Process for enhancing interlayer bonding strength of 3D printed drug pellets

Abstract

The application relates to a process for enhancing the interlayer bonding strength of a 3D printed propellant grain, comprising the following steps: preparing a solid propellant slurry; dividing the printing layer into a first printing layer and a second printing layer, setting the equivalent diameter of the first printing layer filament to be smaller than the equivalent diameter of the second printing layer filament; setting the printing interval of the first printing layer to be larger than the printing interval of the second printing layer, and alternately printing the first printing layer and the second printing layer, so that the filament of the second printing layer fills the printing interval of the first printing layer; and performing a solidification treatment. The equivalent diameter of the deposited filament is controlled in layers, and a specific deposition path is designed, the first printing layer and the second printing layer are alternately printed, an embedded, multi-scale interwoven contact structure is formed between the two printing layers, the actual contact area between the layers is significantly increased, the interface continuity is enhanced, the weak interlayer interface effect is reduced, and finally a propellant grain with excellent structural integrity and combustion consistency is obtained.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and more particularly to a process method for enhancing the interlayer bonding strength of 3D printed propellant cartridges. Background Technology

[0002] Solid propellant grains, as the energy and power source of an engine, directly determine the engine's operational reliability through their structural integrity and combustion stability. In recent years, additive manufacturing technology, particularly extrusion-based 3D printing, has brought revolutionary prospects to solid propellant manufacturing due to its unique advantages in manufacturing complex three-dimensional propellant grain structures. However, the in-depth application of this technology in propellant grain manufacturing is limited by a long-standing and unresolved core problem: poor interlayer adhesion during printing.

[0003] Currently, the printing path planning strategies commonly used in the field of propellant manufacturing, such as the traditional parallel reciprocating scanning path (see...), are... Figure 1 The propellant grain is constructed by stacking extruded filaments in a single plane. This method results in an approximately cylindrical line contact between adjacent layers of extruded filaments, leading to a severe deficiency in the effective physical contact area between layers. According to adhesion theory, bond strength is directly related to the effective contact area, and this inherently weak interface becomes a key factor restricting the improvement of the overall structural performance of the propellant grain. Consequently, a series of problems caused by weak interlayer adhesion are particularly prominent: First, when the propellant grain cures, undergoes temperature changes, or is subjected to mechanical loads, stress easily concentrates at the weak interface, inducing the initiation and propagation of microcracks, and even leading to macroscopic interlayer delamination, severely damaging the structural integrity of the propellant grain. Second, internal interface defects can unpredictably alter the propellant combustion area and propagation path during combustion, easily triggering localized high pressure or even unstable combustion, posing a significant threat to engine safety.

[0004] Although existing technologies attempt to improve interlayer blending by optimizing printing process parameters (such as increasing printing temperature and adjusting extrusion speed), these methods have limited effectiveness and often only address the symptoms, failing to overcome the fundamental bottleneck of "line contact" in terms of interface geometry.

[0005] Therefore, there is an urgent need in this field for a new method that can fundamentally enhance the interlayer adhesion performance of 3D-printed solid propellant grains. This method should not be limited to fine-tuning existing process parameters, but should start from the design of the printing path at its source. Through innovative path planning, it should overturn the traditional interlayer contact mode, substantially increasing the contact area, thereby producing solid propellant grains with dense structure and reliable performance.

[0006] It should be noted that this section is intended to provide background or context for the technical solutions of the invention as set forth in the claims. The description herein does not imply acceptance of prior art simply because it is included in this section. Summary of the Invention

[0007] The purpose of this invention is to provide a process method to enhance the interlayer bonding strength of 3D printed propellant cartridges, thereby at least partially solving one or more problems caused by the limitations and defects of related technologies.

