Extrusion head device for improving interface strength of 3D printing concrete strip and use method

Abstract

The invention relates to the technical field of 3D printing construction, and discloses an extrusion head device for improving the interface strength of a 3D printing concrete strip and a using method, the extrusion head device comprises an extrusion cylinder and an extrusion nozzle, and the extrusion nozzle is detachably connected to one end of the extrusion cylinder; an outlet used for extruding concrete strips is formed in the extrusion nozzle, and a tooth groove structure is arranged at the outlet. According to the extrusion head device for improving the interface strength of the 3D printing concrete strip and the using method, mechanical key grooves are formed in the interface of the concrete strip through tooth groove design, the interlayer occlusion effect is enhanced, and the shear strength and integrity are remarkably improved.

Description

Technical Field

[0009]

[0001] The present invention relates to the technical field of 3D printing construction, and particularly relates to an extrusion head device for enhancing the interface strength of 3D printed concrete strips and a usage method thereof. Background Art

[0002] The 3D printing concrete technology has become an important implementation method of digital construction due to its advantages such as high efficiency, mold-free, and high construction freedom, and there are many successful application cases in projects such as landscape components, small buildings, and pedestrian bridges. However, in terms of material properties, the extrusion stacking forming method results in obvious anisotropy and weak interface bonding strength of 3D printed concrete components, which limits the application range of 3D printed concrete.

[0003] There are obvious problems such as obvious stratification and high porosity in the interface of concrete strips formed by traditional extrusion heads. Since vibration compaction operations cannot be implemented during the printing process, it is difficult to achieve the overall compactness similar to ordinary concrete between the strips, resulting in significantly lower mechanical properties, especially the interlayer shear strength and integrity, of the printed components compared to traditional cast concrete. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention provides an extrusion head device for enhancing the interface strength of 3D printed concrete strips and a usage method thereof. By setting a special tooth groove structure at the extrusion nozzle part, the mechanical咬合作用 is enhanced between the printed concrete strips, thereby effectively enhancing the interlayer interface strength and overall mechanical properties.

[0005] In the first aspect, an extrusion head device for enhancing the interface strength of 3D printed concrete strips is provided, including: An extrusion barrel and an extrusion nozzle, the extrusion nozzle is detachably connected to one end of the extrusion barrel; the extrusion nozzle is provided with an outlet for extruding concrete strips, and a tooth groove structure is provided at the outlet.

[0006] Furthermore, a flange is provided at the end of the extrusion barrel far from the extrusion nozzle, and the flange is used to connect with adjacent components of the 3D printing device.

[0007] Furthermore, an external thread is provided on the outer wall of one end of the extrusion barrel, and an internal thread is provided on the inner wall of the end of the extrusion nozzle opposite to the extrusion barrel. The extrusion nozzle is connected to the extrusion barrel by matching the internal thread with the external thread.

[0008] Furthermore, the extrusion nozzle is formed by lofting from a circle to a rectangle.

[0009] Furthermore, the tooth groove structure is divided into a first side tooth groove and a second side tooth groove along the width direction of the outlet; the contour shape of the first side tooth groove is rectangular, and the contour shape of the second side tooth groove is at least one of sawtooth wave shape, "Ji" shape or triangular wave shape. It should be noted that the term "咬合作用" in the original text seems to be incorrect. I assume it should be "mechanical interlocking effect" and have translated it accordingly. If this is not what you intended, please correct it and I will adjust the translation.

[0010] Furthermore, the height of the first side tooth groove is different from the height of the second side tooth groove, and the first side tooth groove and the second side tooth groove form a height matching relationship.

[0011] Secondly, a method for using an extruder to enhance the interfacial strength of 3D printed concrete strips is provided. Based on any of the extruder devices for enhancing the interfacial strength of 3D printed concrete strips described above, the method includes the following steps: The extrusion nozzle and the extrusion barrel are assembled to form a complete extrusion head; Adjust the position of the extruder head to suit the printing requirements of 3D printed concrete strips; Concrete is extruded through an extrusion head to complete the layer-by-layer printing of 3D printed concrete strips.

