Patent Publication Number: US-2021162663-A1

Title: Three-Dimensional Modeling Apparatus And Three-Dimensional Modeling Method

Description:
This application is a continuation application of U.S. patent application Ser. No. 15/951,350 filed Apr. 12, 2018, which claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2017-089248 filed on Apr. 28, 2017, the entire disclosures of which are expressly incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a three-dimensional modeling technique that uses a thermoplastic. 
     2. Related Art 
     JP-A-2006-192710 describes an extrusion-deposition-lamination modeling apparatus that uses a molten resin. This apparatus melts a wire-like thermoplastic material by using a preheater and extrudes the molten material from an extrusion nozzle by using the rotation of an elongated screw to produce a three-dimensional object. Since such three-dimensional objects produced by extrusion have many gaps and the degree of filling is low, solvent is supplied to the cured material to dissolve the cured material to reduce the gaps in the three-dimensional objects. 
     The above-described known technique extrudes the molten material by the rotation of the elongated screw, and thus the height of the entire apparatus becomes considerably large and downsizing of the apparatus has been hindered. Furthermore, due to lots of gaps in the objects produced by laminating the material extruded from the nozzle, their modeling precision is low, and it is necessary to use solvent to increase the modeling precision. Accordingly, such a three-dimensional modeling technique requires further downsizing of the apparatuses and more precise three-dimensional modeling. 
     SUMMARY 
     The invention has been made to solve at least a part of the problems mentioned above and can be embodied in the following aspects. 
     (1) According to a first aspect of the invention, a three-dimensional modeling apparatus for producing a three-dimensional object using a thermoplastic material is provided. The three-dimensional modeling apparatus includes a drive motor, a plasticizing section having a flat screw configured to be rotated by the drive motor, the plasticizing section being configured to plasticize and convert the material into a molten material by the rotation of the flat screw, and a nozzle configured to inject the molten material. The three-dimensional modeling apparatus according to this aspect plasticizes a material by using the plasticizing section that includes the flat screw, and thus the height of the apparatus can be reduced and the size of the entire apparatus can be reduced. 
     (2) In this three-dimensional modeling apparatus, a cross-section of a nozzle hole of the nozzle may have a shape that enables the molten material injected from the nozzle hole to have a cross-section closer to a polygonal shape than a round shape. According to the three-dimensional modeling apparatus, the molten material injected from nozzle hole has a cross section closer to a polygonal shape than a round shape, and thus gaps in the deposited linear molten material can be reduced. Consequently, the surface roughness of the three-dimensional object becomes small and the modeling precision can be increased. 
     (3) In this three-dimensional modeling apparatus, the cross-section of the nozzle hole may be a substantially quadrangular shape. According to this three-dimensional modeling apparatus, gaps in the deposited linear molten material can be further reduced and thus the surface roughness of the three-dimensional object can be further reduced and the modeling precision can be increased. 
     (4) In this three-dimensional modeling apparatus, the nozzle may have a plurality of nozzle holes. According to this three-dimensional modeling apparatus, the shape of the molten material injected from the nozzle can be adjusted by the arrangement of the nozzle holes. Consequently, the surface roughness can be reduced and the design of the three-dimensional object can be improved. 
     (5) In this three-dimensional modeling apparatus, the nozzle holes may be arranged in a matrix. According to this three-dimensional modeling apparatus, the nozzle holes arranged in the matrix enables the molten material injected from the nozzle to have an entire cross section close to a quadrangular shape, and thus the surface roughness can be further reduced. 
     (6) In this three-dimensional modeling apparatus, the nozzle may be placed so as to form a gap 1.1 times or more and 1.5 times or less than a hole diameter of the nozzle hole of the nozzle between an upper surface of the three-dimensional object being produced and a tip of the nozzle. According to this three-dimensional modeling apparatus, the molten material injected from the tip of the nozzle is deposited on the upper surface of the three-dimensional object in a free state in which the molten material is not pressed against the upper surface of the three-dimensional object being produced. Accordingly, the molten material injected from the nozzle can be deposited while maintaining its cross-sectional shape, and thus the surface roughness of the three-dimensional object can be reduced. As a result, the surface roughness of the three-dimensional object can be further reduced. 