[0008] This invention provides a process for enhancing the interlayer bond strength of 3D printed propellant grains, comprising: S1, prepare solid propellant slurry, control the slurry temperature to 40℃~60℃, set the nozzle diameter of the 3D printing equipment to 0.8mm~2.5mm, and protect the printing environment with inert gas; S2, the printing layer is divided into multiple first printing layers and multiple second printing layers. The equivalent diameter of the filament of the first printing layer is set to be smaller than the equivalent diameter of the filament of the second printing layer, and the equivalent diameter of the filament of the first printing layer and the second printing layer is smaller than the nozzle diameter. S3, set the printing spacing of the first printing layer to be greater than the printing spacing of the second printing layer, and print the first printing layer and the second printing layer alternately, so that the filament of the second printing layer fills the printing gap of the first printing layer, and repeat the printing layer by layer to obtain solid propellant grains; S4 involves solidifying the solid propellant grains.

[0009] In this invention, in S1, the solid propellant slurry comprises the following components by mass percentage: 60%–75% oxidant, 10%–20% aluminum fuel, 8%–15% binder, 2%–6% plasticizer, and 0.5%–3% curing agent.

[0010] In this invention, the following steps are included before S2: A geometric model of a solid propellant grain is generated using 3D modeling software, and then imported into slicing software. The slicing parameters are set using the slicing software, including line width and layer height.

[0011] In this invention, the equivalent diameters of the filaments of the first and second printing layers satisfy the following relationship: d1=(0.4~0.8)D d2=(0.8~1.6)D d1 <d2 Where d1 and d2 are the equivalent diameters of the first and second printing layers, respectively, and D is the nozzle diameter.

[0012] In this invention, the number of layers in the first printing layer is greater than the number of layers in the second printing layer, and the equivalent diameters of the first printing layer and the second printing layer also satisfy the following relationship: m*d1=n*d2=h p*d1+q*d2=L Where m and n are the number of the first and second printing layers, respectively, h is the total printing layer height, p and q are the number of extruded filaments in the first and second printing layers, respectively, and L is the total printing thickness.

[0013] In this invention, in S3, the printing spacing of the first printing layer is (1.0~1.6)D, and the printing spacing of the second printing layer is (0.6~1.4)D.

[0014] In this invention, in step S4, the solid propellant grain is cured at 50°C to 70°C for 24 to 96 hours.

[0015] The technical solution provided by this invention may include the following beneficial effects: In this invention, by layering and controlling the equivalent diameter of the deposited filament and designing a specific deposition path, the first and second printing layers are printed alternately, forming an embedded, multi-scale interwoven contact structure between the two printing layers. This significantly increases the actual contact area between layers, enhances interface continuity, reduces weak interface effects between layers, and ultimately obtains a propellant grain with excellent structural integrity and combustion consistency. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0017] Figure 1 This diagram illustrates the extrusion filament deposition process during the preparation of pharmaceutical columns in the prior art. Figure 2 A flowchart illustrating the process method for enhancing the interlayer bonding strength of 3D printed propellant grains according to the present invention is shown. Figure 3 This diagram illustrates the extrusion filament deposition process during the preparation of the drug column in an embodiment of the present invention. Figure 4 The cross-sectional macroscopic morphology of the samples of the present invention is shown: (a) is the control sample, and (b) is the experimental sample; Figure 5 Cross-sectional CT scan images of the samples of the present invention are shown: (a) is the control sample, and (b) is the experimental sample; Figure 6 This invention presents a 3D contour plot of the pore size of a comparative sample printed with a single extruder head, excluding openings (pore diameter > 1 mm). Figure 7This diagram shows a three-dimensional cloud map of the pore size of an experimental sample printed by alternating coarse and fine extrusion heads in this invention – pores without openings (pore diameter > 1 mm). Detailed Implementation

