Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Consolidation of powder prior to sintering
Reexamination Certificate
2002-01-18
2003-11-11
Jenkins, Daniel J. (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Consolidation of powder prior to sintering
C425S078000
Reexamination Certificate
active
06645426
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a manufacturing method and a manufacturing device of a green compact having a through-hole at a part connected continuously to a base part or a green compact having a pair of leg parts connected continuously at a base part in which a part between both leg parts is an undercut part.
BACKGROUND ART
Conventional machine parts include P/M (powder metallurgy) product shown in FIG.
1
(
a
), FIG.
1
(
b
), and FIG.
3
(
a
). The product shown in FIG.
1
(
a
) comprises a rack
2
at an end of a base part
1
and has an axis hole
3
penetrating a part connected continuously to the base part
1
formed therein. The product shown in FIG.
1
(
b
) comprises a hook part
5
at an end of an arm
4
extending from the base part
1
and has the axis hole
3
penetrating the part connected continuously to the base part
1
formed therein.
On the other hand, the product shown in FIG.
3
(
a
) is composed of a hook part
22
provided at the front end of a rod part
21
and a pair of leg parts
24
,
24
connected continuously at a base part
23
which is the rear end of the rod part
21
, and has an undercut part
25
between the leg parts
24
,
24
.
Methods for manufacturing such a machine part having the axis hole
3
or the undercut part
25
by P/M include a method in which a green compact in a shape without the axis hole
3
or the undercut part
25
is first sintered, and then, the axis hole
3
is provided by drilling work or the undercut part
25
is provided by cutting work and the like, and a method in which the axis hole
3
or the undercut part
25
is provided at the same time of the powder compaction.
As described in the former method, in a case of performing the drilling work or the cutting work on the sintered compact, the powder compacting is performed using a die having a die hole in a shape matching the contour of a desired molded body in a vertical direction and a pair of punches inserted into the die hole from the upside and underside of the die. First, material powder is filled in a cavity which is formed of the die hole and a lower punch inserted into the die hole from the underside of the die. Next, the material powder is pressurized and compressed by the upper and lower punches to a prescribed thickness and the obtained green compact is taken out from the upside of the die hole. The green compact is sintered, and thereafter, the axis hole
3
is formed by the drilling work or the undercut part
25
is formed by the cutting work. In this method, however, the drilling work or the cutting work is time-consuming and requires an extra cost.
On the other hand, in a case of forming the axis hole
3
or the undercut part
25
at the same time as the time of powder compacting as described in the latter method, a powder compacting device is utilized which comprises, in addition to the die and the upper and lower punches, a horizontal punch or a core movable in a direction perpendicular to a pressurizing direction for shaping the axis hole
3
or the undercut part
25
.
As for the powder compacting device comprising the horizontal punch for shaping the axis hole
3
or the undercut part
25
, a method is known in which the cavity formed of the die hole and the lower punch is filled with the material powder while being penetrated by the horizontal punch, the material powder is compressed to the prescribed thickness by the upper and lower punches, the horizontal punch is pulled out from the obtained green compact, and the green compact is taken out from the upside of the die hole. In this manufacturing method, since the cavity is filled with the material powder while being penetrated by the horizontal punch, the material powder is not uniformly filled into a lower part than the horizontal punch in the cavity, and it is sometimes impossible to shape a green compact especially when it has a shape in which thickness of a periphery of the axis hole
3
or the undercut part
25
(the base part
1
or the leg part
24
) is thin.
As for the manufacturing method in which a core in a shape corresponding to the shape of the axis hole
3
or the undercut part
25
is disposed in the cavity in advance, the cavity with the core disposed therein is filled with the material powder, the upper punch is inserted under pressure from an opening of the cavity, and the material powder is pressurized and compressed so as to obtain the green compact. The core is removable from the pressurized and compressed green compact and, by pulling it from the compacted body, the green compact having the axis hole
3
or the undercut part
25
can be obtained. In this manufacturing method, however, it is difficult to obtain the uniform density of the material powder in a lower part and in an upper part than the core when the material powder is filled.
Another method is also known in which the cavity formed of the die hole and the lower punch is filled with the material powder, the material powder is pressurized and compressed by the upper and lower punches, and the axis hole
3
or the undercut part
25
is punched out by a punch-out punch. However, in this manufacturing method, when the green compact obtained by the pressurization and compression is punched out by the punch-out punch, chipping, breakage or the like may be caused in the green compact.
Moreover, if a part of the periphery of the axis hole
3
or the undercut part
25
(the base part
1
or the leg part
24
) becomes thin due to the forming of the axis hole
3
or the undercut part
25
as shown in FIG.
1
(
b
) or FIG.
3
(
a
), both of the manufacturing methods using the core or the punch-out punch have a disadvantage that breakage may be caused in the thin part when the green compact with the axis hole
3
or the undercut part
25
formed therein is taken out. In a case in which the undercut part
25
is formed, there is also a disadvantage that deformation such as warpage may occur in the leg part
24
in sintering which is performed after the powder compaction.
DISCLOSURE OF THE INVENTION
In order to solve these disadvantages, an object of the present invention is to provide a manufacturing method in which a green compact is having a through-hole or an undercut part can be easily manufactured without causing breakage.
Another object of the present invention is to provide a manufacturing device appropriate for the manufacturing method of the green compact having the through-hole or the undercut part.
To achieve these objects, the manufacturing method of the green compact according to the present invention is characterized in that it comprises a step of filling material powder into a cavity formed of a die having in a vertical direction a die hole in a shape matching a contour of the green compact including a through-hole at a part connected continuously to a base part and a lower punch inserted into the die hole from the underside of the die, a step of obtaining a preform by temporarily compressing the material powder filled in the cavity by means of an upper punch inserted from the upside of the die into the die hole and the lower punch, a step of punching out a shape of the through-hole by inserting a punch-out pin having a shape corresponding to a cross-section of the through-hole into the preform, a step of obtaining a green compact by pressurizing and compressing the preform by means of both of the upper and lower punches in a state in which the punch-out pin is being inserted, a step of pulling out the punch-out pin from the green compact, and a step of taking out the green compact from the cavity.
According to the manufacturing method of the present invention, the lower punch is first inserted into the die hole from the underside of the die so that the cavity is formed of the lower punch and the die hole.
The material powder is then filled in the cavity. When the material powder is filled, the upper punch is inserted into the die hole from the upside of the die and the material powder is temporarily compressed between the upper and lower punches so that the preform is obtained. On this occa
Masuda Tadao
Sato Mitsuhiro
Yoshihara Toshiro
Jenkins Daniel J.
Kobayashi Industry Co., Ltd.
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