Metal deforming – Process – Tube making or reshaping
Reexamination Certificate
2001-01-22
2003-06-10
Larson, Lowell A. (Department: 3725)
Metal deforming
Process
Tube making or reshaping
C072S370210, C029S893340
Reexamination Certificate
active
06575009
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for a linear operated type metal forming process for obtaining, efficiently and precisely, a deep recessed pattern on a partial or an entire surface of a tubular blank material having an axial hollow space of a desired cross sectional shape such as triangle, a square, a polygonal, an odd or a circular shape. The present invention can, for example, be preferably utilized for obtaining a so-called VGR type rack bar as a part in a steering device of an automobile. However, the present invention can also be utilized in any different field of application for obtaining a mechanical part or an ornamental product where a formation of a projected or recessed pattern on its surface is required.
2. Description of Related Art
In Japanese Examined Patent Publication (kokoku) No. 3-5892, a metal forming technique for producing, from a hollowed member (a pipe), a rack bar as a part in a steering device is disclosed. In a metal forming process of a rack bar in this patent, a pipe member, which is thermally softened, is held in a die and is subjected to a pressing so that the pipe member is flattened at a location where a rack is to be formed. Then, a die having straight teeth is engaged with the flattened part of the pipe member, while a mandrel is inserted to the central bore of the pipe member. The mandrel is provided with a tapered operating portion, which is engaged with an inner surface of the flattened portion and is forced into the axial bore of the pipe member, which causes the material to be radially outwardly flown into the cavities of the die, thereby forming, on the flattened portion of the pipe member, the straight teeth of which correspond to the straight teeth on the formation die.
The Japanese '892 patent is directed to a formation of a rack bar by a forced penetration of the mandrel into the pipe under an outwardly heated condition. Namely, when the pipe is subjected to a flattening process, the pipe is, at the portion to be flattened, subjected to a heating process, which causes the flattened portion to be softened. Such a softening of the flattened portion causes the later to be inwardly and centrally thickened, thereby causing the flattened portion to be shaped as a convex lens at a transverse cross section thereof. Due to such cross sectional shape of the convex lens of the flattened portion of the pipe, the degree of the engagement of the mandrel with the flattened portion of the pipe can be increased.
The technique disclosed by the Japanese '892 patent is defective in terms of a reduced precision of products, which makes it difficult that the products are actually used. Furthermore, the prior art method is defective also in that its production cost is high due to the fact that the process is complicated, on one hand and that, on the other hand, the cost of the device is high.
SUMMARY OF THE INVENTION
In view of the above, an object of the present invention is to provide a technique for metal forming capable of overcoming the above-noted difficulties in the prior art.
Another object of the present invention is to provide a technique for a metal forming capable of obtaining an increased precision, while preventing the process from being complicated.
According to the first aspect of the present invention, a process is provided for producing an article with toothed portions, such as a pipe shaped rack bar, comprising the steps of:
a) providing a die having, at its inner surface, toothed portions;
b) holding a blank pipe in the die;
c) providing a mandrel having a tapered operating head;
d) inserting, repeatedly, the mandrel into an axial space of the blank pipe, so that the operating head of the mandrel causes the material to flow radially outwardly toward the inner surface of the die, thereby generating toothed portions on the blank pipe corresponding to the toothed portions of the die;
e) keeping, during the repeated insertions of the mandrel, an increased temperature of the work generated by a heat substantially solely by the execution of the insertion of the mandrel to the blank pipe, which temperature is substantially in a range where a so-called work-softening phenomenon is obtained;
f) preventing, during the repeated insertions of the mandrel, the metal from being subjected to an age-hardening, and;
g) maintaining an increased temperature of the work generated substantially solely by a heat due to the execution of the insertion of the mandrel to the blank pipe.
According to this aspect of the invention, during the execution of the metal forming by the repeated insertion of the mandrel to the blank pipe, quasi-warm or semi-warm working condition of a temperature around 200° C. substantially solely generated by the metal is maintained, while preventing an age-hardening from being occurred, resulting in an increased degree of a flowability of metal. Furthermore, under such an increased degree of the flowability of metal, a cancellation of any deviated flow of metal to the die is done, thereby producing a rack bar having teeth of a precision as fine as 32 &mgr;m. Furthermore, according to the present invention, an introduction a blank pipe to the die-set is done under a room temperature, and any pre-heating process is unnecessary. Furthermore, once a clamping of a blank pipe by the die set is done, all the processes for the metal forming of the rack bar are completed without opening the die set. Thus, a highly increased production efficiency is obtained, resulting in a reduced production cost.
According to a second aspect of the invention, a process is provided for producing a rack bar, comprising the steps of:
a) providing a die having, at its inner surface, toothed portions along the length of the die;
b) holding a blank pipe in the die;
c) providing mandrels each having at least one tapered operating head;
d) inserting, repeatedly, the mandrels into an axial space of the blank pipe so that the operating head of the mandrel causes the material to be flown radially outwardly toward the inner surface of the die, thereby generating toothed portions on the blank pipe corresponding to the toothed portions of the die;
e) reversing, alternately, the direction of the insertion of mandrels to the blank pipe for keeping a symmetrical flow of a metal toward the die, and;
f) overlapping the insertion of the mandrel one side of the blank pipe and the withdrawal of the mandrel on the other side of the blank pipe, such that the insertion of the mandrel to the blank pipe in one direction is commenced prior to the completion of withdrawal of the mandrel from the blank pipe in the other direction, and;
g) maintaining an increased temperature of the work generated substantially solely by a heat due to the execution of the insertion of the mandrel to the blank pipe.
According to this aspect, a rack bar of an increased precision can be obtained irrespective of a fact that the production is done under a metal forming principle. Thus, the production efficiency as well as a cost can be highly reduced.
According to the third aspect of the present invention, a pipe shaped rack bar is provided, which is made, purely, of metal forming process from a blank pipe, wherein said metal forming process is such that the blank pipe is subjected to repeated insertions of a mandrel alternately between opposite sides of the blank pipe, while keeping a semi-warm working condition of a temperature around 200° C. substantially solely generated by the execution of the metal forming process, while preventing an age-hardening from being generated, while preventing an occurrence of a deviated flow of metal to the die.
According to this, aspect of the present invention, the rack bar is purely made by a metal forming process. In other words, while any machining process is substantially unnecessary, a precision as fine as 32 micron can be obtained.
According to a fourth aspect of the invention, a pipe shaped rack bar is provided, which is made, purely, of metal forming process from a blank pipe by i
Kabushiki Gaisha Koshingiken
Larson Lowell A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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