Push rod, and process for producing the same

Details Push rod, and process for producing the same Push rod, and process for producing the same

1996-01-29

2001-04-17

Green, Mary Ann (Department: 3682)

Machine element or mechanism

Elements

Pitmans and connecting rods

C123S090610, C029S888200

Reexamination Certificate

active

06216557

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a push rod and particularly, to a push rod including a rod body, and a steel ball bonded to at least one of the end faces of the rod body by an electric resistance welding, as well as a process for producing the same.
This push rod is used in a valve-operating mechanism of an internal combustion engine, a friction clutch and the like.
BACKGROUND ART
There is such a conventionally known push rod including a rod body made of a stainless steel pipe material and a steel ball, which are bonded to each other by projection welding (see Japanese Patent Application Laid-open No. 81909/90).
However, the known push rod has a problem that the push rod is heavy in weight and is expensive in manufacturing cost, because the rod body is made of the stainless steel pipe material.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a push rod of the above-described type, which is lightweight and inexpensive in manufacturing cost.
To achieve the above object, according to the present invention, there is provided a push rod comprised of a rod body, and a steel ball bonded to at least one of the end faces of the rod body by electric resistance welding, wherein the rod body is formed from an aluminum alloy.
The rod body of the above-described push rod is formed from an aluminum alloy and therefore, the push rod itself is light in weight and inexpensive in manufacturing cost, as compared with the push rod having the rod body formed from the stainless steel pipe material.
It is another object of the present invention to provide a process for producing a push rod of the above-described type, wherein the push rod can be mass-produced at an inexpensive cost.
To achieve the above object, according to the present invention, there is provided a process for producing a push rod, comprising the steps of: bringing one of the end faces of a rod body into pressure contact with a steel ball, and supplying an electric current between the rod body and the steel ball to perform an electric resistance welding of the rod body and the steel ball to each other, wherein a pipe material formed of an Al-Mg-Si based alloy is used as the rod body, the welding current I is set in a range of 18,000≦I≦21,000 A, the pressing force P is set in a range of 350 kg f≦P≦400 kg f, and the current supplying time t is set in a range of t<2 cycle.
In the past, it was difficult to weld the aluminum alloy and steel, and it was impossible to obtain a satisfactory welding strength. However, according to the above-described producing process, by specifying the material for the rod body as in the above-described manner, and by setting the welding current I, the pressing force P and the current supplying time as in the above-described ranges, it is possible to firmly bond the aluminum alloy and the steel. Thus, it is possible to mass-produce push rods at an inexpensive cost, the push rods being lightweight and having high bonding strength.
In this case, a strength of bonding between aluminum alloy and steel is equivalent to or exceeds a strength of bonding between steel and steel. It is considered that such an increase in bonding strength is attributable to the fact that a portion of the rod body easily bites into a surface of the steel ball, and such a biting-in portion exhibits an anchoring effect, and/or the fact that a liquid phase produced from the rod body exhibits a good wettability to the steel ball.
However, if the welding current I is smaller than 18,000 A, the bonding strength between the rod body and the steel ball is lowered, and the variation of the bonding strength is increased. On the other hand, if the welding current I>21,000 A, the bonding strength between the rod body and the steel ball is likewise lowered, and the electricity rate is increased. If the pressing force P is smaller than 350 kg f, the bonding strength is likewise low. On the other hand, if the pressing force P is larger than 400 kg f, there is a possibility that the pipe material may be buckled. If the current supplying time t is equal to or larger than 2 cycles, an intermetallic compound is liable to be formed in a bonded area between the rod body and the steel ball, resulting in a substantially lowered bonding strength.


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