Hot end for 3D printing of color and structural gradient ceramic via fused deposition modelling

Abstract

A hot end (16) for a fused deposition modeling (FDM) printer has two inlets for low flowability materials, which may be different in color and / or structure. Two separate channels (21a, 21b) of the hot end (16) lead from the inlet to a common end at the central tube (25). The two channels (21a, 21b) are in the form of two special angled tubes, which intersect at their ends and taper from the extruder (19 ') towards their ends. The central tube (25) extends from the ends of the channels (21a, 21b) to the nozzle (26). The SK-type static mixer (24) is located in the central tube (25) and the heating unit (11) surrounds the hot end (16). A controller (15) operates two extruders (19 ') that supply low flowability material to the two inlets of the hot end (16) to produce a ceramic (e.g., zirconia) object having a 3D color and structural gradient.

Description

(19) State Intellectual Property Office (12) Invention Patent Application (10) Application Publication Number (43) Application Publication Date (21) Application Number 202480056698.0 (22) Application Date 2024.09.02 (30) Priority Data 63 / 584289 2023.09.21 US (85) PCT International Application Entering National Phase Date 2026.03.05 (86) PCT International Application Application Data PCT / CN2024 / 116231 2024.09.02 (87) PCT International Application Publication Data WO2025 / 060867 EN 2025.03.27 (71) Applicant: University of Hong Kong Address: Pok Fu Lam Road, Hong Kong, China (72) Inventors: Xu Jiehan, Zhang Yuqiang, Zhang Junjing (74) Patent Agency: Beijing Panhua Weiye Intellectual Property Agency Co., Ltd. 11280 Patent Attorney Guo Guangxun (51) Int.Cl. B28B 1 / 00 ​​(2006.01) B29C 64 / 209 (2006.01) B33Y 30 / 00 (2006.01) (54) Invention Title Hot End for 3D Printing Color and Structure Gradient Ceramics by Fused Deposition Modeling (57) Abstract A hot end (16) for a fused deposition modeling (FDM) printer having two inlets of low-flow-rate materials that may be different in color and / or structure. Two separate channels (21a, 21b) of the hot end (16) lead from the inlets to a common end at a central tube (25). The two channels (21a, 21b) are in the form of two specially angled inclined tubes that intersect at their ends and gradually narrow from the extruder (19') toward their ends. The central tube (25) extends from the ends of the channels (21a, 21b) to a nozzle (26). An SK-type static mixer (24) is located in a central tube (25), and a heating unit (11) surrounds the hot end (16). A controller (15) operates two extruders (19') that supply low-flow material to the two inlets of the hot end (16) to produce ceramic (e.g., zirconium oxide) objects with 3D color and structural gradients.Claims (2 pages), Description (5 pages), Drawings (5 pages), CN 121794105 A 2026.04.03 CN 1 21 79 41 05 A 1. A hot end for a fused deposition modeling (FDM) printer, comprising: two inlets of low-flow-rate material, wherein the material may be different in color and / or structure; two separate channels extending from the inlets to their ends, the two channels forming two angled tubes that intersect at their ends and gradually narrow towards their ends; a central tube extending from one end of the channels to another end; an outlet nozzle located at the end of the central tube; a static mixer located in the central tube; and a heating unit surrounding the hot end. 2. The hot end of claim 1, wherein the static mixer is an SK static mixer having six or more elements. 3. The hot end of claim 1, wherein if a filament with a diameter of 1.75 mm is to be used in the hot end, the upper diameter of the separated channels is 2.00 mm, and gradually narrows towards their ends to a diameter of 0.80 mm. 4. The hot end of claim 3, wherein the diameter of the nozzle is 0.4 mm. 5. An FDM printer having a hot end according to claim 1. 6. The FDM printer of claim 5, further comprising: two low-flow material sources, the materials being different in color and / or structure; each material source connected to a separate inlet of the hot end; an extruder for extruding the low-flow material from the material sources; and a controller for controlling the extruder to extrude the two filaments in different proportions at varying heights to achieve a three-dimensional color and / or structural gradient effect. 7. A method for forming a three-dimensional (3D) zirconia object, comprising the steps of: providing a first zirconia low-flow filament having a first color and a first structure; providing a second zirconia low-flow filament having a second color and a second structure; designing slices of the object using a software-operated controller, the software determining the ratio of the first zirconia low-flow filament to the second zirconia low-flow filament extruded at each printing level by the hot end of a fused deposition modeling (FDM) printer, starting from the lowest level; the hot end of the FDM printer having two inlets, each inlet for a filament, and mixing the first and second filaments at the stated ratio for each level in a static mixer; and depositing the mixed filaments onto a hot bed to form a green body having a gradient determined by the stated ratio. 8. The method of claim 7, wherein the first zirconia low-flow filament and the second zirconia low-flow filament are prepared by using a 0.4 mm nozzle at a printing speed of 20 mm / s and a printing temperature of 180 degrees Celsius. 9. The method of claim 7, wherein the layer thickness is 0.2 mm.10. The method of claim 7, further comprising the steps of: removing the green body from the hot bed; subjecting the green body to solvent degreasing; after solvent degreasing, treating the green body with thermal degreasing; and subjecting the thermally degreased green body to sintering. 11. The method of claim 10, wherein the solvent degreasing is performed by placing the green body in an acetone bath. 12. The method of claim 10, wherein the thermal degreasing is performed by subjecting the solvent-degreased green body to a heating rate of 8°C / h from 20°C to 500°C, and allowing it to stand for 2.5 days to complete the thermal degreasing. Claims 1 / 2 page 2 CN 121794105 A 13. The method of claim 10, wherein the sintering process is performed in a high-temperature furnace, undergoing the following thermal cycle: from 20°C to 1475°C at a rate of 50°C / h over 29 hours, followed by holding for 1 hour, and then from 1475°C to 20°C at a rate of 100°C / h over 15 hours. Claims 2 / 2 Page 3 CN 121794105 A Hot End for 3D Printing Color and Structure Gradient Ceramics by Fused Deposition Modeling

