of the smaller air foils.

The advantages being that they can achieve manufacturing of more complex, more efficient parts without the hassle of quality control, expensive fixturing/maintenance, and less hands on their proprietary parts and processes.

Most often, a metal alloy part is "printed" using SLA or SLS (commonly), but it's more or less just bonded. Bonding is either done via laser sintering or some form of epoxy for these types of printing processes. The part is pretty much useless for aerospace purposes at this point because you can just break it apart with your hands, as it is very brittle.

Once the metal is bonded in the desired shape, it goes in a furnace to either solidify the sintered material or the epoxy is replaced with another metal such as bronze or nickel. Also during this operation, the part is heat treated to receive the desired material structure. The changes to the material during this process can help set its strength and heat resistance.

A quick Google search on "Inconel 3D Printing" yields a couple companies that can 3D print "exotic" metals such as titanium and inconel. Chances are if a 3D printer can process inconel, it can print most other aerospace materials.

3D printing exotic materials, at this point, is really just gluing sand and baking it in the oven.

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  • $\begingroup$ Thank you for the answer. The problem making mini blisks is that you can not make any air passages for air cooling, as it requires separate blade production, and even so, it is very difficult to produce such a blades in mini-size. Without cooled blades you can not overcome some efficiency treshold. The second part of my question was if any gas (gas, not steam!) turbines are made of titanium alloys. Do you know something about it? $\endgroup$ – Eugene Dec 7 '16 at 1:03
  • $\begingroup$ I'm sorry, I do not personally know on that topic. I'm sure there are some titanium alloys out there, but material science is growing so rapidly now that it's hard to keep track of what materials are being used where now. If I find anything I'll let you know though. $\endgroup$ – tbm0115 Dec 7 '16 at 1:07

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