Metal deforming – By use of closed-die and coacting work-forcer – Forcing work into or within closed die; e.g. – forging
Reexamination Certificate
1999-07-09
2001-03-27
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of closed-die and coacting work-forcer
Forcing work into or within closed die; e.g., forging
C072S478000
Reexamination Certificate
active
06205836
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of manufacturing and a die therefor by which components such as pistons may be forged.
In the interest of reducing weight and improving performance, internal combustion engines normally utilize pistons formed from aluminum or aluminum alloy. Conventionally, these pistons are formed by a casting process. However, when utilizing casting, the full advantages of the aluminum material are not realized. Also, because of the casting process it is generally necessary to make the piston somewhat larger and heavier in order to provide adequate strength, wear resistance and durability.
The full advantages of the aluminum material can be utilized better if the pistons are made by a forging process. However, in connection with the forging of pistons, certain problems may arise.
That is, it is desirable to provide the piston with a dense and relatively uniform structure. However, due to the shape of the piston, this is difficult with conventional forging die, particularly if the forging is done in a single step. That is, the lower portion of the piston, specifically, the lower edges of the skirt and the ribs that connect the skirt to the piston pin bosses require rather extensive extrusion of the material in the forging die.
The area where these parts of the piston are extruded into generally is narrow and there is a problem that cracking of the die in this area may result. In addition, because of the amount of extrusion necessary to form these components of the piston, there is also some possibility of porosity being encountered at the lower extremities of these components.
These problems may be best understood by reference to
FIGS. 1-3
, which show a forged piston of a configuration of the type with which the invention has particular utility and
FIGS. 4 and 5
which are cross-sectional views taken through a conventional forging die arrangement showing the blank in place in FIG.
4
and the finished forging step in FIG.
5
.
As seen in
FIGS. 1-3
, a conventional forged piston is indicated generally by the reference numeral
21
. This forged piston
21
is formed from aluminum alloy and specific materials which may be advantageously used may be described later in the specification. The piston is comprised of a head portion, indicated generally by the reference numeral
22
and which is comprised primarily of an upper surface
23
which cooperates with a recess formed in the cylinder head and the cylinder bore to form the combustion chambers of the engine.
Below this head surface
23
, the head portion
22
is formed with one or more ring grooves
24
in which piston rings are provided for effecting sealing with the associated cylinder bore, These are normally formed by machining the forged blank at the completion of the forging process.
Depending from the head portion
22
on opposite sides thereof are a pair of generally spaced apart skirt portions
25
. These skirt portions
25
are disposed on opposite sides of boss portions
26
in which piston pin receiving openings
27
are formed. Again, the pin receiving openings are machined at the completion of the forging operation. The boss portions
26
are interconnected to the skirt portions
25
by ribs
28
.
Thus, it will be seen that the lower portions of the skirt portions
25
and the ribs
28
must undergo significant extrusion in the forging process in order to form the piston. This may be understood by reference to
FIGS. 4 and 5
which show the forging apparatus by which the piston
21
is formed.
As seen in these figures, there is a female die indicated generally by the reference numeral
29
and which is comprised primarily of two parts consisting of a lower end closure
31
and a cylindrical body member
32
. The end closure
31
has projecting portions that extend upwardly into a cylindrical cavity
33
formed by the cylindrical portion
32
. This cavity is comprised of a pair of side parts
34
which have a deep extent and in which the skirt portions
25
are formed. In addition, there are a pair of circumferentially spaced recessed parts
35
that form the rib portions
28
. These also require substantial extrusion of the material.
A forging male die
36
completes the die assembly and cooperates with the cavities
33
,
34
, and
35
to form the piston
21
.
As may be seen, a blank
37
of the piston material is inserted into the cavity
33
at the upper portion thereof. The pressing die
36
then moves downwardly so as to force the blank into the cavity and downwardly into the portions
34
and
35
so as to form the finished blank, indicated by the reference numeral
38
.
As may be seen, the deep extrusion of the skirt portion
25
and to some extent the rib portions
28
causes two significant problems. First, the clearance in the die is very small in these areas and hence there is a large expansion force that tends to cause cracking the die. In addition, air pockets may form in the lower part of these areas and cause porosity or irregularities in the lower shapes of the skirts
25
and ribs
28
.
It is, therefore, a principal object of this invention to provide an improved forging die and method of forging a piston that will avoid these problems.
It is a further object of this invention to provide a forging die that permits the formation of the skirt and rib portions of the piston without the likelihood of cracking of the die and without causing porosity to exist in these portions of the finished piston.
SUMMARY OF THE INVENTION
A first feature of the invention is adapted to be embodied in a forging die that is comprised of a female die portion defining an internal cavity into which a blank is inserted and extruded through cooperation of a forging die male portion that extends into the cavity and cooperates with the female die so as to extrude a blank into a desired finished shape. This shape conforms generally to the cavity formed by the male and female die portions at the ends of their stroke. This cavity has a deep extrusion portion that defines a relatively narrow lower peripheral edge. One of the die portions is formed from two pieces that have mating edges that extend along the peripheral surface of this cavity extrusion portion and which can move relative to each other slightly so under compressive forces so as to provide stress relief and a path for air escape during the forging process.
Another feature of the invention is adapted to be embodied in a forging process utilizing, a die as set forth in the preceding paragraph. During the forging process, the male and female portions are moved relative to each other with a blank being interposed therebetween to extrude it into the shape formed by the finished cavity. A flash or parting line can be formed in the finished product at the area where the two die pieces meet.
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Koike Toshikatsu
Yamagata Hiroshi
Knobbe Martens Olson & Bear LLP
Larson Lowell A.
Yamaha Hatsudoki Kabushiki Kaisha
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