Riblet formation method and wheel

Abstract

To provide riblet formation method which can form a riblet structure on an edge part which determines an opening to be defined by a rim part, a hub mounting part and spokes easily.SOLUTION: A wheel comprises a rim part 11, a hub mounting part 26, spokes 27 which connect the hub mounting part 26 with the rib part 11 and an opening 31 which is determined by the rim part 11, the hub mounting part 26 and the spokes 27. An edge part 32 which determines the opening 31 comprises a riblet structure 33 in which irregularity extends to an inside and outside direction. The riblet structure 33 is configured so as to form a lower layer convex part for the edge part 32 on which the riblet structure 33 is formed by impacting coating compound droplet at a first resolution by jet printing and to form an upper layer convex part by impacting coating compound droplet at a second resolution which is lower resolution than the first resolution for the lower layer convex part by jet printing.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a riblet forming method for forming a riblet structure in a wheel and a wheel provided with a riblet structure. [Background technology]

[0002] As described in Patent Document 1, some wheels have projections and recesses such as dimples and riblets formed thereon to reduce the air resistance of the airflow flowing from inside the wheel to the outside, thereby reducing adhesion of brake wear powder to the wheel. In addition, the surfaces of wheels are often decorated with paint. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-137340 A Summary of the Invention [Problem to be solved by the invention]

[0004] It is desirable to make it easier to form projections and recesses in wheels to reduce air resistance. [Means for solving the problem]

[0005] The infinite rotating body for solving the above problems has the following features. [Aspect 1] A wheel includes a rim portion, a hub attachment portion, spokes connecting the rim portion and the hub attachment portion, and an opening defined by the rim portion, the hub attachment portion, and the spokes. The wheel includes a forming step of forming a riblet structure having projections and recesses extending inward and outward directions of the wheel on an edge defining the opening, The forming step includes: a first printing step of depositing paint droplets at a first resolution on a printing target surface by inkjet printing to form a lower layer convex portion; a second printing step of applying the paint droplets to the lower layer convex portion by inkjet printing at a second resolution lower than the first resolution to form an upper layer convex portion; The printing process is repeated in the order of the first printing process and the second printing process. Method for forming riblets.

[0006] According to the above configuration, a riblet structure for rectifying the air flow from the inside to the outside of the wheel can be easily formed by inkjet printing. [Aspect 2] In the first printing step, the paint droplets are deposited at the same position at the first resolution to form the lower layer convex portion, and then the paint droplets are deposited at the second resolution on the lower layer convex portion. A method for forming riblets according to [Aspect 1].

[0007] According to the above configuration, a second droplet of a second resolution is ejected onto a lower layer convex portion formed by a first droplet of a first resolution to form an upper layer convex portion, and by repeating this process, convex ridges that constitute a riblet structure can be formed.

[0008] [Aspect 3] The surface to be printed is the surface of the edge portion. A method for forming riblets according to [Aspect 1] or [Aspect 2].

[0009] According to the above configuration, the riblet structure can be formed directly on the edge by inkjet printing. Aspect 4 The printing surface is a surface of a substrate, The forming step includes a bonding step of bonding a base material on which the riblet structure is formed to the edge portion. A method for forming riblets according to [Aspect 1] or [Aspect 2].

[0010] According to the above configuration, a riblet structure can be provided on the edge of a wheel simply by attaching a base material on which the riblet structure is formed to the edge. [Embodiment 5] The riblet structure is formed by a decorative layer formed on a base layer provided on the wheel. A method for forming riblets according to [Aspect 1] or [Aspect 2].

[0011] According to the above configuration, a riblet structure can be provided using the design of the wheel formed by the decorative layer. [Aspect 6] In the riblet structure, the distance between the perpendicular lines extending from the apex to the base of adjacent convex stripes is 50 μm or more and 350 μm or less, The height from the base to the apex of the triangle is 10 μm or more and 250 μm or less. A method for forming riblets according to [Aspect 1].

[0012] According to the above configuration, by setting the riblet structure within this range, it is possible to straighten the air flow that flows from the inside to the outside of the wheel 10. Therefore, while the vehicle is running, the brake device that brakes the wheels can always be adequately cooled by the air flow.

