JP5921397B2 - Apparatus and method for manufacturing brake piston - Google Patents

Description

  The present invention relates to a brake piston manufacturing apparatus, a manufacturing method, and a brake piston.

  In the hydraulic brake, a piston is slid in a cylinder to move a brake pad and brake the vehicle. In recent years, in order to prevent malfunction of the piston due to corrosion of the sliding surface, a hydraulic brake having a waterproof and dustproof boot that prevents dust from entering between the piston and the cylinder is common.

  Pistons manufactured by cutting (for example, refer to Patent Document 1) and those manufactured by spindle molding (which is an example of rotational plastic processing) (for example, refer to Patent Document 2-4). is there.

JP 2006-283948 A JP 2000-140974 A Special table 2009-520931 Japanese Patent No. 3360821 JP 59-80536 A Japanese Patent No. 3089379 Japanese Patent No. 4108752 International Publication No. 03/058088 JP 2011-102598 A JP 2011-179676 A

  When forming a groove for fitting an annular boot to be assembled between a piston fitted to the cylinder and an opening of the cylinder at an annular end of the cylindrical material fitted to the cylinder of the hydraulic brake, the groove is If it provides by cutting, the part which forms the sliding surface of a piston inevitably becomes a thick structure for the sake of ensuring the intensity | strength of a groove periphery. In this regard, if the groove is provided by spindle molding, the annular end portion is not cut, so that the strength around the groove can be ensured even if the portion forming the sliding surface of the piston is made thin.

  However, if the groove for fitting the boot is provided by spindle molding and the cylindrical material that is the material of the piston is made thin, the contact area of the portion of the brake pad that contacts the pressure plate will be reduced. . Since the reduction of the contact area increases the pressure applied locally to each other, consideration may also be required in the design of the pressure plate.

  Therefore, the present application provides a brake piston manufacturing apparatus, a manufacturing method, and a brake piston that can secure a contact area of a portion that contacts the pressure plate while enabling formation of a groove for a boot on a thinned member. The purpose is to do.

  In order to solve the above-described problem, in the present invention, in addition to the first roller that forms the groove into which the boot fits, the thick-walled portion that is pressed from the axial direction side and extruded from the inner peripheral surface of the annular end portion toward the axial center side. It was decided to provide a second roller for forming

  Specifically, in the brake piston manufacturing apparatus, a rotating means for rotating a cylindrical material fitted in a brake cylinder in the circumferential direction, and an annular end on the opening side of the material are arranged on the outer peripheral surface side of the material. A first roller that forms a groove into which an annular boot that is assembled between a piston that fits into the cylinder and an opening of the cylinder is fitted, and the annular end that is pressed against the outer peripheral surface by the first roller A second roller that presses the portion from the axial direction side of the material and forms a thick portion that is pushed from the inner peripheral surface of the annular end portion toward the axial center.

  The brake piston manufacturing apparatus presses an annular end on the opening side of the material with the first roller from the outer peripheral surface side of the material while rotating the cylindrical material fitted to the cylinder of the brake by the rotating means. Thus, a groove is formed into which an annular boot to be assembled is fitted between the piston fitted into the cylinder and the opening of the cylinder. At this time, there is no need to provide means for pressing the annular end portion pressed by the first roller from the inner peripheral surface side of the material. Since the groove is formed by pressing the annular end on the opening side of the material with the first roller from the outer peripheral surface side of the material, the cross-sectional shape around the groove of the piston is wavy, in other words, the corner It becomes a continuous shape without.

  Moreover, the manufacturing apparatus of the said piston for brakes has pressed the cyclic | annular end part with the 2nd roller from the axial direction side of a raw material. When the annular end portion is simply pressed from the axial direction side of the material, the annular end portion can be pushed out to both the axial center side and the centrifugal side. However, the brake piston manufacturing apparatus presses the annular end on the opening side of the material with the first roller from the outer peripheral surface side of the material, and the second end from the axial direction side of the material. Therefore, the deformation of the annular end portion toward the centrifugal side is restricted by the first roller, and the annular end portion is pushed out only to the axial center side. As a result, the piston manufactured by the brake piston manufacturing apparatus is formed with a thick portion so as to be pushed out from the inner peripheral surface of the annular end portion toward the axial center. By forming the thick portion at the annular end, the contact area of the portion of the piston that contacts the pressure plate increases.

