Английский для сварщиков. Гричин С.В. - 92 стр.

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Friction-stir welding

machine

the ratio of frictional to volumetric deformation--induced heating decreases

as the work piece becomes thicker. This is in order to ensure a sufficient heat

input per unit length.

The microstructure of a friction-stir weld depends in detail on the tool

design, the rotation and translation speeds, the applied pressure and the

characteristics of the material being joined. There are a number of zones. The

heat-affected zone (HAZ) is as in conventional welds. The central nugget

region containing the onion-ring flow-pattern is the most severely deformed

region, although it frequently seems to dynamically recrystallise, so that the

detailed microstructure may consist of equiaxed grains. The layered (onion-

ring) structure is a consequence of the way in which a threaded tool deposits

material from the front to the back of the weld. It seems that cylindrical

sheets of material are extruded during each rotation of the tool, which on a

weld cross-section give the characteristic onion-rings.

The thermomechanically-affected zone lies between the HAZ and

nugget; the grains of the original microstructure are retained in this region,

but in a deformed state. The top surface of the weld has a different

microstructure, a consequence of the shearing induced by the rotating tool-

shoulder.

The Machine

This is a picture of a friction stir welding (FSW

shows a typical) machine. This one is at the Joining

and Welding Research Institute (JWRI) of Osaka

University, Japan.

The Tool

An illustration of some types of tools. Each

tool has a shoulder whose rotation against the

substrate generates most of the heat required for

welding. The pin on the tool is plunged into the

substrate and helps stir the metal in the solid state.