Printhead for a 3D printer and method for operating a printhead

A printhead (100) for a 3D printer comprising:

• an actuator device (110) which is arranged in a housing (1) of the printhead (100) for actuating a piston (3), a supply device (2) for a printable material (10), a flange (5) which is arranged on the housing (1) and the supply device (2) and which comprises a cooling device (50), a nozzle head (6) with heating elements (61, 63) in order to convert the material (10) from a solid phase (10) to a liquid phase (12) via a plastic phase (11), and a nozzle (8) for discharging the liquid phase (12) of the material (10) out of the nozzle head (6),
• wherein a pocket piece (7) is arranged on a lower sub-region (42) of a separate piston bushing (4), wherein the pocket piece (7) has a centrally running bore (70) for receiving a piston needle (32) of the piston (3), and the pocket piece (7) has concentrically arranged openings (71) which form a fluidic connection between a cavity (40) arranged in the piston bushing (4) and a melt chamber (81) arranged in a lower part (62) of the nozzle head (6), and
• wherein, during a solidification process (230) for the production of the liquid phase (12) of the material, the nozzle (8) is closed and the piston needle (32) is submerged in the melt chamber (81), such that a portion of the liquid phase (12) is thereby displaced back into the cavity (40) of the piston bushing (4) from an upper region of the melt chamber (81) through the openings (71) of the pocket piece (7), thereby mixing the displaced portion of the liquid phase (12) with the plastic phase (11) in the cavity 40.