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Question
I am welding 18g stainless to stainless sinks in an undermount fashion. (Franke
sinks). The result is extreme expansion warping of the stainless top. TIG pulse
mode, 60 amps peak, 30 amps at low, 50% pulse width, 100 pulse per sec.( Hz.)
Tried a 1″ cold copper bar 1/2 ” from weld on top to draw heat. Max weld
length was 2inches. I tacked it every 2″ prior to welding. even then some minor
tension occurred. PLEASE HELP. Thank you kindly in advance.

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Answer
This question is right in my comfort zone.
I have welded a LOT of stainless sheet.

The problem isn’t expansion, but contraction.
Stainless steel has a high thermal expansion, but a low thermal conductivity so the heat localizes and the expansion/contraction is magnified.

Simple rules.
Use the lowest amperage possible.
Use the smallest filler rod possible.
Weld in short stitches wherever possible.
Back-purge your welds with argon.
Use a pulser whenever possible.
When using a pulser use a spike pulse if available.
Tight, tight, tight joint fit-up.
Clamp everything as solid as possible to heavy pieces of steel, if possible.
Use 308LSI wire when possible, the added Silicon drops the melting temp a bit and makes it wet better.
Pre-heat if possible.
Use a smaller tungsten.

Use an 0.045″ filler rod or better yet 0.035″.

Amperage rule.
1 amp per 0.001″ of thickness – 1/3 for stainless.
Then minus 1/3 for outside corner joint.
So your metal is 18 ga = 0.047″ = 47 amps – 15 = 32 amps – 10 = 22 amps.

If using a pulser you can go to this online calculator to get your settings

http://www.Pro-FusionOnline.com/welding/pulseparams.asp

Feeding the spreadsheet 22 amps, and a spike pulse you get

61 amps peak, 12 amps background, with a 20% on-time.
I can see that working.

So your peak amps was OK, but your background is way too high and your % on-time is too long.

Now your pulse frequency of 100 hz seems high if you are adding filler metal.
It would work OK if you are just flow-welding the edges, but if you are adding filler then try 1.5 – 2 hz.

Your weld technique is going to need to be very tight so you should take every chance possible to cheat here.
Set up a slide bar for your torch hand to make the torch travel as smoooooooth as possible.

Tack every 1/2″, with tiny, tiny, tiny tacks.
If you can get a small bar in behind the tacks, then stretch them before welding with a tiny hammer (4 oz)
Weld in short stitches.
Weld 2″, skip 2″, weld 2″, skip 2″…
Then go back and fill in the gaps.

If you don’t back-purge, the metal won’t flow nice because the backside is being exposed to the air and scorching.

A heat-gun can be used to pre-heat SS sheet.
You want to generally warm the whole piece to a few hundred degrees F.
This isn’t always possible, but does help reduce localization of the heat.

Here is a great collection of tungsten info on types and grind angles.
I am a big fan of 1.5% Lanthanated (gold band).
For what you are doing 0.040″ would work, but 1/16″ are much easier to handle.
I really hope you are using a gas lens collet body with a #8 cup, and around 10 – 15 CFH Argon.

Question
I would like to know how to cut & weld ss dish table & have it look like new I have been in the welding business over 20 years & have all the toys but my results are less than perfect I would like to know a step by step detailed procedure down to the proper finish I hope this is enough info if not please let me know

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Answer
Fabricating Stainless Steel sheet for food service can be very difficult if you don’t have a few special skills and tools at your disposal.
First you have to understand that stainless steels love to warp.
They expand a lot when heated, yet because they are terrible heat conductors, the expansion is localized and therefore made more severe.
When working with stainless sheet you have to either own some BIG sheet metal bending machines or have a shop nearby willing to bend pieces for you.
Most sheet metal shops are willing to do small bend jobs since they are in and out fast.

The most common stainless steel alloy in the world is 304.
It is the most common alloy for food service work.
The old name for 304 was 18-8.
This referred to 18% chrome, 8% nickel, with the remainder mostly iron.
316 is the most common alloy for marine work.
316 has 19% chrome and 16% nickel, which makes it better against salt water.

304 and 316 are harder to drill, cut and bend than mild steel.
When drilling or sawing you need sharp cutters, low cutting speeds and high pressure with lots of cutting fluid.

There are many ways to cut sheet metal.
Plasma cutters are very fast, but have some serious drawbacks for stainless steel sheet metal.
When a plasma cutter cuts stainless it can’t vaporize all the metal, so there is a rather jagged dross left on the lower side of the edge which must be removed by grinding.
Also because of the high distortion effect, the edge shrinks as you cut the sheet, causing the entire panel to warp.
You can hammer the edge to stretch it to remove this warp, but it must be done with care.