     (7) The three-dimensional modeling apparatus may further include a modeling base on which the three-dimensional object being produced is placed, and a moving mechanism configured to change the relative positional relationship between the nozzle and the modeling base. According to this three-dimensional modeling apparatus, by changing the relative positional relationship between the nozzle and the modeling base using the moving mechanism, a three-dimensional object of a desired shape can be produced. 
     (8) In this three-dimensional modeling apparatus, a plurality of injection units each having the drive motor, the plasticizing section, and the nozzle may be provided. According to this three-dimensional modeling apparatus, different molten materials can be injected from the injection units, and thus various three-dimensional objects can be produced. 
     (9) According to a second aspect of the invention, a method for producing a three-dimensional object using a thermoplastic material is provided. This method includes plasticizing and converting the material into a molten material by the rotation of a flat screw, and injecting the molten material by using a nozzle to produce the three-dimensional object. According to this method for producing a three-dimensional object, a material is plasticized by using a plasticizing section that includes a flat screw, and thus the three-dimensional object can be produced by using the small apparatus. 
     It is to be understood that the present invention can be implemented in various forms other than the above-described examples. For example, a computer program for implementing functions of a three-dimensional modeling apparatus and a three-dimensional modeling method, and a non-transitory storage medium storing the computer program may be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a conceptual view of a three-dimensional modeling apparatus. 
         FIG. 2  is a perspective view of a flat screw. 
         FIG. 3  is a plan view of a screw facing section. 
         FIG. 4  illustrates a positional relationship between a three-dimensional object and a nozzle tip. 
         FIG. 5  is a graph showing the change in the injection amount and the injection line outside diameter according to the change in the number of rotations of the screw. 
         FIG. 6  illustrates an example nozzle hole. 
         FIG. 7  illustrates a relationship among the nozzle hole shape, nozzle hole diameter, and surface roughness. 
         FIG. 8  illustrates another example nozzle hole. 
         FIG. 9  illustrates still another example nozzle hole. 
         FIG. 10  illustrates still another example nozzle hole. 
         FIG. 11  is a conceptual view of a three-dimensional modeling apparatus according to another embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1  is a conceptual view of a three-dimensional modeling apparatus according to an embodiment. The three-dimensional modeling apparatus includes an injection unit  100 , a moving mechanism  200 , and a controller  300 .  FIG. 1  shows three mutually perpendicular directions X, Y, and Z. The X direction and the Y direction are horizontal directions, and the Z direction is a vertical direction. These directions are also shown in other drawings as necessary. 
     The injection unit  100  includes a screw case  10 , a hopper  20  for containing a material, a drive motor  30 , a flat screw  40 , a screw facing section  50 , and a nozzle  60  for injecting a molten material. The flat screw  40  and the screw facing section  50  constitute a plasticizing section  90  for plasticizing a thermoplastic material to produce a molten material. The expression “plasticizing” means to heat and melt a material. 
     A thermoplastic material is put into the hopper  20 . Examples of the material include polypropylene (PP), polyethylene (PE), polyacetal (POM), polyvinyl chloride (PVC), polyamide (PA), acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), and polycarbonate (PC). Examples of shape of the materials include shapes of sold materials such as pellets and powder. 
     The flat screw  40  of the plasticizing section  90  is accommodated in the screw case  10  and is rotated by the drive motor  30 . A material is supplied from the hopper  20  to a side surface of the flat screw  40  through a communication path  22 . The material is plasticized by the rotation of the flat screw  40  to become a molten material in a space between a lower surface of the flat screw  40  and an upper surface of the screw facing section  50 . A heater  58  for heating the material is embedded in the screw facing section  50 . The molten material is supplied to the nozzle through a communication hole  56  that is provided at a central portion of the screw facing section  50  and injected by the nozzle  60 . A tip portion of the nozzle  60  has a nozzle hole diameter Dn. 
