Generative design shape optimization using build material strength model for computer aided design and manufacturing

1. A method comprising:

obtaining, by a computer aided design program, a design space for a modeled object, for which a corresponding physical structure will be additively manufactured, design criteria for the modeled object including at least one stress constraint, at least one in-use load case for the physical structure, and a specification of one or more materials from which the physical structure will be additively manufactured, wherein the specification includes information indicating multiple strength values for the one or more materials, the multiple strength values being dependent upon one or both of a thickness of the physical structure to be built using the one or more materials, and a build angle used during additive manufacturing of the physical structure using the one or more materials;

producing, by the computer aided design program, a generatively designed three dimensional shape of the modeled object, including modifying both a geometry of the three dimensional shape and a topology of the three dimensional shape, in accordance with the design criteria, the at least one in-use load case, and the specification of one or more materials, wherein the producing comprises varying, during object shape and topology modification of the modeled object, evaluation of the stress constraint at different locations on or in the modeled object in accordance with respective values from the multiple strength values, wherein each strength value corresponds to one or both of the thickness and the build angle at each one of the different locations; and

providing, by the computer aided design program, the generatively designed three dimensional shape of the modeled object for use in additively manufacturing the physical structure.

2. The method of claim 1 , wherein each strength value corresponds to the thickness or both the thickness and the build angle at each one of the different locations, and wherein the producing comprises

measuring the thickness at each one of the different locations; and

computing a respective strength value based on at least the measured thickness at each one of the different locations.

3. The method of claim 2 , wherein measuring the thickness comprises using a measure of thickness for the generatively designed three dimensional shape of the modeled object that is a combination of at least two distinct thickness measures.

4. The method of claim 3 , wherein the thickness at each one of the different locations comprises a combination of at least

(i) a first distance measure being a length within the modeled object of a ray cast in a negative normal direction from a surface point of the modeled object, and

(ii) a second distance measure being a diameter of a largest sphere that touches the surface point of the modeled object and fits inside the modeled object as determined by checking discrete sampling locations defined on the sphere's surface.

5. The method of claim 1 , wherein modifying both the geometry and the topology of the three dimensional shape comprises enforcing a design criterion that limits a minimum thickness of the generatively designed three dimensional shape of the modeled object, and the minimum thickness being based on a critical fatigue crack length for the material.

6. The method of claim 1 , wherein modifying both the geometry and the topology of the three dimensional shape comprises:

performing numerical simulation of the modeled object in accordance with a current version of the three dimensional shape and the one or more in-use load cases to produce a current numerical assessment of a physical response of the modeled object;

finding a maximized stress or strain element, for each of the one or more in-use load cases for the physical structure, from the current numerical assessment of the physical response of the modeled object;

determining an expected number of loading cycles for each of the one or more in-use load cases for the physical structure using the maximized stress or strain element and data relating fatigue strength to loading cycles;

redefining a fatigue safety factor inequality constraint for the modeled object based on a damage fraction calculated from the required number of loading cycles for the modeled object and the expected number of loading cycles for each of the one or more in-use load cases for the physical structure;

computing shape change velocities for an implicit surface in a level-set representation of the three dimensional shape in accordance with at least the fatigue safety factor inequality constraint;

updating the level-set representation using the shape change velocities to produce an updated version of the three dimensional shape of the modeled object; and

repeating at least the performing, the finding, the determining, the redefining, the computing and the updating until a predefined number of shape modification iterations have been performed or until the generatively designed three dimensional shape of the modeled object in the design space converges to a stable solution for the one or more design criteria and the one or more in-use load cases.

7. The method of claim 1 , wherein each strength value corresponds to the build angle or both the thickness and the build angle at each one of the different locations, wherein the different locations comprises an internal location of the three dimensional shape, and wherein the producing comprises

projecting the internal location along a predetermined build direction, to a surface location of the three dimensional shape; and

determining a build angle for the internal location from an angle of the normal of the surface location with respect to the predetermined build direction.

