Multi-laser coupling auxiliary spraying repair method

Abstract

The invention relates to a multi-laser coupling auxiliary spraying repairing method which comprises the following steps that a first laser beam is emitted to a to-be-repaired workpiece and an area above the to-be-repaired workpiece through a three-dimensional laser emitting system, a three-dimensional preheating space is formed, and the contact face of the first laser beam and the surface of the to-be-repaired workpiece is a preheating softening area; powder is sprayed to the preheating softening area through a spraying system, a spraying area is formed on the surface of the to-be-repaired workpiece, a spraying channel is formed between the spraying area and the spraying system, and the spraying channel penetrates through the three-dimensional preheating space; and a second laser beam is emitted to the spraying area through the laser emitting system, so that the spraying area is subjected to post-treatment, and a post-treatment area is formed on the surface of the to-be-repaired workpiece. Compared with the prior art, the laser-assisted spraying technology and the laser heat treatment technology are combined, deposition of spraying particles and surface post-treatment of a material deposition layer are completed at the same time in the repairing process, and therefore laser wide-area and three-dimensional space preheating is achieved, and the surface repairing process is completed efficiently.

Description

Technical Field

[0001] The invention relates to the technical field of spray repair, and in particular to a multi-laser coupling assisted spray repair method. Background Art

[0002] At present, the mainstream method of traditional spray repair is to remove the material of the defective surface from the original position, spray the repair particles onto the material surface, and then perform subsequent heat treatment on the sprayed surface. However, traditional spray repair has some defects, such as: the surface of the material repaired by traditional spray repair requires a cumbersome post-processing process to obtain a good surface quality, which increases the cost of the repair process and reduces the repair efficiency; traditional spray repair is difficult to achieve in-situ repair, and the entire repair process is complex and difficult; traditional spray repair is generally only used for plane repair, and it is difficult to apply to surface repair situations at complex spatial levels. The difficulty of current laser-assisted spray repair is that the laser spot is too small, the irradiation area of ​​laser heating is very small, it is difficult to achieve wide-area heating, and only two-dimensional spatial thermal field distribution can be performed. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a multi-laser coupling assisted spray repair method, which combines laser-assisted spray technology with laser heat treatment technology, and simultaneously completes the deposition of spray particles and surface post-treatment of the material deposition layer during the repair process, thereby realizing laser wide-range and three-dimensional space preheating, efficiently completing the surface repair process, simplifying the device structure, reducing the device size, and enabling the device to achieve in-situ repair.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] A multi-laser coupling assisted spray repair method comprises the following steps:

[0006] S1. Fix the workpiece to be repaired on the fixture platform;

[0007] S2, emitting a first laser beam to the workpiece to be repaired and the area above it through a three-dimensional laser emission system to form a three-dimensional preheating space, wherein the contact surface between the first laser beam and the surface of the workpiece to be repaired is a preheating softening zone;

[0008] S3, spraying powder on the preheated softened area through a spraying system to form a spraying area on the surface of the workpiece to be repaired, forming a spraying channel between the spraying area and the spraying system, and making the spraying channel pass through the three-dimensional preheating space;

[0009] S4. The laser emitting system emits a second laser beam to the spraying area, so that the laser emitting system performs post-processing on the spraying area, and forms a post-processing area on the surface of the workpiece to be repaired, and the repair is completed.

[0010] Furthermore, for repairing the same area of ​​the workpiece to be repaired, taking the spraying area as a reference, the overlap rate between the preheating softening area and the spraying area is greater than 95%, and the overlap rate between the post-processing area and the spraying area is greater than 95%.

[0011] Furthermore, the areas of the spraying zone, preheating and softening zone, and post-processing zone are respectively, from largest to smallest: preheating and softening zone, spraying zone, and post-processing zone.

[0012] Further, the spraying channel is in the shape of a truncated cone;

[0013] The three-dimensional preheating space is in a cubic shape with a size of 5-15 cm×5-15 cm×5-15 cm. The bottom surface of the space is in contact with the surface of the workpiece to be repaired to form the preheating softening zone.

