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Weld Distortion, Causes and Remedies

Friday, 24th November 2017

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.

Please let me know what you thought of this article by leaving a comment.  Don’t worry, your email address won’t be added to a database or shared and you won’t receive any unsolicited email.

Cheers

Graham

The Welders Warehouse

3 Easy Steps to Perfect Mig Wire Feed Speed

Friday, 17th November 2017

Mig Welders are relatively simple pieces of equipment and are easy to use, the key is getting the machine set up correctly in the first place.  Key to this is the setting the wire feed speed correctly.

A lot of smaller machines on the market, BlueMig BM-150T for example, have a helpful Chart, indicating the settings most likely to suit a given thickness of metal with a given size of wire.

Example of Welding Chart

Mig Wire Feed Speed Chart

3 Steps to Perfect Wire Feed Speed

  1. Set the wire feed speed to a level that you know will be too high for the power output setting you’re using (this may be a best guess).
  2. Start an arc on a scrap piece of metal.  With too much Wire the arc will “Stutter” and you will feel your torch bucking in your hand as the wire repeatedly hits the metal.  If it doesn’t, increase the wire feed speed, whilst welding, until it does!
  3. Whilst maintaining this Stuttering Arc, SLOWLY reduce the wire feed speed.  The Arc will suddenly run smoothly with an even “Crackle” and the torch will stop bucking in your hand.

CONGRATULATIONS, you now have the correct wire feed speed for the Power Output you’ve set on the machine and the size of wire you’re using.

Once you’ve got the setting right, it’s worth making a note of the setting for that wire and power output for future reference.  Essentially, you start writing your own chart!!!

Conclusion

Getting the correct Wire Feed Speed on a Mig Welder is critical to getting a good quality weld.

Too much wire feed will generate a lot of spatter and a lack of penetration, not to mention a weld that looks like a line of Pigeon dropping 🙂

Too little wire feed will generate a weak flat weld, possibly with undercut.

 

Please let me know what you thought of this article by leaving a comment.  Don’t worry, your email address won’t be added to a database or shared and you won’t receive any unsolicited email.

Cheers

Graham

The Welders Warehouse

PS – We have some other Mig Welder related information and videos in our Support area, simply click Mig Welder Info to have a read/view.

Gas Flow Rate for Mig

Monday, 6th November 2017

What’s the right Gas Flow Rate for a Mig is a question we get asked a lot, but like many things in welding, there’s no definitive answer.

The correct Gas Flow Rate for a Mig will depend on a number of factors:

  1. The diameter of the Gas Shroud
  2. The joint configuration
  3. Whether there is any uncontrollable factors that may disrupt the gas shield around the weld, draught/wind being the most obvious

Having said all that, I understand you need a start point, so I’ve produced a simple chart showing suggested Gas Flow Rate for a Mig.

This is based on a formula of the cross sectional area of the Gas Shroud Bore divided by 13.

For Example, let’s assume the Gas Shroud Bore is 10mm.

Cross Sectional Area (as I’m sure we all remember from school Maths), is 𝝅r² so:

𝝅 (3.142 is close enough) x 5 x 5 ÷ 13 = 6.042

We can round that to 6 litres per minute Gas Flow Rate for a Mig with 10mm bore Gas Shroud.

I would stress that this figure is a start point.  Try a test weld, if you see tiny pin holes in the surface of your weld, you need more gas, but in still conditions, this formula should provide enough shielding without wasting gas by using more than necessary.

Gas Flow Rate Chart Mig Welder

Gas Flow Rate Chart Mig Welder

I hope this helps

If you would like a higher resolution copy of the chart, use the “Contact Us” link on our website to drop me a note and I will email you a copy.

Please let me know what you thought of this article by leaving a comment.  Don’t worry, your email address won’t be added to a database or shared and you won’t receive any unsolicited email.

Cheers

Graham

The Welders Warehouse