Coaxial extrusion type 3D printing hydrogel equipment and application

Abstract

The invention discloses coaxial extrusion type 3D printing hydrogel equipment and application, and belongs to the technical field of 3D printing and geotechnical engineering supporting. Comprising a step-shaped shrinkage structure arranged at an inlet of an outer layer channel of a coaxial spray head and used for uniformly distributing a calcium chloride crosslinking solution and stably and uniformly wrapping an outer layer material; the size compensation factor calculation module is integrated in the control unit and is used for calculating and applying a size compensation factor in real time based on the linear shrinkage rate in each direction of the material and the slicing error so as to realize dynamic precision correction of a printing path; the device further comprises a three-axis mechanical arm control system, a two-way independent precise feeding system and a storage device. Through cooperation of a flow guide part and dynamic compensation, the uniformity, the structural consistency and the forming precision of hydrogel printing are remarkably improved, and the method is particularly suitable for high-precision and high-reliability temporary filling and supporting of complex surrounding rock cracks.

Description

Technical Field

[0001] This invention relates to the field of 3D printing technology, and in particular to a coaxial extrusion 3D printing hydrogel device for filling and temporarily supporting rock fissures, which optimizes the nozzle flow channel and dynamically compensates for printing accuracy based on the characteristics of hydrogel materials. Background Technology

[0002] Coaxial 3D printing technology provides an effective means for molding complex hydrogel structures. However, existing technologies face two major challenges in practical applications: First, the flow channel design of traditional coaxial nozzles, especially the inlet method of the outer solution, is prone to uneven circumferential pressure and flow rate, resulting in uneven coating and uncontrolled printing line morphology. Second, the shrinkage of hydrogel materials during cross-linking and curing, as well as the rounding error during slicing, can lead to unpredictable deviations between the printed product size and the design size, affecting the fitting accuracy and reliability of the support structure.

[0003] To address the issue of flow channel uniformity, the common lateral single-inlet annular flow channel design has inherent flaws. Regarding the issue of printing dimensional deviations, there is currently a lack of a systematic solution integrated within the equipment that can automatically compensate in real time. Therefore, developing a coaxial printing device with uniform flow guidance and intelligent dimensional compensation capabilities is of great significance for achieving high-precision and reliable support for fractures in geotechnical engineering. Summary of the Invention

[0004] The purpose of this invention is to provide a coaxial extrusion 3D printing hydrogel device and application to solve the problems in the prior art, such as uneven outer layer solution coating leading to poor consistency of the formed structure, and low printing size accuracy due to material shrinkage and slicing errors.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: This invention provides a coaxial extrusion 3D printing hydrogel device for temporary support of surrounding rock fissures, comprising: The coaxial nozzle has an inner channel and an outer channel. The inner channel is used to deliver sodium alginate hydrogel, and the outer channel is used to deliver calcium chloride crosslinking solution. The inlet of the outer channel is provided with a flow guiding structure to guide the calcium chloride solution to be evenly distributed throughout the entire annular flow channel cross section, thereby forming a uniform and concentric wrapping of the inner hydrogel at the outlet. The control unit is electrically connected to the three-axis robotic arm control system and the feeding system. It is used to receive three-dimensional model data and coordinate the nozzle movement and material extrusion. The control unit integrates a size compensation factor calculation module, which is used to calculate and apply the size compensation factor in real time based on the material shrinkage characteristics and the slicing error of the three-dimensional model, and to perform dynamic accuracy correction on the printing path. The three-axis robotic arm control system is used to control the coaxial nozzle to move in three-dimensional space along the path adjusted by the size compensation factor calculation module; The feeding system includes two independently controlled stepper motor drive units, which are used to precisely control the extrusion rates of the inner and outer layer materials, respectively; for example, it includes a first stepper motor and a second stepper motor, which are connected to the storage device through a screw structure. The storage device includes a sodium alginate storage tank and a calcium chloride solution storage tank, for storing sodium alginate hydrogel and calcium chloride solution respectively. Furthermore, the flow guiding structure is preferably a flow guiding block with a stepped contraction structure disposed near the inlet of the outer channel. Its core function is to equalize the flow resistance of the fluid from one side to the feed inlet at each circumferential position of the annular flow channel of the outer channel by changing the local geometry of the flow channel, thereby eliminating the uneven phenomenon of fast flow velocity at the "near end" and slow flow velocity at the "far end", and ensuring that the outer solution forms a stable annular liquid sheath with a uniform thickness.

