[Otto Nobedder]

I realized, while reading Jeff's reply, I left out an important point...

If you don't solve (or prevent) cracks in the tacks, and fix every one, those cracks will grow into your finish weld.

While there are many causes for a weld to fail in any material, if you have a crack in your tack weld, and don't fix it, you WILL be haunted by it later.

Steve S

[TamJeff]

I realized, while reading Jeff's reply, I left out an important point...

If you don't solve (or prevent) cracks in the tacks, and fix every one, those cracks will grow into your finish weld.

While there are many causes for a weld to fail in any material, if you have a crack in your tack weld, and don't fix it, you WILL be haunted by it later.

Steve S

They are sneaky sometimes too, only showing a faint telegraph of a crack in the weld. You may look once and think you see it, then look again and think something else. I had it happen to me recently with a weld I had reached too far around a pipe away from me and it didn't show until a day or two later and only when the lighting was right. Even then it wasn't entirely visible until I hit it with an arc. I ended up grooving it all the way to the root with an air saw and re-welding it.

[sz.barti]

Cracking tack problem is solve thank you all welders!!! But there is another thing I want to ask you. Dont really weld ally ticker than 3mm as Im working for sheet metal shop but this time I have got 6 mm ally checker plate to weld together. Its a butt joint 1500mm (5ft)long each section is 1200mm (4ft) width I have weld one with your advices and came out good no crack at all but one problem occured I mine it pull like fu** is not usuable. I need to make it again 7 all together so round 3 tomorrow. I have stager the welds 5 inch each 5 inch space plus it was clamped right on the joint so I had 2 inch gap where my torch fit and I tack one side fully tack (aprox 10-15 mm long) around every 5-6 inches and I turn it over. When I welded both side and I took clamps off looks like a brige ( bent all over) why it happens? Im not an ally expert but as far as I know ally cant be cooled it has to cool it self am I right or I should cool it down with air or water?

And please dont laugh

[TamJeff]

No laughing here. It is incredibly difficult to weld that big of aluminum sections with TIG without distortion. Nothing short of sandwiching between heavy steel plates. That operation is better suited for MIG. Even then there is going to be distortion. Look at the many commercial aluminum boat hulls built in heavy plate and there is significant distortion even with MIG. I am not an expert for that type of fit up so take what I say lightly. Personally, I would have to either subdue the joints as mentioned or employ a press after the fact if TIG was the only option.

[weldin mike 27]

Hey,

I realise this is not always posible but 1way to avoid and or limit distortion is to preset your parts. That means to bend or restrain them in the opposite way of the way the are bending so that during welding, when they distort , the end up closer to the right spot because they have had to move farther from the starting point. Simply put, Before welding, curve them the other way to which they are ending up. I DONT KNOW IF THIS IS AN OPTION WITH YOUR JOB. IT MAY NOT SUIT..


Mick.

[weldin mike 27]

Hey,

Ps it is quite normal to straighten things on a press after welding. We had a whole department at my factory for it.

Mick

[Otto Nobedder]

It's unlikely diamondplate will look right straightened in a press.

I think MIG is the better option, and friction-stir the best, but friction-stir is a specialized process.

Perhaps a MIG weld, followed by a thorough planishing in a hammer mill?

Not sure what facilities you may have access to.

Steve S

[TamJeff]

The whole joint would have to be pressed like on a press brake with an adapter or using the cross brake die backed with a piece of flat bar or angle iron. Pre-distorting it does work somewhat.

I have had to weld large sections of 3/16" for sump well covers and I sandwiched each section between two heavy pieces of 1/2"x 12" x 4' steel plate and clamped those where I could with big C's and leaving just enough room for TIG work. It worked well but was a beating to set up each time.

[sz.barti]

Hi mates!!!

I tryied to sandwich those two plates when I was welding it with Tig and really help but still pull a bit, was acceptable any way. Unfortunatley was very slow so at the end I welded it with Mig. Still sandwiched two plates and welded fully both side, and looks very good was quite straight.

It was very good lesson for me I learned a lot. Thank you all welders that you here when I need you.

Thanks

Bart

[weldin mike 27]

Hey, Glad it helped you out. Hope you stay around.

Mick

[sz.barti]

I definetley will stay on the forum, I see you are from oz where are you?

[weldin mike 27]

Hey,

Im in Bendigo, Victoria.

Where are you?

Mick