Abstract: Methods, particularly automated methods, are provided, as well as 3D-printed composite and hollow objects and 3D-printing systems for printing them. Methods comprise deriving a central line of a hollow 3D object model, calculating reference point(s) and/or line(s) along an inner surface of the hollow 3D object model, and filling the hollow 3D object model with material that comprises a thread defined with respect to the central line and the reference point(s) and/or line(s) and with filling material surrounding the thread. The support construction thus formed may be removed from the 3D object by pulling on the thread, extracting it and the surrounding support filling from the hollow object, thus enabling 3D-printing of convoluted or elongated hollow objects and objects with narrow openings. The parameters of the thread, such as type of curve and thickness, are selected to ensure thread extraction without risk of tearing or knotting the thread.

Abstract: A method of printing a 3D object comprising a plurality of discrete elements, the method comprising: receiving a 3D digital model of a shell group comprising one or more shells representing the plurality of discrete elements; defining, in the 3D digital model, a unifying shell to at least partly envelop one or more shells of the shell group to provide a unified digital model comprising the shell group and the unifying shell; assigning the unifying shell with at least one transparent building material that is transparent upon dispensing and solidifying thereof; assigning the one or more shells of the shell group with one or more building materials; and dispensing, in layers, the at least one transparent building material and the one or more building materials according to the unified digital model to form a 3D object comprising one or more discrete elements that are at least partly connected by a unifying element.

Abstract: Methods, particularly automated methods, are provided, as well as 3D-printed composite and hollow objects and 3D-printing systems for printing them. Methods comprise deriving a central line of a hollow 3D object model, calculating reference point(s) and/or line(s) along an inner surface of the hollow 3D object model, and filling the hollow 3D object model with material that comprises a thread defined with respect to the central line and the reference point(s) and/or line(s) and with filling material surrounding the thread. The support construction thus formed may be removed from the 3D object by pulling on the thread, extracting it and the surrounding support filling from the hollow object, thus enabling 3D-printing of convoluted or elongated hollow objects and objects with narrow openings. The parameters of the thread, such as type of curve and thickness, are selected to ensure thread extraction without risk of tearing or knotting the thread.