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Welding fundamentals and history
Weld fundaments
To weld is to to join 2 or more pieces of metal with
the application of heat and sometimes pressure.
Resistance welding is a method of welding in which
the heat required for welding is generated by the
resistance to passage of current in the parts to be
welded. This differs from other forms of welding in
which no filler such as flow, electrodes, etc. are
used, so the metallography of the weld does not
change due to the filler. Resistance welding is
still very different from bonding due to the use of
the application of mechanical force to forge the hot
parts together. The effect of force, we are refining
the grain structure, thus producing a weld with the
physical properties most often equal and sometimes
even higher than the base material.
Welding machines for resistance and its operations
seem mysterious to a layman, when he sees good welds
being made easily and quickly. The same
characteristics can induce the beginner to believe
in a process easier and more widespread application
than the reality. This is the purpose of this
introductory discussion to review the fundamentals
of the process and to discuss some more complex
details.
Welding is really a metallurgical process. Steel has
been described with a suspension of ferrite crystals
of variable composition in a matrix of their own
impurities. This array of impurities, which
increases the electrical resistance of all metals,
the real
importance in electrical resistance welding.
Weld history
The process of resistance welding was invented in
1877 by Elihu Thomson (1853-1937), founder and
president of the Thomson Laboratory, Lynn, Mass..
Thomson was a designer and manufacturer of motors
and transformers. Thomson Laboratory later merged
with Edison General Electric Company being created
then the General Electric Co.Thomson was vice
president and research director of the new company.
The "discovery" of resistance welding occurred when
Thomson was teaching electricity at Central High
School in Philadelphia, demonstrating the operation
of a spark coil. At this time, Thomson was a
professor of chemistry and mechanics (1876-1880).
The first practical demonstration of resistance
welding was performed at the Franklin Institute in
Philadelphia (1879) and was "perfected" in 1886. It
was in 1886 that the first machine resistance
welding was produced: Thomson-Gibb.
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