SYSTEMS AND METHODS FOR ADDITIVELY MANUFACTURING LEAK RESISTANT OBJECTS

Abstract

Systems and methods of additively manufacturing leak resistant objects are disclosed. Provided herein are methods of forming objects having walls and/or surfaces that are resistant to leaks. Objects disclosed are formed from or manufactured from compositions, including metals, polymers, and combinations thereof. Objects provided herein are made from methods of forming individual shells, forming of series shells, and layer-by-layer forming of objects. Further disclosed are methods of interconnecting shells, layers, and processes for transitioning therebetween the shells and layers.

Claims

1. A method for additively manufacturing an object, comprising: depositing a first layer of a printable material, the first layer comprising a first plurality of beads, each bead of the first plurality of beads spaced apart from adjacent beads by a space having a width; depositing a second layer of the printable material, the second layer comprising a second plurality of beads deposited into the spaces between each bead of the first plurality of beads, each bead of the second plurality of beads having a height about one-half a height of the deposited first layer of the printable material; and layer-by-layer forming additional layers of the printable material by alternating between the printing pattern of the first layer and second layer.

2. The method of claim 1, wherein the width for the spacing between each bead of the first plurality of beads is about the width of the printable material.

3. The method of claim 1, wherein the width for the spacing between each bead of the first plurality of beads is less than the width of the printable material.

4. The method of claim 1, wherein depositing the second plurality of beads comprises depositing each bead of the second plurality of beads to have a portion that overlaps a portion of the deposited first plurality of beads.

5. The method of claim 4, wherein the overlap between a plurality of beads of adjacent layers is between 5-30% of the width of each bead.

6. The method of claim 5, wherein forming additional layers minimizes gaps between beads of the deposited layers.

7. The method of claim 6, wherein the gaps between beads of the deposited layers is less than 5% of the width of the spacing between the beads of the same layer.

8. The method of claim 4, wherein the overlap between each bead of the plurality of beads of adjacent layers provides for an increase in a Z-direction strength of the object.

9. The method of claim 4, wherein the overlap between the plurality of beads of adjacent layers provides for contact angles between each bead of the plurality of beads of greater than 90°.

10. The method of claim 2, wherein the height of the first layer of the printable material is from about 50 μm to about 500 μm.

11. The method of claim 1, wherein the width of the spacing between the plurality of beads of the first layer of the printable material is from about 200 μm to about 1000 μm.

12. The method of claim 1, wherein the width of the spacing between the plurality of beads of the second layer of the printable material is from about 200 μm to about 1000 μm.

13. An object, comprising: a first layer made from a printable material, the first layer comprising a first plurality of beads with each bead of the first plurality of beads spaced apart from adjacent beads by a space having a width; a second layer made from the printable material, the second layer comprising a second plurality of beads deposited into the spaces between each bead of the first plurality of beads with each bead of the second plurality of beads having a height about one-half a height of the deposited first layer of the printable material; one or more additional layers made from alternating the printing pattern of the first layer and second layer.

14. The object of claim 13, wherein each bead of the second plurality of beads includes a portion that overlaps a portion of the deposited first plurality of beads.

15. The object of claim 14, wherein the overlap between a plurality of beads of adjacent layers is between 5-30% of the width of each bead.

16. The object of claim 13, having gaps between beads of the deposited layers less than 5% of the width of the spacing between the beads of the same layer.

17. An object produced by a process comprising acts of: depositing a first layer of a printable material, the first layer comprising a first plurality of beads, each bead of the first plurality of beads spaced apart from adjacent beads by a space having a width; depositing a second layer of the printable material, the second layer comprising a second plurality of beads deposited into the spaces between each bead of the first plurality of beads, each bead of the second plurality of beads having a height about one-half a height of the deposited first layer of the printable material; and layer-by-layer forming additional layers of the printable material by alternating between the printing pattern of the first layer and second layer.

18. The object by process of claim 17, wherein the width for the spacing between each bead of the first plurality of beads is about the width of the printable material.

19. The object by process of claim 17, wherein depositing the second plurality of beads comprises depositing each bead of the second plurality of beads to have a portion that overlaps a portion of the deposited first plurality of beads.

20. The object by process of claim 17, wherein forming additional layers produces gaps between beads of the deposited layers having less than 5% of the width of the spacing between the beads of the same layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Various aspects of one or more embodiments are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide an illustration and a further understanding of the various aspects and embodiments. The figures are incorporated in and constitute a part of this specification. But, the figures are not intended as a definition of the limits of any particular embodiment. The drawings, together with the remainder of the specification, serve to explain principles and operations of the described and claimed aspects and embodiments. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures:

[0065] FIGS. 1A-3B are schematic representations illustrating a portion of a layer a wall of an object. The schematic representation, for example, is oriented such that the layer is viewable (from the z-axis) on the print bed from above.

[0066] FIGS. 1A-1B are schematic representations illustrating a layer of an object. The schematic representation shows a series of shells at a perimeter and specifically at a transition location for the series of shells. FIG. 1A illustrates staggering from an inner shell (bottom) to an outer shell (top). FIG. 1B illustrates substantially continuously depositing a transition.

[0067] FIGS. 2A-2B are schematic representations illustrating a layer of an object. The schematic representation shows a series of shells at a perimeter and specifically at a transition location for the series of shells. FIG. 2A illustrates substantially continuously depositing a transition by deviating from a toolpath including diverging at an angle of about 90°. FIG. 2B illustrates substantially continuously depositing a transition by deviating from a toolpath including diverging at an angle of less than about 90°.

[0068] FIGS. 3A-3B are schematic representations illustrating a layer of an object. The schematic representation shows a series of shells at a perimeter and specifically at a transition location for the series of shells. FIG. 3A illustrates substantially continuously depositing a transition by deviating from a toolpath including diverging at an angle of less than about 90°. FIG. 3B illustrates substantially continuously depositing by an increased extrusion deviating from a toolpath including diverging at an angle of less than about 90°.

[0069] FIGS. 4A-4B are schematic representations illustrating a portion of a wall (single perimeter) of an object. FIG. 4A illustrates substantially continuously depositing each shell about centrally above (e.g., along the z-axis, i.e., vertically) a shell of a prior layer and the shells being formed of approximately a same compression as that of the shell of the prior layer. FIG. 4B illustrates substantially continuously depositing each shell at a location approximately centrally above (e.g., along the z-axis, i.e., vertically) a boundary between shells of a prior layer.

[0070] FIGS. 5A-5B are schematic representations illustrating a portion of a wall (single perimeter) of an object. FIG. 5A illustrates substantially continuously depositing each shell about centrally above (e.g., along the z-axis, i.e., vertically) a shell of a prior layer and the shell being under approximately same compression as that of the shell of the prior layer. FIG. 5B illustrates substantially continuously depositing each shell at a location approximately centrally above (e.g., along the z-axis, i.e., vertically) a boundary between shells of a prior layer. FIG. 5B further illustrates shells under approximately same compression as that of the shell of the prior layer. FIG. 5B additionally illustrates increased compression and extrusion such that the width of the shell is varied.

[0071] FIG. 6 is a schematic representation illustrating a portion of a wall (e.g., a single perimeter) of an object. FIG. 6 illustrates depositing a shell about centrally above (e.g., along the z-axis, i.e., vertically) a shell of a prior layer and the shell being under approximately the same compression and extrusion as that of the shell of the prior layer. FIG. 6 further illustrates double height shells for alternating between printed shells.

[0072] FIG. 7 is a schematic representation illustrating a portion of a wall (e.g., single perimeter) of an object. The illustrated portion shows infill material extending from the shells. The illustrated portion further shows a periodic variation in the number of shells per layer (e.g., 6-6-4-4-6-6). The illustrated portion highlights an infill defect that can occur at an interface between shells and infill. This schematic representation illustrates periodically varying the number of shells per layer to avoid consistent alignment of infill-shell interfaces, thereby isolating the shell-infill defect.

[0073] FIGS. 8A-8B are a schematic representation illustrating a portion of a wall (e.g., single perimeter) of an object. FIG. 8A illustrates substantially continuously depositing each shell with a transition between shells. FIG. 8A further illustrates these transitions being substantially aligned above each other (e.g., along the z-axis, i.e., vertically) through the wall, thereby forming an aligned seam. FIG. 8B illustrates substantially continuously depositing each shell with a transition between shells. FIG. 8B further illustrates these transitions being vertically offset having an overlap relative to one another above/below (e.g., along the z-axis, i.e., vertically) through the wall, thereby forming a varied seam.

[0074] FIGS. 9A-9B are a schematic representation illustrating outside surfaces of a portion of a wall of an object. FIG. 9A shows the outside surface of the wall when fabricated using a process forming an aligned seam. FIG. 9B shows the outside surface of the wall when fabricated using a process forming a varied seam.

[0075] FIGS. 10A-10I illustrate the effects of bead thickness and overlap between beads to reduce gaps between each deposited bead. FIGS. 10A-10C illustrate parts made using a 0.3 mm bead with bead overlap of 0% (FIG. 10A), 10% (FIG. 10B), and 20% (FIG. 10C). FIGS. 10D-10F illustrate parts made using a 0.25 mm bead with bead overlap of 0% (FIG. 10D), 10% (FIG. 10E), and 20% (FIG. 10F). FIGS. 10G-10I illustrate parts made using a 0.2 mm bead with bead overlap of 0% (FIG. 10G), 10% (FIG. 10H), and 20% (FIG. 10I).

