Magnetically throttled liquefier assembly

Abstract

A magnetically throttled liquefier assembly for use in an additive manufacturing system and configured to heat a metal-based alloy to an extrudable state includes an array of magnets to generate a magnetic field in order to induce a viscosity in the heated metal-based alloy and to control the flow rate of the heated metal-based alloy through the liquefier for extrusion and the building of a three-dimensional object with the metal-based alloy.

What is claimed: 
     
         1 . A liquefier assembly for use in an additive manufacturing system to print three-dimensional parts, the liquefier assembly comprising:
 a liquefier tube extending through a liquefier and configured to receive and heat a feedstock of a metal-based alloy to an elevated temperature;   at least one magnet positioned in the liquefier assembly and configured to produce a magnetic field in the liquefier assembly;   a flow channel in fluid communication with the liquefier tube and an extrusion tip and positioned within the magnetic field generated by the at least one magnet and configured to magnetically induce an increased viscosity in the heated metal-based alloy flowing therethrough; and   wherein the extrusion tip is configured to receive and deposit the heated metal-based alloy having the magnetically induced viscosity.   
     
     
         2 . The liquefier assembly of  claim 1 , wherein the at least one magnet comprises an array of magnets positioned along a length of the flow channel assembly wherein the magnets are arranged to provide magnetic fields in alternating orientations. 
     
     
         3 . The liquefier assembly of  claim 2 , wherein the array of magnets is oriented to produce magnetic fields in a direction substantially perpendicular to a flow direction of the heated metal-based alloy in the flow channel. 
     
     
         4 . The liquefier assembly of  claim 1 , and further comprising a current source configured to pass an electrical current through the flow channel assembly to the heated metal-based alloy in the flow channel. 
     
     
         5 . The liquefier assembly of  claim 4 , wherein the current source is configured to apply a current to the flow channel in a direction orthogonal to flow of the heated metal-based alloy in the flow channel and to the magnetic field. 
     
     
         6 . The liquefier assembly of  claim 5 , wherein the flow channel is configured to receive an electrode of the current source therein. 
     
     
         7 . The liquefier assembly of  claim 1 , wherein the metal-based alloy is an aluminum based alloy comprising about 90% by weight to 95% by weight aluminum. 
     
     
         8 . The liquefier assembly of  claim 3 , wherein a viscosity is induced in the heated metal-based alloy and the induced viscosity can be estimated according to the following equation: 
       
         
           
             
               
                 η 
                 B 
               
               = 
               
                 
                   
                     
                       B 
                       o 
                       2 
                     
                      
                     
                       h 
                       2 
                     
                      
                     w 
                      
                     
                         
                     
                      
                     π 
                      
                     
                         
                     
                      
                     ρ 
                      
                     
                         
                     
                      
                     k 
                   
                   
                     6 
                      
                     
                       ( 
                       
                         π 
                         + 
                         
                           2 
                            
                           
                               
                           
                            
                           wk 
                         
                       
                       ) 
                     
                   
                 
                 . 
               
             
           
         
       
     
     
         9 . The liquefier assembly of  claim 1 , wherein a softened metal surrounds the flow channel and the array of magnets and is configured to reinforce the flow channel against pressure build-up in the flow channel and to direct the magnetic field lines perpendicularly through the flow channel. 
     
     
         10 . A method for building a three-dimensional object in a layer-by-layer manner with an additive manufacturing system comprising:
 heating a build chamber of the additive manufacturing system to a selected elevated temperature;   heating a metal-based alloy in an extrusion line of the additive manufacturing system, wherein the metal-based alloy is heated to an elevated temperature such that the metal-based alloy is in a flowable state;   generating a first magnetic field along a portion of a length of the extrusion line, the magnetic field lines being perpendicular to a flow direction of the extrusion line;   increasing the viscosity of the heated metal-based alloy by flowing the heated metal-based alloy through a flow channel positioned within the magnetic field;   depositing the heated metal-based alloy having the increased viscosity from a deposition head of the additive manufacturing system onto a build platform of the additive manufacturing system in a predetermined pattern; and   solidifying the heated metal-based alloy to provide a re-solidified alloy.   
     
