Why does my stud not stick?

Make sure the plug of the gun is firmly inserted in the unit's socket and that the correct welding parameters are set on the unit.

Now check the workpiece surface and your equipment:

Rolled or looped welding cables act like a coil, they generate a magnetic field and cause energy loss. Always unroll your welding cable completely.

The surface of the workpiece have to be free of scale, oil, paint and oxide layers. Otherwise, this can lead to disturbances when the stud melts on the workpiece surface.

In case of asymmetrical ground connection, differing material distribution, or welding at the edge of a workpiece, a so-called blowing effect can occur. This is an unwanted deflection of the arc. It leads to one-sided melting of the stud material, increased pore formation and undercuts in the welding area.
Therefore, always make sure that the welding point is located as centrally as possible between the two ground clamps.

If the flange of the stud rests directly against the chuck, the plunging depth is too small. The spring force required for plunging the stud into the melt is reduced. The stud "sticks" to the chuck and the chuck is fused.
Adjust the stop pin on the chuck so that a total dimension of 50 to 51 mm is obtained between the top side of the lock nut ant the underside of the welding element. This corresponds to a distance of about one millimetre between the flange and the edge of the chuck.

If the chuck is not inserted completely into the piston, the plunging depth and thus the spring force are too much for the welding task. The welding tip evaporates faster than desired and the welding time is reduced. Workpiece and stud do not have enough time to fuse together.

The retaining nut secures the chuck in your welding gun. If the retaining nut is not tightened firmly, the contact resistance of the circuit will also increase, resulting in energy losses.

If the welding gun is not pulled straight off the stud after welding, the chuck grips may spread apart. A firm connection between chuck and stud is no longer ensured. Here, too, the contact resistance of the circuit increases.
Therefore, pretension the chuck at regular intervals.
Replace the chuck when the stud can be inserted into the chuck with almost no resistance.

Due to the high energy required for stud welding, the chuck will fuse over time. Short studs lead to increased melting ("burn-off"). Here, too, energy loss due to higher contact resistance applies.

The welding piston is pushed forward by the pressure spring when the welding process is triggered. As a result, the stud is pressed onto the workpiece surface and the stud can dip into the melt.

The bellows protects the welding piston of your welding gun from contamination. If the bellows are damaged, welding spatter can get onto the piston. This increases the friction of the piston on the ball linear bearing, energy losses are the result.
Push the retaining nut from the front and check whether the piston can be easily pressed in. Check the bellows.

During welding, despite utmost care, welding spatters can get onto the chuck and thus contaminate it. When welding with shielding gas shroud, the inside of the shroud may fill up with weld spatter and, together with the dirty chuck, cause considerable malfunctions.
Check the condition of your equipment at regular intervals.