Ultrasonic horn

Abstract

The objective is to provide an ultrasonic horn that suppresses the generation of burr-like protrusions from the workpiece during ultrasonic welding, thereby achieving excellent welding strength. [Solution] The ultrasonic horn of the present disclosure is an ultrasonic horn 100 for ultrasonically welding a workpiece 70 to a workpiece 50, wherein the tip surface 11a that contacts the workpiece 70 with the workpiece 50 is knurled, and a straight section is formed on at least a part of the outer circumference such that the height of the protrusions formed by the knurling is between the peaks and valleys.

Description

[Technical Field]

[0001] This disclosure relates to an ultrasonic horn. [Background technology]

[0002] In conventional ultrasonic devices, the main part of the ultrasonic vibration mechanism consists of an ultrasonic transducer with an ultrasonic horn attached, and the ultrasonic horn has protrusions, irregularities, knurling, etc. on the contact surface of the horn in order to transmit minute vibrations to the workpiece (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2005-152098 (paragraph 0024, Figure 5) [Overview of the project] [Problems that the invention aims to solve]

[0004] However, when using an ultrasonic horn for ultrasonic welding with plastic welders, etc., to ultrasonically weld a sheet-like workpiece such as an insulating sheet to the workpiece (base material), increasing the input energy (load × time) in an attempt to increase the welding strength (peel strength) resulted in burr-like protrusions being generated from the workpiece around the workpiece contact area of ​​the ultrasonic horn. These burr-like protrusions penetrate the sheet, resulting in a failure to obtain sufficient welding strength.

[0005] This disclosure is made to solve the above-mentioned problems and aims to provide an ultrasonic horn that suppresses the generation of burr-like protrusions from the workpiece during ultrasonic welding and provides excellent welding strength. [Means for solving the problem]

[0006] The ultrasonic horn according to this disclosure is an ultrasonic horn for bonding a workpiece by applying ultrasonic vibrations to it, characterized in that the tip surface that contacts the workpiece is knurled, and at least a part of the outer circumference has straight sections formed such that the height of the protrusions formed by the knurling is between the peaks and valleys. [Effects of the Invention]

[0007] According to the ultrasonic horn of this disclosure, when ultrasonic welding, it is possible to suppress the generation of burr-like protrusions from the workpiece and increase the input energy, thereby improving the welding strength. [Brief explanation of the drawing]

[0008] [Figure 1] This is a side view showing the configuration of the ultrasonic horn according to Embodiment 1. [Figure 2] This is a perspective view showing the configuration of the main parts of the ultrasonic horn according to Embodiment 1. [Figure 3] Figures 3A to 3C are a front view, a top view, and a side view showing the configuration of the main parts of the ultrasonic horn according to Embodiment 1. [Figure 4] This is an enlarged perspective view showing the configuration of the knurled surface provided on the ultrasonic horn according to Embodiment 1. [Figure 5] This is a perspective view showing the configuration of the main components of a conventional ultrasonic horn. [Figure 6] Figures 6A to 6C are front, top, and side views showing the main components of a conventional ultrasonic horn. [Figure 7] Figures 7A to 7F are diagrams illustrating the configuration of the quadrilateral knurled surface in the ultrasonic horn according to Embodiment 1. [Figure 8] Figures 8A and 8B are a front view and a side view showing other components of the ultrasonic horn according to Embodiment 1. [Figure 9] Figures 9A and 9B are a front view and a side view showing other components of the ultrasonic horn according to Embodiment 1. [Figure 10]It is a diagram for explaining the configuration of the main part of the ultrasonic horn according to Embodiment 1. [Figure 11] FIGS. 11A and 11B are a front view and a side view showing another configuration of the main part of the ultrasonic horn according to Embodiment 1. [Figure 12] FIGS. 12A and 12B are a front view and a side view showing the configuration of the main part of a conventional ultrasonic horn. [Figure 13] FIGS. 13A and 13B are a front view and a side view showing another configuration of the main part of the ultrasonic horn according to Embodiment 1. [Figure 14] FIGS. 14A to 14B are a front view and a side view showing another configuration of the main part of the ultrasonic horn according to Embodiment 1. [Figure 15] It is a perspective view showing the configuration of the main part of the ultrasonic horn according to Embodiment 2. [Figure 16] FIGS. 16A to 16C are a front view, a top view, and a side view showing the configuration of the main part of the ultrasonic horn according to Embodiment 2.

