Rivets and methods of manufacture

Abstract

A composite rivet blank 2 is formed from thermoset pre-impregnated (“pre-preg”) carbon fibre material. The thermoset may an epoxy resin system binder and the pre-impregnated carbon fibre material may

Description

Field of the Invention The present invention relates to composite rivets and methods for their manufacture and use, and an associated forming tool. Summary of the Invention According to a first aspect of the invention there is provided a composite rivet blank formed from thermoset pre-impregnated (“pre-preg”) carbon fibre material. Optionally, the thermoset is an epoxy resin system binder. Optionally, the rivet blank is substantially cylindrical. Optionally, the pre-impregnated carbon fibre material is a unidirectional carbon fibre material. Optionally, the pre-impregnated carbon material is a woven fabric carbon fibre material. Optionally, the pre-impregnated carbon material is a biaxially oriented carbon fibre material. Optionally, the rivet blank comprises any one or more of pre-impregnated unidirectional carbon fibre, pre-impregnated woven fabric carbon fibre, and / or preimpregnated biaxially oriented carbon fibre material or materials. Optionally, the rivet blank comprises 30-50% by weight thermoset. Optionally, the rivet blank comprises 60-70% carbon fibre. Optionally, the rivet blank is formed by rolling or winding the pre-impregnated carbon fibre material over a mandrel. Optionally, the rolling or winding is cylindrical rolling or winding. Optionally, the rolling or winding is helical rolling or winding. Optionally, the rolling or winding is spiral rolling or winding. Optionally, the mandrel has a diameter in in the range of approximately 0.5 to 1.0 mm. Optionally, the rivet blank is configured for sizing to length by cutting at one or both ends. Optionally, the rivet blank is configured to receive a removable reinforcing member that is longitudinally extensible through the internal opening or bore of the substantially cylindrical blank. Optionally, the reinforcing member is arranged to prevent the closure of said internal opening of the cylindrical rivet blank during cutting. Optionally, the removable reinforcing member is substantially coated with a release agent, optionally wherein the release agent is heat resistant. Optionally, the removable reinforcing member is a Teflon-coated wire. Optionally, the removable reinforcing member is copper or a copper alloy. Optionally, the wire is a resistance wire. Optionally, the resistance wire is configured to impart heat energy to the rivet blank via the interior of the rivet blank. Optionally, the opposing ends of the rivet blank are configured for forming into rivet heads, wherein the rivet heads are formable by means of application of pressure and / or heat energy, and wherein the portion of the rivet intermediate the so formed heads provides a rivet shank. According to a second aspect of the invention there is provided a method of manufacture of a rivet blank from a thermoset pre-impregnated carbon fibre material (“pre-preg”); the method comprising the steps of: cutting the pre-preg material to a required size longitudinal to the fibre direction; winding a length of the pre-preg material over a mandrel to form a substantially cylindrical roll; and removing the rolled blank from the mandrel. Optionally, the winding step is cylindrical rolling or winding. Optionally, the winding is helical rolling or winding. Optionally, the winding is spiral rolling or winding. Optionally, the method includes the step of tensioning the pre-preg material before and / or during winding. Optionally, the method comprises the step of cold storing the rolled blank. Optionally, the method comprises the step of inserting a reinforcing member longitudinally through the internal opening or bore of the rolled blank. Optionally, the removable reinforcing member is substantially coated with a release agent, optionally a heat resistant release agent. Optionally, the removable reinforcing member is a Teflon-coated wire. Optionally, the removable reinforcing member is copper or a copper alloy. Optionally, the wire is a resistance wire. Optionally, the resistance wire is configured to impart heat energy to the rivet blank via the interior of the rivet blank. Optionally, the thermoset of the pre-impregnated material is an epoxy resin system binder. Optionally, the pre-impregnated carbon fibre material is a unidirectional carbon fibre material. Optionally, the pre-impregnated carbon material is a fabric woven carbon fibre material. Optionally, the pre-impregnated carbon material is a biaxially oriented carbon fibre material. According to a third aspect of the invention there is provided a method of use of a composite rivet blank in accordance with the first or second aspects of the invention, comprising the steps of: inserting the rivet blank into an opening or openings an item or items to be riveted; optionally applying an initial compressive force to the opposing