[0012] Furthermore, assembling the extrusion nozzle and extrusion barrel to form a complete extrusion head includes: Based on the interface strength requirements of 3D printed concrete strips, an extrusion nozzle with a corresponding toothed structure is selected. Align and screw the internal thread on the inner wall of one end of the selected extrusion nozzle with the external thread on the outer wall of one end of the extrusion cylinder to fix the extrusion nozzle and the extrusion cylinder in place.

[0013] Furthermore, the position of the extruder head is adjusted to suit the printing requirements of 3D printed concrete strips, including: When printing the first layer of concrete strips, set the initial height between the bottom of the extruder nozzle and the printing reference surface; When printing the upper layer of concrete strips, adjust the lifting height of the extruder according to the height of the lower layer of already printed concrete strips; During printing, keep the rectangular grooves of the extrusion nozzle in front of the printing direction.

[0014] Furthermore, by extruded concrete through an extrusion head, the 3D printed concrete strips are printed layer by layer, including: During the process of extruding concrete to form strips, the toothed structure of the extrusion nozzle is used to scrape the surface of the lower printed concrete strip. By using the high-fitting relationship of the toothed structure, the interface between the lower layer of printed concrete strips and the upper layer of concrete strips to be printed is compacted, so that mechanical keyways are formed between adjacent layers of concrete strips.

[0015] The invention employing the above technical solution has the following advantages: 1. This invention forms a mechanical keyway at the interface of concrete strips through a toothed groove design, which enhances the interlayer interlocking effect and significantly improves shear strength and integrity.

[0016] 2. The present invention uses an asymmetric tooth height design to enable the extrusion process to have both extrusion and compaction functions, reducing interlayer porosity and improving interface density.

[0017] 3. This invention expands the adaptability of the printing process through the interchangeable extrusion nozzle design, allowing different tooth profiles to be selected according to printing needs, thereby optimizing the printing effect. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly described below. In all the drawings, the elements or parts are not necessarily drawn to scale.

[0019] Figure 1 This is a schematic diagram of the extrusion cylinder in the extrusion head device and its usage method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 2 This is a schematic diagram of the extrusion head structure in the extrusion head device and its usage method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 1 ; Figure 3 This is a schematic diagram of the extrusion head structure in the extrusion head device and its usage method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 2 ; Figure 4 This is a schematic diagram of the extrusion nozzle structure in the extrusion head device and its usage method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 1 ; Figure 5 This is a schematic diagram of the extrusion nozzle structure in the extrusion head device and its usage method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 2 ; Figure 6 This is a schematic diagram of the extrusion nozzle structure in the extrusion head device and its usage method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 3 ; Figure 7 This is a schematic diagram of the extrusion nozzle structure in the extrusion head device and its usage method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 4 ; Figure 8 This is a schematic diagram of the toothed shape of the extrusion nozzle in the extrusion head device and its method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 1 ; Figure 9 The extrusion nozzle tooth groove shape structure of the extrusion head device and its method for improving the interfacial strength of 3D printed concrete strips in this invention is explained. Figure 2 ; Figure 10This is a schematic diagram of the toothed shape of the extrusion nozzle in the extrusion head device and its method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 3 ; Figure 11 This is a schematic diagram of the extrusion head printing principle in the extrusion head device and its usage method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 12 This is a schematic diagram illustrating the extrusion strip forming effect in the extrusion head device and its usage method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 1 ; Figure 13 This is a schematic diagram illustrating the extrusion strip forming effect in the extrusion head device and its usage method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 2 ; Figure 14 This is a schematic diagram illustrating the extrusion strip forming effect in the extrusion head device and its usage method for improving the interfacial strength of 3D printed concrete strips according to the present invention. Figure 3 .

[0020] Figure label: Extrusion cylinder 1, flange 11, external thread 12 Extrusion nozzle 2, first side groove 21, second side groove 22. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0023] References to "embodiments" in this application mean that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase may not necessarily refer to the same embodiment when it appears in various places in the specification, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described in this application can be combined with other embodiments.