Bandsaws work well as long as you have fine tooth bi-metal blades, and the saw has a low metal-cutting speed range.

Mechanical shears can cut nice straight lines, but they are large and expensive machines.
Hand held power shears and nibblers can be used, but stainless steels are very tough and reduce the life of the cutting edges and reduce the cutting capacity of these machines.

A lot of simple cuts can be done with a 4-1/2″ right angle grinder with a thin abrasive cut-off wheel.
This has been my preferred method for on-site cutting for many years.
As long as you use very thin wheels, you can cut straight lines fast, and with less distortion than a plasma cutter.
PLEASE use a full face shield and safety glasses when using thin cut-off wheels in a hand grinder, and always keep your face out of the plane of the grinding wheel.
If the wheel is side loaded, or pinched in a cut, it can explode.

You can also have parts cut by CNC plasma, laser or water-jet shops.
This can be expensive, but for complex pieces, can be the fastest solution.

Bending stainless steel requires strong machines so I usually shop this work out to a local sheet metal shop.
I cut the pieces, they bend them and I weld them.

Hydraulic press-brakes are the best tool for this work.

Welding stainless steels is a whole subject beyond just forming it.
Stainless steels have a lower melting than most carbon steels, so they melt faster, but the nickel and the chromium are highly reactive to oxygen in the air when heated.
If you weld on one side of a stainless sheet with the backside exposed to air, you will have black crusty formations when you are done.
We call this “sugarring” as it looks like burnt sugar.
This sugarring is very bad for food service work as it give bacteria a lovely place to hide.
To prevent this we use jets of argon or nitrogen to “purge” te air from the weld area.
Nitrogen is only used if there is no way for it to contaminate the weld arc, such as welding on the outside of a stainless tank.
You don’t necessarily have to purge teh entire inside of a large volume tank if there is some way you can place a dam or bowl on the backside to protect the immediate weld area.
When I weld large brew tanks I use an aluminum pie tin on the inside to localize the argon purge to the weld area.

Another effect specific to stainless steel food service and marine welding is that after welding the weld area must be “passivated”.
When you weld stainless steels you disrupt the careful ballance of nickel, chromium and iron.
This usually leaves smal disassociate iron particles on the surface of the weld.
If these particles are not removed, they will rust.
To remove these particles we use acids.
You can either use a strong acid like UTP’s SS Weld pickling paste, which contains gelatinized nitric and hydroflouric acids, or a mild acid like citric acid and electricity.
Is use the citric acid and electricity combination (called “electro-passivation”) when working in food service or breweries.

You can read about this process from this site

http://www.stellarsolutions.net/

The actual welding of stainless steel is simple, controlling distortion is hard.
TIG is the most useful process, but MIG can be used for heavier plate or tube.
MIG causes the most distortion due to it’s speed.

You can reduce distortion by pre-warming the weld area.
You need to use as little heat as possible for the weld.

TIG amperage rules are simple.

Start with 1 amp per 0.001″ of thickness.

This covers all carbon steels and aluminum in a flat-butt weld , full penetration, single pass.

Subtract 1/3 for outside corner welds.
Add 1/3 for inside corners (fillet welds)

18 gauge sheet metal = 0.047″ thick = 47 amps.
(lets round up to 48 to make the math simpler)

Outside corner joint would be 48 – 16 = 32 amps
Inside corner joint would be 48 + 16 = 64 amps

Now reduce the amperage by 1/3 or 30% for stainless steel.

So 48 amps – 1/3 (or 16) = about 32 amps for the flat butt weld,
(again round up to 33 for simplicity)
33 – 1/3 (or 11) = 22 amps for oustide corner joints
33 + 11 = 44 amps for inside corner joints.

This is simple math.
You see here that we are dealing with extremely low amperages, hence why TIG welding sheet stainless takes a great deal of skill

Use of a pulsed TIG machine makes these weld easier by reducing the overall heat put into the metal while maintaining weld penetration.

I have posted previous answers about this subject.

http://en.allexperts.com/q/Welding-3487/2009/1/welding-18g-stainless.htm

and the follow up…

http://en.allexperts.com/q/Welding-3487/2009/1/welding-18g-stainless-1.htm

BTW a lot of seam welds can be avoided completely by careful use of right angle bends and spot welds or pop-rivets.

Of course there is a whole other area in the surface finishing of stainless steel.
But my fingers are a bit tired so if you have a question on that I will answer it another day.
Bob Vila installing-the-stainless-steel-kitchen-countertop