  According to the brake piston manufacturing apparatus described above, since the groove is formed by pressing the annular end portion on the opening side of the material with the first roller from the outer peripheral surface side of the material, the thin material is removed from the piston. Even if it is adopted as a material, a groove for a boot can be formed. In addition, even when a thin piston material is used, a thick part is formed at the annular end on the opening side, so a sufficient contact area can be secured for the part that contacts the pressure plate. It is.

  The first roller has a first outer peripheral surface that forms a bottom surface of the groove and an edge on the opening side of the material among edges on both sides of the groove. And a second outer peripheral surface having a smaller diameter. In addition to the first outer peripheral surface that forms the bottom surface of the groove, by providing a second outer peripheral surface that forms an edge on the opening side of the material, the second roller can deform the annular end portion to the centrifugal side. As a result, a thick portion is formed which projects the inner peripheral surface of the annular end portion toward the axial center.

  In the first roller, a portion of the wall surface of the groove corresponding to the wall surface on the sliding surface side of the piston is inclined, and the wall surface on the sliding surface side of the piston in the wall surface of the groove. May be formed in a tapered shape. Since the pressing surface of the first roller is formed so that the wall surface is tapered, the gradient at the time of roll removal after molding matches the inclination of the wall surface, which is convenient for manufacturing.

Further, the thickness of the annular end portion of the piston in which the contact surface contacting the pressure plate by the second roller is formed at the annular end portion is 1.1 to 1.5 with respect to the thickness of the cylindrical portion of the material. It may be within the range. By using a material in which the ratio of the thickness of the annular end portion of the piston to the thickness of the cylindrical portion of the material is in such a range, it is possible to manufacture the piston while reducing the weight of the piston.

  The present invention can also grasp the above-described brake piston manufacturing apparatus from the side of a method or a product. For example, the present invention is a brake piston in which a cylindrical material fitted in a brake cylinder is rotated in the circumferential direction to perform rotational plastic working, and an annular end on the opening side of the material is connected to the outer periphery of the material. A groove formed by pressing with a first roller from the surface side and fitted with an annular boot assembled between a piston fitted into the cylinder and an opening of the cylinder, and the outer peripheral surface side pressed by the first roller A thick wall portion that is formed by pressing the annular end portion that is pressed by a second roller from the axial direction side of the material, and that is extruded from the inner peripheral surface of the annular end portion toward the axial center side. It may be. When the brake piston is subjected to rotational plastic processing, the cross-sectional shape of the inner peripheral surface of the piston is formed in a curve. Further, the brake piston is formed such that the thick portion is sandwiched between the first roller and the second roller, so that the surface corresponding to the thick portion of the inner peripheral surface of the piston is As it goes to the opening of the piston, it inclines in a direction approaching the axial center and intersects the contact surface that contacts the pressure plate of the brake pad. For this reason, the area which receives the load added when pressing the pressure plate of a brake pad increases, and the surface pressure concerning the contact part between a pressure plate and a piston reduces. In addition, when a shim is inserted between the pressure plate and the piston for the purpose of prevention of brake squeal and heat insulation, the surface pressure applied to the shim is reduced, and the damping action exerted by the shim is more effectively exhibited. Further reduction in brake noise is expected.

  With the above brake piston manufacturing apparatus, manufacturing method, and brake piston, it is possible to form a boot groove on the thinned member, while ensuring the contact area of the portion that contacts the pressure plate.

It is an example of the block diagram of the manufacturing apparatus of the piston for brakes concerning embodiment. It is an example of the enlarged view of an end surface processing roll and a radial direction roll. It is an example of the figure which showed the manufacturing method of the piston for brakes, and is a figure at the time of seeing a piston from the side with respect to an axial direction. It is an example of the figure which showed the manufacturing method of the piston for brakes, and is a figure at the time of seeing a piston from an axial direction. 1 is an example of a structural diagram of a brake piston manufactured by subjecting a material to rotational plastic working by an end face processing roll and a radial roll. FIG. It is an example of the figure which arranged the piston manufactured by the said method, and the piston which formed the groove | channel by cutting. It is an example of the figure which showed the measurement point of hardness data. It is an example of the table | surface which showed the hardness data. It is an example of the figure which showed the modification of the raw material. It is an example of the figure which showed the manufacturing method of the raw material used with the manufacturing method which concerns on embodiment.

