Abstract:
A method for building a three-dimensional part, the method comprising providing a printed three-dimensional part and support structure, where the support structure comprises at least two polymers having different glass transition temperatures. The method also comprises annealing the three-dimensional part.

Description:
BACKGROUND 
       [0001]    The present disclosure is directed to additive manufacturing techniques for printing three-dimensional (3D) parts. In particular, the present disclosure relates to an additive manufacturing process for printing 3D parts and support structures with extrusion-based additive manufacturing systems. 
         [0002]    An extrusion-based additive manufacturing system is used to print a 3D part or model from a digital representation of the 3D part in a layer-by-layer manner by extruding a flowable part material. The part material is extruded through an extrusion tip carried by a print head, and is deposited as a sequence of roads on a substrate in an x-y plane. The extruded part material fuses to previously deposited modeling material, and solidifies upon a drop in temperature. The position of the print head relative to the substrate is then incremented along a z-axis (perpendicular to the x-y plane), and the process is then repeated to form a 3D part resembling the digital representation. 
         [0003]    Movement of the print head with respect to the substrate is performed under computer control, in accordance with build data that represents the 3D part. The build data is obtained by initially slicing the digital representation of the 3D part into multiple horizontally sliced layers. Then, for each sliced layer, the host computer generates a tool path for depositing roads of the part material to print the 3D part. 
         [0004]    In fabricating 3D parts by depositing layers of a part material, supporting layers or structures are typically built underneath overhanging portions or in cavities of objects under construction, which are not supported by the part material itself. A support structure may be built utilizing the same deposition techniques by which the part material is deposited. The host computer generates additional geometry acting as a support structure for the overhanging or free-space segments of the 3D part being formed. Support material is then deposited from a second extrusion tip pursuant to the generated geometry during the build process. The support material adheres to the part material during fabrication, and is removable from the completed 3D part when the build process is complete. 
       SUMMARY 
       [0005]    An aspect of the present disclosure is directed to a method for printing a three-dimensional part with an extrusion-based additive manufacturing system. The method includes printing a support structure from a support material with the extrusion-based additive manufacturing system using a layer-based additive manufacturing technique, where the support material includes at least two polymers having different glass transition temperatures and that are substantially immiscible with each other. The method also includes, in coordination with the printing of the support structure, printing the three-dimensional part from a part material with the extrusion-based additive manufacturing system using the layer-based additive manufacturing technique. The method further includes heating the printed support structure and the printed three-dimensional part to at least one temperature that is above a glass transition temperature of the part material, and that is below a glass transition temperature of at least one of the polymers of the support material, and cooling the heated support structure and the heated three-dimensional part. 
         [0006]    Another aspect of the present disclosure is directed to a method for building a three-dimensional part. The method includes providing a three-dimensional part and a support structure, where the three-dimensional part is printed from a part material using a layer-based additive manufacturing technique, and where the support structure is printed from a support material in coordination with the three-dimensional part using the layer-based additive manufacturing technique. The support material includes a first polymer having a first glass transition temperature, and a second polymer that is substantially immiscible with the first polymer, the second polymer having a second glass transition temperature that is higher than the first glass transition temperature of the first polymer. The method also includes heating the provided three-dimensional part and the support structure to at least one temperature that is above a glass transition temperature of the part material, that is above the first glass transition temperature of the first polymer of the support material, and that is below the second glass transition temperature of the second polymer of the support material. The method further includes cooling the heated three-dimensional part and the heated support structure. 
         [0007]    Another aspect of the present disclosure is directed to a method for printing a three-dimensional part with an extrusion-based additive manufacturing system, where the method includes providing a support material to the extrusion-based additive manufacturing system, the support material including a first polymer having a first glass transition temperature and a second polymer having a second glass transition temperature. The method also includes providing a part material to the extrusion-based additive manufacturing system, the part material having a glass transition temperature that is less than the second glass transition temperature of the second polymer of the support material. The method further includes heating a build environment of the extrusion-based additive manufacturing system to at least one temperature that is above the glass transition temperature of the part material, that is above the first glass transition temperature of the first polymer of the support material, and that is below the second glass transition temperature of the second polymer of the support material. The method even further includes printing a support structure in the heated build environment from the support material in coordination with printing the three-dimensional part in the heated build environment from the part material, and cooling the printed support structure and the printed three-dimensional part. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a front view of an extrusion-based additive manufacturing system configured to print 3D parts and support structures. 
           [0009]      FIG. 2  is a perspective view of a 3D part and support structure printed with the extrusion-based additive manufacturing system, where the support structure partially encapsulates the 3D part. 
           [0010]      FIGS. 3A-3C  are sectional views of Section  3 A- 3 A taken in  FIG. 2 , depicting a printing and annealing process for building the 3D part and support structure. 
