Cross Reference to Related Application
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This application is based upon and claims the benefit of priority from
Japanese Patent Application No. 2004-103839, filed on March 31, 2004, the entire
content of which is incorporated herein by reference.
Field of the Invention
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The present invention relates to a rolling die for rolling bolts or screws.
More particularly, the invention relates to a rolling die having stabilized formation
precision and high durability.
Background
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Fasteners, such as bolts or screws, continuously form screw crests and
troughs on the peripheral surface with each single rotation by holding a rod-like
workpiece between a pair of flat die pieces provided with moderately inclined
processing teeth on one side surface, and relatively moving one flat die with respect to
the other side surface. Typically, the processing teeth have the same cross-sectional
shape, extending from a bite portion that includes a starting point on one surface side to
a roll-off portion that includes an end point.
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Recently, in order to increase the pinching strength and to lighten the
weight, the raw material of bolts or screws has evolved from carbon steel or processed
steel to relatively hard chrome molybdenum steel (SCM type steel). Corresponding to
the change in raw materials of bolts and screws, cold die steel (SKD type steel) is an
example of raw materials used for rolling dies.
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However, since the cross-sectional shape of the processing teeth of the
rolling dies is the same through a bite portion, a finishing portion, and a roll-off portion,
cracking or localized damage occurs easily near the tooth tip of the bite starting point
where a hardened workpiece is initially processed, and the product life of the die is
shortened.
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In a flat rolling die provided with a bite portion, an interim finishing portion,
and a finishing portion, it has been suggested that the tooth tip line of the interim
finishing portion coincide with that of the finishing portion, that the tooth height become
larger closer to the bite portion, and that the tooth tip of the bite portion be sharpened
more than or the same as that of the interim finishing portion. (See Japanese Laid
Open Utility Model Hei 1-37800).
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In a flat rolling die disclosed in Japanese Laid Open Utility Model Hei1-37800,
the teeth in the bite portion sharply cut into the raw material, and since the
finishing portion presses the raw material with dispersed pressure on both sides,
smooth rolling becomes possible. Because the teeth in the bite potion sharply cut into
the raw material, however, there have been problems of cracking or localized damage
when rolling a workpiece of a hardened raw material.
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Thus, it is desirable to resolve the above problems and provide a rolling
die capable of long product life and precise rolling even for processing hard workpieces.
The present invention is directed to solve one or more of these problems and to provide
a rolling die with processing teeth at a bite portion that include an initial bite starting
point in the workpiece having a cross-sectional shape with an obtuse angle greater than
that of finish processing teeth, the obtuse angle becoming successively greater from
the bite portion to the finishing portion.
SUMMARY OF THE INVENTION
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A rolling die is provided. The rolling die includes a bite portion having bite
processing teeth at a bite starting point for a workpiece, and a finishing portion having
finishing processing teeth. The bite processing teeth at the starting point in the bite
portion have lower tooth height than the finishing processing teeth in the finishing
portion. The bite processing teeth have a larger tooth tip angle and a larger trough
angle than the finishing processing teeth.
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It is to be understood that both the foregoing general description and the
following detailed description are exemplary and explanatory only and are not restrictive
of the invention, as claimed.
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The accompanying drawings, which are incorporated in and constitute a
part of this specification, illustrate embodiments of the invention and together with the
description, serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
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Fig. 1 illustrates a rolling die according to one exemplary embodiment of
the present invention;
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Fig. 2 is a cross-sectional view of a bite starting point of a bite portion of
the rolling die of Fig. 1;
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Fig. 3 is a cross-sectional view of an interim point of the bite portion of the
rolling die of Fig. 1;
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Fig. 4 is a cross-sectional view of an different interim point of the bite
portion of the rolling die of Fig. 1;
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Fig. 5 is a cross-sectional view of a finishing portion of the rolling die of Fig.
1;
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Fig. 6 illustrates the bite portion and the finishing portion of the rolling die
of Fig. 1;
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Fig. 7 illustrates a workpiece being processed at the starting point of the
rolling die of Fig. 1;
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Fig. 8 is a cross-sectional view of the work piece and the rolling die of Fig.