MODE FOR CARRYING OUT THE INVENTION

[0009] Embodiment 1. FIG. 1 is a side view showing the configuration of the ultrasonic horn according to Embodiment 1. FIG. 2 is a perspective view showing the configuration of the tip portion A of the ultrasonic horn of FIG. 1. FIGS. 3A to 3C are a front view, a top view, and a side view showing the configuration of the tip portion A of the ultrasonic horn, respectively. FIG. 4 is an enlarged perspective view showing the configuration of the tip surface provided on the ultrasonic horn.

[0010] As shown in FIG. 1, the ultrasonic horn 100 according to Embodiment 1 includes a horn 11 having a knurling process on the tip surface 11a of the tip portion A, and an ultrasonic vibrator 13 connected to the horn 11 via a connection portion 12.

[0011] The tip surface 11a of the tip A that contacts the workpiece 50 with the workpiece 70 in between is quadrilateral (see Figures 2, 3A and 7B described later), and the tip surface 11a is knurled (see Figures 3A to 3C). The knurled surface Y is composed of multiple square pyramidal prisms T as protrusions (see Figure 4), and each protrusion T is a ridge T P It has.

[0012] As shown in Figures 2 and 3A to 3C, the ultrasonic horn 100 of this embodiment 1 is configured such that the height of the protrusions on the four sides of the quadrilateral that forms the knurled surface Y is between the ridges and valleys. The knurled surface Y is formed by a well-known knurling method.

[0013] Figure 5 is a perspective view showing the configuration of the tip A of a conventional ultrasonic horn. Figures 6A to 6C are a front view, a top view, and a side view, respectively, showing the configuration of the tip A of a conventional ultrasonic horn.

[0014] In conventional ultrasonic horns, as shown in Figures 5 and 6A to 6C, the tip surface 11a of the tip A that contacts the workpiece 70 and the workpiece 50 is quadrilateral, and the tip surface 11a is knurled, but the height of the highest convex part of the quadrilateral that forms the knurled surface Y is the peak T P The knurled surface Y has four ridges T. P Because these ridges are arranged in a line, they act as cutting lines for the sheet-like workpiece, making the sheet-like workpiece more prone to tearing.

[0015] Furthermore, the four sides of the quadrilateral that forms the knurled surface Y have a cross-sectional shape with sharp ridges, which makes it easy for burr-like protrusions to form from the workpiece. These burr-like protrusions can penetrate the sheet-like workpiece, damaging it and reducing the welding strength.

[0016] In the ultrasonic horn 100 of this disclosure, it is not necessary for the height of the protrusions on all four sides of the quadrilateral that forms the knurled surface Y to be between the ridges and valleys. Figures 7A to 7F are diagrams illustrating the configuration of the four sides of the quadrilateral that forms the knurled surface Y in the ultrasonic horn 100. Figures 7A, 7C, and 7E are top views showing the positional relationship between the workpiece 50 and the tip surface 11a of the tip A that contacts the workpiece 50 with the workpiece 70 in between. Figure 7B is a cross-sectional view taken along the line B1B1 in Figure 7A. Figure 7D is a cross-sectional view taken along the line B2B2 in Figure 7C. Figure 7F is a cross-sectional view taken along the line B3B3 in Figure 7E.

[0017] When the workpiece 50 to be welded is smaller than the tip surface 11a of the contacting ultrasonic horn 100, as shown in Figures 7A and 7B, and welding occurs by intersecting only one side 11a1 of the tip surface 11a, the ultrasonic horn 100 can prevent direct damage to the sheet by creating a cutting line with the protrusion of the straight section of the intersecting side 11a1 of the tip surface 11a that contacts the workpiece 50 across the workpiece 70, by making the height of the protrusion between the peak and the valley. This also reduces the likelihood of burr-like protrusions being generated from the workpiece, thereby improving the welding strength.

[0018] Furthermore, by suppressing the generation of burr-like protrusions from the workpiece, it becomes possible to increase the input energy, thereby improving the welding strength. In particular, in the straight section of one intersecting side 11a1 of the tip surface 11a that contacts the workpiece 50 with the workpiece 70 in between, by making the height of the protrusions between the peaks and valleys, it is possible to make the height of all protrusions the same, and the generation of burr-like protrusions can be effectively suppressed.