[0013] [Aspect 7] A bicycle wheel having a rim portion, a hub attachment portion, spokes connecting the rim portion and the hub attachment portion, and an opening defined by the rim portion, the hub attachment portion, and the spokes, The edge portion defining the opening has a riblet structure having projections and recesses extending inward and outward directions; The riblet structure is A lower-layer convex portion is formed by depositing paint droplets at a first resolution on a printing target surface by inkjet printing, and an upper-layer convex portion is formed by depositing the paint droplets at a second resolution, which is lower than the first resolution, on the lower-layer convex portion by inkjet printing. wheel.

[0014] According to the above configuration, by providing a riblet structure on the edge portion defining the opening, it is possible to straighten the air flow flowing from the inside of the wheel to the outside. Effect of the Invention

[0015] According to the present invention, a riblet structure can be easily formed on the edge that defines the opening defined by the rim portion, the hub attachment portion and the spokes. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view of a vehicle wheel according to an embodiment. [Diagram 2] FIG. 2 is a perspective view illustrating a riblet structure according to an embodiment. [Diagram 3] FIG. 3 is a cross-sectional view showing a layer structure (first example) of a vehicle wheel in the embodiment. [Figure 4] FIG. 4 is a cross-sectional view showing a layer structure (second example) of a vehicle wheel in the embodiment. [Diagram 5] FIG. 5 is a cross-sectional view showing a layer structure (third example) of a vehicle wheel in the embodiment. [Figure 6] FIG. 6 is a cross-sectional view showing a layer structure (fourth example) of a vehicle wheel in the embodiment. [Figure 7] FIG. 7 is a cross-sectional view showing a schematic diagram of a protrusion that constitutes the riblet structure in the embodiment. [Figure 8] FIG. 8 is a block diagram of a printing apparatus according to an embodiment. [Figure 9] FIG. 9 is a perspective view showing a process of forming riblets in the embodiment. [Figure 10] FIG. 10 is a continuation of FIG. 9 and is a perspective view showing a process of forming riblets in the embodiment. [Figure 11] FIG. 11 is a continuation of FIG. 10 and is a perspective view showing a process of forming riblets in the embodiment. [Figure 12] FIG. 12 is a continuation of FIG. 11 and is a perspective view showing a process of forming riblets in the embodiment. [Figure 13] FIG. 13 is a continuation of FIG. 12 and is a perspective view showing a process of forming riblets in the embodiment. [Figure 14]FIG. 14 is a continuation of FIG. 13 and is a perspective view showing a process of forming riblets in the embodiment. [Figure 15] FIG. 15 is a schematic diagram of FIG. 14 viewed from a first direction. [Figure 16] FIG. 16 is a schematic diagram of FIG. 14 viewed from a second direction. [Figure 17] FIG. 17 is a schematic diagram of FIG. 14 viewed from a first direction. [Figure 18] FIG. 18 is a schematic diagram of FIG. 14 viewed from a second direction. [Figure 19] FIG. 19 is a perspective view showing an example of attaching a substrate having a riblet structure formed thereon to the edge of a wheel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, a riblet forming method and a wheel according to the present invention will be described with reference to the drawings. <Overall wheel configuration> As shown in Fig. 1, a vehicle wheel 10 according to this embodiment is a wheel used for passenger cars and the like. It is also applicable to wheels for trucks, buses, and commercial vehicles. The wheel 10 includes a substantially cylindrical rim portion 11 to which a pneumatic tire is attached, and a disk portion 12 provided at a position on the outer side (out) of the rim portion 11 in the vehicle width direction. The wheel 10 is a steel wheel or an aluminum wheel.

[0018] The rim portion 11 includes an inner flange portion 21, an inner bead seat portion 22, a drop portion 23, an outer bead seat portion 24, and an outer flange portion 25. The inner flange portion 21 and the inner bead seat portion 22 are located on the inner side in the vehicle width direction, i.e., closer to the vehicle, than the outer bead seat portion 24 and the outer flange portion 25 when the wheel 10 is mounted on the vehicle.