           [0011]      FIGS. 4A-4D  are alternative sectional views of Section  3 A- 3 A taken in  FIG. 2 , depicting an alternative printing and annealing process for building the 3D part and support structure. 
           [0012]      FIG. 5  is a graphical illustration of a first temperature profile for printing and annealing a 3D part and support structure, where the 3D part and support structure are printed and annealed in a single back-to-back process. 
           [0013]      FIG. 6  is a graphical illustration of a second temperature profile for printing and annealing a 3D part and support structure, where the 3D part and support structure are printed and annealed in separate processes that are separated by a cooling step. 
           [0014]      FIG. 7  is a graphical illustration of a third temperature profile for printing and annealing a 3D part and support structure, where the 3D part and support structure are printed and annealed in a simultaneous manner. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The present disclosure is directed to a process for printing a 3D part and support structure, where the support structure at least partially encapsulates the 3D part. The support structure is printed from a support material that compositionally includes at least two polymers having different glass transition temperatures. For example, the support material may include a low-temperature polymer and a high-temperature polymer, where the different polymers are desirably immiscible with each other. Correspondingly, the 3D part is printed from a part material that compositionally includes a polymer having a glass transition temperature, where the glass transition temperature of the part material is lower than a glass transition temperature of at least one of the polymers of the support material. For example, the part material may have a glass transition temperature that is lower than a glass transition temperature of the high-temperature polymer of the support material. 
         [0016]    The process also involves an annealing cycle, in which the 3D part and support structure are heated to one or more temperatures that are above the glass transition temperature of the part material, but that are below the glass transition temperature of at least one of the polymers of the support material (e.g., below the glass transition temperature of the high-temperature polymer of the support material). In a first embodiment, the annealing cycle is performed after the 3D part and support structure are printed. In a second embodiment, at least a portion of the annealing cycle may be performed while the 3D part and the support structure are being printed. As discussed below, the annealing cycles are suitable for enhancing interlayer bonding; increasing part strength, elongation, and toughness; reducing porosity; and providing transparent and/or translucent properties. 
         [0017]    Unless otherwise indicated, the singular form of “polymer” herein refers to a polymer composition rather than a single polymer molecule. For example, a part material that compositionally includes a first polymer and a second polymer includes one or more polymer molecules of a first polymer composition and one or more polymer molecules of a second polymer composition. Furthermore, the terms “about” and “substantially” are used herein with respect to measurable values and ranges due to expected variations known to those skilled in the art (e.g., limitations and variabilities in measurements). All temperatures referred to herein are based on atmospheric pressure (i.e. one atmosphere). 
         [0018]      FIG. 1  illustrates system  10 , which is example of a suitable extrusion-based additive manufacturing system for building 3D parts and support structures pursuant to the process of the present disclosure. System  10  includes build chamber  12 , platen  14 , gantry  16 , print head  18 , and supply sources  20  and  22 . Examples of suitable systems for system  10  include extrusion-based additive manufacturing systems, such as those commercially available by Stratasys, Inc., Eden Prairie, Minn. under the trademarks “FUSED DEPOSITION MODELING” and “FDM”. 
         [0019]    Build chamber  12  contains platen  14 , gantry  16 , and print head  18  for printing a 3D part (referred to as 3D part  24 ) and a corresponding support structure (referred to as support structure  26 ). The environment within build chamber  12 , at least in the region of 3D part  24  and support structure  26 , may be heated to one or more temperatures while printing 3D part and support structure  26 . For example, build chamber  12  may be heated to, and maintained at, one or more temperatures that are in a window between the solidification temperature and the creep relaxation temperature of the part material and/or the support material. This reduces the risk of mechanically distorting (e.g., curling) 3D part  24  and support structure  26 , where the creep relaxation temperature of the part material is proportional to the glass transition temperature of the part material. Examples of suitable techniques for determining the creep relaxation temperatures of the part and support materials are disclosed in Batchelder et al., U.S. Pat. No. 5,866,058. 
         [0020]    Additionally, the environment within build chamber  12 , at least in the region of 3D part  24  and support structure  26 , may be heated to one or more elevated temperatures to anneal 3D part  24 . As discussed below, this involves heating the environment within build chamber  12 , at least in the region of 3D part  24  and support structure  26 , to one or more temperatures above the glass transition temperature of the part material of 3D part  24 . 
