Ii is not always possible or necssary to make metal objects by
shaping and machining Often it is better to construct them by joining several
Picces together. This may be done by wdding.
In fusion welding the welder first heats the edges of melt pieces with
a high temperature From an oxy-acetylene torch until the surfaces melt Then
he usually adds more molten matal from a welding rod to fill the gap between
the two pieces. The filler metat and the melted edges fuse tog ether. When
the metal cools and solidifies : a strong joint forms.
Instead of a gas flame,the welder may use the ea produced by an
electric arct to melt the me tal This is known as arc welding.
Another form of electric welding is called resistance welding.When
an electric current is passed through two overlapping metal parts,thy heat UP.
A little pressure is applied to join the parts together.spot welding and seam
welding are two forms of resistance welding.
In friction welding. The part are wbbed to gether under untit they soften and fuse.
The most recnt method of wethod of welding is by laser beam.Laser welding
is often done where delica te parts must by joined uery accurately.