ends of the rivet blank to initially expand said rivet blank ends in order to maintain the rivet blank in position; and applying a compressive force to the ends of the rivet blank to form rivet heads, wherein the pressure is applied by specifically shaped rivet heading tools; and curing the so-formed rivet. Optionally, the method comprises the precursor step of removing the composite rivet blank from cold storage. Optionally, the method comprises the step of internally heating the rivet blank by means of a resistance wire located through an internal opening or bore of the rivet blank. Optionally, the step of curing the rivet comprises applying heat to said rivet. Optionally, the method comprises the step of removing the resistance wire from the rivet blank when the rivet is formed. Optionally, the compressive force is provided by drawing the opposing rivet heading tools towards each other by electromagnetic means. Optionally, the compressive force is provided by drawing the opposing rivet heading tools towards each other by spring biasing means. Optionally, the step of curing the rivet comprises maintaining said rivets at a temperature of approximately 120 °C, optionally for approximately 45 minutes. Optionally, the heat energy is applied to the rivet via one or both rivet head forming tools. Optionally, the heat energy is generated by electro resistive heating means. Optionally, the heat energy is generated by joule effect heating means. Optionally, the heat energy is generated by ultrasonic heating means. Optionally, the heat energy generated by induction heating means. Optionally, the heat generation means may be incorporated in the rivet head-forming tool in accordance with the invention. In a fourth aspect of the invention there is provided a rivet head forming (or “heading”) tool for use with the rivets and rivet blanks of the first, second and third aspects of the invention, wherein the rivet heading tool is configured to transfer heat from a heating generating means to a rivet. Optionally, the rivet heading tool comprises a heat generating means for heating and / or curing a rivet. Optionally, the heat generating means is an electro resistive heating means. Optionally, the heat generating means is a joule effect heating means. Optionally, the heat generating means is an ultrasonic heating means. Optionally, the heat generating means is an induction heating means. Optionally, the rivet heading tool comprises a head comprising a recessed portion, wherein the recessed portion comprises a substantially circular perimeter, a sidewall that transitions into a peak formation which projects upwardly from the base of said recessed portion. Optionally, the head of the rivet head-forming tool is constructed from a copper or aluminium alloy. Optionally, rivet blank engaging surface of the head-forming tool is provided with a non-stick coating, for example, but not limited to, a Teflon coating. Optionally, the shape of the sidewall is configured to substantially define the shape of the rivet head formed by the rivet-heading tool. Optionally, the sidewall is a curved sidewall. Optionally, the peak formation is configured to extend at least partially into a rivet blank end, and to expand said rivet blank end. Optionally, the peak formation extends to a height that is below the perimeter of the recessed portion. Optionally, the peak formation extends to a height that is above the perimeter of the recessed portion. Optionally, the peak formation extends to a height that is substantially level with the perimeter of the recessed portion. Optionally, the rivet heading tool comprises a longitudinally extending through bore, the bore extending through the apex of the peak formation to the base of the head. In accordance with a fifth aspect of the invention, there is provided a rivet formed from a composite rivet blank in accordance with the first, second and third aspects of the invention. The various aspects of the present invention can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one aspect can typically be combined alone or together with other features in different aspects of the invention. Any subject matter described in this specification can be combined with any other subject matter in the specification. Various aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary aspects and implementations. The invention is also capable of other and different examples and aspects, and its several details can be modified in various respects, all without departing from the scope of the present invention. Accordingly, each example herein should be understood to have broad application, and is meant to illustrate one possible way of carrying out the invention, without intending to suggest that the scope of this disclosure, including the claims, is limited to that example. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. In particular, unless otherwise stated, dimensions and numerical values included herein are presented as examples illustrating one possible aspect of the claimed subject matter, without limiting the disclosure to the particular dimensions or values recited. All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa. Language such as "including", "comprising", "having", "containing", or "involving" and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. Thus, throughout the specification and claims unless the context requires otherwise, the word “comprise” or variations thereof such as “comprises” or “comprising” will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention. In this disclosure, the words “typically” or “optionally” are to be understood as being intended to indicate optional or non-essential features of the invention which are present in certain examples, but which can be omitted in others without departing from the scope of the invention. Brief Description of the Drawings The present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which: Figure 1 is an exemplary schematic of a pre-impregnated carbon fibre sheet (“prepreg”) for forming into a rivet blank; Figure 2 is a schematic diagram of rolling arrangement for winding a rivet blank; Figure 3 is a schematic end view of an exemplary cylindrical spiral wound rivet blank; Figure 4 is a schematic perspective view an exemplary helically wound rivet blank; Figure 5 is a schematic cross-section of an exemplary rivet blank shown in location between two structures; Figure 6 is a schematic cross-section of the exemplary rivet blank of Figure 5, with the rivet blank ends partially expanded. Figures 7a and 7b are schematic diagrams showing rivet head fibre orientations for cylindrical and helically wound rivet blanks, respectively; Figure 8 is a schematic cross-section diagram of the formation of the rivet heads and exemplary associated head forming tool; Figure 9 is a schematic cross-section of an exemplary rivet with formed heads; Figure 10 is a schematic diagram of an exemplary electromagnetic means for drawing the opposing rivet heading tools towards each other; Figure 11 is a schematic diagram of an exemplary spring bias means for drawing the opposing rivet heading tools towards each other; Figure 12 is a schematic perspective cross-section of an exemplary rivet head forming tool in accordance with the invention; and Figure 13 is a schematic cross-section end view of the rivet head forming tool of Figure 12. Detailed description With reference to Figure 1 there is shown exemplary schematic of a pre-impregnated carbon fibre material (“pre-preg”) 1 for forming into a rivet blank 2, wherein the prepreg material is cut to a band of appropriate size, the cut being longitudinal with the fibre direction. The pre-impregnated carbon fibre material may be in the form of a sheet or roll. The size of the sheet is determined by the rivet diameter (or ‘gauge’). For example, a for a 4mm diameter rivet, approximately 110mm. In examples, the pre-preg comprises carbon fibres and thermosetting system binder. The pre-impregnated carbon material may comprise, but is not limited to, a unidirectional carbon fibre material, a woven fabric carbon fibre material, a biaxially oriented carbon fibre material. Optionally, the pre-impregnated material comprises 30 - 50% by weight thermoset binder. In examples, the binder is an epoxy resin system binder. As shown in Figure 2, the pre-preg material, e.g. the sheet or band 1, is wound around a mandrel 11 to form a substantially cylindrical roll 12. Accordingly, the so-formed rivet blank 2 is substantially cylindrical in shape. The sheet may be tensioned, for example by means of tensioners 13, during winding. Optionally, the river blank comprises approximately 60-70% carbon fibres. In examples, the mandrel 11 may have a diameter in the range of approximately 0.5 to 1.0 mm. As shown in Figures 3 and 4, the winding may be spiral with an internal radius (Figure 3), or helical (Figure 4). It has been found that spiral wound blanks 2a (Figure 3) provide rivets having increased tensile strength in their shanks 20 (Figures 5, 6, 9) in comparison to that of a helically wound blank 2b (Figure 4), the shank 20 being the portion of the rivet extending between the opposing rivet heads 23, 24. It has been found that a helically wound rivet blank 2b enables easier formation of the rivet heads in comparison to those formed from a spiral wound blank 2a. With reference to Figure 4, where the blank is helically wound, the pre-preg is provided in the form of a strip having a width that is approximate or around the desired rivet length, taking into account the optimal or desired helix angle 9. The value of the helix angle can vary from less than 30 degrees to more than 75 degrees. The specific helix angle 9 is dependent upon the primary expected external forces that the rivet formed from the blank will encounter in use. For example, if axial loads are prevalent, a lower helix angle (as shown in Figure 4) can be used. Alternatively, if shear load resistance is desired the helix angle 9 should be higher. The higher