Method for cutting long fiber filament in 3D printer

Abstract

To provide a method for cutting a long fiber filament in a 3D printer without using a fiber cutting device.SOLUTION: A lower edge of a guide pipe 41 is used. A motor for moving a print bed 2 or a motor for moving a guide pipe 41 (i.e. a print head 3) is made capable of high speed movement, i.e. made large. Alternatively, the print bed 2 is made into two stages, upper and lower, and a motor is provided to move only an upper stage at high speed. Alternatively, the guide pipe 41 is supported by a cantilever, so it can be displaced by a small load. A long fiber LC is fixed by a guide pipe extrusion unit 41b, and the print bed 2 (or only the upper stage) and the guide pipe 41 (the print head 3) are moved by the motor.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention is directed to a 3D printer for injecting short fiber reinforced resin and long fiber. Method for cutting long fiber filaments in Regarding. [Background technology]

[0002] There are two methods for reinforcing thermoplastic resin structures molded by 3D printers, injection molding, etc. with fibers: one that uses short fibers and one that uses long fibers (continuous fibers) (see Patent Document 1). In particular, carbon fiber reinforced plastic (CFRP) is superior to metals in terms of specific rigidity and specific strength (see Non-Patent Document 1).

[0003] When short fibers are used as reinforcing materials, fine molding is possible by taking advantage of the short fibers, but the mechanical properties of the short fiber reinforced thermoplastic resin structure are not so great. In particular, when electrical conductivity is required, short carbon fibers with a small aspect ratio have lower electrical conductivity than carbon nanotubes or no electrical conductivity at low volume contents, so that electrical conductivity of the short carbon fiber reinforced thermoplastic resin structure cannot be ensured. In addition, the cost is higher than that of carbon black.

[0004] On the other hand, when long fibers are used as a reinforcing material, the mechanical properties are great, but it is difficult to mold a long fiber reinforced thermoplastic resin structure with a complex shape, and the long fibers are folded back at the ends, reducing the strength of those parts. To address this issue, a fiber cutting device is provided to cut the long fiber reinforced thermoplastic resin structure to a specified length.

[0005] FIG. 13 is a cross-sectional view showing a conventional print head for a 3D printer (see Patent Document 2).

[0006] 13, the print head is composed of a screw 101 having a hollow hole 101a at the center and a spiral groove 101b on the outer periphery, a screw cover 102 surrounding the screw 101, a heater 103 provided under the screw cover 102, and a nozzle 104 provided so as to cover the lower tip of the screw 101 protruding from the screw cover 102. In this case, the tip of the screw 101 and the tip of the nozzle 104 are aligned. The screw 101 is rotated by a stepping motor 105, a small drive wheel 106, a transmission belt 107, and a large drive wheel 108. Also, 109 is a fiber cutting device.

[0007] In Fig. 13, the long fiber filament LCF is fed from above into the hollow hole 101a of the screw 101, and at the same time, the thermoplastic resin filament (wire) RF is fed from above into the spiral groove 101b of the screw 101. As a result, the thermoplastic resin filament RF is heated by the heater 103 at the bottom of the screw 101, and in the nozzle tip region (also the screw tip region) N of the nozzle 104, the thermoplastic resin of the thermoplastic resin filament RF is melted and bonded so as to wrap around the long fibers of the long fiber filament LCF. In this way, a long fiber reinforced thermoplastic resin structure SO is formed and cut to a predetermined length by a fiber cutting device 109. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent Publication No. 2022-98042 [Patent Document 2] CN104149339A [Non-patent literature]

[0009] [Non-Patent Document 1] T. Gerngross, D. Nieberl, “Automated manufacturing of large, three-dimensional CFRP parts from dry textiles”, CEAS Aeronautical Journal, 7(2), 2016, 241-257. [Non-Patent Document 2] Y. Imaeda, A. Todoroki, R. Matsuzaki, M. Ueda, Y. Hirano, Composites Part C: Open Access, 6, (2021), #100195. Summary of the Invention [Problem to be solved by the invention]