[0076] FIGS. 11A-11D illustrate a modeling methodology aimed at reducing the spacing between deposited beads. FIG. 11A illustrates the modeling of an individual bead as a hexagon.

[0077] FIG. 11B illustrates an example print using stacked printing of hexagon beads. FIG. 11C illustrates offsetting the hexagon beads in each layer to reduce gaps. FIG. 11D illustrates a printing method disclosed herein that stacks and offsets the hexagon beads to minimize overlap between adjacent beads.

[0078] FIG. 12 illustrates a theoretical part printed using a printing method disclosed herein where the individual beads are numbered in accordance with the order they were deposited.

[0079] FIG. 13 is a schematic representation illustrating a printable fixture for testing leak resistance.

[0080] FIG. 14 is a schematic representation showing a leak test.

[0081] FIG. 15 is a schematic representation showing a leak test, according to some embodiments of the present disclosure.

[0082] FIGS. 16A-16D illustrate parts printed from 17-4PH stainless steel and tested for leaks according to some embodiments of the present disclosure. FIGS. 16A and 16B are 17-4PH stainless steel parts of the same geometry. FIGS. 16C and 16D are 17-4PH stainless steel parts of the same geometry and different from those illustrated in FIGS. 16A and 16B.

[0083] FIGS. 17A-17B illustrate parts printed from H16 tool steel and tested for leaks according to some embodiments of the present disclosure. FIG. 17A is an identical geometry to FIGS. 16A and 16B. FIG. 17B is an identical geometry to FIGS. 16C and 16D.

[0084] FIG. 18 illustrates a schematic of a part printed using a traditional printing method and a printing method disclosed herein using 17-4 stainless steel showing the data to be tested and where images will be collected.

[0085] FIGS. 19A-19F illustrate images of parts printed using a traditional method (FIGS. 19A-19C) and parts using a printing method of this disclosure. FIGS. 19A-19C illustrate parts printed with a traditional method in a green state (FIG. 19A), a polished state post-sintering (FIG. 19B), and a fractured state post-sintering (FIG. 19C). FIGS. 19D-19F illustrate parts printed with a printing method of this disclosure in a green state (FIG. 19D), a polished state post-sintering (FIG. 19E), and a fractured state post-sintering (FIG. 19F).

[0086] FIG. 20 illustrates a cross-section image and a schematic of a zoomed in portion of a part made from a composite material printed using a printing method of this disclosure.

[0087] FIG. 21 illustrates parts printed from a composite material using both traditional printing methods and printing methods of this disclosure with different layer thicknesses and overlaps.

[0088] FIGS. 22A-22B illustrate cross-section images of the parts shown in FIG. 21 printed with a traditional printing method (FIG. 22A) and printed using a printing method of this disclosure (FIG. 22B). Black ovals used to highlight the beads of each layer.

[0089] FIG. 23 illustrates a comparison of the Z-direction tensile strength (in MPa) for parts printed from a composite material using both traditional printing methods and printing methods of this disclosure with different layer thicknesses and overlaps.

[0090] The features and advantages of this disclosure are apparent from the detailed specification, and thus, it is intended that the appended claims cover all systems and methods falling within the true spirit and scope of the disclosure. As used herein, the indefinite articles “a” and “an” mean “at least one” or “one or more.” Similarly, the use of a plural term does not necessarily denote a plurality unless it is unambiguous in the given context. Words such as “and” or “or” mean “and/or” unless specifically directed otherwise. In this application, the terms “comprising” and “including” may be understood to encompass itemized components or steps whether presented by themselves or together with one or more additional components or steps. Unless otherwise stated, the terms “about” and “approximately” may be understood to permit standard variation as would be understood by those of ordinary skill in the art. Where ranges are provided herein, the endpoints are included. As used in this application, the term “comprise” and variations of the term, such as “comprising” and “comprises,” are not intended to exclude other additives, components, integers or steps.

[0091] As used in this application, the terms “about” and “approximately” are used as equivalents. Any numerals used in this application with or without about/approximately are meant to cover any normal fluctuations appreciated by one of ordinary skill in the relevant art. In certain embodiments, the term “approximately” or “about” refers to a range of values that fall within 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either direction (i.e., greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context (except where such number would exceed 100% of a possible value).

[0092] Many methodologies described herein include a step of “determining.” Those of ordinary skill in the art, reading the present specification, will appreciate that such “determining” can utilize or be accomplished through use of any of a variety of techniques available to those skilled in the art, including for example specific techniques explicitly referred to herein. In some embodiments, determining involves manipulation of a physical sample. In some embodiments, determining involves consideration and/or manipulation of data or information, for example utilizing a computer or other processing unit adapted to perform a relevant analysis. In some embodiments, determining involves receiving relevant information and/or materials from a source. In some embodiments, determining involves comparing one or more features of a sample or entity to a comparable reference.

[0093] As used herein, the term “substantially,” and grammatic equivalents, refer to the qualitative condition of exhibiting total or near-total extent or degree of a characteristic or property of interest. One of ordinary skill in the art will understand that chemical phenomena rarely, if ever, go to completion and/or proceed to completeness or achieve or avoid an absolute result.

DETAILED DESCRIPTION

[0094] Among other things, the present disclosure provides systems and methods for additively manufacturing objects having or providing leak resistance. Various embodiments according to the present disclosure are described in detail herein. In particular, the present disclosure includes objects and their use in various applications, including, for example: leak tight or leak resistant parts and cooling channels in molds. Such cooling channels in molds, for example, can facilitate water cooled heat sinks, spot welding arms, and objects of a similar scope. The present disclosure envisions cooling channels in molds, for example that can be extended to encompass conformal cooling channels in tool steel molds and dies. Indeed, more broadly, the present disclosure encompasses a recognition that cooling channels, such as these, may be useful or desirable for any object fabricated by an additive manufacturing process where the object may include walls that are resistant to the flow of gas or liquids.

[0095] Additive manufacturing, sometimes more generally referred to as three-dimensional printing, refers to a class of technologies for the direct fabrication of physical products from a three-dimensional computer model by a layered manufacturing process. In contrast to material removal processes in traditional machining, the three-dimensional printing process adds material, using a layer-by-layer process to construct products. This process can enable the direct printing of products with extremely complex geometry.

[0096] Fused Deposition Modeling (FDM) also referred to as Fused Filament Fabrication (FFF) is an example of additive manufacturing technology used for modeling, production, and prototyping. In an FDM or FFF additive manufacturing process, a moving print head extrudes a filament of material onto a print bed or to an object being printed. The print head and/or the print bed can move in three dimensions relative to each other under computer control to define the printed object.

[0097] In a fused deposition additive manufacturing system, a three-dimensional part or model may be printed from a digital representation of the three-dimensional part in a layer-by-layer manner by extruding a flowable part material along toolpaths. The part material is extruded through an extrusion tip carried by a print head of a three-dimensional printing apparatus, device, or system. The part material is deposited as a sequence of roads on a substrate in a build plane. Extruded part material fuses to previously deposited part material and is then solidified.

[0098] The print head can move in two dimensions to deposit one horizontal plane or a layer of the object. Then, the print head or the print bed can be moved vertically by a small amount to begin another horizontal plane and a new layer of the object. Layer-by-layer object is formed. The position of the print head relative to the substrate is then incremented along one or more print axes, and the process can then be repeated to form an object, i.e., a three-dimensional part resembling the digital representation.

[0099] Additive manufacturing of an object, for example, a fused deposition additive manufacturing process, involves slicing a three-dimensional object into a plurality of two-dimensional layers that are stacked on top of one another (that is, for example, along the z-axis). In an additive manufacturing process, stacking typically may commence, for example at a build plate. Generally printing of the object is done layer-by-layer. A layer, for example, a first layer, is deposited (i.e., extruded) onto the build surface. That is, for example, a horizontal layer is printed with movement of the print head in the X-Y axis. Once this first horizontal layer is completed, a height adjustment is made in the Z-axis. Another horizontal layer of is printed with movement of the print head in the X-Y axis. Once the next horizontal layer is completed, another height adjustment is made in the Z-axis. This process continues, for each layer and layer-by-layer until the object is completed.

[0100] Additive manufacturing of a layer generally involves slicing a two-dimensional layer into a series of shells, that is, beads, lines, or shells. The printing of a layer is typically done shell-by-shell until the one or more shells (i.e., the plurality of shells) are complete. For example, each two-dimensional layer may have a number of shells lining a contour, such as a perimeter of a wall. The process of depositing or extruding shells is typically in a machine-controlled manner according to pre-determined slicing parameters. Additionally, printing of a subsequent shells may include extruding part material by tracing along a contour or path defined by a prior printed shell. A result of such a process can be a highly repeatable extrusion.

[0101] Moreover, each two-dimensional layer may have a different fill pattern filling the interior of the part. Additionally, a fill pattern may be deposited between an inner and an outer perimeter of a wall.