         [0021]    Platen  14  is a platform on which 3D part  24  and support structure  26  are built, and desirably moves along a vertical z-axis based on signals provided from computer-operated controller  28 . Gantry  16  is a guide rail system that is desirably configured to move print head  18  in a horizontal x-y plane within build chamber  12  based on signals provided from controller  28 . The horizontal x-y plane is a plane defined by an x-axis and a y-axis (not shown in  FIG. 1 ), where the x-axis, the y-axis, and the z-axis are orthogonal to each other. In an alternative embodiment, platen  14  may be configured to move in the horizontal x-y plane within build chamber  12 , and print head  18  may be configured to move along the z-axis. Other similar arrangements may also be used such that one or both of platen  14  and print head  18  are moveable relative to each other. 
         [0022]    Print head  18  is supported by gantry  16  for printing 3D part  24  and support structure  26  on platen  14  in a layer-by-layer manner, based on signals provided from controller  28 . In the embodiment shown in  FIG. 1 , print head  18  is a dual-tip extrusion head configured to deposit part and support materials from supply source  20  and supply source  22 , respectively. Examples of suitable extrusion heads for print head  18  include those disclosed in Crump et al., U.S. Pat. No. 5,503,785; Swanson et al., U.S. Pat. No. 6,004,124; LaBossiere, et al., U.S. Pat. No. 7,604,470; Leavitt, U.S. Pat. No. 7,625,200; and U.S. patent application Ser. No. 12/976,111, entitled “Print Head Assembly For Use In Fused Deposition Modeling Systems”. Furthermore, system  10  may include a plurality of print heads  18  for depositing part and/or support materials from one or more tips. 
         [0023]    The part material is supplied to print head  18  from supply source  20  via feed line  28 , thereby allowing print head  18  to deposit the part material to print 3D part  24 . Correspondingly, the support material is supplied to print head  18  from supply source  30  via feed line  30 , thereby allowing print head  18  to deposit the support material to print support structure  26 . 
         [0024]    The part and support materials may be provided to system  10  in a variety of different media. Commonly, the materials may be supplied in the forms of continuous filaments. For example, in system  10 , the part and support materials may be provided as continuous filament strands fed respectively from supply sources  20  and  22 , as disclosed in Swanson et al., U.S. Pat. No. 6,923,634; Comb et al., U.S. Pat. No. 7,122,246; Taatjes et al, U.S. Patent Application Publication Nos. 2010/0096485 and 2010/0096489; and Swanson et al., U.S. Patent Application Publication No. 2010/0283172. Examples of suitable average diameters for the filament strands of the part and support materials range from about 1.27 millimeters (about 0.050 inches) to about 3.0 millimeters (about 0.120 inches). 
         [0025]    As shown, print head  18  includes drive mechanisms  32  and  34 , and liquefier assemblies  36  and  38 . During a print operation, gantry  16  moves print head  18  around in the horizontal x-y plane within build chamber  12 , and drive mechanisms  32  and  34  are directed to intermittently feed the part and support materials from supply sources  20  and  32  through liquefier assemblies  36  and  38 . 
         [0026]    Examples of suitable drive mechanisms for drive mechanisms  32  and  34 , and liquefier assemblies for liquefier assemblies  36  and  38  include those disclosed in Crump et al., U.S. Pat. No. 5,503,785; Swanson et al., U.S. Pat. No. 6,004,124; LaBossiere, et al., U.S. Pat. Nos. 7,384,255 and 7,604,470; Leavitt, U.S. Pat. No. 7,625,200; Batchelder et al., U.S. Pat. No. 7,896,209; and U.S. patent application Ser. No. 12/976,111, entitled “Print Head Assembly For Use In Fused Deposition Modeling Systems”. In alternative embodiments, print head  18  may function as a multiple-stage screw pump, as disclosed in Batchelder et al., U.S. Pat. No. 5,764,521; and Skubic et al., U.S. Pat. No. 7,891,964. 
         [0027]    The received part and support materials are deposited onto platen  14  to print 3D part  24  in coordination with the printing of support structure  26  using a layer-based additive manufacturing technique. As shown in  FIG. 2 , 3D part  24  is printed as a series of successive layers of the part material, and support structure  26  is printed as a series of successive layers of the support material in coordination with the printing of 3D part  24 . 
         [0028]    3D part  24  is an example of a simple block-shaped part having top surface  40 , four lateral surfaces (not shown in  FIG. 2 ), and a bottom surface (not shown in  FIG. 2 ). Support structure  26  is desirably deposited to at least partially encapsulate the layers of 3D part  24 . For example, support structure  26  may be printed to encapsulate the lateral surfaces and the bottom surface of 3D part  24 , as shown. 
         [0029]    In alternative examples, system  10  may print 3D parts having a variety of different geometries. In these examples, system  10  may also print corresponding support structures that at least partially encapsulate the 3D parts, such as at the lateral surfaces and the bottom surfaces of the 3D parts. In such examples, a part orientation may be selected such that the un-encapsulated top surface is the least significant part surface. Additionally, the support structures may provide vertical support along the z-axis for any overhanging regions of the layers of the 3D parts, allowing the 3D parts to be built with a variety of geometries. 
