Powder injection mold assembly and method of molding

Abstract

A mold assembly for powder injection molding of a shaped element includes a first mold portion having a first surface defining a first portion of the mold cavity and releasably engageable to the feedstock and a second mold portion having a second surface defining a second portion of the mold cavity and releasably engageable to the feedstock. The first mold portion has a first thermal capacity and a first thermal conductivity, and the second mold portion has a second thermal capacity and a second thermal conductivity. At least one of the first thermal capacity and the first thermal conductivity is lower than a respective one of the second thermal capacity and the second thermal conductivity and/or than a respective one of the thermal conductivity and thermal capacity of solid metal. A method of molding a green part is also discussed.

1 . A mold assembly for powder injection molding of a shaped element, the mold assembly defining a mold cavity for receiving a feedstock and comprising:
 a first mold portion having a first surface defining a first portion of the mold cavity and releasably engageable to the feedstock, the first mold portion having a first thermal capacity and a first thermal conductivity; and   a second mold portion having a second surface defining a second portion of the mold cavity and releasably engageable to the feedstock, the second mold portion having a second thermal capacity and a second thermal conductivity;   wherein at least one of the first thermal capacity and the first thermal conductivity is lower than a respective one of the second thermal capacity and the second thermal conductivity.   
     
     
         2 . The mold assembly according to  claim 1 , wherein the first mold portion comprises a plurality of pins protruding within the mold cavity for defining holes in the shaped element, and wherein the first portion of the mold cavity adjacent the pins has a cross-section smaller than a cross-section of the second portion of the mold cavity. 
     
     
         3 . The mold assembly according to  claim 2 , wherein the pins are hollow metal pins. 
     
     
         4 . The mold assembly according to  claim 1 , wherein the first mold portion includes a core coated by a layer defining the first surface, the core and layer being made of different materials. 
     
     
         5 . The mold assembly as defined in  claim 4 , wherein the core and the second mold portion are made of the same material. 
     
     
         6 . The mold assembly as defined in  claim 4 , wherein the layer and the second mold portion are made of the same material. 
     
     
         7 . The mold assembly as defined in  claim 1 , wherein the first mold portion is at least partially made of plastic, ceramic, glass or a combination thereof. 
     
     
         8 . The mold assembly according to  claim 1 , wherein the first thermal conductivity is within a range of 0.1 to 0.5 W/mK. 
     
     
         9 . The mold assembly according to  claim 1 , wherein the first mold portion includes a layer defining the first surface and having an internal surface opposed to the first surface, the internal surface defining an insulating cavity. 
     
     
         10 . A mold assembly for powder injection molding of a shaped element, the mold assembly comprising:
 a first mold part and a second mold part cooperating to define a mold cavity, the first mold part and the second mold part being movable relative to one another to selectively open and close the mold cavity, the first and second mold parts being disengageable from the shaped element after molding;   the first mold part comprising an integral mold portion having a surface defining the mold cavity, the mold portion made of a material different from solid metal and having at least one of a thermal capacity and a thermal conductivity lower than that of solid metal.   
     
     
         11 . The mold assembly according to  claim 10 , wherein the mold portion comprises a plurality of pins protruding within the mold cavity for defining holes in the shaped element, and wherein a portion of the mold cavity adjacent the pins has a cross-section smaller than a cross-section of an adjacent portion of the mold cavity. 
     
     
         12 . The mold assembly according to  claim 11 , wherein the pins are hollow metal pins. 
     
     
         13 . The mold assembly according to  claim 10 , wherein the mold portion includes a core coated by a layer forming the surface defining the mold cavity, the core and layer being made of different materials. 
     
     
         14 . The mold assembly according to  claim 10 , wherein the core is made of plastic, ceramic or glass and the layer is a metal layer. 
     
     
         15 . The mold assembly according to  claim 10 , wherein the core is made of metal and the layer is a plastic, ceramic or glass layer. 
     
     
         16 . The mold assembly according to  claim 10 , wherein the thermal conductivity of the mold portion is within a range of 0.1 to 0.5 W/mK. 
     
     
         17 . The mold assembly according to  claim 10 , wherein the mold portion includes a layer forming the surface defining the mold cavity and having an opposed internal surface, the internal surface defining an insulating cavity. 
     
     
         18 . A method of molding a green part, the method comprising:
 injecting a powder injection molding feedstock in a mold cavity defined in a mold assembly;   extracting heat from the feedstock in the mold cavity through a first portion of the mold having a first surface in contact with the feedstock and through a second portion of the mold having a second surface in contact with the feedstock, a first heat flux through the first surface and first portion being lower than a second heat flux through the second surface and second portion to allow the feedstock to fill the mold cavity before solidification;   solidifying the feedstock to create the green part; and   disengaging the green part from the first and second portions of the mold by extracting the green part from the mold cavity.   
     
     
         19 . The method according to  claim 18 , wherein extracting heat from the feedstock comprises providing the first portion with a first thermal capacity lower than a second thermal capacity of the second portion. 
     
     
         20 . The method according to  claim 18 , wherein extracting heat from the feedstock comprises providing the first portion with a first thermal conductivity lower than a second thermal conductivity of the second portion.