JP4846996B2 - Mold piston molding method - Google Patents

Description

  The present invention relates to a mold piston used for a hydraulic cylinder and a hydraulic shock absorber, and a molding method of the mold piston.

  Generally, in a hydraulic cylinder or a hydraulic shock absorber, a piston rod is movably inserted into a cylinder via a molded piston as a piston, and the molded piston is inserted into a cylinder through a synthetic resin ring fitted to the outer periphery of the piston body. It is in sliding contact with the circumference.

  And as what is disclosed in Unexamined-Japanese-Patent No. 2002-276808 (refer patent document 1), as a mold piston used for this kind of hydraulic cylinder or hydraulic shock absorber, for example, it has been developed.

  As shown in FIG. 7, the piston P includes a piston main body 1 coupled to the piston rod 3 and a synthetic resin ring 2 fitted to the outer periphery of the piston main body 1. The ring 2 includes a ring body 2a along the outer periphery of the piston body 1 and a plurality of inner grooves formed on the inner peripheral side of the ring body 2a and fitted into the annular grooves 1a. It is composed of a circumferential annular protrusion 2c and an end lip 2b that is formed at the end of the ring body 1 and warps outward. When the piston P is inserted into the cylinder, the end lip 2b contacts the cylinder inner periphery. It is like that.

  As a method for molding the above-described piston P, the one disclosed in Japanese Patent Laid-Open No. 2002-295679 (see Patent Document 2) has been developed.

  That is, as shown in FIGS. 8A and 8B, the piston P is formed by a piston body 1 having a plurality of annular grooves 1a along the axial direction on the outer periphery, and an outer periphery of the piston body 1. In a mold piston composed of a ring body 2a fitted and a ring 2 composed of an inner circumferential annular projection 2c fitted in each annular groove 1a, a disc-shaped synthetic resin ring base material A The ring body 1 is heated and softened by the die 9 while the inner peripheral end is fitted into the annular groove 1 a on the right end surface side of the piston body 1 and the piston body 1 is fixed by the fixing jigs 7 and 8. The ring main body 2a along the outer periphery of the ring, the inner peripheral ring-shaped protrusions 2c flowed in the respective annular grooves 1a in the next stage, and the lip 2b at the end of the ring main body 2a are formed.

  However, this piston processing method has the following problems. That is, as shown in FIG. 9, when the end lip 2b of the ring 2 is pressed with the die 9 and pressed against the piston main body 1 side, the outer periphery and inner periphery of the end lip 2b are pressed against the die 9 and the piston main body 1, respectively. Therefore, tensile residual stresses X1 and X2 are generated on the outer peripheral side as indicated by arrows, and compression residual stresses Y1 and Y2 are generated on the inner peripheral side.

  As a result, as shown in FIG. 10, the end lip 2b exerts a force on the ring 2 due to the residual stresses X1, X2 and Y1, Y2 immediately after the die 9 is removed with respect to the pressing position Z1 of the die 9. In a state where there is no action, it warps to the position Z2, and if it is left for a long time, it warps greatly to the position Z3.

  For this reason, when trying to insert the piston P into the cylinder with this as it is, the inner diameter of the cylinder is almost equal to the outer shape of the ring 2, so if the end lip 2b is warped at the position Z3, the tightening margin is large. Become.

  Therefore, the upper end edge portion of the end lip 2b is pressed against the inner peripheral surface of the cylinder, and the surface pressure between the end lip 2b and the cylinder is increased to increase the friction.

  This increases the sliding resistance when the piston rod of the hydraulic cylinder or the hydraulic shock absorber is extended, and there is a possibility that smooth movement cannot be achieved, so that the long-term stability of the riding comfort and dryness of the vehicle is lowered.

Therefore, as shown in FIG. 11, after the die 9 is removed, another jig B is used, and the lip 2b is forcibly fitted into the restriction groove 10 of the jig B, so that the lip 2b is attached to the piston body. The piston P as shown in FIG. 7 is formed by bending in one direction and forming a bent portion 2e on the outer periphery.
Japanese Patent Laid-Open No. 2002-276808 (FIG. 1) JP 2002-295679 A (drawing)

  In the conventional molded piston as shown in FIG. 7, the lip 2b is bent toward the piston body 1 and the bent portion 2e is formed on the outer periphery, so that the tightening margin for the cylinder is small, and the bent portion 2e smoothly slides. Although there is a merit that can be performed, in addition to the molding process for fixing the ring 2 to the piston body 1, an additional lip molding process as shown in FIG. 11 is required. There is a problem that the manufacturing cost of the piston increases. Moreover, installation and removal of jigs are difficult and workability is poor.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a mold piston that can be molded only by a normal molding process and can save labor in the molding process and stabilize the manufacturing cost, and a molding method thereof.

In order to achieve the above object, a molding piston molding method according to the present invention includes a piston body having a plurality of annular grooves along the axial direction on the outer periphery, a ring body fitted to the outer periphery of the piston body, and each annular groove. In the molded piston, which is composed of an inner circumferential annular projection fitted to the ring and a ring comprising a lip formed at the end of the ring body, the outer periphery of the ring body is in sliding contact with the inner circumferential surface of the cylinder. Prepare a piston body whose depth of the annular groove is deeper than that of the other annular grooves, and the synthetic resin ring mother whose thickness is also thinner than the dimension between the bottom surface of the outermost annular groove and the inner peripheral surface of the cylinder A material is prepared, and the ring base material is pressed against the outer periphery of the piston main body by a die and pressed, and the ring base material is heated and softened during the pressing step to form the ring main body and the inner peripheral annular protrusion. Process Likewise to be pulled Shin the outer circumference of the end portion of the ring substrate during the process of heating and softening the pushing step is brought into pressure contact with the die, the inner peripheral surface curved surface while leaving a residual tensile stress only to the end outer periphery A step of forming a tapered lip formed, and the outer peripheral surface of the lip is curved while keeping the inner peripheral surface curved by removing the die and cooling, and utilizing the tensile stress of the outer periphery of the end And a step of forming the bent portion raised from the outer peripheral surface of the ring main body to the outer peripheral side at the center or substantially the center of the lip.

  According to the present invention, the following effects can be obtained.

According to the mold piston molding method of the first aspect of the present invention, a piston main body is prepared in which the depth of the outermost annular groove is deeper than the depth of the other annular grooves, and similarly, the bottom surface of the outermost annular groove is prepared. Prepare a synthetic resin ring base material that is thinner than the dimension between the cylinder and the inner surface of the cylinder, press the ring base material against the outer periphery of the piston body with a die and press it, and heat soften the ring base material during the pressing process The ring main body and the inner circumferential annular projection, and the outer periphery of the end of the ring base material is stretched by pressing against the die during the pushing process and the heat softening process. The process of forming a tapered lip with the inner peripheral surface formed into a curved surface while leaving only the residual tensile stress, and the inner peripheral surface is kept curved by removing the die and allowing it to cool A step of forming a curved portion which raised the outer peripheral side of the outer peripheral surface of the ring body by utilizing the tensile stress of the end portion outer peripheral to the central or substantially central lip with curving the outer peripheral surface of serial lip, because made of, No post-processing is required using a jig for bending the lip toward the piston body as in the prior art. This eliminates the need for processing equipment for post-processing, facilitates the processing of the mold piston, increases the speed, and greatly reduces the processing cost of the mold piston. In addition, since the lip is not post-processed with a jig, no forced load is applied to the lip, and the performance and durability of the lip can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The molded piston according to the present invention is used for a hydraulic cylinder, a hydraulic shock absorber, or the like, and the basic structure thereof is shown in FIG. Is the same.

  That is, the piston P obtained by the molding method of the molded piston according to the present invention comprises a piston main body 1 and a ring 2 fitted to the outer periphery of the piston main body 1 as in the prior art. The piston body 1 includes a plurality of annular grooves 1a, 1b, 1c, 1d, 1e, and 1f along the axial direction on the outer periphery, and the ring 2 presses the disc-shaped synthetic resin base material A to the outer periphery of the piston body 1. The ring body 2a along the outer periphery of the piston body 1 formed by heating and softening while being pushed in, the lip 10 provided at the end of the ring body 2a, and the fluid grooves fitted into the annular grooves 1a to 1f It is comprised by the circumference side annular protrusion 2c, and makes the ring main body 1 outer periphery and the lip 10 outer periphery slide-contact with a cylinder inner periphery. In the present invention, the lip 10 is particularly formed in the shape of a cross-sectional brush tip.

  The piston P molding method of the present invention comprises the molding steps shown in FIGS. 8 (a) and 8 (b) and the molding step shown in FIG. 9, and the conventional post-processing step shown in FIG. 11 is omitted. It is.

That is, in the molding piston molding method of the present invention, the piston body 1 having a plurality of annular grooves 1 a, 1 b, 1 c, 1 d, 1 e, 1 f along the outer periphery is fitted to the outer periphery of the piston body 1. A ring 2 comprising a ring body 2a and an inner circumferential annular projection 2c fitted in each of the annular grooves 1a to 1e, and a piston P for sliding the outer circumference of the ring body 2a on the inner circumferential surface of the cylinder. In order to obtain, the piston body 1 is prepared in which the depth of the outermost annular groove 1f is deeper than that of the other annular grooves 1a, 1b, 1c, 1d, and 1e . A synthetic resin ring base material A thinner than the dimension between the bottom surface and the cylinder inner peripheral surface is prepared.

