The present disclosure relates to a viscosity pump for extruding molten materials. More specifically, the present disclosure relates to a viscosity pump having a rotatable impeller which is linearly positionable parallel to an axis of rotation within the viscosity pump. The viscosity pump may be used to extrude materials in an additive manufacturing system.
A viscosity pump may be incorporated into an extruder of the additive manufacturing system to pump a flowable material to an extrusion outlet. However, while viscosity pumps have been previously used with various types of extruders, viscosity pumps are susceptible to clogging at the extrusion outlet which may cause an unwanted variation in the flow rate of the extruded material, resulting in degradation in the quality of the printed part. Even after an impeller has stopped rotating, the viscosity pump is prone to oozing residual material from the extrusion outlet of the pump, which also may result in degradation in the quality of the part being printed. Prior disclosed viscosity pumps also lack the capability of precisely controlling the flow rate of the material. At least for the above-mentioned issues, the flow rate of the extrudable material is difficult to control with a typical viscosity pump, especially when the material has a low viscosity.
When the flowable material is a metal liquid based alloy, the metal based alloy can also cause and accumulation of material, including unwanted slag material, at the extrusion outlet of the viscosity pump, resulting in the partial clogging of the outlet. The accumulation of slag at the pump outlet adversely affects the flow rate of the material and the ability to control the flow rate of the extruded material, especially when the material is used in an additive manufacturing system.
Additive manufacturing systems are used to print or otherwise build 3D parts from digital representations of the 3D parts (e.g., STL format files) using one or more additive manufacturing techniques. Examples of commercially available additive manufacturing techniques include extrusion-based techniques, jetting, selective laser sintering, high speed sintering, powder/binder jetting, electron-beam melting, and stereolithographic processes. For each of these techniques, the digital representation of the 3D part is initially sliced into multiple horizontal layers. For each sliced layer, a tool path is then generated, which provides instructions for the particular additive manufacturing system to print the given layer.
For example, in an extrusion-based additive manufacturing system, a 3D part may be printed from a digital representation of the 3D part in a layer-by-layer manner by extruding a flowable part material. The part material is extruded through an extrusion tip or nozzle carried by a print head of the system, and is deposited as a sequence of roads on a substrate in a build plane, where the build plane is typically an x-y plane. The extruded part material fuses to previously deposited part material, and solidifies upon a reduction in temperature. The position of the print head relative to the substrate is then incremented along an axis perpendicular to the build plane, typically the z-axis, and the process is then repeated to form a 3D part resembling the digital representation.