the invention relates to a mold clamping unit on a plastic injection molding machine , the unit having a clamping mechanism for opening and closing an injection mold , the mechanism having a servo motor as the drive motor . the drive motor drives at least one spindle drive which has a spindle nut and spindle which work together on a bearing position . a cooling system with cooling channels is provided for removing heat from the clamping mechanism . a more efficient cooling of the spindle drive is achieved in that the cooling channels penetrate the bearing position of the spindle drive and / or one of the cooling plates assigned to the bearing position .