Print head and method for starting up a print head

A method for starting up a nozzle channel of a print head for processing liquid molten metal, wherein the print head comprises the following components:

• a crucible for accommodating a metal to be printed,
• a heating device for melting the metal,
• a nozzle connected to the crucible and including a nozzle chamber and a nozzle channel extending along an expulsion direction, wherein the nozzle chamber and the nozzle channel merge into each other,
• an actuator including a piston having a piston tip introducible into the nozzle chamber, wherein the actuator is configured to linearly move the piston back and forth, in a direction parallel to the expulsion direction, the method comprising the following steps:
• A) preparing the print head, wherein metal is melted in the crucible to form a molten metal, and the piston tip is introduced into the nozzle chamber, wherein, in the introduced state, there is a distance, at least in sections, between the piston tip and the nozzle chamber in the radial direction to the expulsion direction
• B) creating an overpressure inside the crucible which encourages molten metal to enter the nozzle chamber,
• C) moving the piston tip in the nozzle chamber, wherein the piston tip is moved back and forth by the actuator at a filling frequency which is larger than or equal to 1 kHz until molten metal is expelled from the nozzle channel out of the print head,
• D) moving the piston tip in the nozzle chamber, wherein the piston tip is moved back and forth by the actuator, wherein the movement is initially performed at a starting amplitude at which the molten metal is expelled from the nozzle channel out of the print head, and subsequently the amplitude of the movement is gradually reduced, and wherein the movement is performed with gradual reduction of the amplitude until molten metal is no longer expelled from the nozzle channel out of the print head, wherein the amplitude at which molten metal is still expelled from the nozzle channel out of the print head, but immediately before molten metal is no longer expelled from the nozzle chamber out of the print head, is defined as the limit amplitude,
• E) repeating process step D) n times in succession, wherein, in each of then repetitions of process step D), the limit amplitude is determined,
• F) concluding the method for starting up a nozzle channel as soon as the determined limit amplitudes are all equal to or smaller than a defined limit amplitude in n+1 repetitions of process step D).