JP2015175462A - Process for manufacture of disc brake piston - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a disc brake piston of which weight is made light and having a sufficient buckling strength when the disc brake piston is manufactured.SOLUTION: This invention comprises a first process in which a steel product is preliminary formed into a disc-like member having an outer diameter equal to an outer diameter of a piston 6; a second process in which a disc-like steel product 11 is formed into a hollow cup-shaped component 12 through a cold-forging; a third process in which an end part 13 of an opening part of the cup-shaped component 12 is drawn and formed at an inclination angle θ of 0°<θ≤30° in respect to its barrel part and a diameter of the end part 13 at the opening part side is reduced, the end part 13 at the opening part side is compressed, and the end part 13 is inclined inwardly in respect to the barrel part 14 of the cup-shaped component 12 to make the opening end surface flat; and a fourth process in which a groove 9 is formed at an outer circumference of the end part 13 of the opening part side through a spinning work.

Description

  The present invention relates to a method for manufacturing a disc brake piston used in an automobile or the like.

  Disc brakes are braked by pressing a disc that rotates with a wheel with a pad, and are widely used as braking means for automobiles and the like. FIG. 5 shows an outline of a general disc brake 51. A piston 56 is disposed in the brake caliper 55, and a pad 54 is attached to the tip of the piston 56. A seal material 57 is provided between the brake caliper 55 and the piston 56, and oil and air are taken in and out of the brake caliper 55, so that the piston 56 moves in the left-right direction in FIG. Press and release 53. A dust boot 58 is mounted near the end of the piston 56 on the opening side so that foreign matter does not enter the brake caliper 55. In order to fit the dust boot 58, a groove is formed in the outer peripheral portion on the opening side of the piston 56. 59 is formed. In such a disc brake 51, the piston 56 is formed in a hollow cup shape in order to reduce the weight of the entire brake, and has sufficient strength to press the pad 54 against the disc 53, and at the same time is lightweight. Is required.

  As a method for manufacturing such a disc brake hollow piston, for example, in Patent Document 1, after forming a bottomed cylindrical body by backward extrusion by cold forging, the open end side of the bottomed cylindrical body is squeezed by forward extrusion. A method of forming is disclosed. However, in this manufacturing method, since the groove into which the dust boot is inserted is formed by cutting, and a portion having a small thickness is generated partially, the buckling strength of that portion is significantly reduced.

  Therefore, as a method for manufacturing a piston for improving the strength around the groove, Patent Document 2 describes a position where a groove is formed by forming a steel rod into a cup-shaped part and then compressing the opening of the cup-shaped part. A method for manufacturing a hollow piston is disclosed in which the thickness is increased and then the outer periphery of the position where the thickness is increased is subjected to spinning to form a groove. This method is capable of securing the buckling strength of the piston even if the thickness of the side wall portion is thin by combining the compression processing by cold forging and spinning to harden the groove portion.

JP 51-46670 A JP 2013-92196 A

  However, the piston with the side wall standing upright does not have sufficient buckling strength, and it is difficult to increase the thickness of the end portion on the opening side. That is, for example, when a reduction in the cross-section of the cup-shaped part is set to 70% or more and a significant weight reduction is achieved, there is a possibility that the upright side wall is buckled and deformed during compression processing. Further, when the cross-section reduction rate of the cup-shaped part is less than 70%, the side wall is thick and requires a large force during compression processing, so that there is a problem that the side wall may be buckled and deformed. .

  An object of the present invention is to provide a method for manufacturing a disc brake piston having a sufficient buckling strength while at the same time reducing the weight.

  In order to solve the above problems, the present invention is a method for manufacturing a disc brake piston, wherein a first step of preforming a steel material into a disk shape having an outer diameter equal to the outer diameter of the piston, and the disk A second step of forming a shaped steel material into a hollow cup-shaped part by cold forging, and an end of the cup-shaped part on the opening side of the cup-shaped part by cold forging 0 ° <θ ≦ 30 ° The end portion on the opening side is reduced in diameter and the end portion on the inner side with respect to the body portion of the cup-shaped part. And a third step of flattening the opening end surface and a fourth step of forming a groove on the outer periphery of the end portion on the opening side by spinning. A method for manufacturing a piston is provided.

  It is preferable to perform the third step so that the thickness of the opening end surface in the horizontal direction is 1 to 1.5 times the thickness of the body side wall of the cup-shaped part.

  The cup-shaped component after the second step may have a cross-section reduction rate of 0.7 to 0.8 with respect to the cross-section of the disk-shaped steel material. Further, in the third step, a mandrel may be inserted into the hollow part of the cup-shaped part to restrict the amount of diameter reduction during drawing.