[0019] The disk portion 12 includes a hub attachment portion 26 provided at the center of rotation, and spokes 27 extending radially from the hub attachment portion 26 toward the rim portion 11 . The hub mounting portion 26 has a hub hole 28 formed in its center and a plurality of bolt holes 29 arranged around the hub hole 28. A plurality of spokes 27 are formed at intervals in the circumferential direction when viewed from the outside (out) in the vehicle width direction. Each spoke 27 is configured to be connected to the rim portion 11. A plurality of substantially fan-shaped openings 31 are provided between adjacent spokes 27 in the circumferential direction, which connect the space on the outside (out) in the vehicle width direction of the disc portion 12 to the space on the inside (in) in the vehicle width direction. The openings 31 are decorative holes defined in the spokes 27 and the edge portion 32 of the outer flange portion 25. The openings 31 are through holes that connect the internal space of the wheel 10 to the external space. A brake device such as a disc brake is arranged inside the wheel 10. When the vehicle is running, air flows from the inside of the wheel 10 to the outside through the openings 31 provided in the wheel 10.

[0020] The edge portion 32 that defines the opening 31 has an inclined surface that widens the opening 31 from the edge of the opening 31 toward the edge of the outer flange portion 25. This edge portion 32 has a riblet structure 33. As shown in FIG. 2, the riblet structure 33 is an uneven structure in which convex ribs 34 and concave ribs 35 are repeatedly provided. The convex ribs 34 and concave ribs 35 extend from the internal space toward the external space. The riblet structure 33 extending inward and outward rectifies the air flow that flows from the inside of the wheel 10 to the outside through the opening 31 provided in the wheel 10 when the vehicle is running. Therefore, the brake device that brakes the wheel is always cooled appropriately by the air flow when the vehicle is running.

[0021] <Wheel layer structure> The riblet structure 33 is composed of a decorative layer 39 provided on a base layer formed on a base 36 which is the material of the wheel 10.

[0022] FIG. 3 is a cross-sectional view showing a layer structure (first example) of the wheel 10. As shown in FIG. The first example includes a primer layer 37 provided on a base 36, a base color layer 38 provided on the primer layer 37, a decorative layer 39 provided on the base color layer 38, and a top coat layer 40 provided on the decorative layer 39.

[0023] The base 36 of the wheel 10 is subjected to pretreatment including cleaning and chemical conversion treatment for the purpose of improving corrosion resistance and adhesion of a coating film. After the pretreatment, a primer layer 37 is provided on the base 36.

[0024] The primer layer 37 is a layer provided for purposes such as rust prevention and leveling, and is provided by applying a primary paint. The base color layer 38 is a paint of a base color of the wheel 10, and is applied on the primer layer 37. The surface of the base color layer 38 is a print forming surface on which a decorative layer 39 on which the riblet structure 33 is formed is printed. The decorative layer 39 is provided on the base color layer 38, and is provided by a printing device 50 described later. One example of the printing device 50 is an inkjet printer. The above-mentioned riblet structure 33 is provided by the decorative layer 39. The top coat layer 40 is provided on the decorative layer 39. The top coat layer 40 is formed by a top clear coating or a color clear coating as a post-treatment.

[0025] FIG. 4 is a cross-sectional view showing a layer structure (second example) of the wheel 10. As shown in FIG. The second example includes a primer layer 37 provided on a base 36, a base color layer 38 provided on the primer layer 37, and a decorative layer 39 provided on the base color layer 38. Unlike the first example, the second example does not include a top coat layer 40.

[0026] FIG. 5 is a cross-sectional view showing a layer structure (third example) of the wheel 10. As shown in FIG. The third example includes a clear layer 41 provided on the base 36, a decorative layer 39 provided on the clear layer 41, and a topcoat layer 40 provided on the decorative layer 39. The clear layer 41 is applied, for example, to a portion where the base 36 is exposed. The clear layer 41 also includes a color clear layer. The surface of the clear layer 41 is a print forming surface on which the decorative layer 39 in which the riblet structure 33 is formed is printed. In the third example, compared to the second example, the primer layer 37 becomes the clear layer 41.

