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21A
STUDWELDING TECHNIQUES
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5. WELDING STUDS LESS THAN 25 mm LONG USING FERRULES.
As we have seen previously, the stud is held in a recess in the chuck and must be long enough to
allow us to set the correct protrusion. A standard chuck has a recess 12 mm deep and ferrules vary
in length up to 13.5 mm high. Thus if a stud is much less than 25 mm LAW we shall not be able to
obtain the correct protrusion, i.e.. The chuck may hit the ferrule on the return stroke and prevent
the stud returning to the plate correctly.
This problem may be overcome by using "shallow recess" chucks (the recess depth is only 6 mm) or
if the studs are required to be very short, by using a special type of stud known as a "break
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off"
type. These studs have an overall LAW of 30 mm and are welded using a standard chuck and ferrule.
The stud is "grooved" at the required length from the welding end. After welding, the surplus
portion of the stud is broken off with a pair of pliers. By these means, very short studs can easily be
welded.
6. USING TEMPLATES TO ENSURE POSITIONAL ACCURACY.
When welding studs around the periphery of a flange, i.e. for cover plates, inspection doors etc.,
positioning of the studs in relation to each other becomes most important. A simple template made
from 2 mm sheet, shaped to suit the component and provided with clamps is usually the answer to
this problem. The position of the studs is accurately marked and holes drilled in these positions to
accept either the ferrule of the stud to be welded or, if using short cycle, the pistol gas shroud. The
size of the holes should be the outside diameter of the ferrule / 0.4 mm. It is also advisable
to provide 2 mm thick pads underneath the template so that there is a space between the
component and template, this space will allow the gases developed during welding to vent properly
from the ferrule / shroud. For any further advice or help in the design of jigging or templates
contact your local field sales engineer.
7. MINIMUM PLATE THICKNESSES WHEN STUD WELDING.
When using standard Drawn Arc with ceramic ferrules, the minimum ratio of stud diameter to plate
thickness is 4 : 1 for plate thickness greater than 3 mm and 3 : 1 for plate thickness between 1.5 mm
and 3 mm. When using the short cycle system with or without gas purging it is possible to weld
equivalent size studs onto slightly thinner sections, due to the short weld duration. These ratios
ensure that the strength of the plate is sufficient to support a stud of a given size when it is loaded,
without there being a tendency for the plate to distort.
Occasionally, however, it may be necessary to weld a stud outside of these ratios. This can
sometimes be accomplished without distortion by "heat sinking" the component, by using a flat
copper or water cooled backing piece behind the weld area, to support the plate and assist in
dissipating heat quickly.
8. WELDING STAINLESS STEEL.
Austenitic stainless steel studs of the 18/8 g/N : weld decay proof type can be supplied for welding
to similar parent material or mild steel. The technique does not differ from that used for mild steel
stud welding. There is a tendency with larger diameters of stainless steel studs for metal transfer
across the arc to take the form of large particles. If short circuits occur then the arc can be heard to
splutter. This may occur with any diameter of stainless steel stud if the lift of the hand tool is not
correct. Due to this tendency to transfer in large particles increased lift may be required and time
settings should be kept as low as possible.
