Laser cladding metal additive manufacturing apparatus

Abstract

The utility model relates to laser cladding processing technical field, concretely is a kind of laser cladding metal additive manufacturing equipment, including the connecting assembly for being connected in the wall of extension long tube spray head, multiple rollers are equipped in the circumferential direction on connecting assembly, the fan blade of coaxial setting is respectively fixedly installed on each roller, and the outer periphery of multiple rollers is used to contact the inner wall of workpiece simultaneously, and with the rotation of workpiece homodirectional rotation, to realize that fan blade rotates under the driving of roller and generates airflow.The utility model can inhibit the elastic deformation of the extension long tube spray head far end by the rotation of roller set, ensure light path transmission and spot size stability, improve cladding layer precision, quality and efficiency.Meanwhile, fan blade rotation can efficiently discharge cladding heat, slow down component aging, prolong service life, protect high-quality cladding layer formation;And fan blade rotation can also discharge excess powder and smoke, improve processing visibility and efficiency, reduce cladding layer surface roughness, improve surface quality.

Description

Technical Field

[0001] This utility model relates to the field of laser cladding processing technology, specifically to a laser cladding metal additive manufacturing equipment. Background Technology

[0002] Laser cladding technology, as an advanced material surface modification and repair technique, has been widely used in various fields in recent years. This technology uses a high-energy laser beam as a heat source to rapidly melt the substrate surface and powder to form a molten pool. The molten pool then rapidly solidifies and cools, thus forming a cladding layer on the substrate surface. Depending on practical engineering needs, laser cladding technology can be used to prepare new materials, strengthen the surface of parts, and repair damaged parts.

[0003] However, current technologies for laser cladding green repair of deep-cavity cylindrical inner surfaces still face numerous challenges. For instance, some existing laser heads and devices for internal hole cladding, such as those disclosed in CN215799897U, CN219731058U, CN116240542A, and CN217127536U (a retractable internal hole laser cladding head), exhibit the following deficiencies in practical applications:

[0004] 1. During the cladding process on the surface of the deep-cavity cylindrical inner body, the distal end of the extended long-tube nozzle is prone to elastic deformation due to gravity (e.g., Figure 11 (As shown in the image). This deformation directly affects the optical path transmission accuracy and the stability of the light spot size, thus impacting the dimensional accuracy and quality of the cladding layer. Furthermore, when the elastic deformation exceeds a certain threshold, surface repair work cannot be carried out normally, severely affecting work efficiency.

[0005] 2. The heat generated during the cladding process on the inner surface of the deep-cavity cylindrical body accumulates inside the workpiece and is difficult to dissipate effectively. This not only accelerates the aging of key components such as nozzles and feed ports, shortens their service life and reduces their performance, but also destroys the formation of a high-quality molten pool, resulting in the inability to obtain a high-quality cladding layer, and may even make the cladding work impossible, which has a double adverse effect on work efficiency and quality.

[0006] 3. Excessive powder and smoke are generated during the cladding process, resulting in unclear processing visibility and seriously affecting processing efficiency; in addition, unmelted powder will also affect the surface roughness of the cladding layer and reduce the surface quality of the repaired parts. Utility Model Content

[0007] This invention provides a laser cladding metal additive manufacturing equipment to solve the problems mentioned in the background art.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows:

[0009] A laser cladding metal additive manufacturing equipment includes a connecting assembly for connecting to the wall of an extended long tube nozzle. The connecting assembly has multiple rollers arranged along the circumferential direction. Each roller has a fan blade fixedly installed on it and arranged coaxially with it. The outer circumferential surfaces of the multiple rollers are used to simultaneously contact the inner wall of the workpiece and rotate in the same direction as the workpiece, so that the fan blades rotate under the drive of the rollers and generate airflow.

[0010] Preferably, the connecting assembly includes a central ring fixedly sleeved on the wall of the extended long pipe nozzle and a plurality of support arms fixedly connected to the outer circumferential surface of the central ring. The plurality of support arms correspond one-to-one with the plurality of rollers, and one end of each support arm is rotatably connected to the corresponding roller.

