Break Bend Testing Aluminium

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argonon
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Break Bend Testing Aluminium

Postby argonon » Tue Feb 19, 2013 2:11 pm

Hello All,
I'm new to welding & this is my first post on this forum. The learning curve has been steep but enjoyable at the same time. I am about to embark on building a plate aluminum boat out of 5083 plate of varying thicknesses, 5mm, 4mm & 3mm. Before I do though, I want to try some break bend testing on my welds but need some advice. Kevin Morin has posted some great articles which have been very beneficial but I want to understand beveling & why it should or shouldn't be used for 'T' joint fillet welds.

Here is a link to Kevin's great post;
viewtopic.php?f=7&t=16564

Kevin demonstrates the point that beveled plates make for stronger welds. What I am trying to understand is how important are beveled welds on 4 or 5mm plate? Most text books only require bevels on much thicker plate. Will a better bonding between both parent metals & the weld occur with bevels rather than without?

I will post up some photos of my weld cross sections & 'T' joints in time, would really appreciate some feedback from experienced aluminum welders.

Cheers,
Bill.
I have to keep telling myself, "it's not a race".

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Lowka53
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Re: Break Bend Testing Aluminium

Postby Lowka53 » Wed Feb 20, 2013 9:59 pm

:? I am not a expert welder I have done construction welding and farm welding but I have had college classes in welding. the principle of the grinding the angle is to give you a better joint when you don't do this you could possibly get a area the is not bound together where the to pieces touch basically you only get a surface weld you do get some penetration but not as much but when you grind the area it puts a weld bond in this area and fills what would before not be bonded. so the weld is stronger this is what i was taught. i hope you understand my rattlings on and hope it helps you understand. :roll:
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argonon
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Re: Break Bend Testing Aluminium

Postby argonon » Thu Feb 21, 2013 1:51 am

Lowka53 wrote::? I am not a expert welder I have done construction welding and farm welding but I have had college classes in welding. the principle of the grinding the angle is to give you a better joint when you don't do this you could possibly get a area the is not bound together where the to pieces touch basically you only get a surface weld you do get some penetration but not as much but when you grind the area it puts a weld bond in this area and fills what would before not be bonded. so the weld is stronger this is what i was taught. i hope you understand my rattlings on and hope it helps you understand. :roll:


Hi,
Yes, I think I understand that, my sketch is basically it? It does make sense too because the weld is given a better chance to penetrate right into the junction
when the vertical member is beveled. So, a bit more time spent in preparing bevels can result in stronger welds.
Also, I can see that beveling would be a very good idea on the top weld seam of a keel weld between two bottom plates which typically would be practically touching at the top edges in order
to get the boats 'V' shape. A bevel to this top edge should also allow for better penetration between the plates.
Thanks for your help.
Cheers,
Bill.
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T-JOINT-WELD.jpg
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Lowka53
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Re: Break Bend Testing Aluminium

Postby Lowka53 » Thu Feb 21, 2013 12:00 pm

8) yes that would be it :wink:
Don't be afraid to attempt anything. You might surprise your self in the attempt.
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Bon Voyage-"Wild Flower" 40' house boat being built
14' Mr John-being built
32' Supper Huck-in design

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Kevin Morin
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Re: Break Bend Testing Aluminium

Postby Kevin Morin » Mon Apr 01, 2013 10:53 am

argonon, the concept is basically correct but the bevels you show are not to scale for the parent metal and they're beveled both sides which IS usually reserved for thicker materials.

I demo'd in 1/4 " an beveled from one side then the bevel proportion was much different than you show and those two differences are more important than they seem without testing your own coupons.

The reasons to consider this in aluminum work are several but the main ones are the heat transfer of aluminum and the MIG process in aluminum.

Aluminum moves heat about 7 times faster from one place in the parent metal to another when compared to steel. So where the steel has just as much arc heat the slower movement of heat away from the weld allow steel welds to 'soak in'/penetrate/fuse deeper/get more surface area in the bottom or root face of the weld.

So if you cut away the one or both edges of the aluminum in a bevel, the weld will have less metal to 'rob'/conduct/cool/chill the weld energy away from the weld zone. This means the molten aluminum will have longer to melt the parent metal and fuse. The chilling effect or freezing the puddle is much more pronounced on an un-beveled weld T fillet than on one where the edge of the one parent metal has been thinned.