[0006] Preferably, the diameter ratio of the upper and lower ends of the flow guiding part is 3:1 to 4:1, the number of steps is 2-3, the lower end of the flow guiding part connects to the upper inlet of the outer channel, and the upper diameter of the flow guiding part is much larger than the upper diameter of the outer channel.

[0007] Furthermore, the size compensation factor calculation module includes at least: The shrinkage rate database, using the coaxial nozzle, experimentally determined the isotropic linear shrinkage rate (S) of different hydrogel material parameters at room temperature. x , S y , S z The hydrogel material comprises sodium alginate hydrogel and calcium chloride crosslinking solution; The slicing error calculation unit is used to analyze the theoretical dimensional deviation caused by path rounding when slicing a 3D model into printing paths. E 切片 ; The size compensation factor synthesis unit, for the Y and Z directions, obtains the linear shrinkage rates S in the Y and Z directions from the shrinkage rate database based on the input hydrogel material parameters. y , S z Directly using the linear shrinkage rate S y , S z The Y and Z directions of the 3D model are compensated as size compensation factors; for the X direction, the linear shrinkage rate S is obtained from the shrinkage rate database based on the input hydrogel material parameters. x The size compensation factor CF in the X direction is calculated using the following formula. x The size compensation factor CF in the X direction x Compensation is applied to the X-direction of the 3D model:

[0008] in, This refers to the design dimension of the specimen in the X direction.

[0009] It is applied to the original 3D model before printing path planning, and the model accuracy is significantly improved through compensation.

[0010] Furthermore, the inner and outer channel outlets of the coaxial nozzle are on the same plane, forming an annular gap of 0.5-1.0 mm between the inner and outer channels. The flow guiding part cooperates with this precise gap to jointly ensure the effect of uniform coating and rapid cross-linking.

[0011] The coaxial extrusion 3D printing hydrogel equipment is used for printing temporary supports for surrounding rock fissures.

[0012] Based on the device provided by this invention, a printing method for temporary support of surrounding rock fissures is also provided. The core steps include: processing the three-dimensional model of the fissure through the size compensation factor calculation module to obtain a printing path with optimized accuracy; using a coaxial nozzle with the flow guiding part to simultaneously extrude inner and outer layer materials at a precisely controlled flow rate ratio to achieve uniform coating and cross-linking; and executing the compensated path through a three-axis robotic arm to complete the printing of a temporary support structure that adapts to the shape of the fissure with high precision.

[0013] Compared with the prior art, the beneficial effects of the present invention are: This invention solves the problem of uneven coating of the outer solution from a fluid dynamics perspective by introducing a flow guiding part, which significantly improves the geometric consistency and mechanical uniformity of the printed lines.

[0014] This invention achieves systematic and automated compensation for material shrinkage and process errors by integrating a size compensation factor calculation module, which greatly improves the fit between the molded structure and the design dimensions.

[0015] This invention, through the synergistic effect of the flow guiding part and the size compensation factor calculation module, enables the device to achieve rapid molding and temporary support of hydrogel structures with high uniformity and high precision in complex and irregular surrounding rock fissures, effectively expanding the practicality and reliability of coaxial 3D printing technology in geotechnical engineering. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this specification. For those skilled in the art, other embodiment illustrations can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the coaxial nozzle of the present invention; Figure 2 for Figure 1 A magnified structural diagram of part A in the middle. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] With reference to the illustrations, the following text will elaborate on the core structural details and practical application value of this innovative solution, aiming to enable practitioners in related fields to accurately grasp the key points of technical implementation and thus clarify the specific boundaries of the claims.

[0020] This invention provides a coaxial extrusion 3D printing hydrogel device for temporary support of surrounding rock fissures, including a coaxial nozzle, a three-axis robotic arm control system, a feeding system, a storage device, and a control unit.

[0021] The coaxial nozzle is made of stainless steel and has a double-layer annular flow channel structure consisting of an inner channel 1 and an outer channel 2. The inner channel is used to deliver sodium alginate hydrogel, and the outer channel is used to deliver calcium chloride crosslinking solution. The outlets of the inner and outer channels are on the same plane, forming a coaxial double-layer extrusion structure. The annular gap width between the inner and outer channels is 0.5–1.0 mm (this width refers to half the difference between the inner diameter of the outer needle tube and the outer diameter of the inner needle tube) to ensure that the inner hydrogel is uniformly coated by the outer solution.