[0001] Cross Reference to Related Patent Applications

[0002] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 548,289, filed September 21, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a hot end for a fused deposition modeling printer, and more particularly, to a hot end for such a printer capable of constructing 3D color and structure gradient ceramic objects. Background Art

[0004] Ceramics such as zirconia are widely used in many applications, especially in the medical and dental fields. Of all ceramic materials used in medicine and dentistry, zirconia ceramics have the strongest mechanical properties. Its high structural strength combined with good aesthetics and excellent biocompatibility makes it particularly suitable for such applications. In medicine, zirconia can be used in implants, such as for hip joints. One useful aspect of zirconia in dentistry is that its color can be gradient and come in a variety of shades to replicate the color of natural teeth. Zirconia used to manufacture dental restorations often requires staining or prefabrication in a gradient manner before sintering, which is complex and technically sensitive.

[0005] There are some additive manufacturing methods available for manufacturing zirconia parts, but these methods generally require slow and expensive specialized machinery. Furthermore, it is difficult to achieve the desired gradient structure or gradient color in zirconia using these methods.

[0006] Fused deposition modeling (FDM) is one of the most popular additive manufacturing (AM) methods for polymer materials. It is commonly used for 3D printing. An FDM printer extrudes thermoplastic filaments in a series of layers over a build plate to construct a three-dimensional object.A key component of an FDM printer is the hot end, which heats the filament and extrudes the material through the nozzle to print the sample. Since the filament is delivered in a single tube, different components cannot be mixed to achieve color and / or structural gradients.

