Abstract:
Example 3D printing methods involve rapid liquid filling of one or more cavities within a hollow and/or porous 3D printed object. In some examples, a conventional applicator computer-controllably dispenses significantly viscous solidifiable fluid in layers to build up a side wall of the object, and that same applicator or another applicator discharges a second solidifiable fluid at relatively low viscosity to rapidly fill the cavity(s), voids and/or porosity defined by the accurately printed side wall. In some examples, the liquid fill solidifies to permanently embed an internal object (e.g., wire or fiberglass mesh, Kevlar fabric, acrylic, bullet resistant armor, structural reinforcing material, etc.). In some examples, the liquid fill material permanently bonds to the accurately printed side wall. In some examples, the liquid fill material shrinks upon solidifying to create beneficial residual compressive stress within the 3D printed side wall and/or within the solidified material itself. In some examples, the liquid fill material does not solidify and is non-Newtonian to improve impact resistance.

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to additive manufacturing processes (3D printing) and more specifically to methods for reducing manufacturing cycle time and/or increasing the strength of additive manufactured products. 
     BACKGROUND 
     The terms, “3D printer” and 3D printing” refer to any machine or method used for processes known as additive manufacturing, rapid prototyping, laser sintering, fused deposition modeling, and steriolithrography, wherein a three-dimensional object, or at least part of it, is built up by sequential layering of material. Stratasys, Ltd. is just one example of a company that provides 3D printers. Although 3D printing is quite versatile, it can be relatively slow in producing large or detailed parts. Faster methods are advantageous. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional side view of an example part being created by an example additive manufacturing method in accordance with the teachings disclosed herein. 
         FIG. 2  is a cross-sectional side view similar to  FIG. 1  but showing another stage of the example additive manufacturing method. 
         FIG. 3  is a cross-sectional side view of an example part being created by an example additive manufacturing method in accordance with the teachings disclosed herein. 
         FIG. 4  is a cross-sectional side view similar to  FIG. 3  but showing another stage of the example additive manufacturing method. 
         FIG. 5  is a block diagram illustrating various methods associated with one or more of the examples shown in  FIGS. 1-4 . 
         FIG. 6  is a cross-sectional side view of an example part being created by an example additive manufacturing method in accordance with the teachings disclosed herein. 
         FIG. 7  is a block diagram illustrating various methods associated with one or more of the examples shown in  FIGS. 5 and 6 . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1-5  illustrate various procedures of an example additive manufacturing method  10  that involves dispensing a solidifiable fluid fill into the pores or into one or more other cavities of an additive manufactured object, such as object  12  of  FIGS. 1 and 2  and object  12 ′ of  FIGS. 3 and 4 . Examples of a cavity or cavities include, but are not limited to, a void, a gap, a hollow space, and/or inherent porosity. Method  10  provides various benefits including, but not limited to, shorter process cycle time, stronger parts, and the advantages of filling with a non-Newtonian fluid for use as armor. 
     Some examples of method  10  involve the use of a 3D printer  14  (e.g., Stratasys, Ltd.) comprising a build platform  16  and at least one applicator  18  (e.g., a first applicator  18   a , a second applicator  18   b , a third applicator  18   c  and/or a fourth applicator  18   d ). The term, “applicator” refers to any device for discharging a fluid that can later be solidified (e.g., solidified by raising or lowering its temperature, drying, setting, welding, freezing, chemical reaction, photochemical reaction, etc.). Depending on the chosen style of applicator, the fluid can be discharged in a desired flow pattern, examples of which include, but are not limited to, a narrow thread-like stream (fused deposition modeling or FDM), a ribbon-like stream, a broader fluid stream (e.g., manually discharged from a syringe, automatically discharged from a pump/valve apparatus, etc.), and discrete droplets (piezoelectric discharge). 