  According to the present invention, a disc brake piston having a light weight and sufficient buckling strength can be manufactured.

It is a longitudinal cross-sectional view which shows the outline | summary of the disc brake using the piston manufactured with the manufacturing method of the piston for disc brakes concerning this Embodiment. It is explanatory drawing which shows the member shape manufactured when each process of the manufacturing method of the piston for disc brakes concerning this Embodiment is implemented, (a) is a 1st process, (b) is a 2nd process, (C) shows the member manufactured by the 3rd process, and (d) shows the member manufactured by the 4th process. It is a longitudinal cross-sectional view which shows the example of the processing method of a 3rd process, (a) is immediately before a process, (b) is in the middle of a process, (c) shows the state at the time of completion of a process. It is a longitudinal cross-sectional view which shows the dimension of the piston shape | molded in the Example. It is a longitudinal cross-sectional view which shows the outline | summary of a general disc brake.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 shows an outline of a disc brake using a piston manufactured by the method for manufacturing a disc brake piston according to the present embodiment. The disc brake 1 presses the disc 3 that rotates together with the tire 2 with pads 4 from both sides to generate frictional force, converts the kinetic energy into heat energy, and brakes the tire 2. As shown in FIG. 1, a piston 6 having a hollow cup shape and having an opening end drawn is formed in a brake caliper 5, and a pad 4 is attached to the opening end of the piston 6. A seal material 7 is provided between the inside of the brake caliper 5 and the outer periphery of the piston 6, and when the oil is taken in and out of the brake caliper 5, the piston 6 moves in the left-right direction in FIG. 1. As the piston 6 moves, the pad 4 attached to the tip of the piston 6 presses the disk 3 or moves away from the disk 3. A dust boot 8 is attached in the vicinity of the opening end of the piston 6, and a groove 9 is formed in the outer peripheral portion of the piston 6 on the opening side in order to fit the dust boot 8.

  FIG. 2 shows the shape of a member manufactured in each step in the method for manufacturing the disc brake piston 6 according to the present embodiment. First, in the first step, as shown in FIG. 2A, a disk-shaped steel material 11 having a size and a shape in which a solid material cut from a bar material or a coil material is matched to the outer peripheral size of the piston 6. And preforming by cold forging. In addition, when using the solid material cut | disconnected from the rod material or coil material match | combined with the outer periphery dimension of piston 6, it is not necessary to preform. Moreover, it is also possible to use as the steel material 11 a material obtained by punching a plate-shaped steel material into a disc shape that matches the outer circumference of the piston 6. In addition, the outer diameter of the steel material 11 should just be substantially equal to the outer diameter of the piston 6 to shape | mold, and does not need to be exactly the same.

Next, as a second step, the disk-shaped steel material 11 is formed into a hollow cup-shaped component 12 as shown in FIG. 2B by backward extrusion of cold forging. In the present embodiment, the cross-sectional area reduction rate (area reduction rate) Rd (= d ² / D ² ) represented by the cross-sectional area of the hollow portion 12a of the cup-shaped component 12 with respect to the cross-sectional area of the disk-shaped steel material 11 is 0.7 to 0.8. If the cross-section reduction rate is less than 0.7, the effect of reducing the weight of the piston 6 is small. On the other hand, if the cross-section reduction rate exceeds 0.8, the die life when cold forging into a cup shape is remarkably shortened. This is because the cross-sectional reduction rate is preferably in the range of 0.7 to 0.8.

  Thereafter, as a third step, the end of the cup-shaped part 12 on the opening side is subjected to compression molding and compression processing to form the cup-shaped part 12 shown in FIG. In order to obtain the cup-shaped component 12 having such a shape, the cup-shaped component 12 is molded by, for example, the processing method shown in FIG. First, as shown to Fig.3 (a), the cup-shaped component 12 shape | molded by the 2nd process is fixed, and the mandrel 21 is inserted in the hollow part 12a. And the metal mold | die 22 which squeezes the edge part by the side of the opening part of the cup-shaped component 12 inside, and presses the opening edge of the cup-shaped component 12 toward a bottom part is pushed toward the downward direction of Fig.3 (a). The mold 22 has an inclined surface 23 that squeezes the side surface of the opening-side end portion 13 of the cup-shaped component 12 inward at a predetermined angle, and a pressing surface that presses the open end of the cup-shaped component 12 downward in FIG. 24. When the mold 22 is pushed downward, as shown in FIG. 3B, first, the end portion 13 on the opening side of the cup-shaped component 12 is gradually inclined inward along the inclined surface 23, and is contracted. Diameter. When the inside of the open end comes into contact with the mandrel 21, the diameter is not further reduced, and the amount of diameter reduction by drawing is restricted. Thereafter, the tip of the cup-shaped component 12 is pressed by the pressing surface 24, and the open end is formed flat as shown in FIG. In this way, it is possible to reduce the diameter of the end 13 on the opening side of the cup-shaped part 12 and at the same time form the opening end flat.