[0027] FIG. 6 is a cross-sectional view showing a layer structure (fourth example) of the wheel 10. As shown in FIG. The fourth example includes a clear layer 41 provided on a base 36, and a decorative layer 39 provided on the clear layer 41. Unlike the third example, the fourth example does not include a top coat layer 40.

[0028] 7, the riblet structure 33 constituting the decorative layer 39 is a concave-convex structure in which convex ribs 34 and concave ribs 35 are repeatedly provided. The convex ribs 34 have, for example, a substantially triangular cross-sectional shape. When viewed in cross-sectional shape, the convex ribs 34 have a substantially triangular basic shape, but the oblique side may not be a straight line but may be combined with a periodic or non-periodic wave shape.

[0029] In the riblet structure 33, the distance L between the perpendicular lines extending from the apex of adjacent ridges 34 to the base (the surface of the base color layer 38, the surface of the clear layer 41, etc.) is 50 μm or more. The apex is the highest point in a cross section at any position of the ridge 34. The distance L is 350 μm or less. The distance L is preferably 250 μm or less, and more preferably 100 μm. The height H from the base to the apex of the ridge 34 is 10 μm or more. The height H is 250 μm or less. The height H is preferably 150 μm or less, and more preferably 100 μm. By setting the height H in this range, the riblet structure 33 can rectify the air flow from the inside to the outside of the wheel 10.

[0030] <Printing device configuration> As shown in FIG. 8, the printing device 50 is an inkjet printing device. The printing device 50 includes a printing unit 51, a robot arm 56, and a control unit 57. The printing unit 51 includes an inkjet head 52 and a UV head 53. The inkjet head 52 includes a pressure generating element such as a piezoelectric element. The inkjet head 52 ejects paint droplets of UV curable ink from the nozzles by fluctuating the pressure in the liquid chamber. The UV curable ink is paint that forms the decorative layer 39. The UV head 53 irradiates the ejected UV curable ink with UV light to cure it.

[0031] The robot arm 56 is configured to be able to hold the wheel 10. The robot arm 56 is configured to be able to move based on a signal from the control unit 57 while holding the wheel 10. Here, the wheel 10 held by the robot arm 56 is a wheel on which painting has been completed up to the base layer of the decorative layer 39 (such as a layer below the decorative layer 39). The control unit 57 is a computer having, for example, a CPU, a memory, etc., which executes a control program, and controls the operations of the printing unit 51 and the robot arm 56.

[0032] The control unit 57 can set the resolution of the inkjet head 52. Specifically, the control unit 57 sets the resolution of the inkjet head 52 to a first resolution and a second resolution. The second resolution is lower than the first resolution. The first resolution is, for example, 360 dpi or higher. Also, the first resolution is 1440 dpi or lower. The first resolution is, for example, 1440 dpi. The second resolution is, for example, 96 dpi or higher. Also, the second resolution is 720 dpi or lower. The second resolution is, for example, 720 dpi.

[0033] First, the control unit 57 controls the robot arm 56 to hold the wheel 10 on the robot arm 56, and moves the wheel 10 so that the edge 32 of the wheel 10 is included in the printable area of ​​the inkjet head 52. Then, the control unit 57 controls the printing unit 51 and the robot arm 56 to adjust the position so that the edge 32, which is the print area, and the multiple nozzles of the inkjet head 52 are approximately parallel. Next, the control unit 57 ejects droplets of UV curable ink onto the edge 32. At this time, the UV head 53 irradiates the droplets of UV curable ink attached to the edge 32 with UV light to cure the droplets of UV curable ink.

[0034] <Riblet structure formation process> 9 to 18 show the order in which one row of ridges 34 is formed. 9, the control unit 57 first ejects the first lower layer droplets 54a at a first resolution onto a predetermined position (surface to be printed) of the base layer 32a of the edge portion 32. Next, the control unit 57 ejects the first lower layer droplets 54a onto the next landing position in the direction in which the convex streak 34 extends. The control unit 57 repeats this process up to the end point of the convex streak 34. In this way, the control unit 57 forms the base of the lower layer convex portion 54 with the first stage of first lower layer droplets 54a at the first resolution.