[0024] As Figures 1 to 14 shown, the extrusion head device for enhancing the interface strength of 3D printed concrete strips according to the present invention includes: An extrusion barrel 1 and an extrusion nozzle 2, the extrusion nozzle 2 is detachably connected to one end of the extrusion barrel 1; the extrusion nozzle 2 is provided with an outlet for extruding concrete strips, and a tooth groove structure is provided at the outlet.

[0025] In this embodiment, a flange 11 is provided at one end of the extrusion barrel 1 away from the extrusion nozzle 2, and the flange 11 is used to connect with adjacent components of the 3D printing device.

[0026] In this embodiment, an external thread 12 is provided on the outer wall of one end of the extrusion barrel 1, and an internal thread is provided on the inner wall of the end of the extrusion nozzle 2 opposite to the extrusion barrel 1. The extrusion nozzle 2 is connected to the external thread 12 of the extrusion barrel 1 by means of the internal thread.

[0027] In this embodiment, the extrusion nozzle 2 is formed by lofting from a circle to a rectangle.

[0028] In this embodiment, the tooth groove structure is divided into a first side tooth groove 21 and a second side tooth groove 22 along the width direction of the outlet; the profile shape of the first side tooth groove 21 is rectangular, and the profile shape of the second side tooth groove 22 is at least one of a sawtooth waveform, a "Ji" shape, or a triangular waveform.

[0029] In this embodiment, the height of the first side tooth groove 21 is different from the height of the second side tooth groove 22, and the first side tooth groove 21 and the second side tooth groove 22 form a height matching relationship.

[0030] Specifically, the extrusion barrel 1 is an integrated structure of "long round straight barrel + flange 11 + external thread 12", and the material is selected as 45 steel (with sufficient compressive strength and wear resistance, adapted to the working pressure of 1.2 - 1.5 MPa during concrete transportation, and avoiding barrel wall deformation). Its main function is to receive the concrete transportation of the 3D printing device and form a stable connection with the extrusion nozzle 2; Main structure: The length of the long round straight barrel is 200 mm (adapted to the length of the extrusion screw of the mainstream 3D printing device, the screw extends into the barrel by 150 mm, and a 50 mm concrete buffer space is reserved), and the inner diameter is 40 mm (matched with the aggregate particle size of C30 printed concrete to avoid blockage); Top connection structure: A circular flange 11 (80mm in diameter and 10mm in thickness) is welded to the top of the straight cylinder. The flange 11 has 4 evenly distributed M12 bolt holes. It is rigidly connected to the flange face of the extrusion module of the 3D printing device through bolts. The bolt tightening torque is 30N·m to ensure no vibration or displacement during the printing process (to avoid uneven concrete extrusion). Bottom connection structure: The outer wall of the bottom 100mm section of the straight cylinder is reinforced with M40×2 fine external threads (fine threads provide good sealing and prevent concrete slurry from leaking through the gaps), and the surface is chrome-plated (to reduce thread wear and extend service life).

[0031] The extrusion nozzle 2 has a gradient structure of "straight cylinder + rectangular outlet + toothed groove structure". It is formed by selective laser melting (SLM) metal 3D printing technology (which can accurately realize complex toothed groove contours with a forming accuracy of ±0.1mm). Its main function is to transform the concrete of the circular channel into a toothed strip and detachably connect it to the extrusion cylinder 1. The threaded connection between the extrusion cylinder 1 and the extrusion nozzle 2 takes into account both "detachability" (easy replacement of different toothed extrusion nozzles 2) and "sealing" (rubber ring to prevent grout leakage). The flange 11 is rigidly connected to the 3D printing device to avoid toothed groove misalignment caused by printing vibration and ensure accurate forming of mechanical keyways.