[0007] U.S. Patent No. 11,358,326 discloses a hot end with an actuating rod in a heated chamber. This rod imparts mechanical energy to the filament within the heated chamber before it is extruded through an exit orifice. However, this patent does not disclose the manufacture of gradient 3D printed objects from low-flow filament materials. U.S. Application Publication No. US2020 / 0338822 discloses a control box for a printer that rotates the desired nozzle into position. However, it does not disclose printing gradient materials or mixing two components to produce gradient colors or structures.

[0008] While additive manufacturing offers many advantages in the manufacture of ceramic parts, printing gradient colors in ceramics remains difficult, and the process is time-consuming and expensive. Summary of the Invention

[0010] This invention relates to a low-cost robocasting system capable of controlling the color (including gradients of a single color) and structural gradients of ceramic (zirconia, for example) objects constructed using an FDM printer. The system is economical and saves manufacturing time.

[0011] The hot end of an FDM printer is used to form the object. According to the invention, the hot end has two tubes, which is the opposite of the single tube in existing FDM printers. However, when the filament material has low flowability, having two tubes makes them prone to clogging. Clogging in the tubes means that the two components cannot be completely mixed. However, the invention has two specially angled tubes with gradually narrowing diameters. This prevents them from being clogged by low-flow filament materials and ensures that the material is ready for mixing. Even when the zirconia filament has low flowability, this special design of the hot end allows for smoother gradient printing. In particular, this special design can be used to print gradient samples when the printing material has low flowability.

[0012] The printer also has six or more metal elements forming a static mixer located in a central tube at the hot end, so that the two components are fully mixed before being expelled from the nozzle at the hot end. The static mixer can fully mix two low-flow materials without any power. Therefore, when two materials in different proportions pass through the static mixer, they can be mixed more thoroughly.

[0013] The entire hot end is surrounded by an electric heater unit. When the hot end is heated, two extruders can be controlled to extrude two filaments in different proportions at different heights of the printed layer to achieve a 3D gradient effect. Therefore, by utilizing the heater, the static mixer design, and the angled tube together, the two components are fully mixed before being extruded into the nozzle. By controlling the delivery ratio and mixing of the two materials, a 3D color and structural gradient of the ceramic filaments can be achieved.

[0014] Therefore, the FDM printer and the static mixer in the customized hot end according to the invention can print controlled gradient zirconia with two different low-flow materials in a more economical and faster manner. Brief Description of the Drawings

[0016] The foregoing and other objects and advantages of the invention will become more apparent when considered in conjunction with the following detailed description and the accompanying drawings, in which like reference numerals denote like elements in the various views, and wherein:

[0017] FIG1 is an illustration of a fused deposition modeling (FDM) printer;

[0018] FIG2A is a schematic diagram of the hot end and nozzle of the FDM of FIG1, and FIG2B is a photograph of the disassembled hot end according to FIG2A;

[0019] FIG3A illustrates the design of a six-element SK-type static mixer for an FDM printer, and FIG3B is a photograph of the static mixer;

[0020] FIG4 is a photograph of a general side view of a white cube, a black cube, and a gradient cube manufactured according to the invention;

[0021] FIG5 is a photograph of a general top view of a white cube, a black cube, and a gradient cube manufactured according to the invention;

[0022] FIG6 is a photograph of a dental crown showing the gradient colors of the crown;

[0023] FIG7 is a photograph of a tooth slice showing the gradient structure of the tooth under light; and

[0024] Figure 8 is a photograph of a green blank of a gradient zirconia crown printed by the hot end of the present invention before polishing; and

[0025] Figure 9 is a schematic diagram of the entire gradient printing process according to the present invention. Best Mode for Carrying Out the Invention

[0027] The present invention is a low-cost machine manufacturing system capable of controlling the color (or color gradient) and structural gradient of ceramic (e.g., zirconia) objects constructed using an FDM printer as shown in Figure 1. It can form objects in an economical and time-saving manner.

