youngs modulus and forging

[azzt]

Hi

I'm currently reverse engineering a gas turbine inlet stub shaft, which I know has been produced by forging. Due to the small amount of these parts rquired per year it has been suggested to use rolled bar and machine to the finished size with heat treatment and so on.

The question I have is that in the original the flow lines in the material wil tend to follow its shape however in the machined part the will not. Would this lead to a significant reduction in Youngs modulus locally at a change in cross section? Does anyone know of any references to this type of query?

Thanks in advance for any suggestions.

allan

 

[EdStainless]

modulus has nothing to do with this. Modulus is an intrinsic property that is dependent on composition, not processing.

The real issue here is fatigue. This is similar to auto crank shafts. There is a reason that racing cranks are forged, even though there are only manufacture a few hundred a year.

Think of the cost, and think of the risk. What happens when one of these fails?

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[metengr]

We have on occasion reverse -engineered shafts that were originally forged to near net shape. These shafts were forged, primarily because of costs associated with machining large transitions or changes in shaft diameter, and to avoid breaks in flow lines at these locations.

Depending on the geometry and function of the shaft it may work, especially for smaller diameter shafts with small transitions or steps. If you have large geometric changes or abrupt steps along the length of the shaft, I would probably stay with the forging.

 

[mog69]

A significant consideration in using forged bar is the possibility of inclusions at or near the centre of the bar. If the centre is not going to be bored through, I would suggest specifying a condition of purchase should be that the supplier should peel the bar and ultrasonically test it for soundness, and certify accordingly.
If you were to purchase a shape specific forging you would have the opportunity of specifying the minimum reduction ratio which would give some certainty of soundness. You do not have that option with forged bar.

 

[dbooker630]

If I had to use bar stock to replace a forging I would make sure the bar reduction was at least 10:1, preferably 15:1. This would eliminate most billet material, restricting you to bloom or ingot cast steel. If the shaft has a significant sized flange on it I would not recommend bar stock, you'll have to pay the premium for a low volume forging.

 

[swall]

An open die forging might be another option.