helix angles are likely to pose problems with the rivet head formation, especially with higher gauge rivets. Experiments should therefore be conducted for any given rivet gauge in order to determine the optimal angle of winding. It will be understood that the rivet blank may be formed from pre-impregnated carbon fibre material comprising any one or more of: a unidirectional carbon fibre material; a woven fabric carbon fibre material; a biaxially oriented carbon fibre material. Similarly, it will be appreciated that a rivet blank 2 may be formed from any combination of unidirectional carbon fibre material, woven fabric carbon fibre material, and / or biaxially oriented carbon fibre material. For example, a rivet blank may comprise a first wrap or series of wraps of one pre-preg material, and one or more subsequent wraps of other pre-preg material or materials. After a blank 2 has been formed around the mandrel 11, it is removed and can be placed into cold storage, for example in a temperature-controlled refrigerator. The ability of the rivet blanks 2 to be manufactured and stored for extended periods is advantageous in that batches of pre-manufactured river blanks can be stockpiled in required amounts for future use, thus obviating the issue of manufacturing speed downstream. When required for use, a rivet blank 2 can be retrieved from cold storage whereupon it is cut into the desired length. Cutting may be made at one or both ends 21, 22 of the rivet blank 2. As the rivet blanks are formed having an internal opening 25 in the form of a through bore, a suitable removable reinforcing member 27 configured to prevent collapse of said internal opening during cutting can be inserted as shown by way of example in Figure 4. Optionally, the removable reinforcing member 27 may be in the form a Teflon-coated copper wire. Upon cutting, the reinforcing member may be removed. The reinforcing member 27 may comprise a resistance wire, the wire configured to impart heat energy to a rivet blank 2 upon electrical energisation of said wire. In this manner, a rivet blank 2 can be heated via the interior of said rivet blank, for example during the rivet forming process, as described by way of example below. Suitable resistance wires and their material compositions are well known in the art. Internal heating of a rivet blank may be carried out as a supplement to external heating of the blank, or as an alternative to external heating of the blank. Optionally, the resistance wire 27 is substantially coated with a release agent, optionally wherein the release agent is heat resistant. After the rivet is formed, the resistance wire can be removed. As shown in Figure 5, a rivet blank 2 is inserted into an opening 51 or openings in the item or items 50A, 50B to be riveted. Items 50A, 50B may comprise composite panels. As shown in Figure 6, an initial compressive force may be applied to the opposing ends 21, 22 of the rivet blank 2 by suitable tools 30 to initially expand the rivet blank’s ends, for example to maintain the rivet blank in position. Figures 7a and 7b show the respective fibre orientations in the initially expanded blank ends 21, 22 of cylindrical wound blanks 2a (Figure 7a) and helically wound blanks 2b (Figure 7b). Helically wound rivet blanks 2a are considered to provide a better fibre distribution during the initial forming process. With reference to Figure 8, the rivet heads 23, 24 are formed by applying compressive force to the ends 21, 22 of the rivet blank 2. Heat may also be applied to help shape and / or cure the rivets 2 and their heads 23, 24. In examples, the step of curing the rivets 2 and / or rivet heads 23, 24 comprises maintaining said rivets and / or rivet heads at a temperature of approximately 120 ° C, optionally for approximately 45 minutes. It will be understood that the temperature and / or duration of the curing step can be altered depending upon factors such as, but mot limited to, the thermoset or the rivet size. As shown in Figure 8, the compressive force is applied by a specifically shaped rivet head forming (or “heading”) tools 40, which are configured to mould the rivet heads 23, 24 into the desired shape. Further detail of an exemplary rivet head forming (or “heading”) tool 40 is described below with reference to Figures 8, 12 and 13. The compressive force may be generated in a number of alternative ways. As shown by way of example in Figure 10, the compressive force may be provided by drawing the opposing rivet heading tools 40 towards each other by electromagnetic means 60, wherein an electromagnetic coil 61 associated with one heading tool 40 (for example the exterior tool) is arranged to attract a corresponding iron core or cores 62 associated with the opposing heading tool 40 (for example the inside, or blind-side, tool). Experiments have shown that a force of around 10N is sufficient for forming the rivet heads. As shown by way of example in Figure 11, the compressive force may be provided by a spring bias means 70, for