HAZ reducing shear capacity.
HAZ reducing shear capacity.
(OP)
I'm reviewing the design of a stout aluminum box beam that has a history of shear failure in the HAZ at the web to flange connection. This is an exercise in optimization, we wish to change the welded detail to increase the shear capacity without overhauling the rest of the beam.
How do you, as the designer, reduce the degradation of the HAZ?
I'm looking at a full penetration bevel with a backer (only access from one side), this increases the bonded surface from the old detail, but adds four times the filler metal. Does that much more filler metal, and therefore heat, have a strong effect on the HAZ?
wadavis
E.I.T.
How do you, as the designer, reduce the degradation of the HAZ?
I'm looking at a full penetration bevel with a backer (only access from one side), this increases the bonded surface from the old detail, but adds four times the filler metal. Does that much more filler metal, and therefore heat, have a strong effect on the HAZ?
wadavis
E.I.T.





RE: HAZ reducing shear capacity.
What is the welding process?
What is your heat input?
Details, details, details.
Best regards - Al
RE: HAZ reducing shear capacity.
GMAW
Heat input fails outside my experience.
The box beam has 2 - 1.5" x 7" flanges with 2 - 5/8" x 9" webs with a 4" wide void inside the box beam. Partial drawing attached. The critical load is shearing load pairs at 12" - 24" apart at both ends, with the transverse shear flow along the HAZ zone failing.
The web to flange connection is semi-accessible on both sides for half the connections, but not for the other half. The current detail is a 1/4" bevel, 3/8" fillet.
wadavis
E.I.T.
RE: HAZ reducing shear capacity.
You say... “an exercise in optimization,” but may actual mean ‘an exercise in futility.’ When working with aluminum and welding and allowable stresses, more weld usually doesn’t work you out of the problem. The heat from the welding process eliminates the temper in the aluminum for an inch or so, in all directions from the weld, and consequently seriously reduced the allowable stresses in those regions. And, in most cases, more weld doesn’t change that or reduce the HAZ. You have to do something with the details, to move the welding zones to regions of much lower stress, not just add weld to reduce the weld stress. In the regions you are welding, you have both high bending normal stress and relatively high shear stress. The short answer to your question is don’t use welding in those regions.
RE: HAZ reducing shear capacity.
The unit stress on the base metal must be considered. As in the case of structural steel, the weld/base metal interface must be considered to prevent the weld from "pulling out" of the base metal. When designing a connection, the yield strength of the HAZ must be considered to ensure the loads are limited to a fraction of the as welded yield strength and within the elastic range.
Reduced tensile test specimens typical break in the HAZ.
The weld is as strong as the base metal in the "as welded" condition if the proper filler metal is selected and the WPS takes into consideration precautions that are somewhat unique to aluminum and its alloys.
When welding with the GMAW welding process, make sure the parameters ensure the spray transfer mode is being used. Do not use pulse or short circuiting transfer when welding aluminum. Keep the interpass temperature low as practical. That means the use of mechanically enhanced cooling, i.e., blowers, directed to the joint between weld passes. Do not use preheat.
Best regards - Al
RE: HAZ reducing shear capacity.
How many of these do you make? What are they used for? I’m not sure I understand the load conditions, show them on your sketch. Do listen to Gtaw’s advice, as always, he knows what he is talking about when it comes to welding. If it’s important enough, why not save the money for all the additional welding and consumables, etc. maybe even less costly base plate materials, using normal weld sizes and detailing and temper or retemper the whole beam after welding.
RE: HAZ reducing shear capacity.
gtaw; It looks like my ignorance of GMAW and preheat process is hindering my progress (The existing design includes pre-heat). Can you recommend reading material regarding spray transfer, circuiting transfer, and the effects of interpass temperature? Can you recommend a welding design guide / textbook?
RE: HAZ reducing shear capacity.
Best regards - Al
RE: HAZ reducing shear capacity.
