On Mon, 05 Jul 2004 00:46:51 GMT, Seppo Renfors
wrote:



Eric Stevens wrote:

On Sun, 04 Jul 2004 01:02:50 GMT, Seppo Renfors
wrote:



Eric Stevens wrote:

On Sat, 03 Jul 2004 07:38:25 GMT, Seppo Renfors
wrote:



Eric Stevens wrote:

On Fri, 02 Jul 2004 13:37:36 GMT, Seppo Renfors
wrote:

[..]
However if one considers that "bubbling" has been claimed to be caused
by "overheating" in a annealing process - then it is saying "melted"
at the same time, as it cannot bubble UNLESS a portion of it is
melted. Also "welding" requires the melting of the metal - or so
goddamned close to it that the friction heat generated by a blow on it
does melt the metal.

Reasonably pure copper can be welded at ambient temperatures merely by
pressure. MIllions of electrical connections rely on this property.

Anything can be welded at virtually any temperature by using pressure.
The Mini Minor crown wheel for the diff started off as a steel disc
cut off from a round billet. This was placed on a mould at the end of
a hydraulic ram, and the other half of the mould was on another
hydraulic ram. To form the crown wheel they were slammed together
under huge pressure - it made a very nice crown wheel - and fast!


You are confusing forging with welding.

Actually I referred to neither. I referred to the use of pressure only
as "merely by pressure" was your point.

But I was discussing welding. You seem to be confusing cold forging
with welding.

You say it started off as a steel disc. You have not mentioned two
pieces which were welded together.

Didn't need to as "welding" wasn't involved in that case - "melting"
was - from a round flat disk to a crown wheel for a diff.

Sorry. There is no melting in either hot or cold forging.


http://www.forging.org/Design/pg6_9.html describes the manufacture of
gears using a similar process to that used for the Mini.

Not quite - the Mini crown wheel blank was not preheated in any
(visible) way at any stage. The process in the URL differs in that
molecular friction alone isn't used to heat the blanks to a momentary
melting point.

In any event this is wandering off topic at the moment.

I'll say.

http://www.tf.uni-kiel.de/matwis/ama...ne/r5_1_1.html
discusses the role of dislocations in metal deformation. Forging is
possible as a result of the mobility of dislocations. All that heating
a billet does is increase their mobility. It is not necessary to cause
melting unless of course one is trying to undertake casting.




Eric Stevens