example wherein tension of a spring 71 in contact with one rivet heading tool 40 acts upon a fixed wire 72 extending from the opposing rivet heading tool 40 and which passes through the bore 25 of the rivet blank 2 and through said first rivet heading tool, draws the respective first and second rivet heading tools towards each other. A collet and nut assembly 73 may be provided for wire retention. As noted above, heat may also be applied to help shape and / or cure the rivet heads 23, 24. The heat may be applied via the rivet heading tools 40. In one example, the heat energy may be generated by electro resistive heating. In this method, the temperature is controlled only on the heating instruments, and not the rivet itself. In one example, the heat energy may be generated by joule effect heating. In this method, DC current is run through the carbon fibres of the rivet, with temperature monitoring achieved by measuring the change in the electrical resistance of the carbon fibre(s). Advantageously, this method consumes minimal electrical energy. Additionally, the heat is concentrated in the whole volume of the rivet, thereby providing a more uniform cure. Optionally, the heat energy is generated by ultrasonic heating. In this method, mechanical vibrations in the 40kHz range are applied to the rivet heads using piezoelectric transducers and ultrasonic energy concentrators (horns). Advantageously, this method permits heating of the rivet from one side and minimises heat dispersal into the items being riveted. Optionally, the heat energy generated by induction heating. In this method, eddy currents are induced in the composite material of the rivet using a high frequency AC magnetic field. Advantageously, this method permits heating of the rivet from one side, and provides uniform heating in the whole volume of the rivet. In examples, the rivet heading tool may be configured to transfer heat from the heat generating means to the rivet / rivet blank. In examples, the heat generation means may be incorporated into, or is integrally included with, the rivet head forming tool of the invention. As the final shape of the rivet shank 20 is formed during the riveting process, rivets 26 (shown for example in Figure 9) formed from rivet blanks in accordance with the present invention can accommodate openings 51 (Figure 5) in the items or panels 50A, 50B being riveted having sizes which differ from a specified nominal. Advantageously, the ability of the rivet shanks 20 to conform to the dimensions of the apertures 51 in which they are used simplifies the requirements on the drilling process. For example, if the opening 51 is oval or oversized, upon formation the rivet 26 will expand and fill the given space. The liquid resin that forms during the riveting process in accordance with the invention will also fill small delaminations (for example arising from inappropriate drilling process or worn out drilling tools) around the opening 51 and will help strengthen the material (especially in fatigue loadings). With reference to Figures 8, 12 and 13, there is shown an exemplary rivet head forming (or “heading”) tool 40 particularly adapted for use with the rivets 26 and rivet 2 blanks in accordance with the invention. With specific reference to Figures 12 and 13, the rivet heading tool 40 comprises a head 41 comprising a recessed portion 42. The recessed portion 42 comprises a substantially circular perimeter 43, a base 44 and a sidewall 45. The sidewall 45 is shaped to substantially define the shape of the rivet head 23, 24 formed by the rivet heading tool 40. In the example shown, the sidewall 45 curves towards the base 44. The curve may be a concave curve. The curved sidewall 45 transitions into a peak formation 46 which projects upwardly from the centre of base 44 of said recessed portion 42. The peak formation 46 is configured to extend at least partially into the end 21,22 of a rivet blank 2. The peak formation 46 may extend to a height that is below the perimeter 43 of the recessed portion 42. Alternatively, the peak formation 46 may extend to a height that is above the perimeter 43 of the recessed portion 42. Alternatively still, the peak formation 46 may extend to a height that is substantially level with the perimeter 43 of the recessed portion 42. In examples, the rivet heading tool 40 may optionally comprise a longitudinally extending through bore 47 (Figure 11 and Figure 12), the bore extending through the apex of the peak formation 46 to the base of the rivet heading tool 40. This 5 arrangement is particularly suited for use in conjunction with a spring biasing means 70 arranged to provide the compressive force which draws the heading tools towards each other in order to form the rivets as described above. The head of the rivet head forming tool may be constructed from a copper or 10 aluminium alloy. The rivet blank engaging surface of the head forming tool may be provided with a non-stick coating, for example, but not limited to, a Teflon coating.

