Distortion issue (welding)

[Valheria]

I am planning to weld a 700x300mm 10mm thick steel sheet on to another 10mm sheet of the same size using a lap joint. I know if i attempt this now ill get distortion and will likely bend.. This thing i am making needs to be bolted to a wall so it has to be perfectly straight but. Since its security related it cant lay down short distance welds as this will signal a weakness someone could exploit. I am not sure if this is enough info (poke for more) but i would love to know how you guys would go about doing this while keeping this perfectly straight and square?

btw the weld bead is going to be 700mm long on 2 sides of the metal

thanks guys !

 

[Rrobson]

What process are you using? Mig would probably result in the least distortion followed by stick.
The only way your going to be able to guarantee minimal distortion is doing multiple weld runs in alternating directions from various start points. You would have real difficulty trying to do an entire edge in one go, even if the plates were bolted down and substantially restrained. If you do a decent tie in you'll not even notice the end of one weld and the start of another, and it certainly won't add any meaningful weakness.

 

[Mark 2]

A picture of the scene might be good, as, if the answer is that there is going to be too much distortion then a plan 'b' might be apparent.

 

[Valheria]

What process are you using? Mig would probably result in the least distortion followed by stick.
The only way your going to be able to guarantee minimal distortion is doing multiple weld runs in alternating directions from various start points. You would have real difficulty trying to do an entire edge in one go, even if the plates were bolted down and substantially restrained. If you do a decent tie in you'll not even notice the end of one weld and the start of another, and it certainly won't add any meaningful weakness.

I am using a mig which can either go on dip or spray which ever would work better. Could you elaborate on the alternating directions with a picture for a 700mm? Just so i know what you mean.

 

[Valheria]

Another thing i was going to plan on doing is preheating the whole thing a bit.. but i only got access to a heatgun. Would that work? even if it takes a fair bit longer