Opening device and apparatus for moulding an opening device on a sheet packaging material

10) Molding apparatus for molding an opening device on a sheet packaging material, said packaging material comprising at least a first layer and a second layer, and having a hole formed through said first layer and sealed by a cover portion of said second layer, said opening device comprising a spout defining a pouring opening, a wall portion closing said pouring opening, and a weakening region interposed between said wall portion and said spout, said molding apparatus comprising a first mold arrangement and a second mold arrangement arranged on opposite sides of said sheet packaging material and which can be set in an open configuration, allowing feed of said packaging material, and in a closed configuration, wherein said first mold arrangement and said second mold arrangement define a mold cavity housing said cover portion and adapted to be filled with said plastic material for defining, when the plastic material sets, said opening device, said mold cavity comprising a first chamber, which houses said cover portion and is arranged to define said wall portion, a second chamber arranged to define said spout, said second chamber being delimited by said second mold arrangement, wherein said molding apparatus further comprises a protrusion extending into said mold cavity and delimiting a small-section passage connecting said first chamber to said second chamber and arranged for defining said weakening region, characterized in that said protrusion extends from said first mold arrangement