Non-contact acoustic inspection method for additive manufacturing processes

1. A method of inspecting an additive manufacturing process in which a directed energy source is used to create a weld pool at an exposed build surface of a mass of powdered material, and to selectively fuse the powdered material to form a workpiece, the method comprising:

using the directed energy source to generate an acoustic wave in the build surface by modulating the directed energy source to a lower power level compared to a power level used to create the weld pool;

using a noncontact method to measure displacement of the build surface in response to the acoustic wave; and

determining at least one sub-surface material property of the workpiece by analyzing the displacement of the build surface.

2. The method of claim 1 wherein the acoustic wave is generated and displacement is measured subsequent to the completion of one or more layers during the additive manufacturing process.

3. The method of claim 1 wherein the surface displacements are measured using a monitoring laser separate from the directed energy source.

4. The method of claim 1 wherein:

a single beam steering apparatus is used to steer a build beam from the directed energy source and a monitoring beam from a monitoring laser.

5. The method of claim 1 wherein the sub-surface property comprises at least one defect in the workpiece.

6. The method of claim 1 further comprising controlling at least one build process parameter in response to the determined sub-surface property of the workpiece.

7. The method of claim 1 further comprising:

identifying a defect of the workpiece by analyzing the displacement of the build surface; and

repairing the defect by using the directed energy source to create a weld pool over the defect, permitting previously-fused material to flow into and fill the defect.

8. The method of claim 1 further comprising controlling at least one build process parameter in response to the determined sub-surface property of the workpiece, in combination with data from at least one other process sensor.

9. The method of claim 1 further comprising comparing the at least one sub-surface material property to a model representative of a known good workpiece.

10. The method of claim 1 wherein the acoustic wave is generated and displacement is measured during the building of a layer in the additive manufacturing process, by alternating between the lower power level used to generate the acoustic wave and a higher power level used to create the weld pool.

11. A method of making a workpiece, comprising:

depositing a powdered material so as to define a build surface;

directing a build beam from a directed energy source to create a weld pool in the build surface, and selectively fuse the powdered material in a pattern corresponding to a cross-sectional layer of the workpiece;

using the directed energy source to generate an acoustic wave in the build surface by modulating the directed energy source to a lower power level compared to a power level used to create the weld pool;

using a noncontact method to measure displacement of the build surface in response to the acoustic wave; and

determining at least one sub-surface material property of the workpiece by analyzing the displacement of the build surface.

12. The method of claim 11 further comprising repeating in a cycle the steps of depositing and fusing to build up the workpiece in a layer-by-layer fashion.

13. The method of claim 11 where the acoustic wave is generated and displacement is measured subsequent to the completion of one or more layers during the additive manufacturing process.

14. The method of claim 11 where the surface displacement is measured using a monitoring laser separate from the directed energy source.

15. The method of claim 11 wherein:

a single beam steering apparatus is used to steer the build beam from the directed energy source and a monitoring beam from a monitoring laser.

16. The method of claim 11 further comprising comparing the at least one sub-surface material property to a model representative of a known good workpiece.

17. The method of claim 11 wherein the acoustic wave is generated and displacement is measured during the building of a layer in the additive manufacturing process, by alternating between the lower power level used to generate the acoustic wave and a higher power level used to create the weld pool.