Headrest stick manufacturing method

Abstract

When applying a rounded chamfer to the tips of both legs of the headrest stay, the tips are thinned by boring without generating any chips. [Solution] The open end of the leg portion of the headrest stay is thinned without cutting its inner wall surface, and the thinned end is plastically processed into a hemispherical shape. A punch is pressed into the opening at the end of a round metal pipe to remove material from the inner wall surface of the end, thus thinning the inner wall of the end. In a round metal pipe headrest stay, the open end portion of the leg portion is thinned, and the open end portion is rounded. The end portion is thinner than the base portion of the stay leg portion, and at the boundary between the thinned portion and the thick base portion, the material that has flowed out due to the pressing process protrudes inward. In the thinning process, a punch that is larger than the inner diameter of the opening and smaller than the outer diameter of the opening is pressed into the open end portion from the opening end to thin the inner wall of the open end portion. First, a star-shaped or gear-shaped punch is pressed in to remove some of the material, and the remaining material is removed by rotating the punch in the circumferential direction and pressing it in. After this, a round punch is pressed in.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a headrest stay, particularly a method for manufacturing a headrest stay with reduced working steps when manufacturing a headrest stay with ensured safety.

Background Art

[0002] Conventionally, regarding automobile seats, regulations on internal protrusions are known for the protection of passengers. To meet this regulation, in the headrest stay of an automobile seat, spinning or swaging is performed on the terminal part of the headrest stay to form, for example, an R chamfer shape with a radius of 5 mm or more. In both this spinning and swaging, while applying rotation to the headrest stay, a spatula or a die is pressed from a direction perpendicular to the rotation axis. There was a problem that cracks and the like occurred when trying to form a shape with a small R and a large draw. Therefore, as a method for manufacturing a headrest stay that solves this problem, the ones described in the following documents are known. That is, when forming an R chamfer at the tip of the headrest stay, boring (inner diameter machining) is performed on the terminal part of an iron round pipe to form a thin part, and then the end of the round pipe is pressed against the bottom surface of a concave round cylindrical hole to shape it into an R chamfer shape.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0004] However, this type of boring process resulted in chips from the cutting tool remaining inside the pipe, requiring a cleaning and removal process. In other words, it increased the manufacturing process, creating room for improvement in terms of time and cost.

[0005] Therefore, after diligent research, the inventor discovered that all of the above-mentioned problems could be solved by thinning the inner wall of the pipe by pressing a punch into the pipe from the open end, rather than by boring, and thus completed this invention.

[0006] In other words, this invention was made to solve these problems, and its purpose is to reduce the number of work steps involved in processing the end portion of the headrest stay into an R-chamfer (hemispherical shape), thereby achieving cost reduction. In addition, it also aims to increase the bending strength of the end portion of the headrest stay by forming an inward projection in that portion. [Means for solving the problem]

[0007] The invention described in claim 1 is a method for manufacturing a headrest stay, comprising a thinning process in which a punch is pressed into the end portion of a headrest stay made of a round metal pipe to thin the end portion, and a hemispherical process in which the end portion is then chamfered with an R chamfer, wherein the thinning process comprises a first pressing step in which a first punch, whose outer diameter is larger than the inner diameter of the end portion and smaller than the outer diameter of the end portion, is pressed into the end portion to thin a part of the inner wall of the end portion, and a second pressing step in which a second punch is pressed into the end portion to thin the remaining inner wall from the first pressing step. The first punch described above may have a non-circular head shape, such as a star shape, gear shape, or regular polygon. The second punch may have a circular head shape different from that of the first punch. The first punch may have a star-shaped or gear-shaped head, and the second punch may have the same shape as the first punch, but in the pressing process, it is pressed in while rotated by a predetermined angle around its axis from the first punch used in the first pressing process. A third pressing process is performed after the second pressing process in which a punch with a circular head is pressed in. Pressing the punch scrapes or peels off a portion of the inner wall (the inner wall surface) of the pipe, and the scraped portion is pushed inward along the pipe axis. In other words, the punching or pressing causes a portion of the inner wall material to flow inward. Even though the inner portion of the inner wall is scraped off, its base (the portion of the flowed material that goes inward into the pipe) remains continuous with the inner wall of the pipe.

[0008] The headrest stay has a pair of legs made of round metal pipes, which are connected at the top to form a gate shape. The open ends of these legs are thinner than their bases. These thinned end portions are processed into a hemispherical shape with a rounded chamfer. At the chamfered open end, a protruding piece is formed at the boundary between the thinned portion and the thickened base, projecting inward in the diameter direction of the opening. This protruding piece is formed by the plastic deformation of the metal when thinning (shaving off a portion of the inner wall) is achieved by pressing a punch from the open end to the end portion. The protruding piece is shaped to protrude inward from the inner wall of the pipe for a predetermined length, for example, in an annular shape. Furthermore, the inner edge, which is the tip of the protruding piece, has a wedge-shaped recess when viewed in cross-section, for example. This is because two deformations are performed by pressing with a punch during the thinning process. The punch head shape may be the same or different. The above method for manufacturing a headrest stay includes a thinning process to thin the lower open end of the leg portion of the headrest stay, and an R-chamfering process to chamfer the thinned open end portion. In the thinning process, a punch (made of steel harder than the pipe; such as high-tensile steel) with an outer diameter larger than the inner diameter of the opening and smaller than the outer diameter of the opening (pipe) is pressed into the opening of the leg portion, for example, using a press machine. As a result, the inner wall of the open end portion is thinned by scraping it off over a predetermined length. After this, the thinned pipe end portion is given a hemispherical shape by normal R-chamfering. For example, the thinned end portion is pressed into a recess (mold) with a radius of 5 mm or more. Furthermore, when thinning the pipe wall by pressing with a punch, the entire outer surface of the pipe itself is fixed with a die or the like, as in conventional processing. In addition, the pressing process includes cases where the pipe is fixed vertically and horizontally.

[0009] The punches used here include, for example, punches with a cross-section having an uneven outer edge, such as those with a head that is an octagon, hexagon, or pentagon, or punches with a wavy, uneven, gear-shaped, or star-shaped outer edge. First, the punch is pressed into the pipe axially from the opening end for a predetermined length (a predetermined depth). To achieve thinning with a desired uniform inner diameter, a punch with a circular cross-section (a head with a circular shape) is then pressed into the leg opening from its opening end for the same length (or shallower than the above depth). With these two stages of pressing, an opening end with a uniform inner diameter, i.e., a thinned end, is obtained. Note that the polygonal punch is not limited to the regular polygonal punch described above. For example, it includes star-shaped polygonal punches. Essentially, the maximum diameter of the punch, whose outer edge is not perfectly round, is shorter than the outer diameter of the pipe. In the first pressing step, a portion of the pipe wall thickness is thinned, and in the subsequent second pressing step, the remaining thick portion is pressed in using, for example, a perfectly round punch, thereby thinning the pipe wall thickness to about half.

[0010] The invention described in claim 2 is a method for manufacturing a headrest stick according to claim 1, wherein the head of the first punch is non-circular, such as star-shaped, gear-shaped, or regular polygonal, and the head of the second punch is circular in shape, different from that of the first punch. Regarding the punch head, for example, it can be a star-shaped polygon (including pentagrams and hexagrams) or a gear shape, including spur gears, but the number of teeth is not specified. Furthermore, if the punch head is perfectly circular, a smaller perfectly circular punch can be used in succession. In addition, a punch with a circular (perfectly circular) head can be pressed in after the second pressing step described above. This is a finishing process to make the inner wall surface smooth and of uniform thickness.

[0011] The invention described in claim 3 is a method for manufacturing a headrest stay as described in claim 1, wherein the first punch has a star-shaped or gear-shaped head, and the second punch has the same shape as the first punch, and is pressed in while rotated by a predetermined angle around its axis from the first punch in the first pressing. For example, this applies when using a star-shaped punch (including pentagrams and hexagrams) for two presses. Also, if the punch has a gear shape with 8 teeth, and the angle between adjacent teeth is 45 degrees, then the first press will remove a portion of the inner wall, and then it will be rotated circumferentially by half that angle (22.5 degrees) to remove the remaining inner wall.

[0012] The invention described in claim 4 is a method for manufacturing a headrest stick according to claim 3, further comprising a third pressing step of pressing a punch having a circular head after the second pressing step. After the thinning process described above, and before the R-chamfering process described above, the process may further include a taper processing step in which the thinned open end portion is processed into a tapered pipe shape. In this tapering process, the thinned open end portion, which has been processed by spinning or other processes, is shaped into a tapered pipe. Subsequently, the R-chamfering process described above is performed to create a chamfer with a radius of, for example, 5 mm or more. This improves the accuracy of the R-chamfering process on tapered pipes. [Effects of the Invention]

[0013] According to the invention described in claim 1, the tip of the leg portion of the headrest stay is rounded off, thus complying with the regulations on internal protrusions in the European unified vehicle regulations and ensuring the safety of the occupant. Furthermore, at the boundary (continuous portion) between the rounded-off portion and the straight portion, a protruding piece is formed that projects inward from the internal hole of the pipe. This increases the bending strength of the continuous portion of the headrest stay, thereby enhancing safety.

[0014] According to the invention described in claims 1 to 4, in the manufacturing process of a headrest stay in which the tip (lower end) of a pair of legs is rounded to form a hemispherical shape, no chips or other debris remain inside the pipe during the thinning process. Therefore, the chip removal (cleaning) process becomes unnecessary, which can be expected to simplify the work process and shorten the work time. As a result, it contributes to reducing the cost of the headrest stay. In addition, since the thinning of the pipe opening end is done in stages using multiple punches of different (or the same) shapes, it is possible to prevent the occurrence of cracks at the end. [Brief explanation of the drawing]

[0015] [Figure 1] This is a partially cutaway front view showing the tip of a headrest stay according to one embodiment of the present invention. [Figure 2] This is a front view (a) showing the tip of a headrest stay and a side view (b) showing the punch head in the pressing process using a regular hexagonal punch head in the manufacture of a headrest stay according to one embodiment of this invention. [Figure 3] This is a front view (a) showing the tip of a headrest stay during the pressing process using a circular punch head in the manufacture of a headrest stay according to one embodiment of this invention, and a side view (b) showing the punch head. [Figure 4]Front view (a) and side view (b) showing the tip of the headrest stay in the taper processing step of the headrest stay according to an embodiment of the present invention. [Figure 5] Front view (a) and side view (b) showing the tip of the headrest stay in the R chamfering step in the manufacture of the headrest stay according to an embodiment of the present invention. [Figure 6] Schematic diagram showing the opening of the stay terminal part which is the object in the manufacturing method of the headrest stay according to another embodiment of the present invention. [Figure 7] Schematic diagram for explaining the first pressing step using a punch having a gear shape with 8 teeth on its outer peripheral edge according to another embodiment of the present invention. [Figure 8] Schematic diagram of the opening for explaining the result (result of the first pressing step) of using a punch having a gear shape with 8 teeth according to another embodiment of the present invention. [Figure 9] Schematic diagram of the opening for explaining the result of pressing after changing the angle of the 8 - tooth punch according to another embodiment of the present invention. [Figure 10] Schematic diagram of the opening for explaining the result of pressing a punch with a perfect - circle head for finishing after pressing the 8 - tooth punch twice according to another embodiment of the present invention.

Embodiments for Carrying out the Invention

[0016] Hereinafter, embodiments of the manufacturing method of the headrest stay according to the present invention will be specifically described with reference to the drawings.

Examples

[0017] Hereinafter, with reference to FIGS. 1 - 5, the manufacturing method of the headrest stay according to an embodiment of the present invention will be described.

[0018] Figure 1 shows the terminal portion of a headrest stay manufactured by the manufacturing method of the headrest stay according to this invention. This headrest stay 11 is formed by bending a single round iron pipe into a gate shape (inverted U shape). Both ends (parallel portions) of the single iron pipe serve as its legs 110 and are detachably fixed to, for example, the upper end of the seat back of an automobile seat. The upper ends of both legs 110 of the headrest stay 11 are connected at the top (in other words, roughly in a U shape), and this top and a part of the legs 110 (upper end) are integrated with a predetermined shaped headrest which is a molded body of foamed plastic such as polyurethane. Furthermore, the open end (terminal portion) 120, which is the lower end (tip) of the pair of legs 110, is chamfered with a radius of R. For example, it is formed into a hemispherical shape with a curvature of 5 mm or more. Also, a through hole is formed at the top of the hemisphere. This R-chamfered open end 120 is formed to be thinner than the leg base 121 that is continuous with it. For example, it is about half the thickness of the base 121. Furthermore, at the boundary between the thin-walled portion 120 and the thick-walled base portion 121, there is a protruding piece portion 122 of a predetermined thickness that extends inward in a disc shape towards the opening (through hole of the pipe) as the wall material flows. This protruding piece portion 122 is formed by, for example, pressing a punch (made of high-tensile steel) into the pipe (open end portion 120), which scrapes off the inner wall (by plastic deformation) and causes it to protrude inward. Since the pressing is performed in the following two steps, a wedge-shaped recess is formed at the tip of the protruding piece portion, as shown in the figure.

