Recoating unit, recoating method, device and method for additive manufacturing of a three-dimensional object

A recoating method carried out in a device for additive manufacturing of a three-dimensional object to be manufactured by selectively solidifying a powder building material, layer by layer by fusing the powder building material in consecutive layers which correspond to respective cross-sections of the object, comprising:

• providing a recoating unit movable across a build area for applying an applied layer of the building material within the build area when being moved in a direction of travel across the build area;
• providing an electromagnetic source of focused energy for selectively solidifying each applied layer at positions corresponding to a cross-section of the object to be manufactured, the device repeating steps of applying and selectively solidifying until the object is completed, the recoating unit having at least first and second recoating rollers each rotatable in a rotational direction and spaced apart from each other in a first direction, so that in the direction of travel across the build area one of the first and second recoating rollers is arranged ahead and the other is arranged behind, the first and second recoating rollers extending in a second direction transverse to the first direction of travel;
• movably adjusting at least one of the first and second recoating rollers in a third direction which is orthogonal to the build area;
• and
• applying at least a first layer of the powder building material by moving the recoating unit across the build area in a first direction of travel, and applying at least a second layer of the powder building material by moving the recoatinger unit across the build area in a second direction of travel opposite to the first direction of travel and back across the build area,
• the recoating roller arranged ahead in the direction of travel drawing out the powder building material to a first layer thickness and the recoating roller arranged behind compacting the applied layer of the powder building material and reducing the thickness of the applied layer from the first layer thickness.

In an apparatus for additive manufacturing of a three-dimensional object through selectively solidifying a powder building material, layer by layer, by fusing the powder building material in consecutive layers which correspond to respective cross-sections of the object, the method comprising:

• providing a recoating unit movable across a build area surface for applying an applied layer of the building material within the build area, the recoating unit moving in a first direction across the build area and then in a second direction of travel opposite that of the first direction back across the build area;
• providing an electromagnetic source of focused energy for selectively solidifying each applied layer at positions corresponding to a cross-section of the object to be manufactured, and repeating the steps of applying and selectively solidifying until the object is completed, the recoating unit having first and second recoating rollers each rotatable in a rotational direction and spaced apart from each other in the first and second directions of travel;
• movably adjusting at least one of the recoating rollers in a third direction which is orthogonal to the build area, such that the at least one roller of the first and second recoating rollers is in a position farther away from the build surface in height than another of the first and second recoating rollers, the recoating roller which is farther away in height being arranged ahead in the first direction of travel as a lead recoating roller and the other recoating roller being arranged behind the lead recoating roller as a following recoating roller;
• applying a layer of the powder building material over the build surface by depositing powder building material on the build surface and then moving the recoating unit across the build area in the first direction, and subsequently applying another layer of the powder building material by depositing powder build material to the build surface and moving the recoating unit across the build area in the second direction and back across the build area,
• the lead recoating roller spreading out the powder building material to a first layer thickness and the following recoating roller further modifying the first layer thickness,
• the first and second recoating rollers exchanging relative positions of height in movement of the recoating unit in the second direction.