Abstract:
An additive manufacturing system operates at least one ejector and an extruder to form three-dimensional objects with photopolymer material and thermoplastic material. The system operates to deposit the two materials in a layer-by-layer manner. The photopolymer material provides high resolution finishes on the objects and the thermoplastic material enables strong and stable formation of internal portions of the objects.

Description:
TECHNICAL FIELD 
       [0001]    The device disclosed in this document relates to printers that produce three-dimensional objects and, more particularly, to systems and methods for producing three-dimensionally printed objects with different types of build material. 
       BACKGROUND 
       [0002]    Digital three-dimensional manufacturing, also known as digital additive manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital model. Three-dimensional printing is an additive process in which one or more printheads eject or deposit successive layers of material on a substrate in different shapes. The substrate is supported either on a platform that can be moved three dimensionally by operation of actuators operatively connected to the platform, or the printhead or printheads are operatively connected to one or more actuators for controlled movement of the printhead or printheads to produce the layers that form the object. Three-dimensional printing is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling. 
         [0003]    Current three-dimensional object inkjet printers have significant limitations with regard to the viscosity range of the photopolymer materials that can be ejected, with most materials having an upper limit between 10 and 20 centipoise (cP). After the photopolymer materials are ejected onto the object being formed, the materials are cured with a ultraviolet (UV) or other appropriate radiation source. These photopolymer materials can be expensive and may physical properties, such as strength and stability, which are useful for the production of sturdy objects capable of a wide range of functionality. Other additive manufacturing methods, such as Fused Filament Fabrication (FFF) or Stereolithography (SLA), expand the range of materials used to produce products. There materials are more durable and are usually much cheaper than cured photopolymer materials. The surface finish of parts made using FFF is not as good as those made using UV inkjet and UV inkjet can more easily make parts with high resolution surfaces. Therefore, a system capable of producing composite objects having cured photopolymer materials and the materials used by the FFF and SLA methods would be advantageous. 
       SUMMARY 
       [0004]    A manufacturing method that integrates extruded build materials with cured photopolymers in a three-dimensional object increases the robustness and durability of the structure. The method includes operating with a controller at least one ejector in a plurality of ejectors to eject drops of a photopolymer material towards a substrate, the drops of photopolymer material being formed with a perimeter portion that extends above a base portion so the perimeter portion and the base portion define a volume, operating with the controller a source of ultraviolet (UV) radiation to cure the drops of photopolymer material at least partially, operating with the controller an extruder to extrude a thermoplastic material within the volume defined by base portion and the perimeter portion, operating with the controller the at least one ejector to eject additional photopolymer material onto the thermoplastic material to form a surface over at least a portion of the thermoplastic material, and operating with the controller the source of UV radiation to cure the drops of photopolymer material and the additional photopolymer material. 
         [0005]    A system that integrates extruded build materials with cured photopolymers in a three-dimensional object increases the robustness and durability of the structure. The system includes a planar member, at least one ejector configured to eject drops of photopolymer material towards the planar member, a source of ultraviolet (UV) radiation, an extruder configured to extrude thermoplastic material towards the planar member, and a controller operatively connected to the at least one ejector, the source of UV radiation, and the extruder. The controller is configured to: operate at least one ejector in a plurality of ejectors to eject drops of a photopolymer material towards the planar member, the drops of photopolymer materials forming a perimeter portion that extends above a base portion so the perimeter portion and the base portion define a volume, operate the source of UV radiation to cure the drops of photopolymer material at least partially, operate the extruder to extrude a thermoplastic material within the volume of the defined by the base portion and the perimeter portion of the at least partially cured photopolymer material, operate the at least one ejector to eject additional photopolymer material onto the thermoplastic material to form a surface over at least a portion of the thermoplastic material, and operate the source of UV radiation to cure the drops of photopolymer material and the additional photopolymer material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The foregoing aspects and other features of a system that integrates extruded build materials with cured photopolymers in an additive manufactured three-dimensional object are explained in the following description, taken in connection with the accompanying drawings. 
           [0007]      FIG. 1  illustrates a system for forming a three-dimensional object with different materials. 
           [0008]      FIG. 2  illustrates an example of a hybrid structure that is formed with the system of  FIG. 1 . 
           [0009]      FIG. 3  illustrates an example of another hybrid structure having sloped walls that is formed with the system of  FIG. 1 . 
           [0010]      FIG. 4  illustrates an example of a hybrid structure having protrusions along a bottom portion of the object that is formed with the system of  FIG. 1 . 
