Selective material dispensing in additive manufacturing

Abstract

Additive manufacturing includes successively forming a plurality of layers on a support. Depositing a layer from the plurality of layers includes dispensing first particles, selectively dispensing second particles in selected regions corresponding to a surface of the object, and fusing at least a portion of the layer. The layer has the first particles throughout and the second particles in the selected regions. Alternatively or in addition, forming the plurality of layers includes depositing multiple groups of layers. Depositing a group of layers includes, for each layer in the group of layers dispensing a feed material to provide the layer, and after dispensing the feed material and before dispensing a subsequent layer fusing a selected portion of the layer. After all layers in the group of layers are dispensed, a volume of the group of layers that extends through all the layers in the group of layers is fused.

What is claimed is: 
     
         1 . An additive manufacturing apparatus for forming an object, comprising:
 a support;   a first dispenser to deliver first particles on the support or an underlying layer;   a second dispenser to selectively deliver second particles on the support or an underlying layer;   an energy source to fuse the first particles and the second particles; and   a controller coupled to the first dispenser, the second dispenser and the energy source and configured to cause the apparatus to successively form a plurality of layers on a support, wherein the controller is configured to form a layer from the plurality of layers by causing the apparatus to
 dispense the first particles and second particles such that the layer has the first particles throughout and the second particles in a selected region, the selected region corresponding to a surface of the object, and 
 fuse at least a first portion of the layer including the selected regions and a second portion of the layer that does not include the selected region. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the selected region corresponds to an exterior surface of the object. 
     
     
         3 . The apparatus of  claim 1 , comprising a first reservoir to hold the first particles and a second reservoir to hold the second particles, and wherein the first particles have a first mean diameter and the second particles have a second mean diameter at least two times smaller than the first mean diameter. 
     
     
         4 . The apparatus of  claim 3 , wherein the first particles and the second particles have the same material composition. 
     
     
         5 . The apparatus of  claim 1 , wherein the controller is configured to cause the second particles to be dispensed after the first particles so that the second particles infiltrate into a layer of first particles. 
     
     
         6 . The apparatus of  claim 1 , wherein the first dispenser comprises a reservoir positioned adjacent the support and a pusher configured to push the first particles from the reservoir across the support or underlying layer. 
     
     
         7 . The apparatus of  claim 6 , wherein the second dispenser comprises an ejector having a nozzle to eject the second particles. 
     
     
         8 . The apparatus of  claim 1 , wherein the second dispenser comprises a mixer configured to receive the first particles and the second particles and provide a mixture of particles to the support or underlying layer. 
     
     
         9 . The apparatus of  claim 8 , wherein the controller is configured to selectively dispense the second particles by controlling ejection of the mixture of particles from a nozzle. 
     
     
         10 . The apparatus of  claim 1 , wherein the energy source comprises a laser or ion beam source.