[0032] Top connection structure: The top of the extrusion nozzle 2 is a straight cylindrical section (50mm in height and 40mm in inner diameter). The inner wall is machined with an M40×2 fine-pitch internal thread (30mm in length to ensure sufficient engagement depth and stable connection) that matches the external thread 12 of the extrusion cylinder 1. An annular sealing groove is provided at the bottom of the internal thread. Main gradient structure: The straight cylindrical section to the bottom rectangular outlet is formed by "circle-rectangle" layout, with a cross-sectional transition length of 80mm (gradient angle of 15° to avoid eddies when the concrete flows and reduce flow resistance). The final rectangular outlet has a width of B=50mm (compatible with common 3D printing strip widths, which can be adjusted to 30-80mm according to project requirements) and a thickness of 10mm (consistent with the design thickness of the concrete strip). Gear groove structure design: The gear grooves are distributed along the width of the rectangular exit, and are divided into "first side gear groove 21" (front side in the printing forward direction) and "second side gear groove 22" (rear side). The two have different heights (forming an asymmetrical height fit). The parameters and structures of the three gear groove shapes are as follows: General parameter requirements for tooth grooves; First side groove 21: The outline shape is fixed as a rectangle, and the height is recorded as hb. It must satisfy hb = hc + 5mm (hc is the height of the second side groove 22. The height difference ensures that the rectangular side prevents concrete from overflowing during extrusion, while the corrugated side achieves scraping and compaction). Second side tooth groove 22: The contour shape can be optionally triangular wave shape, sawtooth wave shape, or "ji" shape. The height is denoted as hc (selected according to the interface strength requirement, and the conventional value is 10 - 20 mm. In this embodiment, hc = 15 mm is uniformly taken, then hb = 20 mm); Tooth groove machining accuracy: Profile tolerance is ±0.05 mm, and surface roughness Ra ≤ 1.6 μm (to prevent concrete from adhering to the tooth groove surface and affecting the forming quality of the strip).

[0033] Specific implementation of three tooth groove shapes: ① Triangular wave-shaped tooth groove (suitable for scenarios with high requirements for uniform interface stress, such as flat components) When the tooth groove shape is triangular wave-shaped, its shape parameters can be calculated through the following function: Among them: L1: The length of the first horizontal segment; hc: Tooth groove height; T: The length of the inverted triangular wave period; L2: The length of the horizontal segment between triangular waves; n: The number of repetitions (the number of repetitions of the sawtooth wave and the horizontal segment L2 between sawtooth waves); B: The width of the extrusion nozzle 2 outlet, satisfying B = 2L1 + n(T + L2)L2; P: The length of each repetition block (sawtooth wave + horizontal segment) P = T + L2.

[0034] Profile function: Along the outlet width direction (x-axis, unit: mm), the profile function f(x) satisfies: When 0 ≤ x ≤ L1, f(x) = hb = 20 mm (the first side rectangular segment); When L1 < x ≤ L1 + T / 2, f(x) = 20 - 2hc(x - L1) / T (the descending segment of the triangular wave); When L1 + T / 2 < x ≤ L1 + T, f(x) = hc + 2hc(x - L1 - T / 2) / T (the ascending segment of the triangular wave); When L1 + T < x ≤ L1 + T + L2, f(x) = hc = 15 mm (the horizontal segment between triangular waves); After repeating n times, when x ≥ L1 + n(T + L2) in the last segment, f(x) = 20 mm (the ending rectangular segment, symmetric with the first side).

[0035] Parameter values: Outlet width B = 50 mm, number of repetitions n = 2 (forming 2 complete triangular waves), triangular wave period T = 8 mm (distance from peak to peak), horizontal segment between waves L2 = 12 mm; Calculated from B = 2L1 + n(T + L2): L1 = (50 - 2×(8 + 12)) / 2 = 5mm (the length of the rectangular segments on both sides is 5mm each); The length of a single repeating block P = T + L2 = 20mm, the total length of the repeating segments n×P = 40mm, plus 2L1 = 10mm on both sides, the total width is 50mm (the same as B).

[0036] Structural function: Symmetrical triangular grooves are formed at the rear side of the formed strip. After the upper layer of concrete is embedded, the interface is stressed evenly, reducing local stress concentration, and is suitable for printing components with gentle stress (such as landscape slabs).