[0011] Preferably, the connecting assembly includes a central base fixedly sleeved on the wall of the extended long tube nozzle, a plurality of support frames movably connected to the central base, and a diameter adjustment mechanism connected to the wall of the extended long tube nozzle. The plurality of support frames correspond one-to-one with the plurality of rollers, and one end of each support frame is rotatably connected to the corresponding roller. The diameter adjustment mechanism is used to drive the support frame to move on the central base so that the plurality of rollers move synchronously closer to or further away from the nozzle wall as the center.

[0012] Preferably, the diameter adjustment mechanism includes a slotted gear movably connected to the wall of the extended long pipe nozzle, a drive gear meshing with the teeth of the slotted gear, and a motor for driving the drive gear to rotate. The end of the support frame away from the roller is disposed in the groove opening on the surface of the slotted gear, and when the slotted gear rotates, one end of the support frame moves along the groove opening.

[0013] Preferably, the slotted gear has multiple slots along the circumferential direction on its surface. The slots are arc-shaped and each slot corresponds to a support frame.

[0014] Preferably, the surface of the central base is provided with multiple rail channels, each of which corresponds to a multiple support frame, and each support frame is slidably disposed in the corresponding rail channel.

[0015] Preferably, the support frame includes a sliding section rotatably connected to the roller and a guide section connected to one end of the sliding section, wherein the sliding section is slidably disposed in the rail groove and the guide section is adapted to the rail groove opening.

[0016] Preferably, the connecting assembly further includes a support plate connected to the wall of the extended long pipe nozzle, and the motor is fixedly mounted on the support plate.

[0017] Preferably, a laser cladding metal additive manufacturing equipment further includes an extended long tube nozzle, the extended long tube nozzle including an extension tube, one end of the extension tube is provided with a collimator device, the end of the extension tube away from the collimator device is connected to a nozzle orifice, and a reflective focusing mirror is provided inside the nozzle orifice, and a convex lens is provided between the reflective focusing mirror and the collimator device.

[0018] Preferably, the extension tube is connected to a connecting seat on its wall.

[0019] By adopting the above technical solution, the beneficial effects achieved by this utility model are as follows:

[0020] In this invention, the mechanical structure is supported at the far end of the extended long-tube nozzle by the rotational support of the roller group, preventing the nozzle from undergoing elastic deformation. This effectively ensures the accuracy of optical path transmission and the size accuracy of the light spot, thereby improving the accuracy, quality, and efficiency of the cladding layer throughout the entire cladding process.

[0021] In this invention, the rotation of the fan blades dissipates heat, which effectively increases the heat dissipation during the cladding process, reduces component aging, extends the lifespan of nozzle-related components, and ensures the formation of a high-quality cladding layer.

[0022] In this invention, the fan blades are rotated to dissipate heat, which allows the fan blade assembly to discharge excess powder and smoke generated during the cladding process, thereby improving visibility and processing efficiency, effectively reducing the surface roughness of the cladding layer, and improving the surface quality of the cladding layer.

[0023] In this invention, a variable radius rotational stabilizing support wheel mechanism formed by rollers, support frame, slotted gear, drive gear, and motor enables the size adjustment of the nozzle distal support according to different inner diameters of the workpiece. This effectively solves the problem of fixed radius roller support structure being limited to a single workpiece inner diameter, while also overcoming the high cost and long cycle caused by frequent replacement of the support mechanism to adapt to different inner diameters. This ensures the adaptability of the lifting device of this invention to inner diameters of multiple workpiece sizes. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the first embodiment of the present utility model.

[0025] Figure 2 This is a schematic diagram of the connection component in the first embodiment of the present invention.

[0026] Figure 3 for Figure 1 Schematic diagram of the left-side view.

[0027] Figure 4 for Figure 1 Frontal view of the cross-sectional structure.

[0028] Figure 5 This is a schematic diagram of the overall structure of the second embodiment of the present invention.

[0029] Figure 6 This is a first-view structural schematic diagram of the connecting component in the second embodiment of the present invention.

