Machining Inconel

[bigandy]

Hello all.

I'm in the process of planning a homebuild gas turbine engine, and one of the machining ops I need to do is to accurately bore a hole (for a shaft) in the turbine disc. I am intending on buyiung a cast Inconel turbine disc, that is unmachined. I'm not sure of the exact grade yet, but I have assked my supplier.

Anyway, I would like to know of any tips/hints people may have for machining materials such as Inconel. To date I have only really machined brasses/aluminium alloys.

Any help/advice would be much appreciated thanks!

Andy

[ajl6549]

Inconel is very difficult to machine. I've milled some keyways/slots etc. The general rule is not to feed to slow. Iscar has carbide grades intended for high alloys like inconel, check with your Iscar rep. Also your casting dosn't sound cheap so you may want to get some practice.

[SeaSchell]

Check your design. Most turbine disc's sre FORGED not cast.

[bigandy]

I'm around 99.9% sure that the turbines are pressure cast inconel 713 (possibly 714), (using a lost wax master). The wheels are only a total diameter of around 60-61mm and I need to bore a hole in the middle.

I had a thought though, Spark erosion might do the trick, without the need for nerve wracking cuts!

Cheers
Andy

[ajl6549]

Originally Posted by bigandy I had a thought though, Spark erosion might do the trick, without the need for nerve wracking cuts! Cheers Andy

"Spark Erosion"? is that the same as what we call EDM, Electrical Discharge Machining

[bigandy]

That's right! Here in the UK it is referred to (usually) as wiring or sparking. Which translates as wire eroding or spark eroding, which are basically slgihtly different methods of EDM...

I've been chatting to one of the toolroom guys where I work, can you tell?!!!

Anyway, he seems to think that the high nickel content alloys are far better being either ground or sparked (EDM!) whereever possible, so using a spark eroder to form the central bore on the turbine wheel would be best, then mounting it in a lathe, or cylindrical grinder, to grind the outer diameter down to size.

It sounds so simple doesn't it, and removes the need for for any "cutting" as such...

Cheers
Andy

[ajl6549]

Interesting. We use the wire method as well as the electrode method. So are the "blades" on the turbine wheel used "as cast" or do they require machining as well?

[bigandy]

The blades/disc is all one piece, and there are basically three machining ops that need doing. First is to bore the hole (for the shaft to pas through). Second is to finish the outer diameter down to the correct dimension. This means taking an amount of material off the tips of the blade.

Finally the disc needs balancing, and there is a sacrificial rim cast into the hub of the wheel that can be partially ground down to aid balancing.

Cheers
Andy

[Beaker]

Turbine wheels for model engines are vacuum cast and made out of 718 or 713 depending on engine temperatures involved.

For the hole carbide cutters makes the job easy, my choice has been the GARR VRX endmills. Use a size smaller first, then bore to final size.
Don't try using an endmill or slotdrill to your final size in a chuck on the lathe as it will more than likely go oversize or make a slight taper stuffing your job. Your turbine hole size is critical.

I use a tool and cutter grinder on the outer blades. Cylindrical grinder is even better.
Don't be tempted to use the lathe as you may bend blades.
Good luck

[acidcustom]

Inconel will more than likely machine very similar to copper , it is very similar , will be very sticky and clog to cutters easierly

[ShaggyVW]

CARBIDE, CARBIDE, CARBIDE, COOLANT , COOLANT, COOLANT. FOR OUR HAAS WE RUN OUR 1/2 BALL AROUND 10000 RPM AND 80 IPM

[cam1]

Hi:
Cast bladed disk assemblies are often referred to BLISC (bladed disc). The ar eroutinely electrochemically machined in order to get the aerofoil contour and surface finish correct.

regards