7;
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Fig. 9 illustrates a workpiece being processed at the interim point of the
bite portion of the rolling die of Fig. 1;
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Fig. 10 is a cross-sectional view of the workpiece and the rolling die of Fig.
9;
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Fig. 11 illustrates a working piece at a different interim point of the bite
portion of the rolling die of Fig. 1;
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Fig. 12 is a cross-sectional view of the work piece and the rolling die of Fig.
11;
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Fig. 13 illustrates a working piece at the finishing portion of the rolling die
of Fig. 1;
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Fig. 14 is a cross-sectional view of the workpiece and the rolling die of Fig.
13;
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Fig. 15 illustrates a rolling die according to another exemplary
embodiment of the present invention; and
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Fig. 16 illustrates a workpiece being processed by the rolling die of Fig. 15.
DESCRIPTION OF THE EMBODIMENTS
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Reference will now be made in detail to exemplary embodiments of the
invention, examples of which are illustrated in the accompanying drawings. Wherever
possible, the same reference numbers will be used throughout the drawings to refer to
the same or like parts.
A rolling die according to one embodiment of the invention includes a bite portion
having bite processing teeth and a finishing portion having finishing processing teeth.
The bite portion includes bite processing teeth at a bite starting point for a workpiece.
The processing teeth at the starting point in the bite portion have a lower tooth height
than the processing teeth in the finishing portion, and the bite processing teeth at the
starting point in the bite portion have a larger tooth tip angle and a larger trough angle
than the finishing processing teeth in the finishing portion.
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In this regard, since the processing teeth of the bite starting point are
shallow and have an obtuse angle for the initial bite at a workpiece processed for bolts
and the like, cracking or localized breakage becomes less likely to occur at the tooth tip
at the bite portion that includes the bite starting point. Furthermore, since the cross-sectional
shape of the bite processing teeth gradually changes from the bite starting
point to the finishing portion, successively deeper and shaper bites are formed in the
workpiece. Consequently, a desired shape of screw crest and trough can be precisely
formed even in a workpiece made of a hard material. This can provide more precise
processing of a workpiece with a hard material and allows a longer product life for the
rolling die.
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The cross-sectional shape of the bite processing teeth gradually changes
to that of the finishing processing teeth from the bite starting point to the finishing
portion. Tooth height as used herein refers to the distance between the tooth tip and
the tooth bottom of the processing teeth, the tooth tip angle refers to the angle (so-called
crest angle) having its center at the tooth tip, and the trough angle refers to the
angle between two processing teeth located next to each other.
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In one embodiment of the rolling die, the tooth height of the bite
processing teeth becomes continuously higher toward the finishing portion, and a trough
becomes deeper and wider from the bite portion to the finishing portion. The processing
teeth at the bite starting point provide bites that are shallow and obtuse. Then the
processing teeth next to the processing teeth at the bite starting point provide shallow
obtuse bites. Another set of processing teeth at the bite portion provide deeper and
sharper bites to the workpiece. Subsequently, as the workpiece is processed at the
finishing portion of the rolling die, a desired shape of screw crests and troughs is
precisely formed. The "trough bottom" as used here refers to a portion at a trough
between the processing teeth, in which its trough angle is smaller than the trough angle
at the tooth tip.
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According to one embodiment of the present invention, the tooth tip angle
and the trough bottom angle in the bite portion may be 60 degrees or greater, and the
trough angle between the processing teeth of the finishing portion may correspond to a
standard valued set for a screw. In this regard, the rolling die may process the
workpiece more accurately with gradually deeper and sharper processing teeth angles
and provides a longer product life. Moreover, the tooth tip and trough angle of the
processing teeth at the bite starting point may be 90 degrees or greater, and the tooth
tip and trough angle of the processing teeth at the finishing portion may be, for example,
60 degrees or greater.