[0102] As provided herein, additive manufacturing processes can include slicing and forming layers and shells that are designed and configured to produce an object that is leak resistant. In some embodiments, the present disclosure includes forming shells and layers of an object having a perimeter wall that is designed and configured to provide leak resistance. In some aspects, an object can be designed and configured with multiple walls. In some aspects, each wall can be designed and configured with multiple perimeters. In some aspects, when a wall has at least an inner and an outer perimeter, an infill layer can be deposited therebetween. In some aspects, the present disclosure further includes forming multiple walls and/or forming multiple perimeters. In some aspects, the present disclosure further includes forming an infill layer between an inner and outer perimeter of a wall.

[0103] In some aspects, the present disclosure provides systems and methods for additively manufacturing objects having at least one wall or surface that is characterized by its leak resistance or being leak resistant. That is, a perimeter of the wall is such that a fluid or gas will not pass through, even under pressure. In some aspects, as used herein leak resistance includes, for example: gas tight, fluid tight, leak tight, liquid tight, watertight, gas proof, fluid proof, liquid proof, water proof, gas resistant, fluid resistant, liquid resistant, and water resistant, etc.

[0104] The present disclosure encompasses a recognition that prior additively manufactured objects made of metals or polymers could exhibit leakage. The leaks could be significant and repeatable such that they prevent using additive manufacturing objects and methods in applications where leakage is not tolerable.

[0105] For example, prior and/or known process for additively manufacturing shells and layers have been used to form walls of an object. Such objects have been made using slicing for layers and shells, for example, to form a metal container capable of being pressurized. Upon pressurization, the objects can exhibit fluid leakage at the wall locations. This is typically due to a common defect found in parts printed using fused filament fabrication in that there are small gaps between beads or layers of deposited filaments that persist beyond final processing. These defects not only are the source of leaks via acting as small holes but are also detrimental for the resulting part's mechanical properties, e.g., tensile strength. Since printed layers are typically laid sequentially in Z-direction, i.e., vertically, such print defects are contained within a plane that is normal to vertical axis by default, and therefore would be detrimental to the Z-strength of a printed part.

[0106] The baseline slicing parameters for these leaky walls can lead to locally induced shell stresses and layer stresses. Such layer stresses and shell stresses, for example, can cause random point defects that are at least sizable enough to pass a fluid.

[0107] As such, these initial baseline deposition parameters are sometimes upgraded to include stress reducing patterns, including one of the following (A) or (B). (A) a first shell is printed in a clockwise direction; and a second shell is printed in a counterclockwise direction. During printing, for each contour or toolpath the print head alternates between clockwise and counterclockwise such that each toolpath or contour within the shell is printed with a different direction than its adjacent toolpaths. Alternating winding (i.e., clock handedness) directions for adjacent toolpaths in each shell, reduces part twists and deformations from embedded stresses. (B) a first shell is printed in a clockwise direction and then each shell on the same layer is also printed in the same clockwise direction. The next layer, a first shell is printed in a counterclockwise direction and then each shell on the same layer is also printed in the same counterclockwise direction. The alternating winding (i.e., clock handedness) directions across the layers offsets the stored torque during post-processing thereby reducing part twists and deformations from embedded stresses.

[0108] However, upon pressurization, the objects formed from these stress reduced parameters and patterns can still exhibit fluid leakage at the wall locations. It is notable that these geometries can enhance part quality and reduce part/object stress, but they do not, alone, provide leak resistance.

[0109] When compared with the slicing patterns that typically induce shell and layer stresses, leaks in objects formed from stress reduced parameters and patterns were slower, but still generally intolerable. Leaks in these stress reduced parts were also sometimes significant and repeatable. Leaks in these parts are such that they likely have prevented the use of additive manufacturing methods and objects formed as a result of these methods in applications where the fluid leakage of the result part is not tolerable.

[0110] Even the addition of more shells and/or layers of material to an object generally fails to eliminate leaks. For example, the addition of material typically does not result in leak resistance or noticeably slower leaks.

[0111] In addition, even an attempted combined effect of reduced stress and the addition of material typically does not result in slower leaks. When compared with the slicing patterns that induced shell and layer stresses, leaks are sometimes slower, but are likely still not tolerable.

[0112] The present disclosure encompasses a recognition that slicing parameters for creating shells and layers and for determining printing toolpaths and extrusion settings for FFF fabrication can result in a creation of wall voids which can lead to leakage. In some embodiments, the present disclosure provides slicing for shells and layers, for example, contours, toolpaths and extrusion printer settings, for FFF fabrication to avoid creation of through wall voids.

Sealing of Shell-to-Shell Transitions

[0113] In some embodiments, the present disclosure includes continuously depositing a single shell to form a layer of an object. In some aspects, beads, lines, and shells are deposited, extruded or printed horizontally across a layer. Layers are printed layer-by-layer vertically by shifting or stepping in the z-axis. In some aspects, printing of a shell or a series of shells includes printing or extruding a deposition of material that does not jump, skip, or stagger. In some aspects, a continuous printing, extruding, or depositing is substantially continuous.

[0114] In some aspects, a continuous deposition or substantially continuous deposition is located at a transition between shells. For example, when forming a shell that lines a contour or perimeter of an object, a bead of printed material may be deposited or continuously deposited along that perimeter such that the bead exhibits no breaks or deviations. In some aspects, continuously depositing and/or substantially continuously depositing can include eliminating and/or substantially extending a leak path or possible leak path. Under prior printing processes, each layer was printed as a series of individual, separate, or unique paths. That is, the paths were not necessarily continuously connected.

[0115] FIGS. 1A-1B are a schematic representation illustrating a portion of a single layer 100. The layer shows series of shells for a wall of an object that is viewable from the z-axis. The illustration shows the series of shells specifically at a transition location for the series of shells. The transition location is the position or location at which the printer deviates, diverges, moves, shifts, transitions, or translates from a completed or printed shell to printing another shell.

[0116] FIG. 1A illustrates the above-described prior method of staggering from an inner shell (bottom) 110 to an outer shell (top) 120. That is, where each layer is printed as a series of separate paths that were not necessarily continuously connected. Under these conditions, a fluid could pass throughout the horizontal layer fairly unimpeded. The transition between each shell of the series of shells is depicted as a dotted line 130. The dotted line represents that the print head performed a non-extruding travel move at those transitions, i.e., staggered or skipped, during extruding or printing at those locations.

[0117] FIG. 1B illustrates substantially continuously depositing a transition 160. For example, when printing from an inner shell (bottom) 140 to an outer shell (top) 150, there is no period or substantially no period where there is non-extruding travel. On the X-Y plane, i.e., the horizontal layer, fluid flow is far more restricted. Specifically, to pass across the wall or perimeter of the surface, the fluid must enter and travel between the shells until it reaches an escape point. An opening and an exit for fluid flow, for example, are start and stop points for the print. By analogy, it is similar to trying to reach or leave a center of a maze. When there is a path directly cut through the side, it is an easier journey. When the maze follows a circuitous path, the journey is far more difficult. Additionally, as below explains when the travel is more and more constrained, the journey (i.e., the leak path) can be rendered impossible.

[0118] In some aspects, the present disclosure includes continuously depositing or substantially continuously depositing contours or toolpaths by angling a transition between shells. In some aspects, the present disclosure includes continuously depositing or substantially continuously depositing a contour or toolpath. Deviating from the toolpath to a transition where deviating includes diverging from the toolpath at an angle of less than about 90°. Returning to the contour or toolpath such that the subsequent shell is approximately adjacent to the prior shell. Returning to the contour or toolpath such that the subsequent shell is tracing the contour of the prior shell.

[0119] FIGS. 2A-2B illustrate a schematic representation of a layer of an object 200. The schematic representation shows a series of shells at a perimeter and specifically at a transition location for the series of shells. FIG. 2A illustrates substantially continuously depositing a transition by deviating from a toolpath including diverging at an angle of about 90° 210. FIG. 2B illustrates substantially continuously depositing a transition by deviating from a toolpath including diverging at an angle of less than about 90° 220.

[0120] In some aspects, continuously depositing a toolpath includes depositing in a spiraling inward or outward manner. In some aspects, an exposed edge, for example, may be machined smooth or otherwise manipulated by post-additive manufacturing processes.

[0121] In some aspects, the present disclosure includes continuously depositing or substantially continuously depositing contours or toolpaths by angling the transition between the shells while substantially narrowing a potential path of fluid travel. In some aspects, the present disclosure includes continuously depositing toolpaths or substantially continuously depositing a transition by deviating from a toolpath, where deviating includes diverging from the toolpath at an angle of less than about 90° and where there is locally an increased extrusion at these shell transitions.

[0122] FIGS. 3A-3B illustrate a schematic representation of a layer of an object 300. The schematic representation shows a series of shells at a perimeter and specifically at a transition location for the series of shells. FIG. 3A illustrates substantially continuously depositing a transition by deviating from a toolpath, where deviating includes diverging from the toolpath at an angle of less than about 90° 310. FIG. 3B, in addition to deviating from a toolpath, where deviating includes diverging from the toolpath at an angle of less than about 90° 320, illustrates substantially continuously depositing by an increased extrusion 330. As illustrated in FIG. 3B, the increased extrusion provides an improved or enhanced packing at the transitions of the shells. That is, a seam aligning or partially aligning shell transitions may have an increased part material volume relative to a bead, contour, standard extrusion, or toolpath. Without wishing to be bound by any particular theory, it is believed that the narrowing at this junction results in a more constricted path and makes it more difficult or challenging for fluid to travel through the shells.

