Tig welding sch10 304 Exhaust manifold

[Alan.m]

Hi guys just looking for a bit of advice on tig welding some 2.77mm thick ss sch10 304 having a bit of trouble finding a good setting and the outside weld always come out a little grey? i understand my it might be my angles but if anyone has any suggestions that would be great. Im using 1/16" gold band, 1/16" 308 Filler.
So this was welded with argon along with argon back purge. settings are 0.7 pre flow, 60 amps, 2.5 down slope, 4.5 post flow. It has around 60% penertration i know my welds are not straight but my main issue is the grey colour and if i go any higher amps it just undercuts?



I tried again but with pulse settings are 0.7 pre flow, 45 main amps, 65%, 5.0hz, 75 pulse amps, 2.5 down slope and 4.5 post. again i know my form is very bad but the colour just seems so dull witch i thought was due to heat but i didnt get any penetration when on these settings?



Does anyone have any suggestions? as i can run a nice bead with penertration and amazing colours on 2mm stainless but i move onto this stuff and it all goes down hill?

Cheers Alan

 

[Tinbasherdan]

Move faster, use the same amps but reduces the heat input. I'd be tempted to just autogenous them, unless the fit up isn't amazing?

 

[Alan.m]

Thanks for the reply, the trouble with moving faster is im struggling to get full penetration as it is? with it being a top mount for a 400bhp setup i dont want any risk of cracking?
What would you suggest for the correct fit up? bevel with a root gap?

 

[hotrodder]

Regardless of what's said on many internet forums weld colour is relatively meaningless*. Especially on an exhaust manifold that's gonna get covered in surface oxides the moment the engine is run in anger and end up grey after a while
The people that bang on about weld colour often achieve their pretty colours in one of several different ways...

• by depositing partial penetration welds an inch or so at a time (pausing for the post flow to ensure the hot weld stays under the gas shield)
• using a massive gas cup for greater argon coverage
• With a bevelled joint running an autogenous (no filler) pass to fuse the root and then a second (often pulsed) pass with filler. For twitface pics obviously you need to weld with lots of pauses for the post flow and exaggerated movements for the 'stack of dimes' [/tongue in cheek]

It looks like you're butting the joints up tightly with zero prep (bevel)? That'll be part of the problem... on thicker wall stuff you want a root gap or a bevelled joint to deposit a full pen weld. The prep/root gap lowers the heat input needed and as a side effect that makes the pretty colours easier to achieve but still fairly irrelevant. Arc length is an important variable... as it gets longer arc voltage, and so heat input, increases while arc focus decreases. When first starting out maintaing arc length on round stuff is more difficult as the angles of attack are constantly changing i.e. it's very easy to end up increasing the arc length as the weld progresses. Get the basics right and, with time, less relevant things like weld colour will take care of themselves

Pulse isn't gonna be that useful on sch 10, it's most useful on thin stuff. The idea behind it is to lower the average heat input without compromising other aspects of the weld, more about setting it up in this thread http://www.mig-welding.co.uk/forum/threads/couple-of-questions-please.16277/#post-181252


* While many people bang on about it and/or think it's a sign of weld quality all it's actually about is shielding quality... with enough attention to shielding or use of a welding chamber/glove box you can cook the crap out of a part and deposit a weld with loads of metallurgical problems and a massive HAZ (heat affected zone which is often confused with heat discolouration but a totally different thing that can't be seen with the naked eye) but zero discolouration. In the real world when stainless is used for corrosion resistance all weld colours including the pretty ones are removed by pickling and passivating as they all lower corrosion resistance

 

[Richard.]

Shiny stainless welding is achieved by keeping a tight arc, reducing heat input and good gas coverage. Even though your not penetrating right through a purge on the inside will improve the quality of the surface finish. Increase your post flow to around 7 seconds. On 2.8mm thick it's quite hefty stuff certainty not thin so I wouldn't bother with a pulse especially one as slow as 5 hz. IMO you should be trying to penetrate it fully with a purge and obtain a sound weld. The surface finish will come as you get things tuned in. Yes you can get it clean and bright on the flat but in the round you have position change to adopt your arc length to. As for colours it's not important to achieve this heat tint which will spread throughout the whole exhaust once the engine gets thrashed. It's more important to aim for a sound fully penetration joint with nice coverage on both sides. If you want colours (which I don't get really) drop your current to around 60 amps, use a 1mm filler. Size 8 gas lens 8lpm and keep the travel speed up not to localise heat input.
If it was my job I'd be at around 80 amps and be aiming for full pen. I'd get clean and shiny runs from the travel speed and the aid of a gas lens and inside purge.

 

[HughF]

I'd echo what has been said before, gas lense, purge, tight arc. I'd also try two stepping it with a feather edge prep and minimal gap.