[0028] The FDM printer has a base 10 and two vertically extending arms 12, on which a carriage 13 can move up and down. A rod 14 extends between the carriages and supports a hot end 16 mounted on the base 10 above a build plate or heated bed 17. Cans 19 contain a low-flow filament material, which may be the same in both cans or different in each can when a gradient is required. The material in the cans is fed to the hot end via an extruder, which may be located in the can. The extrusion machine, described in the extrusion instruction manual (page 2 / 5, CN 121794105 A), is controlled by a controller.

[0029] The FDM printer has a motor (not shown) that moves the carriage 13 up and down on the vertical arm 12 and a motor (not shown) that moves the hot end 16 along the rod 14. These motors and other components of the printer (e.g., the extruder 19') are under the program control of a controller 15 located in the base 10 and execute program control (e.g., g-code).In typical operation, the material in tank 19 is extruded by extruder 19' through two tubes 18A and 18B at its top to hot end 16, where it is mixed together in the required proportions according to the desired gradient. The mixed material is heated and extruded through a nozzle onto hot bed 17. Starting from rod 14 near the hot bed, material is deposited onto the hot bed at a location determined by a controller. An additional layer of filament material is deposited on top of the initial layer, and as rod 14 rises and the hot end moves along rod 14, the object is constructed. In effect, the desired 3D object is printed. The gradient, i.e., the proportion of material at different locations in the object, is controlled by the proportion of material extruded from tank 19, mixed, and laid on top of the previous material layer on hot bed 17.

[0030] A diagram of hot end 16 is shown in Figure 2A, and a photograph of the hot end after disassembly is shown in Figure 2B. In Figure 2A, tubes 18A and 18B are shown as entering the top. They enter channels 21A and 21B respectively from there, which lead to a static mixer 24 located within a central tube 25 at the hot end. To prevent clogging of channels 21A and 21B, they form two specially angled tubes whose diameter gradually narrows towards the central tube 25. This prevents them from being clogged by low-flow materials and ensures that the material is ready for mixing.

[0031] The dimensions of the angled tubes are determined based on the diameter of the filament to be used. In one embodiment of the invention, the diameter of the filament is 1.75 mm, so the upper part of the channel or tube should be slightly larger to ensure that the filament can be extruded into the tube by the remainder of the continuous filament during extrusion. In this embodiment, the upper dimension is designed to be 2 mm. It is good that this dimension is slightly larger than the diameter of the filament. However, it should be clear in this design that the diameter should not be too narrow. If it is too narrow, it may cause the channel to become clogged. In this embodiment, the lower dimension of the channel is set to 0.8 mm, which is narrower than the upper dimension, so that the filaments do not flow back when the two filaments are mixed in the central tube 25 where the static mixer 24 is located. The lower dimension should be smaller than the upper dimension, but not too small, otherwise it may cause blockage or prevent manufacturing. If the filaments have a wider diameter, the tube size can be larger depending on the filaments, and the range of sizes can be wider. Therefore, the size range of the inclined tube is optional, but the form or shape of the hot end is unique.

[0032] A custom static mixer 24 with six (6) or more elements is used to completely mix the two molten components in channels 21A and 21B. The design of the six-element static mixer, designed in SolidWorks and manufactured by stereolithography (SLA), is shown in Figure 3A. Figure 3B is a photograph of the mixer. After the mixer, the hot end has a nozzle 26 (Figure 2A), which has a diameter of 0.4 mm in this embodiment. The nozzle prints samples.

[0033] The static mixer is an improved SK-type static mixer.SK-type static mixers are widely used in industry to mix two components, but due to their large size, they have not yet been used in 3D printing. In this embodiment, the mixer is designed to be quite small, with a width of about 4.5 mm and a length of about 1.75 mm depending on the central tube at the hot end, so that the two filaments can be mixed when they pass through the central tube. The size is optional if the central tube is different. Due to its miniature size, SLA technology is used to 3D print the mixer. In addition, the mixer should have good thermal conductivity and heat resistance, so aluminum alloy was chosen and SLA was used to manufacture the mixer, which is a new way of processing small metal parts.