[0019] When the workpiece 50 to be welded includes one side 11a1 of the tip surface 11a of the contacting ultrasonic horn 100 and intersects with the two sides 11a2 and 11a3, as shown in Figures 7C and 7D, the ultrasonic horn 100 prevents direct damage to the sheet by creating a cutting line with the protrusions of the three sides 11a1, 11a2, and 11a3 of the tip surface 11a that contacts the workpiece 50 with the workpiece 70 in between, by making the height of the protrusions between the ridges and valleys. This also reduces the likelihood of burr-like protrusions being generated from the workpiece, thereby improving the welding strength.

[0020] Furthermore, by suppressing the generation of burr-like protrusions from the workpiece, it becomes possible to increase the input energy, thereby improving the welding strength. In particular, in the straight sections of the three sides 11a1, 11a2, and 11a3 of the tip surface 11a that contacts the workpiece 50 with the workpiece 70 in between, by making the height of the protrusions between the peaks and valleys, it is possible to make the height of all the protrusions the same, and the generation of burr-like protrusions can be effectively suppressed.

[0021] When the workpiece 50 to be welded is larger than the tip surface 11a of the contacting ultrasonic horn 100, as shown in Figures 7E and 7F, and the welding includes the entire tip surface 11a, i.e., all four sides 11a1, 11a2, 11a3, and 11a4, the ultrasonic horn 100 prevents direct damage to the sheet by creating a cutting line with the protrusions on the straight sections of the four sides 11a1, 11a2, 11a3, and 11a4 of the tip surface 11a that contacts the workpiece 50 with the workpiece 70 in between, by making the height of the protrusions between the ridges and valleys, and also prevents burr-like protrusions from being generated from the workpiece to be welded, thereby improving the welding strength.

[0022] Furthermore, by suppressing the generation of burr-like protrusions from the workpiece, it becomes possible to increase the input energy, thereby improving the welding strength. In particular, in the straight sections of the four sides 11a1, 11a2, 11a3, and 11a4 of the tip surface 11a that contacts the workpiece 50 with the workpiece 70 in between, by making the height of the protrusions between the peaks and valleys, it is possible to make the height of all the protrusions the same, and the generation of burr-like protrusions can be effectively suppressed.

[0023] Here, we have described the case where the shape of the tip surface 11a of the ultrasonic horn 100 that contacts the workpiece 70 with the workpiece 50 is quadrilateral, but a similar effect can be obtained if the tip surface 11a of the ultrasonic horn 100 that contacts the workpiece 70 with the workpiece 50 has a straight section on part of its outer circumference, the tip surface 11a is knurled, and the height of the convex portion on at least one side around the tip surface 11a is configured to be between the ridges and valleys.

[0024] There are two main types of knurling methods: rolling and cutting, and each is processed using a predetermined tool. In this embodiment 1, the ridges connecting the valleys and ridges of the knurled surface Y are at a 90-degree angle to each side of the quadrilateral tip surface 11a that contacts the workpiece 70 with the workpiece 50 to be welded, and the case of diamond pattern knurling processed at a 45-degree angle by the processing tool has been described. However, the same effect can be obtained even if the ridges connecting the valleys and ridges of the knurled surface Y are at a 90-degree angle to each side of the quadrilateral tip surface 11a that contacts the workpiece 70 with the workpiece 50 to be welded, and the basket pattern knurling is processed at an angle other than 45 degrees, such as 30 degrees or 60 degrees, by the processing tool. Figures 8A and 8B, and 9A and 9B show the front view and side view of the tip surface 11a with basket pattern knurling. Figures 8A and 8B show a vertical basketweave knurling pattern, while Figures 9A and 9B show a horizontal basketweave knurling pattern.

[0025] In a shape where the contacting tip surface 11a has straight sections on two opposing sides, the relationship between the pitch P1 and the distance D1 between the two opposing sides will be explained. As shown in Figure 10, when machining is performed in a direction offset by θ from side 11a3, the distance between the ridges aligned perpendicular to side 11a3 is 2P1sinθ. If the height of the convex part on side 11a3 is set to be midway between the ridge and the valley, then the height of the convex part on side 11a2 can be set to be midway between the ridge and the valley by making the distance D1 between the two sides satisfy equation (1). D1 = (2n + 1)P1sinθ···(1)

[0026] In Embodiment 1 described above, the cases where the knurling is a diamond pattern and a basketweave pattern were explained, but it is not limited to these. The knurling may also be a grid pattern.