[0123] FIGS. 4A-4B illustrate a schematic representation of a portion of a wall (single perimeter) of an object 400. As explained above, FIG. 4A illustrates four shells horizontally across a bottom layer 410 and another three printed layers above the bottom layer, each having four shells horizontally across (e.g., along the z-axis, i.e., vertically), 415, 420, and 425 respectively. Each shell of layer 415, 420, and 425 is shown formed about centrally above a shell of a prior layer and the shell being under approximately a same level of compression as that of the shell of the prior layer. 430 highlights a gap(s) that can form within shells. These gaps can result from extrusion or printing conditions and thus can be patterned and/or repeatable. FIG. 4B illustrates substantially continuously depositing each shell at a location approximately centrally above (e.g., along the z-axis, i.e., vertically) a boundary between shells of a prior layer. Specifically, FIG. 4B illustrates three shells horizontally across a bottom layer 435 with four shells printed across layer 440. FIG. 4B further illustrates an additional three shells printed across layer 445 followed by four shells printed across layer 450. 455 highlights that centrally positioning a bead between the printed bead of the prior layer can effectively seal shell gaps. Sealing of shell gaps can close off a horizontal (and/or a vertical) fluid path within a printed structure.

[0124] FIGS. 5A-5B illustrate a schematic representation of a portion of a wall (as illustrated, a single perimeter) of an object 500. FIG. 5A illustrates four shells horizontally across a bottom layer 510 and another three printed layers above the bottom layer, each having four shells horizontally across (e.g., along the z-axis, i.e., vertically), 515, 520, and 525 respectively. Each shell of layer 515, 520, and 525 is shown as formed about centrally above a shell of a prior layer and the shell being under approximately a same compression force as that of the shell of the prior layer. 530 highlights a gap(s) that can occur within shells. These gaps can result from extrusion or printing conditions and thus can be patterned and/or repeatable. FIG. 5B illustrates substantially continuously depositing each shell at a location approximately centrally above (e.g., along the z-axis, i.e., vertically) a boundary between shells of a prior layer. Specifically, FIG. 5B illustrates four shells horizontally across a bottom layer 535 with three shells printed with increased compression (or over-extrusion) such that the shells are wider and have an increased volume of part material disposed horizontally across layer 540. Additionally, each of the three shells of layer 540 are centrally formed between two shells of prior layer 535. Another four shells are printed horizontally across a layer 545 followed by three shells printed with increased compression or over-extrusion such that the shells are wider and have an increased volume of part material disposed horizontally across layer 550. For layer 550 (in the same manner as layer 540), each of the three shells of layer 550 are centrally formed between two shells of prior layer 545. 555 highlights that compression, over-extrusion, or the approximately central positioning of a bead (or a combination of these) between the printed bead of the prior layer can effectively seal shell gaps as highlighted. Sealing of shell gaps can close off a horizontal (and/or a vertical) fluid path within a printed structure.

[0125] FIG. 6 illustrates a schematic representation of a portion of a wall (as illustrated, a single perimeter) of an object 600. FIG. 6 illustrates four shells horizontally, 650-680, respectively across a bottom layer 610. The bead printed on layer 610 at shell position 650 and shell position 670 is a single height bead. The bead printed on layer 610 at shell position 660 and shell position 680 is a double height bead. At layer 620 a double height bead is printed at locations 650 and 670. At layer 630 a double height bead is printed at locations 660 and 680. At layer 640 a double height bead is printed at locations 650 and 670. In some aspects, the present disclosure includes alternating double height bead for shells of a layer. 690 highlights that a double height bead of extrusion spanning shells of two printed layers can effectively seal shell gaps as highlighted. Sealing of shell gaps can close off a horizontal (and/or a vertical) fluid path within a printed structure. In some aspects, compression, over-extrusion, double height shells, etc. can work to compensate for repeating or patterned gaps.

Alternating Shell Layer-by-Layer for Sealing and Isolating Defects

[0126] In some embodiments, the present disclosure includes changing a number of shells per layer to avoid an alignment of defects or gaps that may exist between shells. Changing a number of shells per layer can disrupt vertical leak paths within a printed part. In some aspects, the present disclosure includes periodically alternating a number of shells for each layer, i.e., regularly changing a number of shells per layer can disrupt such a pattern of a vertical leak path, defect or gap. Regularly or periodically changing a number of shells per layer can increase sealing and enhance leak resistance. In some aspects, the present disclosure includes periodically alternating a same number of shells for every two layers. In some aspects, forming additional layers comprises periodically alternating a same number of shells for every three layers, for every four layers, or for every five layers, i.e., regularly changing a number of shells, such that there is mechanical stability with the disruption.

[0127] Changing a number of shells or periodically alternating a number of shells may avoid alignment of an infill defect located adjacent to a shell in prior formed layers from repeating in subsequently formed layers. That is, periodically varying the number of shells per layer may avoid consistent alignment of defects that form (i.e., tend to form) adjacent to the shells at the infill (e.g., between the shells and fill), which could make a vertical leak path. FIG. 7 illustrates a schematic representation of a portion of a wall (as illustrated a single perimeter extending into an infill) of an object 700. FIG. 7 illustrates two layers of horizontal shells 710 with each layer including six shells per layer. Disposed above layer 710, are two additional layers of horizontal shells 720 with each layer including four shells per layer. Disposed above layer 720 are two additional layers of horizontal shells 730 with each layer including six shells per layer. FIG. 7 illustrates infill layers 740 corresponding to shells 710; infill layers 750 corresponding to shells 720; and infill layers 760 corresponding to shells 730. As shown, periodically varying a number of shells per layer avoids consistent alignment of infill defect 770 that is aligned at the infill adjacent to the shells, between the shells and fill. Without wishing to be bound by any particular theory, it is believed that alternating shells could eliminate a potential vertical leak path. Additionally, a periodically repeating pattern that eliminate leak paths, for example may be chosen because it aligns with, is compatible with, comports with another sealing scheme, as above provided. Alternatively, a periodically repeating pattern that eliminates leak paths, for example, may be chosen because it aligns with, is compatible with, comports with another scheme, such as one that reduces resultant object stress.

Offsetting Shell Transition Alignment Layer-by-Layer for Sealing

[0128] FIGS. 8A-8B illustrate a schematic representation of a portion of a wall (as illustrated a single perimeter) of an object. FIG. 8A illustrates substantially continuously depositing each shell with a transition between shells. FIG. 8A specifically illustrates four layers of vertical shells 810, 815, 820, and 825 and a shell transition for each layer shown as a gap in the layer. Alignment of the shell transitions and gaps forms a seam 850 within the object. FIG. 8A further illustrates shell transitions being substantially aligned above each other (e.g., along the z-axis, i.e., vertically), thereby forming an aligned seam. The aligned seam 850 is a potential fluid travel path, i.e., a leak path.

[0129] FIG. 8B illustrates these transitions being vertically staggered relative to one another above/below (e.g., along the z-axis, i.e., vertically) through the wall, thereby forming a varied seam. FIG. 8B illustrates four layers of vertical shells 830, 835, 840, and 845 and an overlapping portion, forming an offsetting portion, leading to a varied seam 860. The overlapping portion, offsetting portion, and the varied seam 860 can result from a shell transition if one layer does not align with other shell transitions of other layers. That is, the shell transitions are offset and do not align, for example, because the shell transition for one of the layers overlaps portion of another layer. The varied seam 860 creates a less direct, i.e., more convoluted, fluid travel path leading and more likely leading to leak resistance. FIG. 8B highlights an overlapping portion 870.

[0130] FIGS. 9A-9B illustrate photographs of outside surfaces of a portion of a wall of an object 900. FIG. 9A shows the outside surface of the wall when fabricated using a process forming an aligned seam, which is visible at 910. FIG. 9B shows the outside surface of the wall when fabricated using a process forming a varied seam.

[0131] In another embodiment, an approach to reducing the presence of small gaps in deposited beads and layers is to consider the shape of the filament that is being deposited and how that filament contacts an adjacent filament. Typically, the shape molten materials, i.e., filaments that are heated to a transition temperature, take when undergoing a transition to a solid state in 3D printing are circular, oval, or oblong due to material flow properties relating to the material itself and the geometry of the nozzle it is emitted from. Thus, when the filaments are in contact following deposition, there can be small star-shaped gaps where adjacent filaments are positioned. Offsetting overlapping cylindrical, oval, or oblong filaments can reduce, but not eliminate the issues via a reduction in size of the gaps between filaments. For example, as illustrated in FIGS. 10A-10I, varying bead thickness and overlap between beads can act to reduce gaps between each deposited bead. FIGS. 10A-10C illustrate parts made using a 0.3 mm bead with bead overlap of 0% (FIG. 10A), 10% (FIG. 10B), and 20% (FIG. 10C). FIGS. 10D-10F illustrate parts made using a 0.20 mm bead with bead overlap of 0% (FIG. 10D), 10% (FIG. 10E), and 20% (FIG. 10F). FIGS. 10G-10I illustrate parts made using a 0.2 mm bead with bead overlap of 0% (FIG. 10G), 10% (FIG. 10H), and 20% (FIG. 10I). As seen, by increasing the overlap and decreasing the size, e.g., diameter, of the filament, the spaces between beads in each layer and in adjoining layers can be reduced, but not eliminated. Additionally, unless printing speed is kept deliberately low such that deposited and neighboring beads can thoroughly melt and fuse together, the printed parts still can include defects that will result in leaks upon pressurization of the part and a part having reduced strength, e.g., along an axis of the defect. It is an object of this disclosure to reduce the gaps using printing methods that maximize space-filling shape between adjacent beads in each layer and improving printing speed.