     
         11 . The method of  claim 10 , wherein the extrusion line is disposed outside of the build chamber and the deposition head is disposed within the build chamber, and wherein the method further comprises driving the heated metal-based alloy from the extrusion line to the deposition head through the magnetic field to induce a viscosity in the heated metal-based alloy. 
     
     
         12 . The method of  claim 10 , wherein the metal-based alloy comprises a metal having electrical conductivity. 
     
     
         13 . The method of  claim 12 , wherein the metal-based alloy is an aluminum based alloy comprising about 90% by weight to 95% by weight aluminum. 
     
     
         14 . The method of  claim 10 , and further comprising passing a current through the heated metal-based alloy flowing through the flow channel to regulate the flow of the heated metal-based alloy through the extrusion line. 
     
     
         15 . The method of  claim 14  and further comprising passing the electrical current to the heated metal-based alloy flowing through the flow channel with at least one electrode positioned within the channel. 
     
     
         16 . The method of  claim 15  and further controlling the flow rate of the heated metal-based alloy through the flow channel for extrusion based on the relationship of the magnetic field strength and the electrical current passed to the heated metal-based alloy as the current generates a second magnetic field opposing the direction of the first magnetic field and applies a pressure to the heated metal-based alloy flow in the flow channel along an axis of the flow direction. 
     
     
         17 . The method of  claim 10 , wherein the magnetically induced viscosity can be estimated according to the following equation: 
       
         
           
             
               
                 η 
                 B 
               
               = 
               
                 
                   
                     
                       B 
                       o 
                       2 
                     
                      
                     
                       h 
                       2 
                     
                      
                     w 
                      
                     
                         
                     
                      
                     π 
                      
                     
                         
                     
                      
                     ρ 
                      
                     
                         
                     
                      
                     k 
                   
                   
                     6 
                      
                     
                       ( 
                       
                         π 
                         + 
                         
                           2 
                            
                           
                               
                           
                            
                           wk 
                         
                       
                       ) 
                     
                   
                 
                 . 
               
             
           
         
       
     
     
         18 . A liquefier assembly for use in an additive manufacturing system to print three-dimensional parts, the liquefier assembly comprising:
 a liquefier tube having an inlet end and an outlet end and configured to receive a feedstock of a metal-based alloy;   a heat source positioned proximate the liquifier tube and configured to heat the metal-based alloy feedstock to temperature at which the metal-based alloy becomes liquidus;   an extrusion tip secured to the outlet end of the liquefier tube wherein the extrusion tip is configured to deposit the heated metal-based alloy;   a flow controller in communication with the liquifier tube, the flow controller comprising:
 at least one magnet positioned in the liquefier assembly and configured to produce a magnetic field in the liquefier assembly and configured to induce an increased viscosity in the heated metal-based alloy flowing therethrough wherein a strength of the magnetic field can be varied to manipulate a flow rate of the heated metal-based alloy; and 
 a current source configured to pass a current through the liquifier tube in a direction substantially orthogonal to a direction of flow of the heated metal-based alloy and to the magnetic field and wherein the current source is configured to change a current passed through the liquifier tube to manipulate the flow rate of the heated metal-based alloy. 
   
     
     
         19 . The liquefier assembly of  claim 18 , wherein the at least one magnet comprises an array of magnets positioned along a length of the flow channel assembly wherein the magnets are arranged to provide magnetic fields in alternating orientations. 
     
     
         20 . The liquefier assembly of  claim 19 , wherein the array of magnets is oriented to produce magnetic fields in a direction substantially perpendicular to a flow direction of the heated metal-based alloy in the flow channel.