[0030] Figure 7 This is a second-view structural schematic diagram of the connecting component in the second embodiment of the present invention.

[0031] Figure 8 This is a schematic diagram of the central base structure of this utility model.

[0032] Figure 9 This is a schematic diagram of the assembly process of a portion of the structure in the second embodiment of this utility model.

[0033] Figure 10 This is a schematic diagram of the adjustment state of the roller in the second embodiment of this utility model.

[0034] Figure 11 This is a schematic diagram of the elastic deformation path of an existing extended long-tube nozzle.

[0035] In the diagram: 1. Roller; 2. Fan blade; 3. Central ring; 4. Support arm; 5. Central base; 6. Support frame; 61. Sliding section; 62. Guide section; 7. Slotted gear; 8. Drive gear; 9. Motor; 10. Slotted rail opening; 11. Rail track; 12. Workpiece; 13. Support plate; 14. Extended long pipe nozzle; 141. Extension pipe; 142. Collimator device; 143. Convex lens; 144. Reflecting focusing mirror; 145. Nozzle opening; 15. Connecting seat; 16. Three-jaw chuck. Detailed Implementation

[0036] To better understand the above-mentioned objectives, features, and advantages of this utility model, the present utility model will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0037] Many specific details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed in the following specification.

[0038] like Figures 1-10As shown, this utility model provides a laser cladding metal additive manufacturing equipment, including an extended long tube nozzle 14 and a connecting assembly for connecting to the tube wall of the extended long tube nozzle 14. The connecting assembly is provided with a plurality of rollers 1 along the circumferential direction. Each roller 1 is fixedly mounted with a fan blade 2 coaxially arranged thereon. The outer circumferential surfaces of the plurality of rollers 1 are used to simultaneously contact the inner wall of the workpiece 12 and rotate in the same direction as the workpiece 12 rotates, so that the fan blade 2 rotates under the drive of the rollers 1 and generates airflow.

[0039] Among them, combined Figure 4 As shown, the extended long-tube nozzle 14 includes an extension tube 141. One end of the extension tube 141 is provided with a collimator device 142. The end of the extension tube 141 away from the collimator device 142 is connected to a nozzle port 145. A reflecting focusing mirror 144 is provided inside the nozzle port 145. A convex lens 143 is provided between the reflecting focusing mirror 144 and the collimator device 142. The tube wall of the extension tube 141 is connected to a connecting seat 15 for connecting with a robotic arm, so as to drive the extended long-tube nozzle 14 and the roller 1 to move.

[0040] Specifically, the collimator device 142 is connected to the laser head. After the laser is emitted from the laser head, the laser beam first passes through the collimator device 142, and then is collimated by the convex lens 143 (converting the diverging beam into a parallel beam). The parallel beam then travels to the inside of the nozzle orifice 145, causing the internal reflecting focusing mirror 144 to reflect and focus the parallel beam at the nozzle exit, forming a high-energy-density spot, thereby achieving the cladding effect. It is worth noting that... Figure 4 The blue arrows in the middle represent the laser beam path; it is worth noting that the laser emission and transmission technology or structure described in this article is a publicly known technology in the field, which is well known and applied by those skilled in the art. This article will not describe it in detail, and the specific technical principles can be referred to the prior art documents cited in the background section.

[0041] Combination Figure 2 As shown, in the first embodiment, the connecting assembly includes a central ring 3 fixedly sleeved on the wall of the extended long pipe nozzle 14 and a plurality of support arms 4 fixedly connected to the outer circumferential surface of the central ring 3. The plurality of support arms 4 correspond one-to-one with the plurality of rollers 1, and one end of each support arm 4 is rotatably connected to the corresponding roller 1.