[0019] The manufacturing method of this headrest stay 11 will be described below with reference to Figures 2 to 5. First, Figure 2 shows the first step in the process of thinning the leg end 120 of the headrest stay 11. A punch P1 having a hexagonal head is pressed into the open end of the end 120 (using a press machine, etc.). During pressing, the entire outer surface of the leg end 120 is firmly fixed and held by a fixing jig (such as an outer diameter chuck) over a predetermined length from its open end. Therefore, a regular hexagonal punch head P1 is pressed into the fixed terminal 120 from its open end by a predetermined length, for example, 10 mm from the opening of the terminal. The maximum diameter of the head is set to be smaller than the outer diameter of the pipe opening and larger than its inner diameter. As a result, a portion of the inner wall of the terminal 120 is stripped away (compositionally deformed) by the head, resulting in thinning. Since this thinning is the first stage, a portion of the inner wall of the open terminal 120 remains that is not removed by the head. In other words, thickness variations occur in the circumferential direction of the inner wall of the terminal opening. For example, on the inner wall of the terminal, the sliding contact portion by the vertices of the regular hexagon of the head P1 is thin, while the contact portions of the other straight sides are thicker. Note that because a regular hexagonal head is used, the indentation shape due to plastic deformation by pressing causes a portion of the inner wall surface to deform plastically in the axial direction, but the remaining part of the inner wall (the part outside the pipe) that does not directly contact the head remains without plastic deformation.

[0020] Therefore, as shown in Figure 3(b), a punch head P2, which has a perfectly circular outer shape, is pushed into the terminal 120 from the opening. The terminal 120 had a thick and a thin section over a predetermined length from the pipe opening, but the thick section is pushed in by the circular head P2 with a predetermined external force along its axial direction. In other words, the terminal 120 shown in Figure 3(a) will have a so-called thin-walled section with a uniform thickness (thin wall). After the second push, a thin-walled section 120, which is a uniform and thin cylindrical section, is formed on the terminal for a predetermined length due to plastic deformation. The outer diameter of the circular punch head P2 is the same as the maximum diameter of the head P2. By performing plastic deformation in two stages by pressing in the punch heads P1 and P2 in this manner, cracks and other damage do not occur at the pipe end, and a thin-walled section with a uniform thickness can be formed. Furthermore, the plastic deformation caused by pressing in forms an inwardly protruding projection 122 at the boundary between the pipe end and the thin-walled section. Figure 3(b) shows the shape of a perfectly circular head.

[0021] As described above, the process of thinning the open end portion 120 at the lower end of these legs includes a first step of pressing a punch having a regular polygonal cross-section (such as a regular hexagon or regular octagon) into the opening at the end of the leg to a predetermined depth, and a second step of pressing a punch with a circular cross-section into the same leg opening to the same depth. Next, a tapering process is performed on the thinned terminal 120 to shape its open end into a tapered pipe (for example, spinning: pressing a spatula against the outer surface of a rotating terminal). This process shapes the tip of the thin-walled cylindrical terminal 120 into a tapered shape. 120A becomes a tapered conical tube. This is to facilitate the subsequent R-chamfering process.

[0022] Next, an R-chamfering process is performed to chamfer the tapered, thinned open end portion 120A. The thin-walled tip portion 120A is rounded to form a hemispherical shape. For example, the end portion 120 of an iron round pipe is pressed against a press mold that has an R-shape (concave shape) of 5 mm or more formed on the inner corner portion to create an R-shape at the tip of the pipe.

[0023] Specifically, the thinning process described above is applied to both ends of a round iron pipe of a certain wall thickness, over a length of 1 to 1.5 times the radius of the R-chamfer shape from the end. For example, a round iron pipe with an outer diameter of 15 mm and an initial wall thickness of 2.5 mm is prepared, and a thickness reduction process is applied to both ends by pressing a punch with a thickness reduction of 1.5 mm over a thinning length of 10 mm. It is preferable to use multiple punches of different shapes for this thinning process, as described above. As a result, a thin-walled section with a wall thickness of 1.0 mm is formed at both ends of the iron round pipe, extending 10 mm from the end. The wall thickness of the thin-walled section should preferably be 40-60% of the initial wall thickness of the iron round pipe, for example, within the range of 1.5-2.8 mm. Next, the end of the iron round pipe is pressed against a press die, which has an R-shape with a radius of 5 mm or more formed on its inner corner, by applying a predetermined external force. As a result, an R-shape is formed on the end of the pipe. The press die is provided with a bottomed circular recess whose diameter is slightly larger than the outer diameter of the iron round pipe. The circular recess has a concave curved surface of a predetermined radius formed by its inclined side surface and semicircular bottom surface.