[0035] As shown in FIG. 10, the control unit 57 then forms a second stage with the second lower-layer droplets 54b. Specifically, the control unit 57 ejects the second lower-layer droplets 54b on the first stage first lower-layer droplets 54a at the first resolution. Next, the control unit 57 ejects the second lower-layer droplets 54b on the next first stage first lower-layer droplets 54a in the extension direction of the convex strip 34 at the first resolution. The control unit 57 repeats this up to the end point of the convex strip 34. In this way, the control unit 57 forms the second stage second lower-layer droplets 54b at the first resolution. That is, a lower-layer convex portion 54 in which the second stage second lower-layer droplets 54b are piled up on the first stage first lower-layer droplets 54a is formed (first printing step).

[0036] As shown in FIG. 11, the control unit 57 then ejects the first upper layer droplets 55a onto the lower layer convex portions 54 formed on the edge portion 32 at the second resolution. Next, the control unit 57 ejects the first upper layer droplets 55a onto the next lower layer convex portion 54 in the direction in which the convex stripe 34 extends at the second resolution. The control unit 57 repeats this process up to the end point of the convex stripe 34. This forms the base of the upper layer convex portion 55 on the lower layer convex portion 54. In this embodiment, the second resolution is 1 / 2 the first resolution. Therefore, the first upper layer droplets 55a land on every other lower layer convex portion 54 (second printing process).

[0037] As shown in FIG. 12, the control unit 57 then discharges the third lower layer droplet 54c onto the lower layer convex portion 54 and the upper layer convex portion 55 at the first resolution. Next, the control unit 57 discharges the third lower layer droplet 54c onto the next lower layer convex portion 54 and upper layer convex portion 55 in the extension direction of the convex streak 34 at the first resolution. Thus, the control unit 57 forms the third lower layer droplet 54c of the third stage at the first resolution. The control unit 57 repeats this up to the end point of the convex streak 34. Thus, the control unit 57 forms the third lower layer droplet 54c of the third stage at the first resolution. That is, a lower layer convex portion 54 in which the third stage of the third lower layer droplet 54c is piled up on the second stage of the second lower layer droplet 54b is formed.

[0038] As shown in FIG. 13, the control unit 57 then ejects a fourth lower-layer droplet 54d on the third lower-layer droplet 54c on the third stage at the first resolution. Next, the control unit 57 ejects a fourth lower-layer droplet 54d on the next third lower-layer droplet 54c in the extension direction of the convex strip 34 at the first resolution. The control unit 57 repeats this up to the end point of the convex strip 34. In this way, the control unit 57 forms a fourth lower-layer droplet 54d on the fourth stage at the first resolution. That is, a lower-layer convex portion 54 in which the fourth lower-layer droplet 54d on the third stage of the third lower-layer droplet 54c is piled up is formed (first printing step).

[0039] As shown in FIG. 14, the control unit 57 then ejects the second upper layer droplets 55b at the second resolution onto the lower layer convex portions 54 that have been formed up to the fourth stage. Next, the control unit 57 ejects the second upper layer droplets 55b at the second resolution onto the next lower layer convex portion 54 in the extension direction of the convex stripe 34. The control unit 57 repeats this up to the end point of the convex stripe 34. As a result, two stages of upper layer convex portions 55 are formed on four stages of lower layer convex portions 54. In this embodiment, the second resolution is 1 / 2 of the first resolution. Therefore, the second upper layer droplets 55b land on every other lower layer convex portion 54 (second printing process).

[0040] As shown in Figures 15 and 16, each protrusion 34 is covered with a first upper layer droplet 55a of the first stage, with a first lower layer droplet 54a of the first stage and a second lower layer droplet 54b of the second stage as a core. Furthermore, a second upper layer droplet 55b of the second stage is covered with a third lower layer droplet 54c of the third stage and a fourth lower layer droplet 54d of the fourth stage as a core. As shown in Figures 17 and 18, the first upper layer droplet 55a and the second upper layer droplet 55b drip due to gravity or the like immediately after landing, so that the droplet shape is changed from a spherical or elliptical shape to a drooping shape. Then, each protrusion 34 has a substantially triangular cross section when viewed from the second direction.

