Metal working – Method of mechanical manufacture – Prime mover or fluid pump making
Reexamination Certificate
2001-03-13
2003-03-11
Rosenbaum, I Cuda (Department: 3726)
Metal working
Method of mechanical manufacture
Prime mover or fluid pump making
C029S888040
Reexamination Certificate
active
06530149
ABSTRACT:
This application is based on Japanese Patent Application No. 2000-071675 filed Mar. 15, 2000, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method of producing a hollow piston used for a compressor. More particularly, the invention is concerned with a method of producing the hollow piston from a blank which is formed by forging.
2. Discussion of the Related Art
It is desirable to reduce the weight of a piston used for a compressor, since the piston is reciprocated in a cylinder bore of the compressor. For reducing the weight of the piston, the piston has been made hollow. In general, the piston used for the compressor includes a head portion which is slidably fitted in the cylinder bore of the compressor, and an engaging portion which engages a reciprocating drive device for reciprocating the piston. The head portion of such a piston is generally made hollow. The piston having the hollow head portion is produced by preparing a cylindrical body member having an open end and a closed end and including a hollow cylindrical section and a bottom portion, and fixing a closure member to the cylindrical body member for closing its open end. In the piston having the hollow head portion, the engaging portion is formed integrally with the cylindrical body member as disclosed in JP-A-11-294320, or the engaging portion is formed integrally with the closure member as disclosed in JP-A-11-303747.
It is known that a blank for the piston having the hollow head portion is formed by casting or forging. The piston blank wherein the engaging portion is formed integrally with the cylindrical body member cannot be produced by forging. Such a piston blank can be produced by casting. Where the piston blank has the engaging portion integrally with the closure member, the weight of the closure member can be effectively reduced by forming a recess at one of opposite ends of the closure member which is remote from the engaging portion. However, it has been impossible to form this recess by forging.
In general, the piston blank formed by forging has a higher degree of strength than that formed by casting, since the material of the forged piston blank has a higher strength and the forged blank does not have blow holes or shrinkage cavities. Where the piston blank is formed by cold forging, the draft can be made smaller than where the piston blank is formed by casting. Accordingly, the weight of the hollow piston can be easily reduced where the piston is produced from the forged blank. Where the piston blank is formed by casting of an aluminum alloy, a gas is likely to be trapped in the material during the casting. In welding the cylindrical body member and the closure member together, the trapped gas expands to cause a protrusion or recess to be formed in the welded portion of the two members, resulting in reduced bonding strength or deteriorated appearance at the welded portion. In contrast, the piston blank formed by forging avoids such problems. Although it is desirable to form the piston blank by forging, the configuration of the piston blank is inevitably limited when the piston blank is formed by forging.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to produce a piston blank by forging, with an increased degree of freedom in configuration of the piston blank.
The object indicated above may be achieved according to any one of the following forms or modes of the present invention, each of which is numbered like the appended claims and depend from the other form or forms, where appropriate, to indicate and clarify possible combinations of technical features of the present invention, for easier understanding of the invention. It is to be understood that the present invention is not limited to the technical features and their combinations described below. It is also to be understood that any technical feature described below in combination with other technical features may be a subject matter of the present invention, independently of those other technical features.
(1) A method of producing a hollow piston for a compressor, the piston including a head portion which is slidably fitted in a cylinder bore of the compressor, and an engaging portion which engages a reciprocating drive device of the compressor for reciprocating the piston, at least the head portion of the piston being hollow, the method comprising a step of preparing at least one piston blank by forging, which piston blank includes an engaging-portion-forming section which provides the engaging portion of the piston, and a head-portion-forming section which provides at least a part of the head portion of the piston, the at least one piston blank being prepared by a two-axes forging process which uses a forging die assembly including a set of two first dies which are movable relative to each other along a first axis which is one of two mutually perpendicular axes, and at least one second die which is movable along a second axis which is the other of the two mutually perpendicular axes.
The method of producing the piston according to the above mode (1) of this invention assures a higher degree of freedom in the configuration of the piston blank to be produced than the conventional method which uses a forging die assembly having forging dies which are movable along only one axis, so that the hollow piston having a reduced weight can be more easily produced according to the present method.
(2) A method according to the above mode (1), wherein the first axis along which the two first dies are moved is perpendicular to an axial direction of the piston blank, while the second axis along which the at least one second die is moved is parallel to the axial direction.
The method according to the above mode (2) is effective to produce the piston blank having concave and convex portions formed or extending in its two mutually perpendicular axes, assuring an improved degree of freedom in the configuration of the piton blank to be produced. Further, the present method permits an easy manufacture of the piston blank having a reduced weight and high strength or durability. Depending upon the configuration of the piston blank to be produced, the two first dies may be moved in the axial direction of the piston blank and the at least one second die may be moved in a direction which is perpendicular to the axial direction of the piston blank.
(3) A method according to the above mode (2), wherein the at least one second die consists of at least one side punch, and the step of preparing the piston blank comprises a step of forming, by forging, the head-portion-forming section by inserting the at least one side punch into an intermediate blank which has been formed by forming the engaging-portion-forming section by forging with the two first dies.
In the method according to the above mode (3), the relative movement of the two first dies along the above-indicated first axis which is perpendicular to the axial direction of the piston blank may take place concurrently with the movement of the side punch along the second axis which is parallel to the axial direction of the piston blank. The method according to the above mode (3), however, permits easy forging of the piston blank having high dimensional and configurational accuracy.
(4) A method according to the above mode (3), wherein the at least one side punch includes a cylindrical portion, and a protruding portion which protrudes from a front end face of the cylindrical portion in the axial direction thereof and which has a non-circular shape in transverse cross section.
In the method according to the above mode (4), there is formed a recess in a part of the head-portion-forming section of the piston blank by the protruding portion of the side punch, so that the piston to be produced has a reduced weight. Although the recess may be formed by a cutting operation, the present method does not require any additional step of cutting the recess. Further, it is in general cumbers
Iwamori Hidekazu
Kato Takayuki
Sugiura Manabu
Cuda Rosenbaum I
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Woodcock & Washburn LLP
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