     Some examples of method  10  are performed according to the following sequence. On optional raft material  20  (e.g., glass, porous frangible material, adhesive tape, releasable coating) is placed upon or applied to build platform  16  of 3D printer  14 . In some examples, raft material  20  is 3D printed by second applicator  18   b  depositing raft material  20  in a computer controlled layered manner. In some examples, raft material  20  is 3D printed by yet another applicator (e.g., a fifth applicator), other than applicator  18   a ,  18   b ,  18   c  or  18   d . Raft material  20  can make it easier to release 3D printed object  12  from build platform  16 , and later raft material  20  can be discarded. Applicator  18   a  is computer controlled to deposit a first fluid  22  in a first pass  24  (either directly on platform  16  or on optional raft material  20 ) to create a first layer  26  of a build material  28 . Build material  28  is the solidified form of fluid  22 . 
     The term, “fluid” refers to any material that can flow. Examples of a fluid include, but are not limited to, a liquid, molten material, and powder. More specific examples of first fluid  22  include, but are not limited to, thermoplastics, thermosetting plastic, resins, epoxy, other plastics, metal powder, ABS (acrylonitrile butadiene styrene), PET (polyethylene terephthalate), PLA (polylactic acid or thermoplastic aliphatic polyester), and polyetherimide. 
     Depending on the final shape of object  12 , some examples of method  10  deposit a support material  30  to help support overhanging sections  32  of build material  28 . In some examples, support material  30  is a prefabricated piece that is placed either upon raft material  20  or directly on build platform  16 . In other examples, second applicator  18   b  builds support material  30  layer-by-layer in a manner similar to that of layering material  28 . In some examples, support material  30  is water soluble or non-adhering to first layer  26  and is eventually removed from the finished object  12 . In some examples, support material  30  is the same material as raft material  20 . 
     After first layer  26  solidifies (partially or completely), applicator  18   a  is computer controlled to deposit first fluid  22  in a second pass  34  to create a second layer  36  of build material  28  on top of first layer  26 . Second layer  36  is allowed to solidify, and the process is repeated sequentially for a plurality of layers such as a third layer  38 , a fourth layer  40 , a fifth layer  42 , a sixth layer atop layer  42  or for as many layers necessary for creating object  12  with a desired shape. The so-called sixth layer is not shown but can be situated between fifth layer  42  and a cap  74 , or the sixth layer could be laid as an alternative to installing cap  74 . In some examples, each of layers  26 ,  36 ,  38 ,  40  and  42  and the sixth layer have a layer thickness  44  of about 0.010 inches or preferably within a range of about 0.003 to 0.020 inches. Although layers  26 ,  36 ,  38 ,  40  and  42  have been referred to as first, second, third, fourth and fifth layers, respectively, any two adjacent stacked layers can be referred to as first and second layers. For example, layer  38  can be referred to as a first layer, and layer  40  can be referred to as a second layer, even though layers  26  and  36  were laid prior to layers  38  and  40 . 
     In the illustrated example, the vertical build up of layers  26 ,  36 ,  38 ,  40  and  42  produces a multilayer wall  46  (i.e., layered vertically as viewed in  FIGS. 1-4 ) such that wall  46  defines a cavity  48 , void  50  and/or inherent porosity  83 . In some but not all examples, a solid object  52  (e.g., a carbon fiber  52   a , a wire or fiberglass mesh  52   b , Kevlar fabric, bullet resistant armor, electrical conductor, electrical component, electrical circuit, sensor, transducer, microprocessor, light bulb, light emitting diode, fabric, strain gage, etc.) is placed within cavity  48 . In some but not all examples, object  52  is resistant to bullet penetration thereby making object  12  useful as armor in its finished state. 
     Next, regardless of whether cavity  48  is empty or contains object  52 , applicator  18   c  deposits a second fluid  54  into cavity  48  such that a vertical depth  56  of second fluid  54  in cavity  48  is greater than layer thickness  44 . If cavity  48  contains object  52 , second fluid  54  completely submerges object  52  or at least submerges a part of object  52 . Depth  56  being greater than the vertical thickness of multiple layers enables rapid filling of cavity  48  and/or provides the finished product with various structural advantages. After depositing second fluid  54  into cavity  48 , second fluid  54  solidifies to create a solidified fill material  58  within cavity  48 . In some examples, object  52  becomes embedded within solidified fill material  58 , as shown in  FIG. 2 . Some examples of second fluid  54  include, but are not limited to, thermoplastics, thermosetting plastic, acrylic, resins, epoxy, other plastics, wax, adhesive, dyes, ceramic, plaster (e.g., plaster of Paris), metal powder, liquid metal, liquid resin impregnated with solid powder or fibers, ABS (acrylonitrile butadiene styrene), PET (polyethylene terephthalate), PLA (polylactic acid or thermoplastic aliphatic polyester), polyetherimide, chocolate, butter, cheese, water, gelatin, juice, yogurt, liquid sugar, liquid polymers, etc. 