[0027] Figures 11A and 11B are a front view and a side view, respectively, showing other configurations of the tip surface 11a of the ultrasonic horn according to Embodiment 1. As shown in Figures 11A and 11B, the shape of the tip surface 11a that contacts the workpiece 70 with the workpiece 50 is quadrilateral, and the tip surface 11a is knurled in a grid pattern, with the height of the protrusions on the four sides around the tip surface 11a being between the peaks and valleys.

[0028] In this embodiment, the tip surface 11a of the ultrasonic horn has three ridges in the vertical direction, and by making the height of the convex portion between the ridges and valleys in the straight sections of the four sides 11a1, 11a2, 11a3, and 11a4 of the tip surface 11a, the height of all convex portions is made uniform, effectively suppressing the generation of burr-like protrusions. In Figures 11A and 11B, three ridges are provided in the vertical direction, and the vertical width of the contacting tip surface 11a is 2.5 times the pitch P2.

[0029] Figures 12A and 12B show the configuration of the tip surface 11a of a conventional ultrasonic horn. Figures 12A and 12B are a front view and a side view, respectively. As shown in Figures 12A and 12B, the tip surface 11a of a conventional ultrasonic horn has edges connecting the valleys and ridges of the knurled surface Y at a 45-degree angle to each side of the quadrilateral tip surface 11a that contacts the workpiece 70 with the workpiece 50. The knurled surface is processed with a processing tool to create a grid pattern parallel to the left, right, top, and bottom sides, with valleys arranged along the four sides around the tip surface 11a. In this case, when the knurled surface Y is pressed against the workpiece with the workpiece in between, the valleys are the furthest from the welding surface, making welding difficult.

[0030] In contrast, as in the ultrasonic horn of this embodiment, by positioning the portion between the ridges and valleys at the edge of the knurled surface Y, welding can be expected when the knurled surface Y is pressed against the workpiece with the workpiece in between. Furthermore, since the edge of the knurled surface Y only needs to be aligned with the edge of the area to be welded, the processing accuracy can be improved.

[0031] In addition, the tip surface 11a of the ultrasonic horn shown in Figures 11A and 11B has three ridges in the vertical direction, and the vertical width of the tip surface 11a that contacts the workpiece 70 with the object to be welded 50 is set to 2.5 times the pitch P2, but this is not the only option. Since welding is mainly performed by contacting the object to be welded 50 with the ridges, it is possible to perform welding efficiently by providing a moderate number of ridges.

[0032] Figures 13A and 13B are a front view and a side view showing other configurations of the main parts of the ultrasonic horn according to Embodiment 1. As shown in Figures 13A and 13B, by making the pitch P3 5 / 7 times that of P2, the pitch becomes 3.5 times that of P2 without changing the vertical width of the contacting tip surface 11a.

[0033] In this case, four ridges are created in the vertical direction. This means that the rate of increase in the number of ridges can be made to exceed the rate of reduction in pitch, thus enabling efficient welding. However, if the pitch is made extremely small in order to increase the number of ridges, the height of the ridges will become too low, so more ridges are not always better. The number of ridges and the height of the ridges must be appropriately set, taking into account the fluidity of the material to be welded 50.

[0034] Here, the height of the protrusions on all four sides around the knurling is not limited to being midway between the ridges and valleys; the same effect can be achieved if the height is between the ridges and valleys. Furthermore, it is not necessary for the height of all four protrusions around the knurling to be between the ridges and valleys; it is sufficient for the height of at least one protrusion to be between the ridges and valleys.

[0035] Furthermore, comparing the diamond and basket weave patterns with the grid pattern, the diamond and basket weave patterns have ridges offset by half a pitch, allowing for a smaller distance between ridges compared to the grid pattern. This allows for better distribution of the tensile force applied to the workpiece. Additionally, the staggered arrangement of the ridges also helps to distribute the tensile force applied to the workpiece within the contact surface.

[0036] Furthermore, the knurling may also be in the form of grooves. Figures 14A to 14B are a front view, a top view, and a side view showing other configurations of the tip surface 11a of the ultrasonic horn according to Embodiment 1. As shown in Figures 14A to 14C, the shape of the tip surface 11a that contacts the workpiece 70 with the workpiece 50 is quadrilateral, and the tip surface 11a is knurled with grooves, and the height of the convex portions on the left and right sides of the periphery of the tip surface 11a in Figure 14A is configured to be between the ridges and valleys.

[0037] Figure 14A shows five ridges in the lateral direction. On the straight sections of the left and right sides of the tip surface 11a that contacts the workpiece 70 with the workpiece 50, the height of the protrusions is made to be between the heights of the ridges and valleys, thereby aligning the height of all the protrusions and effectively suppressing burr-like protrusions.

[0038] Since welding is performed primarily by contacting the ridges of the welded material 50, efficient welding can be achieved by providing a moderate number of ridges. Because the rate of increase in ridges can exceed the rate of reduction in pitch, efficient welding can be achieved.

[0039] Here, the height of the protrusions on the left and right sides of the knurling is not limited to being midway between the ridges and valleys; the same effect can be obtained if the height is between the ridges and valleys. Furthermore, the height of the protrusions on both sides of the knurling does not need to be between the ridges and valleys; it is sufficient for the height of the protrusions on at least one side to be between the ridges and valleys.

[0040] As described above, the ultrasonic horn according to Embodiment 1 is an ultrasonic horn 100 for ultrasonically welding a workpiece 70 to a workpiece 50, wherein the tip surface 11a that contacts the workpiece 50 with the workpiece 70 in between is knurled, and a straight section is formed on at least a part of the outer circumference where the height of the protrusions formed by the knurling is between the ridges and valleys. This prevents direct damage to the sheet by creating cut lines with the protrusions on the edges, and also reduces the generation of burr-like protrusions from the workpiece, thereby improving the welding strength. Furthermore, by suppressing the generation of burr-like protrusions from the workpiece, it becomes possible to increase the input energy, thus improving the welding strength.

[0041] When the tip surface 11a is quadrilateral, by making the height of the protrusions equal to the height of all protrusions in the straight sections of the four sides 11a1, 11a2, 11a3, and 11a4 of the tip surface 11a that contact the workpiece 70 with the workpiece 50, the height of all protrusions can be made equal, and the generation of burr-like protrusions can be effectively suppressed.

[0042] Embodiment 2. In Embodiment 1, the case was described in which the height of the convex portion is between the ridge and the valley, with the straight portion around the tip surface 11a being defined by the ridge line connecting the ridge and the valley. In Embodiment 2, however, the case in which the convex portion of the straight portion is defined as the ridge will be described.

[0043] Figure 15 is a perspective view showing the configuration of the tip A of the ultrasonic horn according to Embodiment 2. Figures 16A to 16C are a front view, a top view, and a side view, respectively, showing the configuration of the tip A of the ultrasonic horn according to Embodiment 2.

[0044] As shown in Figures 15 and 16A to 16C, the ultrasonic horn 100 according to Embodiment 2 has a knurled tip surface 11a that contacts the workpiece 50 with the workpiece 70 in between, and the four sides of the quadrilateral tip surface 11a are formed with ridges. The ridges formed on the ridges S The highest ridge T is located within the tip surface 11a. PBy providing a second ridge lower than the first ridge, the height of the convex portion is between the first ridge and the valley.

[0045] Here, all the convex portions on the four sides are the ridge T which is the second ridge. S However, it is not necessary for the height of all the convex portions on the four sides of the front end face 11a to be between the first ridge and the valley. It is sufficient if the height of at least one side of the convex portion is between the first ridge and the valley.

[0046] Regarding other configurations of the ultrasonic horn 100 according to the second embodiment, they are the same as those of the ultrasonic horn 100 according to the first embodiment. Corresponding parts are denoted by the same reference numerals and their descriptions are omitted.

