The present invention relates to tools, for example press tools such as those for piercing work pieces.

Press tools are typically used in manufacturing to provide holes through a work piece, e.g. metal sheets and/or roll formed sections. Such holes may be for one or more purposes including providing datum points for assembly of a larger structure, reducing the weight of a component, providing access to certain parts of a component or assembly during manufacture or repair, providing passages for e.g. pipes and wiring and providing mechanical fixing points.

Burr is typically regarded as a limiting factor in the pressing of work pieces, as increased burr is typically regarded as indicative of lower quality goods and can hinder connections between two work pieces. Burr, which can be regarded as a raised edge or part thereof which remains attached to the work piece after pressing, usually needs to be removed, e.g. by further machining, before a work piece can be used or sold to ensure adherence to relevant quality controls. For example, a 0.3mm burr is often regarded as a maximum height for a commercial product.

As is appreciated by one having skill in the art, any additional machining, whether automated or performed manually, adds cost and complexity to a manufacturing process and would accordingly be desirable to remove. Another drawback of prior art punches is that it is typically necessary to use a stripping tool (e.g. a stripper plate) to remove the punch from a piercing after a cutting operation, as the punch and the piercing formed therefrom often interfere, for example as a result of rebounding ripples in the work piece which are formed when it is struck by the press tool . This stripping operation can cause wear to the punches and therefore necessitate the repair or replacement of the punches at regular intervals. Such maintenance increases operational downtime and hence cost. The inclusion of stripping tools also adds to the cost and complexity of the machinery.

It is therefore an object of the present invention to solve problems associated with the prior art.

In a first aspect, the invention provides a tool for piercing a substrate, the tool comprising an exterior surface defining a cutting edge wherein the exterior surface is adapted to adopt a larger effective profile when the cutting edge is approaching a substrate and to return to a smaller effective profile once the substrate is pierced .

In providing means for increasing the effective profile of the tool as it approaches the tool and retreat to its original smaller profile after the substrate has been pierced, the inventors have found that the tool may be removed from the piercing without the requirement for a stripping tool . Moreover, the cutting edge is not damaged by movement across the surface of the substrate. Accordingly, the lifetime of the tool is extended without the wear associated with the use of such stripping tools and the bearing of the tool against the edge of the piercing. Moreover, the burr produced by tools according to the invention is significantly and unexpectedly reduced compared to the prior art.

Preferably, the tool comprises ejection means for urging material pierced from the substrate away from a first end of the tool, the ejection means positioned within the cutting edge at the first end.

In a second aspect, the invention provides a tool for piercing a substrate, the tool comprising an exterior surface defining a cutting edge at a first end, wherein the tool comprises ejection means for urging material pierced from the substrate away from the first end, the ejection means positioned within the cutting edge at the first end.

The inventors have found that providing such an ejection means ensures that the tool does not need to be pushed as far as would otherwise be necessary into the corresponding die during a piercing action. Accordingly, the lifetime of the tool and the die is increased . Moreover, the burr produced by tools according to the invention is significantly and unexpectedly reduced compared to the prior art.

Preferably the ejection means does not comprise a cutting and/or piercing surface. Preferably, the exterior surface is adapted to adopt a larger effective profile when approaching and/or in contact with a substrate and to return to a smaller effective profile once the substrate is cut.

Preferably, the extension surface adopts the larger effective profile by expanding along a plurality of axes, e.g. 2, 3, 4, 5 or 6 axes.

Preferably the exterior surface adopts the larger effective profile by expanding in at least three directions, e.g. four, five or six directions.

Preferably the exterior surface comprises a shank, the cutting edge defining the periphery of a first end thereof.

Preferably the shank comprises an inner cavity running along a generally longitudinal portion of the shank and having an opening at the first end of the shank within the cutting edge.

Preferably, the shank is longitudinally divided into a plurality of segments such that the segments each make up part of the circumference of at least part of the shank.

Preferably a plurality of slots are provided in the shank between the exterior surface and the cavity, the slots extending from the cutting edge, e.g . to divide the shank into a plurality of segments. Preferably, the slots extend in a direction substantially normal to the cutting edge, e.g. substantially parallel to a longitudinal axis of the shank.

In some embodiments, at least part of at least one of the slots extends at an acute angle from the cutting edge. For example, at least part of the slots may extend from the cutting edge at an angle between 5° and 80°, e.g. between about 30 ^° and 60 ^° . Additionally or alternatively, the angled part of the slot(s) has a length such that it extends in the cutting edge direction for a distance greater than the width of the slot(s).