 

[langy]

Too many amps and slow travel is what you have in my opinion, I weld with those bends all the time and I only use 40-50 ish, I also use 1mm rods

 

[Alan.m]

Ok brilliant advice here guys thanks! I do sort of understand that colour is not everything and i am looking for 100% penetration but always thought the colour i was getting was a sign of a bad weld?
The photos i have taken are some what a bad example for the joins i have not welded yet most have a bevel its only the straights that dont but i will be adding a bevel before welding after hearing all your advice, as for a root all my joins are tight with minimal daylight do you think i should change this? if so what gap should i aim for?
If i run the weld at 80amps i know i will get full pen but the weld always seems to get way from me and undercut really bad? is this due to being to slow and not enough filler or do i undercut then do a second pass? also does the second pass need to be purged still?
I have been using a standard #6 cup but only because that what the welder came with i have since ordered a gas lens kit with #6, #7 and #8 cups but it has not arrived yet, what cup would you guys suggest?

Too many amps and slow travel is what you have in my opinion, I weld with those bends all the time and I only use 40-50 ish, I also use 1mm rods

Hmm i have tried that and i can achieve a good (ish) looking weld but with zero pen? do you get full pen when welding at those amps? if so how?

 

[Richard.]

I wouldn't do that in two runs and if I was to add a bevel it would be very small but tbh I don't think I'd bother. No gap either I'd get through it no problem square edged up tight. The welds in your pics look huge . I'd be looking for no where near that amount of cap reinforcement. I think your oversized filler rod is perhaps chilling too much and effecting toe transition. Although an inside purges main job is to offer underside protection from oxides and coking it also helps a lot with the face side of the weld too so it does no harm having one on a feed if you can. If 80 is a bit hot for you drop it to 70. Don't prioritise looks over full pen though. Aim to get right through. Don't worry about heat tinted welds or even slightly dull grey ones. If it was my job I'd be looking for consistency and a sound joint. I'd more than likely buff the welds up and re grain with a bit of scotchbrite after anyway so the colour wouldn't matter at all. A gas lens is gonna make a substantial difference to this I believe. You will find it narrows things up a little better too when you have a nicer more concentrated gas coverage and will allow you to perhaps run a little hotter and faster too. Cup sizes are people's personal choice really. I generally use a 7 or sometimes an 8 ( I never go bigger than an 8)

 

[Pete.]

Do you really even need full pen on shed 10 to hold up a big turbo? Mine is hanging on 1.6mm dairy pipe and hasn't fell off or cracked despite suffering momumental wheelies on occasion. I once blew the damping adjuster clean out of the threads in the fork bottom

Not saying it's not desirable - but is it critical?

 

[HughF]

Lots of scrap 2" sched10 316 at work, I'll have a play when I'm back from China, be interesting to see how different setups affect the outcome.

I always build my manifolds from steel much easier.

 

[wheresmejumper]

I'd bevel to about 30 degrees,to a knife edge.
Then if unsure,test how long you need to pause at the start to get good penetration or equally good fuse both edges.then just top up with filler before you move

 

[hotrodder]

If i run the weld at 80amps i know i will get full pen but the weld always seems to get way from me and undercut really bad? is this due to being to slow and not enough filler or do i undercut then do a second pass? also does the second pass need to be purged still?

The undercutting could be due to travelling too slowly for the amperage, underfilling or from too long of an arc length. Or some combination of any or all of them
Ignoring the fact that 50A on one machine ain't necessarily the same as 50A on different kit welding is one of those things where if you ask 4 welders how to attack the same butt you'll usually get at least 4 different answers for things like amperage and joint fit up

For an exhaust butting things up without a gap will make life easier from a fabrication, fitting and distortion POV. With 1.5 - 2mm wall tube square edge is ideal, with slightly thicker wall stuff like your sch10 bevelling will make the welding easier as you'll need less juice to sink the root in, a smaller weldpool to control and, if it gets away from you due to torch angles etc, things won't get out of control as quickly. Running a second pass to fix undercutting isn't likely to end well/neatly and on 2.77mm wall thickness it'd still be relatively easy to coke/oxidise the inside without a purge

Do you really even need full pen on shed 10 to hold up a big turbo? Mine is hanging on 1.6mm dairy pipe and hasn't fell off or cracked despite suffering momumental wheelies on occasion. I once blew the damping adjuster clean out of the threads in the fork bottom

Not saying it's not desirable - but is it critical?

Dunno but i'd have thought it could be with sch10? 1.5mm wall 304/316 turbo manifolds have a reputation for cracking, at least when they're stuffed in the hot, cramped engine bay of a car. Personally i think it's more that 1.5mm wall is just very unforgiving (from a design, fabrication and welding flaws POV) rather than totally unsuitable although temps can be pushing things right to the limit for 304L as it's creep strength at those temps is non existant. While a heavier wall will help partial pen welds make for great stress risers, those that use sch40 to make turbo manifolds can get away with all sorts but then they have wall thicknesses in the 3.5 - 4mm range!