     In some examples, the 3-D printed object and method just described include various features and advantages. For instance, in some cases, second fluid  54  permanently bonds to multilayer wall  46 , cavity  48 , void  50 , porosity  83 , and/or edges  64  to comprise a portion of object  12  once all fluids are solidified. 
     In some examples, the 3-D printed object and method just described include various features and advantages. For instance, in some cases, second fluid  54  bonding to wall  46  and shrinking upon solidifying produces a residual compressive stress  62  within object  12  (e.g., within wall  46  and/or within solidified fill material  58  itself). The residual compressive stress  62 , in some examples, increases the strength and load carrying capacity of object  12 . In addition or as an alternative to second fluid  54  bonding to wall  46 , some examples of method  10  have solidified fill material  58  and/or object  52  mechanically engaging or interlocking with certain 3D printed edges  64  of object  12 . 
     In some examples, object  52  can increase the strength of object  12  regardless of any residual compressive stress. In some examples, object  52  mechanically engages, mates or interlocks with 3D printed object  12  to assist in proper placement of object  52  within cavity  48  and/or to improve the structural integrity of 3D printed object  12 . 
     In some examples, first applicator  18   a  carefully and controllably deposits first fluid  22  at a desired first viscosity, at a first mass flow rate, and in rather thin layers (e.g., 0.003 to 0.020 inches thick) to achieve dimensional accuracy of 3D printed object  12 . Later or alternatingly, second fluid  54  is injected into cavity  48  at a lower second viscosity and at a higher second mass flow rate. The term, “mass flow rate” refers to the average mass flow rate while the fluid is being deposited or dispensed. In some examples, third applicator  18   c  simply pours or pumps second fluid  54  into cavity  48  without the need for accurately locating applicator  18   c  or necessarily following any particular layering technique. In some examples, third applicator  18   c  is a manually operated syringe or a power operated pump or valve arrangement. In some examples, applicator  18   c  discharges second fluid  54  along multiple passes, but in such examples, a second pass is laid without having to wait for a previous pass to harden. In some examples, the first and second fluids  22  and  54  are comprised of the same material, and the viscosity of second fluid  54  is less than that of first fluid  22  by virtue of second fluid  54  being at a higher temperature. In some examples, first applicator  18   a  is used for dispensing both fluids  22  and  54 . In some examples, the first and second fluids  22  and  54  are comprised of different materials, and the viscosity of second fluid  54  is less than first fluid  22  by virtue of their different material properties. In some examples, only first fluid  22  or second fluid  54  is of a thermoplastic material to achieve desired material properties and dispensing characteristics. 
     To accurately build up multilayer wall  46  in a controlled manner and then filling cavity  48 , void  50  and/or porosity  83  at a much faster rate, some example methods discharge first fluid  22  through a first discharge opening  68  and discharge second fluid  54  through a significantly larger second discharge opening  70 . In the illustrated example, first applicator  18   a  provides first discharge opening  68 , and third applicator  18   c  provides second discharge opening  70 . The difference in discharge opening size is just one example of how applicators  18   a  and  18   c  are each of a construction that is physically distinguishable from each other. Other examples of physical distinctions include, but are not limited to, physical size, mode of fluid discharge, type or shape of nozzle, etc. In some examples, the rapid fill of cavity  48  allows the solidified fill material  58  to be of a much greater volume (second volume) than the combined volumes of the first and second layers  38  and  40  (combined first volume) while maintaining a reasonable process cycle time even in examples where solidifying second fluid  54  in cavity  48  consumes more time than solidifying first fluid  22  in second pass  40 . 