         [0030]      FIGS. 3A-3C  illustrate the process of the present disclosure for printing and annealing 3D part  24  and support structure  26  with system  10 . While the process is described herein with reference to 3D part  24  and support structure  26 , the process is also suitable for printing and annealing 3D parts and support structures having a variety of geometries. As shown in  FIG. 3A , each layer of 3D part  24  is printed in a series of layers  42  to define the geometry of 3D part  24 , having top surface  40 , lateral surfaces  44 , and bottom surface  46 . 
         [0031]    As discussed above, 3D part  24  is printed from a part material that compositionally includes a polymer having a glass transition temperature T g (p). Examples of suitable part materials include thermoplastic materials, such as acrylonitrile-butadiene-styrene (ABS) copolymers, polycarbonates, polysulfones, polyethersulfones, polyphenylsulfones, polyetherimides, polyamides modified variations thereof (e.g., ABS-M30 copolymers), polystyrene, polypropylenes, copolyesters, and blends thereof. 
         [0032]    In some embodiments, the part material may also includes one or more additives, such as plasticizers, rheology modifiers, inert fillers, colorants, stabilizers, and combinations thereof. In embodiments in which the part material includes additional additives, examples of suitable combined concentrations of the additional additives in the part material range from about 1% by weight to about 10% by weight, with particularly suitable concentrations ranging from about 1% by weight to about 5% by weight, based on the entire weight of the part material. 
         [0033]    Each layer of support structure  26  is printed in a series of layers  48  in coordination with the printing of layers  42  of 3D part  24 , where the printed layers  48  of support structure  26  encapsulate lateral surfaces  44  and bottom surface  46  of 3D part  24 . In the shown example, however, top surface  40  is not encapsulated by layers  48  of support structure  26 . Additionally, in the shown embodiment, the layer-based additive manufacturing technique used to print layers  42  and  48  is performed to provide layers  42  and  48  having substantially the same layer thicknesses. In an alternative embodiment, the layer-based additive manufacturing technique prints multiple layers  48  for each layer  42 , such that the layer thicknesses of each layer  48  is thinner than the layer thicknesses of each layer  42 , as disclosed in Zinniel et al., U.S. Pat. No. 7,236,166. 
         [0034]    As also discussed above, support structure  26  is printed from a support material that compositionally includes at least two polymers having different glass transition temperatures, and that maybe substantially immiscible with each other to provide a heterogeneous polymer blend. For example, the support material may include one or more low-temperature polymers that are substantially miscible with each other, and one or more high-temperature polymers that are miscible or substantially miscible with each other, where the low-temperature polymer(s) are desirably immiscible with the high-temperature polymer(s). 
         [0035]    For ease of discussion, the support material will be referred to as including a low-temperature polymer having a first glass transition temperature T g (s 1 ), and a high-temperature polymer having a second glass transition temperature T g (s 2 ), where the low-temperature polymer and the high-temperature polymer are substantially immiscible with each other, and where T g (s 2 ) is greater than T g (s 1 ). However, the support material may alternatively include multiple low-temperature polymers that are substantially miscible with each other to provide the first glass transition temperature T g (s 1 ) as an average of the individual glass transition temperatures of the multiple low-temperature polymers. Similarly, the support material may also alternatively include multiple high-temperature polymers that are substantially miscible with each other to provide the second glass transition temperature T g (s 2 ) as an average of the individual glass transition temperatures of the multiple high-temperature polymers. 
         [0036]    Examples of suitable differences between the first glass transition temperature T g (s 1 ) of the low-temperature polymer and the second glass transition temperature T g (s 2 ) of the high-temperature polymer include temperature differences of at least about 10° C., more desirably by at least about 20° C. In one embodiment, the second glass transition temperature T g (s 2 ) of the high-temperature polymer is greater than the first glass transition temperature T g (s 1 ) of the low-temperature polymer by a temperature difference ranging from about 25° C. to about 50° C. In another embodiment, the second glass transition temperature T g (s 2 ) of the high-temperature polymer is greater than the first glass transition temperature T g (s 1 ) of the low-temperature polymer by a temperature difference ranging from about 35° C. to about 50° C. 
         [0037]    Additionally, as discussed above, the glass transition temperature T g (p) of the part material is lower than the second glass transition temperature T g (s 2 ) of the high-temperature polymer of the support material. In some embodiments, the glass transition temperature T g (s 1 ) of the low-temperature polymer may be the same as or similar to the glass transition temperature T g (p) of the part material. Examples of suitable differences between the glass transition temperature T g (p) of the part material and the first glass transition temperature T g (s 1 ) of the low-temperature polymer include temperature differences less than about 30° C., and more desirably less than about 20° C. 
