Displacement controlled welding

In welding by distance, also called displacement controlled welding, the process described above is modified by using rigid mechanical stops to control the welding process and the part dimensions. Parts are... 

The welds of Ti-6-4 were made in displacement control rather than z-axis load control. Typically, this resulted in the formation of a small lack of penetration (LOP) defect in the weld nugget. The lack of penetration defect caused tensile failure to occur through the weld nugget. The low elongation can also be attributed to the LOP defect. Tensile properties of a second friction stir welded Ti-6-4 specimen which did not contain a LOP defect is also shown in the Table. As can be seen from this table the % elongation is much higher in this case. 

Friction shr welds were produced using tools machined from a W-25%Re alloy. A tool with a shoulder diameter of 14 mm ( /i6 in.) and a pin length of /.9 mm (0.075 in.) was used to produce all of the welds discussed here. No threads or other profiles were used on the pin. Tool plunging was completed under displacement control. The tool was maintained at a forward tilt angle of 1° for welding, and the welds were run under load control of the axial (z) force. The welds were produced with a tool rotation rate of 200 rpm and a travel rate of 100 mm/min (4.0 in./min), using an axial load of either 9.8 or 10.7... 

Practical use of this phenomenon is now being made in the control of IGSCC in the heat-affected zones adjacent to welds in Type 304SS recirculation piping in commercial nuclear boiling-water reactors (BWRs). The criterion for protection is that the potential should be displaced to a value more negative than -0.23 Vshe indeed, this value has been accepted by the Nuclear Regulatory Commission based upon short-term in-reactor tests [30]. 

Molten layer thickness is an important determinant of weld strength. If the thickness of the molten layer is less than the melt stop displacement, melt stops cannot contact holding stops, part dimensions cannot be controlled, and joint quality is poor due to limited inter-molecular diffusion. In addition to contributing to weld strength, adequate displacement in phases I and II compensates for part surface irregularities and ensures that contaminated surface layers flow out before the joining phase. [ 1... 

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