[0010] However, in the conventional 3D printer print head of FIG. 13, the tip of the screw 101 and the tip of the nozzle 104 are aligned, so the long fibers of the long fiber filament LCF and the thermoplastic resin R are melt-bonded in the nozzle tip region N. In this case, since the nozzle tip region N of the nozzle 104 is still in a high temperature state, as shown in FIG. 14, when the long fiber reinforced thermoplastic resin structure SO is printed by the print head 110, the long fibers LC become soft in the high temperature nozzle tip region N of the nozzle 104, and at the same time, are pulled in the orientation direction by the nozzle 104 and pulled in the opposite orientation direction by the long fibers LC in the already solidified pass. Therefore, the long fibers LC pulled in both directions are bent in the opposite orientation direction in the nozzle tip region N of the nozzle 104, and the long fibers LC move upward. As a result, gaps (voids) V are generated in the long fiber reinforced thermoplastic resin structure SO. In addition, since a fiber cutting device 109 is required to cut the long fiber LC, the manufacturing cost of the 3D printer is high. There is a problem that... [Means for solving the problem]

[0011] In order to solve the above problems, the 3D printer according to the present invention Method for cutting long fiber filaments in teeth, A 3D printer having a print bed that can move in the left-right, front-back, and back directions, and a print head that can move in the left-right, front-back, and up-down directions on the print bed, wherein the print head isA screw having a screw hollow hole in the center and a screw spiral groove on the outer periphery, a heat block having a heat block hollow hole in the center and accommodating the screw, a concentric twin-shaft nozzle having a nozzle hollow hole in the center and provided at the tip of the heat block, and a concentric twin-shaft nozzle passing through the screw hollow hole, the heat block hollow hole, and the nozzle central hole. from A protruding guide pipe is provided. In a 3D printer in which a long fiber filament is passed from top to bottom through a guide pipe, and thermoplastic resin is passed from top to bottom through the screw spiral groove, the gap between the hollow hole in the heat block and the guide pipe, and the gap between the concentric twin-axis nozzle and the guide pipe, this is done by moving the guide pipe and the print bed with the long fiber filament fixed. It is something. Effect of the Invention

[0012] According to the present invention, Cutting of long fiber filaments without the use of fiber cutting equipment Can be made As a result, the manufacturing costs of 3D printers can be reduced. do. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing a 3D printer including a first embodiment of a print head for a 3D printer according to the present invention. [Diagram 2] 2A and 2B show the details of the print head in FIG. 1, with (A) being a perspective view, (B) being a partially cutaway cross-sectional view, and (B') being a partially enlarged cross-sectional view of (B). [Diagram 3] 3A and 3B show the screw of FIG. 2, in which FIG. 3A is a perspective view and FIG. 3B is a partially cut-away cross-sectional view. [Figure 4] 3 shows the hopper of FIG. 2, where (A) is a perspective view, (B) is a longitudinal sectional view, (C) is a transverse sectional view, and (D) shows resin pellets being put into the hopper. [Diagram 5] 3A and 3B are diagrams for explaining the operation of the print head in FIG. 2, in which (A) is a cross-sectional view of the lower part of the print head, (A') is a partially enlarged cross-sectional view of (A), (B) is a cross-sectional view of a molded long-fiber reinforced thermoplastic resin structure (print path) S, and (C) is an enlarged cross-sectional view of one print path of (B). [Figure 6] FIG. 11 is a diagram for explaining a first comparative example of a print head, in which (A) is a bottom cross-sectional view of the first comparative example of a print head, (A') is a partially enlarged cross-sectional view of (A), and (B) is an enlarged cross-sectional view of one print pass of a molded short fiber / long fiber competitively reinforced thermoplastic resin structure (print pass) S. [Figure 7] FIG. 11 is a diagram for explaining a second comparative example of a print head, in which (A) is a bottom cross-sectional view of the second comparative example of a print head, (A') is a partially enlarged cross-sectional view of (A), and (B) is an enlarged cross-sectional view of one print pass of a molded short fiber / long fiber competitively reinforced thermoplastic resin structure (print pass) S. [Figure 8] 5 and 7, where (A) is a perspective view explaining the direction of print head movement, and (B) is a diagram explaining the size of the concentric twin-axis nozzle and guide pipe of the print head. [Figure 9] FIG. 9 is a diagram for explaining the operation of the print head in FIG. 8. [Figure 10] 1 shows a second embodiment of a print head for a 3D printer according to the present invention, in which (A) is a cross-sectional view of the bottom of the print head, (B) is a perspective view of the nozzle cap, (C) is a perspective view of the nozzle cap attached, and (D) is a cross-sectional view with a portion cut away of (C). [Figure 11] FIG. 2 is a diagram for explaining a fiber cutting function of the print head for the 3D printer in FIG. 1. [Figure 12] FIG. 13 is a diagram showing a third embodiment of a print head for a 3D printer according to the present invention. [Figure 13] FIG. 1 is a cross-sectional view showing a conventional print head for a 3D printer. [Figure 14] FIG. 14 is a diagram for explaining a problem with the print head in FIG. 13. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] FIG. 1 is a diagram showing a 3D printer including a first embodiment of a print head according to the present invention.

