An apparatus for three-dimensional (3D) printing of an object comprises a print head having at least one inlet for receiving material to be extruded and an outlet. The print head is configured, when the outlet is completely unblocked, to extrude a sheet of material of the width and height of the outlet. One or more actuators are positioned along the width of the print head and arranged to controllably block one or more sections along the width to prevent material from being extruded through the blocked sections, enabling selective extrusion of material through sections that are not blocked in order to selectively print a width of an entire layer of the object in a single pass. The print head and the object move relative to one another via one motion of the print head or of the object.

According to one aspect, there is provided apparatus for forming a layer of build material for three-dimensional printing. The apparatus comprises a spreader to spread a volume of build material to form a layer of build material on a build platform, wherein at least one end of the spreader is to remain a constant distance from a build material retaining wall in proximity to at least one edge of the build platform as the spreader is moved over the surface of the build platform, and further wherein at least a portion of the spreader is below the top of the retaining wall.

According to one aspect, there is provided apparatus for forming a layer of build material for three-dimensional printing. The apparatus comprises a spreader to spread a volume of build material to form a layer of build material on a build platform, wherein at least one end of the spreader is to remain a constant distance from a build material retaining wall in proximity to at least one edge of the build platform as the spreader is moved over the surface of the build platform, and further wherein at least a portion of the spreader is below the top of the retaining wall.

An apparatus for three-dimensional printing includes a print head having at least one inlet for receiving material to be extruded, and an outlet. The print is configured, when the outlet is unblocked, to extrude a sheet of material of the width and height of the outlet. Actuators positioned along the width of the print head are arranged to controllably block one or more sections along the width of the outlet in such a manner to prevent material from being extruded, thus enabling selective extrusion of material through a remainder of sections of the outlet that are not blocked to selectively print a width of an entire layer of the object in a single pass. The apparatus includes an extrusion drive for material to be extruded to the print head. An electronic controller controls an amount and rate of material to be provided to the print head via the extrusion drive.

According to examples, a three-dimensional (3D) fabrication system may include a controller to identify a feature of an object to be fabricated and based on the identified feature having a size that is smaller than a predefined size, determine a thermal support for the identified feature. The controller may also control fabrication components to form, through application of energy, the determined thermal support from a first set of particles, form an intermediate section adjacent to the formed thermal support from a second set of particles, and form, through application of energy, the feature adjacent to the intermediate section from a third set of particles, in which heat from the thermal support is to reduce a thermal bleed rate of the third set of particles.

According to examples, a three-dimensional (3D) fabrication system may include a controller to identify a feature of an object to be fabricated and based on the identified feature having a size that is smaller than a predefined size, determine a thermal support for the identified feature. The controller may also control fabrication components to form, through application of energy, the determined thermal support from a first set of particles, form an intermediate section adjacent to the formed thermal support from a second set of particles, and form, through application of energy, the feature adjacent to the intermediate section from a third set of particles, in which heat from the thermal support is to reduce a thermal bleed rate of the third set of particles.

A build material dispensing device may include a material spreader to spread an amount of build material along a build platform, and at least one hopper for dispensing the build material. The at least one hopper dispenses a plurality of doses of the build material in front of the progression of the material spreader as the material spreader is moved over the build platform.

A build material dispensing device may include a material spreader to spread an amount of build material along a build platform, and at least one hopper for dispensing the build material. The at least one hopper dispenses a plurality of doses of the build material in front of the progression of the material spreader as the material spreader is moved over the build platform.

A system for recoating a powder bed includes a build platform holding a powder bed and an electrode assembly including an electrode and an insulating shield. A voltage supply produces a high voltage alternating current and communicates with the powder bed and the electrode. The electrode assembly is positionable over the powder bed, such that when the electrode assembly is over the powder bed, the shield is between the electrode and the powder bed's top surface. The voltage supply produces a high voltage alternating current that creates an alternating electric field between the electrode and the powder bed that causes the powder of the powder bed top surface to oscillate in a region between the shield and the bed and then reposition themselves on the bed such that the top layer of the powder bed is smoother than it was prior to when the powder particles began oscillating.

A system for recoating a powder bed includes a build platform holding a powder bed and an electrode assembly including an electrode and an insulating shield. A voltage supply produces a high voltage alternating current and communicates with the powder bed and the electrode. The electrode assembly is positionable over the powder bed, such that when the electrode assembly is over the powder bed, the shield is between the electrode and the powder bed's top surface. The voltage supply produces a high voltage alternating current that creates an alternating electric field between the electrode and the powder bed that causes the powder of the powder bed top surface to oscillate in a region between the shield and the bed and then reposition themselves on the bed such that the top layer of the powder bed is smoother than it was prior to when the powder particles began oscillating.