  The third step is performed such that the inclination angle θ of the end 13 on the opening side of the cup-shaped part 12 shown in FIG. 2C is 0 ° <θ ≦ 30 ° with respect to the body portion 14. Is preferred. The reason why the inclination angle θ is provided is to increase the thickness of the side wall portion from the groove 9 to the cup inner diameter side when the groove 9 is formed in a fourth step described later. If this wall thickness is thin, the piston 6 will buckle when it receives pressure from the pad 4. However, if θ exceeds 30 °, there is a possibility that the product shape does not hold when the end portion 13 is compressed in the third step or when the groove 9 is formed in the fourth step.

  Further, it is preferable that the horizontal thickness L of the opening end face after the compression processing is 1 to 1.5 times the thickness t of the body portion 14 of the cup-shaped part 12. The piston 6 of the disc brake is a mechanism that presses the disc 3 through the pad 4 and receives the load at the open end surface of the piston 6. If the area of the end face of the opening is small, the surface pressure of the end face increases and plastic deformation may occur. Therefore, it is preferable that the area of the end face is large. Therefore, the horizontal thickness L of the opening end face needs to be equal to or greater than the thickness of the body portion 14 of the cup-shaped part 12. On the other hand, in order to increase the thickness L of the opening end face, it is necessary to push in the mold 22 at the time of molding in FIG. 3B, but in order to exceed 1.5 times the side wall thickness t. The load on the mold 22 is increased, and the life of the mold 22 is significantly reduced.

  In FIG. 3, the mandrel 21 is inserted into the hollow portion 12 a and the thickness of the upper end surface of the cup-shaped component 12 is increased by the mold 22. This is because, in actual production, variations in product dimensions occur due to variations in material weight and lubrication, so the mandrel 21 is used to stably produce the thickness L. If the product does not require the dimensional accuracy of the thickness L, or if the material has a small variation in weight, the mandrel 21 may not be inserted.

  The end 13 is thickened and hardened by plastic deformation by cold forging performed in the third step.

  Further, in the third step of the present embodiment, the end portion 13 is bent with respect to the body portion 14, so that when the compressive force is applied to the end portion 13, the body portion 14 is less likely to buckle. In the above-mentioned Patent Document 2, the upper end of the cup is compressed by increasing the thickness of the upper part of the cup with the entire side wall standing upright. However, in order to increase only the upper part of the cup by plastic deformation, (In the present invention, the mold 22 in FIG. 3), it is necessary to reduce the friction of the portion in contact with the upper end surface of the cup, and it is necessary to manage by wrapping so that the surface roughness of the mold is reduced. . If the mold surface is rough, the thickness L of the upper end surface of the cup does not increase, and the entire side wall of the cup may be deformed, or the side wall may buckle in some cases.

  A fourth step is performed on the cup-shaped part 12 formed in the third step including drawing and compression. In the fourth step, as shown in FIG. 2 (d), a groove 9 for fitting the dust boot is formed on the outer periphery of the end portion 13 on the opening side reduced in the third step by spinning. Thus, the piston 6 is completed. By forming the groove 9 by plastic deformation that is not a cutting but a spinning process, the groove 9 and its peripheral part can be work-hardened without cutting the forging line. That is, the groove 9 has a sufficient buckling strength against the load received from the pad 4 due to the increase in the thickness of the end portion 13 in the third step and the two work hardenings in the third step and the fourth step. Can be secured.

  Therefore, according to the present embodiment, the cross-sectional reduction rate of the cup-shaped component is 0.7 or more, and sufficient buckling strength can be ensured even when the thickness of the side wall is reduced. And since the cross-section reduction rate can be increased, the weight of the piston 6 can be reduced as compared with the prior art.

  By the way, the end surface on the opening side of the piston 6 needs to be flat in order to press the pad 4 of the disc brake 1. In this regard, when only drawing is performed in the third step, the end surface must be formed by providing a roll or the like for forming the upper end of the cup flat during the spinning process, which is the next step. Complicated and time-consuming. In the present embodiment, as described above, the drawing process and the compression process of the end face are performed simultaneously in the third step, so that the piston 6 can be manufactured with simple equipment. In addition, when the groove part is formed while the upper end surface of the cup is formed flat in the fourth step, there is a problem that the close contact between the groove part forming roll and the material becomes strong and the life of the groove part forming roll is deteriorated.

