Metal working – Method of mechanical manufacture – Prime mover or fluid pump making
Reexamination Certificate
2000-06-01
2002-08-06
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
Prime mover or fluid pump making
C029S888090, C072S328000, C072S334000, C072S353200, C072S354600, C072S453020
Reexamination Certificate
active
06427326
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a connecting rod which connects a piston and a crank shaft together in an engine.
2. Description of Related Art
A connecting rod for an engine has a large-end portion into which is inserted a crank pin which is formed in a crank shaft, a small-end portion into which is inserted a piston pin to be mounted on a piston, and a rod portion which lies between the large-end portion and the small-end portion. A rod main body which is made up by integrally forming the small-end portion, the rod portion, and that half part of the large-end portion which is on the side of the rod portion is connected to a large-end cap which forms the remaining half part of the large-end portion, whereby a connecting rod is assembled.
As a conventional method of manufacturing a connecting rod, there is known the following. Namely, a connecting rod blank which has a large-end potion, a small-end portion, and a rod portion between the small-end and the large-end portion and which is shaped into an integral combination of the rod main body and the large-end cap is manufactured by casting. The connecting rod blank is then divided into the rod main body and the large-end cap (see Japanese Published Unexamined Patent Application No. 195408/1988). However, the connecting rod manufactured by casting has a tendency of being insufficient in strength. As a solution, in a connecting rod in which a high strength is required, the rod main body and the large-end cap are ordinarily manufactured separately by forging. In this conventional method, however, the control of accuracy in the connecting or coupling surfaces of the rod main body and the large-end cap becomes troublesome and a cost reduction becomes difficult.
In Japanese Published Unexamined Patent Application No. 39439/1984, the following method is known. Namely, at the time of cold-coining a forged product which is manufactured by hot-striking, excess metal which is left in a portion to be pierced with a hole is punched out to thereby form a pierced product. It is considered to form the following connecting rod blank by utilizing this art. Namely, a connecting rod blank which has not formed therein holes for the large-end portion and a small-end portion is hot-forged. Then, at the time of cold-coining, a hole is punched in the large-end portion and the small-end portion, respectively, to thereby form a connecting rod blank.
In this method, however, the forming of the entire shape of the connecting rod blank is performed in a hot treatment. Therefore, the step of removing the scales which occur at the time of hot-forging is required and, further, a heating apparatus become necessary. As a result, the cost of manufacturing the connecting rod cannot be reduced to a large extent.
The applicants of this application have earlier proposed the following cold-forged steel in Japanese Patent Application No. 303400/1996. Namely, the steel in question contains in percent by weight (wt %) the following component composition, i.e., 0.05-0.25% of carbon (C), 0.35-0.60% of silica (Si), 0.20-1.30% of manganese (Mn), 0.15-0.60% of chromium (Cr), and further contains one or more selected from the group consisting of 0.030-0.100% of sulfur (S), 0.005-0.040% of tellurium (Te), 0.03-0.30% of lead (Pb), 0.03-0.20% of bismuth (Bi), 0.0005-0.0050% of calcium (Ca), the remaining part being iron (Fe), and also meets the following equations
19≦85(%C)+9(%Si)+3(%Mn)+5(%Cr)≦25 (1)
100(%C)+3(%Si)+3(%Mn)−9(%Cr)+100(%S)−20(%Te)≦23 (2)
This steel is superior in the workability in cold forging and in fatigue strength, so that it is suitable for forming mechanical parts by cold forging.
In view of the above points, the present invention has an object of providing a method of manufacturing a connecting rod in which the connecting rod blank which is shaped into an integral combination of a rod main body and a large-end cap is cold-forged in a single pressing cycle to thereby largely reduce the cost of manufacturing the connecting rod.
SUMMARY OF THE INVENTION
In order to attain the above and other objects, the present invention is a method of manufacturing a connecting rod for an engine, the connecting rod comprising a rod main body and a large-end cap. The method comprises the steps of: forming, by cold forging, a connecting rod blank which is shaped into an integral combination of a rod main body and a large-end cap and which has a large-end portion, a small-end portion, and a rod portion therebetween; and splitting the connecting rod blank into the rod main body and the large-end cap. The step of forming the connecting rod blank is performed by a double-action type of forging apparatus comprising: an upper die which is movable up and down; a lower die; a large-end portion punch which is respectively provided in each of the dies so as to be movable therethrough and to lie opposite to each other at a portion to pierce the large-end portion of the connecting rod blank; and a small-end portion punch which is respectively provided in each of the dies so as to be movable therethrough and so as to lie opposite to each other at a portion to pierce the small-end portion of the connecting rod blank. The step of forming the connecting rod blank comprises: a first forging step of closing the upper die toward the lower die while forging a preform having a shaft portion which corresponds to the rod portion of the connecting rod blank, that large-end mass portion on one end of the shaft portion which corresponds to the large-end portion of the connecting rod blank, and that small-end mass portion of the connecting rod blank which corresponds to the small-end portion of the connecting rod blank, to thereby roughly form the preform into the shape of the connecting rod blank; a second forging step of protruding each of the large-end portion punches and each of the small-end portion punches, respectively, into a forming space between both the dies while forging those parts of the large-end portion and the small-end portion which are to be pierced, to thereby fill underfills inside the forming space; and a piercing step of protruding the large-end portion punch and the small-end portion punch which are provided in one of the upper and lower dies until they reach the other of the dies while pushing out, from the forming space, the large-end portion punch and the small-end portion punch which are provided in the other of the upper and lower dies, to thereby punch out pads remaining in those parts of the large-end portion and the small-end portion which are to be pierced. The first and second forging steps as well as the piercing step are carried out in a single pressing cycle.
According to this invention, the connecting rod blank is split into the rod main body and the large-end cap after the connecting rod blank has been formed. Therefore, special control of accuracy in the connecting surfaces of the rod main body and the large-end cap is not required any more, with the result that the cost of manufacturing the connecting rod becomes smaller. Further, those parts of the large-end portion and the small-end portion which are to be pierced or punched with a hole, respectively, are forged with the large-end portion punch and the small-end portion punch, respectively, in the second forging step. In this manner, it becomes possible to push the material of the preform into underfills (or underfilled parts) which are likely to occur in the cold forging, to thereby fill the underfills with the material. The accuracy in shape of the connecting rod can thus be secured. Thereafter, the pads left in the parts to be pierced is finally punched out by the large-end portion punch and the small-end portion punch which are provided in one of the upper and lower dies. It is thus possible to form by cold forging the connecting rod blank in one pressing cycle with a good accuracy. This results in a large reduction in the cost of manufacturing the connect
Akimoto Seiichi
Akiyama Yoshiro
Asada Takashi
Hatayama Tadatomo
Kihara Takashi
Armstrong Westerman & Hattori, LLP
Compton Eric
Honda Giken Kogyo Kabushiki Kaisha
Hughes S. Thomas
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