Claims

1. A composite rivet blank formed from thermoset pre-impregnated (“pre-preg”) carbon fibre material.

2. A composite rivet blank as claimed in claim 1, wherein the thermoset is an epoxy resin system binder.

3. A composite rivet blank as claimed in claim 1 or claim 2, wherein the preimpregnated carbon fibre material comprises any one or more of: a unidirectional carbon fibre material; a woven fabric carbon fibre material; a biaxially oriented carbon fibre material.

4. A composite rivet blank as claimed in any preceding claim, wherein the rivet blank is formed by rolling or winding the pre-impregnated carbon fibre material over a mandrel.

5. A composite rivet blank as claimed in claim 4, wherein the rolling or winding is any one of cylindrical rolling or winding, helical rolling or winding, or spiral rolling or winding.

6. A composite rivet blank as claimed in claim 4, wherein the mandrel has a diameter in in the range of approximately 0.5 to 1.0 mm.

7. A composite rivet blank as claimed in any preceding claim, wherein the rivet blank is formed in a substantially cylindrical form having an internal opening or bore, wherein the bore is configured to receive a removable reinforcing member that is longitudinally extensible through said bore, and wherein the reinforcing member is arranged to prevent the closure of said bore when the blank is cut.

8. A composite rivet blank as claimed in any preceding claim, wherein opposing ends of the rivet blank are configured for forming into rivet heads, the rivet heads being formable by means of application of pressure and / or heat energy, and wherein the portion of the blank intermediate said rivet heads provides a rivet shank.

9. A method for manufacturing a rivet blank from a thermoset pre-impregnated (“pre-preg”) carbon fibre material; the method comprising the steps of:cutting the pre-preg material to a required size longitudinal to the fibre direction;winding a length of the pre-preg material over a mandrel to form a substantially cylindrical roll;and removing the rolled blank from the mandrel.

10. A method as claimed in claim 9, further comprising the step of tensioning the pre-preg material before and / or during winding.

11. A method as claimed in claim 9 or claim 10, further comprising the step of cold storing the rolled blank.

12. A method as claimed in any one of claims 9 to 11, further comprising the step of inserting a reinforcing member longitudinally through the bore of the rolled blank13, A method as claimed in any one of claims 9 to 12, wherein the thermoset of the pre-preg material is an epoxy resin system binder.

14. A method as claimed in any one of claims 9 to 13, wherein the pre-preg carbon fibre material comprises any one or more of: a unidirectional carbon fibre material; a fabric woven carbon fibre material; a biaxially oriented carbon fibre material.

15. A method as claimed in any one of claims 9 to 14, wherein the winding step comprises any one or more of cylindrical winding, helical winding, or spiral winding.

16. A method of using a composite rivet blank as claimed in any one of claims 1 to 15, comprising the steps of:inserting the rivet blank into an opening or openings in an item or items to be riveted;optionally applying an initial compressive force to the opposing ends of the rivet blank to initially expand said rivet blank ends in order to maintain the rivet blank in position;applying a compressive force to the ends of the rivet blank to form rivet heads, wherein the pressure is applied by shaped rivet heading tools;and curing the so-formed rivet.

17. A method as claimed in claim 16, wherein the compressive force is provided by drawing the opposing rivet heading tools towards each other by electromagnetic means.

18. A method as claimed in claim 16, wherein the compressive force is provided by drawing the opposing rivet heading tools towards each other by spring biasing means.

19. A method as claimed in any one of claims 16 to 18, wherein the step of curing the rivet comprises applying heat to said rivet, optionally via one or both rivet heading tools.

20. A method as claimed in claim 19, wherein the heat is generated by any one or more of an electro resistive heating means, a joule effect heating means, an ultrasonic heating means, an induction heating means.

21. A method as claimed in claim 19 or claim 20, wherein the heat generation means is incorporated in the rivet heading tool or tools.

22. A method as claimed in any one of claims 16 to 21, comprising the step of internally heating the rivet blank by means of a resistance wire located through an internal opening or bore of the rivet blank.

23. A rivet heading tool suitable for use with the rivet blanks and rivets in accordance with claims 1 to 15, and / or the method of claims 16 to 22,wherein the rivet heading tool comprises a head configured to transfer heat from a heat generating means to a rivet or rivet blank.

24. A rivet heading tool as claimed in claim 23, wherein the rivet heading tool comprises the heat generating means for heating and / or curing a rivet blank or rivet heat.

25. A rivet heading tool as claimed in claim 23 or claim 24, wherein the heat generating means is any one or more of: an electro resistive heating means, a joule effect heating means, an ultrasonic heating means, an induction heating means.

26. A rivet heading tool as claimed in any one of claims 23 to 25, wherein the head comprises a recessed portion, wherein the recessed portion comprises a substantially circular perimeter, and a sidewall that transitions into a peak formation which projects upwardly from the base of said recessed portion.

27. A rivet heading tool as claimed in claim 26, wherein the shape of the sidewall is configured to substantially define the shape of the rivet head to be formed by the rivet-heading tool.

28. A rivet heading tool as claimed in claim 26 or claim 27, wherein the sidewall is a curved sidewall.

29. A rivet heading tool as claimed in any one of claims 26 to 28, wherein the peak formation is configured to extend at least partially into a rivet blank end to expand said rivet blank end.

30. A rivet heading tool as claimed in any one of claims 26 to 29, wherein the rivet heading tool comprises a longitudinally extending through bore, the bore extending through the apex of the peak formation to the base of the head.

31. A rivet formed from a composite rivet blank in accordance with any one of claims 1 to 22.21

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