[0014] Furthermore, the spraying channel is perpendicular to the surface of the workpiece to be repaired; the first laser beam and the second laser beam are respectively located on both sides of the normal line of the surface of the workpiece to be repaired;

[0015] The angle between the first laser beam and the normal line of the surface of the workpiece to be repaired is 15° to 45°;

[0016] The angle between the second laser beam and the normal line of the surface of the workpiece to be repaired is 15° to 45°.

[0017] Furthermore, the spraying thickness of the spraying zone is 2mm to 5mm; the thickness of the preheating and softening zone is greater than the thickness of the zone; and the thickness of the post-treatment zone is 2mm to 4mm.

[0018] Furthermore, the powder sprayed by the spraying system is metal powder, including Ni powder and Ti powder, and the particle size is 10 to 40 μm;

[0019] The workpiece to be repaired is a material that can be repaired by cold spraying, including metal.

[0020] Furthermore, the spraying parameters of the spraying system are: spraying speed is 30mm / s, spraying distance is 15mm-30mm, the specific parameters are determined according to the actual repair material situation, the powder feeding rate is 20g / mm-25g / mm; the high-pressure gas source used in the spraying process is nitrogen, the pressure is 1-3MPa, and the flow rate is 30-45Nm 3 / min.

[0021] Furthermore, the parameters of the first laser beam of the three-dimensional laser emission system are: the laser power of the first laser beam is 1000-3000W, the shape of the focal spot of the first laser beam is circular, the diameter of the focal spot of the first laser beam is 0.5-1mm, and the first laser beam travels along the moving direction of the spraying system.

[0022] Furthermore, the parameters of the second laser beam of the laser emitting system are: the laser power of the second laser beam is 1000-3000W, the shape of the focal spot of the second laser beam is circular, the diameter of the focal spot of the second laser beam is 0.5-1mm, and the second laser beam travels along the moving direction of the spraying system.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The present invention combines laser-assisted spray repair technology with laser heat treatment technology. In the laser-assisted spray repair part, by synchronously introducing the first laser beam into the spray processing process, the first laser beam is used to heat the spray particles and the workpiece to be repaired to soften them, and the mechanical properties and collision deposition state of the material are instantly adjusted and improved, which can not only maintain the solid deposition characteristics of the spray, but also improve the performance of the coating; in the laser heat treatment part, a high-energy, high-repetition-frequency, high-power second laser beam is used to irradiate the surface of the workpiece to be repaired, and the surface is post-processed by the instantaneous high energy of the second laser beam to obtain a high-quality processed surface. Through the combination of the two technologies, the invention has the characteristics of being able to deposit a fully cured coating with uniform density and controllable porosity in a large range of irradiation areas and three-dimensional space, and has the characteristics of high deposition speed and low scrap rate. At the same time, the post-processing of the processed surface can be completed quickly after the solid particle deposition is completed.

[0025] (2) In the part of the surface of the workpiece to be repaired that is not irradiated by the laser, since it still maintains its own hard properties, if spraying is performed directly, the bonding between the repair particles and the surface of the workpiece to be repaired is poor. When the particles are sprayed onto the surface of the workpiece to be repaired, some of the particles will rebound, which will not only reduce the material repair rate, but may even damage the repair particles and the surface of the matrix material. The first laser beam is emitted by the three-dimensional laser emission system. Since the first laser beam falls on the surface of the workpiece to be repaired before the sprayed particles, a three-dimensional preheating space is formed on the surface of the workpiece to be repaired and above it, and the surface of the workpiece to be repaired and the sprayed particles are softened. Since the first laser beam falls before the sprayed powder, the irradiation area of ​​the first laser beam will form a preheating softening zone at the attachment point of the sprayed particles. In this area, the bonding between the material surface and the sprayed particles is better.

[0026] (3) In the laser spray deposition part, due to the impact and deposition of the sprayed material, some defects such as pores / microcracks may be formed on the surface of the workpiece to be repaired, and the surface still needs to be post-processed. By setting a single / multiple laser beam behind the nozzle of the spray system along the moving path to perform post-processing operations on the surface after deposition, a better surface quality can be obtained. Through this part of the device, it is possible to achieve effects such as improving coating quality, improving surface properties, reducing residual stress, and optimizing microstructure. In addition, according to the different materials used for repair, by setting different laser post-processing parameters, technologies such as laser shock strengthening, laser polishing, and laser surface modification can be implemented to obtain repair surface quality that meets different requirements.