  Hereinafter, embodiments of the present invention will be described. The embodiment described below exemplifies one aspect of the present invention, and does not limit the technical scope of the present invention to the following aspect.

  FIG. 1 is an example of a configuration diagram of a brake piston manufacturing apparatus (hereinafter simply referred to as “manufacturing apparatus”) according to an embodiment. The manufacturing apparatus 1 is a so-called rotary plastic processing apparatus (which is an example of a spinning processing apparatus), a collet chuck (which is an example of “rotating means” in the present invention) 2 that grips a workpiece, and an outer peripheral surface of the workpiece. A radial roll (which is an example of a “first roller” in the present invention) 3, and an end surface processing roll (an example of a “second roller” in the present invention) 4 which processes an end surface of a workpiece. Prepare. The collet chuck 2 is connected to a drive shaft of a rotary drive device (not shown) and can rotate the gripped work. In addition, the manufacturing apparatus 1 includes a core pushing rod 5 that is supported so as to be rotatable concentrically with the collet chuck 2. The core push bar 5 presses the work gripped by the collet chuck 2 and supports the work. The radial roll 3 and the end face processing roll 4 are fastened to a rail or the like (not shown) and can move in any direction with respect to the rotation axis of the collet chuck 2.

  FIG. 2 is an example of an enlarged view of the radial roll 3 and the end face processing roll 4. Since the radial roll 3 is a roll that forms grooves on the outer peripheral surface of the workpiece, it has a two-step outer peripheral surface. That is, the outer peripheral surface 13B on the large diameter side and the outer peripheral surface 13S on the small diameter side are formed on the outer peripheral surface of the radial roll 3. On the other hand, since the end surface processing roll 4 is a roll that flattens the end surface of the work by pressing it from the axial direction side, it has a stepless outer peripheral surface.

  Hereinafter, a method of manufacturing a brake piston using the manufacturing apparatus 1 will be described. When the brake piston is manufactured using the manufacturing apparatus 1, a cylindrical material 10 (an example of the “work”) prepared in advance is attached to the collet chuck 2. The material 10 is a cylindrical material that is open at one end, and can be fitted into a hydraulic brake cylinder after the piston is manufactured. As shown in FIG. 2, the material 10 is subjected to drawing processing at the tip end portion on the opening side. The material 10 may be manufactured by any processing method. For example, if a round steel material or a steel plate material is used and cold forged into a cup shape, the material 10 is compared with a material that is not plastically deformed. Thus, it is possible to realize a high-strength piston with improved mechanical properties. Moreover, if the raw material 10 is manufactured using the forging method as described above, the round bottom portion and the like can be formed on a continuous and smooth surface, which is advantageous in terms of strength and enables further thinning. Moreover, since it can be processed into a rounded and smooth surface state as a whole, it can be expected to prevent plating defects, plating cracks, peeling, and corrosion progress. Thus, since the raw material 10 using the forging method can be expected to have various functions and effects, it is more advantageous than a conventional molded product using sheet metal or resin.

  FIG. 3 is an example of a diagram illustrating a method for manufacturing a brake piston, and is a diagram when the piston is viewed from the side with respect to the axial direction. FIG. 4 is an example of a diagram illustrating a method for manufacturing a brake piston, and is a diagram when the piston is viewed from the axial direction. After the material 10 is attached to the collet chuck 2, a rotation drive device (not shown) is started to rotate the material 10. After starting the rotation driving device, the annular end 11 on the opening side of the material 10 is pressed by the end face processing roll 4 from the axial direction side of the material 10 while the material 10 is rotated. It presses with the radial direction roll 3 from the outer peripheral surface of the raw material 10. FIG. Since it is not pressed from the inner peripheral surface side of the material 10 or held by a clamp, setting when the material 10 is processed by the manufacturing apparatus 1 is easy, and the lead time can be shortened.

