Method of additive manufacturing and heat treatment

1. A method of additive manufacturing and heat treatment, the method comprising:

a. securing a substrate to a fixture;

b. operating an additive manufacturing system to perform a build process by building a part on the substrate secured to the fixture, the part being built by forming a series of layers of metallic material on the substrate, the metallic material melting and solidifying during the build process thereby bonding the part to the substrate and creating thermally induced stress in the part;

c. moving the part, the substrate and the fixture from the additive manufacturing system to a heat treatment system, wherein the substrate remains secured to the fixture and the part remains bonded to the substrate as they are moved;

d. operating the heat treatment system to perform a heat treatment process by heating the part, the substrate and the fixture together thereby relieving the thermally induced stress in the part, the substrate remaining secured to the fixture during the heat treatment process;

e. releasing the substrate from the fixture and separating the part and the substrate from the fixture, wherein the part remains bonded to the substrate as they are separated from the fixture; and,

wherein a bending stiffness of the fixture is greater than a bending stiffness of the part, wherein the fixture comprises a layer which contacts the substrate and is formed from a different material to the substrate, and wherein the layer is a separate layer or a coating on the fixture.

2. The method of claim 1 wherein the substrate is secured to the fixture by an attachment system in step a.; and the attachment system is released in step e. so that the substrate is no longer secured to the fixture by the attachment system.

3. The method of claim 2 wherein the attachment system comprises one or more attachment members which are engaged with the substrate in step a. and disengaged from the substrate in step e.

4. The method of claim 2 wherein the fixture and attachment system have a collective mass or thermal mass which is less than ten times a collective mass or thermal mass of the substrate and the part.

5. The method of claim 4 wherein the fixture and attachment system have a mass or thermal mass which is less than two times a collective mass or thermal mass of the substrate and the part.

6. The method of claim 2 , wherein the fixture and attachment system have a collective mass or thermal mass which is less than five times a collective mass or thermal mass of the substrate and the part.

7. The method of claim 1 wherein the substrate is secured to the fixture by one or more clamps or fasteners in step a.; and the (or each) clamp or fastener is released in step e. so that the substrate is no longer secured to the fixture.

8. The method of claim 7 wherein the substrate is secured to the fixture by one or more fasteners in step a. by passing the (or each) fastener through a respective pre-formed hole in the substrate; and the (or each) fastener is released in step e. by removing it from its respective pre-formed hole in the substrate.

9. The method of claim 1 wherein during the heat treatment process the temperatures of the part, the substrate and the fixture are increased to above 150° C. and maintained above 150° C. for more than 30 minutes.

10. The method of claim 1 wherein during the heat treatment process the temperatures of the part, the substrate and the fixture are increased to above 500° C. and maintained above 500° C. for more than 30 minutes.

11. The method of claim 1 , wherein the build process defines an axis along which deposition of the metallic material takes place, and a bending stiffness of the fixture is greater than a bending stiffness of the part measured perpendicular to the axis along which deposition of the metallic material takes place.

12. The method of claim 1 , wherein the layer comprises an interface layer.

13. The method of claim 12 wherein the substrate contacts the interface layer at a substrate/fixture interface during the heat treatment process, and the substrate and interface layer are formed from dissimilar materials at the substrate/fixture interface, thereby inhibiting bonding between them at the substrate/fixture interface during the heat treatment process.

14. The method of claim 12 , wherein the interface layer comprises a heat resistant interface layer.

15. A method of additive manufacturing and heat treatment, the method comprising:

a. securing a substrate to a fixture;

b. operating an additive manufacturing system to perform a build process by building a part on the substrate secured to the fixture, the part being built by forming a series of layers of metallic material on the substrate, the metallic material melting and solidifying during the build process thereby bonding the part to the substrate and creating thermally induced stress in the part;

c. moving the part, the substrate and the fixture from the additive manufacturing system to a heat treatment system, wherein the substrate remains secured to the fixture and the part remains bonded to the substrate as they are moved;

d. operating the heat treatment system to perform a heat treatment process by heating the part, the substrate and the fixture together thereby relieving the thermally induced stress in the part, the substrate remaining secured to the fixture during the heat treatment process;

e. releasing the substrate from the fixture and separating the part and the substrate from the fixture, wherein the part remains bonded to the substrate as they are separated from the fixture; and,

wherein a bending stiffness of the fixture is greater than a bending stiffness of the part, wherein the fixture comprises a layer which contacts the substrate and is formed from a different material to the substrate, wherein the layer comprises a coating on the fixture.

16. A method of additive manufacturing and heat treatment, the method comprising:

a. securing a substrate to a fixture;

b. operating an additive manufacturing system to perform a build process by building a part on the substrate secured to the fixture, the part being built by forming a series of layers of metallic material on the substrate, the metallic material melting and solidifying during the build process thereby bonding the part to the substrate and creating thermally induced stress in the part;

c. moving the part, the substrate and the fixture from the additive manufacturing system to a heat treatment system, wherein the substrate remains secured to the fixture and the part remains bonded to the substrate as they are moved;

d. operating the heat treatment system to perform a heat treatment process by heating the part, the substrate and the fixture together thereby relieving the thermally induced stress in the part, the substrate remaining secured to the fixture during the heat treatment process; and

e. releasing the substrate from the fixture and separating the part and the substrate from the fixture, wherein the part remains bonded to the substrate as they are separated from the fixture,

wherein a bending stiffness of the fixture is greater than a bending stiffness of the part, wherein the fixture comprises a layer which contacts the substrate and is formed from a different material to the substrate,

and wherein the part, the substrate and the fixture are allowed to distort during the build process; and the part and the fixture are formed from materials which are selected such that the part and the fixture have a difference in bending stiffness which increases as they are heated during the heat treatment process; the increased difference in bending stiffness causing at least some of the distortion which occurred during the build process to be removed during the heat treatment process.

17. A method of additive manufacturing and heat treatment, the method comprising:

a. securing a substrate to a fixture;

b. operating an additive manufacturing system to perform a build process by building a part on the substrate secured to the fixture, the part being built by forming a series of layers of metallic material on the substrate, the metallic material melting and solidifying during the build process thereby bonding the part to the substrate and creating thermally induced stress in the part;

c. moving the part, the substrate and the fixture from the additive manufacturing system to a heat treatment system, wherein the substrate remains secured to the fixture and the part remains bonded to the substrate as they are moved;

d. operating the heat treatment system to perform a heat treatment process by heating the part, the substrate and the fixture together thereby relieving the thermally induced stress in the part, the substrate remaining secured to the fixture during the heat treatment process; and

e. releasing the substrate from the fixture and separating the part and the substrate from the fixture, wherein the part remains bonded to the substrate as they are separated from the fixture,

wherein a bending stiffness of the fixture is greater than a bending stiffness of the part, wherein the fixture comprises a layer which contacts the substrate and is formed from a different material to the substrate,

and wherein the fixture has a mass or thermal mass which is less than ten times a collective mass or thermal mass of the substrate and the part.

18. The method of claim 17 wherein the fixture has a mass or thermal mass which is less than two times a collective mass or thermal mass of the substrate and the part.

19. The method of claim 17 , wherein the fixture has a mass or thermal mass which is less than five times a collective mass or thermal mass of the substrate and the part.