[0034] The static mixer of the mixer of the present invention can be used not only for ceramic materials, but also for other low-flow materials. In addition, although the minimum number of units in the mixer is 6, more units can be used when used for different purposes.

[0035] It should be noted that the six parts of the mixer are similar to each other, that is, they are inclined on both sides of the central peak opposite to the curved base. As can be seen in Figure 3A, the six parts are arranged alternately with (a) peak upward and base downward, and (b) peak downward and base upward. The static mixer inside the printer allows the two molten low-flow filament components to be completely mixed. In particular, the static mixer can completely mix the two low-flow materials without any power. Therefore, when two materials in different proportions pass through the static mixer, they can be mixed more thoroughly.

[0036] The entire hot end 16 is surrounded by an electric heater unit 11 (Figure 1). When the hot end is heated, the two extruders 19' can be controlled by g-codes in the controller 15 to extrude two filaments in different proportions at different heights to achieve a gradient effect. Thus, by means of the heater along with the static mixer design and the angled tubes or channels 21A, channel 21B, the two components are completely mixed before being extruded through the nozzle 26. By controlling the delivery and mixing of the two materials, both color and structural gradients of ceramic filaments, such as zirconium oxide, can be achieved.

[0037] In testing this invention, two colored zirconia filaments were formed from 1.75 mm white zirconia (Zetamix, France) and 1.75 mm black zirconia (Zetamix, France). Samples were prepared using a 0.4 mm nozzle at a printing speed of 20 mm / s and a printing temperature of 180 degrees Celsius. The sample model was sliced ​​using the slicing software Ultimaker Cura 5.3.1 (Ultimaker, Netherlands) with a layer thickness of 0.2 mm. The g-code was then edited to set the ratio of the two filaments from (E0: E1 = 100%: 0%) to (E0: E1 = 0%: 100%), starting from a height of 0 mm. The fill rate was set to 100%.The sample is deposited on a flexible plate or heated bed 17 to ensure removal without damage. The green sample is then printed as shown in Figure 4.

[0038] After removal from the heated bed, the green sample is placed in an acetone bath for solvent degreasing. Thermal degreasing is then performed, consisting of a heating rate of 8°C / h from 20°C to 500°C, taking 2.5 days to complete the degreasing process. Sintering is performed in a high-temperature furnace. The thermal cycle is: from 20°C to 1475°C at a rate of 50°C / h over 29 hours, followed by a 1-hour holding, and then from 1475°C to 20°C at a rate of 100°C / h over 15 hours. The final sample is shown in Figure 5.

[0039] Figures 4 and 5 show a gradient cube formed by mixing white and black zirconia filaments and printing a gradient cube using the hot end of the present invention. The top surfaces of the three samples are identical, except for the white sample, which is not clearly visible due to its white color. This design is simply a result of the nozzle movement path. This path relies on slicing software that can edit g-code to control the movement of the hot end to print a cube.

[0040] Figure 6 is a photograph of a crown showing the gradient colors of a normal tooth. Figure 7 is a photograph of a tooth slice showing the gradient structure of a tooth under light. The different colors in the photograph indicate that the tooth structure is gradient as the tooth grows. Figure 8 shows a green blank of a gradient zirconia crown printed by the hot end before polishing.

[0041] Therefore, the customized hot end of the present invention can print controlled gradient zirconia objects in a faster and more economical manner. A schematic diagram of the entire gradient printing process of the present invention is shown in Figure 9. Before printing, as described above, in step 90, a customized SK static mixer is designed. In step 91, the mixer is installed in a specially designed hot end of an FDM printer. The hot end has two input ends with angled tilt tubes that converge to the central tube where the mixer is located. In step 92, a program is created for a specific object with structural and / or color gradients. In step 93, a slicing procedure is performed on the object, which generates g-codes for driving the extruder and motor of the FDM printer.