[0041] In this embodiment, the lower layer droplets are configured with four stages and the upper layer droplets are configured with two stages, but the lower layer droplets may be configured with three or more stages and the upper layer droplets may be configured with three or more stages accordingly. The lower layer droplets may be configured with two stages and the upper layer droplets may be configured with one stage. That is, by stacking the lower layer droplets in multiple stages and then landing the upper layer droplets once while adjusting the first resolution and the second resolution, the height H and distance L of the convex ridges 34 that make up the riblet structure 33 can be adjusted.

[0042] The timing of UV light irradiation may be set so that UV light is irradiated immediately after the lower layer droplets 54a to 54d land at the first resolution. UV light may be irradiated immediately after the upper layer droplets 55a, 55b land at the second resolution. Furthermore, UV light may be irradiated once after the second upper layer droplet 55b is discharged, that is, at the end. Furthermore, UV light may be irradiated after the lower layer droplets 54a, 54b are formed. Furthermore, UV light may be irradiated after the lower layer droplets 54c, 54d are formed. That is, the timing of UV light irradiation is set according to the shapes of the convex streaks 34 and the concave streaks 35 being formed.

[0043] <Effects of the embodiment> The above-described riblet forming method and wheel 10 can provide the following effects.

[0044] (1) The riblet structure 33 for straightening the air flow from the inside to the outside of the wheel 10 can be easily formed by inkjet printing. (2) A second upper layer droplet of a second resolution is ejected onto a lower layer convex portion formed by a first lower layer droplet of a first resolution to form an upper layer convex portion, and by repeating this process, a convex ridge that constitutes a riblet structure can be formed.

[0045] (3) The riblet structure 33 can be provided using the design of the wheel 10 formed by the decorative layer 39. (4) The riblet structure 33 is formed by the decorative layer 39. Even if an upper layer is provided on the decorative layer 39, the thickness of the upper layer is suppressed. Therefore, it is possible to prevent the concaves and convexes of the riblet structure 33 formed by the decorative layer 39 from being buried.

[0046] (5) The distance L between the protrusions 34 constituting the riblet structure 33 is set to 50 μm or more and 350 μm or less, and the height H is set to 10 μm or more and 250 μm or less. This makes it possible to obtain a riblet structure 33 that can rectify the air flow that flows from the inside of the wheel 10 to the outside.

[0047] (6) The wheel 10 is provided with a riblet structure 33 on the edge that defines the opening 31, thereby enabling the airflow flowing from the inside to the outside of the wheel 10 to be straightened. The riblet forming method and wheel can also be modified as appropriate as follows.

[0048] In the printing device 50, the robot arm 56 may hold the printing unit 51 instead of the wheel 10. In this case, the robot arm 56 moves the printing unit 51 to the printing position. Also, the printing device 50 may align the relative positions of the printing position and the printing unit 51 by means of a means other than the robot arm 56.

[0049] In the above-described embodiment, the riblet structure 33 is directly inkjet printed on the edge 32. However, as shown in FIG. 19, a substrate 60 such as a sheet on which the riblet structure 33 constituting the decorative layer 39 is inkjet printed may be attached. The substrate 60 is, for example, a translucent sheet material. The substrate 60 is a resin or metal sheet material. The substrate 60 may be a flat plate material or a curved plate material. The substrate 60 may or may not be flexible. The substrate 60 is attached to the edge 32 with an adhesive or the like.

[0050] In such a case, the riblet structure 33 can be inkjet printed on the printing surface of the substrate 60 more easily than by inkjet printing the riblet structure 33 on the edge 32. Then, the substrate 60 can be cut into the shape of the edge 32 and attached to the edge 32. According to such a method, the robot arm 56 is not required, and the printing device can be simplified.

[0051] 3 to 6, the base material 60 may be one in which a base layer for the decorative layer 39 is provided, and the decorative layer 39 having the riblet structure 33 is provided thereon. In this case, for example, the base material 60 is attached after the edge portion 32 is subjected to a pretreatment.

[0052] The base material 60 may be provided with a decorative layer 39 and a layer (such as a topcoat layer 40) above the decorative layer 39. In this case, the surface to which the base material 60 is attached may be a surface that has been subjected to a pretreatment, or a base layer may be provided thereon.

