Metallic sheet hydroforming method, forming die, and formed...

Details Metallic sheet hydroforming method, forming die, and formed... Metallic sheet hydroforming method, forming die, and formed...

2002-05-09

2004-04-20

Jordan, Charles T. (Department: 3644)

Metal working

Method of mechanical manufacture

Shaping by direct application of fluent pressure

C029S890044, C029S463000, C029S524000

Reexamination Certificate

active

06722009

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a metallic sheet hydroforming method using metallic sheets as blanks, as well as a forming die used in the method and a formed part on workpiece.
DESCRIPTION OF THE PRIOR ART
A sheet hydroforming method is known in which peripheral portions of two metallic sheets (hereinafter referred to also as “blanks”) are bonded together, then a fluid is introduced between the blanks, followed by the application of pressure of the fluid, causing the blanks to be bulged.
FIGS. 1A
,
1
B,
1
C, and
1
D illustrate a forming method described in Japanese Patent Application Laid Open No. 47-033864.
FIG. 1A
is a perspective view of two blanks which are each in a ring shape,
FIG. 1B
is a sectional view of a die portion before a forming work in which two blanks bonded together at their peripheral portions are set between upper and lower dies,
FIG. 1C
is a sectional view of the die portion in a completed state of sheet hydroforming, and
FIG. 1D
is a perspective view of a bent tubular part obtained by cutting a formed part on workpiece crosswise.
The blanks shown in
FIG. 1A
are in a state before being subjected to peripheral bonding into a single blank. The blanks are two ring-like blanks
100
and
102
. A pipe-like nozzle
101
is bonded, for example by welding, to the position of a thru-hole formed in a planar portion of the blank
100
. The blanks
100
and
102
are put one on the other and are bonded together for example by welding throughout the whole inner and outer peripheries thereof to afford a workpiece (“bonded blank” hereinafter).
First, as shown in
FIG. 1B
, the bonded blank, indicated at
103
, is set on a lower die
104
, then an upper die
105
is brought down from above by means of a drive unit (not shown), an outer peripheral portion
103
a
and an inner peripheral portion
103
b
of the bonded blank are pressed and sandwiched in between the upper and lower dies, and the nozzle and a pipe
106
are connected together through a thru-hole
105
b
formed in the upper die. Die cavities
104
a
and
105
a
having an inner contour shape which is the same as an outer contour shape of product are formed in the lower die
104
and upper die
105
, respectively. Then, a fluid is introduced between mating surfaces of the bonded blank from a pump (not shown) through the pipe and nozzle, followed by the application of pressure, causing the bonded blank to bulge.
The full-circled bonding of the blanks
100
and
102
is for the purpose of preventing the leakage of fluid from the mating surfaces of the bonded blank.
As shown in
FIG. 1C
, by raising the pressure of the fluid
107
, the metallic sheets bulge into contact with inner walls of the die cavities
104
a
and
105
a
and the forming work is completed. Thereafter, the internal fluid pressure is decreased, the pipe is pulled out, the upper die is raised, a ring-like hollow shell
108
is taken out, and the interior fluid is discharged from the nozzle. The formed part on workpiece is cut crosswise into a desired product size, affording a bent tubular part
109
.
The above method brings about the following advantages in comparison with a method wherein upper and lower parts are manufactured separately by a press stamping method for example and thereafter both are bonded and assembled together by, say, welding.
The first advantage is that the bonding is easy because the blanks are bonded in a flat state. In case of bonding upper and lower stamped parts, it is necessary to use a jig for shape correction and alignment with respect to each of elastically recovered stamped parts, and the number of working steps increases.
The second advantage is that since the working is done using upper and lower dies and fluid, the tool expenses are low in comparison with the press stamping method.
The third advantage is that since a stretch formed portion is created by forming with a tensile stress based on a fluid pressure, a problem such as body wrinkling, which is often observed in press stamping, is difficult to occur.
These advantages are also true of the following prior art examples.
FIGS. 2A and 2B
are diagrams for explaining a forming method disclosed in Japanese Patent Application Laid Open No. 63-295029.
FIG. 2A
is a perspective view of a bonded blank before forming and
FIG. 2B
is a perspective view of a formed part on workpiece.
In this method, as shown in
FIG. 2A
, two blanks
110
and
111
, which are fabricated in a developed shape of a desired product by a press punching method for example, are put one on the other and outer peripheral edges
112
of their mating surfaces are bonded together by a laser welding method for example to afford a bonded blank
113
. The bonded blank
113
is then set within upper and lower dies and pressurized fluid is introduced between the mating surfaces from a suitable bonded blank opening, causing the blank to bulge. As shown in
FIG. 2B
, the resulting formed part is an engine manifold part
117
having a welded line
116
, in which manifold portions
114
and a trunk portion
115
are cut at their end portions.
FIGS. 3A
,
3
B,
3
C,
3
D, and
3
E are diagrams explanatory of a forming method disclosed in Japanese Patent Application Laid Open No. 09-029329.
FIG. 3A
shows blanks
120
and
121
before bonding, the blanks
120
and
121
being formed with half conical recesses
120
a
and
121
a
on flange, respectively, by press stamping.
FIG. 3B
shows a bonded blank
123
obtained by superimposing blanks
120
and
121
one on the other and bonding the two by, say, laser welding along a continuous welded line
123
b
except a conical inlet
123
a
.
FIG. 3C
shows a state in which a peripheral portion of the bonded blank
123
is held grippingly by lower die
125
and upper die
126
attached to a press machine (not shown), then a conical head
127
b
of an injection nozzle
127
is inserted into the inlet
123
by means of a drive unit (not shown) and is pushed against half conical recesses
125
b
and
126
b
on die surfaces. Then, pressurized fluid is injected between the blank mating surfaces from a pump (not shown) through an intra-nozzle channel
127
a
, causing die cavities
125
a
and
126
a
having the same inner contour shape as an outer contour shape of product to bulge. With this bulging motion, a flange
123
c
which has been held grippingly by the dies
125
and
126
moves gradually toward the die cavities
125
a
and
126
a
except the portion near the inlet.
FIG. 3D
shows a completely bulged state in which the blanks were brought into contact with inner walls of the die cavities
125
a
and
126
a
by increasing the pressure of fluid
128
. Thereafter, the pressure of the fluid is decreased and the fluid is discharged from the inlet
123
a
to afford a formed part
129
.
FIG. 3E
shows an example of a tubular part
129
obtained by cutting off the portion located outside the welded line
123
b
and also cutting off both ends of the stretch formed portion of workpiece.
In the above sheet hydroforming methods, the following problems are encountered in injecting the pressurized fluid between the mating surfaces of blanks.
In the forming method shown in
FIGS. 1A
,
1
B,
1
C, and
1
D it is necessary that the nozzle be bonded to the associated blank while assuming a position which permits smooth insertion of the nozzle into the thru-hole formed in the upper die as the bulging motion proceeds. This requirement may not be satisfied in some particular sectional shape of product. Besides, since connection and disconnection between the nozzle and the pipe are troublesome, the productivity is low and automation is difficult.
In the forming method disclosed in Japanese Patent Application Laid Open No. 63-295029, which is illustrated in
FIGS. 2A and 2B
, there is made no reference to a pressurized fluid injecting method.
In the forming method illustrated in
FIGS. 3A
,
3
B,
3
C,
3
D, and
3
E there arises a problem of how to seal the pressurized fluid between the bonded blank inlet and the conical portion of the nozzle.

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