8. The method of claim 1 , wherein the producing further comprises:

computing shape change velocities for an implicit surface in a level-set representation of the three dimensional shape in accordance with the at least one stress constraint; and

updating the level-set representation using the shape change velocities to produce an updated version of the three dimensional shape of the modeled object.

9. The method of claim 8 , wherein computing the shape change velocities comprises computing at least one shape change velocity using a gradient determined from a shape derivative of one or both of the thickness and the build angle at each of the different locations.

10. The method of claim 8 , wherein computing the shape change velocities comprises computing at least one shape change velocity using an amount determined from a shape derivative formula that approximates a shape derivative of one or both of the thickness and the build angle at each of the different locations.

11. The method of claim 10 , wherein the shape derivative formula comprises a volume fraction based inequality constraint that is modified using an importance factor, which is adjusted based on whether or not one or more other constraints were violated in a prior iteration of the iteratively modifying.

12. A system comprising:

a non-transitory storage medium having instructions of a computer aided design program stored thereon; and

one or more data processing apparatus configured to run the instructions of the computer aided design program to:

obtain a design space for a modeled object, for which a corresponding physical structure will be additively manufactured, design criteria for the modeled object including at least one stress constraint, at least one in-use load case for the physical structure, and a specification of one or more materials from which the physical structure will be additively manufactured, wherein the specification includes information indicating multiple strength values for the one or more materials, the multiple strength values being dependent upon one or both of a thickness of the physical structure to be built using the one or more materials, and a build angle used during additive manufacturing of the physical structure using the one or more materials;

produce a generatively designed three dimensional shape of the modeled object, including modifying both a geometry of the three dimensional shape and a topology of the three dimensional shape, in accordance with the design criteria, the at least one in-use load case, and the specification of one or more materials, wherein the producing comprises varying, during object shape and topology modification of the modeled object, evaluation of the stress constraint at different locations on or in the modeled object in accordance with respective values from the multiple strength values, wherein each strength value corresponds to one or both of the thickness and the build angle at each one of the different locations; and

provide the generatively designed three dimensional shape of the modeled object for use in additively manufacturing the physical structure.

13. The system of claim 12 , comprising an additive manufacturing machine, wherein the one or more data processing apparatus are configured to run the instructions of the computer aided design program to generate toolpath specifications for the additive manufacturing machine from the three dimensional model, and manufacture the physical structure corresponding to the object with the additive manufacturing machine using the toolpath specifications.

14. A non-transitory computer-readable medium encoding a computer aided design program operable to cause one or more data processing apparatus to perform operations comprising:

obtaining, by a computer aided design program, a design space for a modeled object, for which a corresponding physical structure will be additively manufactured, design criteria for the modeled object including at least one stress constraint, at least one in-use load case for the physical structure, and a specification of one or more materials from which the physical structure will be additively manufactured, wherein the specification includes information indicating multiple strength values for the one or more materials, the multiple strength values being dependent upon one or both of a thickness of the physical structure to be built using the one or more materials, and a build angle used during additive manufacturing of the physical structure using the one or more materials;

producing, by the computer aided design program, a generatively designed three dimensional shape of the modeled object, including modifying both a geometry of the three dimensional shape and a topology of the three dimensional shape, in accordance with the design criteria, the at least one in-use load case, and the specification of one or more materials, wherein the producing comprises varying, during object shape and topology modification of the modeled object, evaluation of the stress constraint at different locations on or in the modeled object in accordance with respective values from the multiple strength values, wherein each strength value corresponds to one or both of the thickness and the build angle at each one of the different locations; and

providing, by the computer aided design program, the generatively designed three dimensional shape of the modeled object for use in additively manufacturing the physical structure.

