to improve the sliding properties of the inclined faces 26 36 of the recesses 25 35 and those of the inner faces 74 75 of the tenons 72 73 it is possible for them to comprise bearing plates made of a material the sliding properties of which are better than those of the material of the half molds 2 3 or of the latch 7 moreover the bearing plates may constitute wearing parts which prevents damaging the parting line 11 the figures represent a locking device in which figures the latch is a mechanical part usually in a block which is housed in recesses provided in the side surface of the half molds that said a variant of the invention consists in using a magnetic latch comprising an electromagnet the use of an electromagnet makes it possible to control the locking and unlocking of the device the operation of the mold 1 fitted with locking devices 6 will now be described with reference to fig4 a 4 b and 4 c with reference to an injection molding system first of all the mold 1 is open as illustrated in fig4 a this means on the one hand that the half molds 2 3 are separated from one another and on the other hand that the locking devices 6 are in the open position then by virtue of means for opening and closing the mold the movable half mold 3 and the movable platen 5 move toward the fixed half mold 2 and the fixed platen in.