The ‘rest position’ is the normal resting position of the welding gun. When a stud and a ferrule are inserted into the pistol and the trigger is pressed, the stud moves forward from the rest position until the welder detects that the stud has touched the metal plate. This is done by measuring the electrical resistance between the stud and the plate. If the resistance is too high (i.e. bad contact) the stud will refuse to fire. This is to ensure that the surface of the plate is free from any oxide scale, primer, or dirt. The rest position is approximately 0.5-1.0 mm inside the end of the ferrule base prior to welding. This allows for better metallic “searching.”
The second position is called the ‘zero position’ and is the point where the stud makes contact with the metal plate. With the stud at the zero position, the pilot current is turned on and the stud is moved up at a speed that is determined by the Up Velocity parameter.
The pilot current will create an arc, but the current is insufficient to cause welding and will prevent the stud from bonding to the base plate. (This is called sticking). The stud will move down 5mm to seek the metal base. It will also compensate for any length discrepancy in the stud.
Once the stud has reached the Pre-Up Height Position, (approximately 0.2 mm) the main current is turned on and the stud is moved up to the final “Up Height”. The stud moves up according to the Pre-Up Height with a predetermined velocity (UpVel) and a 15 Amp pilot (pre-) -current.
When the stud is at the ‘Up-Height’ position, the main current is monitored and controlled so that it stays at the value set by the Weld Current parameter. The stud will stay at the Up Height position for a pre-determined length of time.
With the current still ON, the stud is moved down into the molten weld pool at a velocity set by the Down Velocity parameter. When the initial zero position is reached the stud is further plunged into the weld pool to a depth determined by the Down Height parameter.
As the stud moves down; the current is kept on to keep the weld pool from solidifying.
On reaching 50% (the suggested setting) of the Down Height the current is turned OFF and the stud then proceeds to the pre-determined Down Height. The current is turned off just above the weld pool. This ‘hot plunge’ feature will ensure that the stud and the base metal form a full metallurgical homogeneity.
When the stud’s in the ‘Down Height’ position the weld is complete and the computer will display the average current value during the sequence of the weld. If this average value is within the pre-determined Current Error Allowance then the green LED on the back of the Pistol will light up and confirm a ‘good’ weld.
After the weld is allowed to cool the operator removes the pistol from the stud and the pistol motor returns the stud holder to its rest position.
The stud continues its drive into the hot metallic pool; at the same time the speed is decelerated over the last 25% of its path to achieve a smoothly controlled penetration. Due to its fluidity the molten metal will circumvent the stud very easily.
The cycle can be repeated over and over again with the same precision giving identical welding characteristics to every single stud weld. In addition to the precise actions of the weld; the stud-welder will simultaneously control the current level of the preset level chosen by the operator, the cable length, the internal temperature, and the voltage fluctuations.