[0015] In Fig. 1, a print bed 2 movable in left / right, front / rear directions (XY directions) is provided below a print body 1, a print head 3 movable in left / right, front / rear, up / down directions (XYZ directions) relative to the print body 1 is provided, and a long fiber filament loop 4 movable in left / right, front / rear directions (XY directions) relative to the print body 1 is provided. In this case, the print head 3 and the long fiber filament loop 4 are linked. A long fiber filament 4a formed into a thread shape is wound around the long fiber filament loop 4. The long fiber filament 4a is a composite of long fibers such as carbon fiber and glass fiber and resin, and has better adhesion between adjacent passes than long fiber filaments that do not contain resin.

[0016] The 3D printer shown in Figure 1 is a fused deposition model 3D printer that does not require a mold and can create complex shapes, which helps reduce the number of parts, simplify prototyping, and reduce labor costs.The 3D printer shown in Figure 1 is also a 3D printer that can concentrically inject long fibers with excellent mechanical properties and resin pellets that are expected to improve the range of material selection.

[0017] FIG. 2 shows the details of the print head 3 in FIG. 1, where (A) is a perspective view, (B) is a partially cutaway cross-sectional view, and (B') is a partially enlarged cross-sectional view of (B).

[0018] 2A and 2B, the print head 3 is composed of a screw 31 having a hollow hole 31a in the center and a spiral groove 31b on the outer periphery, a heat block 32 made of an aluminum alloy (A5052) provided around the lower periphery of the screw 31, a heater 33 attached to the heat block 32, a barrel 34 and a heat sink 34a made of A5052 provided around the screw 31 above the heat block 32, and a hopper 35 provided around the screw 31 above the barrel 34. H is a heating area provided by the heat block 32, and F is a feeding area provided by the barrel 34 and the heat sink 34a.

[0019] The upper part of the screw 31 is rotatably supported by a stainless steel casing 36 via a bearing 37. The screw 31 is fixed to a worm wheel 38a, which is rotated by a stepping motor 39 via a worm 38b. The torque is increased by a reduction mechanism with a large reduction ratio between the worm wheel 38a and the worm 38b.

[0020] A brass concentric twin-axis nozzle 40 is provided on the outside of the heat block 32 at the tip of the screw 31 .

[0021] A metal guide pipe 41 is provided in the hollow hole 31a of the screw 31 and the hollow hole 40a of the concentric twin-shaft nozzle 40 to allow the long fibers derived from the long fiber filaments 4a to pass therethrough. The guide pipe 41 is in close contact with the inner wall of the hollow hole 31a of the screw 31 but does not contact the inner wall of the hollow hole 40a of the concentric twin-shaft nozzle 40. Moreover, the guide pipe 41 protrudes slightly, for example, by 0.2 mm, from the concentric twin-shaft nozzle 40. Therefore, the long fibers pass through the hollow hole 31a of the screw 31 and the guide pipe 41 in the hollow hole 40a of the concentric twin-shaft nozzle 40 while being heated by the heat block 32, whereas the short fiber reinforced plastic resin (SCFRP) derived from the resin pellets in the hopper 35 passes through the spiral groove 31b of the screw 31, the inner wall of the hollow hole 40a in the concentric twin-shaft nozzle 40, and the passage 40b formed in the guide pipe 41 while being heated by the heat block 32. As a result, the short fiber reinforced plastic resin (SCFRP) derived from the resin pellets melts and bonds the long fibers by wrapping them in the guide pipe tip region G of the guide pipe 41, which has a temperature slightly lower than that of the nozzle tip region N. In this way, the screw 31 makes it possible to supply the long fiber and short fiber reinforced resin, while the concentric twin-shaft nozzle 40 makes it possible to supply the long fiber and short fiber reinforced resin concentrically. Furthermore, the protruding tip of the guide pipe 41 makes it possible to reduce voids V.

[0022] FIG. 3 shows the screw 31 of FIG. 2, (A) being a perspective view, and (B) being a partially cut-away cross-sectional view.