         [0038]    Suitable support materials for building support structure  26  include blends of amorphous thermoplastic polymers, where the low-temperature polymer(s) and the high-temperature polymer(s) are desirably immiscible with each other to provide a heterogeneous polymer blend. Furthermore, suitable support materials may be soluble or at least partially soluble in water and/or an aqueous alkaline solution, which is suitable for removing support structure  26  in a convenient manner without damaging 3D part  24 . 
         [0039]    Examples of suitable low-temperature polymers for use in the support material include materials commercially available under the trademarks “SR10”, “SR20”, and “SR30” Soluble Supports from Stratasys, Inc., Eden Prairie, Minn.; and those disclosed in Lombardi et al., U.S. Pat. Nos. 6,070,107 and 6,228,923; Priedeman et al., U.S. Pat. Nos. 6,790,403 and 7,754,807; and Hopkins et al., U.S. Patent Application Publication No. 2010/0096072. 
         [0040]    Examples of suitable high-temperature polymers for use in the support material include acrylate and acrylic-acid based materials, such as copolymers polymerized from monomers of carboxylic acids (e.g., acrylic acid and methacrylic acid), ionic salts of carboxylic acids (e.g., neutralized salts of acrylic acid and/or methacrylic acid), alkyl acrylates (e.g., methyl acrylate), alkyl methacrylates (e.g., methyl methacrylate), and combinations thereof. Such copolymers may have number-average molecular weights ranging from about 100,000 grams/mole to about 150,000 grams/mole. 
         [0041]    Suitable weight ratios of the high-temperature polymer(s) to the low-temperature polymer(s) in the support material may vary depending on the particular polymers used. The high-temperature polymer(s) desirably constitute at least about 33% by weight of the support material, and the low-temperature polymer(s) desirably constitute at least about 33% by weight of the support material. In some embodiments, the support material includes from about 50% by weight to about 75% by weight of the high-temperature polymer(s), and from about 25% by weight to about 50% by weight of the low-temperature polymer(s). Examples of suitable weight ratios of the high-temperature polymer(s) to the low-temperature polymer(s) range from about 1:3 to about 4:1, more desirably from about 1:1 to about 3:1, and even more desirably from about 3:2 to about 3:1. 
         [0042]    After the print operation is complete, 3D part  24  and support structure  26  may then undergo an annealing cycle. As discussed below, this involves increasing the temperature of the environment within build chamber  12 , at least in the region of 3D part  24  and support structure  26 , to one or more elevated temperatures that are above the glass transition temperature T g (p) of the part material, that are above the glass transition temperature T g (s 1 ) of the low-temperature polymer of the support material, and that are below the glass transition temperature T g (s 2 ) of the high-temperature polymer of the support material. 
         [0043]    As shown in  FIG. 3B , the elevated temperature within build chamber  12  allows the part material of layers  42  to flow and conform to the dimensions of support structure  26 . The low-temperature polymer of support structure  26  also softens under the elevated temperature. However, the high-temperature polymer of support structure  26  maintains its modulus, and hence its shape, at the elevated temperature. The immiscibility of the different polymers of the support material creates a matrix of the high-temperature polymer in the softened low-temperature polymer. In this manner, the low-temperature polymer may function as a flexibilizer for the high-temperature polymer, reducing the brittleness of support structure  26 . 
         [0044]    After maintaining build chamber  12  at the elevated temperature for a suitable duration, the temperature may be gradually reduced along a temperature profile to cool and solidify 3D part  24 . The reflowing and cooling of the part material accordingly reduces porosity in 3D part  24 , increases interlayer bonding, and produces isotropic properties. This may accordingly increase the strength, elongation, toughness, and modulus of 3D part  24 . Additionally, in embodiments in which the part material compositionally includes a clear polymer, 3D part  24  may exhibit transparent and/or translucent properties. Such transparent/translucent properties are typically unattainable with extrusion-based additive manufacturing systems due to the road-based layers and porosity that are produced, which otherwise scatter any penetrating light. 
         [0045]    As shown in  FIG. 3C , after the annealing cycle is completed, the resulting 3D part  24 /support structure  26  may be removed from build chamber  12 , and support structure  26  may be removed from 3D part  24 . For example, in embodiments in which the support material is at least partially soluble in water or an aqueous alkaline solution, the resulting 3D part  24 /support structure  26  may be immersed in water and/or an aqueous alkaline solution bath to dissolve support structure  26  apart from 3D part  24 . The resulting 3D part  24  accordingly exhibits bulk, isotropic properties, with dimensions corresponding to the encapsulation dimensions of support structure  26  prior to removal. 