Preferably a first section of the slots extends from the cutting edge at an acute angle, e.g. between 30° and 80°. Preferably a second section of the slots extends from the first sections in a direction substantially parallel to the or a longitudinal axis of the shank.

Preferably, the slots comprise a first strengthening, e.g. circular, section between the first section and the second section.

Preferably, the slots extend only along a part of the length of the shank.

Preferably the one or more slots comprise a first alcove, e.g. circular, section in, or at a terminal end of the first section, or between the first section and the or a second section. Preferably the internal cavity comprises a tapered region, the larger end thereof facing or being towards the first end of the shank. Preferably, a wall of the tapered portion defines an angle of around 1° to around 10° to the or a longitudinal axis of the shank.

Preferably at least part of the insert is correspondingly shaped with the tapered region of the cavity, such that if the insert is urged into the cavity toward the second end of the shank, the segments of the shank are urged apart to provide the larger effective profile of the tool .

Preferably the insert is resiliently mounted within the cavity, e.g. such that in its normal state, a portion of the insert protrudes from the second end . Preferably the or a ejection means comprises the insert.

Preferably the insert is resiliently mounted in the cavity by an resilient means. Preferably, the resilient means comprised a coil spring. Alternatively, the resilient means comprises a gas or compressed air spring.

Preferably the tool comprises connection means for connecting the tool to a machine tool.

In a third aspect, the invention provides a machine tool comprising a press, a tool as described above and a die. In a fourth aspect, the invention provides a method of operating a machine tool as described above, the method comprising placing a substrate on the die, operating the press to engage the cutting edge of the tool with the substrate and withdrawing the tool before it enters the die.

Embodiments of the present invention will now be described with reference to the accompanying drawings, in which :

Figure 1 shows a tool according to the invention;

Figure 2 shows steps in a method according to the invention;

Figure 3 shows a tool according to the invention;

Figure 1 shows a punch 10 comprising a body 12 having a shank 14 at its lower end 16. The shank 14 is of generally circular cross-section and incorporates a cutting edge 18 at outermost periphery of the lower end 16. Internally of the punch 10 is an elongate cavity 20 running axially to the punch 10 substantially the entire length of the shank 14 and body 12. The cavity 20 extends to an opening 22 at the base 24 of the shank 14 to form a frusto conical section 26 within the shank 14. From the top of the frusto conical section 26, a substantially cylindrical portion 28 of the cavity 20 extends to a wall 30 near the top 32 of the body 12.

Within the cavity is retained a core portion 34. The core portion 34 comprises a cylindrical section 35 dimensioned to fit snugly and slidably within the cylindrical region 28 of the cavity 20, and a frusto conical section 38 designed to cooperate with the frusto conical region 26 of the cavity 20.

The cylindrical section 36 of the core portion 34 is separated from the upper wall 30 of the cavity 20 by means of a resilient member 40, such as a coil spring . The resilient member 40 is biased such that in a resting position at the least part of the frusto conical section 38 at the core portion 34 protrudes beyond the cutting edge 18 of the shank 14.

As can be seen in Figure I B, a series of slots 42 (e.g. 3, 4, 5 or 6 slots) are provided around the shank 14. the slots 42 each extend through the shank 14 to the cavity 20 and comprise an elongate portion 44 extending substantially normally to the cutting edge 18 to a circular portion 46 positioned between the uppermost region of the shank 14 and the frusto conical region 26 of the cavity 20, thereby dividing the shank 14 into a corresponding series of segments 43. At the upper end 32 of the body 12, a lip 48 provides means for attaching the punch 10 to a machine tool .

Use of the punch 10 in concert with a die 50 to pierce a work piece 52 (e.g. a sheet metal work piece) is shown in Figure 2.

Figure 2A shows the punch 10 ready to pierce a work piece 52 held atop a die 50. The resilient member 10 is extended in its equilibrium or rest position such that the core portion 34 protrudes beyond the cutting edge 18 of the shank 14. As the punch 10 is forced downwardly to contact the work piece 52, the core portion 34 moves downwardly at the same velocity.

Figure 2B shows the initial contact between the punch 10 and the work piece 52. As the leading edge 54 of the core portion 34 contacts the work piece 52 it moves upwardly relative to the body 12 of the punch 10. this relative movement brings the frusto conical section of the core portion 34 to bear against the wall of the frusto conical region 26 of the cavity 20, urging the segments 43 in an outwardly radial direction, expanding the surface area bounded by the cutting edge 18 of the punch 10, as indicated by arrows A.

