what causes alloy welds to crack?? pics inside

[lomas]

dont know much about alloy welding, is there different rods, power settings available? just as was only running 8psi and the welds on the inlet split, what is it down too?

[Jamie_Hastings1]

I am guessing and saying there wasn't enough penetration.

[paddy>gsi/turbo]

yeah agree. as split is dead straight. nice weld though!

[game1]

Who made the inlet - pm if you like

[turbo gav]

Happens often when a flush corner joint is used,full open corner joints have full penatration,material thickness to thin and it bellows in and out and the welds fatigue and crack.

[chip]

People underestimate how much of a pulsing effect there is on the inlet at close throttle in particular, this causes it to flex the inlet when its thin ally and it fatigues, if the welds are strong, it just tears the metal elsewhere anyway, so the problem isnt just the weld, its the design of whatever inlet that is on as well potentially, it will probably need additional bracing inside it. Its not on boost that the problems are caused normally as thats at full throttle so less of a pressure differential during the cycle.
My mate started making them in stainless sheet instead as its so much more durable, but obviously its heavier too, so depends on application if its suitable or not.

[paddy>gsi/turbo]

turbo gav your spot on

a inch of mig weld done right, can take a ton in weight

[chip]

turbo gav your spot on

a inch of mig weld done right, can take a ton in weight

Correct but it cant take being flexed because its on an improperly specced structure

[paddy>gsi/turbo]

chip if weld let go would be jagged. let go on weak point edge. not enough pentration could be structure also

weld looks neat, wish i could ally weld like that is a skill

[Gary_808]

Hope I don't have this problem although my inlet it made from 6mm. Over engineered

[Jack]

Hang on a minute. Haaaaaaaaang on a minute. Have you seriously... blown the welds on your intake?

[MattJ]

lmaolmaolmaolmao

i was gonna quote that ffs jack

[Jack]

lmao lmao lmao

Hope his passenger footwell survived. lmao

[cheekyalex]

lol was thinking the same thing jack, now hes gonna need to get the 'mad scientist' on the case

[lomas]

had the welds all redone and there was quite a few holes in the welds, its held to day at 10psi, going to turn it up to 15psi the morro and if it cracks think the new one will have to be more curved

[dewismotorsport]

The inside has to have full penertraion, else your always gonna have problems with bursting

this is the inside of mine


I like to weld hot but I used 160-170 amps with a 2.4mm White tungsten and 15 LPM of pureshield and the material is 3mm thick, hope some of that info helps you out mate

[Stefan]

Lack of weld penetration (as been said above) is the most likely cause. It would leave a sharp re-entrant corner on the inside of the plenum, where the crack would form and propagate through and along the weld.

Whilst welding the corners of aluminium plates to form the plenum is the most common method used by amateur builders and tuners it is not the best. It may work for most street turbo and some entry level racing turbo applications but a proper racing intake needs a little more thought in its design.

Some points on “box type” plenum designs;

1. On a rectangular or square box under internal pressure the bending moment diagram for the section would be like this:-



You can see that the corners and the centre of the spans have the highest bending moment, therefore stress.

2. With aluminium alloys no matter what heat treat the parent material was e.g. T6 condition, the strength of the weld will always be reduced to that of the alloy in its annealed or “soft” condition.

3. Re-entrant corners in structures always have a stress concentration associated with them. The sharper the corner the higher the stress concentration will be.

With these three points in mind you can see that the above method of construction is rather limited. In a properly designed and constructed intake the welds are kept away from corners or the centre of spans. This can be achieved by using folded sections and machined end caps rather than flat plates.

[chip]

Stefan, good info, people definately underestimate how much effect the shape of the plenum has on the strains that the welds see over time as it all fatigues.

[MSG]

not enough Beef and no resonance damping deployed.