Method for winding a filament for an additive manufacturing device

Abstract

The present document relates to a method for winding a filament (4) of an additive manufacturing device, comprising the following steps: • - providing a filament (4) filled with at least 80% by mass of a metal powder; • - heating the filament (4) to a temperature of up to at least 70°C and maintaining the filament at this temperature; • - winding the filament (4) around an axis of a coil (110, 142), the coil being preferably made of metal, the diameter of the coil (110, 142) in an unloaded state being greater than or equal to a diameter of 100 mm.

Description

Technical Field

[0001] This article relates to a method for winding a filament at a high metal powder loading rate. This filament is intended for use in additive manufacturing apparatuses. Background Technology

[0002] When manufacturing components via additive manufacturing, filaments are melted and solidified to create the component layer by layer. The storage of the consumable filaments is carried out around the coil.

[0003] Conventionally, in the fused wire fabrication (FFF) process, filaments are used, which include a binder comprising polymers such as polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polycarbonate, nylon, glycolated polyethylene terephthalate (PETG), etc. Generally, these filaments are not filled with metal powder. Sometimes, they are slightly filled with, for example, carbon fibers to enhance the final properties of the part. In the case of additive manufacturing of metal parts via the FFF process, the filaments achieve extremely high metal powder filling rates because the aim is to produce a composite part called a "green part." This part undergoes several post-printing operations to remove the polymer portion of the part and densify it to ultimately obtain a completely metallic part.

[0004] Generally, the FFF process comprises 80% by mass and preferably between 85% and 91% by mass of metal powder. The filaments typically have a diameter between 1.5 mm and 5 mm and preferably between 1.65 mm and 1.85 mm.

[0005] This process is very similar to metal powder injection molding, also known as "metal injection molding" (MIM). The difference between FFF and MIM is that in FFF, the part is printed out, rather than being injection molded using a press and mold as in MIM.

[0006] It is important to understand the MIM process as a whole in order to understand the necessity and importance of having filaments with a metal powder content of 80% or more by mass in the FFF process.

[0007] Figure 1 The MIM process 1 is illustrated in a conventional manner. In this MIM process 1, binder 2 and metal powder 4 are mixed in mixer 6 and then extruded integrally in extruder 8. Filaments 10 are obtained and injection molded using press 12. A green part 14 is obtained.

[0008] Figure 2The FFF process 3 is illustrated. In this FFF process 3, the filament 10 is obtained in the same manner as in the MIM process 1. However, in the FFF process 3, the filament 10 does not pass through the press 12, but the green part 14 is printed by means of a 3D printer 16, in which the filament 10 filled with metal powder is loaded.

[0009] Subsequently, Figure 1 The MIM process 1 and shown in the figure Figure 2 In the FFF process 3 illustrated, the green part 14 passes through a first debinding furnace 18. As the name suggests, this first operation removes the polymer binder. In this step, the polymer portion contained in the part is removed. At the end of this step, the debinded part 20 consists almost entirely of metal powder. Only a small amount of binder remains between the powder particles to hold the part in place. If all the binder is removed at this step, the part will shrink. At the end of this step, sintering 22 occurs. At this stage, we discuss the brown part 24. Once 90% of the binder has been removed, the fragile and porous part passes through a second sintering furnace, which densifies the part. At the end of this sintering step, the part will be entirely metallic, and the porosity left during the debinding step by removing the binder will almost completely disappear. Correspondingly, the volume will decrease. Therefore, the higher the proportion of binder in the green part, the greater the change in the final volume of the part. For this reason, it is desirable to print or injection mold parts with the highest metal content to minimize volume changes and to more easily predict the final geometry of the part. Contraction is typically isotropic on all three axes.

[0010] therefore, Figure 3 It is illustrated Figure 3 In A, the green component 14 and Figure 3 The volume change between the sintered component or brown component 24 in B. The higher the metal powder filling rate, the lower the volume change. However, a high metal powder filling rate makes the filament extremely fragile.

[0011] Figure 4 The evolution of bending stress σ in megapascals (MPa) as a function of strain rate ε is illustrated.

[0012] Three-point bending tests on this filament with a high metal powder filling rate showed that at room temperature, i.e., at a temperature between 18°C ​​and 22°C, the elasticity of the filament was extremely low and less than or equal to 1%.