[0027] (4) The multi-laser coupling assisted spray repair method of the present invention is suitable for workpieces to be repaired with a large repair area. When single-point laser irradiation is used, the spot size is small and cannot cover the preheating area. Under typical single-point laser irradiation conditions, the laser thermal field will be uneven in the jet area and the heat treatment area, which will lead to inconsistent bonding of the materials in the repair area and affect the surface performance of the repaired material. Therefore, a laser scanning motion scheme is adopted for the laser used in the processing, and the heating area in the three-dimensional space is realized by rotating and scanning the front-end laser generating device in the horizontal and vertical planes, and the laser heating field is optimized to ensure that a uniform temperature distribution is formed on the surface of the target object.

[0028] (5) Since the spraying system and the laser emitting system have the freedom to move in the horizontal direction, the three-dimensional laser emitting system has the freedom to move in three-dimensional space. The irradiation point of the first laser beam is always located at the front end of the moving path of the spraying system; the second laser beam is always located at the rear end of the moving path of the spraying system. In any area of ​​the surface of the workpiece to be repaired, the first laser beam falls before the spraying powder, and the irradiated area will form a preheating softening zone at the attachment point of the spraying particles. In this area, the bonding degree between the material surface and the spraying particles is better. Finally, the second laser beam is irradiated to perform post-processing operations on the surface after deposition to obtain better surface quality.

[0029] (6) Since the spraying system and the laser emitting system have the freedom to move in the horizontal direction, and the three-dimensional laser emitting system has the freedom to move in three-dimensional space, during the repair process, the laser emitting system, the spraying system, and the laser emitting system are operated simultaneously. Through the relationship between the positions of the first laser beam, the spraying powder, and the second laser beam, for the same repair area, the first laser beam precedes the spraying powder, and the spraying powder precedes the second laser beam. In this case, at the same time, the irradiation areas of the first laser beam and the second laser beam overlap, so that the energy density in this area is higher due to laser coupling, which can better soften the substrate and the spraying particles. At the same time, the center points of the two parts of the laser irradiation are not in the same position, so that the heating area of ​​the repaired particles will not have high energy concentration points, avoiding the phenomenon of excessive melting of the repaired particles, and further expanding the wide range of the laser irradiation uniform thermal field. The laser head of the three-dimensional laser emitting system will perform scanning actions in the horizontal and vertical planes at the same time during the repair process, so that preheating in three-dimensional space can be achieved and the heating effect of the sprayed particles can be optimized. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the multi-laser coupling assisted spray repair method shown in Example 1;

[0031] Figure 2 It is a position relationship diagram of the preheating and softening zone, the spraying zone, and the post-treatment zone shown in Example 1;

[0032] Figure 3 This is a schematic diagram of the effect of the first laser beam assisted spray repair shown in Example 1;

[0033] Figure 4 This is a schematic diagram of the effect of post-processing the second laser beam shown in Example 1;

[0034] Figure 5 Schematic diagram of the multi-laser coupling assisted spray repair method shown in Example 2, wherein arrow A indicates that the spray system moves in the horizontal plane, arrow B indicates that the laser emission system rotates in the horizontal plane, arrow C indicates that the three-dimensional laser emission system rotates in the horizontal plane, and arrow D indicates that the three-dimensional laser emission system rotates in the vertical plane;

[0035] Figure 6 This is the moving path of the first laser beam on the surface of the workpiece to be repaired shown in Example 2.

[0036] Description of the markings in the figure:

[0037] 1-Workpiece to be repaired;

[0038] 2-spraying system, 21-spraying area, 22-spraying channel;

[0039] 3-three-dimensional laser emission system, 31-three-dimensional preheating space, 32-preheating softening zone, 33-first laser beam;

[0040] 4-laser emission system, 41-post-processing area, 42-second laser beam. DETAILED DESCRIPTION

[0041] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments. Based on the given embodiments, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0042] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art.

