mig weld penetration

[God mode restorations]

hi all....
this is a good example how a mig weld can look nice and lack the penetration needed....

 

[BrokenBiker]

have you etched that? just looks polished to me in which case you wont see the penetration anyway

 

[God mode restorations]

i have not as yet..the reason why is if you look close to the pic you can just see a line at the bottom toe edge....

 

[God mode restorations]

what are the chemicals used for etching......

 

[BrokenBiker]

you can use oven cleaner I think, there are quite a few posts about it on here.

when you etch it the weld material will be darker than the parent metal, showing the penetration better. I have found that trying to look at it when it is polished may look like you can see the penetration but when you etch it it looks totally different

 

[backpurge]

I tend to use potassium persulphate crystals, lot safer than having bottles of acid lying around and pretty cheap as wel

 

[God mode restorations]

ok chaps...will do it tomorrow and see....

 

[Rig Pig]

A drop of dye penetrant will soon find any flaws

 

[Bill Edwards]

Yes, penetrant would show where there are actual gaps. But in this case when it's etched it'll be quite obvious I think.
I think that most acids work to etch, including the type used in rust converters (phosphoric), and not forgetting sulfuric (battery) acid.

Aside from showing a closeup of the etch results don't forget the other key part of this - a picture of the weld that looks 'nice'!

 

[God mode restorations]

yes..i forgot to add the picture.......

 

[God mode restorations]

its not the best weld ....but its half ok....i no the corners dont meet up..but these are just tests...for those that weld on a professional basis dont really have these problems...but for those that are starting to learn to weld or have little experiance and are practicing this was an exsample of what might look ok can fail in penetration.......

 

[backpurge]

Welds look neat but there is a bit too much weld metal there which can give a clue as to why the penetration may be inadequate

 

[God mode restorations]

ok cool .. Well i have turned the power up a notch and wire speed...but if to much heat is added then distortion comes in to play...and it was glowing .....is there a bead width measurement in relation to metal thickness.....should i keep to original settings and less of a weave to reduce the size of need and i guess direct more heat between the join....

 

[backpurge]

1st rule of MIG welded fillets in any position other than vertical up is don't weave. I conduct around 200 welder approval tests a year and the ones that fail more than owt else are MIG fillets where people have adopted some sort of weaving technique, it serves absolutely no purpose and generally results in reduced/no penetration and fusion

Your leg lengths want to be about the same as your material thickness ie 6mm material requires a 6mm leg length fillet

 

[God mode restorations]

ok cool..and thanks for the advice..i will drop down to my original settings and concentrate on reducing the bead width..the box section is 3mm wall so i should be looking for the same in bead width.. Thanks again......

 

[backpurge]

Not bead width, leg length, you probably will not be able to achieve a weld with only 3mm leg so just keep it as small as possible

 

[BrokenBiker]

you want the weld to measure the same as the metal thickness when you measure from the root of the weld to the end of the leg. the leg is the line that would be there is the parent metal was still visible. starts at the root and ends where the weld ends. for a fillet the legs will be an L shape

 

[God mode restorations]

right..i understand now.....thanks for your help..will be on it tomorrow.....

 

[Jan]

If you look carefully at the left hand weld you can just see that the top section has lifted clear of the bottom one due to slight imperfections in the surface(s) or even possibly heat warping. This 'crack' has even extended into the weld as the metal has cooled meaning that there is NEGATIVE penetration.