Angles change after welding :/

[phil81uk]

Hi,

I'm new to welding so this probably seems like a novice question.

I'm welding up a "skid plate" (aka bash plate, or diff guard) for a 4x4. It's made of 5mm sheet steel. Basically a rectangle with some bends in it. I don't have any photos but here's a similar one (only made of aluminium):

The way I'm doing the folds/bends, is that I cut 3/4 of the way through the sheet steel with an angle grinder, bend it, and then weld up the cut.

What's happened, is that I did the cuts, did the bends, and checked that it fitted the 4x4 properly. It did. So I then welded it up. When I went to fit it again the angles had changed! I am guessing that the welds "pulled in" the angles (I've had this happen before).

I'm trying to think of ways to overcome this. Any suggestions?

1. Cut right through the metal and then weld on both sides, bit by bit, so that the "pull" cancels out.

2. Use some side braces to stop the angles changing (not ideal as the skid plate would then be too stiff - it needs some flex to absorb shock without transferring it all to the car chassis)

Hmmm?

 

[oilcooled :)]

tack a a couple of gusset plates fix your angle, weld it allow it to cool and break off the gusset plates

 

[phil81uk]

tack a a couple of gusset plates fix your angle, weld it allow it to cool and break off the gusset plates

Will the angle not change after I remove the gusset plates?

 

[Robotstar5]

Run a weld up the inside to "pull" it back?

 

[phil81uk]

Run a weld up the inside to "pull" it back?

Considered that, but in my total lack of experience, I don't know if it would pull back equally.

 

[pedrobedro]

Cut the bends, fit it to the vehicle then weld it. (And hope you never need to take it off )

 

[phil81uk]

Cut the bends, fit it to the vehicle then weld it. (And hope you never need to take it off )

Haha! It would actualy have to come of pretty often. I'm always destroying the car and need to replace bits.

 

[gordon stephenson]

Welcome to the world of distortion!!! I'm with robotstar5. put a decent run along the inside, start off welding a couple of inches leave a 3" gap and go right across like that, Let it cool and check the result, then decide how much more welding is requires if any,

 

[phil81uk]

Welcome to the world of distortion!!! I'm with robotstar5. put a decent run along the inside, start off welding a couple of inches leave a 3" gap and go right across like that, Let it cool and check the result, then decide how much more welding is requires if any,

So weld the opposite side only enough to correct the angle? Smart

 

[Engineer]

Get some angle iron and make a simple jig, which you can clamp the sheet to before welding. Then stitch weld around 100mm at a time, first on one side then the other.

Should come out pretty straight, and you will find the time it takes to make a jig is well worth it, as this method will allow you to avoid an awful lot of hassle.

 

[phil81uk]

Get some angle iron and make a simple jig, which you can clamp the sheet to before welding. Then stitch weld around 100mm at a time, first on one side then the other.

Should come out pretty straight, and you will find the time it takes to make a jig is well worth it, as this method will allow you to avoid an awful lot of hassle.

Do you have any pics of such a jig?

 

[Drains]

As suggested above - don't weld it all at once. Do a bit in one section, go to another section, go back to the original. Let the welds cool. Keep an eye on what it's doing as it cools, weld both sides, prep so that the weld is as big one side as the other. Restrict distortion during cooling. Pre heat to reduce temperature differentials....

So many things you can try. Distortion is something you ALWAYS have to consider when welding. Sometimes it's negligible, sometimes you can avoid particular runs of weld so you can restrict it, or just stitch weld - a small amount of weld can go an awfully long way.

 

[Wozzaaah]

Another tip is to allow for the amount of distortion beforehand, i.e if you know how much the weld pulls the angle in, set the angle so that as it cools it's pulled back to the correct angle.

 

[Drains]

And another thing...

With TIG, particularly, a hotter, faster weld puts in less heat than a cool, slower one. EG, ramp up the amps and go like the devil. Less heat = less distortion.

 

[Paul.]

Another tip is to allow for the amount of distortion beforehand, i.e if you know how much the weld pulls the angle in, set the angle so that as it cools it's pulled back to the correct angle.

Known as pre setting . 5mm isnt really that heavy in fabrication terms, a few well placed hammer blows will soon set the angle, or a pull on a solid bench with a decent clamp, various ways of doing it, everyone has their favorite.

Tigs not really the best process for a job like this, If you don't have the option of mig welding it, you should consider setting your tig set up with an electrode holder and stick weld it.

 

[Engineer]

Do you have any pics of such a jig?

You simply need to make an angle iron frame, incorporating the same angles as the finished sump guard, and ideally also the mounting holes. Personally I would MIG weld something like this if its steel, as you will find thats an awful lot easier than TIG, and far far faster.

 

[phil81uk]

Why is Tig not the best method for this? I no longer have the Mig welder as I was enjoying the Tig so much that I never thought I'd look back.

I recut the plate and tried again. This time using short stitches and monitoring the angle. Within three 1" stitches the angle had changed a lot. I think that the plate needs to be braced anyway (a friend has a 5mm plate on the same car and it is severely bent from off-roading). So I am thinking of using the braces (gussets I think they are called) to hold the angle.

 

[hotrodder]

Speed (cost) and being a slower, higher heat input process distortion is a potentially a bigger issue i.e. if you turn something into a pretzel when welding it'll typically be more pretzeled with TIG than with stick or MIG.

A few articles on the subject...
http://www.twi.co.uk/content/jk34.html looks at design aspects
http://www.twi.co.uk/content/jk36.html techniques
http://www.twi.co.uk/content/jk37.html and what can be done when it goes wrong

 

[fluxcored]

Speed (cost) and being a slower, higher heat input process distortion is a potentially a bigger issue i.e. if you turn something into a pretzel when welding it'll typically be more pretzeled with TIG than with stick or MIG.

A few articles on the subject...
http://www.twi.co.uk/content/jk34.html looks at design aspects
http://www.twi.co.uk/content/jk36.html techniques
http://www.twi.co.uk/content/jk37.html and what can be done when it goes wrong

Very nice. Especially the bit on flame straightening.

 

[Ian D]

Go to someone with the gear to fold it, with a template, slip them a quid or 2, job done.