×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Brazing a structural component - thinkable?

Brazing a structural component - thinkable?

Brazing a structural component - thinkable?

(OP)
Hi all.

We are looking to reinforce a stainless steel stressed skin structure. The stainless steel used is 301LN 1/2 Hd. Someone suggested exploring the addition of a brazed stainless steel flat bar, because it may be easier than welding. Existing skin is spot-welded to stiffeners, but seems too thin with insufficient spot welds.

Naturally, I have many questions.

Static shear strength of brazed joint
Fatigue strength (or any data)
Any long-term corrosion issues?

Any references would help.

tg

RE: Brazing a structural component - thinkable?

Brazing of common steel plates with copper alloy rods is done all the time and you would see that in auto body shops. Brazed joints of copper alloy object with silver solder is also a regular practice. With stainless steel, you may want to check compatibility issues with brazing rods. As far as I am concerned brazed joints are very strong, however, I am not familiar with the practice that you are suggesting and perhaps other responders are. Try it on a couple of specimen, document the procedure used and the stress calculations, and test the specimen by an independent lab before going full production; inform your clients of what you have done to improve your product.

RE: Brazing a structural component - thinkable?

try one of the BAg-7 fillers. The rules are in the back half of ASME Sect IX.

RE: Brazing a structural component - thinkable?

Brazing a stiffening bar to a sheet metal panel surface would seem like a good application for brazing. Lots of surface area for the joint. The common silver based brazing alloys used with 300 series cres would have a tensile strength of 30ksi or more. The main things to consider are the temperatures (>1200degF) used for the brazing process and fixturing needed to position the parts during brazing. As for corrosion issues, here is a link that discusses the problem.

RE: Brazing a structural component - thinkable?

I'll second the BAg-7.
You will need to check and see what degree of stress relief you get on the 301LN after the 1400F braze cycle.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Brazing a structural component - thinkable?

OP said - "but seems too thin with insufficient spot welds."

I'm unclear what is "too thin" and why it "seems" that way.
Poor product performance, or visual based concerns with weld quality or the stiffener itself, or problems with manufacturing?


Are you leaning toward brazing the existing stiffener, or brazing an entirely new style of stiffener ?

Are you making the panels in-house, or buying them? Regardless, if this panel creation is a significant part of the product cost I'm thinking spot welding is likely to be the most economical method of attaching ribs or stiffeners, by a long shot.

Perhaps it is a matter of re-designing the stiffeners a bit, and adding a few strategically spaced spot welds.

Spot welding is good enough for Porsche much of the time. (and other OEMs as well)

https://www.youtube.com/watch?v=des-xY65nMs

RE: Brazing a structural component - thinkable?

What are the implications of a structural fire on the joint? Would the loss of strength as the braze heats up up (melts out ?) drop the structure on the fire fighters/rest of building?

RE: Brazing a structural component - thinkable?

trainguy-

There was quite a bit of basic research conducted by the US aerospace industry regarding furnace brazing of lightweight structures using high-temp metals (like stainless steel) back in the 1960's. So you should be able to find plenty of technical references on the NTRS and DTIC websites. Here's one fairly recent paper on analyzing brazed joints.

RE: Brazing a structural component - thinkable?

There are a lot of panels made with PH stainless honeycomb internal and 3xx stainless skins. These are all brazed with self fluxing alloys (since these use B you cannot braze to high N grades like 301LN).

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources