Patent Publication Number: US-11046035-B2

Title: Fiber feathering in additive manufacturing

Description:
This application is related to U.S. patent application Ser. No. 16/037,706, filed on Jul. 17, 2018, entitled “Generating Tool Paths to Preserve Filament Continuity in Additive Manufacturing”, which is assigned to the assignee of the present application and incorporated by reference herein in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates generally to aspects of additive manufacturing of three-dimensional articles, and, more particularly, to improved techniques for fabricating articles of manufacture employing fiber feathering as addressed further herein. 
     BACKGROUND 
     In general, there are two complementary approaches to fabricate an article of manufacture: additive manufacturing and subtractive manufacturing. 
     Additive manufacturing involves aggregating material to form the desired article of manufacture. In contrast, subtractive manufacturing involves removing material to form the desired article of manufacture. In practice, many articles of manufacture are fabricated using a combination of additive and subtractive techniques. 
     A form of additive manufacturing—colloquially known as “3D printing”—is the subject of intense research and development because it enables the fabrication of articles of manufacture with complex geometries. Furthermore, 3D printing enables the mass customization of articles of manufacture with different dimensions and characteristics. See, for example, U.S. patent application Ser. No. 15/899,361, filed Feb. 19, 2018, entitled “Hexagonal Sparse Infill Made of Linear Segments of Filament,” and U.S. patent application Ser. No. 15/899,360, filed Feb. 19, 2018, entitled “Quadrilateral Sparse Infill Made of Linear Segments of Filament”, both of which are assigned to the assignee of the present application and incorporated by reference in their entirety. There remain, however, many challenges in the design, manufacture, and use of 3D printers, as well as, in the advancement of 3D printing processes. 
     Consider the task of designing an article to be sufficiently strong to resist a wide array of forces encountered in real world usage, but lightweight. An article of a given material, a given external geometry, and a solid interior is typically stronger than an article with a hollow interior. In contrast, an article of a given material, a given external geometry, and a hollow interior is typically lighter than an article with a solid interior. 
     There are, however, more options for the interior and one such option is a sparse infill. A sparse infill (herein also called an “infill”) is a porous or skeletal or cellular structure that is stronger than a hollow interior and lighter in weight than a solid interior. 
     Infills are commonly incorporated into articles that are 3D printed, and it is well-known how to make an infill using a 3D printing technology in which the structural integrity of the infill is independent of the macroscopic properties of the materials used to make the structure. For example, the structural integrity of an infill made of acrylonitrile butadiene styrene (ABS) is independent of how the plastic is cut up and assembled. It is well-known in the prior art how to make an infill using ABS with fused-deposition modeling (“FDM”). 
     SUMMARY OF THE INVENTION 
     In contrast, the structural integrity of the infill is dependent on the macroscopic properties of some materials. For example, the structural integrity of an infill made of fiber-reinforced thermoplastic filament is dependent on how the filament is cut up and assembled. In general, one structural advantage of a fiber-reinforced filament is diminished when the filament is cut, and, therefore, cuts are to be avoided when possible and should be strategically placed as addressed further herein. Put otherwise, longer uninterrupted fiber reinforced filament runs are generally stronger than shorter runs. Thus, for an article of manufacture having an edge or edges requiring extra strength, a long uninterrupted filament run is desirable along such edges. 
     As noted above, for some materials, such as ABS plastic, the discontinuity can be addressed by fusing the first and second segments together. But, for other materials, the mere act of cutting the filament significantly weakens the material by cutting internal reinforcing fibers, and fusing the various segments does not fix the problem as an aligned series of fused joints is susceptible to failure upon application of a shearing force. 
     Beyond the difficulties addressed advantageously by the related applications addressed above and elsewhere herein, a different class or type of problem is encountered by article geometries which require a filament to be cut or otherwise applied in a discontinuous manner as shown in  FIG. 1A . In  FIG. 1A , three filaments  10 ,  20 , and  30  are shown each having an internal reinforcing fiber or fibers represented by dashed lines. While represented by dashes, these fibers are typically long continuous fibers. In  FIG. 1A , the filaments  10 ,  20 , and  30  have been cut or otherwise deposited in a discontinuous manner and then fused in regions  14 ,  24 , and  34 , respectively. As these fused regions  14 ,  24 , and  34  do not include continuous internal reinforcing fibers they are weaker than the remainder of the filaments  10 ,  20  and  30 . As a result, a much smaller force F 1  is required to damage the aligned fused regions  14 ,  24 , and  34  than the force F 2  required to cause damage to the filaments  10 ,  20  and  30  where F 2  is applied along a length of filament  30  where continuous reinforcing fibers  32  help spread and dissipate that force. 
     In  FIG. 1B , regions  14 ′,  24 ′ and  34 ′ in filaments  10 ′,  20 ′ and  30 ′, respectively, have been moved so that that they no longer align. The separation of the regions  14 ′,  24 ′ and  34 ′ in the x-dimension is preferably at least a predetermined distance, d, where that spacing is possible. 
     While  FIGS. 1A and 1B  illustrate an advantageous solution to a problem in the xy plane, the present invention also provides an advantageous technique for generating a tool path to distribute starting and ending filament points across slices in the z-plane as well, as addressed further herein in connection with  FIG. 21 , for example. 
     Among its several aspects, the present invention recognizes as a general matter, when a number of filament strands end in a straight line or end near each other (see region  320  of  FIG. 3 , for an example), there is a seam which will be a weaker spot in the part. While a few simple shapes might have very long uninterrupted filament runs with few cuts, due to process or mechanical constraints, there will usually be some spots in a typical part where multiple filaments will have to end near each other. Instead of having them line up in a perfect seam, having them staggered as shown in  FIG. 1B  will provide an advantageous benefit. While a long continuous filament without a seam or cuts is preferable, this preferred end is difficult to achieve given the process and mechanical constraints of real world articles of manufacture. Such articles often have both long edges and short edges and one or more acute angles between such edges, as illustrated by an exemplary bicycle frame addressed herein. 
     As used herein, filament feathering is when the ends of tool paths defining runs of material, such as fiber reinforced filament, meet in a staggered pattern as addressed in further detail herein. One presently preferred fiber feathering approach addressed herein is an outcome of an edge-offsetting strategy flowing from a tool path generation technique to preserve filament continuity used to generate tool paths for material runs. 
     Embodiments of the present invention enable an article to be fabricated with fiber reinforced filament without some of the costs and disadvantages for doing so in the prior art. For example, some embodiments of the present invention deposit segments of filament in shapes and locations in which discontinuities would otherwise occur so that the number of aligned discontinuities, filament cuts, or other weak seams and the like are reduced. Furthermore, some embodiments of the present invention deposit segments of filament in shapes and locations so that the harmful effects of aligned discontinuance are at least partially eliminated. In general, this advantageous result is achieved by depositing the segments of filament employing filament feathering to carefully distribute the locations of filament beginnings and endings, cuts, or discontinuities, and the like. 
     Embodiments of the present invention are described in detail that enable the fabrication of a wide variety of articles of manufacture having a better balance of strength resulting from long uninterrupted lengths of filament where required without an excess of aligned filament cuts or discontinuities as addressed further herein. 
     A more complete understanding of the present invention, as well as further features and advantages of the invention, will be apparent from the following Detailed Description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  provide a simplified illustration of the type of problem presented by filament discontinuity and an application of filament feathering in accordance with the present invention to advantageously address this problem. 
         FIG. 2  depicts an illustration of the components of an additive manufacturing system  100  suitably adapted to provide fiber feathering in accordance with an illustrative embodiment of the present invention. 
         FIG. 3  illustrates a top view of a bicycle frame with material runs that illustrate a weak seam which would result if a print head could be ideally controlled to turn with a turning radius of zero. 
         FIG. 4  illustrates a top view of a single horizontal layer of a portion of a bicycle frame employing filament feathering printed with gaps in accordance with the present invention. 
         FIG. 5  illustrates a top view of a single horizontal layer of a portion of a bicycle frame employing filament feathering printed with overlaps in accordance with the present invention. 
         FIGS. 6A and 6B  further illustrate the differences between fiber feathering with gaps and overlaps, respectively. 
         FIG. 7  shows a top view of the entirety of the bicycle frame of  FIG. 4  with four long edges to illustrate an edge-offsetting strategy in accordance with the present invention. 
         FIG. 8A  shows a first offset edge. 
         FIG. 8B  shows a second offset edge. 
         FIG. 8C  shows a third offset edge. 
         FIG. 8D  shows a fourth offset edge. 
         FIG. 8E  shows a fifth offset edge. 
         FIGS. 9A and 9B  show the starting edges of a bicycle frame and a starting clipping outline of the bicycle frame, respectively. 
         FIGS. 10A and 10B  show offset edge one and clipping outline one side by side. 
         FIGS. 11A and 11B  show offset edge two and clipping outline two side by side. 
         FIGS. 12A and 12B  show offset edge three and clipping outline three side by side. 
         FIGS. 13A and 13B  show offset edge four and clipping outline four side by side. 
         FIGS. 14A and 14B  show offset edge five and clipping outline five side by side. 
         FIGS. 15A and 15B  show offset edge six and clipping outline six side by side. 
         FIGS. 16A and 16B  show offset edge seven and clipping outline seven side by side. 
         FIGS. 17A and 17B  show offset edge eight and clipping outline eight side by side. 
         FIGS. 18A and 18B  show offset edge nine and clipping outline nine, respectively, side by side. 
         FIG. 19  shows a process for filament feathering in accordance with the present invention. 
         FIG. 20  shows a process for edge-offsetting to implement slicing to preserve filament continuity in accordance with the present invention. 
         FIG. 21  shows a cross-sectional illustration of fiber reinforced filaments beginning and ending in a series of horizontal xy plane slices that have been further sliced in the z plane to illustrate distribution of the beginnings and endings in the z dimension in accordance with aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  depicts an illustration of the components of an exemplary additive manufacturing system  100  in accordance with the illustrative embodiments of the present invention. Additive manufacturing system  100  comprises: controller  101 , build chamber  102 , turntable  110 , deposition build plate  111 , robot  121 , deposition head  122 , filament conditioning unit  129 , filament source  130 , and thermoplastic filament  131 . The purpose of manufacturing system  100  is to fabricate articles of manufacture, such as illustrative article  151  of  FIG. 1 , as well as the article of  FIG. 7 , for example. It will be recognized that the teachings of the present invention are applicable to a wide range of articles of manufacture and the particular illustrations herein are exemplary. 
     Controller  101  comprises the hardware and software necessary to direct build chamber  102 , robot  121 , deposition head  122 , and turntable  110 , in order to fabricate the article  151  or other desired articles. In light of the present teachings, it will be clear to those skilled in the art how to make and use controller  101  to perform filament feathering and tool path generation to preserve filament continuity in additive manufacturing as addressed further in connection with  FIGS. 3-21  below. 
     Build chamber  102  is a thermally-insulated, temperature-controlled environment in which article  151  is fabricated. 
     Turntable  110  comprises a stepper motor—under the control of controller  101 —that is capable of rotating build plate  111  (and, consequently article  151 ) around the Z-axis (i.e., orthogonal to the build plate). In particular, turntable  110  is capable of:
         i. rotating build plate  111  clockwise around the Z-axis from any angle to any angle, and   ii. rotating build plate  111  counter-clockwise around the Z-axis from any angle to any angle, and   iii. rotating build plate  111  at varying rates, and as desired for a particular application, and   iv. maintaining (statically) the position of build plate  111  at any angle.       

     Build plate  111  is a platform comprising hardware on which article  151  is fabricated. Build plate  111  is configured to receive heated filament deposited by deposition head  122 . 
     Robot  121  is capable of depositing a segment of fiber-reinforced thermoplastic filament from any three-dimensional coordinate in build chamber  102  to any other three-dimensional coordinate in build chamber  102  with deposition head  122  at any approach angle. To this end, robot  121  comprises a multi-axis (e.g., six-axis, seven-axis, etc.), mechanical arm that is under the control of controller  101 . Software for controller  101  generates tool paths to generate feathering as addressed further herein. The mechanical arm comprises first arm segment  123 , second arm segment  124 , and third arm segment  125 . The joints between adjoining arm segments are under the control of controller  101 . A non-limiting example of robot  121  is the IRB 4600 robot offered by ABB. 
     The mechanical arm of robot  121  can move deposition head  122  in:
         i. the +X direction,   ii. the −X direction,   iii. the +Y direction,   iv. the −Y direction,   v. the +Z direction,   vi. the −Z direction, and   vii. any combination of i, ii, iii, iv, v, and vi,
 
while rotating the approach angle of deposition head  122  around any point or temporal series of points. While the present application is explained utilizing an x, y, z coordinate system, it will be appreciated the present teachings can be translated to other coordinate systems if desired. Further, while the robot  121  can be controlled as addressed above, it can also be more simply implemented and controlled more simply in an xy plane and then stepped up a step in the z plane, an operation sometimes referred to as 2.5D.
       

     Deposition head  122  comprises hardware that is under the control of controller  101  and that deposits fiber-reinforced thermoplastic filament  131 . Deposition head  122  is described in detail in pending United States patent applications:
         (i) Ser. No. 15/827,721, entitled “Filament Guide,” filed on Nov. 30, 2017;   (ii) Ser. No. 15/827,711, entitled “Filament Heating in 3D Printing Systems,” filed on Nov. 30, 2017;   (iii) Ser. No. 15/854,673, entitled “Alleviating Torsional Forces on Fiber-Reinforced Thermoplastic Filament,” filed on Dec. 26, 2017;   (iv) Ser. No. 15/854,676, entitled “Depositing Arced Portions of Fiber-Reinforced Thermoplastic Filament,” filed Dec. 26, 2017;
 
all of which are incorporated by reference in their entirety and particularly for the purpose of describing additive manufacturing system  100  in general, and deposition head  122  in particular. The following patent applications are incorporated by reference for their description of how to make and use additive manufacturing system  100 :
   U.S. patent application Ser. No. 15/438,559, filing date Feb. 21, 2017;   U.S. patent application Ser. No. 15/375,832, filing date Dec. 12, 2016;   U.S. patent application Ser. No. 15/232,767, filing date Aug. 9, 2016;   U.S. patent application Ser. No. 14/574,237, filing date Dec. 17, 2014; and   U.S. patent application Ser. No. 14/623,471, filing date Feb. 16, 2015.       

     Filament conditioning unit  129  comprises hardware that pre-heats filament  131  prior to deposition. 
     Filament  131  comprises a tow of reinforcing fibers that is substantially parallel to its longitudinal axis. In accordance with the illustrative embodiments, filament  131  comprises a cylindrical towpreg of contiguous 12K carbon fiber that is impregnated with thermoplastic resin. Thermoplastic filament  131  comprises contiguous carbon fiber, but it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which thermoplastic filament  131  has a different fiber composition. 
     It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which filament  131  comprises a different number of fibers (e.g., 1K, 3K, 6K, 24K, etc.). It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which the fibers in filament  131  are made of a different material (e.g., fiberglass, aramid, carbon nanotubes, etc.). 
     In accordance with the illustrative embodiments, the thermoplastic is, in general, a semi-crystalline polymer and, in particular, the polyaryletherketone (PAEK) known as polyetherketone (PEK). In accordance with some alternative embodiments of the present invention, the semi-crystalline material is the polyaryletherketone (PAEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetheretherketoneketone (PEEKK), or polyetherketoneetherketoneketone (PEKEKK). As those who are skilled in the art will appreciate after reading this specification, the disclosed annealing process, as it pertains to a semi-crystalline polymer in general, takes place at a temperature that is above the glass transition temperature, Tg. 
     In accordance with some alternative embodiments of the present invention, the semi-crystalline polymer is not a polyaryletherketone (PAEK) but another semi-crystalline thermoplastic (e.g., polyamide (PA), polybutylene terephthalate (PBT), poly(p-phenylene sulfide) (PPS), etc.) or a mixture of a semi-crystalline polymer and an amorphous polymer. 
     When the filament comprises a blend of an amorphous polymer with a semi-crystalline polymer, the semi-crystalline polymer can be one of the aforementioned materials and the amorphous polymer can be a polyarylsulfone, such as polysulfone (PSU), polyethersulfone (PESU), polyphenylsulfone (PPSU), polyethersulfone (PES), or polyetherimide (PEI). In some additional embodiments, the amorphous polymer can be, for example and without limitation, polyphenylene oxides (PPOs), acrylonitrile butadiene styrene (ABS), methyl methacrylate acrylonitrile butadiene styrene copolymer (ABSi), polystyrene (PS), or polycarbonate (PC). As those who are skilled in the art will appreciate after reading this specification, the disclosed annealing process, as it pertains to a blend of an amorphous polymer with a semi-crystalline polymer, takes place generally at a lower temperature than a semi-crystalline polymer with the same glass transition temperature; in some cases, the annealing process can take place at a temperature slightly below the glass transition temperature. 
     When the filament comprises a blend of an amorphous polymer with a semi-crystalline polymer, the weight ratio of semi-crystalline material to amorphous material can be in the range of about 50:50 to about 95:05, inclusive, or about 50:50 to about 90:10, inclusive. Preferably, the weight ratio of semi-crystalline material to amorphous material in the blend is between 60:40 and 80:20, inclusive. The ratio selected for any particular application may vary primarily as a function of the materials used and the properties desired for the printed article. 
     In some alternative embodiments of the present invention, the filament comprises a metal. For example, and without limitation, the filament can be a wire comprising stainless steel, Inconel® (nickel/chrome), titanium, aluminum, cobalt chrome, copper, bronze, iron, precious metals (e.g., platinum, gold, silver, etc.). 
     To design an article of manufacture, such as article  151  or a bicycle frame like the one shown in  FIG. 7 , a human designer uses a computer-aided-design system (e.g., Dassault Systemes SolidWorks®, etc.) to specify the desired spatial, structural, and other physical properties of the article of manufacture. The salient spatial features of a single slice of an article in the xy plane are depicted in  FIGS. 4-18B . The human designer and computer-aided-design system select an infill archetype for article  151 , and generate a fully-custom infill—based on the selected infill archetype—for article  151  that satisfies the structural and other physical properties with the adaptations and modifications addressed further below. 
     In accordance with the first illustrative embodiment, each segment in each layer has—after deposition—a thickness of 500 μm or 0.5 mm, and, therefore, each layer has a thickness of 0.5 mm. It will be clear to those skilled in the art, however, after reading this disclosure, how to make and use alternative embodiments of the present invention in which each segment in each layer has—after deposition—another thickness. Furthermore, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which one or more layers has a different thickness than one or more other layers. 
       FIG. 3  shows a slice in the xy plane of a part, a bicycle frame,  300  that is generated by creating concentric offset paths from the outline edges of the part  300 . The paths are shown as continuous through a sharp angle  310 , and at some point are not possible to print given current constraints which limit the printhead to a turning radius of about 20 mm. In  FIG. 3 , while long continuous material paths are shown, a large number of paths terminate into each other at a sharp angle. The fiber ends, such as end  325 , in region  320  all are in a straight line and would cause a weak seam in the part even if it was possible to print continuously through the sharp angle. Such a seam is weak since the sharp angle turn of the fibers within the filament does not allow much, if any, stress to get dissipated by the fibers. In accordance with the illustrative embodiments, article  300  is 81.3 cm by 45.7 cm by 2.0 cm. These dimensions are for a representative bike frame test part. It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention to manufacture actual bicycle frames having differing widths, lengths, and depths, such as 73 cm×58 cm×6.4 cm, as well as a wide variety of different articles as desired. 
     An alternative xy plane slice of a portion of an article or part  400  is shown in  FIG. 4 . By contrast, with  FIG. 3 ,  FIG. 4  shows an example of fiber feathering in accordance with the present invention applied to a part  400  which again may suitably be a bicycle frame. As addressed further below, the feathering in region  420  is a result of offsetting from some of the edges of the part, but not all the edges seen in the entire outline of the part. It is seen that the edges terminate into each other in a staggered fashion with gaps as illustrated in greater detail in  FIG. 6A . It will be noted that the filament segments shown in  FIGS. 6A and 6B  have fiber reinforcement which is not illustrated in these figures. 
     The section of the part  400  in region  420  is weaker than in some other regions but is better than having the edges all aligned in a single line as shown in  FIG. 3 . It will also be noticed in this image that there is a little bit of a gap between the path ends. In this embodiment, it has been chosen to have a gap instead of an overlap between two fibers. In this regard, it will be recognized that the heated filament will tend to spread so that any small gaps will tend to fill. In contrast, where overlaps are employed while gaps are eliminated any unevenness can possibly propagate upwards in the z-direction. 
       FIG. 5  shows an alternative feathering arrangement with overlaps and no gaps of an alternative part  500 . The feathering is seen in regions  520 ,  530  and  540  and the laps are most clearly seen in regions  530  and  540  and are further illustrated in  FIG. 6B . 
     There are pros and cons to both gaps and overlaps. Gaps are generally preferred because an overlap can cause excess material build up and thus result in issues in printing on top of them. With gaps, usually some excess material will fill in the voids as filament is deposited, but small gaps may still remain and the area filled only with spread without reinforcing fiber will still present a weaker area. 
       FIG. 7  shows a top view of the entirety of an xy slice of bicycle frame  700  portions  400  and  500  of which are shown in  FIGS. 4 and 5 . Consistent with a design goal of long uninterrupted edges, four long edges  702 ,  704 ,  706 , and  708  are identified. A portion of long edge  702  corresponds to a down tube of the bicycle frame  700 . Another portion comprises a bottom bracket. A portion of long edge  704  corresponds to a chainstay and a further portion comprises a seat tube. A portion of long edge  706  defines a top tube. 
     Toward the end of avoiding the problems illustrated in  FIG. 3 , for example, short edges  712 ,  714 , and  716  are identified and omitted as part of the design process to eliminate or reduce sharp corners and acute angle turns by the print head. Thus, when a first material run or edge path  702  is printed, it starts near omitted edge  716  and is cut or ended just before reaching omitted edge  712 . Similarly, second and third material runs or edge paths  704  and  706  begin and end near their respective omitted edges  712  and  714  and  714  and  716 , respectively. A fourth material run or edge path  708  can begin at a point such as point x 0    718  and end there as well. As discussed above, subsequent offset edges around void or opening  720  will be offset as shown in  FIG. 1B  and  FIG. 8A  starting and ending at an offset point x 1    818 , for example. As further shown in  FIG. 8E , a further offset edge surrounding void or opening  720  might start and end at point x 2    820 . 
     In  FIG. 8A , a first offset edge  801  is generated which is offset from edge material path or edge  708 . As a centerline of edge  708  is spaced a distance the width, w, of edge  708  divided by two from the part&#39;s intended edge, the centerline of offset edge  801  is 3w/2 from the intended edge. In  FIG. 8B , a second offset edge  803  is generated beside edge  704 . In  FIG. 8C , a third offset edge  805  is generated beside edge  706 . In  FIG. 8D , a fourth offset edge  807  is generated beside edge  702 . The process continues in  FIG. 8E  with a fifth offset edge  809  beside the first offset edge  801 . 
     As can be seen in  FIGS. 8A-8E  as each new edge is added, the edge gets clipped or otherwise ended just before it intersects with a previous edge that is already present. Examples of this clipping are when second offset edge  803  is added, it is clipped just before it reaches original edge  702 . Similarly, when fourth offset edge  807  is added, it is clipped as it intersects second offset edge  803  in region  840 . A result of this strategy is fiber feathering in areas  842  and  844  of  FIG. 8D , respectively. 
     To achieve the desired clipping, the present invention advantageously employs a clipping outline that is used to clip the edges to the correct size as addressed further herein. The present approach maintains a desired two dimensional polygon of the empty space remaining that can be filled with tool paths or material runs. As each edge is added, the clipping outline is updated with the empty space being reduced appropriately. The updated clipping outline is then used to clip the next edge that is added. As further edges are generated, the clipping outline is continually updated to maintain an accurate representation of the empty space left to be filled. The space remaining once all the edges are generated can be filled with an infill pattern or could be left empty depending upon design constraints regarding weight, strength, cost and the like. 
       FIG. 9A  shows starting edges  702 ,  704 ,  706 , and  708  for the bicycle frame  700  corresponding to those shown in  FIG. 7  alongside a starting clipping outline  900  having external edge  912  and internal edge  914  as shown in  FIG. 9B . Edge  912  surrounds the exterior of the desired bike frame and edge  914  surrounds void  720 . As the edges  702 ,  704 ,  706 , and  708  have a width, w, and are printed with a centerline inset a distance w/2, from where the actual edge of the bicycle frame is desired, the starting clip outline  900  is established at the actual edge of the bicycle frame as a frame of reference for the external starting edges and the edge around the void. 
     In  FIG. 10A , first offset edge  1002  is added with its center line 3w/2 from the intended edge of the bicycle frame, the clipping outline  914  is adjustably spaced in from the edge of the void resulting in a new clipping outline  1000  with a portion  1014  surrounding the void moved to a distance 2w from the edge of void  1006  and the other edges moved to a distance w from the intended external edge. The net effect of the first clipping outline is to rule out filament or material printing outside that outline which in turn is advantageously utilized to achieve the desired clipping and the feathering addressed in connection with  FIGS. 8B and 8D  above. 
     In  FIG. 11A , second offset edge  1102  is added beside existing starting edge  704 . In second clipping outline  1100  of  FIG. 11B , the clipping outline portion  1104  along edge  704  is now moved from w to a distance 2w from the intended bicycle frame edge. 
     Similarly, in  FIG. 12A , third offset edge  1202  is added in  FIG. 12A  beside existing starting edge  706 . In third clipping outline  1200  of  FIG. 12B , clipping outline portion  1204  along edge  706  is now moved from w to a distance 2w from the intended bicycle frame edge. 
     In  FIG. 13A , fourth offset edge  1302  is added beside existing starting edge  702 . In fourth clipping outline  1300  of  FIG. 13B , portion  1304  of the clipping outline along edge  702  is now moved from w to a distance 2w from the intended bicycle frame edge. 
     In  FIG. 14A , fifth offset edge  1402  is added beside first offset edge  1002  and starting edge  708 . In fifth clipping outline  1400  of  FIG. 14B , portion of clipping outline  1404  is now moved from 2w to 3w. 
     In  FIG. 15A , sixth offset edge  1502  is added beside second offset edge  1102  and starting edge  704 . In sixth clipping outline  1500  of  FIG. 15B , clipping outline portion  1504  is now moved from 2w to 3w. 
     In  FIG. 16A , seventh offset edge  1602  is added beside third offset edge  1202 . In the seventh clipping outline  1760  of  FIG. 16B , clipping outline portion  1604  is now moved from 2w to 3w. 
     In  FIG. 17A , eighth offset edge  1702  is added beside offset edge  1302  and starting edge  702 . In the eighth clipping outline  1700  of  FIG. 17B , portion of clipping outline  1704  is now moved from 2w to 3w. 
     Finally, in  FIG. 18A , ninth offset edge  1802  is added beside offset edges  1802 ,  1402 ,  1002  and starting edge  708 . Clipping outline  1800  as shown in  FIG. 18B  is generated. Looking at clipping outline  1800 , it is seen that the remaining space is largely concentrated in three voids  1810 ,  1812 , and  1814 . Depending upon the design parameters of the bicycle frame  700 , these voids might be left open or filled using a variety of infill techniques. 
     In the process and examples above, edge offsetting has been employed with turns being taken offsetting from each starting edge one by one. All of the tool paths and material runs illustrated are within one layer. Each edge gets a number of continuous paths offset from it until the part is finished. 
     It will be recognized that another suitable approach is to choose a single dominant edge and to continue offsetting as many paths as possible from it until the path gets broken up into smaller ones that are no longer either long or continuous. At that point, offsetting paths from the other non-dominant edges are started. More particularly, a predetermined length can be established and once that length is reached, then other edges can be offset from. 
     If after a first minimum length is reached, all the remaining edges have similar strength requirements, the alternating format discussed above in connection with  FIGS. 9A-18B  can be utilized. If all the remaining edges have differing strength requirements, the edge having the next highest strength demand can be utilized as the edge to offset from until the minimum length is again reached. 
     One reason it may be desired to employ the alternative approach is because more strength is desired along a particular edge which may be referred to as a dominant edge. The more long and continuous fiber reinforced filaments there are following that edge, the stronger that section of the part will be. 
     Once the ability is provided as taught herein to generate tool paths from a dominant edge, the edge which is the dominant edge may vary layer by layer as desired. Layers may be included in the design of an article of manufacture where all edges hold the same weight as addressed above in detail. Rotating between all of these options per layer or per second layers provides good overall strength in the part as all the layers stack up. Each layer would have a different contribution to the overall strength of the part due to the dominant edges that have more fiber paths. 
     It is further recognized that these approaches may be implemented in 2.5D, as well as, true 3D. 
     In accordance with one design of a bicycle frame, the number of layers L in the fully-custom infill for article  151  is based on the desired thickness of the article (i.e., 50 to 60 mm) and the thickness of each layer (i.e., 0.5 mm). In particular, the fully-custom infill for article  151 , in accordance with the first illustrative embodiment, comprises: 
                   L   =         50   -     60   ⁢           ⁢   mm         .5   ⁢           ⁢   mm       =     100   -     120   ⁢           ⁢   layers                 (     Eq   .           ⁢   1     )               
It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which the fully-custom infill comprises a different number of layers L.
 
     The radius r of the turns in all of the segments is equal to or greater than 20 mm 
                   r   ≥     ρ   2             (     Eq   .           ⁢   3     )               
It will be recognized alternative equipment might have a larger turning radius or that future equipment might have a smaller turning radius. Various turning radii can be readily adapted to given the teachings of the present invention.
 
       FIG. 19  shows a process of feathering  1900  in accordance with the present invention. In step  1902 , a first filament layout for an article of manufacture is determined without consideration of feathering. In step  1904 , an area or areas within the layout where weakness occurs are determined as a result of an alignment of filament ends, an alignment of acutely angled filament edges or the like. At step  1906 , a second filament layout applying feathering principles to reduce part weakness flowing from alignment of filament and the like is devised. In step  1908 , an article of manufacture is printed employing fiber reinforced filament and utilizing the second filament layout. Among the tools developed by the present invention to implement the process  1900 , techniques are provided to sort long edges from short edges. For example, straight edges of a potential tool path having a length greater than a predetermined length may be identified. More generally, edges having less than a maximum rate of curvature over a length greater than the predetermined length are identified. Acute angle turns along an exterior edge of a slice are also identified, as well as, the relationship of such identified acute angle turns to subsequent angles of redirected tool path movement. For example, a short edge may be identified as occurring over a distance less than a predetermined distance between a first acute and a subsequent angle less than a predetermined number of degrees. Any sufficiently short edge may be removed from the process of generating offset edges as addressed further above. 
       FIG. 20  shows a process of generating tool paths to preserve continuity of fiber reinforced filaments  2000  in accordance with the present invention. In step  2002 , a clipping outline comprising a two dimensional polygon for a part to be printed is established. This clipping outline maintains a record of the empty space that can be filled with material paths or runs. If the cross-section of the desired three dimensional part varies, the clipping outline for each side will be varied to reflect such variation as needed. 
     In step  2004 , a first edge, a material run, is added utilizing the clipping outline to clip the first edge when another edge in the clipping outline is reached. For example, when edge  704  reaches the portion of clipping outline  912  corresponding to omitted edge  712 . 
     In step  2006 , the clipping outline is updated to reflect the space remaining after the first edge is added in step  2004 . 
     In step  2008 , a second edge is added utilizing the updated clipping outline from step  2006  to clip the second edge. 
     In step  2010 , the clipping outline is updated to reflect the space remaining after the second edge is added. 
     In step  2012 , the process is repeated until all needed edges have been added. 
     The presently preferred approach to generating tool paths to prevent weak spots as a result of the alignment of material run starts and stops can advantageously also be applied in the z dimension, as well as the xy plane. For cyclic paths which repeat across slices, it is not desirable to have all the start and end points line up across all or multiple layers in the part. As was the case in the xy plane, such alignment would cause a weak seam in the part where it is more likely to fail. As seen in  FIG. 21 , starts s 1 , s 2 , s 3 , s 4  . . . s n-1  and ends e 1 , e 2 , e 3 , e 4  . . . e n-1  and e n  are shown for layers or slices I 1 , I 2 , I 3 , I 4  . . . I n-1  and I n .  FIG. 21  shows a cross-section or slice in the z-dimension to illustrate in broad terms, a distribution of starts and stops across layers or slices of the bike frame  700 . 
     To address the issue, an algorithm has been implemented to distribute the starts of cyclic paths. Another constraint utilized is that it is much less desirable to start or end a path on a curve. So, in addition to distributing the starts, it is desirable to put them in locations where the filament will be relatively straight. Consequently, all of the straight segments of a path are first identified. After identifying these regions, the path is analyzed looking for a starting point that is at least a predetermined distance away from all the other start points that have been determined so far. This distance is advantageously a user established parameter. When checking if a point is far enough away from other points, the algorithm has been designed to only look a certain number of layers below the current layer. This number is again a user selectable parameter. Once a suitable start point is established the array of points defining the tool path is rotated so the path starts at the point. It is possible that no ideal starting point can be found, in which case, a random location can be selected. It will be recognized an alternative approach can be employed in which constraints are gradually loosened until a point meeting the loosened constraints is picked. 
     For the user selectable parameters, a minimum separation of 5-40 mm and 2-5 layers down are possible ranges to be selectable from. 
     It is to be understood that the above-described embodiments are merely illustrative of the present invention and that many variations of the above-described embodiments can be devised by those skilled in the art without departing from the scope of the invention. It is therefore intended that such variations be included within the scope of the following claims and their equivalents. 
     For example, while the present invention is described in the context of presently preferred systems and materials, it will be recognized that these systems and materials are likely to evolve with time and that the disclosed solutions to problems are generally applicable to additive manufacturing contexts, where these problems arise. 
     Also, while many of the originally filed claims are directed to articles of manufacture, it will be understood that machines and processes are described herein and may also be claimed by this application or a continuation hereof.