FIG. 5 is an example of a structural diagram of a brake piston manufactured by subjecting the material 10 to rotational plastic working by the end face processing roll 4 and the radial roll 3. The annular end portion 11 tends to be deformed in the outer or inner diameter direction by being pressed by the end face processing roll 4. However, since the outer peripheral surface of the annular end portion 11 is pressed by the radial roll 3, the annular end portion 11 of the material 10 is pushed and expanded in the radial inner direction by the end face processing roll 4. As a result, the annular end portion 11 rises so that the inner peripheral surface protrudes toward the axial center side, and a thick portion 12 that is pushed out from the inner peripheral surface of the annular end portion 11 toward the axial center side is formed. The thick wall portion 12 is sandwiched between the radial roll 3 and the end face processing roll 4 so that the inner diameter of the piston 18 gradually becomes narrower toward the opening side. Further, since the annular end portion 11 is pressed by the radial roll 3 having a two-step outer peripheral surface, a groove 14 is formed by the outer peripheral surface 13B on the large diameter side of the outer peripheral surface of the radial roll 3, An edge 15 adjacent to the groove 14 is formed by the outer peripheral surface 13S on the smaller diameter side of the outer peripheral surface of the radial roll 3. The groove 14 is a groove into which an annular boot assembled between the opening of the cylinder of the hydraulic brake and the piston 18 is fitted. Further, the edge 15 adjacent to the groove 14 is higher than the bottom surface of the groove 14 in order to maintain the fitted state of the boot fitted in the groove 14, but the boot is interposed between the piston 18 and the opening of the cylinder. It is lower than the sliding surface 16 of the piston 18 so as to ensure a space for accommodation. Further, the groove 14 of the piston 18 is tapered with a wall surface 17 on the sliding surface 16 side being inclined. The wall surface 17 is formed in a taper shape by a portion of the pressing surface of the radial roll 3 corresponding to the wall surface 17 being inclined. Since the pressing surface of the radial roll 3 is formed so that the wall surface 17 is tapered, the gradient when the roll is removed after molding matches the inclination of the wall surface 17, which is convenient for manufacturing. Moreover, it is easy to increase the thickness HM described later. The piston 18 manufactured in this way can be finally assembled to the brake caliper, for example, by polishing or plating the sliding surface 16. Further, since the end surface processing roll 4 performs processing while the sliding surface 16 of the material 10 is chucked by the collet chuck 2, the flatness of the contact surface 19 that contacts the pressure plate of the brake pad, and the sliding surface of the contact surface 19. A squareness with respect to 16 is sufficiently secured, and there is no need to perform a new cutting process.

  If the brake piston 18 is manufactured by the above method, cutting waste can be reduced and the yield of the material can be improved as compared with the case where the groove is formed by cutting.

  Moreover, if it is the piston 18 manufactured by the said method, weight reduction and the improvement of an intensity | strength will be aimed at. FIG. 6 is an example of a diagram in which the piston 18 manufactured by the above method and the piston 118 having grooves formed by cutting are arranged.

  When the groove is formed by cutting, the thickness HS of the portion of the piston 118 where the sliding surface 116 is formed is excessively increased in order to ensure the thickness HM of the portion of the piston 118 where the groove 114 is formed. There is a need to.

  On the other hand, when the piston 18 is manufactured by the method according to the embodiment, the groove 14 is formed by rotational plastic working. Therefore, the thickness HS of the part forming the sliding surface 16 of the piston 18 can be arbitrarily determined without being restricted by the dimension of the part forming the groove 14. Therefore, if it is the manufacturing method which concerns on the said embodiment, the lightweight piston 18 which thinned the site | part which forms the sliding face 16 is producible. For example, in the case of the piston 18 according to the present embodiment, the weight can be reduced by about 20% compared to the piston 118 according to the conventional example.

  In the method according to the above embodiment, the thickness HT of the annular end portion 11 of the piston 18 in which the contact surface 19 that contacts the pressure plate by the end face processing roll 4 is formed on the annular end portion 11 is determined when the piston 18 is manufactured. It is desirable that the ratio of the cylindrical portion 10 of the material 10 to the thickness HS is within a range of 1.1 to 1.5. When the ratio of the thickness HT to the thickness HS is 1.0 or less, the weight of the piston 18 is not reduced, and insufficient surface pressure due to insufficient area of the contact surface 19 in contact with the pressure plate or brake squealing. This is because it has been confirmed by experiment that the piston 18 cannot be manufactured by the method according to the above-described embodiment when a problem such as occurrence occurs.

Further, when the piston 18 is manufactured by the method according to the above-described embodiment, the rotary plastic working is performed without pressing the inner peripheral surface of the annular end portion 11, and the annular end portion 11 has a thick structure. The contact area of the surface 19 is larger than the piston 118 manufactured by the conventional method. As a result, it is possible to reduce the thickness of the pressure plate and suppress uneven wear of the brake pads. Further, since the contact area of the contact surface 19 is larger than the contact surface of the piston 118 manufactured by the conventional method, it is possible to reduce brake noise.

