EP1626828A1

EP1626828A1 - Inhibiting metal fatigue in a tool secured in a tool holder

Info

Publication number: EP1626828A1
Application number: EP03720294A
Authority: EP
Inventors: Svend-Helge Sell Sorensen
Original assignee: Enkotec AS
Current assignee: Enkotec AS
Priority date: 2003-05-14
Filing date: 2003-05-14
Publication date: 2006-02-22
Also published as: AU2003223933A1; MXPA05012174A; NO20055833D0; CN100355516C; CN1774308A; NO20055833L; BR0318294A; CA2524636A1; WO2004101194A1; CA2524636C

Abstract

The present invention relates to a method of at least inhibiting metal fatigue in a tool (2) secured in a tool holder (4), which tool comprises a front side (6) shaped for use in forming of metal wire into nails, screws etc., and which tool holder comprises a recess (8) adapted for receiving the tool. New aspects of the method involve that the tool (2) comprises two sides (10,12) forming a wedge-shaped, which is narrowing towards the front side (6) of the tool, where the angle (A´) of the wedge-shaped is between 0.5 and 45 degrees, and preferably between 1 and 15 degrees. It is thereby obtained that the tool may be 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 compressive stresses may reach a high level. 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.

Description

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 A1 and the corresponding WO 03/015955 A1. 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 a

CONRRMATION COPY 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 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.

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 tighten- ing 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 in- volve 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 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.

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

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

Fig.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.

Fig. 5 shows 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.

Fig. 6 shows 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 corre- sponding 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 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. 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.

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 sym- metric 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.

Claims

1. A method of at least inhibiting metal fatigue in a tool secured in a tool holder, which tool(2) comprises a front side(6) including a shaping por- tion(36) shaped for use in forming of metal wire into nails, screws, etc., and which tool holder(4) comprises a recess(8) adapted for receiving the tool(2), said tool(2) comprising two sides(10,12) forming a wedge-shape, which is narrowing towards the front side(6) of the tool, where the angle(A') of the wedge-shape is between 0.5 and 45 degrees, and preferably between 1 and 15 degrees, and where the tool(2) further comprises a back side(18), and where the tool(2) is placed in the recess(8) and forced in the direction of the front side(6), by applying pressure on said back side(18) of the tool with fastening means(20), in a way such that the two sides( 10,12) of the tool are compressed against corresponding sides(14,16) of the recess and compres- sive stresses are introduced in the tool between said two sides(10,12), said compressive stresses being present at least in a region by the shaping por- tion(36).

2. A method according to claim 1 , wherein 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.

3. A method according to claim 1 or 2, wherein the region with compressive stresses makes out at least the majority of the tool(2), and preferably the entire tool(2) in general.

4. A method according to claims 1 - 3, wherein the two sides(10,12) of the tool(2) are formed with a wedge-shape relative to a bottom side(22) of the recess, which wedge-shape is narrowing away from said bottom side.

5. A method according to claims 1 - 4, wherein the back side(18) of the tool is sloped relative to the bottom side(22) of the recess, and where a wedge(24) is placed with one side against the back side(18), which wedge(24) comprises a hole(26), through which hole a bolt(28) is connected to the tool holder(4), and where pressure is applied on said back side(18) by tightening the bolt(28) against the wedge(24).

6. A tool system for practising a method according to any of claims 1- 5, said tool system comprising a tool(2) and a tool holder(4), which tool comprises a front side(6) shaped for use in forming of metal wire into nails, screws, etc., and which tool holder(4) comprises a recess(8) adapted for receiving the tool and wherein the tool(2) is placed, wherein the tool(2) comprises two sides(10,12) forming a wedge-shape, which is narrowing towards the front side(6) of the tool, where the angle(A') of the wedge-shape is between 0.5 and 45 degrees, and preferably between 1 and 15 degrees, and where the recess(8) in the tool holder comprises two corresponding sides(14,16), which have substantially the same wedge-shape as the tool(2), and where the tool comprises a back side(18), and where the tool(2) can be forced in the direction of the front side(6), by the application of pressure on said back side(18) of the tool with fastening means(20), in a way such that the two sides(10,12) of the tool will be compressed against corresponding sides(14,16) of the recess.

7. A tool system according to claim 6, wherein the back side(18) of the tool is sloped relative to a bottom side(22) of the recess, and where the system further includes a wedge(24) placed with one side against the back side(18) and the opposite side against an end side(30) of the recess, which wedge(24) comprises a hole(26), through which hole a bolt(28) is connected to the tool holder(4), and where pressure can be applied to the back side(18) of the tool(2) by tightening the bolt(28) against the wedge(24).

8. A tool for a tool system according to claim 6 or 7, wherein the tool(2) comprises a front side(6) shaped for use in forming of metal wire into nails, screws, etc., said tool(2) being adapted to be placed in a tool holder(4), said tool holder comprising a recess(8) shaped for receiving the tool, wherein the tool(2) comprises two sides(10,12) forming a wedge-shape, which is narrowing towards the front side(6) of the tool, where the angle(A') of the wedge- shape is between 0.5 and 45 degrees, and preferably between 1 and 15 degrees.

9. A tool according to claim 8, wherein the tool(2) comprises a back side(18), which back side is sloped and adapted for cooperation with a wedge(24).

10. A tool according to claim 8 or 9, wherein the two sides(10,12) of the tool(2) are further forming a wedge-shape, which is narrowing away from a bottom side(38) of the tool, and where the angle(Z') of the. wedge-shape is between 0.5 and 15 degrees.

11. Use of a tool(2) according to any of claims 8-10 in a machine process for the manufacture of nails, screws and similar items.