[0022] At the inlet of the outer channel of the coaxial nozzle, a flow guide section 5 is provided. This section adopts a stepped contraction structure with an upper and lower diameter ratio of 3:1 to 4:1 and 2-3 steps, located at the upper end of the outer channel 2. Specifically, the flow guide section connects to the annular flow channel section of the outer channel through local stepped contraction (the upper diameter of the flow guide section is much larger than the upper diameter of the outer channel), so that the calcium chloride solution entering from the side feed inlet 4 is symmetrically divided and guided before flowing into the outer channel, thereby balancing the fluid resistance in each direction.

[0023] The upper end of the inner flow channel 1 is connected to the feed port 3 of the sodium alginate hydrogel, and there is a certain distance between the upper end of the guide part and the lower end of the feed port 3 of the sodium alginate hydrogel.

[0024] Traditional coaxial nozzles often employ a side-inlet annular flow channel, with the side inlet directly connected to the outer flow channel 2. This results in a significant difference in fluid path length between the "proximal end" and the "distal end" of the outer channel, leading to uneven flow velocity and pressure distribution, which in turn causes extrusion fluctuations and uneven coating. This invention, through a stepped contraction structure, effectively increases the local resistance of the "proximal end" flow path while guiding the fluid to fill the "distal end" more smoothly. This achieves a uniform distribution of flow velocity and pressure across the annular cross-section of the outer channel, enabling the calcium chloride solution to form a stable and continuous annular liquid sheath, achieving 360° uniform encapsulation and cross-linking of the inner hydrogel.

[0025] The three-axis robotic arm control system is driven by a servo motor, combined with a precision ball screw and linear guide rail, to achieve precise positioning of the nozzle in the X, Y, and Z directions. The robotic arm has a working range of 216mm×160mm×195mm, a repeatability of ±0.05mm, and a maximum movement speed of 200mm / s, which can meet the filling requirements of complex fissure structures.

[0026] The feeding system employs two independently controlled high-precision injection pumps, which respectively drive the delivery of the inner layer of sodium alginate hydrogel and the outer layer of calcium chloride solution. Each injection pump is equipped with a high-thrust stepper motor, driven by a precision screw, allowing for continuous adjustment of the extrusion rate within the range of 0.1-10 mL / min, with a flow rate control accuracy better than ±2%. The injection pumps are also equipped with a portable power supply and an independent controller, supporting remote control and parameter setting.

[0027] The storage device adopts a syringe-type structure, which can be implemented according to existing technology. It has a capacity of 50mL and includes an adjusting nut handle, a dosage control nut, a graduated threaded tube, double-layer sealing rings, and a standard flange. The double-layer sealing rings are made of medical-grade silicone material, ensuring good sealing performance even under working pressures of 0.2-0.8MPa.

[0028] The control unit is electrically connected to the three-axis robotic arm control system and the feeding system, and is used to receive three-dimensional model data and coordinate the nozzle movement and material extrusion.

[0029] A size compensation factor calculation module is embedded within the control unit. The construction process of the size compensation factor calculation module is as follows: The shrinkage rate database, using the coaxial nozzle, experimentally determined the anisotropic linear shrinkage rate (S) of different hydrogel materials (sodium alginate hydrogel and calcium chloride crosslinked solution) at room temperature. x , S y , S z : Taking the X direction as an example, ; in, These are the design and actual dimensions of the specimen to be printed in the X direction, respectively; S x A positive value usually indicates contraction. Due to anisotropy, the design dimensions in the three directions need to be automatically identified using the slicing software Simplify3D, and the origin positions for calculating the dimensions in the three directions need to be determined. Measure the actual dimensions of the specimen printed through the coaxial nozzle in three directions according to the origin position of the specimen in the slicing software. Obtain the linear shrinkage rates S in the X, Y, and Z directions according to the above formula. x , S y , S z ; Slicing Error Calculation Unit: Used to analyze the theoretical dimensional deviation caused by path rounding when slicing a 3D model into printing paths. E 切片 The theoretical dimensional deviation E is calculated using the following formula based on the difference between the theoretical number of paths and the actual number of paths after slicing the 3D model. 切片 : ; The actual number of paths in the X direction is related to the X-direction dimension K of the 3D model, and is calculated according to the following formula:

[0030] For example, if the model's X-direction dimension K = 50 mm, and K is rounded down to the nearest odd number, then the actual number of paths is 49; if the model's X-direction dimension K = 49 mm, and K is an odd number, then the actual number of paths is 49 - 2 = 47; if the model's X-direction dimension K = 47.1 mm, and K is rounded down to the nearest odd number, then the actual number of paths is 47.