15. The non-transitory computer-readable medium of claim 14 , wherein the one or more computer-controlled manufacturing systems comprise an additive manufacturing machine, and the operations comprise:

generating toolpath specifications for the additive manufacturing machine from the three dimensional model; and

manufacturing the physical structure corresponding to the object with the additive manufacturing machine using the toolpath specifications.

16. The non-transitory computer-readable medium of claim 14 , wherein each strength value corresponds to the thickness or both the thickness and the build angle at each one of the different locations, and wherein the producing comprises

measuring the thickness at each one of the different locations; and

computing a respective strength value based on at least the measured thickness at each one of the different locations.

17. The non-transitory computer-readable medium of claim 16 , wherein measuring the thickness comprises using a measure of thickness for the generatively designed three dimensional shape of the modeled object that is a combination of at least two distinct thickness measures.

18. The non-transitory computer-readable medium of claim 17 , wherein the thickness at each one of the different locations comprises a combination of at least

(i) a first distance measure being a length within the modeled object of a ray cast in a negative normal direction from a surface point of the modeled object, and

(ii) a second distance measure being a diameter of a largest sphere that touches the surface point of the modeled object and fits inside the modeled object as determined by checking discrete sampling locations defined on the sphere's surface.

19. The non-transitory computer-readable medium of claim 14 , wherein modifying both the geometry and the topology of the three dimensional shape comprises enforcing a design criterion that limits a minimum thickness of the generatively designed three dimensional shape of the modeled object, and the minimum thickness being based on a critical fatigue crack length for the material.

20. The non-transitory computer-readable medium of claim 14 , wherein modifying both the geometry and the topology of the three dimensional shape comprises:

performing numerical simulation of the modeled object in accordance with a current version of the three dimensional shape and the one or more in-use load cases to produce a current numerical assessment of a physical response of the modeled object;

finding a maximized stress or strain element, for each of the one or more in-use load cases for the physical structure, from the current numerical assessment of the physical response of the modeled object;

determining an expected number of loading cycles for each of the one or more in-use load cases for the physical structure using the maximized stress or strain element and data relating fatigue strength to loading cycles;

redefining a fatigue safety factor inequality constraint for the modeled object based on a damage fraction calculated from the required number of loading cycles for the modeled object and the expected number of loading cycles for each of the one or more in-use load cases for the physical structure;

computing shape change velocities for an implicit surface in a level-set representation of the three dimensional shape in accordance with at least the fatigue safety factor inequality constraint;

updating the level-set representation using the shape change velocities to produce an updated version of the three dimensional shape of the modeled object; and

repeating at least the performing, the finding, the determining, the redefining, the computing and the updating until a predefined number of shape modification iterations have been performed or until the generatively designed three dimensional shape of the modeled object in the design space converges to a stable solution for the one or more design criteria and the one or more in-use load cases.

21. The non-transitory computer-readable medium of claim 14 , wherein each strength value corresponds to the build angle or both the thickness and the build angle at each one of the different locations, wherein the different locations comprises an internal location of the three dimensional shape, and wherein the producing comprises

projecting the internal location along a predetermined build direction, to a surface location of the three dimensional shape; and

determining a build angle for the internal location from an angle of the normal of the surface location with respect to the predetermined build direction.

22. The non-transitory computer-readable medium of claim 14 , wherein the producing further comprises:

computing shape change velocities for an implicit surface in a level-set representation of the three dimensional shape in accordance with the at least one stress constraint; and

updating the level-set representation using the shape change velocities to produce an updated version of the three dimensional shape of the modeled object.

23. The non-transitory computer-readable medium of claim 22 , wherein computing the shape change velocities comprises computing at least one shape change velocity using a gradient determined from a shape derivative of one or both of the thickness and the build angle at each of the different locations.

24. The non-transitory computer-readable medium of claim 22 , wherein computing the shape change velocities comprises computing at least one shape change velocity using an amount determined from a shape derivative formula that approximates a shape derivative of one or both of the thickness and the build angle at each of the different locations.