     The moving mechanism  200  is a three-axis positioner that can move a modeling base  220  that is placed on a table  210  in the three directions of the X direction, Y direction, and Z direction. The moving mechanism  200  has a function for changing the relative positional relationship between the nozzle  60  and the modeling base  220 . The change in the relative positional relationship between the nozzle  60  and the modeling base  220  by the moving mechanism  200  enables production of a three-dimensional object of a desired shape. In this embodiment, the moving mechanism  200  three-dimensionally moves the modeling base  220 ; however, as the moving mechanism  200 , a mechanism that three-dimensionally moves the nozzle  60  (the injection unit  100 ) may be employed. Alternatively, a mechanism in which one of the nozzle  60  (the injection unit  100 ) and the modeling base  220  is moved in one or two axial directions and the other one is moved in the remaining axial direction may be employed. 
     The controller  300  controls the drive motor  30  of the injection unit  100  and the moving mechanism  200 . The controller  300  can be implemented, for example, by a computer that includes a processor such as a central processing unit (CPU), a main memory, and a nonvolatile memory. A nonvolatile memory in the controller  300  stores a computer program for controlling the three-dimensional modeling apparatus. 
       FIG. 2  is a perspective view illustrating the flat screw  40 . The flat screw  40  is a substantially cylindrical screw and the height of the flat screw  40  in the axial direction is smaller than its diameter. The flat screw  40  has a plurality of scroll grooves  42  on a surface that faces the screw facing section  50  ( FIG. 1 ). The surface on which the scroll grooves  42  are formed is referred to as a “scroll-groove formed surface  48 ”. The scroll grooves  42  are formed in a shape like the involute of a circle or a spiral shape from the outer periphery of the flat screw  40  toward a central portion  46  of the scroll-groove formed surface  48 . The scroll grooves  42  are continuous with material inlets  44  that are formed on the side surface of the flat screw  40 . The material inlets  44  accept a material supplied from the hopper  20  through the communication path  22 . The rotating flat screw  40  heats and plasticizes the material to melt, converting it into a molten material. 
       FIG. 3  is a plan view of the screw facing section  50 . The screw facing section  50  has a screw facing surface that faces the scroll-groove formed surface  48  of the flat screw  40 . The screw facing surface  52  has a plurality of guide grooves  54  formed in a spiral shape. At a central portion of the screw facing surface  52 , a communication hole for supplying a molten material to the nozzle  60  is formed. The guide grooves  54  have a function to guide a molten material to the communication hole  56 . As illustrated in  FIG. 1 , the heater  58  for heating a material is embedded in the screw facing section  50 . The heating by the heater  58  and the rotation of the flat screw  40  plasticize a material. 
     A molten material is heated to its glass transition point or more and is injected from the nozzle  60  in a completely melted state. For example, an ABS resin has a glass transition point of about 120 C.° and is inject from the nozzle  60  at a temperature about 200 C°. To inject the molten material at such a high temperature, a heater may be provided around the nozzle  60 . 