[0023] 3, the hollow hole 31a of the metal screw 31 has a diameter of 1 to 2 mm to pass the metal guide pipe 41. The spiral groove 31b of the screw 31 has a groove depth of 4 to 5 mm and a screw pitch of 15 to 17 mm to supply the resin pellets P charged in the hopper 35 to the heat region H, forming a simple screw with no compression ratio.

[0024] FIG. 4 shows the hopper 35 of FIG. 2, in which (A) is a perspective view, (B) is a vertical cross-sectional view, (C) is a horizontal cross-sectional view, and (D) shows the resin pellets P put into the hopper 35.

[0025] As shown in (A), (B), and (C) of FIG. 4, the hopper 35 has a gentle slope at the front side and an acute angle at the rear side so that the resin pellets P shown in (D) of FIG. 4 can be sufficiently charged. The resin pellets P may be made of either PAN-based short carbon fiber or pitch-based short carbon fiber. The resin pellets P that do not use filaments do not require filament shape forming, so the range of material selection is widened and material costs can be reduced. For example, short fiber reinforced resin pellets Carbon Fiber Nylon6 Pellets manufactured by 3DXTech Co., Ltd., in which about 15% short carbon fiber is compounded with the base material PA6, are used as the resin pellets P. If the temperature of the resin pellets P is less than 230°C, the amount of resin discharged from the resin pellets P is significantly reduced, while if the temperature of the resin pellets P exceeds 245°C, the amount of molten resin increases and it becomes difficult to control the amount of resin discharged.

[0026] 5 is a diagram for explaining the operation of the print head of FIG. 2, in which (A) is a cross-sectional view of the lower part of the print head 3, (A') is a partially enlarged cross-sectional view of (A), (B) is a cross-sectional view of the molded short fiber / long fiber competitively reinforced thermoplastic resin structure (print path) S, and (C) is an enlarged cross-sectional view of one print path of (B).

[0027] As shown in (A) and (A') of FIG. 5, the guide pipe 41 passes through the hollow hole 31a of the screw 31 and the hollow hole 40a of the coaxial nozzle 40 having an inner diameter of 2.5 mm, and protrudes from the tip of the coaxial nozzle 40 by a predetermined amount, for example, about 0.2 mm. As described later, this predetermined amount is a positive value, and its maximum value is determined by the value at which the groove GV described later is backfilled. Therefore, in the guide pipe tip area G, not in the nozzle tip area N, the long fiber LC of the long fiber filament 4a is impregnated with the short fiber reinforced thermoplastic resin SC of the resin pellet P. In this case, since the temperature of the guide pipe tip area G is lower than the temperature of the nozzle tip area N, for example, 235°C, as shown in (B) of FIG. 5, the long fiber LC is injected in a state in which it is wrapped in the short fiber reinforced resin SCFRP. Therefore, as shown in (C) of FIG. 5, the bending of the long fiber LC of the long fiber filament 4a in the print-molded short fiber / long fiber competitively reinforced thermoplastic resin structure (print path) S becomes small, and the long fiber LC is located at the middle position. As a result, almost no voids V are generated between the long fiber LC and the short fiber reinforced thermoplastic resin SCFRP, and inside the short fiber reinforced thermoplastic resin SCFRP.

[0028] 6 is a diagram for explaining a first comparative example of the print head of FIG. 2, in which (A) is a bottom cross-sectional view of the first comparative example of the print head, (A') is a partially enlarged cross-sectional view of (A), and (B) is an enlarged cross-sectional view of one print pass of the molded short fiber / long fiber competitively reinforced thermoplastic resin structure (print pass) S.

[0029] 6(A) and 6(A'), the tip position of the guide pipe 41 is located about 1 mm inside the tip position of the concentric twin-axis nozzle 40. Therefore, the guide pipe tip region G is located inside the concentric twin-axis nozzle 40. As a result, the short fiber reinforced thermoplastic resin SC of the resin pellets P is impregnated into the long fibers LC of the long fiber filaments 4a in the guide pipe tip region G, not in the nozzle tip region N.