[0042] As further explained, in this embodiment, three rollers 1 are used as the support structure, and the three rollers 1 constitute a roller group 1. Thus, the fixed support arm 4 makes this embodiment a fixed-radius three-roller 1 support structure. When this fixed-radius three-roller 1 support structure is installed on the inner wall of the shaft-like part, it can effectively prevent the distal end deformation of the extended long-tube nozzle 14 during the processing of the inner wall of the shaft-like part, ensuring the transmission accuracy of the optical path and the stability of the light spot size, and improving the dimensional accuracy and quality of the cladding layer. Furthermore, when the rollers 1 drive the fan blades 2 to rotate, the airflow generated by the rotation of the fan blades 2 can discharge unmelted powder, smoke, and heat generated during the cladding process. The heat dissipation can effectively reduce the aging of key components such as the nozzle and feed port, ensuring their service life and performance, and ensuring the cladding layer (see reference). Figure 3 Normal operation of the red part on the inner wall of workpiece 12.

[0043] Specifically, when the three-jaw chuck 16 clamps the workpiece 12 and rotates it, the roller 1 supported on its inner wall rotates accordingly. The roller 1 converts the static friction generated by the rotation of the workpiece 12 into dynamic friction, which not only extends its service life but also drives the corresponding fan blade 2 to rotate. This allows the fan blade 2 to discharge unmelted powder, fumes, and heat generated during the cladding process. Thus, by discharging the unmelted powder to the outside of the processed part through the fan blade 2, the adhesion of unmelted powder to the surface of the cladding layer is effectively reduced, thereby reducing surface roughness and improving the surface quality of the cladding layer. The fume emission is to improve the clarity of observation during use and ensure processing efficiency (because, if necessary, a CCD device needs to be added to the built-in nozzle to observe the morphology of the cladding layer and the state of the cladding process in real time, the fume emission needs to be considered in the implementation of this solution). Furthermore, the purpose of releasing heat is to improve heat dissipation, which not only reduces the aging of components but also ensures the formation of a high-quality cladding layer (because during the cladding process in the inner cavity, as heat accumulates, high heat can easily destroy the formation of a high-quality molten pool, thus preventing the formation of a high-quality cladding layer, or even making it impossible to carry out cladding work, affecting work efficiency and quality).

[0044] In summary, in the first embodiment, because the fixed-radius roller 1 support structure used in this embodiment is only suitable for a single workpiece 12 inner diameter, when dealing with different workpiece 12 inner diameters, there are problems such as increased costs and longer processing cycles due to equipment adjustments. Therefore, to address the problems existing in the first embodiment, a second embodiment is adopted for solution, as follows:

[0045] Combination Figures 5-10As shown, in the second embodiment, the structure of the roller 1 and the fan blade 2 is the same as in the first embodiment, but the difference is that the connecting assembly includes a central base 5 fixedly sleeved on the wall of the extended long pipe nozzle 14, multiple support frames 6 movably connected to the central base 5, and a diameter adjustment mechanism connected to the wall of the extended long pipe nozzle 14. The multiple support frames 6 correspond one-to-one with the multiple rollers 1, and one end of each support frame 6 is rotatably connected to the corresponding roller 1. The diameter adjustment mechanism is used to drive the support frame 6 to move on the central base 5 so that the multiple rollers 1 move synchronously closer to or further away from the nozzle wall.

[0046] Combination Figure 6 , Figure 7 and Figure 8 As shown, as a further step, the diameter adjustment mechanism includes a slotted gear 7 movably connected to the wall of the extended long pipe nozzle 14, a drive gear 8 meshing with the teeth of the slotted gear 7, and a motor 9 for driving the drive gear 8 to rotate. The end of the support frame 6 away from the roller 1 is disposed in the groove 10 on the surface of the slotted gear 7, and when the slotted gear 7 rotates, one end of the support frame 6 moves along the groove 10. The connecting assembly also includes a support plate 13 connected to the wall of the extended long pipe nozzle 14, and the motor 9 is fixedly mounted on the support plate 13.

[0047] The slotted gear 7 has multiple slots 10 along the circumferential direction on its surface. The slots 10 are arc-shaped and correspond one-to-one with multiple support frames 6. The central base 5 has multiple rail channels 11 on its surface. The rail channels 11 correspond one-to-one with multiple support frames 6, and each support frame 6 is slidably disposed in the corresponding rail channel 11 to constrain the linear movement of the support frame 6.