[0132] In accordance with an aspect, there is provided a method for additively manufacturing an object. The method includes depositing a first layer of a printable material. The first layer may include a first plurality of beads where each bead of the first plurality of beads may be spaced apart from adjacent beads by a space having a width. The method includes depositing a second layer of the printable material. The second layer includes a second plurality of beads deposited into the spaces between each bead of the first plurality of beads where each bead of the second plurality of beads having a height about one-half a height of the deposited first layer of the printable material. The method additionally includes layer-by-layer forming additional layers of the printable material by alternating between the printing pattern of the first layer and second layer. The forming of additional layers of the printable material can maximize bead-to-bead contact area.

[0133] Without wishing to be bound by any particular theory, perfectly round filaments, i.e., cylinders, are less efficient at packing. If the filaments are modeled in a different shape that provides for better space-filling properties, such as the hexagon filaments illustrated in FIGS. 11A-11D, the gaps between deposited filaments may be minimized, and the methods disclosed herein using layered and interleaved printing can take advantage of the more efficient space packing of the filaments. For example, as illustrated in FIG. 11B, hexagon shaped filaments that are stacked in the Z-direction provide for large square-shaped spaces between each hexagon. Similarly, offsetting the next hexagon layer in the Z-direction by one-half of the dimension of a single hexagon, such as illustrated in FIG. 11C, does not remedy the problem as there remain triangle-shaped gaps between the offset hexagons. A solution to these gaps represents a hybrid approach where the beads are printed in a spaced layout where the next layer in the Z-direction fills the spaces formed in the preceding layer to improve the packing efficiency. For example, as illustrated in FIG. 11D, when modeled as hexagons, printing a first layer with the beads spaced apart by the width of one hexagon, i.e., width for the spacing between each bead of the first plurality of beads may be about the width of the printable material, permits printing of the second layer into the gaps between the first layer. Thus, beads of the next layer can be nested between beads of the previous layer. In this configuration, as the height of the printable material is generally uniform between adjacent layers, depositing the second plurality of beads into the spaces between the first plurality of beads can result in the second layer having a height of about half that of the first. To achieve the about one-half height offset in the Z-direction, one embodiment of a method disclosed herein includes depositing a half-height layer as a bottom or lower of an object or part, e.g., to raise the additional layers by about one-half a bead height, then printing additional layers onto this first half-height layer.

[0134] In some cases, the width for the spacing between each bead of the first plurality of beads is less than the width of the printable material. In either embodiment, this type of spaced offset or interleaved printing can be repeated for the full Z-height of the part. In this configuration, as illustrated, there are little to no gaps between each of the individual beads and the beads have filled in the spaces.

[0135] In some aspects, the height of the first layer of the printable material is from about 50 μm to about 500 μm. For example, the height of the first layer of the printable material is from about 50 μm to about 500 μm, about 100 μm to about 450 μm, about 150 μm to about 400 μm, about 200 μm to about 350 μm, or about 250 μm to about 300 μm, e.g., e.g., about 50 μm, about 60 μm, about 70 μm, about 80 μm, about 90 μm, about 100 μm, about 110 μm, about 120 μm, about 130 μm, about 140 μm, about 150 μm, about 160 μm, about 170 μm, about 180 μm, about 190 μm, about 200 μm, about 210 μm, about 220 μm, about 230 μm, about 240 μm, about 250 μm, about 260 μm, about 270 μm, about 280 μm, about 290 μm, about 300 μm, about 310 μm, about 320 μm, about 330 μm, about 340 μm, about 350 μm, about 360 μm, about 370 μm, about 380 μm, about 390 μm, about 400 μm, about 410 μm, about 420 μm, about 430 μm, about 440 μm, about 450 μm, about 460 μm, about 470 μm, about 480 μm, about 490 μm, or about 500 μm.

[0136] In some aspects, the width of the spacing between the plurality of beads of the first layer of the printable material and/or the width of the spacing between the plurality of beads of the second layer of the printable material is from about 200 μm to about 1000 μm. For example, the width of the spacing between the plurality of beads of the first layer of the printable material and/or the width of the spacing between the plurality of beads of the second layer of the printable material is from about 200 μm to about 1000 μm, about 250 μm to about 950 μm, 300 μm to about 900 μm, about 350 μm to about 850 μm, 400 μm to about 800 μm, about 450 μm to about 750 μm, 500 μm to about 700 μm, or about 550 μm to about 650 μm, e.g., about 200 μm, about 210 μm, about 220 μm, about 230 μm, about 240 μm, about 250 μm, about 260 μm, about 270 μm, about 280 μm, about 290 μm, about 300 μm, about 310 μm, about 320 μm, about 330 μm, about 340 μm, about 350 μm, about 360 μm, about 370 μm, about 380 μm, about 390 μm, about 400 μm, about 410 μm, about 420 μm, about 430 μm, about 440 μm, about 450 μm, about 460 μm, about 470 μm, about 480 μm, about 490 μm, about 500 μm, about 510 μm, about 520 μm, about 530 μm, about 540 μm, about 550 μm, about 560 μm, about 570 μm, about 580 μm, about 590 μm, about 600 μm, about 610 μm, about 620 μm, about 630 μm, about 640 μm, about 650 μm, about 660 μm, about 670 μm, about 680 μm, about 690 μm, about 700 μm, about 710 μm, about 720 μm, about 730 μm, about 740 μm, about 750 μm, about 760 μm, about 770 μm, about 780 μm, about 790 μm, about 800 μm, about 810 μm, about 820 μm, about 830 μm, about 840 μm, about 850 μm, about 860 μm, about 870 μm, about 880 μm, about 890 μm, about 900 μm, about 910 μm, about 920 μm, about 930 μm, about 940 μm, about 950 μm, about 960 μm, about 970 μm, about 980 μm, about 990 μm, about 1000 μm.

[0137] A schematic illustration of this type of printing is shown in FIG. 12 using numbered oval representing the individual beads. As seen in FIG. 12, when printing the beads in numerical order, e.g., 1-13, the bead deposition space is constrained vertically by printing at half layer height and horizontally by adjacent beads, i.e., each next printing layer height offset in relation to previous layer equals half of the printed layer height. As is illustrated, depositing the second plurality of beads (and additional beads) includes depositing each bead of the second plurality of beads to have a portion that overlaps a portion of the deposited first plurality of beads. For example, the overlap between a plurality of beads of adjacent layers may be between 5-30%, e.g., 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%, of the width of each bead.

[0138] In this configuration, the side-by-side bead-to-bead contact area is increased by the nesting layers which minimizes any gaps between adjoining beads or the beads of an adjacent layer in the Z-direction. By increasing the bead-to-bead contact, the adhesion of new beads to an existing layer is improved as the contact angles between the new and adjacent beads are always greater than 90 degrees. The improved adhesion from forming additional layers having maximum bead-to-bead contact area may minimize gaps between beads of the deposited layers. The gaps between beads of the deposited layers is less than 5%, e.g., less than 5%, less than 4%, less than 3%, less than 2%, less than 1%, less than 0.5%, or less than 0.25%, of the width of the spacing between the beads of the same layer. The reduced gaps between adjoining beads or the beads of an adjacent layer in the Z-direction further reduce heat loss to the surrounding environment as there are fewer and smaller spaces for heat to leak from. The reduced heat loss generally results in more efficient thermal transfer when layers are deposited using a contact print head or a part is sintered in a furnace following binder removal, i.e., improved bead-to-bead fusion. The defect rate generally increases as printing speed increases, and typical printing methods that stack beads vertically may inconsistently deposit beads as the speed increases, creating defects. Using spaced offset printing as disclosed herein may result in increased printing speed with a lower risk of developing additional defects as the spaces are filled between beads at speed. Further, as the resulting parts have smaller gaps between beads of adjacent layers, the resulting part has increased strength, e.g., tensile strength, fatigue toughness, and fracture toughness, along the direction of the layer deposition without sacrificing the quality of the print or an increase in printing time.

Materials

[0139] Suitable materials for printing leak resistant shells and layers may include, for example, polymer-based composites, metals, and combinations thereof.

[0140] Composite materials may include core and matrix materials. Matrix materials may include, for example, acrylonitrile-butadiene-styrene (ABS) terpolymer, epoxy or vinyl ester prepolymer, nylon/polyamide, polyetherimide (PEI), poly(ether ether ketone) (PEEK), poly(lactic acid) (PLA), or liquid crystal polyester (LCP). The core or strands of the core may reinforce structurally, conductively (electrically and/or thermally), insulatively (electrically and/or thermally), optically and/or in a manner to provide fluidic transport, such as carbon fibers, aramid fibers, high strength nylon fiber, or fiberglass.

[0141] Commercially valuable metals suitable for printing include aluminum, copper, steel, stainless steel, titanium and/or alloys as well as other metals resistant to oxidation at both high and low temperatures (e.g., amorphous metal, glassy metal, or metallic glass). For example, suitable metals for printing leak-resistant shells and layers may include, but not limited to, copper, tool steels, e.g., H13, A2, and D2, stainless steels, e.g., 17-4PH, metal alloys, e.g., INCONEL® 625, among other metals.

[0142] Indeed, the present disclosure encompasses a recognition that applications for any printable materials, both polymer composites and metals could benefit from leak resistance.

[0143] An infill, no matter its location in a printed part, may be any material, a same material or different material from that of shells and layers. An infill pattern can be any pattern, including, for example, solid or patterned, such as honeycomb.

[0144] In some aspects, beads, shells, and other printed deposits are extruded physically larger, e.g., of a greater volume of part material, than a typical extrusion; this is known as over-extrusion. In some aspects, beads or shells are extruded at a percentage greater than typical extrusion parameters. In some aspects, beads or shells are extruded about 1% greater than typical, about 2% greater, about 3% greater, about 4% greater, about 5% greater, about 6% greater, about 7% greater, about 8% greater, about 9% greater, about 10% greater, about 11% greater, about 12% greater, about 13% greater, about 14% greater, about 15% greater, about 20% greater, about 25% greater, about 30% greater, about 35% greater, about 40% greater, about 45% greater, about 50% greater, about 55% greater, about 60% greater, about 65% greater, about 70% greater, about 75% greater, about 80% greater, about 85% greater, about 90% greater, about 95% greater, or about 100% greater.

[0145] In some aspects, over-extrusion may be used in a strategic manner to form different components of the same finished parts. For example, in some aspects where over-extrusion is utilized to form parts, forming walls may have a different amount of over-extrusion than the depositing of infill. In some non-limiting aspects, forming walls may utilize about 1% to about 20% over-extrusion over a typical deposition, e.g., about 1% over-extrusion, about 2% over-extrusion, about 3% over-extrusion, about 4% over-extrusion, about 5% over-extrusion, about 6% over-extrusion, about 7% over-extrusion, about 8% over-extrusion, about 9% over-extrusion, about 10% over-extrusion, about 11% over-extrusion, about 12% over-extrusion, about 13% over-extrusion, about 14% over-extrusion, about 15% over-extrusion, about 16% over-extrusion, about 17% over-extrusion, about 18% over-extrusion, about 19% over-extrusion, or about 20% over-extrusion. In some non-limiting aspects, forming infill may utilize about 1% to about 30% over-extrusion over a typical deposition, e.g., about 1% over-extrusion, about 2% over-extrusion, about 3% over-extrusion, about 4% over-extrusion, about 5% over-extrusion, about 6% over-extrusion, about 7% over-extrusion, about 8% over-extrusion, about 9% over-extrusion, about 10% over-extrusion, about 11% over-extrusion, about 12% over-extrusion, about 13% over-extrusion, about 14% over-extrusion, about 15% over-extrusion, about 16% over-extrusion, about 17% over-extrusion, about 18% over-extrusion, about 19% over-extrusion, about 20% over-extrusion, about 21% over-extrusion, about 22% over-extrusion, about 23% over-extrusion, about 24% over-extrusion, about 25% over-extrusion, about 26% over-extrusion, about 27% over-extrusion, about 28% over-extrusion, about 29% over-extrusion, or 30% over-extrusion.

[0146] Without wishing to be bound by any particular theory, deposited materials, i.e., metal particles arranged in shells and layers, generally sinter as deposited. Thus, under certain circumstances, a part that is printed with an insufficient amount of part material may have gaps present in the pre-sintered or green body part that remain upon sintering, resulting in a leak. In contrast, a part formed by the over-extrusion of part material may result in the deposition of a greater amount than necessary, causing the part material to leak of the of the part as it sinters to create a part larger than the listed specification. In either scenario, a defect formed either under- or over-extrusion may carry over into the finished parts reducing part quality. In some aspects, the amount of over-extrusions is controlled such that a balance is struck between depositing a sufficient amount of material to reduce leakage and not depositing more material than necessary.

[0147] As noted herein, a defect present in a finished part may present or compound as a surface defect and increase the surface roughness of a finished part. In some aspects, the part may be printed by the selective use of over-extrusion in areas of the part where leak-resistance is needed. For example, in some aspects, over extrusion may be used on certain layers, e.g., an inner layer or inner shell, of a part to aid in providing leak-resistance with the remainder of the part printed under typical printing condition. The selective use of over-extrusion reduces the likelihood of a defect propagating to other printed areas of a part. This is only one aspect of the selective use of over-extrusion, and the invention is not limited in this regard. It is envisioned that other over-extrusion strategies for forming leak-resistant parts are within the scope of this disclosure.

[0148] In some cases, over-extrusion-induced defects may be reduced by providing for dimensional control of the position of the printing nozzle or print head. Dimensional control of the nozzle position should be considered as the parts printed using over-extrusion are, prior to sintering, larger than the specification may call for. In order to compensate for the increased size of parts printed in this manner, the offset of the print head or print nozzle may be adjusted in the appropriate direction. The offset of the print head or print nozzle may aid in preserving tolerances of ±0.5 mm (±0.02″) for parts less than 60 mm (2.36″) and ±1.0% for parts 60-90 mm (2.36-3.54″) as measured using a suitable measurement device (e.g., mechanical or optical measurement, i.e., a laser).

[0149] In some aspects, strategically not compensating for leak resistance, i.e., selectively over-extruding part material for form a part, aids in producing a finished part having a desirable surface roughness, as measured in μm Ra, within acceptable tolerances.

ENUMERATED EMBODIMENTS

[0150] The invention is further described with reference to the following enumerated embodiments. [0151] 1. A method for additively manufacturing an object having a wall, comprising steps of: [0152] forming a base layer of the wall, comprising: [0153] substantially continuously depositing a composition along a contour to form a shell of one or more shells, [0154] forming subsequent shells of the one or more shells from the substantially continuously deposited composition along neighboring paths to the contour, [0155] prior to the step of forming the subsequent shells, between each shell of the subsequent shells of the one or more shells, substantially continuously depositing a transition therebetween; and [0156] layer-by-layer forming additional layers to form the wall of the object. [0157] 2. The method of embodiment 1, further comprising forming a multi-perimeter wall, comprising steps of: [0158] prior to forming additional layers, staggering the contour from a first perimeter location to a second perimeter location; [0159] forming the layer of the wall at the second perimeter location; and layer-by-layer forming additional layers of the wall to form the multi-perimeter wall of [0160] the object. [0161] 3. The method of any of the previous embodiments, further comprising offsetting the staggered contour such that each subsequent layer of the additional layers overlaps the transitions therebetween the shells of the one or more shells. [0162] 4. The method of any of the previous embodiments, further comprising forming an infill between the perimeters of the walls of the object. [0163] 5. The method of any of the previous embodiments, wherein the step of substantially continuously depositing a transition therebetween comprises forming an unbroken connection between each shell of the one or more shells. [0164] 6. The method of any of the previous embodiments, wherein the wall is characterized by its resistant to fluid flow. [0165] 7. The method of any of the previous embodiments, wherein when the object is pressurized with a gas, the wall holds pressure. [0166] 8. The method of any of the previous embodiments, wherein when the object is pressurized with a gas, the wall is resistant to leaks. [0167] 9. The method of any of the previous embodiments, wherein the wall holds pressure in a pressure range between about 20 psi and about 80 psi. [0168] 10. The method of any of the previous embodiments, wherein the step of substantially continuously depositing a transition therebetween, further comprises angling the transition. [0169] 11. The method of any of the previous embodiments, wherein the step of angling the transition, comprises deviating from a trajectory of a toolpath at an angle of about less than about 90°. [0170] 12. The method of any of the previous embodiments, wherein the step of substantially continuously depositing a transition therebetween, further comprises increasing a volume of the deposit at the transition. [0171] 13. The method of any of the previous embodiments, wherein the step of increasing comprises at least about a 5% increase. [0172] 14. The method of any of the previous embodiments, wherein the step of increasing comprises at least about a 10% increase. [0173] 15. The method of any of the previous embodiments, wherein the step of increasing comprises a 5× increase. [0174] 16. The method of any of the previous embodiments, wherein the step of increasing comprises a 10× increase. [0175] 17. The method of any of the previous embodiments, wherein the step of layer-by-layer forming additional layers comprises, for each layer, forming a different number of shells from the immediate prior layer. [0176] 18. The method of any of the previous embodiments, wherein the step of layer-by-layer forming additional layers comprises, periodically alternating a number of shells for each layer. [0177] 19. The method of any of the previous embodiments, wherein the step of layer-by-layer forming additional layers comprises, periodically alternating a same number of shells for every two layers. [0178] 20. The method of any of the previous embodiments, wherein the step of layer-by-layer forming additional layers comprises, periodically alternating a same number of shells for every three layers. [0179] 21. The method of any of the previous embodiments, wherein the step of layer-by-layer forming additional layers comprises, periodically alternating a same number of shells for every four layers. [0180] 22. The method of any of the previous embodiments, wherein the step of layer-by-layer forming additional layers comprises, periodically alternating a same number of shells for every five layers. [0181] 23. The method of any of the previous embodiments, wherein the step of periodically alternating isolates an infill defect located adjacent to a shell in prior formed layers or subsequently formed layers. [0182] 24. The method of any of the previous embodiments, wherein the step of layer-by-layer forming additional layers comprises, prior to the step of substantially continuously depositing the composition, centrally aligning a shell above a transition therebetween shells of an immediate prior layer. [0183] 25. The method of any of the previous embodiments, wherein the step of layer-by-layer forming additional layers comprises, prior to the step of substantially continuously depositing the composition, centrally aligning a shell above a transition therebetween shells of an immediate prior layer, and increasing a volume of layer extrusion, thereby forming an over-extruded layer. [0184] 26. The method of any of the previous embodiments, wherein the step of layer-by-layer forming additional layers comprises, periodically alternating between the base layer and the over-extruded layer. [0185] 27. The method of any of the previous embodiments, wherein the step of substantially continuously depositing the composition for at least one shell of the one or more shells, comprises over extruding deposition for each shell layer. [0186] 28. The method of any of the previous embodiments, wherein the step of forming subsequent shells, each subsequent shell approximately follows an adjacent contour of each prior shell. [0187] 29. The method of any of the previous embodiments, wherein the step of forming each subsequent shell comprises deviating from the contour to form the transition. [0188] 30. The method of any of the previous embodiments, wherein the step of deviating comprises diverging from the prior toolpath. [0189] 31. The method of any of the previous embodiments, wherein the step of deviating comprises diverging from the prior toolpath at an angle of less than 90°. [0190] 32. The method of any of the previous embodiments, the step of forming subsequent shells of the one or more shells, comprises after the step of deviating, aligning the neighboring path to the contour adjacent to the prior contour; and tracing the prior contour. [0191] 33. The method of any of the previous embodiments, further comprising overlapping a portion of the contour of each shell of the one or more shells such that the transition therebetween and the subsequent shells of the one or more shells are offset relative to those of a prior shell. [0192] 34. The method of any of the previous embodiments, wherein the step of forming the infill comprises depositing infill. [0193] 35. The method of any of the previous embodiments, wherein the step of forming the infill comprises extruding infill. [0194] 36. The method of any of the previous embodiments, wherein the infill comprises a same material as a shell material. [0195] 37. The method of any of the previous embodiments, wherein the step of forming the infill comprises depositing a honeycomb infill. [0196] 38. The method of embodiment 1, wherein the wall is a multi-perimeter wall, the method further comprising steps of: prior to the step of forming additional layers, staggering the contour from a first perimeter location to a second perimeter location; forming an additional layer of the wall at the second perimeter location; and layer-by-layer, at the first perimeter location and the second perimeter location, forming additional layers of the wall to form the multi-perimeter wall of the object. [0197] 39. The method of embodiment 38, further comprising offsetting the staggered contour such that each subsequent layer of the additional layers overlaps the transitions therebetween the shells of the one or more shells. [0198] 40. The method of embodiment 38 or 39, further comprising forming an infill between the first perimeter and second perimeter of the walls of the object

[0199] 41. The method of any previous embodiment, wherein the step of substantially continuously depositing a transition therebetween comprises: [0200] forming an unbroken connection between each shell of the one or more shells; [0201] angling the transition, optionally wherein angling comprises deviating from a trajectory of a toolpath at an angle of about less than about 90°;
increasing a volume of the deposit at the transition; or [0202] over extruding deposition for each shell layer of at least one shell of the one or more shells. [0203] 42. The method of any previous embodiment, wherein the wall is characterized by its resistance to fluid flow. [0204] 43. The method of any previous embodiment, wherein when the object is pressurized with a gas: [0205] the wall is configured to hold pressure; [0206] the wall is configured to be resistant to leaks; or [0207] the wall is configured to hold pressure in a pressure range between about 20 psi and about 80 psi. [0208] 44. The method of embodiment 41, wherein the step of increasing comprises: [0209] increasing by at least 5%; [0210] increasing by at least 10%; [0211] increasing by at least 5×; or [0212] increasing by at least 10×. [0213] 45. The method of any previous embodiment, wherein the step of layer-by-layer forming additional layers comprises: [0214] for each layer, forming a different number of shells from the immediate prior layer; [0215] periodically alternating a number of shells for each layer; [0216] periodically alternating a same number of shells for every two layers; [0217] periodically alternating a same number of shells for every three layers; [0218] periodically alternating a same number of shells for every four layers; [0219] periodically alternating a same number of shells for every two layers; or [0220] periodically alternating between the base layer and the over-extruded layer, [0221] optionally wherein the step of periodically alternating any number of shells isolates an infill defect located adjacent to a shell in prior formed layers or subsequently formed layers. [0222] 46. The method of any previous embodiment, wherein the step of layer-by-layer forming additional layers comprises, prior to the step of substantially continuously depositing the composition, [0223] centrally aligning a shell above a transition therebetween shells of an immediate prior layer; or [0224] centrally aligning a shell above a transition therebetween shells of an immediate prior layer, and increasing a volume of layer extrusion, thereby forming an over-extruded layer. [0225] 47. The method of any previous embodiment, wherein the step of forming each subsequent shell comprises: [0226] approximately following an adjacent contour of each prior shell; or [0227] deviating from the contour to form the transition, optionally wherein the step of deviating comprises: [0228] diverging from the prior toolpath; or [0229] diverging from the prior toolpath at an angle of less than 90°. [0230] 48. The method of any previous embodiment, further comprising overlapping a portion of the contour of each shell of the one or more shells such that the transition therebetween and the subsequent shells of the one or more shells are offset relative to those of a prior shell. [0231] 49. The method of embodiment 4, wherein the step of forming the infill comprises: [0232] depositing infill; [0233] extruding infill; or [0234] depositing a honeycomb infill. [0235] 50. The method of embodiment 49, wherein the infill comprises a same material as a shell material or a different material than a shell material.

EXAMPLES

[0236] The following examples illustrate some embodiments and aspects of the disclosure. It will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be performed without altering the spirit or scope of the disclosure, and such modifications and variations are encompassed within the scope of the disclosure as defined in the claims which follow. The following examples do not in any way limit the disclosure.

Example 1

[0237] Example 1 describes a method of forming a leak resistant object.

Materials and Methods

[0238] Samples were printed using a Markforged Metal X extruding a filament including a copper composite,

[0239] FIG. 13 illustrates a schematic representation of a printed object 1320, showing ½″ NPT threads for direct coupling to an m-type air fitting 1310 for connection of the test setup.

[0240] Pressure was tested using dean dry air at 50 psi. Pressures were applied in excess of 5 minutes. FIG. 14 is a photograph showing the compressed air testing of a baseline part As illustrated, the baseline part has bubbles emanating from the part, indicating that the layers of part material have gaps therebetween and are not fully sealed.

[0241] Objects were also additively manufactured using pathing as disclosed above, for example, the substantially continuous depositing of shells, the inclusion of printing beads that are 10% greater in dimension than typical printed beads, the printing of shells having a greater volume of part material at seams, and/or the periodic alternating of a number of shells across layers, e.g., in a 4-4-6-6 pattern and filled by a solid infill). As is noted throughout, multiple schemes may be used together to achieve leak resistance.

[0242] FIG. 15 is a photograph showing the part made as described in the prior paragraph. The part is shown holding 50 psi for greater than 5 minutes without showing evidence of a leak, indicating that the pathing techniques described above (e.g., continuous printing or over-extrusions) can be successful in creating a leak resistant part.

Example 2

[0243] Example 2 describes a method of forming leak resistant objects of a controlled surface finish.

Materials and Methods

[0244] Samples were printed using a Markforged Metal X extruding metal powder filaments. Filaments included 17-4PH stainless steel and H13 tool steel. Surface finish of printed parts was measured with a surface profilometer in the Z-direction (Mitutoyo). Parts were printed having walls with a periodic variation in the number of deposited shells per layer. Example patterns included 4 layers with a 2-1-4-3 number of shells per layer and 6 layers with a 2-1-6-5-4-3 number of shells per layer. In both printed parts, interior shells 2 and 1 were not printed using either continuous pathing or over-extrusion: and as a result, by not using these print methods enhanced the surface finish was enhanced and surface roughness was reduced. Table 1 lists the requirements for parts printed using the methods of this example.

TABLE-US-00001 TABLE 1 Printed part specifications Property Requirement Leak Resistance No leaks or bubbles under constant pressure of 50 PSI held for 5 minutes Surface Finish 10-15 μm Ra (average) (Z direction)

[0245] FIGS. 16A-161) and 14A-14B illustrate finished parts of two different geometries printed using different materials. Specifically, FIGS. 16A-16D illustrate parts printed from 17-4PH stainless steel, with FIGS. 16A and 16B illustrating a part geometry with less fine structure and FIGS. 16C and 16D illustrating a part geometry with different types of fine structural elements. FIGS. 17A-17B illustrate parts printed from H13 tool steel with the part in FIG. 17A having the same geometry as illustrated in FIGS. 16A-16B and the part illustrated in FIG. 17B having the same geometry as the part illustrated in FIGS. 16C-16D. As is illustrated in FIGS. 63A-16D and 17A-17B, none of the printed parts exhibited the formation of bubbles when pressurized under water, indicating that the printing process using the aforementioned shell patterns with either continuous printing or over-extrusions resulted in leak-free final parts.

[0246] Another metric used to evaluate printed parts printed using the shell pattern as described in this Example is the surface finish. For the printed parts to be considered acceptable, as noted in Table 1, the finished pasts should have an average surface finish in the Z-direction, as measured by a profilometer, of 10-15 μm Ra. As shown in Table 2, each of the parts illustrated in FIGS. 16C, 16D, and 17B had a surface roughness of between 12.7-13.5 μm Ra, well within the acceptable range.