[0031] Size compensation factor synthesis unit: For the Y and Z directions, the linear shrinkage rate S is directly used. y , S z The size compensation factors are used to compensate for the Y and Z directions of the 3D model; the size compensation factor CF in the X direction is calculated according to the following formula. x The size compensation factor CF in the X direction x Compensation is applied to the X-direction of the 3D model.

[0032]

[0033] The compensated dimensions are then input into the slicing software Simplify3D, and the slices are re-sliced ​​to make the final dimensions equal to the design dimensions. The size compensation factor will be applied to the 3D model before slicing to achieve comprehensive compensation for shrinkage and slicing errors.

[0034] In practical applications, an initial filling path is first generated based on the size data of the surrounding rock fissures. Then, through a size compensation factor calculation module integrated into the control unit, the path size is intelligently compensated and optimized based on the material's anisotropic linear shrinkage rate and slicing error to obtain a high-precision printing trajectory. Next, the prepared sodium alginate hydrogel (2%-4% mass concentration, ensuring high specimen strength) and calcium chloride solution (2%-5% mass concentration) are respectively loaded into the storage device. After the equipment is started, the control system coordinates the movement of the three-axis robotic arm and the extrusion action of the injection pump. The inner and outer layers of material are deposited layer by layer in the fissures according to the set flow rate ratio and the compensated and adjusted path. During extrusion, the hydrogel comes into contact with the crosslinking solution (calcium chloride solution), completing in-situ crosslinking within 10 seconds. This instantaneous crosslinking forms a temporary support structure with precise dimensions, uniform structure, and sufficient supporting strength.

[0035] In this embodiment, the flow rate ratio of the inner and outer layer materials is 3:1, the mass concentration of sodium alginate hydrogel is 2%, and the mass concentration of calcium chloride solution is 5%, which enables the inner layer to be uniformly wrapped by the outer layer.

[0036] To adapt to different engineering needs, this invention also provides several implementation variations: In one variation, the coaxial nozzle may employ different combinations of needles, such as 21G / 16G or 24G / 22G, to accommodate printing requirements for materials of different viscosities and cracks of different sizes.

[0037] In another variation, the storage device may be equipped with a temperature control system to maintain the material at the optimal operating temperature (20-30°C) through a heating jacket and temperature sensors, ensuring that the hydrogel maintains good rheological properties.

[0038] The coaxial extrusion 3D printing hydrogel equipment provided in this invention has the following advantages: The coaxial nozzle has a stepped contraction guide section at the entrance of the outer channel, which can effectively eliminate the uneven circumferential flow velocity and pressure distribution caused by the difference in path length in the annular flow channel that directly connects to the outer channel from a single side entrance. This allows the calcium chloride solution to uniformly and stably coat the inner sodium alginate hydrogel at 360°, thereby significantly improving the cross-sectional uniformity and structural consistency of the printed lines and avoiding breakage or morphological loss of control due to uneven coating. By combining the flow uniformity of the guide section with the intelligent size correction of the size compensation factor, stable extrusion and high-precision molding of the hydrogel in complex fractures are achieved. It has good engineering adaptability and printing controllability, and can achieve efficient, reliable and dimensionally accurate temporary support in actual engineering such as rock support. It has advantages such as high molding quality, intelligent operation, and stable support effect.

[0039] Meanwhile, the equipment integrates a size compensation factor calculation module, which can calculate and apply the size compensation factor in real time based on the material's anisotropic linear shrinkage rate and slicing error. It intelligently scales the 3D model before printing, thereby comprehensively compensating for material shrinkage and path slicing deviation during the printing process, achieving high-precision molding, and ensuring that the printed structure closely matches the design dimensions.

