The invention provides a removable mold of a joining apparatus. The mold comprises the following components: a mold head with an upper side and a bottom side; a mold shaft, which extends vertically from the bottom side of the mold head and can be locked in the mold convex circle without rotation. The mold shaft comprises the following components: at least a first radial web, whose double ends form radial undercuts; at least one second exposed radial web, whose radial length is adapted to the diameter of the mold convex circle in order to guarantee the mold shaft is transversely guided in the mold convex circle; and an ejected surface, by which the removable mold is removed from the mold convex circle and is arranged at the free end of the mold shaft which is opposite to the mold. The invention relates to a mold changing device of the removable mold for the joining apparatus, the removable mold adapted to the mold changing device, the mold convex circle adpated to the removable mold, a method for removing the removable mold of the joining apparatus, and a method for inserting the removable mold to the joining apparatus.