[0013] Available from Figure 4 Note that the bending stress σ increases rapidly until it reaches 17 MPa at a strain rate of 0.4%. Then, for strains above 0.4%, the bending stress σ suddenly decreases, indicating the breakage of the filament.

[0014] Under such conditions, such as Figure 5 As illustrated, the filament is particularly brittle at room temperature. Therefore, it is impossible to wind and unwind the filament onto the coil of the additive manufacturing apparatus without any risk of cracking 102 or breakage. Breakage or fracture of the filament during winding around the coil renders it unusable. In fact, in the FFF process, the printhead and drive system require a continuous filament with a constant cross-section to ensure a consistent flow rate.

[0015] To overcome this difficulty, it is known that by surrounding such... Figure 6 The filament 104 illustrated is protected by a polymer surface layer 106. Adding this 50 μm thick polymer surface layer 106 around the filament 104 allows for the achievement of the radius of curvature required for winding the filament and promotes the printing material because it makes the filament less brittle and less viscous. However, this solution increases the matrix content in the filament 4, which induces other difficulties, such as increased residual stress in the part formed from the filament. A higher proportion of binder leads to greater shrinkage and makes it less predictable. The presence of the polymer surface layer around the filament can cause uneven distribution of powder and binder in the part.

[0016] Therefore, it is important to provide a technical solution that does not modify the composition of the filament and ensures its integrity (i.e., there are no cracks or breaks in the filament). Summary of the Invention

[0017] This article relates to a method for winding filaments for an additive manufacturing apparatus, comprising the following steps:

[0018] - Provide filaments filled with at least 80% by mass of metal powder;

[0019] - Heating the filament to a temperature of at least 70°C and maintaining the filament at that temperature;

[0020] - The filament is wound around the axis of a coil, preferably made of metal, the diameter of which is greater than or equal to 120 mm in the unloaded state.

[0021] Under such conditions, it is possible to wind fine filaments without causing breakage or cracks in them. This allows the coil to be placed under favorable elastic conditions. Additionally, the coil is preferably made of metal, which prevents it from deforming due to heat.

[0022] The diameter of the coil can be between 100mm and 140mm, preferably between 120mm and 140mm.

[0023] The filament can be heated to a temperature between 70°C and 140°C, preferably between 70°C and 90°C.

[0024] This article relates to a device for winding filaments onto coils used in additive manufacturing apparatus, comprising:

[0025] - Fine filament extruder;

[0026] -Stretching aids;

[0027] - A component for heating the filament to a temperature of at least 70°C;

[0028] -Drive components;

[0029] - A component for winding the filament around the coil, which is preferably made of metal, wherein the diameter of the coil in the unloaded state is greater than or equal to 100 mm.

[0030] The heating element can be inserted between the stretching element and the winding.

[0031] The tensioning member may include a traction belt.

[0032] The component for heating the filament may include a component for blowing air at the temperature.

[0033] The component for heating the filament may include an infrared heating component.

[0034] The driving component may include at least one driving roller. Attached Figure Description

[0035] [ Figure 1 The symbol represents metal powder injection molding, also known as "metal injection molding" (MIM).

[0036] [ Figure 2 The symbol ] indicates the fused wire manufacturing process, also known as "fused wire manufacturing" (FFF);

[0037] [ Figure 3 ]express Figure 3 The green blank component in A and Figure 3 Volume changes between sintered portions in B.

[0038] [ Figure 4 ] represents a three-point bending test of a filament at room temperature, and more specifically, the evolution of the bending stress σ of the filament in megapascals (MPa) as a function of strain rate ε.

[0039] [ Figure 5 ] indicates an instance of a damaged filament, including a crack;

[0040] [ Figure 6 ] indicates a filament surrounded by a polymer surface;

[0041] [ Figure 7 [This refers to an extrusion apparatus or industrial extrusion line for filaments according to the present invention;]

[0042] [ Figure 8 ]exist Figure 12 A represents the coil according to the present invention and in Figure 12 B represents a conventional coil.

[0043] [ Figure 9 [This represents the evolution of the elastic modulus G' of a filament as a function of temperature T during dynamic thermomechanical analysis (DMTA) according to the present invention;

[0044] [ Figure 10 [This indicates a three-point bending test of a filament at a temperature T of 80°C according to the present invention, and more specifically, the evolution of the bending stress σ of the filament in megapascals (MPa) as a function of strain rate ε.]

