Introduction to Basic Manufacturing Processes and ... - always yours

334 Introduction to Basic Manufacturing Processes and Workshop Technology
17.8.1 Forge Welding
In this welding process, the work-pieces to be welded are heated to the plastic condition
(above 1000°C), and then placed together and forged while hot by applying force. Force may
be applied by hammering, rolling, drawing or squeezing to achieve the forging action. Forge
welding was originally the first process of welding. In this process the two metal pieces to be
joined are heated in a forge or furnace to a plait condition and then they are united by
pressure. The ends to be joined are heated in a furnace to plastic condition and formed to
the required shape by upsetting. Then they are brought together and hammered, so as to get
the finished joint similarly, a butt joint can be prepared by forge welding as shown in Fig.
17.3. Before joining the two pieces, their ends are formed to the required shape according to
the type of joint. The forge welding is a manual process and is limited to light work because
all forming and welding are done with a hand sledge. It is a slow process and there is
considerable danger of an oxide scale forming on tile surfaces. The tendency to oxidize can
be counteracted somewhat by using a thick fuel bed and by covering the surfaces with a
fluxing material, which dissolves the oxides. Borax in combination with salt ammoniac is
commonly used as flux. The forge welding is recommended to such metals, which have a large
welding temperature range like low carbon steel and wrought iron. By the increase of carbon
content, this range decreases rapidly. High carbon steels alloy steels require considerably
more care in controlling temperature and producing the welds. Large work may be welded
in hammer forges driven by steam. Welded steel pipe is made mechanically by running the
preheated strips through rolls, which form the pipe to size and apply the necessary pressure
for the weld.
17.8.2 Friction Welding
In this process, the heat for welding is obtained from mechanically induced sliding motion
between rubbing surfaces of work-pieces as shown in Fig. 17.27. In friction welding, one part
is firmly held while the other (usually cylindrical) is rotated under simultaneous application
of axial pressure. As these parts are brought to rub against each other under pressure, they
get heated due to friction. When the desired forging temperature is attained, the rotation is
stopped and the axial pressure is increased to obtain forging action and hence welded joint.
Most of the metals and their dissimilar combinations such as aluminium and titanium, copper
and steel, aluminium and steel etc. can be welded using friction welding.
Belt
Rotating
chuck
Brake
Sliding
chuck
Thrust
cylinder
Motor
Fig. 17.27 Friction welding process