Next, MIG in aluminum is done best on the edge between the spray mode and the short arc mode of welding. In the pure spray mode (fogging/hissing/humming sound with a flat top bead) the weld is somewhat weaker than a well laid short arc spray combination. IN a purely short arc mode (crackling/popping/snapping/bubbling sound with ripples in the weld bead) the rate of travel is usually slower, and the heat builds up so that usually reduces the break bend strength.

So if the weld can be deposited when the lead arc is in spray mode to get the best arc heat at the toe or lead edge, then the puddle can be moved slightly in an e or c movement and while in motion transition to a short arc mode, as was done in the demo-post; then the gases at the bottom of the root face have longer to bubble up and be cleaned away by the argon before the puddle freezes.

Therefore, if the weld is deposited to the T fillet faces with the higher rate of heat transfer the time to remain molten is shorter and more of the gases will be trapped as bubble within the weld because of the cooler overall parent metal. AND coupled with that the shorter molten period will mean there is less time in the puddle while it is molten.

Now to the bevel's impact or the arc cone and surface wetting. Beveling even thin plate puts the location of the contraction plane more in line with the T joint's vertical member instead of pulling the flat panel up toward the T. So this means if you put a bulkhead or frame member in a boat an weld without beveling the weld zones there will be more weld contraction force to pull the bottom or sides in a wrinkled or 'hungry horse' warp.

Even if you are stitching in longs or x-verse bulkheads instead of continuous welding, its best practice to bevel the weld areas so the weld can be the most inline to the added T element to reduce the effect of contraction on the outer or flat part of the T.

Finally, a MIG arc's lead edge or cone perimeter will 'run to' the nearest DC charged parent metal. So a narrow bevel's edge, as you've drawn in your sketch, will collect a small rim of molten aluminum droplets and begin to build up weld material while working to shield the bottom of the root face. In otherwords if the bevel in the T fillet is not wide enough angle, and is not tall or open enough it will leave the beveled a hollow gap because the weld will 'run-to' and collect on the upper beveled edge and build up a round roll of molten metal stopping the arc from wetting the bottom of the bevel and allowing the weld to fuse fully.

Metal's strength comes from alloy and cross section, so the bevel of metal as thing a 1/8" is good practice so that the edges of the T can become a fully as possible one solid piece of the strongest alloy possible from welding the parent metals as fast as possible with as little remaining gas pockets while cleaning the root face with hot argon just before the molten metal is finally cooled to its lasting shape.

I hope this helps with the reasoning, the best thing possible it to set up your own shop tests, and get your own results. I learned most of this in the first dozen skiffs when I started building and still consider these to be facts.

Incidently the welds you show in the sketch are way out of proportion to the plates the welds should the about the thickness or less on the face not the legs.

Cheers,
Kevin Morin
Kevin Morin

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argonon
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Re: Break Bend Testing Aluminium

Postby argonon » Mon Apr 01, 2013 7:40 pm

Kevin Morin wrote:argonon, the concept is basically correct but the bevels you show are not to scale for the parent metal and they're beveled both sides which IS usually reserved for thicker materials.

I demo'd in 1/4 " an beveled from one side then the bevel proportion was much different than you show and those two differences are more important than they seem without testing your own coupons.

The reasons to consider this in aluminum work are several but the main ones are the heat transfer of aluminum and the MIG process in aluminum.

Aluminum moves heat about 7 times faster from one place in the parent metal to another when compared to steel. So where the steel has just as much arc heat the slower movement of heat away from the weld allow steel welds to 'soak in'/penetrate/fuse deeper/get more surface area in the bottom or root face of the weld.

So if you cut away the one or both edges of the aluminum in a bevel, the weld will have less metal to 'rob'/conduct/cool/chill the weld energy away from the weld zone. This means the molten aluminum will have longer to melt the parent metal and fuse. The chilling effect or freezing the puddle is much more pronounced on an un-beveled weld T fillet than on one where the edge of the one parent metal has been thinned.

Next, MIG in aluminum is done best on the edge between the spray mode and the short arc mode of welding. In the pure spray mode (fogging/hissing/humming sound with a flat top bead) the weld is somewhat weaker than a well laid short arc spray combination. IN a purely short arc mode (crackling/popping/snapping/bubbling sound with ripples in the weld bead) the rate of travel is usually slower, and the heat builds up so that usually reduces the break bend strength.

