JP2008286254A - Piston forming method and piston - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem wherein a dispersion conventionally exists between molded pistons. <P>SOLUTION: This piston forming method comprises cutting a billet at a predetermined length to obtain a billet piece, preliminarily pressing the billet piece to form a centering positioning portion thereon, and then pressing and extrusion molding the billet piece with punching work using the centering positioning portion as a criterion to mold a cylindrically peripheral wall and a fitting portion in a concentric shape at the same time. In this case, pressing and extrusion molding can be performed so that the outer diameter of the cylindrically peripheral wall is a predetermined (designed) size without the need for cutting the outer peripheral face of the cylindrically peripheral wall. In this case, the billet is constrained and cut and the billet piece is cut at a predetermined length, whereby the pressing and extrusion molding is performed so that the outer diameter of cylindrically peripheral wall is the predetermined size without the need for cutting the outer peripheral face of the cylindrically peripheral wall. This piston is obtained by pressing and extrusion molding the billet piece in this method to mold the cylindrical peripheral wall and the fitting portion. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piston forming method including a fitting portion capable of fitting a tip end portion of a piston rod inside a head portion of a cylindrical peripheral wall having an opening on the bottom surface, and a piston.

  As shown in FIGS. 1 and 2, the conventional piston has an opening 2 on the bottom surface of the cylindrical peripheral wall 1, and a fitting portion 4 is formed inwardly at the center of the inner side of the head 3 of the cylindrical peripheral wall 1. The fitting portion 4 is recessed in an arc shape that can be fitted with the tip of the piston rod, and two concave grooves 6 for fitting an O-ring are formed on the outer peripheral surface 5 of the cylindrical peripheral wall 1. The conventional forming method of this piston is that a billet piece obtained by cutting a billet (metal round bar) into a predetermined length is pre-pressed to adjust its thickness, and then press-extruded with a punch to form a cylindrical peripheral wall 1 and an opening. After forming the portion 2, the head 3, and the fitting portion 4, the outer peripheral surface 5 of the cylindrical peripheral wall 1 is cut or ground to form a concave groove 6 for fitting an O-ring on the outer peripheral surface 5 in a ring shape. Two are formed, and the outer peripheral surface 5 is cut or ground until a predetermined outer diameter is obtained, and the end surface portion (opening portion end surface: skirt portion) 7 and the head portion 3 of the opening portion 2 are also cut.

In the conventional piston forming method, the billet is cut to a predetermined length (free cutting) without being constrained (fixed) reliably, so that the length, shape, outer diameter size, etc. of the cut billet pieces vary. For this reason, there were the following problems.
(1) The outer diameter and thickness of the cylindrical peripheral wall 1 of the obtained piston, the end face portion of the opening 2 from the head 3 even if the billet piece is pre-pressed to adjust its thickness and then subjected to pressure extrusion molding. Design dimensions and errors in dimensions (length) up to 7, etc., or dimensions vary from piston to piston.
(2) Even if the pre-pressed billet piece has an error or variation in thickness, shape, outer diameter, etc., the punch is likely to be misaligned from the center of the billet piece when pressed and extruded with a punch. Variations are likely to occur in the shape, thickness, outer dimensions, and the like of the cylindrical peripheral wall 1 of the molded piston.
(3) In order to cut or grind the outer peripheral surface 5 of the cylindrical peripheral wall 1 having variations and finish it to a predetermined size, the cutting amount or the grinding amount varies depending on the individual pistons.
(4) When the billet piece is longer than the predetermined cutting dimension, the length of the cylindrical peripheral wall 1 to be extruded is increased (the depth is increased), so that the cutting for cutting the piston into the predetermined full length dimension is performed. The amount increases and the billet piece (material) is wasted, which contributes to high costs.
(5) If a billet piece with variations in shape and outer diameter is pressed and extruded with a punch as it is, the punch will be easily displaced from the center of the billet piece, and if the position is displaced, the shape and dimensions of the molded piston will also vary. coming out.

  The present invention is a piston forming method capable of pressure-extruding the outer peripheral surface of the outer peripheral surface according to a predetermined size (for example, design size) without cutting or / and grinding the outer peripheral surface of the cylindrical peripheral wall. The present invention provides a molding method and a piston capable of solving the above-mentioned problems.

  The piston forming method of the present application is a method for forming a piston in which a fitting portion capable of fitting a piston rod tip portion is formed inside a head portion of a cylindrical peripheral wall having an opening on a bottom surface, and a billet is cut to a predetermined length. To obtain a billet piece, pre-press the billet piece to form a centering positioning portion on the billet piece, and then press and extrude the billet piece with a punch on the basis of the centering positioning portion to form the cylindrical peripheral wall, This is a method of forming a piston having the fitting part, the opening part, and the head part. In this case, even if the outer peripheral surface of the cylindrical peripheral wall is not cut or / and ground, it can be pressure-extruded so that the outer diameter of the cylindrical peripheral wall becomes a predetermined dimension. In this case, the billet may be constrained or freely cut, but the constrained cutting makes it easy to cut the billet piece into a predetermined length, and the outer peripheral surface of the cylindrical peripheral wall is cut or / and ground. At least, the outer diameter dimension of the cylindrical peripheral wall is set to a predetermined dimension to facilitate extrusion molding.

  In the piston of the present application, the billet piece formed with the centering positioning part is pressure-extruded to form the cylindrical peripheral wall, the fitting part, the opening part, the head part, and the opening end face, and the cylindrical peripheral wall. The outer diameter dimension and the dimension of the end face of the opening are formed into predetermined dimensions (design dimensions) without cutting or / and grinding.

In the piston forming method of the present application, a pre-pressurization forms a centering positioning portion on a billet piece cut to a predetermined length, and the billet piece is subjected to pressure extrusion molding based on the centering positioning portion to form a cylindrical shape. Since the peripheral wall and the fitting portion are formed, the following effects are obtained.
(1) The piston can be pressed and extruded without misalignment, the cylindrical peripheral wall can be formed to a uniform wall thickness, and the outer dimensions can be formed to the design dimensions without cutting or / and grinding. Piston can be molded.
(2) Especially when the billet is constrained and cut, a billet piece having a predetermined length and little external deformation can be obtained. Since the billet is molded, there is almost no variation in the thickness and outer diameter of the cylindrical peripheral wall. For this reason, there is almost no need to perform cutting and / or grinding after molding, there is no problem such as labor and dispersion of the machining, uniform quality pistons can be molded, and piston molding time is shortened, so productivity is improved. It is possible to improve the work and reduce the cost.
(3) Material waste due to cutting is reduced, which can contribute to cost reduction.

  Since the piston of the present application is pressure-extruded to a predetermined size without being subjected to cutting or / and grinding, it becomes a product of uniform quality and low cost.

(Embodiment 1)
An example of a piston forming method and a piston embodiment of the present invention will be described with reference to FIGS. The piston 8 of FIGS. 1 and 2 has an opening 2 on the bottom surface of the cylindrical peripheral wall 1, and an arc-shaped tip (not shown) of a rod can be fitted to the inner central portion of the head 3 of the cylindrical peripheral wall 1. The fitting part 4 is provided. The piston 8 is formed by the following procedure.

(Cutting billet)
As shown in FIGS. 3 and 4, the billet 10 having a round metal bar shape is cut into billet pieces 12 having a predetermined length by the lowering of the cutting punch 11. At this time, the billet 10 is inserted into the billet insertion hole 14 of the holder 13 so that the billet 10 protrudes by a predetermined length, and in this state, the billet 10 is held (restrained) so as not to be displaced, and the protruding portion is lowered by the cutting punch 11. To obtain a disk-shaped billet piece 12 having a predetermined length (predetermined thickness).

(Pre-pressurization)
The billet piece 12 is set in a set space 16 of a disk-shaped pre-pressing die 15 as shown in FIG. The billet piece 12 is set on a liftable knockout 17 disposed below the set space 16. The billet piece 12 is pressed from above by the lowering of the pre-pressing punch 18, and is hemispherically formed at the center of the surface (upper surface) of the billet piece 12 as shown in FIGS. 5 (a), 6 (a) and 6 (b). A recessed centering positioning portion 19 is formed. The pre-pressurizing punch 18 has a convex portion 20 protruding from the center of the bottom surface, and the centering positioning portion 19 can be formed by pressing the convex portion 20 from above. For example, the centering positioning portion 19 may be formed in a ring groove shape near the outer periphery of the billet piece 12 as shown in FIGS. 7A and 7B, for example. As shown in FIGS. 8A and 8B, both the centering positioning part 19 recessed in a hemispherical shape at the center of the surface of the billet piece 12 and the ring groove-shaped centering positioning part 19 outside thereof are provided. Can be formed, and other positions and shapes can also be used.