What if the vertical parts looked like this ] [ instead of flat pieces?
You would need to make the top and bottom plates thinner by 5/8" in order to keep the total flange thickness constant.
It might be worth some modeling to see.
= = = = = = = = = = = = = = = = = = = =
Plymouth Tube
RE: HAZ reducing shear capacity.
... with really generous radii at the flange to web intersection, of course, and maybe even hourglass tapered webs. Pretty much anything is possible with a big-ass ball end cutter in a 3-axis CNC milling machine. All you gotta do is shovel out the chips.
Mike Halloran
Pembroke Pines, FL, USA
RE: HAZ reducing shear capacity.
Any comments on the value of Welding Aluminum: Theory and Practice, Fourth Edition?
RE: HAZ reducing shear capacity.
Maybe you can find one on Fleabay.
The title is "Welding Alcoa Aluminum", naturally.
Mike Halloran
Pembroke Pines, FL, USA
RE: HAZ reducing shear capacity.
There will be some distortion and post-treat straightening required. If that's not acceptable, then the suggestion to move the welds or avoid welding is a good one.
If there's no welding at the end of re-design, 7xxx series aluminum has even higher strengths, allowing smaller sections for less material. 7075, for example.
RE: HAZ reducing shear capacity.
Best regards - Al
RE: HAZ reducing shear capacity.
I finally took a look at the drawing. It's a good candidate for extrusion if the qty is high enough. The cost of the die and the minimum run balance against the cost of cutting out the pieces and setting up to weld with welding's subsequent problems of a HAZ, porosity, and other weld-related failure modes. Still have to add the round cross-rod, but that's it.
RE: HAZ reducing shear capacity.
If you moved the webs inboard a bit, you could extrude the flanges with a curve on the distal part, and press them flat before heat treating. This is commonly done for large heat sinks; they are extruded with a circular section and flattened while still soft.
Also, there surely must be a bigger press somewhere by now, so extrusion as per your drawing should be possible, and is worth exploring.
The good news is that the minimum order quantity for that big press was only 5000 lbs., which is not a huge length of such a heavy section, and extrusion dies are surprisingly inexpensive.
The closed box section adds some complexity to the die, so if your application could use a single thick web, that would save you some bucks.
Mike Halloran
Pembroke Pines, FL, USA
RE: HAZ reducing shear capacity.
http://www.shapesllc.com/cap_extrusion.cfm claim a 24 inch circle and up to 40 pounds per foot.
http://www.bonlalum.com/large-aluminum-extrusions.... are at 16 inches wide, but wimp at 20 pounds per foot.
and Holy Heck! http://www.aluhorizon.com/custom_shape.html scroll down the page a bit. Thin walled, but still.
When I started out if a section wasn't in the shapes book, forget it. Even then it better be on a rack.
RE: HAZ reducing shear capacity.
You can even get competitive bids on the part.
... I suggest that you do.
... after adding some nice fillets to the web/flange interfaces.
Mike Halloran
Pembroke Pines, FL, USA
RE: HAZ reducing shear capacity.
I do think getting a weldment heat treated will be on the easier side in the short term than getting time on a giant extruder, but it's still impressive, the chair especially.
What I want to see someday is variable section extruders. Dang - someone beat me to it: Patent US 5989466. Wonder if one's been built yet.
RE: HAZ reducing shear capacity.
Let me put it in perspective: The 5000# minimum order for that 13" extruder corresponds to exactly _one_ stroke. Building the die will be the biggest delay, and it probably won't be as bad as what you're imagining.
As for stepped sections, you could thin the web of your part with a 1/2" router, or of course a common CNC mill.
Mike Halloran
Pembroke Pines, FL, USA
RE: HAZ reducing shear capacity.
Alternative uses would be producing a sinuous web to prevent buckling or a constant wall thickness but a tapered tube.
I also wonder if a rotating embosser could add pre-formed gear teeth as the material is extruded, even if they were only a good approximation there's some value.