In this state, as shown in FIGS. 8 (a) and 8 (b), FIG. 2, the molding process of the present invention is a process of pressing the ring base material A against the outer periphery 1 of the piston main body 1 with a die 9, and the pressing process. The ring base material A is heated and softened to form the ring body 2a and the inner peripheral annular protrusion 2c, and the outer periphery of the end of the ring base material A during the pushing process and the heat softening process. A step of forming a tapered lip 10 in which the inner peripheral surface is formed into a curved surface while leaving a tensile residual stress only on the outer periphery of the end portion while being pressed against the die 9, and by removing the die 9 and allowing it to cool lordosis was raised on an outer peripheral side of the outer peripheral surface of the ring body 2a by utilizing the tensile stress of the end portion outer peripheral with curving the outer peripheral surface of the lip 10 while maintaining the bent state the inner peripheral surface A step of forming the center or substantially the center of the lip 10 of the part 10A, is made of.

  What should be noted in the molding method of the above-described mold piston is the dimensional relationship between the piston body 1 and the ring base material A. FIG. 2 shows the process of pressure forming the ring base material A with the die 9, and the dimensional relationship will be described assuming that the inner peripheral surface of the die 9 is the inner peripheral surface of the cylinder.

  As the ring base material A, a material set to a wall thickness t as shown in FIG.

  Similarly, as shown in FIG. 2 as the piston body 1, the depth (radius L1) of the endmost annular groove 1f is made deeper (L2> L1) than the depth (radius L2) of the other annular groove 2c, and the piston A difference is prepared in which the difference between the radius L3 of the main body 1 and the radius L1 of the outermost annular groove 1f is H1, in other words, the height of the land 1R is H1.

  When the distance between the outer peripheral surface of the piston body 1 (the outer surface of the land 1R) and the inner peripheral surface of the cylinder is H2, the thickness t of the ring base material A has a dimension that satisfies t <H1 + H2. Prepare in advance.

  In the above case, the length of the ring base material A in the axial direction is equal to the length of the piston body 1 in the axial direction, or slightly closer to the endmost annular groove 1f side than the end of the land 1R of the piston body 1. It is necessary to shape in advance to a length that extends.

  In FIG. 2, the left side surface of the land 1 </ b> R is formed as an inclined surface, but the left side surface may be a vertical surface or a concave or convex curved surface.

  In the molding piston molding method of the present invention, in the above-described state, as shown in FIGS. 8A, 8B and 2, the ring base material A is pressed against the outer periphery of the piston body 1 by a die 9 and pushed. During this pushing process, the ring base material A is softened by heating, and the ring body 2a along the outer periphery of the piston body 1, the inner circumferential annular protrusion 2c flowing into the annular grooves 1a to 1e, and the endmost annular groove 1f. A corresponding lip 10 is formed.

As a result, the tensile residual stress indicated by arrows X and Y remains only on the outer peripheral side of the end portion of the ring base material A, and the lip 10 is formed by this residual stress. Molded into a shape. That is, the tapered lip 10 is formed by forming the inner peripheral surface into a curved surface using the tensile stress at the outer periphery of the end portion.

  As a result, the tensile residual stress indicated by arrows X and Y remains only on the outer peripheral side of the end portion of the ring base material A, and the lip 10 is formed by this residual stress. Molded into a shape.

  In this case, the wall thickness t1 of the base portion of the lip 10 is slightly thicker than the wall thickness t of the ring base material A, but it is clear from experiments that both are substantially equal. The piston body 1 and the ring base material A may be prepared so as to satisfy the condition of H + H2.

  By the way, in the above-described processing step, the ring base material A is heated and softened to the piston body 1 while being heated, but the die 9 is removed and cooled as shown in FIG.

  At that time, the entire ring 2 shrinks in accordance with the temperature drop. At this time, since the thermal expansion coefficient of the synthetic resin which is the ring base material A is much larger than the thermal expansion coefficient of the piston main body 1 made of a metal-based material, the resin material in a portion that can be deformed corresponding to the gap 11. The lip 10 apparently shrinks from the position of the dotted line S to the inner peripheral side in the arrow W direction.

  That is, the root portion of the lip 10 is constrained by contact with the side surface of the land 1R of the piston body 1, and the left end of the lip 10 is not constrained and is sharpened in the shape of an arrow W because it is pointed like a brush tip. The tip of the lip 10 automatically falls to the inner peripheral side after cooling.