[0037] ② Sawtooth wave-shaped grooves (suitable for scenarios with high requirements for interface shear strength, such as load-bearing components) When the groove shape is sawtooth wave-shaped, its shape parameters can be calculated through the following function: L1: The length of the first horizontal segment; hc: The height of the groove; T: The length of the inverted sawtooth wave period; L2: The length of the horizontal segment between sawtooth waves; n: The total number of repetitions (the number of repetitions of sawtooth waves and the horizontal segments between sawtooth waves); B: The width of the outlet of the extrusion nozzle 2, satisfying B = 2L1 + n(T + L2)L2; P: The length of each repeating block (sawtooth wave + horizontal segment) P = T + L2; k: The sawtooth wave repetition parameter.

[0038] Profile function: Along the x-axis, the profile function f(x) satisfies: When 0 ≤ x ≤ L1, f(x) = 20mm (the first rectangular segment on one side); When L1 < x ≤ L1 + T, f(x) = 20 - hc(x - L1)k / T (the one-way descending segment of the sawtooth wave, k is the repetition parameter, taking 1.2, controlling the descending slope); When L1 + T < x ≤ L1 + T + L2, f(x) = 15mm (the horizontal segment between sawtooth waves); After repeating n times, the ending segment f(x) = 20mm.

[0039] Parameter values: B = 50mm, n = 2, the sawtooth wave period T = 10mm (the length of the sawtooth), the horizontal segment between waves L2 = 10mm, k = 1.2; Calculated from B = 2L1 + n(T + L2): L1 = (50 - 2×(10 + 10)) / 2 = 5mm; The length of a single repeating block \(P = T+L2 = 20\mathrm{mm}\), the total length of the repeating section is \(40\mathrm{mm}\), the rectangular sections on both sides are \(10\mathrm{mm}\), and the total width is \(50\mathrm{mm}\).

[0040] Structural function: A unidirectionally inclined sawtooth groove is formed at the rear side of the formed strip. After the upper-layer concrete is embedded, the inclined surface of the sawtooth can withstand greater shear force, which is suitable for printing small load-bearing components (such as pedestrian bridge decks).

[0041] ③ The "Ji" - shaped tooth groove (suitable for scenarios with high requirements for interface integrity, such as closed components) When the tooth groove shape is triangular waveform, its shape parameters can be calculated through the following function: Where: A: The height of the tooth groove (\(\mathrm{mm}\)); L1: The height of the straight section at the bottom of the tooth groove (\(\mathrm{mm}\)); L2: The width of the inclined straight section of the tooth groove (\(\mathrm{mm}\)); L3: The width of the straight section at the top of the tooth groove (\(\mathrm{mm}\)); B: The width of the outlet of the extrusion nozzle 2 (\(\mathrm{mm}\)), \(B = L1 + 2L2+L3\).

[0042] Profile function: Along the x-axis, the profile function \(f(x)\) satisfies: When \(0\leq x\leq L1\), \(f(x)=20\mathrm{mm}\) (the first side rectangular section); When \(L1\lt x\leq L1 + L2\), \(f(x)=20 - A(x - L1) / L2\) (the descending section on the left side of the "Ji" character, \(A = hc = 15\mathrm{mm}\)); When \(L1 + L2\lt x\leq L1 + L2+L3\), \(f(x)=5\mathrm{mm}\) (the straight section at the bottom of the "Ji" character, \(20 - 15 = 5\mathrm{mm}\)); When \(L1 + L2+L3\lt x\leq L1 + 2L2+L3\), \(f(x)=5+A(x - L1 - L2 - L3) / L2\) (the ascending section on the right side of the "Ji" character); The ending section \(f(x)=20\mathrm{mm}\) (symmetric to the first side).

[0043] Parameter values: \(B = 50\mathrm{mm}\), \(A = 15\mathrm{mm}\), the straight section at the bottom of the "Ji" character \(L3 = 10\mathrm{mm}\) (to ensure sufficient embedding depth), the inclined straight sections on both sides \(L2 = 15\mathrm{mm}\) (to control the inclination angle and avoid difficulty in concrete filling); Calculated from \(B = L1 + 2L2 + L3\): \(L1=50 - 2\times15 - 10 = 10\mathrm{mm}\) (the length of the first side rectangular section is \(10\mathrm{mm}\)).

[0044] Structural function: A "Ji" - shaped structure of "groove + protrusion" is formed at the rear side of the formed strip. The upper - layer concrete and the lower - layer form a nested bite, and the interface contact area is larger than the previous two waveforms, with stronger integrity, and is suitable for printing closed components.