As shown in Figure 2C, once the cutting edge 18 contacts and begins to pierce the work piece 52, the core portion 34 and the body 12 of the punch 10 again move downwardly at the same velocity.

Figure 2D shows the first rupture of the work piece 52 at failure line 56. The resilient member 40 is then able to urge the core portion 34 downwardly at a greater velocity than the body 12 and shank 14 of the punch 10. This in turn urges the slug 58 downwardly from the work piece 52, as shown in Figure 2E without the requirement that the shank 14 must enter the die 50. Moreover, as the core portion 34 again is urged to protrude beyond the cutting edge 18, the segments 43 of the shank 14 contract to their original positions, as indicated by arrows B, thus reducing the effective area bound by the cutting edge and ensuring the shank 14 can be easily withdrawn from the piercing 60 without the requirement for a stripping tool, as is shown in Figure 2F. The clearance between the punch 10 and the and the piercing 60 on withdrawal is preferably around 0.25mm.

A further embodiment of the invention is shown in Figure 3.

The punch 70 comprises a body 12 and a shank 14 formed from a lower end thereof, just as does the embodiment shown in Figure 1. Similarly, the punch 70 comprises a cavity 20 and a core portion 34 resiliently mounted therein.

Slots 62 are provided around the shank 14 from the cutting edge 18, dividing the shank 14 into segments 43.

A first portion 64 of the slots 62, adjacent the cutting edge 18 extends upwardly from the cutting edge 18, at an angle (for example between 40° and 80°) which is not perpendicular to the cutting edge, to a first alcove portion 66. The length L of the first portion 64 is such that the edge 64a of the first portion distal from the cutting edge 18 extends across the entire opening 64b of the slot 62 at the cutting edge 18.

A second portion 68 of the slot 62 then extends upwardly from the first alcove portion 66, substantially perpendicular to the cutting edge 18 to a second alcove portion 69. The first alcove portion 66 is offset from the intersection of the slot 62 and the cutting edge 18 {i.e. in the longitudinal direction of the shank 14), such that the angled first portion 64 of the slot 62 has a length component parallel to the cutting edge extends which is longer than the width of the slot 62 at the intersection of the slot 62 and the cutting edge 18.

The angle and length of the first portion 64 of the slot 62 ensures that no burr is left on the inside of a pressing corresponding to the position of a slot 62 because the linear vertical portion of the punch 70 will ensure the burr is shaved off. The first alcove portion 66 providing space for receiving the removed burr material at least until the punch procedure is complete.

The skilled person would recognise that, for example, curved slots could offer similar functionality.

Example 1

A punch as described in relation to Figure 1 was attached to a press and used to pierce a 1mm gauge steel sheet.

Once the piercing was made the punch was easily withdrawn without the requirement for a stripper. The punch did not enter the die upon pressing .

Comparative Example 1

A prior art punch of the same cutting diameter as that of Example 1 was used to press a 2.6mm gauge metal sheet 126,000 times. The punch and the die were found to be worn and required replacement or rework. The machine therefore required down time for the repairs.

Example 2

A punch as described in Example 1 was used to pierce a 2.6mm gauge steel sheet 126,000 times. The punch and the die were each found to be in good condition thereafter. The burr associated with each piercing was then measured . Little variation in the burr was found, with the mean burr being approximately 0.01mm proud of the sheet surface.

Comparative Example 2

A prior art 16mm punch as described in Comparative Example 1 was, using a press, used to pierce 16 piercings in a 2.6mm gauge steel sheet. The burr associated with each of the piercings was measured. Each was found to be approximately 0.3mm proud of the surface of the sheet, thereby requiring further machining for some end uses.

Example 3

A 16mm punch as described in Example 1 was used in a press to pierce 16 piercings in a 2.6mm gauge steel sheet. The burr associated with each piercing was then measured. Each burr was found to be approximately 0.01mm proud of the sheet surface. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto. For example, it is envisaged that electronic or electromechanical means may be used to expand the cutting edge of the tool as it approaches initial contact with a work piece or substrate. Similarly, such means may be used to provide the ejection means.

Moreover, tools according to the present invention may be provided with many different cutting profiles, for example circular, square, rectangular, rhomboid, or regular or irregular triangular, pentagonal, hexagonal, star shaped and the like.