[0043] In the following embodiments, the laser emission system 3 uses a 4kW infrared laser with a wavelength of 940nm; the model of the spraying system 2 is 4000 series, manufactured by Impact Innovations of Germany.

[0044] Example 1

[0045] A multi-laser coupling assisted spray repair method comprises the following steps:

[0046] S1, fixing the workpiece 1 to be repaired on the fixture platform;

[0047] S2, emitting a first laser beam 33 to the workpiece 1 to be repaired and the area above it through the three-dimensional laser emitting system 3, so as to form a three-dimensional preheating space 31, wherein the contact surface between the first laser beam 33 and the surface of the workpiece 1 to be repaired is a preheating softening zone 32;

[0048] S3, spraying powder on the preheating softening zone 32 through the spraying system 2, forming a spraying zone 21 on the surface of the workpiece 1 to be repaired, forming a spraying channel 22 between the spraying zone 21 and the spraying system 2, and making the spraying channel 22 pass through the three-dimensional preheating space 31;

[0049] S4. The laser emitting system 4 emits a second laser beam 42 to the spraying area 22 to post-process the spraying area 22, thereby forming a post-processing area 41 on the surface of the workpiece 1 to be repaired, and the repair is completed.

[0050] In this embodiment, for the repair of the same area of ​​the workpiece 1 to be repaired, taking the spraying area 22 as a reference, the overlap rate between the preheating softening area 32 and the spraying area 22 is 98%, and the overlap rate between the post-processing area 41 and the spraying area 22 is 98%.

[0051] In this embodiment, the areas of the spraying zone 22 , the preheating and softening zone 32 , and the post-processing zone 41 are respectively, from large to small: the preheating and softening zone 32 , the spraying zone 22 , and the post-processing zone 41 .

[0052] In this embodiment, the spray channel 22 is in the shape of a truncated cone;

[0053] The three-dimensional preheating space 31 is in a cubic shape, and its bottom surface contacts the surface of the workpiece 1 to be repaired, forming the preheating softening zone 32 .

[0054] In this embodiment, the spray channel 22 is perpendicular to the surface of the workpiece 1 to be repaired; the first laser beam 33 and the second laser beam 42 are respectively located on both sides of the normal line of the surface of the workpiece 1 to be repaired;

[0055] The angle between the first laser beam 33 and the normal line of the surface of the workpiece 1 to be repaired is 30°;

[0056] The angle between the second laser beam 42 and the normal line of the surface of the workpiece 1 to be repaired is 30°.

[0057] In this embodiment, the spraying thickness of the spraying area 22 is 3 mm; the thickness of the preheating and softening area 32 is 3.5 mm; the thickness of the post-processing area 41 is 3 mm;

[0058] The spray channel 22 has a size of 8 cm×8 cm×8 cm.

[0059] In this embodiment, the powder sprayed by the spraying system 2 is metal Ti powder with a particle size of 10 to 40 μm; and the workpiece 1 to be repaired is titanium alloy.

[0060] In this embodiment, the spraying parameters of the spraying system 2 are: spraying speed is 30mm / s, spraying distance is 15mm, powder feeding rate is 25g / min; the high-pressure gas source used in the spraying process is nitrogen, the pressure is 1-3MPa, and the flow rate is 30-45Nm 3 / min.

[0061] In this embodiment, the parameters of the first laser beam 33 of the three-dimensional laser emitting system 3 are: the laser power of the first laser beam 33 is 1500W, the shape of the focal spot of the first laser beam 33 is circular, the diameter of the focal spot of the first laser beam 33 is 1mm, and the processing time of the first laser beam 33 is determined according to the actual repair volume, which is 3 minutes in this embodiment.

[0062] In this embodiment, the parameters of the second laser beam 42 of the laser emitting system 4 are: the laser power of the second laser beam 42 is 1500W, the shape of the focal spot of the second laser beam 42 is circular, the diameter of the focal spot of the second laser beam 42 is 1mm, and the processing time of the second laser beam 42 is determined according to the actual repair volume, which is 3 minutes in this embodiment.

