Note: Descriptions are shown in the official language in which they were submitted.
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INHIBITING METAL FATIGUE IN A TOOL SECURED IN A TOOL HOLDER
The present invention relates to a method of at least inhibiting metal fatigue
in
a tool secured in a tool holder, which tool comprises a front side shaped for
use in forming of metal wire into nails, screws, etc., and which tool holder
comprises a recess adapted for receiving the tool. The invention further
relates to a tool system and to a tool as well as to a use of such a tool.
Securing a tool in a tool holder and devices with such purpose have formerly
been employed. In EP 406,202 A2 a clamping device for making nails is
disclosed, where a die (tool) is mounted in a die holder. The die holder is
provided with an opening for receiving the die. The back side of the opening
is provided with an extension to obtain a slight elasticity, and across said
extension a bolt is mounted to clamp the die in the die holder. However, the
force from the bolt is relatively small compared to the forces exerted on the
die during the nail making process. The tensile stresses in the die are
relatively large, and in the die's life span the stresses are applied and
relieved
in a large number of times, such that the well known phenomena of metal
fatigue appears. This often leads to cracked dies which have to be replaced,
leading to extra costs and lost production output due to lost time.
Another example of securing a tool in a tool holder is known from
US application US 2003/0032489 Al and the corresponding WO 03/015955
Al. In these documents a wear resistant octagonal tool is secured in a recess
and a wedge is used to obtain a tight hold. The angle between the sides of
the octagonal is at the front contact zones (marked 6) with the recess more
than 60 degrees according to the displayed embodiments. Also mentioned
are embodiments where the tool is rectangular or cylindrical.
The problem of metal fatigue is addressed in EP 870,558 A2 and the
corresponding US 5,979,216, where the tool (die/insert) has been divided in
two parts in order to remove harming effects of tensile stresses, i.e.
providing
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a crack in a determined position. The solution is costly, since more parts,
which must fit accurately together, have to be made. Also another
phenomenon known as fretting may appear, which leads to deterioration of
the tool inserts anyway. The presence of fretting is caused due to the bolt,
which is also employed in this technique, being inadequate to provide
sufficient clamping force. With inadequate clamping force, the two parts on
each side of the artificial crack are moving slightly away from each other
during each loading cycle, and back when the load is removed. The slight
movement causes wear and consequently fretting.
The basic problem has not been solved, namely that the tool (die/ insert) is
subject to too high tensile stresses. When clamping a wire, the shaping
portion of the tool is subject to a high pressure, which pressure is
substantially
radially directed on the concave shaping portion of the tool. The pressure
results in compressive stresses near the surface, where the contact is
between the tool and the wire, but slightly further away from the surface,
tangentially oriented to the concave shaping portion, tensile stresses
prevail.
In case of a flat shaping portion, the pressure also results in compressive
stresses near the surface, where the contact is between the tool and the wire,
and slightly further away from the surface, tangentially oriented to the
origin of
contact, tensile stresses also prevail.
One object of the present invention is to provide a method of at least
inhibiting
metal fatigue in a tool secured in a tool holder, such that compressive
stresses are initially present in the tool (built-in), when the tool is
subjected to
the tensile stresses caused by the nail/screw making process, in order to at
least reduce the resulting tensile stresses. Another object is to improve the
life
span of the tool and further to reduce down time in the production.
New and inventive aspects of the method according to the invention comprise
that the tool comprises two sides forming a wedge-shape, which is narrowing
towards the front side of the tool, where the angle of the wedge-shape is
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between 0.5 and 45 degrees, and preferably between 1 and 15 degrees, and
where the tool further comprises a back side, and where the tool is placed in
the recess and forced in the direction of the front side, by applying pressure
on said back side of the tool with fastening means, in a way such that the two
sides of the tool are compressed against corresponding sides of the recess
and compressive stresses are introduced in the tool between said two sides,
said compressive stresses being present at least in a region by the shaping
portion.
