STRESS RELAXATION IN ADDITIVELY MANUFACTURED PARTS

1 . A method for building a part with a deposition-based additive manufacturing system having a deposition head that deposits a composite including a polymer-based binder and a powdered sinterable metal, the method comprising:

receiving a first tool path for a layer of the part by a controller, wherein the received first tool path comprises a perimeter contour segment;

receiving a second tool path for a layer of the part by the controller, wherein the received second tool path comprises a parallel segment adjacent the perimeter contour segment;

moving the deposition head to deposit the composite in a pattern that follows the perimeter contour segment of the received first tool path to produce a perimeter path of the composite; and

moving the deposition head to deposit the composite in a pattern that follows the parallel segment of the received second tool path to produce a stress-offsetting retrograde adjacent path of the composite, wherein the perimeter path and the stress-offsetting retrograde adjacent path are deposited in retrograde directions with respect to one another so that directions of residual stress within the polymer-based binder of the composite are opposite in the perimeter path and the stress-offsetting retrograde adjacent path.

2 . The method according to claim 1 , wherein the second tool path is continuously adjacent to and parallel to at least 90 percent of a length of the first tool path within a same layer.

3 . The method according to claim 1 , wherein the second tool path is continuously adjacent to and parallel to at least 90 percent of a length of the first tool path within an adjacent layer.

4 . The method according to claim 1 , further comprising:

moving the deposition head to deposit the composite in a pattern along a direction changing tool path segment, wherein the direction changing tool path segment is a reflex angle continuation joining the first tool path and the second tool path within a same layer.

5 . A method for building a part with a deposition-based additive manufacturing system having a deposition head that deposits a composite including a polymer-based binder and a powdered sinterable metal, the method comprising:

receiving a first tool path for a layer of the part by a controller, wherein the received first tool path comprises a perimeter contour segment;

receiving a second tool path for a layer of the part by the controller, wherein the received second tool path comprises a parallel segment adjacent the perimeter contour segment;

moving the deposition head to deposit the composite in a pattern that follows the perimeter contour segment of the received first tool path to produce a perimeter path of the composite;

moving the deposition head to deposit the composite in a pattern that follows the parallel segment of the received second tool path in a retrograde direction with respect to the perimeter path to produce a stress-offsetting adjacent path of the composite;

debinding the polymer-based matrix sufficient to form a shape-retaining brown part; and

sintering the shape-retaining brown part to densify the part as neighboring metal particles throughout the shape-retaining brown part undergo atomic diffusion, wherein the deposition of the composite positions residual stresses within the polymer-based binder in opposing directions in the perimeter path and the stress-offsetting adjacent path and reduces part twist caused by stress and relaxation of polymer chains in the composite.

6 . The method according to claim 5 , wherein the second tool path is continuously adjacent to and parallel to at least 90 percent of a length of the first tool path within a same layer.

7 . The method according to claim 5 , wherein the second tool path is continuously adjacent to and parallel to at least 90 percent of a length of the first tool path within an adjacent layer.

8 . The method according to claim 5 , further comprising:

moving the deposition head to deposit the composite in a pattern along a direction changing tool path segment, wherein the direction changing tool path segment is a reflex angle continuation joining the first tool path and the second tool path within a same layer.

9 . A method for building a part with a deposition-based additive manufacturing system having a deposition head that deposits a composite including a polymer-based matrix and a powdered sinterable metal, the method comprising:

forming the part by moving the deposition head to deposit the composite along tool paths, wherein adjacent tool paths are traced in retrograde directions during the forming of the part to produce stress-offsetting parallel paths of the composite;

forming sintering supports of the composite below the part;

forming release layers of a release composite between the part and the sintering supports, the release composite including a ceramic particulate filler and a binder; and

debinding the polymer-based matrix sufficient to form a shape-retaining brown assembly including a part and sintering supports;

debinding the binder of the release layers, leaving ceramic particulate facilitating release of the part from the sintering supports;

sintering the shape-retaining brown assembly to densify the part and the sintering supports as neighboring metal particles throughout the shape-retaining brown part undergo atomic diffusion, wherein the deposition of the composite in retrograde directions during the forming of the part positions residual stresses within the polymer-based matrix in opposing directions in the stress-offsetting parallel paths, and reduces part twist caused by stress and relaxation of polymer chains in the composite; and

separating the part from the sintering supports along the release layers.

10 . The method according to claim 9 , wherein adjacent tool paths within a same layer are traced in retrograde directions during the forming of the part and sintering supports to produce stress-offsetting parallel paths of the composite.

11 . The method according to claim 9 , wherein adjacent tool paths within adjacent layers are traced in retrograde directions during the forming of the part and sintering supports to produce stress-offsetting parallel paths of the composite.

12 . The method according to claim 9 , further comprising:

forming soluble support structures including a soluble material, the soluble support structures resisting downward forces during the forming of the part; and

before sintering the shape-retaining brown part assembly, debinding the soluble material of the soluble support structures.

13 . The method according to claim 9 , further comprising:

forming a densification linking platform of the composite ½ mm-10 mm in height beneath the part and the sintering supports;

tacking the densification linking platform to the part at a plurality of positions dispersed about an exterior of the part to substantially counteract a friction force between the shape-retaining brown assembly and a surface beneath the densification linking platform.

14 . The method according to claim 13 , wherein the densification platform is horizontally larger than the part and has a cross-sectional area having no concavities.

15 . A method for building a part with a deposition-based additive manufacturing system having a deposition head that deposits a composite including a polymer-based matrix and a powdered sinterable metal, the method comprising:

forming the part by moving the deposition head to deposit the composite along tool paths, wherein adjacent tool paths are traced in retrograde directions during the forming of the part to produce stress-offsetting parallel paths of the composite;

forming sintering supports of the composite below the part;

forming a platform of the composite beneath the part and sintering supports, the platform being horizontally larger than the part;

tacking the part to the platform at a plurality of positions;

forming release layers of a release composite between the part and the sintering supports, the release composite including a ceramic particulate filler and a binder; and

debinding the polymer-based matrix to form a brown assembly including the part, the sintering supports, and the interconnecting platform;

debinding the binder of the release layers, leaving ceramic particulate facilitating release of the part from the sintering supports;

sintering the brown assembly to densify the part, the sintering supports and the platform as neighboring metal particles throughout the shape-retaining brown part undergo atomic diffusion, wherein tacking the part to the platform substantially counteracts a friction force between the brown assembly and a surface beneath the platform, and the stress-offsetting parallel paths reduces part twist caused by stress and relaxation of polymer chains in the composite; and

separating the part from the sintering supports along the release layers.

16 . The method according to claim 15 , further comprising:

forming a sliding release layer below the platform of equal or larger surface area than a bottom of the platform that reduces lateral resistance between the platform and the surface beneath the platform.

17 . The method according to claim 1 , further comprising:

separably interconnecting the sintering supports to a side of the part by forming separable attachment protrusions of the composite between the sintering supports and the side of the part.

18 . The method according to claim 17 , wherein the separable attachment protrusions have a minimum cross-sectional area of less than ⅓ mm.

19 . The method according to claim 17 , further comprising:

connecting the sintering supports to the platform by connections of the composite of greater cross-sectional area than the separable attachment protrusions.

20 . The method according to claim 1 , further comprising:

forming a lateral support shell of the composite following at least a portion of a lateral contour of the part; and

connecting the lateral support shell to the lateral contour of the part by forming separable attachment protrusions of the composite between the lateral support shell and the part.