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It should be noted that, in one embodiment of the present invention, the
rolling die may be provided with a roll-off portion with a roll-off angle in the finishing
portion at the opposite side from the bite portion. The roll-off portion may include
processing teeth having the same tooth height and tooth tip angle as the processing
teeth at the finishing portion. With such a roll-off portion, it is possible to process a
workpiece with desired screw crests and troughs and release the workpiece from the
rolling die smoothly.
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In addition, a rolling die according to one embodiment may include a pair
of die members of a solid-rectangular shape that has the bite portion and the finishing
portion on its side. The rolling die may provide rolling by means of a set of flat dies and
extend the product life of the rolling dies. Moreover, in a pair of die members, one
member may be fixed (coast side) and the other member may be movable (drive side).
Alternatively, both members may be movable with respect to each other, and such a
rolling die may be called a dual-drive type.
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In another embodiment, the rolling die may include a pair of die members
having a cylindrical shape that has the bite portion and the finishing portion on their
surfaces. The rolling die having the pair of cylindrical die members may provide
accurate processing of a workpiece and extend the product life of the die.
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Fig. 1 illustrates a rolling die for rolling screws according to one exemplary
embodiment of the present invention. The rolling die 1 includes a first die 2 at a
movable (drive) side and a die 10 at a fixed (coast) side. Dies 2, 10 may be formed, for
example, from cold die steel (JIS: SKD 11). As shown in Figure 1, the dies 2, 10 may
have die members 3, 13 that provide a solid-rectangular shape. Each of the die
members may include, at the side facing the other 4, 14, bite portions 6,16, finishing
portion 7, 17, and roll-off portion 8, 18 in the reverse direction. Processing teeth a, b, c,
d slightly inclined relative to the side surfaces 4 and 14 and having different cross-sectional
shapes from bite starting points 5, 15 to finishing points 9, 19 are provided at
each of the portions 6-8, 16-18.
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As shown in Fig. 7, the bite portions 6, 16 are provided with a bite angle
slightly inclined relative to the back surfaces (opposite side of the side surfaces 4, 14) of
die members 3, 13. The roll-off portions 8, 18 are provided with a roll-off angle inclined
opposite to the bite angle at the bite portions 6, 16. In addition, the finishing portion 7,
17 are parallel to the backside of the die members 3, 13. Furthermore, the processing
teeth a, b, c, d are symmetrically positioned with a plane view of the side surfaces 4, 14
of the dies 2, 10.
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Moreover, the dies 2,10 may be fixed to a rolling device (not shown in
figures) by clamps (not shown in figures).
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One example of the cross-sectional surface of the dies 2,10 is described
as follows:
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Vertical: 35mm x Lateral: 38mm, Length of the die 2 on the movable side:
380mm, Length of the die 10 on the fixed side: 370mm.
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The die 2 on the movable side may be 10mm longer than the die 10 on
the fixed side to achieve a smooth bite of a workpiece between the bite portion 6 at the
side surface 4 and the starting point 15 at the side surface 14. This also provides a
smooth release of the workpiece from the roll-off portion 8 at the side surface 4 and the
finishing point 19 at the side surface 14. In other words, when rolling the workpiece
between the starting points 5, 15 at the side surfaces 4, 14, the workpiece may be
prevented from being accidentally released and from being damaged during release
from the finishing points 9, 19.
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The processing teeth a at the starting points 5, 15 in the bite portions 6, 16
of the dies 2, 10, as shown in Fig. 2, may include a plurality of processing teeth t1
formed in parallel having a pitch p of, for example, approximately 1.6mm. The
processing tooth t1 has a low tooth height h1 and may have a tooth tip angle 3 of
about 90 degrees, and a trough angle 91 between the processing teeth t1 and t1 of 90
degrees. Moreover, the tooth height h1 is the distance between the tooth tip m1 and
the trough bottom v1. In addition, the difference in distance between the tooth tip m1
and the tooth tip m4 of the processing teeth d (processing tooth t4) at the finishing
portion 7, 17 is roughly 0.4mm, originating in the bite angle comprising an inclination of
bites 6 and 16.