By the new and inventive aspects it is obtained, that the tool is compressed
between the sides of the recess, such that compressive stresses are
introduced in the tool. Due to the angle of the wedge-shape of the tool and
the recess, the amount of pressure applied to the back side is amplified
several times on the sides of the tool, whereby the compressive stresses
reach a high level introduced and maintained by the fastening means. The
amplification is a function of inverse sinus to the half the angle in case of
a
symmetric wedge-shape. At angles less than 45 degrees the effect
is therefore rapidly increasing, and becomes very high for angles less than
15 degrees. When the tool is afterwards used in the nail/screw making
process, the tensile stresses caused thereby must relieve or overcome the
built-in compressive stresses before a state of tensile stress in the tool can
be
present. Hence, the resulting tensile stress level is at least reduced, or
completely avoided.
Preferably, the region with compressive stresses is ranging from around the
shaping portion and a distance away, which is at least equal to two times the
active width of the shaping portion, and preferably more than five times the
active width of the shaping portion. Such a range will include the maximum
tensile stresses, whereby at least the peaks are reduced.
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Even more preferred should the region with compressive stresses make out at
least the majority of the tool, and preferably the entire tool in general.
This
may reduce the majority of the tensile stresses or even remove most of the
tensile stresses.
The two sides of the tool may further be formed with a wedge-shape relative
to a bottom side of the recess, which wedge-shape is narrowing away from
said bottom side. Hereby a considerable compression may be obtained
similarly to the effect obtained as mentioned and explained above, however in
a different direction. This includes a direction parallel to the direction of
another force present in the nail/screw making process, which force is caused
when forming the flat head on the nail or screw. Said force introduces shear
as well as tensile stresses near and on the surface portion of the tool being
in
contact with the metal wire. i.e., a pre-stressed compression will also in
this
respect reduce the maximum tensile stresses, inhibit metal fatigue and
improve life span of the tool.
Also preferred is that the back side of the tool is sloped relative to the
bottom
side of the recess, and that a wedge is placed with one side against the back
side, which wedge comprises a hole, through which hole a bolt is connected
to the tool holder, and that pressure is applied on said back side by
tightening
the bolt against the wedge. Hereby a way of amplifying the force from the bolt
is obtained, which also may be used to further amplify the compression in the
tool.
New and inventive aspects of the tool system according to the invention
involve that the tool system comprises a tool and a tool holder, which tool
comprises a front side shaped for use in forming of metal wire into nails,
screws, etc., and which tool holder comprises a recess adapted for receiving
the tool and wherein the tool is placed, wherein the tool comprises two sides
forming a wedge-shape, which is narrowing towards the front side of the tool,
where the angle of the wedge-shape is between 0.5 and 45 degrees, and
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preferably between 1 and 15 degrees, and where the recess in the tool holder
comprises two corresponding sides, which have substantially the same
wedge-shape as the tool, and where the tool comprises a back side, and
where the tool can be forced in the direction of the front side, by the
application of pressure on said back side of the tool with fastening means, in
a
way such that the two sides of the tool will be compressed against
corresponding sides of the recess. Hereby it is obtained, that the tool may be
compressed between the two sides of the recess, such that compressive
stresses are introduced in the tool, which involves the aforementioned
advantages.
In a preferred embodiment of the system, the back side of the tool is sloped
relative to a bottom side of the recess, and the system further includes a
wedge placed with one side against the back side and the opposite side
against an end side of the recess, which wedge comprises a hole, through
which hole a bolt may be connected to the tool holder, and where pressure
can be applied to the back side of the tool by tightening the bolt against the
wedge. Such a design provides a positive amplification of the force from the
bolt via the wedge to the back side of the tool.
The present invention further includes a tool involving new and inventive
aspects, including that the tool comprises a front side shaped for use in
forming of metal wire into nails, screws, etc., said tool being adapted to be
placed in a tool holder, said tool holder comprising a recess shaped
for receiving the tool, wherein the tool comprises two sides forming a
wedge-shape, which is narrowing towards the front side of the tool, where the
angle of the wedge-shape is between 0.5 and 45 degrees, and preferably
between 1 and 15 degrees. The tool is hereby well suited to be secured in a
corresponding recess in a tool holder, in a way where a state pre-stressed
compression may be obtained to inhibit metal fatigue caused by the forming of
metal wire.