TABLE-US-00002 TABLE 2 Resulting surface finish of printed parts FIG. Reference Material Surface Roughness (μm Ra) FIG. 16C 17-4PH 12.7 FIG. 16D 17-4PH 13.5 FIG. 17B H13 13.5

Example 3

[0247] Example 3 describes a method of printing objects from stainless steel using bead spaced overlapped printing methods disclosed herein.

Materials and Methods

[0248] Samples were printed using a Markforged Metal X extruding metal powder filaments. Filaments included 17-4 v2 stainless steel. A schematic of the printing scheme is illustrated in FIG. 18. As illustrated, the larger part was printed in the X-direction and the test pieces were cut from this larger part in the Y-direction. As a control, a large part was printed using the same material with a traditional bead stacking style of printing in the X-direction and the control pieces were cut from this larger part in the Y-direction. For all text and control pieces, mechanical tests were performed in two separate states: green parts and sintered parts. The mechanical test included testing the transverse mechanical properties tested in a 3-point bend test to evaluate elastic modulus, fracture stress, and part elongation at the point of fracture.

Results

[0249] Table 3 shows the change in elastic modulus (in MPa or GPa), the pressure needed to fracture the test part (in MPa), and the change in elongation, taken as a percentage from the printed length, for parts printed using the traditional stacked printing method and the spaced overlapping printing method disclosed herein. Parts were tested both before, i.e., green, and after sintering. As is seen, printing parts using the spaced overlapping printing method disclosed herein improves the mechanical properties of the resulting parts, as evidenced by the increased force needed to bend and fracture the parts in addition to the increased lengthen of the parts before fracturing.

TABLE-US-00003 TABLE 3 Mechanical testing On samples Elongation Sample Condition Elastic Modulus Fracture Stress at Fracture Green, Standard 517 MPa   4.1 MPa  4.2% Green, New 597 MPa   7.1 MPa 13.5% Relative Change 15% 73%  227% Sintered, Standard 147 GPa 1573 MPa  4.5% Sintered, New 155 GPa 2096 MPa 12.3% Relative Change  5% 33%  173%

[0250] FIGS. 19A-19F illustrate images of parts printed using a traditional method (FIGS. 19A-19C) and parts using a printing method of this disclosure (FIG. 19D-19F), consistent with the data in Table 3. FIGS. 19A-19C illustrate parts printed with a traditional method in a green state (FIG. 19A), a polished state post-sintering (FIG. 19B), and a fractured state post-sintering (FIG. 19C). FIGS. 19D-19F illustrate parts printed with a printing method of this disclosure in a green state (FIG. 19D), a polished state post-sintering (FIG. 19E), and a fractured state post-sintering (FIG. 19F). As clearly seen in FIGS. 19A-19C, the parts printed using a traditional stacked bead printing method produced definite gaps in the green part (FIG. 19A), which persisted in the part following sintering (FIG. 19B). FIG. 19C is an image of the fracture point of the printed part of FIGS. 19A-19B. This part showed clear striations in the deposited layers, indicating the presence of gaps that were weak points during mechanical bend testing. In contrast, the part made using the spaced overlapped printing method of this disclosure is more uniform in composition, with no visible gaps between deposited layers visible in the green part (FIG. 19D). Upon sintering, there were no visible gaps between deposited layers, indicating that thermal losses were minimal and the part evenly sintered. FIG. 19F is an image of the fracture point of the printed part of FIGS. 19D-19E This part showed a mostly homogenous composition at the fracture point. This suggests a uniformly sintered part without inherent stress points to serve as a fracture location. This is also reflected in Table 3 above, where the sintered parts exhibited an increased elastic modulus, increased pressure needed to fracture, and increased lengthening before fracturing.

Example 4

[0251] Example 4 describes a method of printing objects from stainless steel using head spaced overlapped printing methods disclosed herein.

Materials and Methods

[0252] Two rectangular samples were printed using a Markforged Metal X extruding metal powder filaments. Filaments included 17-4 PH stainless steel. Beads in both plates were printed in one direction—parallel to 75 mm long side. The rectangular samples were printed as a solid with no infill. Sample 1 was printed using a traditional printing method and Sample #2 was printed using the printing method disclosed herein. Following printing, the green density of both samples was measured. The density of Sample 1 was measured at 4.92 g/cm.sup.3 and the density of Sample 2 was measured at 5.01 g/cm.sup.3.

[0253] Next, both samples were cut into six rectangular bars for each plate, each rectangle being 150 mm×75 mm×7 mm Then, three samples of each plate were tested in 3-point flexure mode in green state, and 3 samples of each plate were subjected to solvent debinding, followed by a sintering operation and subsequently tested in 3-point flexure mode to evaluate part strength and part elongation at the point of fracture.

Results

[0254] Table 4 shows the pressure needed to fracture the test part (“strength” in MPa) and the change in elongation, taken as a percentage from the printed length, the rectangles cut from the different Samples. Parts were tested both before, i.e., green, and after sintering. As is seen, printing parts using the spaced overlapping printing method disclosed herein improves the mechanical properties of the resulting parts, as evidenced by the increased force needed to bend and fracture the parts in addition to the increased lengthen of the parts before fracturing. As is clear from Table 4, the printing method disclosed herein resulted in improved mechanical properties of both green and sintered metal samples measured in transverse i.e., to print direction, sample orientation.

TABLE-US-00004 TABLE 4 Mechanical testing On samples Sample # and Green Green Green Green Print Type Strength Elongation Strength Elongation Sample 1, Standard 1 MPa 1 h 1500 MPa  3% Sample 2, New 5 MPa 5% 2000 MPa 11%

Example 5

[0255] Example 5 describes a method of printing objects from a composite material using bead spaced overlapped printing methods disclosed herein.

Materials and Methods

[0256] Two rectangular prism shaped samples were printed using Markforged Onyx One and Mark Two filament printers using a carbon fiber-filled nylon composite filament. Each rectangular prism had dimensions of 150 mm×13 mm×4 mm with the long axis oriented in the Z-direction. These samples were then machined into an ASTM D638 dog bone geometry. Five (5) sample parts of 65 μm, 100 μm, 150 μm, 200 μm, and 300 μm layer heights were printed using the printing method disclosed herein with spaced offsets and nested layers. A control sample having a 100 μm layer height was printed using standard Markforged slicer settings. All samples were dried in a vacuum oven for 2 days at 75 Samples were placed into a purged dry box with a desiccant after drying in the vacuum oven. For mechanical testing, a sample was removed from the dry box and tested within five minutes of removal to reduce moisture uptake. A cross-section image of a dog bone sample is illustrated in FIG. 20 and post-testing images of the dog bone samples with different layer heights are illustrated in FIG. 21.

Results

[0257] Table 5 shows the change in dry tensile strength in the rectangular prisms and dog bone samples compared to control samples printed with the traditional printing method and the nested/spaced offset printing method of this disclosure. As seen in Table 5, parts printed using the spaced offset/nested printing method of this disclosure approached isotropic mechanical strength, i.e., strength of solid, non-printed material, without sacrificing the quality of the print. The improvement in mechanical properties was in part attributed to the reduction in spaces between beads in adjacent layers in the parts printed with the nested/spaced offset printing method of this disclosure compared to a part made using traditional stacked printing. Microscopy images of the cross-sections of the samples printed with both methods is illustrated in FIG. 22A-22B. The cross-section of the control sample illustrated in FIG. 22A shows large spaces between the beads pointed out by the white arrows where the layers did not fully fuse. In contrast, the cross-section of a sample printed using the nested/spaced offset printing method of this disclosure shows few spaces between the beads of the adjacent layers.

[0258] FIG. 23 expands Table 5 by showing the maximum Z-direction tensile strength (in MPa) for an five dog hone samples printed with varying layer heights compared to the control sample. FIG. 23 shows that the printing method disclosed herein resulted in greatly improved mechanical properties measured in the Z-direction for composites compared to a control sample.

TABLE-US-00005 TABLE 5 Mechanical testing on dog bone samples Tensile Strength % Change Sample Type Trad. New over Control Rectangular Prisms* 29.9 MPa     48.5 MPa   +62% Dog Bones** 29.6 MPa 49.3-54.2 MPa +67-83% *200 μm layer height control; 150 μm interleaved: replicates at same layer height to be tested; samples tested as printed. **100 μm layer height control; 65 μm, 100 μm. 150 μm. 200 μm, 300 μm interleaved; replicates at various layer heights to be tested; samples machined into dog bone shape before testing.

Other Embodiments and Equivalents

[0259] While the present disclosure has explicitly discussed certain particular embodiments and examples of the present disclosure, those skilled in the art will appreciate that the disclosure is not intended to be limited to such embodiments or examples. On the contrary, the present disclosure encompasses various alternatives, modifications, and equivalents of such particular embodiments and/or example, as will be appreciated by those of skill in the art.

[0260] Accordingly, for example, methods and diagrams of should not be read as limited to a particular described order or arrangement of steps or elements unless explicitly stated or clearly required from context (e.g., otherwise inoperable). Furthermore, different features of particular elements that may be exemplified in different embodiments may be combined with one another in some embodiments.