[0063] The multi-laser coupling assisted spray repair method proposed in the present invention realizes an additive manufacturing technology for high efficiency, large range and high performance. Due to the use of multi-zone laser irradiation, the range of the thermal field is greatly improved, the distribution of a wide-area uniform thermal field on the repair surface is achieved, and three-dimensional spatial heating of the spray particles is achieved, thereby improving the heating effect.

[0064] like Figure 3 As shown, in the surface portion of the workpiece 1 to be repaired that is not irradiated by the laser, since it still maintains its own hard properties, if spraying is performed directly, the bonding between the repair particles and the surface of the workpiece 1 to be repaired is poor. When the particles are sprayed onto the surface of the workpiece 1 to be repaired, some of the particles will rebound, which will not only reduce the repair rate of the material, but also damage the repair particles and the surface of the matrix material. The first laser beam 33 is emitted by the three-dimensional laser emitting system 3. Since the first laser beam 33 falls on the surface of the workpiece 1 to be repaired before the spraying particles, a three-dimensional preheating space 31 is formed on and above the surface of the workpiece 1 to be repaired, and the surface of the workpiece 1 to be repaired and the spraying particles are softened. Since the first laser beam 33 falls before the spraying powder, the irradiation area of ​​the first laser beam 33 will form a preheating softening zone 32 at the attachment point of the spraying particles, and the bonding between the material surface and the spraying particles in this area is better.

[0065] like Figure 4 As shown, in the laser spray deposition part, due to the impact and deposition of the spray material, some defects such as pores / micro cracks may be formed on the surface of the workpiece 1 to be repaired, and the surface still needs to be post-processed. By setting a second laser beam 42 behind the nozzle of the spray system 2 along the moving path direction to perform a post-processing operation on the surface after deposition, a better surface quality can be obtained. Through this part of the device, the effects of improving coating quality, improving surface properties, reducing residual stress, optimizing microstructure, etc. can be achieved.

[0066] Example 2

[0067] like Figure 5 and 6 As shown, compared with Example 1, most of them are the same, except:

[0068] During the spraying process, the first laser beam 33 travels along the moving direction of the spraying system 2, the second laser beam 42 travels along the moving direction of the spraying system 2, and the spraying system 2 travels in a transverse direction.

[0069] In this embodiment, during the movement of the spraying system 2, the laser emitting system 4, and the three-dimensional laser emitting system 3, the irradiation area of ​​the first laser beam 33 and the second laser beam 42 on the surface of the workpiece to be repaired 1 has an overlapping area, and the center points of the laser irradiation of the first laser beam 33 and the second laser beam 42 are not always in the same position.

[0070] Due to the simultaneous use of multi-area laser irradiation and laser scanning paths, the irradiation areas of the first laser beam 33 and the second laser beam 42 on the surface of the workpiece 1 to be repaired have overlapping areas, and the center points of the laser irradiation of the first laser beam 33 and the second laser beam 42 are not always in the same position. This prevents high energy concentration points from appearing in the heating area of ​​the repaired particles, avoids the phenomenon of excessive melting of the repaired particles, and further expands the wide range of the uniform thermal field of laser irradiation.

[0071] By using a multi-laser coupling assisted spray repair method of the present invention to perform spray repair, compared with a traditional cold spray device, the bonding strength between the coating and the workpiece to be repaired is improved after laser pretreatment, and the bonding force is improved by 30%-50%; the density of the coating is significantly improved after laser post-treatment, and the porosity is less than 5%; based on laser coupling, the range of the heat-affected zone is reduced by 20%-30%, reducing thermal damage to the workpiece to be repaired; the overall spray time efficiency is improved by 15%-30%; the overall spray material bonding rate is improved by 20%-40%; and the surface roughness is reduced by 20%-40% after the overall spraying is completed.