[0048] Specifically, when the motor 9 drives the drive gear 8 to rotate, the rotation of the drive gear 8 can cause the slotted gear 7 to rotate synchronously. Then, by utilizing the design of the slotted gear 7's upper slot rail 10 and the design of the upper rail groove 11 of the center base 5, the slotted gear 7 can convert the rotational motion into the radial linear motion of the support frame 6, thereby realizing stepless adjustment of the radius of multiple rollers 1.

[0049] Combination Figure 10 As shown, specifically, when the motor 9 drives the drive gear 8 to rotate clockwise, the drive gear 8 can drive the slotted gear 7 to rotate counterclockwise; thus, the slotted gear 7 can drive the support frame 6 to move outward in a straight line, thereby increasing the radius of the roller 1 group to adapt to the cladding of the inner surface of the large-sized workpiece 12.

[0050] When motor 9 drives the drive gear 8 to reverse, the drive gear 8 can drive the slotted gear 7 to rotate clockwise; thus, the slotted gear 7 can drive the support frame 6 to move inward in a linear motion, realizing the reduction of the radius of the roller set 1, which is used to adapt to the inner surface cladding of small-sized workpieces 12. It is worth noting that... Figure 10 The orange arrow in the middle indicates the direction of movement of support frame 6.

[0051] In summary, this embodiment uses a motor 9 to drive a gear set (i.e., slotted gear 7 and drive gear 8) to convert gear rotation into linear motion of the support frame 6, thereby enabling the roller 1 set to have a variable radius. This allows it to adapt to the inner diameter of various workpieces 12, effectively solving the problems of fixed radius roller 1 support structure being limited to a single inner diameter of workpiece 12, and having high cost and long cycle time. This embodiment improves the equipment's adaptability to the inner diameter of workpieces 12 of various sizes.

[0052] As a further step, the support frame 6 includes a sliding section 61 rotatably connected to the roller 1 and a guide section 62 connected to one end of the sliding section 61. The sliding section 61 is slidably disposed in the rail groove 11, and the guide section 62 is adapted to the rail opening 10.

[0053] Combination Figure 6 and Figure 7 As shown, roller 1, fan blade 2, and connecting assembly together form a variable-radius rotationally stable support wheel mechanism, and the assembly process of this mechanism is as follows: Figure 9 As shown, firstly, the support frame 6 connected to the roller 1 is installed one by one into the rail groove 11 of the central base 5. Then, the slotted gear 7, the drive gear 8 and the motor 9 are installed in sequence to complete the assembly.

[0054] In summary, this utility model adopts a "roller 1 rotating support + fan blade 2 heat dissipation" technical solution in the embodiments. Through mechanical structure support at the distal end of the extended long-tube nozzle 14, elastic deformation of the nozzle is prevented, effectively ensuring the accuracy of optical path transmission and the dimensional accuracy of the light spot. This improves the accuracy, quality, and efficiency of the cladding layer throughout the cladding process. Furthermore, by integrating the fan blade 2 into the rotating support structure (i.e., the combined term for the connecting component and roller 1), heat dissipation during the cladding process is effectively improved, extending the lifespan of nozzle-related components. Simultaneously, the fan blade 2 discharges excess powder and fumes generated during the cladding process, improving visibility and processing efficiency, reducing surface roughness, and enhancing the surface quality of the cladding layer. Moreover, the technical implementation scheme of this utility model further adds a variable radius rotating stable support wheel mechanism (i.e., the structural scheme of the second embodiment of this solution), enabling the utility model to adjust the distal end support of the nozzle according to different inner diameters of the workpiece 12, thus improving the adaptability of the device.

[0055] In this invention, the term "plural" refers to two or more items unless otherwise expressly defined. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. The terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; "linking" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0056] It should be noted that when a component is referred to as being "assembled on," "mounted on," "fixed to," or "set on" another component, it can be directly on the other component or there may be an intermediate component. When a component is considered to be "connected to" another component, it can be directly connected to the other component or there may be an intermediate component present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0057] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present 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.

