Build material supply systems for apparatus for the layerwise manufacture of 3d objects and method of build material transport

A build material supply system for an apparatus for the layerwise manufacture of 3D objects from build material, the build material supply system comprising:

• a dosing device configured to supply a dosed amount of build material to a work surface of the apparatus, the dosed amount comprising a layer amount and an excess amount surplus to forming the layer;
• a buffer tank configured to mix build material for supplying to the dosing device;
• an excess return chamber for receiving excess build material from a distribution device;
• a supply tank for holding fresh build material for replenishing the buffer tank;
• a build material pump for transporting build material within the build material supply system;
• and
• a controller;
• wherein an inlet of the build material pump is coupled to the supply tank via a first valve and to an outlet of the excess return chamber;
• an outlet of the pump is coupled to an inlet of the buffer tank;
• and an outlet of the buffer tank is coupled to an inlet of the dosing device;
• wherein the controller is coupled to the pump and the first valve and, so as to control the amount of fresh build material compared to the amount of excess build material transported into the buffer tank, the controller is configured to:
• control the first valve to open and the pump to operate to allow fresh build material to flow along a supply flow path from the supply tank through the pump and into the buffer tank;
• and
• operate the pump to allow excess build material to flow along an excess return flow path from the excess return chamber through the pump and into the buffer tank.

A method of transporting build material through a build material supply system of an apparatus for the layerwise manufacture of 3D objects from build material, the method comprising:

• (a) operating a build material pump while opening a dosing flow path, from a buffer tank to a dosing device, to transport build material from the buffer tank to the dosing device;
• (b) dosing a dosed amount of build material to a work surface of an apparatus, the dosed amount comprising a layer amount for forming a layer and an excess amount surplus to forming a layer;
• (c) receiving excess build material within an excess return chamber;
• (d) operating the build material pump while opening an excess return flow path to return excess build material from the excess return chamber to the buffer tank;
• (e) operating the build material pump while opening a supply flow path, from a supply tank to the buffer tank, to transport build material from a supply tank to the buffer tank, until either a predetermined fill duration has passed or upon detecting that the level of build material in the buffer tank has reached a predefined fill level;
• and
• (f) mixing the excess amount with the build material in the buffer tank.