[0045] The asymmetric height (hb = hc + 5mm) enables the extrusion nozzle 2 to have both the functions of "extrusion" (the rectangular side guides the concrete flow) and "compaction" (the waveform side squeezes the interface). Different waveform grooves improve the interface performance through "shape - adaptation requirements". The triangular wave is evenly stressed, the saw - tooth wave strengthens shear resistance, and the "Ji" - shaped one enhances the overall strength.

[0046] In some other embodiments, a method of using an extrusion head for enhancing the interface strength of 3D - printed concrete strips is provided. Based on the extrusion head device for enhancing the interface strength of 3D - printed concrete strips in any one of the foregoing, it includes the following steps: Assemble the extrusion nozzle 2 and the extrusion barrel 1 to form a complete extrusion head; Adjust the position of the extrusion head to adapt to the printing requirements of 3D - printed concrete strips; Extrude concrete through the extrusion head to complete the layer - by - layer printing of 3D - printed concrete strips.

[0047] In this embodiment, assembling the extrusion nozzle 2 and the extrusion barrel 1 to form a complete extrusion head includes: According to the interface strength requirements of 3D - printed concrete strips, select an extrusion nozzle 2 with a corresponding groove structure; Align the internal thread on the inner wall of one end of the selected extrusion nozzle 2 with the external thread 12 on the outer wall of one end of the extrusion barrel 1 and screw them together to fixedly connect the extrusion nozzle 2 and the extrusion barrel 1.

[0048] In this embodiment, adjusting the position of the extrusion head to adapt to the printing requirements of 3D - printed concrete strips includes: When printing the first - layer concrete strip, set the initial height between the bottom of the extrusion nozzle 2 and the printing reference plane; When printing the upper - layer concrete strip, adjust the lifting height of the extrusion nozzle 2 according to the height of the lower - layer already - printed concrete strip; During the printing process, keep the rectangular groove of the extrusion nozzle 2 on the front side of the printing forward direction.

[0049] In this embodiment, extruding concrete through the extrusion head to complete the layer - by - layer printing of 3D - printed concrete strips includes: During the process of extruding concrete to form a strip, use the groove structure of the extrusion nozzle 2 to scrape the surface of the lower - layer already - printed concrete strip; Through the height - matching relationship of the groove structure, compact the interface between the lower - layer already - printed concrete strip and the upper - layer to - be - printed concrete strip, so as to form a mechanical key - groove between adjacent - layer concrete strips.

[0050] Specifically, this method is based on the above-mentioned extrusion head device, and the specific steps are as follows. Each step needs to cooperate with the control system of the 3D printing device (such as the PLC control system) to achieve automatic coordination: Extrusion head assembly steps; Selection of extrusion nozzle 2: Select the extrusion nozzle 2 with the corresponding tooth groove structure according to the interface performance requirements of the 3D printing component. For the landscape flat plate, select the triangular waveform; for the load-bearing component, select the sawtooth waveform; for the closed component, select the "ji" shape. In this embodiment, the sawtooth waveform extrusion nozzle 2 is selected.

[0051] Installation of the seal: Take out the suitable nitrile rubber ring (cross-sectional diameter 3mm) and embed it into the annular seal groove of the straight cylindrical section at the top of the extrusion nozzle 2, ensuring that the rubber ring is not distorted and completely fits the groove wall.

[0052] Thread screwing connection: Align the internal thread of the extrusion nozzle 2 with the external thread 12 of the extrusion barrel 1, manually screw it 3 - 5 turns until there is no jamming, and then use an open-end wrench (suitable for M40 thread) to tighten it clockwise. The tightening torque is controlled at 28 - 30 N·m (calibrated with a torque wrench. Excessive torque will cause thread damage, and too small torque will result in poor sealing). After assembly, check the coaxiality of the extrusion nozzle 2 and the extrusion barrel 1 to ensure that the deviation ≤ 0.1mm to avoid the deviation of concrete flow.

