3D printing system for preparing a three-dimensional object with a surface melting section

A method for preparing a three-dimensional object made at least partially of an expanded polymer, the method being performed in a three-dimensional printing system comprising:

• a printing device configured to transport and deposit a strand of the expanded polymer including a blowing agent onto a surface and
• a three-dimensional movement device configured to enable depositing of the strand of the expanded polymer at a predetermined time at a precise position within a three-dimensional matrix,
• the printing device comprising:
• a feed section,
• a transporting section,
• a surface melting section and
• a terminal printing head section configured to deposit the strand of the expanded polymer onto the surface,
• each of the feed section, the transporting section, the surface melting section, and the printing head section is a tubular section having the same inner diameter,
• the surface melting section comprising a solid-state welding element, a laser beam, a generator of hot gas or liquid, or a generator of heat by an exothermal reaction,
• the strand of the expanded polymer with a solid core and an outer layer having a lower melting point than the solid core so that the outer layer can be molten, without melting the solid core, is prepared by extruding a polymer including the blowing agent and a nucleating agent into the strand of the expanded polymer with an at least partially crystalline foamed core and a substantially amorphous outer layer, or is prepared by coextruding a first polymer including the blowing agent and the nucleating agent and a second polymer into the strand of the expanded polymer with an at least partially crystalline foamed core of the first polymer and a substantially amorphous outer layer of the second polymer before the strand of the expanded polymer is fed into the feed section of the printing device of the three-dimensional printing system.