A bottom-up powder conveying mechanism for a powder bed-based laser melting (PBLM) system includes a powder reservoir having a movable floor operable as a piston to convey powder towards an upper opening in the powder reservoir opposite the floor and through the upper opening to a working plane of the PBLM system. The bottom-up powder conveying mechanism further includes an external reservoir connected, via a sloping conduit, to the powder reservoir for conducting powder to the powder reservoir. The powder reservoir includes a side wall with a lower opening that is lower than the upper opening in the powder reservoir and through which the powder reservoir can be filled with the powder. The lower opening is connected in a gas-tight and releasable manner to the sloping conduit in order to be able to conduct the powder in a gravity-driven manner from the external reservoir into the powder reservoir.