high strength stainless tubing

[sleuth14]

I'm working on reducing the cost of a torque-tube that is machined and hollowed out from 17-4PH round bar stock. The existing design has 1.5" OD with 1.22" ID. Part is appx. 15" long.

Preferably, I'd like to keep my OD the same and change to a material that has equivalent or better strength. I would also like to find tubing instead of bar-stock, so as to eliminate all the machine-time it takes to hollow one of these things out. If I change my OD, then I have to resize all the mounting hardware and I add weight, which I've got to minimize.

I've been looking for 440-series tubing and have come up empty handed. The only thing I've found so far is at

http://www.mcmaster.com

and the tubing is 4x more expensive than the bar-stock, which seems really counter-intuitive.

Does anyone have any suggestions?

 

[MikeHalloran]

Well, you have to pay someone to remove the middle, somehow. Hollow bar is cheap if it saves a lot of machining time.

Talk to your tooling supplier about drilling that center hole. He may recommend using a different tool, e.g. a carbide spade drill, or pushing the tools you've got a lot harder.

Macarco is good for comparing costs, and for small quantities, but your local steel distributors can do much better if you buy whole bars. Quotes are free. Be sure to tell them what dimensions you really need; they may have something with thicker wall that can be rebored easily.

The only valid basis on which to compare raw material costs is by comparing resultant finished part costs. So, for this comparison, you need to calculate and optimize your machining costs for boring solid bar, and for reboring hollow bar.



Mike Halloran
Pembroke Pines, FL, USA

 

[sleuth14]

Thanks for the reply, Mike.

ID is not critical for this application, except that we need to get the wall thickness to its minimum point for weight savings. We can rebore a tube if necessary, and it's still going to be cheaper than boring a solid bar.

At this point, I'm still in the conceptual design phase, and was looking for a tool to compare costs before I send out for quote. The difficulty is finding anything online that can show me availability and appx. costs for high-strength tubing to aid me in my research.

Our organization generally will only send out for a ROM quote once and a final quote after the drawings were made. Maybe I can press my project engineer to talk to our suppliers directly.

 

[EdStainless]

Do you have strength, fatigue and corrosion resistance requirements quantified?
What heat treat condition are you using for the 17-4?

There are a number of ways of doing this. An alloy that cold works to high hardness could be provided as-cold-drawn, or a higher strength PH grade could be used, as two examples.
The price per foot of the tube will be high, but you will save a huge amount of machining costs.
Let me know more details. One important item is the quantity that you need.

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