  The C amount of the steel material used as the material for the piston is preferably about 0.06 to 0.25% by mass. However, in this embodiment, as described above, in order to reduce the weight of the piston, it is desirable that the cross-sectional reduction rate Rd is 0.7 or more. In this case, if the amount of C exceeds 0.15% by mass, molding is performed. The load on the mold at the time increases, and the mold life decreases. Moreover, since the intensity | strength of a piston cannot be ensured if C amount is less than 0.06 mass%, it is still more preferable that C amount is 0.06-0.15 mass%.

  2 and 3, the longitudinal section of the end portion 13 of the cup-shaped part 12 drawn in the third step is linearly inclined and reduced in diameter, but the longitudinal section of the end portion 13 is curved. The diameter may be reduced so as to have a curved shape having a portion.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to this example. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

  Hereinafter, the effects of the present invention will be made clearer by examples. In addition, this invention is not limited to a following example, In the range which does not change the summary, it can change suitably and can implement.

  JIS G4051 (1979) machine structural carbon steel S10C (C: 0.11 mass%, Si: 0.22 mass%, Mn: 0.45 mass%, P: 0.021 mass%, S as work material : 0.010 mass%), and various cup-shaped pistons having different shapes were molded. As shown in FIG. 4, the dimension of the groove in the vertical direction was constant 4 mm, the depth of the groove was 2 mm or more, and the groove was provided from a position 5 mm from the upper end. The height H of the molded product was equal to the outer diameter D, and the thickness of the bottom was t1, which was equal to the wall thickness of the side wall.

  As an example of this invention, it shape | molded with the manufacturing method described in the claim (No. 1-14). Moreover, as a comparative example, after cold forging, a piston (No. 20 to 23) according to a conventional method in which a groove is formed by cutting, and in the third step, the end portion on the opening side is not drawn (No. 17). 18), in the third step, the one in which the angle of drawing at the end on the opening side is outside the range of claim 1 (No. 15, 16, 19) was formed. For cold forging, a 10000 kN crank forging machine was used. The spinning molding was performed using a CNC spinning machine.

  Table 1 shows a list of the shape of each molded product, the drawn shape, and the weight of the product. When the groove is formed into a predetermined shape by spinning, the wall thickness t2 of the groove shown in FIG. 4 is obtained. To secure the buckling strength of the piston, it is necessary to ensure the wall thickness t2 of the groove more than a certain value. . In this example, it was determined that the buckling strength was sufficient when the wall thickness t2 of the groove portion was 4% or more of the outer diameter D (D × 0.04 ≦ t2).

  As shown in Table 1, in the examples of the present invention, the piston could be formed in all cases. In contrast, no. Since 20-23 form a groove | channel by cutting, it is necessary to enlarge thickness t1, and a weight becomes heavy. No. For Nos. 17 and 18, since the third step was not performed, the end face accuracy was poor and the end face thickness L was non-uniform. Moreover, t2 is thin and buckling strength is low. No. Since 15, 16 and 19 had a large inclination angle θ, buckling occurred in the drawing process in the third step, and the shape became defective and the machining was impossible.

  The present invention is useful for manufacturing a piston for a disc brake.

DESCRIPTION OF SYMBOLS 1 Disc brake 2 Tire 3 Disc 4 Pad 5 Brake caliper 6 Piston 7 Seal material 8 Dust boot 9 Groove 11 Steel material 12 Cup-shaped part 13 End part 14 Body part 21 Mandrel 22 Mold

Claims (4)

A method of manufacturing a disc brake piston,
A first step of preforming a steel material into a disk shape having an outer diameter equal to the outer diameter of the piston;
A second step of forming the disk-shaped steel material into a hollow cup-shaped part by cold forging;
By cold forging, the end on the opening side of the cup-shaped part is drawn with an inclination angle θ of 0 ° <θ ≦ 30 ° with respect to the body, and the end on the opening side is compressed. A third step of reducing the diameter of the end on the opening side, inclining the end to the inside of the body of the cup-shaped part, and flattening the opening end surface;
And a fourth step of forming a groove on the outer periphery of the end portion on the opening side by a spinning process.   The third step is performed such that the horizontal thickness of the opening end face is 1 to 1.5 times the wall thickness of the body side wall of the cup-shaped part. 2. A method of manufacturing a disc brake piston according to 1.   3. The disc brake according to claim 1, wherein the cup-shaped part after the second step has a cross-sectional reduction rate of 0.7 to 0.8 with respect to a cross-section of the disk-shaped steel material. For manufacturing a piston for an automobile.   The disc brake according to any one of claims 1 to 3, wherein, in the third step, a mandrel is inserted into a hollow portion of the cup-shaped part to restrict a reduction in diameter at the time of drawing. For manufacturing a piston for an automobile.

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