       FIG. 4  illustrates a positional relationship between a three-dimensional object and the nozzle tip. On the modeling base  220 , a three-dimensional object OB that is being produced is placed. A gap G is provided between the tip of the nozzle  60  and the upper surface OBt of the three-dimensional object OB. Here, “the upper surface OBt of the three-dimensional object OB” means a portion onto which a molten material injected from the nozzle  60  will land in the vicinity of an area immediately below the nozzle  60 . It is preferable that the size of the gap G be, for example, 1.1 times or more and 1.5 times or less than the hole diameter Dn ( FIG. 1 ) of the nozzle hole of the nozzle  60  and more preferably, 1.1 times or more and 1.3 times or less. With this gap, the molten material injected from the tip of the nozzle  60  is deposited on the upper surface OBt of the three-dimensional object OB in a free state in which the molten material is not pressed against the upper surface OBt of the three-dimensional object OB being produced. Accordingly, the molten material injected from the nozzle  60  can be deposited while maintaining its cross-sectional shape, and thus the surface roughness of the three-dimensional object OB can be reduced. With a heater provided around the nozzle  60  to inject the molten material at a high temperature, if the molten material is deposited by the nozzle  60  while being pressed against the upper surface OBt of the three-dimensional object, the deposited material is continuously heated and overheated by the nozzle  60 , causing problems such as discoloration and deterioration. However, if the gap G is provided between the tip of the nozzle  60  and the upper surface OBt of the three-dimensional object OB, such overheating of the material can be prevented. Furthermore, if the gap G is larger than 1.5 times the hole diameter Dn ( FIG. 1 ) of the nozzle hole, the accuracy with respect to the portion onto which the molten material will land and the adhesion to the upper surface OBt of the three-dimensional object OB being produced may be lowered. 
       FIG. 5  is a graph showing the change in the injection amount and the injection line outside diameter according to the change in the number of rotations of the screw. The horizontal axis shows the number of rotations (rpm) of the flat screw  40 . The vertical axis on the left side and the line graph show the amount (g/s) of the injected molten material. The vertical axis on the right side and the bar graph show the outside diameter (mm) of the injection line of the molten material. Here, “outside diameter of the injection line” means an outside diameter of a linear material injected from the nozzle  60 . The outside diameter of the injection line is a dimension measured after a molten material has been injected from the nozzle  60  vertically downward in a free state. In this embodiment, an ABS resin was used as the material and a nozzle that has nozzle holes of four circular cross sections of nozzle hole diameters of 0.3 mm, 0.5 mm, 1.0 mm, and 2 mm was used as the nozzle  60 . The plasticizing section  90  was set to 260 C°, and the nozzle  60  was set to 200 C°. 
     The line graph of the injection amount shows that the injection amount increased substantially linearly as the number of rotations of the screw increased within the range the number of rotations of the screw was 24 rpm or less. In contrast, after the number of rotations of the screw exceeded 24 rpm, the injection amount hardly increased even if the number of rotations of the screw increased. Consequently, it is preferable to perform the modeling at a screw rotation speed of 24 rpm or less. 
     The bar graph of the outside diameter of the injection line shows that the outside diameter of the injection line was approximately constant irrespective of the number of rotations of the screw. Consequently, even if the injection amount is increased, the outside diameter of the injection line does not increase. The outside diameter of the injection line is generally a major factor in determining the surface roughness of a three-dimensional object. Specifically, the larger the outside diameter of the injection line, the larger the surface roughness of the three-dimensional object, and the lower the modeling precision. According to the injection unit  100  in this embodiment, the outside diameter of the injection line is substantially constant even if the injection amount is increased, and thus the modeling can be performed at a high speed without increasing the surface roughness. 
     The injection unit  100  according to the embodiment plasticizes and changes a material into a molten state by using the flat screw  40  and injects the molten material from the nozzle  60  to produce a three-dimensional object. Accordingly, various materials of various shapes can be used to produce a three-dimensional object. This feature is a great advantage over known fused deposition molding (FDM) three-dimensional (3D) printers, that is, thermal-melt-lamination 3D printers that require a filament of a material. 
       FIG. 6  illustrates an example nozzle hole. A nozzle hole  62   a  of a nozzle  60   a  has a substantially quadrangular cross section. Specifically, the cross section of the nozzle hole  62   a  is a square shape and its four corners are R-chamfered at R0.1. The nozzle  60   a  of such a shape enables the molten material injected from the nozzle hole  62   a  to have a cross section that is closer to a square shape than a round shape. Consequently, the gaps in the deposited linear molten material can be reduced. The shape of the cross section of the nozzle hole  62   a  may be a shape close to a polygonal shape other than a quadrangular shape, for example, a hexagonal shape. 