So if the weld can be deposited when the lead arc is in spray mode to get the best arc heat at the toe or lead edge, then the puddle can be moved slightly in an e or c movement and while in motion transition to a short arc mode, as was done in the demo-post; then the gases at the bottom of the root face have longer to bubble up and be cleaned away by the argon before the puddle freezes.

Therefore, if the weld is deposited to the T fillet faces with the higher rate of heat transfer the time to remain molten is shorter and more of the gases will be trapped as bubble within the weld because of the cooler overall parent metal. AND coupled with that the shorter molten period will mean there is less time in the puddle while it is molten.

Now to the bevel's impact or the arc cone and surface wetting. Beveling even thin plate puts the location of the contraction plane more in line with the T joint's vertical member instead of pulling the flat panel up toward the T. So this means if you put a bulkhead or frame member in a boat an weld without beveling the weld zones there will be more weld contraction force to pull the bottom or sides in a wrinkled or 'hungry horse' warp.

Even if you are stitching in longs or x-verse bulkheads instead of continuous welding, its best practice to bevel the weld areas so the weld can be the most inline to the added T element to reduce the effect of contraction on the outer or flat part of the T.

Finally, a MIG arc's lead edge or cone perimeter will 'run to' the nearest DC charged parent metal. So a narrow bevel's edge, as you've drawn in your sketch, will collect a small rim of molten aluminum droplets and begin to build up weld material while working to shield the bottom of the root face. In otherwords if the bevel in the T fillet is not wide enough angle, and is not tall or open enough it will leave the beveled a hollow gap because the weld will 'run-to' and collect on the upper beveled edge and build up a round roll of molten metal stopping the arc from wetting the bottom of the bevel and allowing the weld to fuse fully.

Metal's strength comes from alloy and cross section, so the bevel of metal as thing a 1/8" is good practice so that the edges of the T can become a fully as possible one solid piece of the strongest alloy possible from welding the parent metals as fast as possible with as little remaining gas pockets while cleaning the root face with hot argon just before the molten metal is finally cooled to its lasting shape.

I hope this helps with the reasoning, the best thing possible it to set up your own shop tests, and get your own results. I learned most of this in the first dozen skiffs when I started building and still consider these to be facts.

Incidently the welds you show in the sketch are way out of proportion to the plates the welds should the about the thickness or less on the face not the legs.

Cheers,
Kevin Morin


Hi Kevin,
You have given me an awful lot to think of, when I read your posts it's like being a 'fly on the wall' of the weld process, it's easy to imagine what is actually happening with the weld and this is very much appreciated. I understand my sketch was completely out of scale.

The plate I will be welding is 4mm and 5mm. Also, the stringers or longs are staggered-stitch welded with 60mm welds each side (this is the designers specification)
The stringers are also full length of the hull so beveling all these locally for welds didn't seem like a practical thing to do?

I have tried some break bend tests on 4mm 5083 H321 plate - no bevels though, here;

http://www.metalboatbuilding.org/phpBB3 ... f=34&t=900

I do plan on doing more tests, these were just a practice before the real tests but my samples kind of went 'crack' at 45 deg but were still hanging on a thread at 90 deg.
These tests were bent over the weld face and on a one-sided weld, what I am not sure about is what would an acceptable angle for the first 'crack' be usually?

I have pretty much also decided to use a simple drag technique for my welds - My 'weave' motion consisted of small back and forth movements or it could even be a miniature 'c' movement. I find it really hard to do a steady 'e' or 'c' that is obvious in it's movement. My machine isn't pulsed so maybe this is the reason I can't hang a weld on for too long in spray mode. The drag seems to work nicely, good tie in top and bottom too. I persisted with the drag technique in practice over the weekend and I feel very comfortable doing it this way. My settings I believe also weld in a transition between spray & slightly short arc mode but I had no idea how the movement can also do this for you until I read your reply.

I wish I could see you weld in person so I can learn from a master but alas there is a lot of land and water between our locations!

Kevin, for all your posts which I read over and over and always discover more relevant information as my knowledge
and practice grows, for this I thank you! There doesn't seem to be a lot of information on aluminum welding out there so your sharing and the sharing of others is really important for people learning.

Cheers,
Bill.

PS: Hopefully you don't mind if I PM some questions :)
I have to keep telling myself, "it's not a race".


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