Why is turbine Blade made by casting?
Why is turbine Blade made by casting?
(OP)
Hi All,
I was reading somewhere mentioned most turbine blade is made by casting? Made me thinking, why not forged or machined from block?
I won't think cost is the reason for such high end product. My limited understanding is that investment casting generally is not as good as forged product. Could some expert share some thoughts?
Cheers.
I was reading somewhere mentioned most turbine blade is made by casting? Made me thinking, why not forged or machined from block?
I won't think cost is the reason for such high end product. My limited understanding is that investment casting generally is not as good as forged product. Could some expert share some thoughts?
Cheers.





RE: Why is turbine Blade made by casting?
A.
RE: Why is turbine Blade made by casting?
Some larger blades or "buckets" (such as for steam turbines) will have internal cooling channels, casting is the preferred manufacturing process.
Smaller blades for high performance jet engines will be forged from solid blanks.
TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com
RE: Why is turbine Blade made by casting?
B.E.
You are judged not by what you know, but by what you can do.
RE: Why is turbine Blade made by casting?
The HP turbine blades and nozzle guide vanes of modern gas turbine engines use very sophisticated internal air cooling and external surface air film cooling to maintain safe operating temperatures. There are serpentine (multi-pass) air cooling passages inside the blades/guide vanes, and also internal passages for supplying air to the film cooling orifices. Currently, the most practical production method for making this type of structure is investment casting.
RE: Why is turbine Blade made by casting?
One factor is the desire to have a blade end up as one single crystal. No grain boundaries.
To make this happen, some clever sacrificial geometry is added to the casting: a "pigtail". As I understand it, the material solidifies and multiple crystals begin to propagate through the pigtail. After some distance, though, only one crystal survives and propagates through the actual part.
RE: Why is turbine Blade made by casting?
https://www.siemens.com/innovation/en/home/picture...
"Even,if you are a minority of one, truth is the truth."
Mahatma Gandhi.
RE: Why is turbine Blade made by casting?
They are controlling heat input and solidification rates so that hey can grow new tips with the original single crystal orientation.
The biggest problem with AM today is that you don't what microstructure/properties you will have until you make a part and then destructively test it. This is a big deal in alloys that are not cubic structure (such as Ti) because you different strength, fatigue, modulus, and even CTE in different orientations within the same part. That, and the fatigue and impact properties are very poor.
This isn't a big deal if you are taking a part that is over designed by 50x and reducing that to 20x. You still cut the weight by 60% and you still have good safety margins.
Once people develop closed loop control systems that allow prediction and control of structure and properties then they will have a breakthrough.
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P.E. Metallurgy, Plymouth Tube
RE: Why is turbine Blade made by casting?
Link
A little side note: The car division is colloquially called Rolls and the aero division Royce's. They are actually completely separate companies.
RE: Why is turbine Blade made by casting?
There has been quite a bit of development work done recently by GE and other engine OEMs using additive manufacturing with CMC materials for producing turbine engine components. CMC is light, strong, and can tolerate temperatures 300-400 degF higher than nickel superalloys. But the CMC materials produced by ALM are not quite ready for production manufacture of critical engine components like HP turbine blades/nozzle vanes. Some other less critical engine components like combustor panels and nozzle shrouds are now being made from CMC material, but they are manufactured using a conventional process.
RE: Why is turbine Blade made by casting?
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Why is turbine Blade made by casting?
My own work relates to development of patterns and core boxes in plastics, using 3D printing and now developing cores and moulds.
"Even,if you are a minority of one, truth is the truth."
Mahatma Gandhi.
RE: Why is turbine Blade made by casting?
One more issue with AM is the lack of process tracking as it relates to internal part uniformity and NDT. If the local temp, weld pool size, brightness, or about 10 other parameters change you should know exactly where in the volume that occurred. NDT methods such as Xray will find voids, but what if the defect is a local area with a different grain size?
The CMCs are great for static parts in the hot gas path (nozzles and first stage stationary vanes).
Most people don't realize that current cast metallic blades have two or three layers of coating on them with cermets and ceramics used extensively.
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P.E. Metallurgy, Plymouth Tube