           [0011]      FIG. 5  illustrates an example of a hybrid support structure that is formed with the system of  FIG. 1 . 
           [0012]      FIG. 6  illustrates an example of a hybrid structure having a plurality of thermoplastic members that are oriented different with respect to one another that is formed with the system of  FIG. 1 . 
           [0013]      FIG. 7A  is a cross-sectional side view of a matrix structure similar to the one shown in  FIG. 6  and  FIG. 7B  is a top view of the matrix structure in  FIG. 7A . The view of  FIG. 7A  depicts the inclusion of solid layers of material in the matrix structure to prevent the flow of liquid photopolymer into the matrix too deeply. 
           [0014]      FIG. 8  is a flow diagram of an additive manufacturing method for manufacturing three-dimensional objects with different materials. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    For a general understanding of the environment for the system and method disclosed herein as well as the details for the system and method, reference is made to the drawings. In the drawings, like reference numerals designate like elements. As used in this document, the term “extruder” refers to a device that is capable of producing a continuous stream of thermoplastic material in a semi-solid form. The term “semi-solid” means a material state at which a material is malleable, but has not transitioned to a liquid phase. The term “ejector” refers to a device that expels drops of a liquid material. An ejector can be an inkjet printhead having an array of devices that expel liquid drops or it can be an array of pin ejectors, each one of which expels liquid drops. The term “leveling device” means a device that has an abrasive surface, smooth rotating surface, or a cutter that removes a portion of a material forming structure in a three-dimensional object. The term “thermoplastic” means a material that is solidly rigid at a temperature below its glass transition temperature and that is semi-solid above its glass transition temperature. Examples of thermoplastics include, but are not limited to, polymethyl methacrylate, acrylonitrile butadiene styrene (ABS), polyamides, poly carbonates, and the like. Of the commonly used thermoplastics for printing three-dimensional objects, polylactic acid (PLA) is especially useful because it has a relatively low extrusion temperature compared to other thermoplastic materials such as ABS. The term “photopolymer” refers to materials that undergo structural changes when exposed to electromagnetic radiation. 
         [0016]    An additive manufacturing system for producing three-dimensional objects with multiple materials is shown in  FIG. 1 . The system  10  includes a planar member  14 , one or more ejectors  18 , a leveling device  22 , a source of ultraviolet (UV) radiation  26 , one or more extruders  30 , a cooler  34 , and a controller  40 . The ejectors  18  can be configured as inkjet printheads. At least one of the ejectors  18  is configured to eject drops of photopolymer material towards the planar member  14 . The extruder  30  is configured to extrude thermoplastic material towards the planar member  14 . An actuator  38  is operatively connected to the planar member  14  and is configured to move the planar member  14  selectively beneath the extruder  30 , the ejectors  18 , the UV source  26 , the cooler  34 , and the leveling device  22  to enable the controller  34  to operate these components and form a three-dimensional object  42  on the planar member  14 . Alternatively, the actuator(s)  38  are operatively connected to the ejectors  18 , the UV radiation source  26 , the leveling device  22 , the cooler  34 , and the extruder  30  to enable the controller to move these components with reference to the planar member  14  for the manufacture of an object  42 . The cooler  34  is a device that cools the photopolymer after it is cured and can be implemented with a fan. 
         [0017]    The controller  40  is operatively connected to the ejectors  18 , the leveling device  22 , the UV source  26 , and the extruder  30 . The controller is configured with programmed instructions stored in a memory operatively connected to the controller to operate the components of system  10 . Specifically, the controller  40  is configured to operate at least one ejector  18  in the plurality of ejectors to eject drops of a photopolymer material to form at least one layer of a photopolymer material on the planar member  14 . As shown in  FIG. 1 , the at least one layer is formed with a perimeter portion  46  that extends above a base portion  50  so the perimeter portion and the base portion define a volume  54 . The controller is also configured to operate the source of UV radiation  26  to cure the at least one layer of photopolymer at least partially and to operate the extruder  30  to extrude a thermoplastic material within the volume  54  of the at least one layer of the at least partially cured photopolymer material. The controller  40  is also configured to operate one or more of the ejectors  18  to eject additional photopolymer material onto the thermoplastic material in the volume  54  to form a surface over at least a portion of the thermoplastic material, as shown in the perimeter portion  46  of the right side of the object  42 . The controller is configured to operate the UV radiation source  26  to finish the curing of the photopolymer material and the additional photopolymer material. In this manner, the interior of the object has been formed with thermoplastic material and the exterior has been formed with photopolymer material. As noted previously, the system  10  also includes the leveling device  22 , which is operatively connected to the controller  40  and the controller  34  is further configured to operate the leveling device  26  to remove a portion of the at least one layer of photopolymer material to ensure that an upper surface of the perimeter portion is located at a predetermined height above the base portion of the photopolymer material. The controller  40  is also configured to operate the cooler to remove heat from cured photopolymer. 
