Can any one explain or point me in the direction of information about weld sequences, in order to maintain minimum distortion on my work, i always thought tacking would stop it disfiguring but my brother tells me otherwise.
Tacking will help stop the parts from moving where you don't want them to go, particularly during welding, as they are expanding. But that wont stop distortion in the finished job. Heavier materials can be clamped until cool.
For welding sheets you can use step back welding, eg weld a few inches from right to left, then move past the beginning of the first weld by the same number of inches and weld right to left again till you join up with the first lot. Keep doing that. You spread the heat more evenly, plus you don't have to deal with cold starts.
Or you can stitch weld. Weld a couple of inches, leave a gap, weld a couple of inches. Or you weld evenly each side of a fillet or butt.
Or, if you know a weld (say across a piece of square section box), is going to leave the piece distorted, weld somewhere else instead - not across it, but along, somewhere.
It depends on the job mate, but in general if you can keep heat out of the job, or allow it to cool before carrying on, you will limit distortion.
Oh, and no, I can't (point you in the direction of weld sequences!)
My approach is not to let anything get too hot. Spent an afternoon on my floorpan (details of how I went about distortion avoidance on the floorpan page). Tacked everything, then an inch of weld at one end, then an inch at the other, then a bit in the middle. By the time I got back somewhere near the first weld it had cooled down.
Still get lots of inch long local distortion. Tends to dip away from the welder which is the right direction to level with body filler. Not sure of the way around that other than a backer to take the heat out (very effective for polished alu finish).
Another method of distortion control wouldbe to 'preset' the parts.
As you will know, a fillet weld will pull over when cooling. One way would be to set the joint out of square so when you weld it will pull into square.
Theres not really a rule of thumb for this, it just comes with experience.
Not so much a sequence, but another way around a problem.