[0045] [ Figure 11 ]exist Figure 11 A represents the evolution of the bending stress σ of the filament, in megapascals (MPa), according to the invention, as a function of strain rate ε, and in Figure 11 B represents the evolution of the minimum radius of curvature R of the central roller of the coil, in millimeters (mm), so that the filament will not be damaged as the strain rate ε changes;

[0046] [ Figure 12 [] represents a diagram showing the radius of curvature as a function of strain obtained during a three-point bending test. Detailed Implementation

[0047] This article pertains to the background of additive manufacturing apparatuses that allow for the layer-by-layer construction of components by depositing molten filaments that solidify upon cooling.

[0048] Figure 7 A facility 108 is illustrated for extruding filament 104 and winding it onto coil 110 for subsequent use in an additive manufacturing apparatus.

[0049] In this facility, filament 104 is produced by means of an extruder 112. This filament 104 has a diameter between 1.5 mm and 5 mm. The filament comprises one to three polymers and is filled with at least 80% by mass of metal powder.

[0050] Subsequently, the filament 104 is stretched by stretching members 114. These stretching members 114 include traction belts 116. The filament 104 is then heated to a temperature of at least 80°C by heating members 118. These heating members 118 include members 120 for heating air to said temperature and / or infrared heating members 122. Thus, the filament 104 is heated and maintained at said temperature: one of the adhesive compounds remains in a molten state to soften the filament. The filament is then driven toward the coil 110 by driving members 124. These driving members include at least one drive roller 126.

[0051] The filament 104 is then wound around the coil 110 by the winding member 127. This coil includes a central roller 128 or cylindrical portion having a circular base around which the filament is wound. The central roller 128 includes the outer periphery of its base, which is inscribed in a circle, such that the central roller 128 can be a cylindrical portion having a polygonal base. This central roller 128 has a diameter greater than or equal to 100 mm, preferably between 100 mm and 140 mm, and still more preferably between 120 mm and 140 mm.

[0052] Figure 8 It is illustrated Figure 12 The standard coil 140 in B and Figure 12 A comparison between coils 142 for winding the metal powder-filled filaments according to the invention, as described in section A. In the coil 142 according to the invention, the diameter of the central roller 128 is 120 mm, and the coil is preferably made of metal. Figure 12 As shown in Figure A, the diameter of the central roller 128 is relative to... Figure 12 The conventional coil 140 in B is smaller. The coil 142 according to the invention includes a first cylindrical flange 144 and a second cylindrical flange 146, each having a diameter larger than that of the central roller 128.

[0053] In operation, due to these elastic properties, the filament can be wound without breaking or cracking, starting at a temperature of at least 70°C, preferably between 70°C and 90°C. Once wound while hot, the filament retains its wound shape as it cools down. To unwind the filament without causing it to break or crack, it is necessary to heat the filament to a temperature up to at least 70°C, preferably between 70°C and 140°C, and still more preferably between 70°C and 90°C.

[0054] Figure 9The evolution of the elastic modulus G' of the filament in megapascals (MPa) as a function of temperature T during a dynamic thermomechanical analysis test, also known as DMTA, is illustrated. This elastic modulus G' indicates both the stiffness and elastic components of the material. The elastic modulus G' has a value of 9.5 × 10⁻⁶ at a temperature of approximately 50 °C. 3 The value of MPa decreases with increasing temperature. Softening is carried out at temperatures between 80°C and 140°C, thereby imparting the desired properties to the filament for winding around a coil without breakage or fracture. At a temperature T of 80°C, the elastic modulus G' decreases to 4.4 × 10⁻⁶. 3 MPa and decreases to less than 10 at a temperature T of 140℃. 3 MPa.

[0055] Figure 10 The diagram illustrates a three-point bending test performed on the filament at a temperature of 80°C, and more specifically, this... Figure 10 This demonstrates the evolution of bending stress σ in megapascals (MPa) as a function of strain rate ε. Four curves corresponding to four identical tests are presented. Figure 4 Compared to the results of the three-point bending test conducted at room temperature, the bending stress σ is lower in this paper. A plateau is reached starting from a strain rate of approximately 1%, where the bending stress σ is between 7 MPa and 9 MPa. Therefore, even at a strain rate of 5%, the filament will not break or fracture due to these stresses.

[0056] based on Figure 9 The results of the three-point bending test illustrated in the figure may be able to determine the minimum acceptable radius of curvature R of the filament before it breaks at a given temperature and under these conditions at 80°C. This is in Figure 11 Shown in the middle.