[0058] Although embodiments of the present invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A laser cladding metal additive manufacturing apparatus, characterized by, It includes a connecting assembly for connecting to the wall of an extended long pipe nozzle (14). The connecting assembly is provided with multiple rollers (1) along the circumferential direction. Each roller (1) is fixedly mounted with a fan blade (2) coaxially arranged therewith. The outer circumferential surfaces of the multiple rollers (1) are used to simultaneously contact the inner wall of the workpiece (12) and rotate in the same direction as the workpiece (12) rotates, so that the fan blade (2) rotates under the drive of the rollers (1) and generates airflow.

2. The laser cladding metal additive manufacturing apparatus of claim 1, wherein, The connecting assembly includes a central ring (3) fixedly sleeved on the wall of the extended long pipe nozzle (14) and a plurality of support arms (4) fixedly connected to the outer circumferential surface of the central ring (3). The plurality of support arms (4) correspond one-to-one with the plurality of rollers (1), and one end of each support arm (4) is rotatably connected to the corresponding roller (1).

3. The laser cladding metal additive manufacturing equipment according to claim 1, characterized in that, The connecting assembly includes a central base (5) fixedly sleeved on the wall of the extended long pipe nozzle (14), a plurality of support frames (6) movably connected to the central base (5), and a diameter adjustment mechanism connected to the wall of the extended long pipe nozzle (14). The plurality of support frames (6) correspond one-to-one with the plurality of rollers (1), and one end of each support frame (6) is rotatably connected to the corresponding roller (1). The diameter adjustment mechanism is used to drive the support frame (6) to move on the central base (5) so that the plurality of rollers (1) move synchronously closer to or further away from the nozzle wall.

4. The laser cladding metal additive manufacturing equipment according to claim 3, characterized in that, The diameter adjustment mechanism includes a slotted gear (7) movably connected to the wall of the extended long pipe nozzle (14), a drive gear (8) meshing with the teeth of the slotted gear (7), and a motor (9) for driving the drive gear (8) to rotate. The end of the support frame (6) away from the roller (1) is located in the groove opening (10) on the surface of the slotted gear (7), and when the slotted gear (7) rotates, one end of the support frame (6) moves along the groove opening (10).

5. The laser cladding metal additive manufacturing equipment according to claim 4, characterized in that, The slotted gear (7) has multiple slots (10) along the circumferential direction on its surface. The slots (10) are arc-shaped slots, and each slot (10) corresponds to a support frame (6).

6. The laser cladding metal additive manufacturing equipment according to claim 5, characterized in that, The surface of the central base (5) is provided with multiple rail channels (11), and the multiple rail channels (11) correspond one-to-one with multiple support frames (6), and each support frame (6) is slidably disposed in the corresponding rail channel (11).

7. The laser cladding metal additive manufacturing equipment according to claim 6, characterized in that, The support frame (6) includes a sliding section (61) rotatably connected to the roller (1) and a guide section (62) connected to one end of the sliding section (61). The sliding section (61) is slidably disposed in the rail channel (11), and the guide section (62) is adapted to the rail opening (10).

8. The laser cladding metal additive manufacturing equipment according to claim 4, characterized in that, The connecting assembly also includes a support plate (13) connected to the wall of the extended long pipe nozzle (14), and the motor (9) is fixedly mounted on the support plate (13).

9. The laser cladding metal additive manufacturing equipment according to claim 1, characterized in that, It also includes an extended long tube nozzle (14), which includes an extension tube (141), one end of which is provided with a collimator device (142), and the other end of the extension tube (141) away from the collimator device (142) is connected to a nozzle port (145), and a reflecting focusing mirror (144) is provided inside the nozzle port (145), and a convex lens (143) is provided between the reflecting focusing mirror (144) and the collimator device (142).

10. The laser cladding metal additive manufacturing equipment according to claim 9, characterized in that, The extension tube (141) is connected to a connecting seat (15) on its wall.

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