[0072] Although the present invention has been described in detail above by means of general description, specific implementation methods and tests, it is obvious to those skilled in the art that some modifications or improvements may be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A multi-laser coupling assisted spray repair method, characterized in that: The following steps are involved: S1, fixing the workpiece to be repaired (1) on a fixture platform; S2, emitting a first laser beam (33) to the workpiece (1) to be repaired and the area above it through a three-dimensional laser emitting system (3), so as to form a three-dimensional preheating space (31), wherein the contact surface between the first laser beam (33) and the surface of the workpiece (1) to be repaired is a preheating softening zone (32); S3, spraying powder on the preheated softened area (32) through a spraying system (2), forming a spraying area (21) on the surface of the workpiece (1) to be repaired, forming a spraying channel (22) between the spraying area (21) and the spraying system (2), and allowing the spraying channel (22) to pass through the three-dimensional preheating space (31); S4. The laser emitting system (4) emits a second laser beam (42) to the spraying area (22), so that the spraying area (22) is post-processed to form a post-processing area (41) on the surface of the workpiece (1) to be repaired, and the repair is completed.

2. A multi-laser coupling assisted spray repair method according to claim 1, characterized in that: For repairing the same area of ​​the workpiece (1) to be repaired, taking the spraying area (22) as a reference, the overlap rate between the preheating softening area (32) and the spraying area (22) is greater than 95%, and the overlap rate between the post-processing area (41) and the spraying area (22) is greater than 95%.

3. A multi-laser coupling assisted spray repair method according to claim 1, characterized in that: The areas of the spraying zone (22), the preheating and softening zone (32), and the post-processing zone (41) are, from largest to smallest, respectively: the preheating and softening zone (32), the spraying zone (22), and the post-processing zone (41).

4. The multi-laser coupling assisted spray repair method according to claim 1, characterized in that: The spraying channel (22) is in the shape of a truncated cone; The three-dimensional preheating space (31) is in the shape of a cube, with dimensions of 5-15 cm×5-15 cm×5-15 cm, and its bottom surface contacts the surface of the workpiece (1) to be repaired, forming the preheating softening zone (32).

5. The multi-laser coupling assisted spray repair method according to claim 1, characterized in that: The spraying channel (22) is perpendicular to the surface of the workpiece (1) to be repaired; the first laser beam (33) and the second laser beam (42) are respectively located on both sides of the normal line of the surface of the workpiece (1) to be repaired; The angle between the first laser beam (33) and the normal line of the surface of the workpiece (1) to be repaired is 15° to 45°; The angle between the second laser beam (42) and the normal line of the surface of the workpiece (1) to be repaired is 15° to 45°.

6. The multi-laser coupling assisted spray repair method according to claim 1, characterized in that: The spraying thickness of the spraying zone (22) is 2 mm to 5 mm; the thickness of the preheating and softening zone (32) is greater than the thickness of the zone (22); and the thickness of the post-processing zone (41) is 2 mm to 4 mm.

7. The multi-laser coupling assisted spray repair method according to claim 1, characterized in that: The powder sprayed by the spraying system (2) is metal powder, including Ni powder and Ti powder, and the particle size is 10 to 40 μm; The workpiece (1) to be repaired is a material that can be repaired by cold spraying, including metal.

8. The multi-laser coupling assisted spray repair method according to claim 1, characterized in that: The spraying parameters of the spraying system (2) are as follows: the spraying speed is 30 mm / s, the spraying distance is 15 mm to 30 mm, the specific parameters are determined according to the actual repair material conditions, the powder feeding rate is 20 g / mm to 25 g / mm; the high-pressure gas source used in the spraying process is nitrogen, the pressure is 1 to 3 MPa, and the flow rate is 30 to 45 Nm 3 / min.

9. The multi-laser coupling assisted spray repair method according to claim 1, characterized in that: The parameters of the first laser beam (33) of the three-dimensional laser emission system (3) are as follows: the laser power of the first laser beam (33) is 1000-3000W, the shape of the focal spot of the first laser beam (33) is circular, the diameter of the focal spot of the first laser beam (33) is 0.5-1mm, and the first laser beam (33) moves along the moving direction of the spraying system (2).

10. The multi-laser coupling assisted spray repair method according to claim 1, characterized in that: The parameters of the second laser beam (42) of the laser emitting system (4) are as follows: the laser power of the second laser beam (42) is 1000-3000W, the shape of the focal spot of the second laser beam (42) is circular, the diameter of the focal spot of the second laser beam (42) is 0.5-1mm, and the second laser beam (42) moves along the moving direction of the spraying system (2).

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