[0057] Figure 11 B illustrates the radius of curvature R of the central roller of the coil, expressed in millimeters (mm), as a function of the strain rate ε. Figure 11 B is known as... Figure 12 The position of the three red dots shown in the figure was obtained during the three-point bending test. The machine records the displacement of the center point 160, while the two other support points 162 and 164 remain in fixed positions. Therefore, due to the positions of the three points 160, 162, and 164, and thus based on the displacement of the center point, it is possible to determine the radius of curvature R of the component shown by curve 166 during the three-point bending test through small geometric calculations.

[0058] In recording these displacements and stresses throughout the entire three-point bending test, the radius of curvature R can be represented by the displacement of the center point, which varies with the stress in the component. Ultimately, it is possible to plot a curve representing the radius of curvature R as a function of strain rate ε for each location corresponding to the center point, and thus determine the maximum radius of curvature R acceptable to the filament, such as... Figure 10 As shown in Figure B.

[0059] Therefore, based on the calculations performed, a critical strain rate ε that should not be exceeded to avoid damaging the filament has been deduced. This critical strain is between 2% and 4%, and preferably less than 4%. Figure 11 A corresponds to Figure 6 And allows with Figure 11 B is used for connection. For example... Figure 11 As shown in Figure B, the breakage of the filaments occurs between 5.5% and 6.5%, as indicated by the two dashed lines 150 and 152.

[0060] Figure 11 The curve in B shows that the greater the strain rate ε, the smaller the minimum radius of curvature R will be, and it should not exceed the minimum radius of curvature to avoid damaging the filament. Under the aforementioned conditions, i.e., when the strain rate is less than 4%, as indicated by the limit line 154, the minimum diameter of the central roller of the coil is between 100 mm and 140 mm, and preferably greater than or equal to 120 mm.

Claims

1. A method for winding a filament (4) of an additive manufacturing device, comprising the steps of: - providing a filament (4) filled with at least 80% by mass of metal powder; - heating the filament (4) to a temperature of up to at least 70°C and maintaining the filament (4) at said temperature; - winding the filament (4) around an axis of a coil (10) having a diameter greater than or equal to 100 mm in an unloaded state.

2. The method for winding a filament (4) of an additive manufacturing device according to claim 1, characterized in that, The coil is a metallic coil.

3. The method for winding a filament (4) of an additive manufacturing device according to claim 1, characterized in that, The diameter of the coil is between 100 mm and 140 mm.

4. The method for winding a filament (4) of an additive manufacturing device according to claim 3, characterized in that, The diameter of the coil is between 120 mm and 140 mm.

5. The method for winding a filament for an additive manufacturing device according to any of the preceding claims, characterized in that, The filament (4) is heated to a temperature between 70°C and 140°C.

6. The method for winding a filament (4) of an additive manufacturing device according to claim 5, characterized in that, The filament (4) is heated to a temperature between 70°C and 90°C.

7. A facility (8) for winding a filament (4) onto a coil (10) of an additive manufacturing device, comprising: - a filament (4) extruder (12); - a stretching member (14); - a heating member (18) for heating the filament (4) and maintaining it at a temperature of at least 70°C; - a drive member (24); - a winding member (27) for winding the filament (4) around the coil (10), the coil (10) having a diameter greater than or equal to 100 mm in an unloaded state.

8. The device for winding a filament (4) onto a coil (10) of an additive manufacturing apparatus according to claim 7, characterized in that The coil is a metallic coil.

9. The device for winding a filament (4) onto a coil (10) of an additive manufacturing apparatus according to claim 7, characterized in that The heating member (18) for heating the filament and maintaining it at a temperature of at least 70°C is between the stretching member (14) and the winding member (27).

10. The facility for winding a filament onto a coil of an additive manufacturing device according to claim 7 or 9, characterized in that The stretching member (14) comprises a traction belt.

11. The facility for winding a filament onto a coil of an additive manufacturing device according to claim 7 or 9, characterized in that The heating member (18) for heating the filament comprises a member (20) for blowing air at the temperature.

12. The facility for winding a filament onto a coil of an additive manufacturing device according to claim 7 or 9, characterized in that The heating member (18) for heating the filament comprises an infrared heating member (22).

13. The facility for winding a filament onto a coil of an additive manufacturing device according to claim 7 or 9, characterized in that The drive member (24) comprises at least one drive roller (26).

Images