         [0046]      FIGS. 4A-4D  illustrate an alternative process of the present disclosure for printing and annealing 3D parts and support structures with system  10  (shown in  FIG. 1 ), where corresponding reference labels are increased by “100”. As shown in  FIG. 4A , 3D part  124  may be printed in the same manner as discussed above for 3D part  24  with layers  142 , and includes top surface  140 , lateral surfaces  144 , and bottom surface  146 . Similarly support structure  126  may be printed in the same manner as discussed above for support structure  26  with layers  148 . 
         [0047]    However, in this example, support structure  126  also partially encapsulates top surface  140 , providing sprue hole  150 . After the print operation is complete, 3D part  124  and support structure  126  may then undergo an annealing cycle. This involves increasing the temperature of the environment within build chamber  12 , at least in the region of 3D part  124  and support structure  126 , to one or more elevated temperatures that are above the glass transition temperature T g (p) of the part material, that are above the glass transition temperature T g (s 1 ) of the low-temperature polymer of the support material, and that are below the glass transition temperature T g (s 2 ) of the high-temperature polymer of the support material. 
         [0048]    As shown in  FIG. 4B , the elevated temperature within build chamber  12  allows the part material of roads  140  to flow and conform to the dimensions of support structure  126 . The low-temperature polymer of support structure  126  also softens under the elevated temperature. However, the high-temperature polymer of support structure  126  maintains its modulus, and hence its shape, at the elevated temperature, as discussed above. 
         [0049]    After maintaining build chamber  12  at the elevated temperature for a suitable duration, the temperature may be gradually reduced along a temperature profile to cool and solidify 3D part  124 . In comparison to 3D part  24  as shown in  FIG. 3B , in some situations, the part material may contract and shrink upon cooling, thereby reducing the dimensions of 3D part  124 . This is illustrated by top surface  140  being located below the overhanging top surface of support structure  126 . 
         [0050]    To compensate for this shrinkage of 3D part  124 , print head  18  may extrude additional amounts of the part material through spue hole  150 , as illustrated by arrow  152 . This additional extrusion may be performed during the heating portion of the annealing cycle, while build chamber  12  is maintained at the elevated temperature, and/or during the subsequent cooling portion of the annealing cycle. 
         [0051]    As shown in  FIG. 4C , the additional extrusion may fill in any voids between 3D part  124  and support structure  126  to attain the originally desired dimensions for 3D part  124 . As discussed above, the annealing cycle accordingly reduces porosity in 3D part  124 , increases interlayer bonding, and produces isotropic properties. 
         [0052]    As shown in  FIG. 4D , after the annealing cycle is completed, the resulting 3D part  124 /support structure  126  may be removed from build chamber  12 , and support structure  126  may be removed from 3D part  124 . The resulting 3D part  124  accordingly exhibits bulk, isotropic properties, with dimensions corresponding to the encapsulation dimensions of support structure  126  prior to removal. 
         [0053]      FIGS. 5-7  illustrate example heating and cooling profiles for printing and annealing 3D parts and support structures with system  10  (shown in  FIG. 1 ).  FIG. 5  illustrates profile  200 , which is a suitable profile for printing and annealing 3D parts entirely within build chamber  12  a single back-to-back process. As shown, profile  200  includes segment  202 , during which build chamber  12  is heated and maintained at one or more temperatures that are in a window between the solidification temperature T s (p) of the part material and the creep relaxation temperature T c (p) of the part material for performing the print operation to build the 3D part and support structure. As discussed above, the support structure is printed to at least partially encapsulate the 3D part. 
         [0054]    After the print operation is completed, build chamber  12  may then heated to one or more elevated temperatures over a heating ramp profile, as depicted by segment  204 . Examples of suitable heating ramp ramp profiles for segment  202  include temperature increases ranging from about 5° C./minute to about 20° C./minute. As discussed above, the elevated temperature of build chamber  12  is above the glass transition temperature T g (p) of the part material and below the second glass transition temperature T g (s 2 ) of the high-temperature polymer of the support material, as illustrated by segment  206 . Additionally, the elevated temperature of build chamber  12  is also above the second glass transition temperature T g (s 1 ). 
         [0055]    Build chamber  12  may be maintained at the elevated temperature for a suitable duration to allow the part material of the 3D part to flow and conform to the dimensions of the support structure. The suitable duration may vary depending on the relative values between the elevated temperature of build chamber  12  and the glass transition temperature T g (p) of the part material, and on the dimensions of the 3D part and the support structure. Additionally, the elevated temperature and the suitable duration are desirably selected to be low and short enough to prevent the part material from thermally degrading. Examples of suitable durations for segment  206  range from about 30 minutes to about 10 hours. In some embodiments, suitable durations for segment  206  range from about 2 hours to about 5 hours. 
