Posted by Mike West to the VintagVW & VintageBus lists
I have run across the term “hammer welding” several times in the last few weeks. It seems to be associated with welding contoured pieces of metal.
Can someone point me toward a source of more detailed information about this process or at least sketch an outline of it? I have begun dabbling in the worlds of mig and oxy/acetylene welding and am very interested in learning what is practical to aspire to once I become comfortable with the basics.
mark fitzsimons — mfitzsim_at_aol_dot_com
Hammer welding in the sense they are using it is a misnomer . .
It just seems like hammer welding . . . What they are doing is controling their shrinkage with a hammer.
First condition: we are butt-welding a section into the outside of a car . . . on all? vehicles, even “flat” sections have a slight curve outward . .
This panel you are putting in fits perfect with a .02" (1/2mm) gap all the way around . . all surfaces of the patch are aligned with all the adjacent surfaces of the the “parent” . . .
Now you want to “tack-weld” the patch into it's final resting place.
You do this like lacing up a boot . . one on this side and one directly opposite on the other side so the tacks pull against each other . .
Now we have to look at the tack-weld itself . . If you're using a coat hanger for filler metal, it's eqiv. to a 60XX weld rod . . . if you are using my mickey mouse wire welder, it has a E-70XX . . . there are numbers where those X's are but they vary . .
That 60 and 70 are the tensile strength of the filler material . .
That reads 60 thousand psi and 70 thousand psi . .
Getting back to the weld itself, lets take a tack 1" (25mm) long with a 1/8" (3mm) thick . . . this gives a cross-section of .12 sq. inches times the 70 thou. tensile gives 8400 psi that tack is pulling with.
While I admit to gross over-simpification there, that's a fair look at what is happening . . . so this tack just pulled your contoured surface flat . . .
We don't want that, so put a dolly on the back side and whack that weld a sharp blow . . . this thins the weld and expands it in the plane that relaxes its pull . . .
When you get the whole patch back where it's supposed to be, you make another tack on the opposite side and go thru all this again . .
Now if you aren't too good at this “shrinkage” thing, you will do a lot of hammering . . :-)
Real Hammer welding has been around as long as the forge . . It's done in a forge / anvil setup . . .
Get the two ends of metal to be welded white hot, lap them and hammer the lap into a single thickness again . . Now lap the metal again, like the seam on your blue-jeans and hammer it back down to one thickness again . .
Several heatings and treating the faying surface with flux, were left out of the above for clarity . . :-)
The Japanese Samuri Swords are a famous example of hammer welding . . besides being an early example of high-carbon steel . . .
Some-how none of the above lends itself to slamming a new panel in the side of a car-door tho . . .
west