[0030] In the cases of (A) and (A') in Fig. 6, the temperature of the guide pipe tip region G is higher than the temperature of the nozzle tip region N, for example 235°C, so as shown in (B) in Fig. 6, only the lower side of the long fiber LC is wrapped in short fiber reinforced resin SCFRP when injected. Therefore, the bending of the long fiber LC of the long fiber filament 4a in the print-molded short fiber / long fiber competitively reinforced thermoplastic resin structure (print path) S becomes large, and the long fiber LC is located at the upper position. As a result, large voids V are generated between the long fiber LC and the short fiber reinforced thermoplastic resin SCFRP and inside the short fiber reinforced thermoplastic resin SCFRP.

[0031] 7 is a diagram for explaining a second comparative example of the print head of FIG. 2, in which (A) is a bottom cross-sectional view of the second comparative example of the print head, (A') is a partially enlarged cross-sectional view of (A), and (B) is an enlarged cross-sectional view of one print pass of the molded short fiber / long fiber competitively reinforced thermoplastic resin structure (print pass) S.

[0032] In (A) of Fig. 7, the tip position of the guide pipe 41 is located approximately 0.5 mm outside the tip position of the coaxial nozzle 40. Therefore, the guide pipe tip region G is located even farther away than the tip of the coaxial nozzle 40. In other words, it is set to be more than half the lamination pitch of 0.6 mm. As a result, in the guide pipe tip region G, not in the nozzle tip region N, the short fiber reinforced thermoplastic resin SC of the resin pellet P is impregnated into the long fibers LC of the long fiber filaments 4a.

[0033] In the cases of (A) and (A') in Fig. 7, the temperature of the guide pipe tip region G is lower than the temperature of the nozzle tip region N, for example, 235°C, so as shown in (B) in Fig. 7, only the upper side of the long fiber LC is wrapped in short fiber reinforced resin SCFRP when it is injected. Therefore, the bending of the long fiber LC of the long fiber filament 4a in the print-molded short fiber / long fiber competitively reinforced thermoplastic resin structure (print path) S becomes smaller, and the long fiber LC is located at a lower position. As a result, voids V and grooves GV are generated inside the short fiber reinforced thermoplastic resin SCFRP.

[0034] The print path groove GV in FIG. 7B will now be described in detail.

[0035] 8 shows how print paths S are printed on the print bed 2 of FIGS. 5 and 7, where (A) is a perspective view illustrating the movement direction of the print head 3, and (B) is a diagram illustrating the size of the print head 3.

[0036] As shown in FIG. 8A, when the print head 3 moves in the moving direction M, a groove GV is formed in the print path S. In this case, the dimension of the groove GV is the width d of the guide pipe 41 shown in FIG. 8B. i It becomes.

[0037] A top view of FIG. 8(A) is shown in FIG. 9(A). The double circle in FIG. 9(A) represents the concentric twin-shaft nozzle 40. When viewed from above the print bed 2 in FIG. 8(A) (viewed from above the Z axis in FIG. 8(A)), the concentric twin-shaft nozzle 40 moves to the right along a straight line A1-A2. Let the inner diameter of the concentric twin-shaft nozzle 40 be d. o , the outer diameter of the guide pipe 41 is d i 9A, the solid double circle indicates the nozzle position of the coaxial nozzle 40 at time t0 (center position a0).

[0038] The concentric twin nozzle 40 is spaced apart by a distance L = (d o +d i The nozzle position at time t1 (t1>t0) when the nozzle advances to the left by ) / 2 is shown by a double broken circle (center position a3). For simplicity, only the line A1-A2 is considered. The molten resin injected to the right of the position a1 at the right end of the guide pipe 41 at time t0 (center position a0) moves to the right as the guide pipe 41 moves to the right, and the nozzle position at time t1 .... h At this time, as shown in FIG. 8B, the width of the groove GV is d i In this way, the distance d from the tip of the coaxial nozzle 40 is hThe short fiber reinforced thermoplastic resin SCFRP injected from the concentric twin-shaft nozzle 40 shown by the solid line in FIG. 9(A) between a1 and a2 is guided to a depth d by the guide pipe 41 protruding by a distance of d. h Only the remaining part is deleted.