  Moreover, when manufacturing piston 18 by the method which concerns on the said embodiment, the site | part which forms the groove | channel 14 of the piston 18 is wavy shape. That is, when the rotational plastic working is performed as in the above manufacturing method, the cross-sectional shape of the inner peripheral surface of the piston 18 is formed in a curve. The part formed in a curve includes not only the part corresponding to the groove 14 but also the part corresponding to the thick portion 12. For example, the surface corresponding to the thick portion 12 of the inner peripheral surface of the piston 18 is rotationally plastic processed so that the thick portion 12 is sandwiched between the radial roll 3 and the end face processing roll 4. As it goes to the part, it is inclined so as to approach the axial center and intersects with the contact surface 19. For this reason, the area which receives the load applied when the piston 18 presses the pressure plate increases, and the surface pressure applied to the contact portion between the pressure plate and the piston 18 decreases. Further, when a shim is inserted between the pressure plate and the piston 18 for the purpose of preventing brake squealing and heat insulation, the reduction of the surface pressure applied to the shim makes the damping effect exhibited by the shim more effective. It can be expected to further reduce brake noise.

  Further, when the piston 18 is manufactured by the method according to the above-described embodiment, since the annular end portion 11 is plastically processed, it is possible to increase the hardness of the member as compared with the piston 118 of the related art in which cutting is performed. . FIG. 7 is an example of a diagram illustrating measurement points of hardness data. FIG. 8 is an example of a table showing hardness data. In the table of FIG. 8, “Example” is a piston manufactured by the method according to the above embodiment, and “Comparative Example 1” is a piston in which grooves are formed by cutting a forged cylindrical member, “Comparative Example 2” is formed from a test piece plate in a cup shape. The test piece plate according to the “Comparative Example 2” is a plate material having the same strength as the bar material used in producing the “Example” and the “Comparative Example”, and after drawing by a press. Finished by cutting. As shown in the table of FIG. 8, it can be seen that the piston manufactured by the method according to the above embodiment has higher hardness at any measurement point than “Comparative Examples 1 and 2”. In particular, it can be seen that the hardness is remarkably increased at the measurement point B having the smallest cross-sectional area in the case of cutting. That is, if it is the manufacturing method which concerns on the said embodiment, it is possible to raise the mechanical strength (for example, buckling strength) as components. Also, the measurement point C has higher hardness than “Comparative Example 1”, and it can be confirmed from this measurement data that the hardness that can withstand the load from the pressure plate is obtained. Further, according to the method according to the above embodiment, in addition to such an improvement in hardness, for example, an improvement in surface roughness was also observed. According to the experiment, it was confirmed that the surface roughness (Rz), for example, was about 8 to 16 μm in the cutting process and 4 to 6 μm in the manufacturing by the method according to the above embodiment.

  The manufacturing apparatus and the manufacturing method according to the above embodiment may be modified as follows, for example. That is, in the manufacturing apparatus and manufacturing method according to the above embodiment, no means for pressing the annular end portion 11 pressed by the radial roll 3 from the inner peripheral surface side of the material 10 is provided. It is also possible to provide a means for pressing from the inner peripheral surface side with respect to a portion that does not hinder the formation of 12 and the formation of undulation around the groove 14. Moreover, you may give further cutting etc. with respect to the groove | channel 14 and the end surface 19 which were shape | molded with the said manufacturing method.

FIG. 9 is an example of a diagram showing a modification of the material 10. The material applicable to the manufacturing apparatus 1 is not limited to a material in which the leading end on the opening side is subjected to a drawing process like the material 10, for example, a material 110 shown in FIG. 9. In addition, the tip of the opening side may not be drawn. The magnitude of the load that the manufacturing apparatus 1 can tolerate during spinning molding depends on the size of the brake piston to be manufactured, the capacity of the manufacturing apparatus 1, and the like. For example, when the size of the brake piston to be manufactured is relatively large, a load such as that of the material 10 has an excessive load during spinning molding, and the groove 14 and the like cannot be sufficiently molded. It is also possible. However, even if there is such a possibility, as shown in the material 10 shown in FIG. 2, the tip end portion is pushed and narrowed to the axial center side by drawing the tip end portion on the open side. If the produced material is used, it is possible to alleviate the load at the time of spinning molding in the manufacturing apparatus 1 and complete the piston 18 having a desired shape. Moreover, by using such a raw material 10, the dispersion | variation in the internal diameter of the site | part which forms the thick part 12 is suppressed, and it is possible to raise the precision of the piston 18 completed. However, as long as the groove 14 and the like can be sufficiently formed and the accuracy of the completed piston 18 can satisfy the requirements, the material is not limited to the material 10 as shown in FIG. The piston 18 may be manufactured using a material 110 that is not subjected to drawing processing at the open end as shown in FIG.