  On the other hand, since the residual stress as shown in FIG. 2 remains on the outer peripheral side of the lip 10, when the die 9 is removed, the lip 10 is positioned at the dotted line T as shown in FIG. The curved portion 10A that is slightly raised to the outer peripheral side from the outer peripheral surface of the ring body 2a is formed in the center or almost the center of the lip 10 while maintaining the shape of the brush tip. Is done.

  The reason why the above lip shape is generated is that the generated tip shape is generated by heat shrinkage or release of residual stress of the synthetic resin itself, which is the material of the lip portion.

  The curved portion 10A does not increase in surface pressure even when slidably in contact with the inner peripheral surface of the cylinder, does not cut the oil film on the inner periphery of the cylinder, and can prevent the occurrence of stick-slip.

  FIG. 5 shows another embodiment of the piston P of the present invention, which forms a step portion 1g on the left side surface of the land 1R in a two-step or multi-step manner, reliably crushes the ring base material A, The coupling with the piston body 1 is made stronger. Other structures and operational effects are the same as those of the embodiment of FIG.

  Similarly, FIG. 6 shows another embodiment of the present invention, in which the outermost annular groove 1f is formed as a tapered surface whose diameter is reduced toward the outer end (left side in FIG. 6), and the gap 11 is enlarged. Thus, the deformation of the lip 10 toward the inner peripheral side is performed well and reliably. Other structures, operations, and effects are the same as those of the embodiment of FIG.

  In each of the above embodiments, in order to form the gap 11 between the lip 10 and the endmost annular groove 1f, as shown in FIG. 2, the depth of the endmost annular groove 1f is changed to another annular groove. The piston body 1 is prepared in advance with a depth greater than the depths 1a to 1f or with the bottom surface of the endmost annular groove 1f as a tapered surface as shown in FIG. 6, but the following method can also be used as another embodiment. .

  That is, the ring body 1a to 1f having the same depth is prepared as the piston body 1, and the ring corresponding to the lip 10 with respect to the wall thickness t corresponding to the ring body 2a side of the ring base material A is prepared. The tip of the base material A having a thickness less than the thickness t is prepared in advance, and in this state, the same processing method as described above is performed, thereby forming the brush tip-shaped lip 10 and the lip 10 and the outermost lip 10 together. A gap 11 is formed between the end annular groove 1f.

It is a partially cut longitudinal front view of a mold piston according to the present invention. It is an expanded sectional view of the state pressed with the die | dye at the time of mold piston shaping | molding of FIG. It is an expanded sectional view of the state which removed the dice | dies at the time of mold piston shaping | molding of FIG. It is a partial expanded sectional view of the mold piston after shaping | molding. It is a partially expanded front view of the mold piston which concerns on other embodiment. It is a partially expanded front view of the mold piston which concerns on other embodiment. It is a partially cut longitudinal front view of a conventional mold piston. (A) and (b) are sectional views of a piston body, a ring base material, and a die showing a process of forming a conventional molded piston. It is an expanded sectional view which shows the residual stress at the time of the conventional mold piston shaping | molding. It is an expanded sectional view of the edge part lip part generated at the time of conventional mold piston molding. It is an expanded sectional view which shows the post-process of the lip | rip of the conventional mold piston.

Explanation of symbols

1 Piston body 2 Ring 1a, 1b, 1c, 1d, 1e, 1f Annular groove 2a Ring body 2c Protrusion 9 Die 10 Lip A Synthetic resin material P Mold piston

Claims (1)

Formed at the end of the ring body with a piston body with a plurality of annular grooves along the axial direction on the outer circumference, a ring body fitted to the outer circumference of the piston body, an inner circumferential annular protrusion fitted to each annular groove In the molded piston, which is composed of a ring made of a lip, and in which the outer periphery of the ring body is slidably contacted with the inner peripheral surface of the cylinder, the piston body whose depth of the outermost annular groove is deeper than the depth of the other annular grooves Prepare a synthetic resin ring base material whose wall thickness is thinner than the dimension between the bottom surface of the outermost annular groove and the inner peripheral surface of the cylinder, and press the ring base material on the outer periphery of the piston body with a die. Pressing the ring base material during the pressing step and softening the ring base material to form the ring main body and the inner peripheral annular projection, and the ring base material during the pressing step and the heat softening step. Outside edge A step to be pulled Shin in pressure contact with the dice, forming a lip tapered inner circumferential surface while leaving a residual tensile stress only to the end outer periphery and formed into curved surface, and then cooled to remove the dice While curving the outer peripheral surface of the lip while keeping the inner peripheral surface curved , the curved portion raised from the outer peripheral surface of the ring body to the outer peripheral side using the tensile stress of the outer periphery of the end Or a molding piston molding method characterized by comprising the step of molding in the substantially center.

Images