[0018] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that the invention will be more comprehensive and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0019] Furthermore, the accompanying drawings are merely illustrative diagrams of embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0020] This example embodiment provides a process method to enhance the interlayer bond strength of 3D printed propellant grains, referencing... Figure 2 and Figure 3 As shown, the method includes the following steps: S1, prepare solid propellant slurry, control the slurry temperature to 40℃~60℃, set the nozzle diameter of the 3D printing equipment to 0.8mm~2.5mm, and protect the printing environment with inert gas; S2, the printing layer is divided into multiple first printing layers and multiple second printing layers. The equivalent diameter of the filament of the first printing layer is set to be smaller than the equivalent diameter of the filament of the second printing layer, and the equivalent diameter of the filament of the first printing layer and the second printing layer is smaller than the nozzle diameter. S3, set the printing spacing of the first printing layer to be greater than the printing spacing of the second printing layer, and print the first printing layer and the second printing layer alternately, so that the filament of the second printing layer fills the printing gap of the first printing layer, and repeat the printing layer by layer to obtain solid propellant grains; S4 involves solidifying the solid propellant grains.

[0021] In this embodiment, by layering and controlling the equivalent diameter of the deposited filament and designing a specific deposition path, the first and second printing layers are printed alternately, forming an embedded, multi-scale interwoven contact structure between the two printing layers. This significantly increases the actual contact area between layers, enhances interface continuity, reduces weak interface effects between layers, and ultimately obtains a propellant grain with excellent structural integrity and combustion consistency.

[0022] The steps in the above embodiments are described in detail below.

[0023] In S1, the solid propellant slurry comprises the following components by mass percentage: 60%–75% oxidant, 10%–20% aluminum fuel, 8%–15% binder, 2%–6% plasticizer, and 0.5%–3% curing agent. The above components are based on what is achievable in existing technology and are not specifically limited here. The solid propellant slurry exhibits shear thinning and thixotropic recovery properties. The above components are stirred at 40°C–60°C under vacuum for 30–120 minutes until homogeneous, resulting in a high-solids-content slurry without significant air bubbles. During subsequent deposition and printing, the slurry temperature is maintained at 40°C–60°C to preserve suitable viscosity and rheological properties.

[0024] The printing equipment can be an extrusion 3D printer, which includes a material reservoir, an extrusion mechanism, and a motion platform; existing printing equipment is sufficient. The material reservoir has precise temperature control to regulate the temperature of the slurry. The nozzle diameter of the printing equipment is 0.8mm to 2.5mm, for example, 1.0mm, 1.5mm, 2.0mm, etc., but is not limited to these. The printing environment is protected with an inert gas, and the oxygen content (by volume) does not exceed 5%.

[0025] Next, a geometric model of the required solid propellant grain is generated using 3D modeling software (such as CAD) and exported as an STL file. This model is then imported into slicing software with custom path scripting capabilities (such as a Python-based custom slicing program). Slicing parameters are then set, including linewidth and layer height. Both the linewidth and layer height are slightly smaller than the nozzle diameter to ensure sufficient compression deformation between the two printed deposition layers. For example, the linewidth can be set to 0.6-2.3 mm, and the layer height to 0.6-2.3 mm. The slurry is extruded from the nozzle to form a filament, which typically has a flat, elongated rectangular cross-section. The width of this rectangle is called the linewidth, and its height is called the layer height.

[0026] In S2, the printing layer is divided into multiple first printing layers and multiple second printing layers. The number of first printing layers is greater than the number of second printing layers. When the two are printed alternately, the following printing strategies can be adopted: print one second printing layer on the first printing layer after printing two first printing layers; or print one second printing layer on the first printing layer after printing three first printing layers; or print one second printing layer on the first printing layer in a local printing area after printing one first printing layer.

[0027] Before printing, the equivalent diameter of the printed layer needs to be set. The rectangular cross-section mentioned above is converted into a circle; the diameter of this circle is the equivalent diameter described in this application. Therefore, the equivalent diameter is calculated using the linewidth and layer height values. The linewidth and layer height are determined by the nozzle diameter, extrusion flow rate, printing speed, and material rheological properties. Therefore, the equivalent diameter can also be adjusted by changing the nozzle diameter, printing speed, multi-nozzle switching, or pulse extrusion mode. For example, by adjusting the extrusion flow rate... Q and printing speed v , making the equivalent diameter d Satisfying the relation: And adjust synchronously during layer switching. The ratio of the two values ​​is used to achieve stable switching of the deposited filament size between different layers.

