Weld distortion is the bane of every welders life!

You start out with two beautifully flat pieces of metal, then a few minutes welding later, the shape is more akin to a Donkey’s Hind Leg!!

Believe me, weld distortion is something I have FAR too much experience of  🙂

Back in my Days as a Sheet Metal Worker I had to dress out a LOT of weld distortion.  As an Apprentice I HATED the job as I never seemed to get it right, but with time, I learnt the knack.  I still hated it 🙂 but got good at sorting it.

Weld Distortion – Causes

Weld distortion has two causes:

1. Heat that’s introduced to the job by the welding process.  This will vary depending on the welding process used.
2. The Weld metal shrinking as it cools.

Lets put a bit more detail on those!

Welding Processes (part 1)

In my experience, by far the worst welding process for introducing heat into the job is Gas Welding, partly because it’s a slow process but mainly because the heat from the flame goes everywhere.  Mig Welders and Tig Welders introduce much less heat to the job, despite an arc being far hotter than a flame.

Mig because it’s faster and Tig because it’s more precise about where the heat is focused, ie is where it’s needed.

Reducing Heat Input

There’s not loads you can do about reducing the amount of heat that goes into the job, but here are a few preparitory things you can do that will help.

1. Ensure a nice tight joint (unless a gap is necessary for penetration).
2. Don’t use excessive power, or move slower than necessary.  Clearly you need to uses enough power and move at the right speed for a sound weld, but the objective is not to avoid putting unnecessary heat into the job.
3. If possible, place heatsinks (blocks of metal for example), close to each side of the weld.  Avoid placing these directly under the joint as this may affect penetration.

Weld Metal Shrinkage

Like most materials, metal expands when it gets hot and shrinks when it cools.

When you produce a weld your putting down Moulten Metal, which will be in an expanded state.

As the weld metal solidifies and cools it contracts, pulling on the metal around it, causing weld distortion.

The easiest way to correct this distortion is to place a solid block of metal behind the weld and gently dress the weld with a Hammer.  This will stretch the weld and relieve the pull effect on the surrounding metal.  This process should be carried out a little at a time because if you over stretch the weld, you can’t go back and you will still have distortion, only this time caused by a stretched weld rather than a shrunken one!! So be patient, take your time and hammer along the whole weld a little, then repeat as necessary until the distortion is relieved.

Welding Processes (part 2)

The choice of welding process will have an effect on the amount of weld shrink distortion and the ease with which it can be relieved.

Gas Welding and Tig Welding allow the operator better control of the size of the weld.  Whilst the weld needs to be big enough to do the job, clearly the bigger the weld the more it will shrink and cause distortion.  Mig Welding on the other hand is harder to control when it comes to weld size.

Gas Welding and Tig Welding produce a soft, more malleable weld deposit which is easier to dress, whilst Mig Welding produces a harder weld that can be more prone to cracking when dressed.  This hardness is made worse if pure Co2 is used as a shielding gas, so I would alway recommend an Argon/Co2 mix where distortion is likely to be a problem.

If you found this article helpful, you may also find this article on Welding Defects helpful.

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Cheers

Graham