[0024] Figures 6 to 10 are schematic diagrams illustrating the relationship between a punch and a pipe (stay end portion) to illustrate another embodiment of this invention. Figure 6 shows the pipe before punching. Figure 7 shows the first punching process. Figure 8 shows the state after the first punching is complete. Figure 9 shows the pipe after the second punching is complete. Figure 10 shows the result of the third punching with a circular punch (showing the pipe opening end with half the wall thickness). In this embodiment, in the first pressing step, pressing is performed using a punch P11 having a gear-like shape with an uneven outer edge in its cross-sectional shape (tip shape). The depth is 10 mm. The maximum diameter of the gear (the peaks) is set to a length that leaves half the wall thickness of the pipe end 120A, while the minimum diameter (the valleys) is formed to be shorter than the inner diameter of the pipe 120A. As a result, the initial plastic deformation during pressing (partial scraping off of the inner wall of the end 120A) can be carried out smoothly. The scraped-off portion of the inner wall remains inside the pipe as a protruding part (it is not cut off). In Figure 8, 131 are the eight recesses formed by plastic deformation at the peaks of the gear. 132 shows the remaining portion of the inner wall. The thick-walled portion of pipe 120A that remains undeformed is scraped off and plastically deformed in the same way as above by pressing in a punch P11 with the same head shape, rotated by a predetermined angle (22.5 degrees) in the circumferential direction. The pressing depth is 8 mm. This is shown in Figure 9. In this figure, 133 are the eight recesses formed by scraping off material during the second pressing. These recesses 133 are arranged alternately in contact with the above recesses 131 in the circumferential direction. Therefore, thin protrusions 134 remain at the boundaries of these recesses. Although not shown in the diagram, a circular punch is then pressed in to remove these protrusions 134 (the material of the protrusions remains on the inner wall of the pipe) (to a depth of 6 mm). The outer diameter of the circular punch is half the thickness of the pipe wall to remove all of the protrusions 134. The inner surface of the pipe is then formed as a smoothly curved inner wall from the opening to a depth of 6 mm. As shown in Figure 10, this state results in obtaining a terminal 120A of the stay leg with a terminal wall thickness of approximately half, and the R chamfer can then be made in the desired shape, as in the embodiment described above. Note that Figures 8 to 10 do not show the inwardly protruding portion of the inner wall of the pipe that has been removed. The other configurations are the same as in the above embodiment.

[0025] First, a round iron pipe with rounded edges at both ends is bent into an inverted U-shape, and then plated on the outer surface to obtain a headrest stay. After this, the headrest stay is set in a urethane foam molding mold, liquid urethane raw material is injected and allowed to foam and solidify, integrating it with the headrest pad to form the headrest. [Industrial applicability]

[0026] This invention is useful as a manufacturing technique for headrest stays. [Explanation of symbols]

[0027] 11 Headrest stays, 120 Terminal section (leg terminal), 121 Base of the leg, 122 Projecting piece, P1 Punch head (regular hexagon), P2 Punch Head (Perfectly Round) P11 Punch head (gear-shaped).

Claims

1. A method for manufacturing a headrest stay, comprising a thinning process in which a punch is pressed into the end portion of a headrest stay made of a round metal pipe to thin the end portion, and a hemispherical process in which the end portion is then rounded, wherein the thinning process comprises a first pressing step in which a first punch, whose outer diameter is larger than the inner diameter of the end portion and smaller than the outer diameter of the end portion, is pressed into the end portion to thin a portion of the inner wall of the end portion, and a second pressing step in which a second punch is pressed into the end portion to thin the remaining inner wall from the first pressing step.

2. The method for manufacturing a headrest stick according to claim 1, wherein the head of the first punch is non-circular, such as star-shaped, gear-shaped, or regular polygonal, and the head of the second punch is circular in shape, different from that of the first punch.

3. The method for manufacturing a headrest stay according to claim 1, wherein the first punch has a star-shaped or gear-shaped head, and the second punch has the same shape as the first punch, and is pressed in while rotated by a predetermined angle around its axis from the first punch used in the first pressing.

4. A method for manufacturing a headrest stay according to claim 3, further comprising a third pressing step of pressing a punch having a circular head after the second pressing step described above.

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