Re: "keyhole" shape?

Hi everyone

In keyholing you place yourself in the hands of the control of surface
tension. Surface tension is the dangling bonds of the atoms at the
surface kind-of "linking arms" for company and pulling a bit harder
than the bonds in volume. That pull tries to draw a liquid to a
smallest surface area. That's why a free-falling liquid droplet tends
to be sperical. And why a thin flow of water from a tap is
so close to cylindrical. In the case of keyholing it draws metal back
to fill the weld root gap.

Placing trust in surface tension is a good trust. You run at a rate
which keeps the keyhole well-formed, with nature and physics being the
higher controlling authority. Surface tension draws the metal to the
back of the weld, making a full-penetration (ie. full-height) joint.
There is filler metal coming off the welding rod to make up the volume
of the root gap and the extra small amount of penetration bead. So if
you were out-of-sync: too slow and the keyhole would choke up with
liquid metal (?); too fast and the keyhole would become big and
malformed, thirsting for liquid metal. Keyholing is a lovely to
technique to get the hang of and is a big sense of satisfaction in
progression of skills having mastered smooth fillet runs. Well I
think so :-)

Richard Smith
.