[0053] Furthermore, the base material 60 may be provided with only the decorative layer 39. In this case, after the base material 60 is attached to the edge portion, the top coat layer 40 and the like may be provided. As long as the airflow can be rectified, the distance L between the protrusions 34 constituting the riblet structure 33 may be outside the range of 50 μm or more and 350 μm or less. In addition, the height H may be outside the range of 10 μm or more and 250 μm or less.

[0054] In the layer structure of the wheel 10, the decorative layer 39 may be provided on another layer. The riblet structure 33 may be provided at a location on the wheel 10 other than the edge 32 of the opening 31.

[0055] The paint for forming the riblet structure 33 may be a paint that is cured by infrared rays, hot air, laser irradiation, or the like, in addition to an ultraviolet-curing paint. In the case of an aluminum wheel, as described above, the wheel may be made up of two parts, a rim portion and a disc portion having a hub attachment portion and spokes. In this case, the rim portion and disc portion are joined by bolts and nuts, welding, etc. Furthermore, the rim portion may be divided in the axial direction and made up of three parts. Furthermore, the wheel may be made up of one part by casting.

[0056] The metal of the wheel 10 may be aluminum alloy, steel, titanium alloy, magnesium alloy, etc. [Explanation of symbols]

[0057] 10…Wheels 11…Rim section 12...Disc section 26…Hub mounting part 27…Spokes 31...Aperture 32…Edge 32a…base layer 33…Riblet structure 34…Convex stripe 35...concave line 36...Base 37…Primer layer 38...Base color layer 39…Decorative layer 40…Top coat layer 41…Clear layer 50...Printing device 51...Printing Department 52...Inkjet head 53…UV head 54…Lower convex part 54a...first lower layer droplet 54b…Second lower layer droplet 54c…Third lower layer droplet 54d...Fourth lower layer droplet 55…Upper convex part 55a...first upper layer droplet 55b…Second upper layer droplet 56…Robot arm 57...Control section

Claims

1. a forming step of forming a riblet structure having projections and recesses extending inward and outward directions of the wheel on an edge portion that defines the opening of a wheel including a rim portion, a hub attachment portion, spokes connecting the rim portion and the hub attachment portion, and an opening defined by the rim portion, the hub attachment portion, and the spokes; The forming step includes: a first printing step of depositing paint droplets at a first resolution on a printing target surface by inkjet printing to form a lower layer convex portion; a second printing step of applying the paint droplets to the lower layer convex portion by inkjet printing at a second resolution lower than the first resolution to form an upper layer convex portion; The printing process is repeated in the order of the first printing process and the second printing process. Method for forming riblets.

2. In the first printing step, the paint droplets are deposited at the same position at the first resolution to form the lower layer convex portion, and then the paint droplets are deposited on the lower layer convex portion at the second resolution. The method for forming riblets according to claim 1.

3. The surface to be printed is the surface of the edge portion. The method for forming riblets according to claim 1 or 2.

4. The printing surface is a surface of a substrate, The forming step includes a bonding step of bonding a base material on which the riblet structure is formed to the edge portion. The method for forming riblets according to claim 1 or 2.

5. The riblet structure is formed by a decorative layer formed on a base layer provided on the wheel. The method for forming riblets according to claim 1 or 2.

6. In the riblet structure, the distance between perpendicular lines extending from the apexes to the bases of adjacent convex stripes is 50 μm or more and 350 μm or less, The height from the base to the apex of the protrusion is 10 μm or more and 250 μm or less. The method for forming riblets according to claim 1.

7. a rim portion, a hub attachment portion, spokes connecting the rim portion and the hub attachment portion, and an opening defined by the rim portion, the hub attachment portion and the spokes, The edge portion defining the opening has a riblet structure having projections and recesses extending inward and outward directions; The riblet structure is A lower layer convex portion is formed by applying paint droplets at a first resolution to a printing target surface by inkjet printing, and an upper layer convex portion is formed by applying the paint droplets at a second resolution lower than the first resolution to the lower layer convex portion by inkjet printing. wheel.

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