[0042] During printing step 94, g-codes from the controller guide the extruders of two different low-flow materials (e.g., black zirconium oxide and white zirconium oxide) through the hot end, while the motor moves the hot end connected to the carriage to 3D print the object. As shown in step 95, the object is a sphere with a color gradient, i.e., whiter towards the top and blacker towards the bottom. This gradient object undergoes sintering in step 96 to form the final part in step 97.

[0043] The above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications or substitutions that are obvious to those skilled in the art should fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0044] Although the present invention has been explained in conjunction with specific embodiments, it should be understood that various modifications will become apparent to those skilled in the art upon reading the specification. Therefore, it should be understood that the invention disclosed herein is intended to cover such modifications falling within the scope of the claims appended to CN 121794105 A on pages 4 / 5 of the specification. (Pages 5 / 5 of the specification, CN 121794105 A, Figures 1 and 2A are referenced.)

Claims

1. A hot end for a fused deposition modeling (FDM) printer, comprising: Two inlets for low-flow materials, wherein the materials may be different from each other in color and / or structure; Two separate channels leading from the inlet to their ends form two specially angled tubes that intersect at their ends and gradually narrow toward their ends; A central tube extending from one end of the channel; The outlet nozzle is located at the end of the central tube; A static mixer located in the central tube; and Heating unit surrounding the hot end.

2. The hot end of claim 1, wherein the static mixer is an SK static mixer having six or more elements.

3. The hot end of claim 1, wherein if a 1.75 mm diameter filament is to be used in the hot end, the upper diameter of the separated channels is 2.00 mm, and they gradually narrow to a diameter of 0.80 mm towards their ends.

4. The hot end of claim 3, wherein the diameter of the nozzle is 0.4 mm.

5. An FDM printer having a hot end as claimed in claim 1.

6. The FDM printer of claim 5, further comprising: Two low-flowability material sources, which may be different in color and / or structure; each material source is connected to a separate inlet at the hot end. An extruder for extruding the low-flow-rate material from the material source, and A controller is used to control the extruder to extrude two filaments in different proportions at different heights to achieve a three-dimensional color and / or structural gradient effect.

7. A method for forming a three-dimensional (3D) zirconia object, comprising the following steps: Provide a first zirconia low-flow filament having a first color and a first structure; Provide a second zirconium oxide low-flow filament with a second color and a second structure; The software-operated controller designs slices of an object, the software determining the ratio of a first zirconia low-flow filament to a second zirconia low-flow filament extruded at each printing level through the hot end of a fused deposition modeling (FDM) printer, starting from the lowest level; the hot end of the FDM printer has two inlets, each for a filament, and the first and second filaments are mixed in a static mixer at the stated ratio for each level. as well as The mixed filaments are deposited onto a heated bed to form a green body with a gradient determined by the stated proportions.

8. The method of claim 7, wherein the first zirconia low-flow filament and the second zirconia low-flow filament are prepared by using a 0.4 mm nozzle at a printing speed of 20 mm / s and a printing temperature of 180 degrees Celsius.

9. The method of claim 7, wherein the layer thickness is 0.2 mm.

10. The method of claim 7, further comprising the step of: Remove the green blank from the heated bed; The green body is subjected to solvent degreasing; After solvent degreasing, the green body is treated with thermal degreasing; and The hot-degreased green body is subjected to sintering treatment.

11. The method of claim 10, wherein the solvent degreasing is performed by placing the green body in an acetone bath.

12. The method of claim 10, wherein the thermal degreasing is performed by subjecting a solvent-degreased blank to a heating rate of 8°C per hour from 20°C to 500°C and allowing it to stand for 2.5 days to complete the thermal degreasing.

13. The method of claim 10, wherein the sintering process is carried out in a high-temperature furnace and undergoes the following thermal cycle: from 20°C to 1475°C at a rate of 50°C / h over 29 hours, followed by holding for 1 hour, and then from 1475°C to 20°C at a rate of 100°C / h over 15 hours.

Images