     In the description of  FIG. 6 , the small letter “a” attached to the end of the reference numerals of the nozzle  60   a  and the nozzle hole  62   a  is an additional reference numeral for indicating a specific example shape. In a case where such an additional reference numeral is not necessary, the reference numeral “a” is omitted in the description. The same applies to reference numerals “b” and “c” in the following other examples. 
       FIG. 7  illustrates a relationship among the shape, the nozzle hole diameter, and the surface roughness of the nozzle hole  62 . As the nozzle  60 , the nozzle holes  62  of circular cross sections (nozzle numbers # 1  and # 2 ) and a quadrangular cross section (nozzle number # 3 ) were used. The nozzle of the nozzle number # 3  is the nozzle  60   a  in  FIG. 6  described above. The diameter of the nozzle hole  62  of the nozzle number # 1  is 1 mm, the diameter of the nozzle hole  62  of the nozzle number # 2  is 0.3 mm, and each side of the nozzle hole  62  of the nozzle number # 3  is 1 mm. Using these three types of nozzles  60 , three-dimensional objects of the three types were produced respectively, and their surface roughness Rz were measured. The surface roughness Rz is a “maximum height Rz” that is defined by JIS B 0601: 2013. 
     In this specification, “the diameter of the nozzle hole  62 ” means its diameter when the cross section of the nozzle hole  62  is circular. When the cross section of the nozzle hole  62  is a square shape, it means the length of one side of the nozzle hole  62 . When the cross section of the nozzle hole  62  is a quadrangular shape, it means the length of a long side. 
     When the nozzle  60  of the nozzle numbers # 1  and # 2  having the circular cross sections in the nozzle hole  62  were used, the surface roughness Rz was about half of the hole diameter of the nozzle hole  62 . This is because, from the nozzle hole  62  having circular cross sections, the linear molten materials having substantially circular cross sections were injected and deposited respectively, and thus half of the diameters were the surface roughness (maximum heights Rz) of the three-dimensional objects. In contrast, when the nozzle  60  of the nozzle number # 3  having the quadrangular cross section (to be specific, square) in the nozzle hole  62  was used, the surface roughness Rz was much smaller than half of the hole diameter (1 mm on each side) of the nozzle hole  62 . This is because, from the nozzle hole  62  having the quadrangular cross section, the linear molten material having a substantially quadrangular cross section was injected and deposited, and thus small gaps in the substantially quadrangular corners of the material were the surface roughness (maximum heights Rz) of the three-dimensional object. From this result, it is preferable that the cross section of the nozzle hole  62  of the nozzle  60  be closer to a quadrangular shape than a round shape. 
       FIG. 8  illustrates another example nozzle hole  62 . A nozzle hole  62   b  of a nozzle  60   b  has a cross section that is distorted like a pincushion. Specifically, the four sides of the cross section of the nozzle hole  62   b  are concavely curved from the corners toward the center respectively. The cross-sectional shape of the nozzle hole  62   d  is also a substantially quadrangular shape. The nozzle  60   b  of such a shape enables the molten material injected from the nozzle hole  62   b  to have a cross section that is further closer to a quadrangular shape or a square shape than the nozzle  60   a  in  FIG. 6 . Consequently, the gaps in the deposited linear molten material can be further reduced. 
     As will be understood from the above-described examples in  FIG. 6  and  FIG. 8 , it is preferable that the cross section of the nozzle hole  62  have the shape that enable the molten material injected from the nozzle hole  62  to have a cross section closer to a polygonal shape (particularly, a quadrangular shape) than a round shape. With this shape, the molten material injected from nozzle hole  62  has a cross section closer to a polygonal shape than a round shape, and thus the gaps in the deposited linear molten material can be reduced. Consequently, the surface roughness of the three-dimensional object is reduced and the modeling precision can be increased. 
