Spot Welding Tube

[loktinl]

Hi,

I was wondering if it is possible to spot weld a piece of flat sheet metal to the shank of a round steel tube. The size of the tube I have in mind is small (roughly 1/4"OD), and the sheet thickness is yet to be determined.

If anybody has any suggestions as to where I can go to look up more information on the related topic, I would greatly appreciate it!

Regards,
loktinl

 

[metengr]

I would use a small tack weld, GTAW (TIG) process.

 

[berkshire]

It is possible to spotweld thin sheet to thinwall tube.
You can use a process which uses two electrodes on the side of the sheet metal whereby the current passes into and out of the sheet metal not the tube.
It is tricky to set up,custom fixtures must be made, squeeze pressures and times must be right, or you will get flash away or incomplete welds.
This process works best on clean mild steel or stainless tube.
The welder shown in the link is a hand held one, there are fixed one as well.

http://www.weldingnet.com/wt-catalog.pdf

check page 17.

B.E.

 

[BrianPetersen]

Is this a production situation or a one-off situation?

If it is a one-off situation, just drill a hole approx 6 - 8 mm diameter in the sheet metal at the location where you would like the weld to be, hold it in place against the tube, and use a MIG to fill the hole with weld. If you have production MIG equipment then this will work in a production situation, also.

 

[loktinl]

Thanks for the reply everybody.

This is a one-off situation for a prototype part. I shall look into my options, but all the above comments are much appreciated.

What are the tolerances that I could expect from this procedure? I presume it is all down to the sturdiness of the setup.

 

[yoshimitsuspeed]

What exactly are you trying to do? It's hard to help with the amount of information given. There are many ways you could do it. Do you have welding equipment available?
What tolerances are you interested in?

 

[loktinl]

The device I am making is a prototype surgical tool. The form factor is about the size of a hot glue gun. The distal end is roughly 30cm away from the handle, so a stainless steel tube is used to provide rigidity.

Are there possibilities to bending the sheet metal into a roll and inserting the pipe into the roll? I have access to basic sheet metal machinery such as a press brake, manual bender and cutters. I plan on waterjetting the sheet metal.

As for tolerance, The pipe needs to be axially aligned to a motor that will be mounted on the sheet metal part. I need the tube to be within 10 thou positionally from the axis of the motor, and if the shaft is cock-eyed, the distal end of the tube cannot wander from the axis of the motor by more than 10 thou.

Those tolerances are based on primitive calculations. Does anyone have an idea of what kind of tolerances I could achieve?

 

[MikeHalloran]

Your press brake tooling catalog should show you what a hinge leaf punch/die set looks like and how to use it. If standard hinge leaf sizes don't work for you, you can probably have a short custom one made by your local machine shop to dimensions appropriate to your assembly.

You can get any tolerance you're willing to pay for. Not meaning to be snarky, the little information you've provided suggests that you may end up paying a lot for your stated extended tolerance zone.



Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

Adding to what Mike has said, A wiring die setup for a punch press
will give you a roll on the edge of a sheet of metal as long or as short as the die.
Also based on your latest information, you could use conventional spot welding equipment to place a weld on opposite sides of the part to secure your sheet metal to the tube.
If you have a qualified sheet metal worker to go along with your sheet metal equipment, he could hand wire an edge over your 1/4" tube for your prototype sheet metal, using a spinning jenny.
B.E.

 

[berkshire]

Adding to last nights comments, here is a link to the kind of die I was talking about. These are wiring or curling dies.

http://www.midwestpressbrake.com/page_11.htm

B.E.

 

[yoshimitsuspeed]

I pretty much agree that you can get the tolerances you are willing to pay for. Is your concern the ID or the OD of the pipe? After the mental image of a hot glue gun I have it in my head that the ID of the tube is the important part. If this was so I would select some tubing just slightly undersized on the ID and with a plenty big enough OD and then I would weld that as accurately as possible to the plate. Once I welded it I would machine the bore which would make tolerances of a few thou pretty easily achievable.

I'm still having a hard time imagining exactly what you are doing but just generally the next best option is to make a jig that holds the material you are trying to weld as rigidly as possible.
It really sounds like what you are trying to do would be quite easy but much harder to imagine and or help much over the internetz.