A mould-closing unit for an injection moulding machine for processing plastics has a mould support which is movable relative to a stationary mould support (10). A mould-moving device is provided to move the movable mould support into and out of closure of an injection mould. At least one force transmission element is connected to the movable mould support and at its end remote from the movable mould support has a section (14a) which is assigned to the stationary mould support (10) and can be actuated for operative engagement. The stationary mould support (10) is assigned a locking device (15), which can be moved into interlocking operative connection with the actuatable section (14a) to apply a closing force during closure of the injection mould. According to the method, these elements are used to create a method for locking a force transmission element to a mould support of the injection moulding machine. The fact that the locking device (15) has floating clamping jaws (16) which can be moved into interlocking operative connection with the actuatable section (14a) during closure of the mould to lock the force transmission element and the stationary mould support (10) and at the same time are connected to at least one piston (18) of a piston-cylinder unit (17) for applying the closing force, means that a mould-closing unit is created in which the locking mechanism for locking the tie bars to the mould support is integrated in a common unit with the unit for applying the closing force.