[0053] Preparation of concrete mixture: Use a forced mixer to prepare the 3D printing concrete mixture. The raw materials are P.O42.5 cement, quartz sand, and water. The mixing process is as follows: First, dry-mix the cement and quartz sand for 2 minutes, and then add water and water reducer and wet-mix for 3 minutes to ensure the uniformity of the mixture. The performance of the mixture is controlled at a slump of 180 ± 5mm and an expansion degree of 450 ± 10mm to meet the extrusion fluidity requirements (detected by a slump cone and an expansion degree board).

[0054] Calibration of the extrusion head position: Install the assembled extrusion head at the end of the robotic arm of the 3D printing device, and calibrate the initial position at the bottom of the extrusion nozzle 2 through the visual positioning system of the device, ensuring that the outlet plane of the extrusion nozzle 2 is parallel to the printing reference plane (such as the workbench surface), and the parallelism deviation ≤ 0.05mm.

[0055] Setting of printing parameters: Input parameters in the 3D printing control system. The extrusion pressure is 0.8 - 1.2MPa (adjusted according to the fluidity of the mixture, taking the upper limit when the fluidity is poor), the printing forward speed is 30 - 50mm / s (matched with the extrusion rate to ensure continuous and unbroken strips), the initial height ha of the bottom of the extrusion nozzle 2 from the printing reference plane in the first layer is 10mm (it can be reduced to 8 - 9mm when the fluidity is poor, and increased to 11 - 12mm when the fluidity is good), and the lifting height of the upper extrusion nozzle 2 = ha + hc = 25mm (hc = 15mm, ensuring that the tooth groove can scrape the surface of the lower layer strip without crushing the lower layer strip).

[0056] First-layer strip printing: Start the concrete delivery pump of the 3D printing device. Concrete enters the extrusion nozzle 2 through the extrusion cylinder 1 and is extruded through the rectangular outlet and the serrated wave groove to form the first-layer strip with serrated grooves. During the printing process, keep the rectangular groove of the extrusion nozzle 2 in front of the printing direction (ensuring the direction positioning by the robotic arm) to ensure that the grooves are aligned and prepare for the upper layer to bite.

[0057] Upper strip printing: After the first layer printing is completed, the robotic arm drives the extruder head to be raised to a set height (25mm) and moved to the upper layer printing start position; when printing the upper strip, the sawtooth wave groove of the extruder nozzle 2 will scrape the surface of the lower layer printed strip to remove the surface laitance, and at the same time squeeze the upper layer concrete into the sawtooth groove of the lower layer strip to form a mechanical keyway; during the printing process, the force sensor of the device monitors the contact force between the extruder nozzle 2 and the lower layer strip in real time, and controls the contact force to be 50-80N to ensure the compaction effect without damaging the lower layer strip.

[0058] Replacement of extrusion nozzle 2: If it is necessary to replace the extrusion nozzle 2 with a different tooth groove during the printing process, first turn off the concrete delivery pump. After the residual concrete in the extrusion cylinder 1 is discharged, use a wrench to loosen the old extrusion nozzle 2 in the opposite direction (loosening torque ≤25N・m), remove the old rubber ring and replace it with a new ring. Then install the new extrusion nozzle 2 according to the "assembly steps". After installation, recalibrate the position and parameters.

[0059] Specimen preparation: After printing the laminated components, the components were cut into 100mm×100mm×100mm cubic specimens (3 specimens per group, including the control group: specimens printed by a traditional smooth rectangular extruder with an extrusion nozzle size of 50mm×20mm) using a diamond saw. Avoid damaging the strip interface during cutting.

[0060] Interface porosity detection: The specimen was scanned using a microfocus CT device (5μm resolution), and the scanning range covered the entire interface area. The scanned images were analyzed using Image-Pro Plus software to statistically analyze the interface porosity. The average porosity of the specimen with the traditional smooth extrusion head was 12.3%, while the average porosity of the specimen with the sawtooth waveform extrusion head in this embodiment was 5.6%, which significantly reduced the interlayer porosity.