(Main molding by pressure extrusion)
When the formation of the centering positioning portion 19 is completed, the knockout 17 of FIG. 5A is lowered to take out the billet piece 12 from above the knockout 17, and as shown in FIG. Is set in a set space 22 opened at the center of each. A disk-shaped die pad 23 and a die bolster 24 are laminated under the forming die 21. The billet piece 12 set in the set space 22 of the forming die 21 is press-extruded by a forming punch 25 as shown in FIG. 5B, and the piston 8 having the shape shown in FIGS. 1 and 2 is formed. .

  As shown in FIGS. 5B and 9, the molding punch 25 has a ring-shaped space portion forming projection 26 formed at the tip portion, and a fitting portion forming projection 28 formed concentrically at the inner center portion thereof. The distal end portion 27 of the fitting portion forming projection 28 is formed in a spherical shape, and the distal end portion 27 of the fitting portion forming projection 28 protrudes below the distal end surface 29 of the space portion forming projection 26. In addition, an outer pressurizing portion 30 is formed on the outer peripheral surface of the space portion forming protrusion 26, and an inner pressurizing portion 31 is formed on the inner peripheral surface of the space portion forming protrusion 26. When the forming punch 25 is lowered to press the billet piece 12 shown in FIG. 5B, the tip surface 27 of the fitting portion forming projection 28 is fitted to the centering positioning portion 19 at the center of the billet piece 12. After that, the distal end portion 29 of the space portion forming projection 26 presses against the surface of the billet piece 12, and in this state, the molding punch 25 further descends and is pressed and extruded to form the cylindrical peripheral wall of the piston 8. 1, the opening part 2, the head part 3, the fitting part 4, the outer peripheral surface 5 of the cylindrical peripheral wall 1, and the opening end surface 7 are simultaneously formed. The cylindrical peripheral wall 1 and the opening 2 are pressed and extruded by the space forming protrusion 26, the fitting part 4 is pressed and pressed by the fitting forming protrusion 28, and the opening end surface 7 is pressed by the outer pressing part 30. The fitting peripheral wall end surface 4a is formed by pressure by the inner pressure part 31, and the head 3 is formed by pressing the billet piece 12 flat against the die pad 23 during the pressure extrusion. According to this molding method, the molding punch 25 is positioned by fitting the tip end face 27 of the fitting portion forming projection 28 and the centering positioning portion 19 recessed in a hemispherical shape, and the billet piece is not displaced. Since the whole 12 can be evenly pressurized, the piston 8 having no thickness deviation or eccentricity is formed. In addition, the shape and size of the fitting portion forming protrusion 28, the tip portion 27, the space portion forming protrusion 26, the tip surface 29, the outer pressurizing portion 30, and the inner pressurizing portion 31 of the piston for pressure extrusion molding. If the cylindrical peripheral wall 1, the opening 2, the head 3, the fitting part 4, the outer peripheral surface 5 of the cylindrical peripheral wall 1, the shape of the opening end surface 7, the size, the depth, etc. The outer diameter and length of the cylindrical peripheral wall 1 of the piston 8, the diameter and depth of the opening 2 are formed as designed values.

  The shape and structure of the molding punch 25 may be other than those shown in FIG. 9, and the billet piece 12 is not misaligned according to the position, shape, etc. of the centering positioning portion 5 of the billet piece 12. Any shape and structure that can be pressure-extruded can be used as long as the piston 8 can be molded as designed.

(Groove formation, finishing)
Two concave grooves 6 for fitting O-rings are formed on the outer peripheral surface 5 of the cylindrical peripheral wall 1 of the piston in which the cylindrical peripheral wall 1 and the fitting portion 2 are formed by cutting or grinding, and are shown in FIGS. It is assumed that the piston 8 has the shape shown. In addition to this, the piston 8 is finished by grinding the entire outer peripheral surface 5 or cutting or polishing the opening end surface 7 and the head 3. It can also be plated or painted as needed.