[0028] Equivalent diameter is generally used to indirectly quantify the amount of filament extruded. In this application, two nozzle sizes (e.g., 1.5 mm and 2.0 mm) are used to extrude the filaments of the first and second printing layers, respectively.

[0029] The equivalent diameters of the filaments in the first and second printed layers satisfy the following relationship: d1=(0.4~0.8)D d2=(0.8~1.6)D d1 <d2 m*d1=n*d2=h p*d1+q*d2=L Where d1 and d2 are the equivalent diameters of the first and second printed layers, respectively, and D is the nozzle diameter. m and n are the number of the first and second printed layers, respectively, h is the total height of the printed layers, p and q are the number of extruded filaments in the first and second printed layers, respectively, and L is the total thickness of the printed material.

[0030] S3 is the process of designing the deposition path structure. Please refer to [link / reference]. Figure 3 , Figure 3 In the diagram, A represents the second printed layer, and B represents the first printed layer. The printing spacing of the first printed layer is set to be larger than that of the second printed layer. The first printed layer uses a larger printing spacing, for example (1.0–1.6)D, forming a skeletal structure with gaps. The second printed layer uses a smaller printing spacing, for example (0.6–1.4)D. Under these parameter settings, the deposited filament of the second printed layer can be embedded in the gaps between its adjacent first printed layers. Due to the set linewidth and layer height, the adjacent printed layers undergo a certain degree of compaction deformation under the weight of the filament, expanding the interlayer contact from a single contact interface to a multi-region contact interface, forming an embedded structure. This process is repeated layer by layer, ultimately constructing a solid propellant grain with large-area three-dimensional curved surface contact between layers.

[0031] The above path structure design allows the path to intersect with the previous layer in space when printing the next layer, thus creating an interlocking three-dimensional interface with large-area bonding after deposition. This forms a three-dimensional interlocking structure that can effectively disperse and absorb stress, effectively suppress the initiation and propagation of microcracks between layers from the source, significantly reduce the internal defects of the propellant grain, and greatly improve its structural density and integrity.

[0032] It should be noted that the deposition path can be a parallel path, a grid path, an intersecting path, or a continuous curved path, etc.

[0033] S4. After printing, place the solid propellant column in a curing oven and cure it at 50℃~70℃ for 24h~96h to allow the interlayer materials to cross-link and fuse, further eliminating interface differences. The curing temperature can be 55℃, 60℃, etc., and the curing time can be 36h, 48h, 72h, etc.

[0034] After complete curing, standard mechanical test specimens are prepared by cutting the sample, and interlaminar shear strength and tensile strength are tested using a universal testing machine.

[0035] The comparative samples were used to test solid propellant grain samples (experimental samples) prepared using the process method of this application, and the following results were obtained.

[0036] 1. Surface morphology The comparison sample was printed using a single extrusion nozzle (2mm), while the experimental sample was printed using two nozzles (1.5mm and 2mm). Macroscopic photographs of both are shown below. Figure 4 .from Figure 4 As can be seen, the experimental sample is flatter and has a higher consistency in surface morphology.

[0037] 2. MicroCT testing The microCT test results for the comparison sample and the experimental sample are shown in the figure. Figure 5 ,from Figure 5 The cross-sectional CT slices show that the pore distribution area of ​​the single-printhead sample is relatively large, with a large number of circular pores; the experimental samples printed with alternating coarse and fine extrusion heads have a small number of strip-shaped defects at the sample boundaries. Meanwhile, based on the three-dimensional pore cloud maps of each sample (…),… Figure 6 , Figure 7 It can be calculated that the porosity of a sample printed with a single extruder head accounts for 2.89% of the total volume, while the porosity of a sample printed with alternating coarse and fine extruder heads accounts for 2.33% of the total volume. Compared with the sample printed with a single extruder head, the porosity is reduced by 19.4%, and the porosity of the sample is greatly improved.