[0061] Interface splitting strength test: The interface splitting strength test was conducted according to the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T 50081-2019), with a loading rate of 0.05 mm / min, and the failure strength of each specimen was recorded. The test results showed that the average interface splitting strength of the specimen with the traditional smooth extrusion head was 3.59 MPa, while the average interface splitting strength of the specimen in this embodiment was 4.06 MPa, with a strength increase of 13.1%, verifying the interface strengthening effect.

[0062] Table 1 Comparison of splitting tensile strength test results for 3D printed concrete interfaces Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. Extrusion head device for improving the interfacial strength of 3D printed concrete strips, characterized in that, The extrusion head device for improving the interface strength of 3D printed concrete strips comprises: an extrusion barrel and an extrusion nozzle, the extrusion nozzle being detachably connected to one end of the extrusion barrel; the extrusion nozzle is provided with an outlet for extruding concrete strips, and the outlet is provided with a tooth groove structure.

2. The extrusion head device for enhancing the interfacial strength of 3D printed concrete strips according to claim 1, characterized in that, The end of the extrusion barrel away from the extrusion nozzle is provided with a flange, which is used to connect with the adjacent components of the 3D printing device.

3. The extrusion head device for enhancing the interfacial strength of 3D printed concrete strips according to claim 1, characterized in that, The outer wall of one end of the extrusion barrel is provided with external threads, and the inner wall of the opposite end of the extrusion nozzle is provided with internal threads, and the extrusion nozzle is connected with the extrusion barrel through the cooperation of the internal threads and the external threads.

4. The extrusion head device for enhancing the interfacial strength of 3D printed concrete strips according to claim 1, wherein, The extrusion nozzle is shaped by lofting from a circle to a rectangle.

5. The extrusion head device for enhancing the interfacial strength of 3D printed concrete strips according to claim 1, wherein, The tooth groove structure is divided into a first side tooth groove and a second side tooth groove along the width direction of the outlet; the profile shape of the first side tooth groove is rectangular, and the profile shape of the second side tooth groove is at least one of sawtooth wave, "j" shape or triangular wave.

6. The extrusion head device for enhancing the interfacial strength of 3D printed concrete strips according to claim 5, characterized in that, The height of the first side tooth groove is different from the height of the second side tooth groove, and the first side tooth groove and the second side tooth groove form a height matching relationship.

7. A method for using an extruder to improve the interfacial strength of 3D printed concrete strips, characterized in that, The extrusion head device for improving the interface strength of 3D printed concrete strips based on any one of claims 1 to 6 comprises the following steps: Assembling the extrusion nozzle and the extrusion barrel to form a complete extrusion head; Adjusting the position of the extrusion head to adapt to the printing requirements of the 3D printed concrete strips; Extruding concrete through the extrusion head to complete the layer-by-layer printing of the 3D printed concrete strips.

8. The method of claim 7, wherein the method further comprises: Assembling the extrusion nozzle and the extrusion barrel to form a complete extrusion head comprises: Selecting an extrusion nozzle with a corresponding tooth groove structure according to the interface strength requirements of the 3D printed concrete strips; Aligning and screwing the internal threads on the inner wall of one end of the selected extrusion nozzle with the external threads on the outer wall of one end of the extrusion barrel to fixedly connect the extrusion nozzle and the extrusion barrel.

9. The method of claim 7, wherein the method further comprises: Adjusting the position of the extrusion head to adapt to the printing requirements of the 3D printed concrete strips comprises: When printing the first layer of concrete strips, setting the initial height between the bottom of the extrusion nozzle and the printing reference surface; When printing the upper layer of concrete strips, adjusting the lifting height of the extrusion nozzle according to the height of the lower layer of printed concrete strips; During the printing process, the rectangular tooth groove of the extrusion nozzle is kept on the front side of the printing direction.

10. The method of claim 7, wherein the method further comprises: Extruding concrete through the extrusion head to complete the layer-by-layer printing of the 3D printed concrete strips comprises: During the process of extruding concrete to form strips, using the tooth groove structure of the extrusion nozzle to scrape the surface of the lower layer of printed concrete strips; Through the height matching relationship of the tooth groove structure, compacting the interface between the lower layer of printed concrete strips and the upper layer of to-be-printed concrete strips, so as to form mechanical key grooves between adjacent layers of concrete strips.

Images