       FIG. 9  illustrates still another example nozzle hole  62 . A nozzle  60   c  has four nozzle holes  62   c  that are arranged in a matrix. The cross section of each nozzle hole  62   c  has a substantially quadrangular shape. As in this example, with the plurality of nozzle holes  62   c , the shape of the molten material injected from the nozzle  60   c  can be adjusted by the arrangement of the nozzle holes  62   c . Consequently, the surface roughness can be reduced and the design of the three-dimensional object can be improved. The arrangement of the nozzle holes  62   c  may be other arrangements than the matrix. However, the nozzle holes  62   c  arranged in the matrix enable the molten material injected from the nozzle  60   c  to have an entire cross section close to a quadrangular shape, and thus the surface roughness can be further reduced. 
       FIG. 10  illustrates still another example nozzle hole  62 . A nozzle  60   d  has five nozzle holes  62   d  that are arranged in the layout of the spots of “5” of a die. With this arrangement of the nozzle holes  62   d , the molten material injected from the nozzle  60   d  can be intentionally arranged to have an uneven unique shape. Consequently, the design of the surface of the three-dimensional object can be enhanced. 
     It should be noted that the cross sectional shapes and arrangements of the nozzle holes  62  illustrated in  FIG. 6 ,  FIG. 8 ,  FIG. 9 , and  FIG. 10  are only examples, and various cross sectional shapes and arrangements other than these examples may be employed. 
     As described above, the three-dimensional modeling apparatus according to the embodiment plasticizes a material by using the plasticizing section  90 , which includes the flat screw  40 , and thus the height of the apparatus can be reduced and the size of the entire apparatus can be reduced. Furthermore, by devising the shapes, the number, and the arrangements of the nozzle holes  62  of the nozzle  60 , the modeling precision and design of three-dimensional objects can be improved. 
       FIG. 11  is a conceptual view of a three-dimensional modeling apparatus according to another embodiment. This three-dimensional modeling apparatus is different from the embodiment illustrated in  FIG. 1  in that the three-dimensional modeling apparatus includes two injection units  100   a  and  100   b , and other components are similar to those in  FIG. 1 . The structure of each of the injection units  100   a  and  100   b  is similar to that of the injection unit  100  illustrated in  FIG. 1 , and its description will be omitted. 
     The three-dimensional modeling apparatus includes the injection units  100   a  and  100   b  and thus two different materials can be used to produce a three-dimensional object. Example combinations of two materials include the following combinations. 
     (1) Materials of Different Colors 
     With materials of different colors, a three-dimensional object of two different colors can be produced. 
     (2) Material for Support Material and Material for Modeling 
     A support material is a member for supporting the shape of a three-dimensional object and is a member to be removed after completion of the modeling. First, a support material is injected from one of the injection units  100   a  and  100   b  to produce a support member, and then, using the support member, a three-dimensional object is produced. With this method, more complicated and various three-dimensional objects can be produced. 
     (3) Materials of Different Properties 
     For example, with materials of different properties, a three-dimensional object of the materials suitable for its purpose can be produced. 
     It should be noted that the number of the injection units  100  is not limited to two, and alternatively, three or more injection units  100  may be provided. 
     The present invention is not limited to the above-described examples and embodiments, and various modifications can be made without departing from the scope of the invention. For example, the following modifications may be provided. 
     Modification 1 
     In the above-described embodiments, the three-dimensional modeling apparatuses include the hopper  20 ; however, the hopper  20  may be omitted. 
     The present invention is not limited to the above-described embodiments and modification, and various structures can be provided without departing from the scope of the invention. For example, technical features in the embodiments, examples, and modifications corresponding to the technical features in each embodiment described in SUMMARY may be replaced or combined to solve some or all of the above problems or to achieve some or all of the above-described effects. Unless the technical features are described as essential in this specification, the technical features may be omitted as appropriate.