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The processing tooth t1 is located at the bite starting points 5, 15 in the
bite portions 6, 16, and until approximately the middle of the bite portions 6, 16, the
cross-sectional shape of the tooth t1 gradually becomes closer to that of the processing
teeth b (processing tooth t2) by continuously changing its depth and width of the trough
angle 92.
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In the bite portions 6,16 of the dies 2, 10, the processing teeth b located
approximately 60mm from the starting points 5, 15, as shown in Fig. 3, have a plurality
of processing teeth t2 in parallel and the same pitch p described above. Each
processing tooth t2 has a slightly higher tooth height h1 and may have its tooth tip angle
3 of 90 degrees, a tooth tip angle 4 of 60 degrees. Between the processing teeth t2
and t2, a trough bottom angle 2 of the trough bottom v2 having a trapezoidal shape
may be 60 degrees, and the trough angle 1 near the tooth tip m2 may be 90 degrees.
In other words, the processing tooth t2 near the tooth tip m2 has the same shape as
that of the processing tooth t1, but has a trough bottom v2 that has a narrow trough
angle 2, providing a concave groove.
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A cross-sectional shape having the same shape as that of the processing
tooth t2 is gradually become prevalent from the starting points 5, 15 to the middle of the
bite portions 6, 16. Near the finishing portions 7, 17, the depth and width of the trough
bottoms v2, v3 having a trough angle 2 continuously becomes deeper and larger, and
the cross-sectional shape of the tooth t2 gradually becomes closer to that of the
processing teeth c (processing tooth t3).
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In the dies 2, 10, the processing tooth c located approximately 120mm
from the starting points 5, 15, or in the finishing portions 7, 17, as shown in Fig. 4, has a
plurality of processing teeth t3 in parallel and the same pitch p described above. The
processing tooth t3 has a higher tooth height than the tooth heights h1 and h2, and may
have a tooth end angle 4 of 60 degrees. Between the processing teeth t3 and t3, the
trough angle 2 at the trough bottom v 3 may be 60 degrees, and the trough angle 1 of
the tooth tip m3 remains at 90 degrees. However, the trough bottom v3 that has a
trough angle 2 is deeper and wider than the processing teeth b, and the trough angle
1 is shallower and narrower than that of the processing teeth b.
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Furthermore, the cross-sectional shape of the processing tooth t3 is
substantially an equilateral triangle, and only the tooth tip m3 has the same shape as
the tooth tips m1 and m2 of the processing teeth t1 and t2. Therefore, the trough
bottom v3 becomes an even narrower concave groove in comparison with the trough
bottom v2.
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The cross-sectional shape which is the same as that of the processing
teeth t3 gradually becomes prevalent from the middle of the bite portions 6, 16 to the
area close to the finishing portions 7, 17. Until the finishing portions, 7, 17, the depth
and width of the trough bottom v3 having a trough angle 2 continuously becomes
deeper and larger, and the cross-sectional shape of the tooth t3 gradually becomes
closer to that of the processing teeth d (processing tooth t4).
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The finishing portions 7, 17 of the dies 2,10 and the processing teeth d of
the roll-off portions 8, 18, as shown in Fig. 5, have a plurality of processing teeth t4 in
parallel and the same pitch p as that described above. The processing teeth t4 have a
higher tooth height than the tooth heights h1-h3, and may have a tooth angle 4 of 60
degrees and the trough angle 2 between the processing teeth t3 and t3 of 60 degrees.
The trough angle 2 may correspond to a standard value set for a screw. In other
words, the processing teeth t4, as shown in Fig. 5, are formed such that the entire
cross-sectional shape is a substantially equilateral triangle. However, the crest of the
tooth near the tooth tip m4 may have a smaller arch than the tooth tip m1-m3 of the
processing teeth t1-t3. As a result, the trough bottom v4 becomes a deep concave
groove that is narrower in comparison with bottom trough v3.