(Embodiment 2)
In the piston forming method of the present invention, if the billet 10 can be cut to a predetermined length, it is possible to cut the billet 10 without being restrained by the holder 13 (free cutting). It is preferable to hold the billet 10 by this method.

(Embodiment 3)
In the piston forming method of the present invention, part or all of the operations of billet cutting, pre-pressurization, pressure extrusion molding, groove formation, and finishing are performed in a batch manner, or in a fully automatic continuous operation. You can also.

  The piston forming method and piston of the present invention are not limited to the forming method and piston, but can be applied to pressure extrusion molding of other metal products and metal products.

The perspective explanatory view showing an example of the embodiment of the piston of the present invention. Cross-sectional explanatory drawing which shows the piston shown in FIG. An explanatory perspective view showing a state in which a billet piece is formed by cutting a billet. Explanatory drawing which shows a mode that a billet is restrained and cut | disconnected and a billet piece is formed. (A) is explanatory drawing which shows a mode that the preforming which pressurizes a billet piece and forms a centering positioning part in a billet piece, (b) pressurizes a billet piece on the basis of a centering positioning part, and is a cylindrical surrounding wall Explanatory drawing which shows a mode that this fitting part is shape-molded, (c) is explanatory drawing at the time of pressure extrusion molding. (A) is a perspective view which shows an example of a mode that the centering positioning part was formed in the billet piece surface center part, (b) is sectional drawing of (a). (A) is a perspective view which shows the other example of a mode that the centering positioning part was formed in the billet piece outer periphery side position, (b) is sectional drawing of (a). (A) is a perspective view which shows the other example of a mode that the centering positioning part was formed in the billet piece surface center part and the outer periphery position, (b) is sectional drawing of (a). Explanatory perspective view showing a forming punch for pressurizing a billet piece to form a cylindrical peripheral wall and a fitting part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylindrical surrounding wall 2 Opening part 3 Head 4 Fitting part 5 Outer peripheral surface 6 Concave groove 7 Skirt part 8 Piston 10 Billet 11 Cutting punch 12 Billet piece 13 Holder 14 Billet insertion hole 15 Pre-pressurizing die 16 Set space 17 Knockout 18 Pre-pressing punch 19 Centering positioning portion 20 Protruding portion 21 Molding die 22 Set space 23 Die pad 24 Die bolster 25 Molding punch 26 Space portion forming protrusion 27 Tip portion of fitting portion forming protrusion 28 Fitting portion forming protrusion 29 Front end surface of the space forming protrusion 30 Outer pressurizing portion 31 Inner pressurizing portion

Claims (4)

  In a piston forming method in which a fitting portion capable of fitting a piston rod tip portion is formed inside a head portion of a cylindrical peripheral wall having an opening on a bottom surface, a billet piece is obtained by cutting a billet into a predetermined length, and a billet Pre-pressing the piece to form a centering positioning portion on the billet piece, and then pressing and molding the billet piece on the basis of the centering positioning portion to form the cylindrical peripheral wall, the fitting portion, the opening, A piston forming method, wherein a piston having a head is formed.   2. The piston forming method according to claim 1, wherein the outer diameter of the cylindrical peripheral wall and the dimension of the end of the opening become predetermined dimensions without cutting or / and grinding the outer peripheral surface and the opening end face of the cylindrical peripheral wall. A method of forming a piston, characterized in that pressure extrusion molding is performed.   3. A piston forming method according to claim 1, wherein the billet is constrained or freely cut.   In a piston in which a fitting portion capable of fitting a piston rod tip portion is formed inside the head of a cylindrical peripheral wall having an opening on the bottom surface, a billet piece of a predetermined length formed with a centering positioning portion is a centering positioning portion. The cylindrical peripheral wall, the fitting part, the opening, the head, and the end face of the opening are molded with the outer diameter dimension of the cylindrical peripheral wall and the dimension of the end face of the opening being cut. Or / and a piston formed into a predetermined dimension without grinding.

Images