Print head and method for printing composite structure and temporary support

1. A print head, comprising:

a nozzle tip;

a first matrix source configured to selectively supply a structural matrix to the nozzle tip;

a second matrix source configured to selectively supply a temporary support matrix to the nozzle tip;

a reinforcement supply configured to supply a continuous reinforcement through the nozzle tip;

a matrix reservoir in fluid communication with the nozzle tip; and

a tube that extends from the second matrix source through the matrix reservoir to the nozzle tip, wherein the first matrix source is configured to direct the structural matrix into the matrix reservoir.

2. The head of claim 1 , wherein the temporary support matrix is dissolvable via the application of at least one of water, air, heat, and light.

3. The head of claim 1 , wherein the structural matrix is a thermoset resin.

4. The head of claim 1 , wherein the second matrix source is also configured to direct the temporary support matrix into the matrix reservoir.

5. The head of claim 1 , further including a unidirectional valve located at a tip end of the tube.

6. The head of claim 5 , further including an actuator configured to selectively move the tube to open the unidirectional valve.

7. The head of claim 1 , further including a cure enhancer mounted adjacent the nozzle tip and configured to initiate curing of at least one of the structural matrix and the temporary support matrix.

8. A print head, comprising:

a nozzle tip;

a first matrix source configured to selectively supply a structural matrix to the nozzle tip;

a second matrix source configured to selectively supply a temporary support matrix to the nozzle tip;

a reinforcement supply configured to supply a continuous reinforcement through the nozzle tip; and

a perforated fiber guide passing through the matrix reservoir.

9. A print head, comprising:

a nozzle tip;

a first matrix source configured to selectively supply a structural matrix to the nozzle tip;

a second matrix source configured to selectively supply a temporary support matrix to the nozzle tip;

a reinforcement supply configured to supply a continuous reinforcement through the nozzle tip; and

a cutting mechanism configured to sever the continuous reinforcement during switching between discharging of the structural matrix and discharging of the temporary support matrix, wherein the cutting mechanism includes an inner set of arms configured to grasp the continuous reinforcement and an outer set of arms configured to cut through the continuous reinforcement.

10. A system for additively manufacturing a composite structure, comprising:

a head configured to discharge a continuous reinforcement at least partially coated with a matrix, the head including:

a nozzle tip;

a first matrix source configured to selectively supply a structural matrix to the nozzle tip;

a second matrix source configured to selectively supply a temporary support matrix to the nozzle tip;

a reinforcement supply configured to supply the continuous reinforcement through the nozzle tip when activated; and

a cure enhancer configured to expose at least one of the structural matrix and the temporary support matrix to a cure energy;

a frame configured to move the head during discharging; and

a controller configured to:

selectively fluidly connect the first and second matrix supplies with the nozzle tip;

energize the cure enhancer; and

cause the frame to move the head based on specifications for the composite structure; and

activate the reinforcement supply when only the first matrix source is supplying the structural matrix to the nozzle tip.

11. The system of claim 10 , wherein:

the temporary support matrix is dissolvable via the application of at least one of water, air, heat, and light; and

the structural matrix is a thermoset resin.

12. The system of claim 10 , wherein:

the head includes a matrix reservoir in fluid communication with the nozzle tip; and

the first matrix source is configured to direct the structural matrix into the matrix reservoir.

13. The system of claim 12 , wherein the second matrix source is also configured to direct the temporary support matrix into the matrix reservoir.

14. The system of claim 12 , further including:

a tube that extends from the second matrix source through the matrix reservoir to the nozzle tip; and

a unidirectional valve located at a tip end of the tube.

15. The system of claim 14 , further including an actuator configured to selectively move the tube to open the unidirectional valve.

16. The system of claim 10 , further including a perforated fiber guide passing through the matrix reservoir.

17. A method for additively manufacturing a composite structure, comprising:

receiving specifications for the composite structure;

alternatingly discharging one of a resin-wetted continuous reinforcement and a continuous reinforcement-free support matrix through a common print head nozzle based on the specifications;

moving the print head nozzle during discharging to form a three-dimensional trajectory of the composite structure; and

exposing at least the resin-wetted continuous reinforcement to a cure energy during discharging to harden the resin-wetted continuous reinforcement.