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The processing teeth t4 are located roughly 180mm from the starting
points 5, 15 and in the entire surface of the finishing portions 7, 17 and continues the
same cross-sectional shape to the finishing points 9, 19 in the roll-off portions 8, 18.
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The processing teeth a-d (processing teeth t1-t4) such as those described
above are illustrated in Fig. 6 and are formed in the side surfaces 4, 14 of the die
members 3, 13 by, for example, a grinding process by a numerically controlled device or
an electric discharge process.
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A rolling method of a bolt by using the rolling die 1 will be described. As
shown Fig. 7, the die 2 on the movable side is slid along in the direction of the arrow in
the figure with respect the die 10 on the fixed side. A rod shaped workpiece n0 is rolled
between the bite portion6 of the die 2 and the starting point 15 of the die 10. The
workpiece n0 includes a rod steel formed from a relatively hard chrome molybdenum
steel (SCM type steel).
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The rolled workpiece n0 shown in Fig. 7 rotates between the starting
points 5, 15 of the dies 2,10. At this time, as shown in Fig. 8, in the peripheral surface
of the workpiece n0 rolled between the processing teeth a, a at the bite starting points 5,
15 in the bite portions 6, 16, a trough z1 having a moderate arch shape is formed by the
tooth tip m1 of the processing tooth t1 having a moderately shallow bite.
Simultaneously, the peripheral surface of the workpiece n0 is smoothly inserted into the
shallow trough v1 between the processing teeth t1 and t1, and for example, a crest y1
of the moderate arch is formed so that the crest angle 1 is, for example, 90 degrees.
As a result, a workpiece n1 is initially formed with the crest y1 and the trough z1 having
a moderately arched shape in alternative positions.
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At the starting points 5, 15 of the dies 2, 10, only the tooth tip m1 of the
processed tooth a(t1) moderately bite into the workpiece, and the periphery of the
workpiece n0 is expanded by the shallow trough bottom v1. Thus, cracking and
breakage may be prevented, and smooth elastic deformation may be achieved with a
dispersed load.
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As shown in Fig. 9, the movable die 2 is moved further to the left, and the
workpiece n1 is rolled between the middle of the bite portions 6, 16 of the movable die 2
and the fixed die 10. At this time, the workpiece n1, as shown in Fig. 10, is processed
between the processing teeth b and b (t2 and t2) in the bite portions 6, 16. At the
trough z1, the tooth tip m2 of the tooth t2 bits into the workpiece n1 to form a slightly
deeper trough z2, and the crest y1 pressed in the narrower trough v2 between the
processing teeth b and b to form a slightly shaper crest y2.
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The trough bottom v2 of the processing teeth b(t2) is formed by gradually
deepening and widening at the trough angle 2 from the trough bottom v1 of the
processing teeth a(t1) from starting points 5, 15. As a result, as shown in Fig. 10, a
workpiece n2 is formed with the alternatively positioned peripheral crest y2 and trough
z2.
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Furthermore, as shown in Fig. 11, by moving the movable dies 2 further to
the left, the workpiece n2 is rolled between the bite portions 6, 16 near the finishing
portions 7, 17. At this time, the workpiece n2, as shown in Fig. 12, is positioned
between the processing teeth c and c, and the tooth tip m3 of the processing teeth c(t3)
bites in the trough z2 to form a deeper and larger trough z3. In the trough bottom v3
between the processing teeth t3 and t3, a crest y2 is pressed to form a shaper crest y3.
The trough bottom v3 of the processing teeth c(t3) is formed by gradually deepening
and widening the trough bottom v2 of the processing tooth t2. As a result, as shown in
Fig. 12, a workpiece n3 is formed with the alternatively positioned crest y3 and trough
z3.