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In a preferred embodiment the tool may comprise a back side, which back
side is sloped and adapted for cooperation with a wedge. The pressure from
the wedge will then have a component urging the tool downwards against the
bottom of the recess. This contributes to also obtaining a compression in that
direction.
In a further preferred embodiment the two sides of the tool may further be
forming a wedge-shape, which is narrowing away from a bottom side of the
tool, and where the angle of the wedge-shape is between 0.5 and 15 degrees.
Thereby it may be obtained that harmful effects from the shear as well as
tensile stresses near the contact portion of the tool from the making of the
nail/screw head may be reduced. A pre-stressed state of compression will
also in this respect reduce the maximum tensile stresses and improve life
span of the tool.
New and inventive aspects of the use of the tool according to the invention
comprise that it is used in a machine or a process for the manufacture of
nails, screws and similar items, whereby lost production time is decreased.
In the following the invention is further explained with the use of drawings,
where examples of embodiments are shown.
Fig. 1 is an exploded view of a tool system.
Fig. 2 is a perspective view of a tool system.
Fig. 3 is a top view of a tool system.
Fig. 4 is a front view of a tool system.
Fig. 5 is a cross sectional view along the line C-C of Fig. 3.
Fig. 6 is a cross sectional view along the line B-B of Fig. 4.
Fig. 7 is a top view of a tool holder.
Fig. 8 is a cross sectional view along the line D-D of Fig. 7.
Fig. 9 is a cross sectional view of a tool holder.
Fig. 10 is a perspective view of a tool.
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Fig. 11 is a perspective view of a tool.
Fig. 12 is a top view of a tool.
Fig. 13 is a side view of a tool.
Fig. 14 is a front view of a tool.
Fig. 15 is a front view of a tool.
Figs. 16-18 are other examples of embodiments of a tool according to the
invention, displayed in top view.
In Fig. 1 a tool holder 4 with a wedge-shaped recess 8 is shown. A tool 2 is
to
be placed in the recess 8 and fastened by fastening means 20, which in this
example comprise a wedge 24 with a hole 26 and a bolt 28. The bolt 28 is to
be engaged with a threaded hole in the bottom of the recess 8 (not shown).
In Fig. 2 - 4 a tool 2 is fastened by fastening means 20 in a wedge-shaped
recess 8 of a tool holder 4, which wedge-shape is indicated by an angle A.
The tool comprises a front side 6 shaped for use in forming of metal wire into
nails, screws or similar products. The tool 2 may be made of a hardened
metal alloy. In Fig. 3 an angle A is shown, which angle refers to the
wedge-shape of the recess 8. Preferably, the tool 2 is provided with a similar
wedge-shape. The fastening means 20 are pressing the tool 2 towards the
narrowing end of the recess 8 in order to compress the tool 2 against the
recess 8. The fastening means 20,24,26,28 shown in Fig. 1-3 are for a skilled
person easily substituted, e.g. with a bolt through the tool holder 4 in the
longitudinal direction, pressing directly on the tool 2, or a hydraulic
cylinder
built into the holder 4 etc.
In Fig. 5 the cross section C-C from Fig. 3 is shown, displaying a cross
section of a tool 2 placed in a recess 8 in a holder 4. As displayed, the tool
2
and the recess 8 are fitted closely.
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In Fig. 6 the cross section B-B from Fig. 4 is shown, displaying another cross
section in a tool 2 and a tool holder 4. Pressure is exerted on a back side 18
of the tool 2 by a wedge 24. The back side 18 is sloped relative to a
bottom 22 of the recess. The wedge 24 comprises a shape corresponding to
the sloped shape on one side and a shape corresponding to an end side 30 of
the recess. The end side 30 may be placed at a right angle to the bottom
side 22 or with a slope. The wedge 24 comprises a through-going hole 26,
through which a bolt 28 may be inserted and engaged with a threaded hole 32
in the holder 4. At first the tool 2 is placed in a recess 8, after which the
wedge 24 is inserted between the tool 2 and the end side 30. Afterwards, the
bolt 28 is inserted and engaged with the threaded hole 32 and tightened. The
tightening forces the wedge 24 downwards, whereby a high force is directed
on the sloped back side 18 of the tool 2, said high force compressing the tool
forwards against the recess 8.