         [0018]    The configuration of the system  10  and its controller as described above enables the controller to operate in numerous ways to form particular structures in three-dimensional objects. For example, as shown in  FIG. 2 , the controller  34  operates one or more of the ejectors  18  to form the volume  54  with a predetermined height of t 1 . The controller  34  then operates the extruder  30  to extrude the thermoplastic material within the volume of the photopolymer structure to position an upper surface of the thermoplastic material at a predetermined height t 2  that is less than the predetermined height t 1  of the perimeter portion above the base portion of the at least one layer of photopolymer material. The difference Delta between the two heights enables the controller  34  to operate the leveling device  26  to level the next layers of photopolymer material without contacting the thermoplastic material. The difference Delta can be in a range of about 25 to about 150 microns, although other ranges are possible. 
         [0019]      FIG. 3  shows a sloped wall structure that can be formed with the system  10 . To form this type of structure, the controller  34  operates at least one ejector  18  to form the perimeter portion  46  with at least one surface that is positioned at a non-perpendicular angle with respect to the planar member that supports the base portion  50  of the photopolymer material. As shown in the figure, the external walls  60  can be slanted away from the volume  54 . Likewise, the internal walls of the volume  54  can be shaped for different accommodations of the thermoplastic material. For example, internal wall  64  is first formed as being perpendicular to the base portion  50 , while the internal wall  68  slopes away from the volume  54 . Also, as shown in the figure, the thermoplastic material  76  can be extruded into the volume  54  with a height that is less than the height of the volume as described above. The wall  64  can then be extended over the extruded thermoplastic material as shown in the lower two depictions presented in the figure. The controller  34  can also operate one or more ejectors  18  or the extruder  30  to eject drops of support material to form support for one of the sloping external walls  60 . The extent of the tip of the extruder may limit the ability to extrude thermoplastic material all the way up to walls  64  or  68  and completely fill the difference delta. Consequently, this gap can be filled with photopolymer material in subsequent passes. 
         [0020]    Leaving openings in the edges of the thermoplastic layers allows printing of interdigitated photopolymer. The interdigitated photopolymer allows the layers to interlock and to ensure improved adherence at walls. Also by varying the direction and the position of the boundary between the photopolymer material and thermoplastic material at different heights, the interlocking of the materials can improve the quality of the interface and thus the part. 
         [0021]    System  10  can also form the useful structure shown in  FIG. 4 . In  FIG. 4 , the controller  34  operates at least one ejector  18  to form the base portion  50  with protrusions  80  that extend from the base portion  50  into the volume formed by the perimeter portion  46  and the base portion  50  or with indentations formed in the surface of base portion  50 . The controller  34  then operates the extruder  30  to fill areas between the protrusions with the thermoplastic material  76 . This type of structure helps improve the adhesion between the thermoplastic material in the volume with the photopolymer forming the base portion  50 .  FIG. 5  depicts a support structure that is more economically formed with thermoplastic material and photopolymer material together. The controller  34  operates another extruder  30  to extrude a support thermoplastic material and then operates one of the ejectors to eject drops of another support material  104 . The ejected support material  104  is different than the extruded thermoplastic support material  100 . The extruded support material is positioned in an area adjacent to an external wall of the perimeter portion  46  and the ejected support material covers the thermoplastic support material to form a surface over the extruded support material. The controller  34  then operates one of the ejectors  18  to eject drops of photopolymer material  108  on the ejected support material  104  to extend the perimeter portion  46  over the surface formed over the other ejected support material  104 . This hybrid structure is more economical than one formed with the ejected support material alone. Another useful hybrid structure that can be formed within a three-dimensional object and is useful for upper portions of an object where photopolymer material is deposited on top of extruded thermoplastic is shown in  FIG. 6 . In that figure, the controller  34  operated the extruder  30  to form a first plurality of thermoplastic members  110  having a first orientation and to form a second plurality of thermoplastic members  114  having a second orientation that is different than the first orientation over the first plurality of thermoplastic members. The first plurality and the second plurality of thermoplastic members form interstitial spaces between the thermoplastic members in the first plurality of thermoplastic members and the thermoplastic members in the second plurality of thermoplastic members. The controller  34  also operates one of the ejectors to eject drops of photopolymer material into at least some of the interstitial spaces between the thermoplastic members in the first plurality of thermoplastic members  110  and the thermoplastic members in the second plurality of thermoplastic members  114  before forming a surface with