V-21A
4
INTRODUCTION
INTRODUCTION
Taylor Studwelding Systems Capacitor Discharge units are compact, portable Stud Welding
equipment. The units are specically designed to enable a small diameter range of ferrous and
non-ferrous weld studs to be welded to light gauge, self-nish or pre-coated materials, in most
cases with lile or no reverse marking.
The equipment typically consists of a control unit, a welding pistol and the necessary
interconnecng cables and accessories.
THE PROCESS
Capacitor Discharge stud welding is a form of welding in which the energy required for the
welding process is derived from a bank of charged capacitors. This stored energy is discharged
across the gap between the two surfaces to be welded as they are propelled towards each other.
The arc produced heats the two surfaces, melng a thin lm of metal on each surface and the
propelling force closes the gap between the two faces, thus forming a weld.
There are two sub-processes of this type of welding. One is known colloquially as contact,
the other as gap or li gap.
In contact welding the stud to be welded is forced by a strong spring in the pistol against
the work piece. At this point the arc gap between the two components is maintained by a small
pip on the welding face of the stud. On iniaon of the high current pulse from the capacitors,
this pip vaporises and an arc is drawn between the work piece and the stud. The heat from this
arc melts the base of the stud and the area of the work piece directly beneath the stud, whilst
the spring pressure from the pistol accelerates the weld stud towards the work piece. Within 3 to
4 milliseconds of inialisaon the stud hits the work piece and the arc is exnguished. The kinec
energy contained in the moving stud and the remaining spring pressure, forge the molten parts
together to form a weld.
Li gap or gap welding diers in that the spring in the pistol is much soer. This is
specically to allow the welding of soer non-ferrous materials where the stronger pistol spring
may cause mechanical damage to the stud pip before the weld can be inialised. The soer
spring however, does not have sucient force to close the gap both quickly and forcefully
enough. Therefore a li gap pistol also contains an electrical solenoid li coil. When the weld is
iniated the li coil briey lis the weld stud away from the work piece to an operator set height.
As the coil releases, the high current pulse from the capacitors is iniated so that upon contact of
the pip to the work piece the weld begins. As the pip vaporises, the momentum of the moving
stud closes the gap quickly and forcefully enough to complete the weld. Usually in under 3
milliseconds. This faster weld is very important as most non-ferrous metals are much beer
thermal conductors and a faster weld ensures that the heat generated in the weld is not
conducted away before the arc gap closes.
