Butt Joint or Overlap

[AZ79K5Project]

I posted this over in the tools thread a few days ago at the end of another thread. Thanks dremu.

I am building a tube/winch bumper. Is there a difference, issue or problem overlapping the plate and welding on all four sides rather than doing a butt joint?

Is the overlap weaker in some way?

 

[dhcomp]

my beginner welding skills and mech engineering training say that the overlap will be way stronger, but lets see what experienced ppl say.

 

[AZ79K5Project]

I was initially thinking the same, but then I started thinking about the weld penetration. At best, I am getting maybe 1/2 thickness. This would only give the joint 1/2 thickness. A piece is only as strong as the weakest link.

Wouldn't the front and side edge theoretically have full thickness penetration?

 

[AZ79K5Project]

bump

 

[BGKYK5]

I'd like to hear an answer to this too. My guess is that each has it's preferred application, but I'd like to hear from an experienced welder....

 

[think_07]

How thick of plate are you welding?
Maximum penetration thickness for an unprepped buttjoint from one side is 1/8", if you welded it from both sides that would give you 1/4" of penetration, unless you made a single or double V groove. A good fillet weld should be plenty strong for what you are making (the lap welds in your picture). If you can, you could weld all the joints on both sides of the plate and you'd be set. What type of welder are you using? Personally I would suggest either 7018 stick or a fluxcore wire with shielding gas, i'm not a real fan of hardwire or metalcore, but yes i'm sure you'll be happy with the fillet welds as long as you get good fusion and have some welding experience.

 

[macg]

Generally, a good quality full penetration butt weld is preferable because it is a lot less welding compared welding a fillet weld all around two overlapped pieces, and provides the "smoothest" stress distribution through the joint. If two plates are overlapped, it would be good to seal weld them so that you wont get corrosion between the plates. Overlapped plates won't be aligned with each other and you will get some additional stresses if they are pulled on for example. I think that for a bumper either way would work fine. If you are not sure about your welding, the fillet welds all around will somewhat distribute the loads to more area and you may have enough good weld to make up for any bad spots. It really depends on the situation and loading, but I would usually prefer the butt weld for joining two plates, (although you may have to bevel one of the edges).

 

[AZ79K5Project]

Hobart 180 (220Volt) Mig 0.035 solid wire. 1/4" plate