In Fig. 7 a tool holder 4 is shown, which holder comprises a wedge-shaped
recess 8 with two sides 14, 16 and an end side 30. A bottom side 22 of the
recess is provided with a threaded hole 32.
In Fig. 8 the cross section D-D from Fig. 7 is shown. The two sides 14 and 16
may be placed in right angles with a bottom side 22 of a recess 8. The
transition between the side 14 and the bottom side 22 respectively the side 16
and the bottom side 22 may be provided with an undercut fillet 34 to reduce
local stress levels and to ensure that sufficient space is available for a
tool.
In Fig. 9 it is shown that the two sides 14, 16 may additionally be placed to
form a wedge-shape with an angle Z. Said wedge-shape is suited to
compress a tool with a force component downwardly against the bottom
side 22. In that way, both a compression in a plane parallel to the bottom
side 22, as well as in a plane perpendicular to the bottom side 22, may be
obtained. This provides a tool 2 with built-in compressive stresses, which
stresses have to be overcome before a state of tensile stress may appear.
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Tensile stresses, which are present from forces exerted on the front side 6 of
a tool 2 from using said tool, will be reduced by the built-in compressive
stresses. i.e. the magnitude of the tensile stresses actually occurring in the
tool 2 is reduced or removed.
Fig. 10 shows a tool 2 comprising a side 12 and a front side 6 with a concave
shaping portion 36 for shaping a nail or screw etc.
Fig. 11 shows a different or counteracting tool 2 comprising a side 10 and a
front side 6 with a shaping portion 36. Such a tool may be used in a cutting
process.
Fig. 12 shows a tool 2 with a front side 6 comprising a shaping portion 36,
said shaping portion being concave. The tool 2 comprises two sides 10
and 12 forming a wedge-shape, in that they are placed in an angle A'. The
angle A of Fig. 3 and the angle A' are at least substantially corresponding.
In Fig. 13 a tool 2 is shown comprising a front side 6, a side 12, a sloped
back
side 18 and a bottom side (38).
Fig. 14 shows an embodiment of a tool 2 with sides 10 and 12, and a front
side 6 with a shaping portion 36.
Fig. 15 displays another embodiment of a tool 2 with sides 10 and 12, and a
front side 6 with a shaping portion 36, as well as a bottom side (38). The two
sides 10 and 12 are placed under an angle Z' to form a wedge-shape. The
angle Z' is preferably substantially corresponding to the angle Z on Fig. 9.
Figures 16 - 18 display other examples of embodiments of a tool. In Fig. 16 is
shown that the wedge-shape of the sides 10 and 12 does not necessarily
need to run in the entire length of the tool 2, and that the sides of the tool
may
also have e.g. straight side portions 10.1 and 12.1, as well as they may
include chamfered sections 40 towards the back side 18.
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In Fig. 17 it is shown that the wedge-shape of the sides 10 and 12 may
involve that one of the sides is substantially perpendicular to the front side
6.
In Fig. 18 it is shown that the tool 2 may be symmetric about a plane E-E and
include two shaping portions 36.
It is to be noted that the wedge-shape of the tool 2 may preferably be
symmetric about a plane perpendicular to the front side 6 and through the
shaping portion 36, but non-symmetric shapes will also improve life span in a
similar way.
The term "active width" of the shaping portion 36 is in the present context to
be understood as the transverse extent of the part of the shaping portion,
which is in contact with the metal wire during use of the tool 2.
It is to be understood that the invention as disclosed in the description and
in
the figures may be modified and changed and still be within the scope of the
invention as claimed hereinafter.