[0039] The long fiber LC injected from the guide pipe 41 is h The short fiber reinforced thermoplastic resin SCFRP is fused to the surrounding short fiber reinforced thermoplastic resin SCFRP at a position lower than the position shown in FIG. 8B. Therefore, the depth of the groove GV by the guide pipe 41 is d h In the case where the resin flow is not taken into consideration, this groove GV is backfilled by the injection of short fiber reinforced thermoplastic resin SCFRP from the concentric twin-shaft nozzle 40 when the guide pipe 41 moves to the right (injection of short fiber reinforced thermoplastic resin SCFRP between a1-a2 on the A1-A2 line in (A) of FIG. 9). In the analysis of 3D printing of short fiber reinforced thermoplastic resin SCFRP by Imaeda et al. using a particle method (see Non-Patent Document 2), the short fiber reinforced thermoplastic resin SCFRP injected in the part that does not contact the nozzle edge of the guide pipe 41 immediately solidifies. The groove GV created by the guide pipe 41 does not remelt when the concentric twin-shaft nozzle 40 moves, unless molten short fiber reinforced thermoplastic resin SCFRP is supplied from the concentric twin-shaft nozzle 40, and it is considered that the resin movement due to melting is small.

[0040] For simplicity, the injection volume per unit area and unit time injected from the concentric twin-shaft nozzle 40 is assumed to be uniform, W (mm / s), and the nozzle movement speed is V (mm / s) (generally W=V). As shown in FIG. 9(A), on the line A1-A2, when the right end of the guide pipe 41 reaches position a1, a groove GV is created by pipe movement, and when the left end of the guide pipe 41 reaches position a2, backfilling of the groove at position a1 by the concentric twin-shaft nozzle 40 is completed. The nozzle movement distance is L=(d o +d i) / 2, so the time Δt for the nozzle center position to move from a0 to a3 is given by Δt=L / V. However, the time until the left end of the concentric twin-shaft nozzle 40 passes position a1 is used for forming the groove GV by the guide pipe 41, so this travel time is not used for backfilling the groove. This is shown in FIG. 9B. The position shown by the dashed line in FIG. 9B is not used for backfilling the groove because the guide pipe 41 has passed position a1. The nozzle center at this time is shifted to the right from a0 by twice the radius of the guide pipe 41 (pipe diameter). Therefore, it is necessary to subtract the time it takes for the nozzle to move by the diameter of the guide pipe 41 from the travel distance L of the nozzle, and the actual backfilling time Δt T is Δt T =(Ld i ) / V=(d o -d i ) / (2V).

[0041] The above Δt T The volume of short fiber reinforced thermoplastic resin (SCFRP) injected per unit area in time is Δt T Therefore, the height of the short fiber reinforced thermoplastic resin SCFRP per unit area injected into the groove GV formed by the guide pipe 41 is Δt T If this is greater than the depth of the groove GV created by the guide pipe 41, the groove GV is filled. The depth of the groove GV created by the guide pipe 41 is d h Therefore, the pipe installation condition is given by the following equation: Δt T W>d h (1) In the experiment, the injection speed W = V = 100 (mm / min) (1.67 (mm / s)), so equation (1) becomes the following equation (2). (d o -d i ) / 2>d h (2) The inner diameter of the concentric twin-axis nozzle 40 is 2.5 (mm), and the outer diameter of the guide pipe 41 is 1.2 (mm). By substituting these into formula (2), the following condition is obtained. 0.65(mm) > dh (3) In Figure 5, d h = 0.2 (mm), which fully satisfies formula (3). In Fig. 7, d h =0.5 (mm), which satisfies formula (3), but the groove GV is not filled. d h It is considered that when the gap is deep, bending elastic deformation occurs in the guide pipe 41 due to the resistance force pushing aside the short fiber reinforced thermoplastic resin SCFRP. This is shown in Fig. 9(C) as a schematic diagram. The guide pipe 41 is bent and deformed to the left, opposite to the nozzle travel direction (right), due to the resistance force pushing aside the short fiber reinforced thermoplastic resin SCFRP. This bending deformation is called d b Let us assume that d b Since the backfilling start time is delayed by this amount, and the nozzle movement speed does not change, the backfilling end time does not change, so the time available for backfilling becomes shorter.

[0042] Looking at the cross section of Fig. 7(C), it can be seen that the long fibers LC are observed just below the groove GV and are not backfilled at all. This is presumably because the guide pipe 41 is in contact with the left end of the coaxial twin-shaft nozzle 40 in Fig. 9(C).

[0043] FIG. 10 shows a second embodiment of a print head for a 3D printer according to the present invention, in which (A) is a cross-sectional view of the bottom of the print head, (B) is a perspective view of the nozzle cap, (C) is a perspective view of the nozzle cap attached, and (D) is a cross-sectional view with a part cut away of (C).