photopolymer material over the extruded thermoplastic material. The drops of photopolymer material can be ejected into these interstitial spaces because the diameters of the drops are smaller than the width of the extruded thermoplastic members. Because the photopolymer is fluid until cured, it tends to flow around the thermoplastic. If the photopolymer penetrates too deeply into the matrix of interstitial spaces between thermoplastic members, then it can be difficult to cure. To prevent this excessive penetration, solid layers can be formed within the spaces to inhibit flow too far into the thermoplastic matrix. The solid layers can be formed by operating an extruder to form the solid layers with thermoplastic material or by operating an ejector to form the solid layers with photopolymer material that is cured before the thermoplastic members are formed over them. A side view of a volume formed with thermoplastic members is shown in  FIG. 7A  and a top view of that structure is shown in  FIG. 7B . The thermoplastic members  604  extend into and out of the plane of the figure and the thermoplastic members  608  are generally orthogonal to the members  604  another other angular orientations can be used. The layers  612  illustrate solid layers of thermoplastic material that prevents the ingress of photopolymer into the matrix structure too deeply. Because the liquid photopolymer penetrates no further than the solid layers, it stays close enough to the surface to be cured with scattered or transmitted light if not exposed directly. Choosing a thermoplastic without colorants that absorb the light used for curing is also beneficial. 
         [0022]    An additive manufacturing method  200  that forms objects with different materials from different types of material applicators is shown in  FIG. 8 . In the description of this method, statements that a process is performing some task or function refers to a controller or general purpose processor executing programmed instructions stored in a memory operatively connected to the controller or processor to manipulate data or to operate one or more components in the printer to perform the task or function. The controller  34  noted above can be such a controller or processor. Alternatively, the controller  34  can be implemented with more than one processor and associated circuitry and components, each of which is configured to form one or more tasks or functions described herein. 
         [0023]    The method begins with the controller operating at least one ejector in a plurality of ejectors to eject drops of a photopolymer material towards a substrate (block  204 ). The photopolymer material is formed with a perimeter portion that extends above a base portion so the perimeter portion and the base portion define a volume as shown in  FIG. 2 . The controller operates a leveling device to remove a portion of the drops of photopolymer material on the substrate to enable the perimeter portion to have an upper surface located at a predetermined height about the base portion (block  208 ). The controller operates an ultraviolet (UV) radiation source to cure the one or more layers of photopolymer partially (block  212 ). As used in this document, “operates an UV radiation source” means to activate the source so it radiates, move the source so radiation from the source impinges on photopolymer material, or open and close a shutter that enables emission of the radiation selectively. The controller then operates an extruder to extrude a thermoplastic material within the volume of the partially cured photopolymer material to position an upper surface of the thermoplastic material at a height that is less than the predetermined height of the perimeter portion above the base portion of the at least one layer of photopolymer material (block  216 ). One or more ejectors are operated by the controller to eject additional photopolymer material onto the thermoplastic material to form a surface over at least a portion of the thermoplastic material (block  220 ). The UV radiation source is again operated by the controller to cure the earlier ejected photopolymer material and the additional photopolymer material (block  224 ). 
         [0024]    As explained above, the internal and external walls of the perimeter portion can be slanted and the upper surface of the base portion can be formed with protrusions that extend from the base portion into the volume formed by the perimeter portion and the base portion. The controller then operates the extruder to fill areas between the protrusions with the thermoplastic material. This process can also be used to extrude a support material in an area adjacent to an external wall of the perimeter portion, eject another support material that is different than the ejected support material over the extruded support material to form a surface over the extruded support material, and eject drops of photopolymer material over the ejected support material to extend the perimeter portion over the surface formed over the other ejected support material. This process also enables the controller to operate the extruder to form a first plurality of thermoplastic members having a first orientation and to form a second plurality of thermoplastic members having a second orientation that is different than the first orientation over the first plurality of thermoplastic members. The interstitial spaces between the thermoplastic members in the first plurality of thermoplastic members and the thermoplastic members in the second plurality of thermoplastic members can be filled with photopolymer material or left empty to reduce the weight of the object. 
         [0025]    It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements may be subsequently made by those skilled in the art that are also intended to be encompassed by the following claims.