  In addition, the raw material 10 shown in FIG. 2 used in the said embodiment can be manufactured by the following methods, for example. FIG. 10 is an example of a diagram illustrating a method for manufacturing the material 10 used in the manufacturing method according to the embodiment.

  When manufacturing the material 10 with the tip portion pushed to the axial center side, for example, as shown in FIG. 10A, the raw material 10 set in the die 51 is pressed by a punch 52 and a counter punch 53. Then, the edge of the surface where the brake piston receives the pressure of the brake oil is machined. Next, for example, as shown in FIG. 10 (B), a punch 52 ′ that presses the center of the material 10 to erect a circumferential wall surface, and a counter punch 53 ′ that processes a surface that receives the pressure of the brake oil. Then, the raw material of the raw material 10 is further pressed and processed into a cup shape. Next, as shown in FIG. 10 (C), the raw material 10 which is turned upside down is punched with a punch 52 "for pressing the raw material 10 in the axial direction and a counter punch 53 for drawing the outer peripheral surface of the raw material 10 toward the axial center. Further press to complete the material 10.

1. Manufacturing equipment: 2. Collet chuck: 3. Radial roll: 4. End face processing roll: 5. Core push rod: 10, 110. Material: 11. Ring end: 12 .... Thick part: 13B, 13S, outer peripheral surface: 14, 114, groove: 15, edge: 16, 116, sliding surface: 17, wall surface: 18, 118, piston: 19, end surface: 51 · · Die: 52, 52 ', 52 "· Punch: 53, 53', 53" · Counter punch

Claims (5)

A rotating means for rotating a cylindrical material fitted in a cylinder of the brake in a circumferential direction;
The annular end on the opening side of the material is pressed from the outer peripheral surface side of the material in a state where there is no means for pressing the annular end portion from the inner peripheral surface side of the material, and the piston fitted into the cylinder and the piston A first roller forming a groove into which an annular boot to be assembled between the opening of the cylinder fits;
The second end that presses the annular end portion, the outer peripheral surface of which is pressed by the first roller, from the axial direction side of the material to form a thick portion that is extruded from the inner peripheral surface of the annular end portion toward the axial center. And a roller,
The second roller moves in the axial direction of the material while the peripheral surface of the second roller is in contact with the material and presses the annular end.
Equipment for manufacturing brake pistons. The first roller forms a first outer peripheral surface that forms the bottom surface of the groove, and an edge on the opening side of the material among edges on both sides of the groove, than the first outer peripheral surface. A second outer peripheral surface having a small diameter,
The brake piston manufacturing apparatus according to claim 1. In the first roller, a portion of the wall surface of the groove corresponding to the wall surface on the sliding surface side of the piston is inclined, and the wall surface on the sliding surface side of the piston in the wall surface of the groove is tapered. To form,
The manufacturing apparatus of the piston for brakes of Claim 1 or 2. The contact surface that contacts the pressure plate by the second roller is formed at the annular end. The thickness of the annular end of the piston is in the range of 1.1 to 1.5 with respect to the thickness of the cylindrical portion of the material. Is within,
The brake piston manufacturing apparatus according to any one of claims 1 to 3. Rotating a cylindrical material that fits in a brake cylinder in the circumferential direction;
The cylinder is pressed by the first roller from the outer peripheral surface side of the material in a state where there is no means for pressing the annular end portion from the inner peripheral surface side of the material. Forming a groove into which an annular boot assembled between the piston fitted into the cylinder and the opening of the cylinder;
A thick-walled portion that is pressed from the inner peripheral surface of the annular end portion toward the axial center side by pressing the annular end portion that is pressed on the outer peripheral surface side by the first roller from the axial direction side of the material. Forming a step, and
The second roller moves in the axial direction of the material while the peripheral surface of the second roller is in contact with the material and presses the annular end.
Manufacturing method of brake piston.

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