Dissimilar thickness welds 2

[TVP]

Is there a rule-of-thumb for the maximum difference in material thickness for two members to be joined by GMAW? I am interested in general applications, but a specific geometry is as follows:

50 mm tube OD x 2.25 mm thickness
low carbon steel (HSLA or plain carbon)

3.5 mm bracket
low carbon steel (HSLA or plain carbon)

The bracket encircles the outside of the tube, creating a lap joint. The concern is that excessive heat will cause burn-through of the thinner tube. Let me know if I forgot anything.

 

[evelrod]

Very typical sizing and material for most of my roll cages. (1 1/2" to 2" .090 to .125 wall 1020 DOM and 1/8 to 3/16 inch plate) I usually have no problems. I don't understand your concerns if your work is done by a competent mechanic.

Rod

 

[CWIC]

TVP:

I agree with evelrod. With an experienced welder and the right equipment you can weld these materials and thicknesses with relative ease.

However, any tubing that used for gas or fluid service may be another story regarding burn-through.
What is the application?

 

[TVP]

CWIC,

Gas and fluid service.

Actually, the parts are for an automotive strut. Parts must not leak (gas or oil) during service. We haven't had any problems with this design, but I couldn't remember the general rule. We may need to increase bracket thickness with tube thickness remaining the same, so I'm curious where it starts to become a problem.

 

[CWIC]

TVP:
Is this a reservoir or the strut body?

Are there moving parts in your weldment such as pistons or valves which would require a uniform surface or precision finish?

Will the tube ID be machined after welding?

Will the parts be manually (semiautomatically) welded or by mechanized or robotic process control?

FYI: There will be some distortion of the tubing at the location of the weld on the opposite side of the joint (tube ID).
Not trying to confuse you, just making sure all the bases are covered and you (or this reply) have not overlooked any potential problems after welding.

 

[sayee1]

This is a lap joint with fillet weld. The tube thickness being the lower thickness, what size of fillet are you considering/has been designed? Is it 2.25 mm or the complete thickness of the bracket i.e. 3.5mm? I would presume a weld of leg length of 2.25 mm should suffice. More the weld, greater would be the problem in distortion. Use a lower diameter wire for welding and try stagerring the weld in four sectors, 6-9, 3-12, 9-12 and 6-3 O Clock. Being 2 " OD pipe, this should be possible. This may help reduce the excessive heat bulid up associated with continuous welding and may help reduce chances of burnthru', and distortion. Depends on how many joints you have though. BTW, why GMAW for this application. The joints being so small, you are not going to have significant productivity increase by using GMAW. If quality/burnthrough is very important, why not consider autogenous pulseTIG (without filler wire). A seal weld type of weld in which the bracket edge is fused to get the weld metal.....Just thinking out loud!!

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
The whole of science is nothing more than a refinement of everyday thinking!!!

 

[TVP]

CWIC,

1. Strut body
2. No
3. No
4. Robot

Sayee,

GMAW will be used because this is the equipment that the production facility already has-- a common problem with high volume automotive manufacturing. I like your suggestion of autogenous GTAW welding, but there is no opportunity to use this method. Alas...

Thanks for the replies. If anyone comes across a design guide, handbook, etc. with a recommendation on thickness differential not to exceed, feel free to post it.

 

[CWIC]

TVP:
The GMAW process complimented by robotics will work just fine for your application. You will not be limited by thickness either, to a point. Very thin materials (thinner than the ones you are joining) can be welded using a set-up such as yours. 0.030" dia. electrodes may weld relatively thin materials.
Robotic cells, once dialed in correctly, will perform satisfactorily for an application such as yours.

The best of luck (not that you'll need it!)

Another FYI;
Last year during an audit of a manufacturing facility, a client wanted to show off their robotic cell. (Tube to flange w/fillet weld appplication.) They used magnetic part-positioning methods. It was a disaster as far as demonstrations go, the arm just touched one of the parts resulting in a dominoe effect which moved several other parts out of position during the cycle. I got to watch all of the parts that were set-up get knocked all over the table by the arm, one of them was partially welded to the table. Not too impressive...

 

[flamby]

In Indian welding code, there is a thumb rule. It does not say anything about difference in thicknesses but the weld size. It says, weld size not to exceed (thickness of thinner member - 1.5 mm). I guess 1.5 mm less is done to reduce the heat induced damage.