Metal tools and implements – making – Blank or process – Die
Reexamination Certificate
2002-02-19
2004-09-21
Payer, Hwei-Siu (Department: 3724)
Metal tools and implements, making
Blank or process
Die
Reexamination Certificate
active
06792828
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a press die for molding a sipe blade and a method for making the press die. More particularly, it relates to a press die for molding a sipe blade which can efficiently mold a sipe blade having a complicated shape such as three-dimensional shape and having excellent mechanical strength characteristics and which can reduce production cost due to its simple structure, and a method for simply and efficiently making a press die for molding a sipe blade having a complicated shape such as a three-dimensional shape by a casting method.
Tire molds are difficult to make by machining methods because they have complicated designs with sharp dent-shaped corner portions or undercut shapes, and generally they are made by casting methods. Of these molds, many of them are made of aluminum alloys, cast irons or cast steels. This tendency is conspicuous, especially, when the design shapes of tires have many grooves of about 0.1-3.0 mm in width which are called “sipes” (specifically, studless tires, etc.) and these tire molds cannot be made by mechanical methods.
Here, the term “machining method” means forming methods other than those causing contraction in the molding, such as casting, and as examples thereof, mention may be made of various molding methods employed in conventional methods for making metal molds for molding two-dimensional shape sipe blades, such as wire electric discharge machining, NC machining which uses a ball end mill, and additionally, various methods which can directly mold the shape of metal molds, such as ultrasonic machining and electric discharge machining. Usually, wire electric discharge machining is employed because partial metal molds consisting of a pair of top and bottom molds can be obtained at a time. As for other molding methods, for example, partial metal molds consisting of a pair of top and bottom molds are obtained by making one of the molds and then making a reversal mold thereof.
As shown in
FIG. 36
, thick grooves
102
and
103
such as ribs and lugs are formed on a tire
101
, but for special uses such as studless tires, sipes
104
which are thin grooves of about 0.1-3.0 mm in width are sometimes formed in addition to ribs and lugs to improve gripping force and drainage.
The sipes
104
are two-dimensional in shape, such as corrugated shape and zigzag shape at the ground contact face (profile face) for obtaining the effects of improving gripping force and drainage due to edge effects. Recently, for further improvement of tire performance, it is demanded that not only the profile face, but also the shape in the direction of diameter of tire have the similar two-dimensional shape (moreover, complicated curved faces such as a three-dimensional shape), namely, it is demanded to make the shape of sipes into three-dimensional shapes.
As shown in FIGS.
37
(
a
)-
37
(
e
), since a three-dimensional shape sipe
107
b
can improve block stiffness of tire
106
as compared with the conventional two-dimensional shape sipe
107
a
, the tire
106
does not undergo buckling even at driving and braking and can be further improved in gripping force.
When the shape of a tire mold having the above sipes is made by casting out, the mold strength is sometimes insufficient, and in this case, especially, when a tire mold made of an aluminum alloy is used, there is generally employed a method of casting-in a sipe blade previously made of a material of high strength. In this case, since a tire mold having sipe is complicated in its design, a casting method is used instead of machining method.
As shown in FIGS.
38
(
a
)-
38
(
e
), according to conventional methods for producing a tire, it is generally produced by a method which comprises disposing a sipe blade
111
(hereinafter sometimes referred to merely as “blade”) at a pattern
112
for casting a tire mold(hereinafter sometimes referred to merely as “pattern”) and then casting with a molten metal a blade
114
having finally a shape complementary to sipe
104
(see
FIG. 36
) to integrate with a metal mold
116
for molding a tire which is a reversal mold. In
FIGS. 38
, a rubber mold
113
and a gypsum mold
115
are used.
As shown in FIGS.
39
(
a
) and
39
(
b
), as a result of pursuing both the cost and the productivity, the sipe blade
111
which is used for conventional method for producing a tire has been mainly produced by a method which comprises press molding a thin plate material
121
which is punched or laser cut (wire electric discharging cutting) using a press die
10
a
made by wire electric discharge machining.
However, as shown in FIGS.
39
(
a
) and
39
(
b
), since the press die
10
a
is made by wire electric discharge machining, this method can be adapted to only the press die
10
a
having a two-dimensional shape formed by linearly moving a wire
117
, and the resulting sipe blade ill is limited to one which has a two-dimensional shape (having a corrugated shape in the monoaxial direction). Thus, it is difficult to obtain a sipe blade which can remarkably improve the tire performance. The sipe blade
111
shown in
FIG. 39
(
c
) consists of a cross vent hole
122
, a locking hole
123
, a sipe formed portion
124
, and a portion
125
which is cast in the metal mold for molding.
As a method for making a sipe blade having a three-dimensional shape, a method is known which comprises subjecting a press die for molding to three-dimensional NC machining by a ball end mill, and press molding a thin raw material using the press die, but this method is high in cost and is not practical.
Furthermore, there is proposed a method of making a press die for molding by a casting method (JP-A-62001-25831). However, according to this method, preparation of shape data or setting of complicated shape is sometimes difficult, and, for example, it has been very difficult to optionally combine a plurality of molded shapes as one protrusion unit of protrusive mountain shape (protrusive mountain shape or protrusive dimple shape).
Moreover, in many cases, a sipe blade of three-dimensional shape is required to be a combination of a plurality of those having basic shapes in which the number of the molded protrusive mountains is changed in the range of about 1-20 protrusive mountains. Therefore, according to conventional methods, metal mold or casting pattern must be made one by one, and this is troublesome.
For solving these problems, it is known that as shown in FIGS.
40
(
a
) and
40
(
b
), many divided press dies
131
,
132
in which a minimum number of molded protrusive mountain shapes are divided are previously made (FIG.
40
(
a
)), and these are combined in a desired shape to make one press die (combined (fabricated) mold). However, there is a problem that such combined (fabricated) press dies
133
,
134
,
135
are not suitable for mass-production from the point of strength or from the practical point.
As shown in FIGS.
41
(
a
) and
41
(
b
), when it is necessary that the sipe blade
141
has a basic shape (primary shape) consisting of protruded shapes (protrusive dimple)
144
and dented shapes (dented dimple)
145
(FIG.
41
(
a
)), and additionally a molded shape (secondary shape)
143
which is larger than the basic shape in size is given to the whole sipe blade
141
(FIG.
41
(
b
)), position of disposition of the primary shapes at the top and bottom molds of the divided press die must be changed, and it is very difficult to make a press die for molding with taking these points into consideration.
As shown in FIG.
42
(
a
), there is a further problem that at the time of actual molding of sipe blades, in the case of the shape being more complicated, such as having the two-dimensional shape
153
and the three-dimensional shape
154
, the drawn shape of the sipe blade after press molding has the curved shape
152
, being different from the shape
151
assumed before press molding. Thus, it is difficult to put the peripheral shape in a given scope. This problem can be solved by trimming the peripheral shape of the sipe blade after press molding.
Burr & Brown
NGK Insulators Ltd.
Payer Hwei-Siu
LandOfFree
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