[0044] In FIG. 10A, a nozzle cap 42 is added to the components in FIG. 5A. The nozzle cap 42 has a hole 41a for inserting the concentric twin-axis nozzle 40, as shown in FIG. 10B. Therefore, as shown in FIG. 10A, FIG. 10C, and FIG. 10D, the nozzle cap 42 is attached so as to cover the concentric twin-axis nozzle 40, thereby substantially increasing the cross-sectional area of ​​the concentric twin-axis nozzle 40 and preventing the short fiber reinforced resin SCFRP injected from the concentric twin-axis nozzle 40 from being cooled. Therefore, the fluidity of the short fiber reinforced resin SCFRP can be maintained, and the voids generated in the short fiber / long fiber competitively reinforced thermoplastic resin structure S after injection can be reduced, and the adhesion between the short fiber / long fiber competitively reinforced thermoplastic resin structures S can be improved. In order to make the temperature of the nozzle cap 42 the same as the print head temperature, the material of the nozzle cap 42 is the same as the material of the heat block 32, for example, aluminum alloy (A5052).

[0045] In the above-mentioned first and second embodiments, when it is necessary to cut the short fiber / long fiber competitively reinforced thermoplastic resin structure S containing long fibers, especially the long fibers LC, a fiber cutting function may be provided in the guide pipe 41. This will be described with reference to FIG.

[0046] For example, as shown in FIG. 11(A), a grooved guide pipe 41a is provided instead of the guide pipe 41 in FIG. 2. When cutting the long fibers LC, the grooved guide pipe 41a is rotated manually to fix the long fibers LC in the grooves 41a-1 of the grooved guide pipe 41a. Next, the concentric twin-shaft nozzle 40 or the print bed 2 is moved at high speed to cut the long fibers LC by impact force. On the other hand, as shown in FIG. 11(B), the lower edge of the guide pipe 41 is utilized. The motor for moving the print bed 2 or the guide pipe 41 (i.e. print head 3)The motor for moving the print bed 2 is made capable of high-speed movement, i.e., it is made large. Alternatively, the print bed 2 is divided into two stages, upper and lower, and a motor is provided to move only the upper stage at high speed. Alternatively, the guide pipe 41 is supported by a cantilever, so it can be displaced by a small load. Therefore, the long fiber LC is fixed by the guide pipe pushing unit 41b, and the print bed 2 (or only its upper stage) or the guide pipe 41 is moved by a motor. (Print Head 3) or by striking the upper portion of the guide pipe 41 with a thin plate-shaped hammer, the guide pipe 41 is moved, thereby cutting the long fibers LC. For example, the long fibers LC are cut by a combination of vertical movement of the guide pipe 41 (print head 3) and left / right and front / rear movement of the print bed 2. In this manner, the temperature in the vicinity of the guide pipe 41 of the short fiber / long fiber competitively reinforced thermoplastic resin structure S becomes a temperature suitable for cutting.

[0047] In the above embodiment, only one guide pipe 41 or grooved guide pipe 41a is provided in the hollow hole 31a of the screw 31, but multiple guide pipes 41 or grooved guide pipes 41a may be provided in the hollow hole 31a of the screw 31. In this case, the protruding amounts of 0.2 mm of the guide pipes 41 or grooved guide pipes 41a may be slightly different from each other to disperse the long fibers LC within the print path.

[0048] Furthermore, in the above embodiment, the guide pipe 41 is provided so as to pass through the hollow hole 31a of the screw 31, the hollow hole 32a of the heat block, and the hollow hole 40a of the concentric twin-shaft nozzle 40. However, instead of the guide pipe 41, a first nozzle for long fibers that passes through the hollow hole 31a of the screw 31 may be provided below the heat block 32, and instead of the concentric twin-shaft nozzle 40, a second nozzle for thermoplastic resin or short fiber reinforced thermoplastic resin (SCFRP) that passes through the screw spiral groove 31b may be provided below the heat block 32, and the first nozzle may protrude a predetermined amount from the second nozzle. In this case, the predetermined amount d h teeth, 0 <d h <(d o -d i ) / 2 However, d o is the inner diameter of the second nozzle, d i is the outer diameter of the first nozzle It is.

[0049] Furthermore, although the screw 31 is provided in the above-mentioned first and second embodiments, it is not necessary to provide the screw 31. This will be described with reference to FIG.

[0050] FIG. 12 is a diagram showing a third embodiment of a print head for a 3D printer according to the present invention.