[0038] 3. Mechanical properties During testing, the stretching direction of the sample was perpendicular to the direction of travel, meaning the test results reflected the interfacial adhesion performance between the propellant extrusion filaments. The mechanical test results of the comparative sample and the experimental sample are shown in Table 1. Table 1 shows that the mechanical properties of the sample printed with alternating coarse and fine extrusion heads were all higher than those printed with a single extrusion head, indicating better mechanical properties and a significantly improved interfacial adhesion performance.

[0039] Table 1. Test results of mechanical properties of printed samples

[0040] The solid propellant grains prepared in this application have an actual interlayer contact area increased by more than 30% (compared to printing with the same diameter), and the interlayer shear strength is also significantly improved. The internal macroscopic layered interfaces are significantly reduced or eliminated, and the overall structural integrity of the product is significantly improved.

[0041] It should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise" that may appear in the above description indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0042] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0043] In the embodiments of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0044] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature may include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature include the first feature being directly above or diagonally above the second feature, or simply indicating that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature include the first feature being directly below or diagonally below the second feature, or simply indicating that the first feature is at a lower horizontal level than the second feature.

[0045] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0046] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the appended claims.

Claims

1. A process for enhancing the interlayer adhesion strength of 3D printed propellant grains, characterized in that, include: S1, prepare solid propellant slurry, control the slurry temperature to 40℃~60℃, set the nozzle diameter of the 3D printing equipment to 0.8mm~2.5mm, and protect the printing environment with inert gas; S2, the printing layer is divided into multiple first printing layers and multiple second printing layers. The equivalent diameter of the filament of the first printing layer is set to be smaller than the equivalent diameter of the filament of the second printing layer, and the equivalent diameter of the filament of the first printing layer and the second printing layer is smaller than the nozzle diameter. S3, set the printing spacing of the first printing layer to be greater than the printing spacing of the second printing layer, and print the first printing layer and the second printing layer alternately, so that the filament of the second printing layer fills the printing gap of the first printing layer, and repeat the printing layer by layer to obtain solid propellant grains; S4 involves solidifying the solid propellant grains.

2. The process method for enhancing the interlayer adhesion strength of 3D printed propellant cartridges according to claim 1, characterized in that, In S1, the solid propellant slurry comprises the following components by mass percentage: 60%–75% oxidant, 10%–20% aluminum fuel, 8%–15% binder, 2%–6% plasticizer, and 0.5%–3% curing agent.

3. The process method for enhancing the interlayer adhesion strength of 3D printed propellant cells according to claim 1, characterized in that, The steps preceding S2 are as follows: A geometric model of a solid propellant grain is generated using 3D modeling software, and then imported into slicing software. The slicing parameters are set using the slicing software, including line width and layer height.

4. The process method for enhancing the interlayer adhesion strength of 3D printed propellant columns according to claim 3, characterized in that, The equivalent diameters of the first and second printed layers satisfy the following relationship: d1=(0.4~0.8)D d2=(0.8~1.6)D d1 <d2 Where d1 and d2 are the equivalent diameters of the first and second printing layers, respectively, and D is the nozzle diameter.

5. The process method for enhancing the interlayer adhesion strength of 3D printed propellant cells according to claim 4, characterized in that, The number of layers in the first printing layer is greater than the number of layers in the second printing layer, and the equivalent diameters of the filaments in the first and second printing layers also satisfy the following relationship: m*d1=n*d2=h p*d1+q*d2=L Where m and n are the number of the first and second printing layers, respectively, h is the total printing layer height, p and q are the number of extruded filaments in the first and second printing layers, respectively, and L is the total printing thickness.

6. The process method for enhancing the interlayer adhesion strength of 3D printed propellant cells according to claim 4, characterized in that, In S3, the printing spacing of the first printing layer is (1.0~1.6)D, and the printing spacing of the second printing layer is (0.6~1.4)D.

7. The process method for enhancing the interlayer adhesion strength of 3D printed propellant cartridges according to any one of claims 1 to 6, characterized in that, In S4, the solid propellant grains are cured at 50℃~70℃ for 24h~96h.

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