welding steel near aluminum, insert wisdom here!?

I have 2 pieces of aluminum that make up a kind of finger hinge.  The two sections are each 3/4" wide pipe each ending in finger joints with a hole drilled through the fingers.  A cotter pin has been used as the hinge pin during the mock up, but now a permanent hinge pin is required and due to space regulations it must be very flush and end on either side with a flat round, similar to a nails head (striking surface).  I was going to merely insert a nail, then put a tightly fitting washer over the other end, and briefly mig weld the end of the nail protruding through the washer too the washer.  The opposite end will have a small thin piece of cardboard as a temporary spacer to ensure a snug but not too tight of fit.  Of course the rest of the aluminum will be shielded from weld spatter.  The weld would then be ground flush.  There will not be a lot of tension put on this weld, but some minor vibration. There will 5 of these pipe section with 3 joints per section each, they will be very close together and require the ability to move independently from each other, so no shared pins.

• Will a very brief weld cause the pin/nail to heat up to a point that it causes the surrounding aluminum to melt and "horribly" cause the 2 joints to fuse?
• The 3/4 span is much to wide for a pop rivet and would have to much of a bump on the sides.
• Bolt and nut would also have to much of a bump, and introduces the destructive effects of a steel thread running through an aluminum body.
• Philadelphia screws are just too wide for this application
• Actually peening a real rivet will put to much stress on the aluminum pieces.
• No I do not have the means to weld aluminum, as this is a solder core wire feed welder, not a true mig.

Any suggestions?  I have done similar welds before, but all pieces were steel, not mixed.

Comments

[rickharris]

IF your very quick just a dot to hold the washer should be OK.

How long does the aluminium hinge with a steel pin need to last because they will corrode and the steel will wear through the aluminium.

[iminthebathroom]

Not long really, indoor sculpture minimal movement and only when initiated. I actually tried it last night and nothing fused. So I will spot weld the pins in.

[RavingMadStudios]

Maybe the nut/bolt assemblies that are used to secure knife handles would work?
http://www.texasknife.com/vcom/product_info.php?cPath=52_36_620&products_id=948

Basically, they bolt into the piece and then you grind the heads flush, so that it winds up looking like a pin instead of a bolt.

Knifemakers also use two-piece rivets that work prety much the same way.

[iminthebathroom]

Similar to a Philadelphia rivet, where they screw into each other. Looked into the website and others similar to it, unfortunately I need it to be one solid bar, same dimensions through out rather then stepping down. I will think of these in the future though, for a later rendition for the piece I am building though. Still hoping for a welding answer in regards to the whole aluminum/steel idea.

[aeray]

Sex bolts, if you get the correct size, are the same dimension throughout. I've even cut them down before to get the exact size I needed.

[steveastrouk]

I am intrigued. WTF IS a "Sex bolt" ???? Obviously a screw is involved.

Steve

[RavingMadStudios]

Sex bolt - The act of dropping whatever you're doing and sprinting toward the bedroom because your SO is suddenly "in the mood".

[steveastrouk]

Cor, you can remember better than I can.

[RavingMadStudios]

Nah, just conjecture....

[aeray]

I ate at a restaurant in Mexico once where the menus seemed identical, except that the ones they gave to the women in our party had no prices. Later, I asked how they kept them separate. The waiter pointed out that the sex bolts that held the the covers and pages together only had a screwdriver slot on one end. On the "male" menus, the "head" showed, and on the "female" menus, the "slot" was hidden... not quite as chivalrous as I'd first thought.

[steveastrouk]

ROFL. Nice anecdote !

[orksecurity]

Ugly answer: Epoxy a cap nut onto the end of the pin? Possibly with a washer between cap nut and hinge, to help keep the epoxy from migrating.

Might not be "very flush" enough. One could argue about whether it's permanent enough, though peened ends can be ground off too.

[iminthebathroom]

Yes, thought of this as well, when I temporarily put it together using finishing nails as pins, and bending them almost flush, even that was too much. Think of a roofing nail, with that paper thin wide flat round head. I built an animatronic life size salmon for the local museum and where the sections had exposed metal I welded in a bolt and nut, then ground the heads thinner then that of a roofing nail. This worked on awesome on STEEL! Curses, why did I dabble in aluminum... I've thought of counter sinking the bolts as well but sadly did not leave enough material to guarantee a a lot of strength. this is definitely a learning experience for me.

[aeray]

"Sex bolts" or "mating bolts" may work. They have no exposed threads when fastened, and the heads are generally much thinner (low profile) than regular bolts: http://www.boltdepot.com/sex-bolts-and-mating-screws.aspx
Or is this what you are referring to as a "Philadelphia screw"?