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As shown in Fig. 13, by moving the movable die 2 further to the left, the
workpiece n3 is rolled between the finishing portions 7, 17 of the fixed die 10 and the
movable die 2. As shown in Fig. 13, at this time, the workpiece n3 is positioned
between the processing teeth d and d of the finishing portions 7, 17. The tooth tip m4 of
the processing teeth d(t4) bites in the trough z3 to form a trough (screw trough) z4
having a desired configuration, and the crest y 3 is inserted in a deeper trough bottom
v4 between the processing teeth t4 and t4 to form a crest (screw crest) y4 having a
desired configuration. The tooth tip m4 and trough bottom v4 of the processing teeth
d(t4) have the same cross-sectional shape from the finishing portions 7, 17 to the
finishing points 9, 19 in the roll-off portions 8, 18. Since the roll-off portions 8, 18 have
a roll-off angle, a small gap is formed between the processing teeth d(t4) and the
workpiece n4. As a result, the workpiece n3 can be formed into the workpiece n4 (a
bolt) with desired screw crests and troughs, and absorb the elastic deformation from the
pressure release in the roll-off portions 8, 18 to form a bolt N with the alternatively
positioned crest y4 and trough z4 with the crest and trough angle 2 of 60 degrees, as
shown in Fig. 14.
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By using the rolling die described above, the workpiece n0 is subjected to
a shallow, moderate deformation between the processing teeth a, a at the starting
points 5, 15. Furthermore, as it is rolled between the bite portions 6, 16, the finishing
portions 7, 17, and the roll-off portions 8 and 18, the workpieces n1-n4 are smoothly
and continuously formed with the crest y2-y4 with the higher tooth heights h2-h4 and
the gradually deepener and narrower trough z2-z4. Furthermore, since the dies 2, 10
continuously perform each process while dispersing the load, cracking or localized
breakage loss is reduced at the starting points 5, 15. Bolts and screws with more
precise shapes and screw crests and troughs can be efficiently rolled, with a longer
product life for the rolling die 1.
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In another embodiment, both of the dies 2, 10 may be movable.
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Bolts (M. diameter: 12mm x pitch: 1mm) were rolled by the rolling die
described above from a rod type workpiece n0 made of SCM415. As a result, even
after precisely rolling of multiple bolts, no cracking or damage occurred near the starting
points 5, 15. When bolts were rolled by using a conventional die from workpiece made
of the same material, cracking and peeling (breakage loss) occurred in the tooth tip at
the starting point when a fewer number of bolts were rolled.
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Fig. 15 and 16 illustrate another embodiment of the rolling die according to
the invention. The rolling die 20, as shown in Fig. 16, includes a pair of dies 20a, 20b
that have a substantially cylindrical shape. As shown in Fig. 15, the die 20a is provided
at the periphery 24 from the starting point 25 to the finishing point 27 with processing
teeth a, b, c, d of the same cross-sectional shape as those described in the previous
embodiment.
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With the exception of the processing teeth d in finishing portions q and
roll-off portions r, processing teeth a, b, c are formed in a specific position at the
periphery 24 of bite portions p. Moreover, between the starting point 25 and the finish
point 27, a sharp angular cut-out 23 is formed, and an axial bore 26 with a key groove
25 is formed in the center of the die member 22. A rotating axis 28 is disposed in the
axial bore 26, as shown in Fig. 16.
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A cylindrical workpiece n is rolled between the starting points 25, 25 of the
dies 20a, 20b, and both rotating axes 28 are rotated in a synchronized motion. As
shown in Fig. 15, the processing teeth a, b, c, d in the bite portions p, the finishing
portions q, and the roll-off portions r bite into the workpiece n gradually deeper and
shaper. As a result, when passing between the finishing points 27, 27 of the dies 20a,
20b, a screw (N) is rolled with a specified shape and measurement. The screw, at the
cutouts 23, 23, will be automatically dropped toward the front or rear direction in Fig. 16.
At the same time, a new workpiece n is rolled between the starting points 25, 25, and
screws can be continuously, precisely and efficiently rolled.
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Other embodiments of the invention will be apparent to those skilled in the
art from consideration of the specification and practice of the invention disclosed herein.
It is intended that the specification and examples be considered as exemplary only, with
a true scope and spirit of the invention being indicated by the following claims.