         [0056]    As illustrated by segments  208 ,  210 , and  212 , the temperature within build chamber  12  may then be gradually reduced along a cool ramp profile to cool and solidify the 3D part. For example, as indicate by segment  208 , the temperature may be reduced at a suitable rate until an intermediate temperature is reached. Examples of suitable cooling ramp profiles for segment  208  include temperature decreases ranging from about 5° C./minute to about 15° C./minute. 
         [0057]    The intermediate temperature is desirably below the glass transition temperature T g (p) of the part material (e.g., at the creep relaxation temperature T c (p) of the part material). As indicated by segment  210 , build chamber  12  may be maintained at the intermediate temperature to allow the part material to slowly cool with reduced levels of distortion (e.g., curl). As indicated by segment  212 , the temperature within build chamber  12  may then be gradually reduced along an additional cooling ramp profile to cool and solidify 3D part  24  down below the solidification temperature T s (p) of the part material (e.g., down to 25° C.). Examples of suitable cooling ramp profiles for segment  212  include temperature decreases ranging from about 5° C./minute to about 15° C./minute. 
         [0058]    While illustrated with a single intermediate temperature step at segment  210 , profile  200  may alternatively include multiple intermediate temperature steps, as desired. After the annealing cycle is completed, the resulting 3D part and support structure may be removed from build chamber  12 , and the support structure may be removed from the 3D part. As discussed above, the reflowing and cooling of the part material reduces porosity in the 3D part, increases interlayer bonding, and produces isotropic properties. This may accordingly increase the strength, elongation, toughness, and modulus of the 3D part. Additionally, in embodiments in which the part material compositionally includes a clear polymer, the 3D part may exhibit transparent and/or translucent properties. 
         [0059]      FIG. 6  illustrates profile  300 , which is also a suitable profile for printing and annealing 3D parts either entirely or partially within build chamber  12 . As shown, profile  300  includes segments  302 - 316 , where the steps of segments  302 ,  306 ,  308 ,  310 , and  312  may be performed in the same manner as discussed above for steps for segments  202 ,  206 ,  208 ,  210 , and  212  of profile  200  (shown in  FIG. 5 ). However, profile  300  also includes a cooling step at segment  314  and, optionally, a delay step at segment  316 , between the printing step of segment  302  and the heating step of segment  304 . 
         [0060]    In this embodiment, after the 3D part and the support structure are printed in build chamber  12 , as indicated by segment  302 , the 3D part and the support structure may be cooled down to room temperature (e.g., 25° C.) and removed from build chamber  12 . This is indicated by segment  314 . Examples of suitable cooling ramp profiles for segment  314  include temperature decreases ranging from about 5° C./minute to about 15° C./minute. 
         [0061]    If desired, the resulting 3D part and support structure may then be stored and/or transported to another location for the subsequent annealing cycle, as indicated by segment  316 . The resulting 3D part and support structure then be placed in an oven (or back into build chamber  12 ) and heated from room temperature up to the one or more elevated temperatures for the annealing cycle, as indicated by segment  304 . Accordingly, the annealing cycles of the present disclosure may be performed as a single back-to-back process with the printing operation in build chamber  12  (as illustrated by profile  200 ) or as a separate step that is independent of the printing operation (as illustrated by profile  300 ). 
         [0062]      FIG. 7  illustrates profile  400 , which is a suitable profile for printing and annealing 3D parts entirely within build chamber  12 , where at least a portion of the annealing cycle may be performed while the 3D part and the support structure are being printed. As shown, profile includes segments  408 - 412  and  418 , where the steps of segments  408 ,  410 , and  412  may be performed in the same manner as discussed above for steps of segments  208 ,  210 , and  212  of profile  200  (shown in  FIG. 5 ). 
         [0063]    In comparison to the step of segments  202 ,  204 , and  206  of profile  200 , however, at segment  318  of profile  400 , build chamber  12  is heated to the one or more elevated temperatures prior to or during the printing operation to print the 3D part and the support structure. Accordingly, the layers of the part material may flow and conform to the dimensions of the layers of the support structure during the printing operation, where a given layer of the 3D part is desirably printed after the respective layer of the support structure. 
         [0064]    When the printing operation is complete, the temperature within build chamber  12  may then be gradually reduced along a cooling ramp profile to cool and solidify the 3D part, as illustrated by segments  408 ,  410 , and  412 . As discussed above for profiles  200  and  300 , the reflowing and cooling of the part material reduces porosity in the 3D part, increases interlayer bonding, and produces isotropic properties. This may accordingly increase the strength, elongation, toughness, and modulus of the 3D part. Additionally, in embodiments in which the part material compositionally includes a clear polymer, the 3D part may exhibit transparent and/or translucent properties. 