     In some cases, it can be difficult or impossible to 3D print a layer over a liquid or over open space, so some examples of method  10  include manually or otherwise installing  72  cap  74  atop the plurality of 3D printed layers (on top of layer  42  or on top of the sixth layer) to extend over cavity  48 . In some examples, cap  74  includes one or more openings  76  for dispensing or depositing  78  second fluid  54  into cavity  48  after cap  74  is installed. Some openings  76  can be used for venting gas displaced by second fluid  54  entering cavity  48 . In some examples, second fluid  54  within cavity  48 , void  50  or pores  83  is allowed to solidify and another first layer  26  is dispensed atop the solidified fluid (solidified fill material  58 ). 
       FIGS. 3 and 4  show an example method of using this present invention for creating a casting  58 ′.  FIG. 3  represents fluid  84  being dispensed  82  (e.g., via fourth applicator  18   d ) and broadcast  88  by pressure, vibration or centrifugal force to create coating  98  inside cavity  90  defined by a multilayer wall  92  of additive manufactured object  12 ′ (in this example, object  12 ′ is a mold). Arrow  94  of  FIG. 4  represents depositing second fluid  54  into the coated cavity, and arrow  96  of  FIG. 4  represents separating solidified fill material  58  (solidified form of fluid  54 ) from coating  98 . In some examples, coating  98  is a ceramic material, and solidified fill material  58  is a metal dispensed originally as a molten metal. 
     In some examples, additive manufacturing method  10  is carried out as shown in  FIG. 5 . In this example, block  100  represents depositing first fluid  22  in first pass  38 . Block  102  represents solidifying first fluid  22  in a first pass to create first layer  38  of build material  28 , wherein first layer  38  has predetermined layer thickness  44 . Block  104  represents depositing first fluid  22  in a second pass. Block  106  represents solidifying first fluid  22  in the second pass to create second layer  40  of build material  28  atop first layer  38  so as to create multilayer wall  46  that defines cavity  48 , wherein second layer  40  has is of the predetermined layer thickness  44 , and multilayer wall  46  has height  56  being greater than predetermined thickness  44 . Block  108  represents after creating multiplayer wall  46 , depositing second fluid  54  into cavity  48  such that vertical depth  56  of second fluid  54  in cavity  48  is greater than layer thickness  44 . Block  110  represents after depositing second liquid  54  into cavity  48  to vertical depth  56 , solidifying second liquid  54  to create solidified fill material  58  within cavity  48 . 
     In some examples, multiple objects  4  are 3D printed in a stack to create one larger object  101 , as shown in  FIG. 6 . In this example, cap  74  is omitted, and raft material  20  is optional. Including raft material  20  allows larger object  101  to be readily separated into a plurality of individual objects  12 . In some examples, raft material  20  is comprised of support material  30  which may be water soluable. However, if raft material  20  is omitted, larger object  101  can remain as one cohesive product comprising multiple integral objects  12 . 
       FIG. 7  is an example diagram illustrating a method for producing object  101 , wherein block  112  represents after completing block  110 , to create new layers  26 ,  36 ,  38 , 40 , and  42  (and optionally one or more additional layers, such as a sixth layer as an alternative to cap  74 ) of layer thickness  44  using first fluid  22 , thereby creating a second cavity above the first cavity. Block  114  represents after completing block  112 , to deposit more of second fluid  54  into second cavity of block  112 . Block  116  represents after completing block  114 , to create a second raft material  20  atop the stacked results of block  114 . Block  118  represents after completing block  116 , to create new layers  26 ,  36 ,  38 , 40 , and  42  (and optionally one or more additional layers, such as a sixth layer as an alternative to cap  74 ) of layer thickness  44  using first fluid  22 , thereby creating a third cavity above the second raft material. Block  120  represents after completing block  118 , to continue repeating this process of stacking separable 3D printed objects atop the previous ones, using raft material  20  in between to allow separation once all the materials are solidified. 
     Although certain example methods, apparatus and articles of manufacture have been described herein, the scope of the coverage of this patent is not limited thereto. Rather, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.