Edge weld on sheet metal box 3

[imagineers]

I am creating a water tight sheet metal box, and would like to specify on the drawing where and how to weld the edges closed. WHat would I put on the notes and would I use a fillet weld on the outside edge then grind flush for a neet and clean look? or do I weld on the inside edge (probably harder)?

 

[imagineers]

i put in an edge flange weld with a concave grind symbol does this make sense?

 

[MintJulep]

This is an edge flange weld.

Does your joint look like that?

 

[imagineers]

I ended up using a fillet weld on the outside edge and a convex grind note on it

 

[racookpe1978]

how thick the metal walls?

 

[berkshire]

I think the weld you are trying to describe is an outside corner weld, the weld symbol shown is for both sides, just delete the symbol for the side you do not want welded.
B.E.

You are judged not by what you know, but by what you can do.

 

[imagineers]

0.9mm thick sheet metal, so I am assuming maybe a 1-2mm outside fillet weld with grind convex finish??

 

[MintJulep]

By definition a fillet weld can only be made where there is an inside corner to work with.

http://en.wikipedia.org/wiki/Fillet_weld

We can't tell from your sketch what the joint configuration is or what type of edge prep could be possible.

We can't tell from your posts what strength is required.

We can't tell from your posts how nasty looking an inside appearance you are willing to accept.

"Water tight" means nothing by itself. Are you trying to keep water in, or to keep water out? How much? What is the pressure differential? Spray? Submerged? Hot? Cold?

Designing a weld joint is more than sticking a random weld symbol on a drawing. It starts with quantified requirements.

 

[imagineers]

strength not an issue, want to prevent water from leaking, not submerged just a liquid leak from a tank inside not a spray. easiset answer please

 

[imagineers]

I want an outdie clean appearance on the edges, so I am imagining some grinding before paint would be the route? Not sure aobut edge prep. When I place a weld in solidworks it is using a fillet on the outside edge, just asking your opinion as I am not 100% sure what to spec in the drawing guys

 

[qcrobert]

We build a similar box weldment that requires to be moisture proof to protect cathodic equipment in exposed environment.

Usually drawn as a corner weld. But to assure leak proof welds, I use a Zyglo dye penetrant with aid of an ultraviolet (black) light to test weldment for thru wall leaks.

Robert

 

[racookpe1978]

I try very hard NOT to try any corner welds on material less than 2-3 mm thick without a lap joint or a tab folded at the corner. 0.9 mm to 0.9 mm at a "free folded corner with no backing metal is very tricky to avoid burn-through and re-re-re-rework.

Fold the corners up so there is a backing piece behind the two plates. Clamp the folded corner into a jog or fixture tightly to hold the corner square and pretty, then try to tack first weld from the inside at at least two locations. Then finsih the joint from the inside so your GTAW tip can cross from one side to the other. You'll have better access from the outside, but a much more difficiult weld.

Alternative: Use a folded joint with a "flap" or lapping side behind the corner, then braze the joint. The braze will "suck into" the very small gap between the two sides instead of melting the two walls.

Alternative: It will take four more "parts" but fold up the walls into position, but clamp them into an angle iron going up the corner from bottom to top. Then braze or weld up the corner joint. Use the angle iron as reinforcement after assembly, and as a built-in jig to hold the corner square and perpendicular during assembly.

 

[dhengr]

You guys are going to shoot yourself in the foot (I mean your welded joint or other joint) if you keep going much further. With mat’l. .9mm thick, the toughest part of the process is going to be jigging the two sheets together, so the weld can actually be made. Giving some thought to this is also part of the design process. Maybe some small back-up corner piece is in order, so you can press the two sheets to it, and then make the weld. A guy who knew what he was doing with a gas torch, would melt those two sheets together, with a nice rounded corner which wouldn’t require any grinding.

 

[berkshire]

imagineers (Mechanical) (OP)
I was not paying attention to the thickness of sheet you were specifying .9 of a mm is equivalent to 20gauge sheet metal. In normal industrial practice it is more common to put a spot welded tab flange with a sealant, rather than a weld.
If you insist on torch welding this part (TIG) heliarc is recommended. Then I would suggest you up the gauge to 18 gauge ( 1.25MM ) This will give your welder a far easier time with less chance of burn through and distortion.
B.E.



You are judged not by what you know, but by what you can do.

 

[tbuelna]

Looking at the first sketch, it appears that your box has gaps at the vertical corner joints and simple un-grooved butt joints along the horizontal bottom corners. Given the minimal thickness of these panels, I recommend using inside fillet welds for your watertight enclosure.

 

[imagineers]

Well, thats alot to absorb talking about Zyglo dye penetrant, no clue what that is. not everyone is in agreement on this. some say an inside fillet weld, others say butt joint, and some say a secondary corner piece. I understand the concern of burn through because of thickness, and maybe thickening to 1.2 is an option, but do I need an inside flange on this or can I just leave the bent edges as they are and fillet weld inside or outside then grind it without adding a secondary piece

 

[MikeHalloran]

You need to walk away from the CAD station, and spend a few hours in the shop where the part will be made, talking to the people who will do the work, and assessing the shop's capabilities. ... as the shop people will be assessing your capabilities.

Bring donuts.


Mike Halloran
Pembroke Pines, FL, USA

 

[gtaw]

Mike, I like your approach. All too often, the wall separating the designer from the production floor is never breached. More often than not, a brief discussion with the fabricator will save time and money by improving the design. The feasibility or ease of fabrication is overlooked.

Best regards - Al

 

[imagineers]

Thanks guys, that's probably a good idea to go down to the local shop and see what they suggest as the best approach