[0040] It should be noted that the various embodiments in this invention are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0041] The above description of the disclosed embodiments is intended to enable those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0042] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A coaxial extrusion 3D printing hydrogel device, characterized in that, The device includes: The coaxial nozzle has an inner channel and an outer channel. The inner channel is used to transport sodium alginate hydrogel, and the outer channel is used to transport calcium chloride crosslinking solution. The inlet of the outer channel is provided with a flow guiding part, which is a stepped contraction structure, to make the calcium chloride solution entering the outer channel uniformly distributed circumferentially, thereby forming an annular liquid sheath uniformly enveloping the inner hydrogel at the outlet. The control unit is used to coordinate the overall operation of the equipment; the control unit integrates a size compensation factor calculation module, which is used to calculate and apply the size compensation factor in real time based on the shrinkage characteristics of the hydrogel material and the slicing error of the three-dimensional model, and dynamically adjust the printing path. The three-axis robotic arm control system is used to control the coaxial nozzle to move in three-dimensional space along the path adjusted by the size compensation factor calculation module; The feeding system includes two independently controlled stepper motor drive units, which are used to precisely control the extrusion rates of the inner and outer layer materials, respectively. Storage device for storing sodium alginate hydrogel and calcium chloride solution separately.

2. The coaxial extrusion 3D printing hydrogel equipment according to claim 1, characterized in that, The flow guide section changes the cross-sectional shape of the flow channel at the inlet of the outer channel, so that the flow resistance of the annular flow of fluid entering from the side feed port to the outer channel tends to be balanced.

3. The coaxial extrusion 3D printing hydrogel equipment according to claim 1, characterized in that, The size compensation factor calculation module includes: The shrinkage rate database, using the coaxial nozzle, experimentally determined the isotropic linear shrinkage rate (S) of different hydrogel material parameters at room temperature. x , S y , S z The hydrogel material comprises sodium alginate hydrogel and calcium chloride crosslinking solution; The slicing error calculation unit is used to analyze the theoretical dimensional deviation caused by path rounding when slicing a 3D model into printing paths. E 切片 ; The size compensation factor synthesis unit, for the Y and Z directions, obtains the linear shrinkage rates S in the Y and Z directions from the shrinkage rate database based on the input hydrogel material parameters. y , S z Directly using the linear shrinkage rate S y , S z The Y and Z directions of the 3D model are compensated as size compensation factors; for the X direction, the linear shrinkage rate S is obtained from the shrinkage rate database based on the input hydrogel material parameters. x The size compensation factor CF in the X direction is calculated using the following formula. x The size compensation factor CF in the X direction x Compensation is applied to the X-direction of the 3D model: ， in, This refers to the design dimension of the specimen in the X direction.

4. The coaxial extrusion 3D printing hydrogel device according to claim 1, characterized in that: The stepper motor is connected to the storage container via a screw or piston structure to achieve quantitative extrusion of materials.

5. The coaxial extrusion 3D printing hydrogel equipment according to claim 1, characterized in that, The inner and outer channel outlets of the coaxial nozzle are on the same plane, and the annular gap width between the inner and outer channels is 0.5-1.0 mm.

6. The coaxial extrusion 3D printing hydrogel device according to claim 1, characterized in that: The sodium alginate hydrogel has a mass concentration of 2%-4%, the calcium chloride solution has a mass concentration of 2%-5%, and the flow rate ratio of the two is 2~4:

1.

7. The coaxial extrusion 3D printing hydrogel device according to claim 1, characterized in that: The diameter ratio of the upper and lower ends of the flow guiding section is 3:1 to 4:1, and the number of steps is 2-3. The lower end of the flow guiding section connects to the upper entrance of the outer channel, and the diameter of the upper end of the flow guiding section is much larger than the diameter of the upper end of the outer channel.

8. The coaxial extrusion 3D printing hydrogel equipment according to claim 1, used for printing temporary support for surrounding rock fissures.

9. A printing method for temporary support of a crack using the device according to any one of claims 1-7, characterized in that, Includes the following steps: A three-dimensional model of the crack is obtained, and the model data is processed by the size compensation factor calculation module to generate a size-compensated printing path. The material is loaded into the storage device and then conveyed to the coaxial nozzle through the feeding system at a preset flow rate ratio. After the calcium chloride solution is evenly distributed through the guide section, it is coaxially extruded with the sodium alginate hydrogel at the nozzle outlet and cross-links. A three-axis robotic arm controls the nozzle to move along a compensated path to achieve precise deposition of the hydrogel structure. The printing process completes, creating a precisely sized, uniformly cross-linked temporary support structure within the cracks.

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