       EXAMPLES 
       [0065]    The present disclosure is more particularly described in the following examples that are intended as illustrations only, since numerous modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise noted, all parts, percentages, and ratios reported in the following examples are on a weight basis, and all reagents used in the examples were obtained, or are available, from the chemical suppliers described below, or may be synthesized by conventional techniques. 
         [0066]    3D parts and support structures were printed using an extrusion-based additive manufacturing system commercially under the trademarks “FUSED DEPOSITION MODELING” and “FDM” from available Stratasys, Inc., Eden Prairie, Minn. The 3D parts were printed from a part material that compositionally included a copolyester commercially available under the trade designation “EASTAR” 6763 Copolyester from Eastman Chemical Company, Kingsport, Tenn., which had a glass transition temperature T g (p) of about 80° C. 
         [0067]    The support structures were printed from a support material that included a blend of a low-temperature polymer and two high-temperature polymers, where the high-temperature polymers were miscible with each other, but were immiscible with the low-temperature polymer. The low-temperature polymer was an alkaline water-soluble copolymer blend commercially available under the trademark “SR30” Soluble Supports from Stratasys, Inc., Eden Prairie, Minn., which included a terpolymer having a plurality of carboxyl groups, a plurality of phenyl groups, and a plurality of carboxylate ester groups; and a copolymer having a plurality of epoxy groups and a plurality of carboxylate ester groups; and which had a glass transition temperature T g (s 1 ) of about 110° C. The first high-temperature polymer was a copolymer of methacrylic acid and methyl methacrylate (1:1 ratio), and the second high-temperature polymer copolymer of methacrylic acid and methyl methacrylate (1:2 ratio). The first and second high-temperature polymers each had a glass transition temperature T g (s 2 ) greater than about 150° C., and a number-average molecular weight of about 125,000 grams/mole. Table 1 lists the weight percent ratios of the components of the support material. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Component 
                 Percent by Weight 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Low-temperature terpolymer 
                 36.05 
               
               
                   
                 1:1 high-temperature copolymer 
                 54.05 
               
               
                   
                 1:2 high-temperature copolymer 
                 9.90 
               
               
                   
                   
               
             
          
         
       
     
         [0068]    As shown in Table 1, the support material included about 64% by weight of the high-temperature polymers and about 36% by weight of the low-temperature polymer. Accordingly, the immiscible polymers of the support material provided a glass transition temperature difference (i.e., T g (s 2 )−T g (s 1 )) of more than 40° C. 
         [0069]    After each 3D part and support structure were printed, they were removed from the build chamber of the extrusion-based additive manufacturing system and allowed to cool to room temperature for inspection. The resulting 3D part and support structure were then placed in an oven to undergo an annealing cycle. During the annealing cycle, the oven was heated up from 25° C. to 145° C. at a heating ramp rate of 10° C./minute. The oven was then held at 145° C. for a duration of 3.5 hours. 
         [0070]    During this step, the elevated temperature within the oven allowed the part material of the 3D part to flow and conform to the dimensions of the support structure. The low-temperature polymer of the support structure also softened under the elevated temperature. However, the high-temperature polymers of the support structure maintained their moduli and shape at the elevated temperature. As discussed above, the immiscibility of the polymers of the support material created a matrix of the high-temperature polymers in the softened low-temperature polymer. As such, the low-temperature polymer functioned as a flexibilizer for the high-temperature polymers, reducing the brittleness of the support structure and allowing the support structure to maintain its structural integrity. 
         [0071]    After the heating duration, the oven was then cooled down from 145° C. to 70° C. at a cooling ramp rate of 10° C. The oven was then held at 70° C. for 20 minutes, and then cooled down from 70° C. to 25° C. at a cooling ramp rate of 10° C. After the annealing cycle was completed, the annealed 3D part and support structure were then placed in a support removal tank with a support removal solution commercially available under the trademark “WATERWORKS” from available Stratasys, Inc., Eden Prairie, Minn. This dissolved the support structure from the annealed 3D part. 
         [0072]    Each resulting 3D part exhibited isotropic properties with reduced porosity and increased interlayer bonding, and also had clear, translucent properties. Furthermore, the part material did not have any visible thermal degradation. As such, the annealing cycle allowed the part material to flow and conform to the dimensions of the support structure, thereby providing bulk isotropic properties for each of the 3D parts. 
         [0073]    Although the present disclosure has been described with reference to several embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the disclosure.