[0051] As shown in FIG. 12, instead of the screw 31 in FIG. 2 and FIG. 10, a hollow tube 51 having a hollow hole 31a for passing the continuous fiber LC or continuous fiber filament and hollow tubes 52-1, 52-2 having hollow holes 52-1a, 52-2a for passing the resin or short fiber resin filament SCFRP are provided. The number of hollow tubes 52-1, 52-2 may be one or three or more. The heat block 32 has a heat block hollow hole 32a connected to the hollow tubes 51, 52-1, 52-2. The concentric twin-shaft nozzle 40 has a nozzle hollow hole 40a communicating with the heat block hollow hole 32a. The guide pipe 41 passes through the hollow hole 51a, the heat block hollow hole 32a, and the nozzle hollow hole 40a, and protrudes a predetermined amount, for example, 0.2 mm, from the concentric twin-shaft nozzle 40. The hollow tubes 52-1 and 52-2 are connected to the gap between the heat block hollow hole 32a and the guide pipe 41 and the gap between the concentric twin-axis nozzle 40 and the guide pipe 41. In this case, the predetermined amount d h teeth, 0 <d h <(d o -d i ) / 2 However, d o is the inner diameter of the concentric twin-shaft nozzle 40, d i is the outer diameter of the guide pipe 41 It is.

[0052] Furthermore, in the above-described embodiment, carbon fibers are used, but other fibers, such as glass fibers, Kevlar (registered trademark) fibers, SiC fibers, alumina fibers, and the like, may be used.

[0053] Furthermore, the thermoplastic resin may be other resins such as polyphenylene sulfide resin (PPS), PLA, ABS, PC, PEI, and PEEK, in addition to nylon (registered trademark). In addition, when using a photocurable resin, it is necessary to apply ultraviolet rays to the nozzle from all sides.

[0054] Furthermore, the present invention can be applied to any modifications within the obvious scope of the above-described embodiment. [Explanation of symbols]

[0055] 1: Printed body 2: Print bed 3: Print head 4: Long fiber filament loop 4a: Long fiber filament 31: Screw 31a: Hollow hole 31b: Spiral groove 32: Heat block (heat area) 33: Heater 34: Barrel (feed area) 34: Heat sink 35: Hopper 36: Casing 37: Bearing 38a: Worm wheel 38b: Worm gear 39: Stepping motor SCFRP: Short fiber reinforced plastic 40: Concentric twin-shaft nozzle 40a: Hollow hole 40b:Aisle 41: Guide pipe 41a: Grooved guide pipe 42: Nozzle cap 42a: hole 51, 52-1, 52-2: Hollow tube N: Nozzle tip area G: Guide pipe tip area SC: Short fiber SCFRP: Short fiber reinforced plastic GV: Groove 101: Screw 101a: Hollow hole 101b: Spiral groove 102: Screw cover 103: Heater 104: Nozzle 105: Stepping motor 106: Small drive wheel 107: Conduction belt 108: Large drive wheel 109: Fiber cutting device LCF: Long fiber filament LC: Long fiber RF: Thermoplastic filament SO: Long fiber reinforced thermoplastic resin structure N: Nozzle tip area (screw tip area)

Claims

1. A 3D printer having a print bed that can move in left-right, front-back, and up-down directions, and a print head that can move on the print bed in left-right, front-back, and up-down directions, The print head includes: a screw having a screw hollow hole at the center and a screw helical groove on the outer periphery; a heat block having a central heat block hollow hole for accommodating the screw; A concentric twin-axis nozzle having a nozzle hollow hole at the center and provided at the tip of the heat block; a guide pipe passing through the screw hollow hole, the heat block hollow hole, and the nozzle central hole and projecting from the concentric twin-axis nozzle; Equipped with The long fiber filaments are passed through the guide pipe from top to bottom, In a 3D printer in which a thermoplastic resin is passed from above to below through the screw spiral groove, the gap between the heat block hollow hole and the guide pipe, and the gap between the concentric twin-axis nozzle and the guide pipe, A method for cutting a long fiber filament in a 3D printer, the method being performed by moving the guide pipe and the print bed while the long fiber filament is fixed.

2. A method for cutting a long fiber filament in a 3D printer as described in claim 1, wherein the fixation of the long fiber filament is performed by a guide pipe extrusion unit positioned above the concentric twin-axis nozzle.

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