[0047] As described above, according to the ultrasonic horn 100 according to the second embodiment, on the straight portion around the front end face 11a, there is a ridge T which is a second ridge lower than the ridge T which is the first ridge provided in the front end face 11a. P By providing a ridge T which is a second ridge lower than the ridge T which is the first ridge provided in the front end face 11a, the height of the convex portion is between the ridge T S and the valley, so that it is possible to prevent directly damaging the sheet to create a cut line with the convex portion on the side, and it is difficult for burr-like protrusions to occur from the welded object, and the welding strength can be improved. Also, by suppressing the occurrence of burr-like protrusions from the welded object, it becomes possible to increase the input energy, so the welding strength can be improved. P Although various exemplary embodiments and examples are described in the present application, the various features, aspects, and functions described in one or more of the embodiments are not limited to the application of a specific embodiment, but are applicable to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are envisioned within the scope of the technology disclosed in the present specification. For example, it includes cases where at least one component is deformed, added, or omitted, and further cases where at least one component is extracted and combined with components of other embodiments.

[0048] Although various exemplary embodiments and examples are described in the present application, the various features, aspects, and functions described in one or more of the embodiments are not limited to the application of a specific embodiment, but are applicable to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are envisioned within the scope of the technology disclosed in the present specification. For example, it includes cases where at least one component is deformed, added, or omitted, and further cases where at least one component is extracted and combined with components of other embodiments.

[0049] Hereinafter, aspects of the present disclosure are collectively described as appendices.

[0050] (Note 1) An ultrasonic horn for ultrasonically welding a workpiece to an object to be welded, An ultrasonic horn characterized in that the tip surface that contacts the workpiece with the workpiece in between is knurled, and at least a part of the outer circumference has a straight section formed where the height of the protrusions formed by the knurling is between the peaks and valleys. (Note 2) The ultrasonic horn according to Appendix 1, characterized in that the tip surface is quadrilateral. (Note 3) The ultrasonic horn according to Appendix 1 or Appendix 2, characterized in that the knurling is in the shape of a diamond pattern or a basketweave pattern. (Note 4) The ultrasonic horn according to Appendix 1 or Appendix 2, characterized in that the knurling is in the form of grooves or a grid. (Note 5) The ultrasonic horn described in any one of the appendices 1 to 4 is characterized in that the straight section is provided on two opposing sides of the tip surface, and satisfies the following equation when the pitch of the knurling is p, the distance between the two opposing sides is d, and the inclination of the pitch direction with respect to the straight section is θ. d = (2n + 1)psinθ (where n is a natural number) (Note 6) The ultrasonic horn according to any one of the appendices 1 to 5, characterized in that the straight section has a ridge line connecting the peak and the valley, and the height of the convex section is between the peak and the valley. (Note 7) The ultrasonic horn according to any one of the appendices 1 to 4, characterized in that the straight portion has a second ridge that is lower than the first ridge provided in the tip surface, so that the height of the convex portion is between the ridge and the valley. [Explanation of Symbols]

[0051] 11a Tip surface, 11a1, 11a2, 11a3, 11a4 side (straight part), 50 Welded object, 70 Workpiece, Y Knurling surface, T P Mine, 100 ultrasonic horn.

Claims

1. An ultrasonic horn for ultrasonically welding a workpiece to an object to be welded, An ultrasonic horn characterized in that the tip surface that contacts the workpiece with the workpiece in between is knurled, and at least a part of the outer circumference has a straight section formed where the height of the protrusions formed by the knurling is between the peaks and valleys.

2. The ultrasonic horn according to claim 1, characterized in that the tip surface is quadrilateral.

3. The ultrasonic horn according to claim 1 or 2, characterized in that the knurling is in the form of a diamond pattern or a basketweave pattern.

4. The ultrasonic horn according to claim 1 or 2, characterized in that the knurling is in the form of grooves or a grid.

5. The ultrasonic horn according to claim 1 or 2, wherein the straight section is provided on two opposing sides of the tip surface, and the following equation is satisfied when the pitch of the knurling is p, the distance between the two opposing sides is d, and the inclination of the pitch direction relative to the straight section is θ. d = (2n + 1)psinθ (where n is a natural number)

6. The ultrasonic horn according to claim 1 or 2, characterized in that the height of the convex portion is between the peak and the valley, as defined by the ridge line connecting the peak and the valley.

7. The ultrasonic horn according to claim 1 or 2, characterized in that the straight portion has a second ridge that is lower than the first ridge provided in the tip surface, so that the height of the convex portion is between the ridge and the valley.

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