Capacitor Discharge (CD) Stud Welding is also a semi-automatic arc welding process. However, with CD welding small diameter fasteners (1/4" and under) are end welded to extremely thin guage parent metal. The CD process operates on the principle of capacitor stored energy which is instantaneously discharged by the equipment system through a special weld "timing" tip. CD welding permits stud welding of dissimilar metals.