Page 77 - Welding Robots Technology, System Issues, and Applications

Welding Robots
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from 1 to 12 m/min are used for steels, though lower values of force and speed are
applied in aluminum alloys.

Carbon, low-alloy, stainless and coated steels are currently welded using this
process. Welding of light alloys requires additional precautions because of their
lower electrical resistivity and lower melting temperature. A new process named
conductive heat resistance seam welding allows one to increase the welding speed
and reduce joint preparation cost in difficult-to-weld aluminum alloys [37].

RSEW is largely used in the automotive industry as well as in manufacturing of
heat exchangers, non-pressurized tanks and several types of cans.

Main advantages of this process when compared with resistance spot welding are
the capacity to produce gas-tight and liquid-tight welds as well as the possibility of
reduction of the overlap width of the sheets. However, the weld must progress in a
straight line or in a uniformly curved line of large radius and thermal distortion can
be higher than in resistance spot welding.

This process has several variants such as mash-seam welding, butt seam welding,
high frequency resistance welding and high frequency induction welding [38] but
they are outside the scope of this introduction.

2.5 Friction Stir Welding (FSW)

Friction stir welding (FSW) is a solid state joining process invented at The Welding
Institute (TWI) in 1991 [39], in which a non-consumable rotating tool is slowly
plunged into the butting faces of the work-pieces and traversed along the joint line,
see Figure 2.24a. Pieces to be welded have to be clamped in order to prevent joint
faces from being moved out of position.

Heat is generated by tool friction, under the tool shoulder and on the probe surface,
and by plastic deformation of the material [40]. Heat generated is lost to the work-
pieces, to the tool and to the anvil, as represented schematically in Figure 2.24b.
Maximum temperatures are attained close the tool shoulder and are lower than the
melting temperature of the materials being welded [41], though incipient melting
has been reported for some materials. Heat produced creates a softened plasticized
region around the tool, which facilitates the movement of the tool along the joint
line. Plasticized material is chaotic mixed or extruded from the advancing side to
the retreating side of the tool [42],[43] and it is forged by the contact of the tool
shoulder and of the pin, producing a solid phase bond between the two pieces.