Liquefier assembly for use in additive manufacturing system

1. A liquefier assembly for use in an additive manufacturing system, the liquefier assembly comprising:

a liquefier tube compositionally comprising a first metallic material, and having an inlet end and outlet end offset along a longitudinal axis, and a channel extending between the inlet end and the outlet end;

a nozzle secured to the outlet end of the liquefier tube;

a heating element extending at least partially around the liquefier tube, wherein the heating element is configured to generate a hot zone in the liquefier tube;

at least one hollow spacer compositionally comprising a second metallic material, the at least one hollow spacer being disposed in the channel and having a first end adjacent to the nozzle and a second end that defines a shoulder that is upstream along the longitudinal axis from the hot zone when generated by the heating element; and

a hollow liner compositionally comprising a fluoropolymer, the hollow liner being disposed in the channel and having a first end abutting against the shoulder of the at least one hollow spacer.

2. The liquefier assembly of claim 1 , wherein the fluoropolymer of the hollow liner comprises polytetrafluoroethylene.

3. The liquefier assembly of claim 1 , wherein the hollow liner further compositionally comprises from about 0.1% to about 30% of one or more fillers.

4. The liquefier assembly of claim 1 , wherein the first metallic material of the liquefier tube and the second metallic material of the at least one hollow spacer each comprise stainless steel.

5. The liquefier assembly of claim 1 , wherein the shoulder of the at least one hollow spacer is located at an offset distance above the hot zone that ranges from about 0.15 inches to about 1.0 inch.

6. The liquefier assembly of claim 1 , wherein the at least one hollow spacer comprises a plurality of hollow spacers each having an inner surface derived from a different material.

7. The liquefier assembly of claim 1 , wherein the at least one hollow spacer and the hollow liner each provide an average cross-sectional gap relative to a received filament less than about 0.01 inches.

8. A liquefier assembly for use in an additive manufacturing system, the liquefier assembly comprising:

a liquefier tube having an inlet end, an outlet end, and a channel extending therebetween;

a nozzle secured to the outlet end of the liquefier tube;

a heating element extending at least partially around the liquefier tube, wherein the heating element is configured to generate a hot zone in the liquefier tube;

a hollow spacer disposed in the channel, the hollow spacer having a downstream end adjacent to the nozzle and an upstream end defining a shoulder; and

a hollow liner disposed in the channel and having a downstream end abutting against the shoulder of the hollow spacer, wherein the shoulder of the hollow spacer is positioned along the channel such that the downstream end of the hollow liner remains at least about 35° C. below a temperature of an upstream edge of the hot zone when generated by the thermal element.

9. The liquefier assembly of claim 8 , wherein the shoulder of the hollow spacer is positioned along the channel such that the downstream end of the hollow liner remains at least about 50° C. below the temperature of the upstream edge of the hot zone when generated by the thermal element.

10. The liquefier assembly of claim 9 , wherein the shoulder of the hollow spacer is positioned along the channel such that the downstream end of the hollow liner remains at least about 60° C. below the temperature of the upstream edge of the hot zone when generated by the thermal element.

11. The liquefier assembly of claim 8 , wherein the shoulder of the hollow spacer is positioned along the channel such that the downstream end of the hollow liner remains below about 185° C. when the thermal element generates that hot zone in the liquefier tube.

12. The liquefier assembly of claim 11 , wherein the shoulder of the hollow spacer is positioned along the channel such that the downstream end of the hollow liner remains below about 175° C. when the thermal element generates that hot zone in the liquefier tube.

13. The liquefier assembly of claim 8 , wherein the hollow liner compositionally comprises a fluoropolymer, and wherein the hollow spacer compositionally comprises a metallic material.

14. The liquefier assembly of claim 13 , wherein the hollow liner further compositionally comprises from about 0.1% to about 30% of one or more fillers.