The present invention relates to a fastener element, to a component assembly comprising the fastener element and a stack of panels and to a method of manufacturing the composite assembly

A rivet element is known from the document WO2012113463 and is used for joining either brittle components of magnesium or magnesium alloys or panels of composite materials, for example fiber reinforced composite materials. The rivet element is used in a self- piercing manner, i.e. it is used to pierce slugs from first and second stacked panels so that the head of the rivet comes to lie against the exposed surface of a first panel, or is countersunk into it, and the opposite end of the rivet is deformed to form a rivet bead, which is recessed in the opposite exposed surface of the second panel. The shaft of the rivet is provided with one or more circumferentially extending grooves into which material of the components extends in the riveted together state.

Basically the document WO2012113463 discloses a fastener element for joining at last first and second panel members and having: a) a head portion for engaging a first panel member,

b) a shaft portion of smaller diameter than the head portion,

c) a plurality of circumferentially extending grooves provided at said shaft portion and disposed to receive material from a second panel member, when the material is displaced into at least some of the circumferentially extending grooves , for example by the action of a punch or setting head. This design is problematic, especially when joining panels of composite material by riveting them together using the fastener element described above which is realized as a rivet element.

The deformation or upsetting of the so-called foot end of the rivet, i.e. the end opposite the head end, can only take place to a restricted extent so that the clamping effect of the rivet element is restricted when using composite panels and the number of rivet elements required per unit area of the panel assembly is higher than it need be. This adds cost and complexity to the riveted panel assembly. Moreover, the tendency to cracking when cyclic loads are applied to the panel assembly is not good.

In addition, the extent to which composite material can be deformed into the circumferential grooves and provide good anchorage there leaves something to be desired. In addi- tion there is a significant problem that the compressive loading of the panel assembly during riveting can lead to damage to the panels, with cracking and crumbling of the composite materials occurring, which leads to weakened panel assemblies and poor fatigue behavior under cyclic loads, with the cracks acting as stress raisers. It is the object of the present invention to provide an improved element which significantly mitigates the above described problems and which provides an element which is more flexible in use, making it possible to join panel materials of differing thickness and composition with one and the same design of element, thus reducing stockholding needs. In order to satisfy the above objects there is provided, in accordance with the present invention, a fastener element of the kind known from the document WO2012113463, the fastener element being characterized in that: d) it is formed as a press-in element and

e) the shaft portion has a larger diameter portion adjacent the head portion and a smaller diameter portion provided with the circumferentially extending grooves, with

f) the larger diameter portion forming a shoulder adjacent the smaller diameter portion and axially spaced from the head portion, the shoulder being positioned to restrict compression of the panel members on deforming the material of the second panel member into at least some of the circumferentially extending grooves. When reference is made here to first and second panels then it should be understood that this wording is not intended to be restricted to the presence of just two panels but also encompasses the use of a third panel and of a third panel and a fourth panel and also of further panels if desired. The second panel which is deformed into the circumferentially extending grooves is generally an outside panel of the panel assembly and is made of a metal. It can be a sheet metal part in its own right or can be a metal washer or a load spreading plate of metal.

The first panel disposed adjacent the head portion of the press-in element is also generally an outside panel of the panel assembly and is made of a metal. Again, it can be a sheet metal part in its own right or can be a metal washer or a load spreading plate of metal. The panel assembly or stack of panels can for example be at least any of the following combinations: a) first and second sheet metal parts without any further panel members

b) a first sheet metal part, at least one composite panel and a second sheet metal part

c) a first sheet metal part in the form of a washer or a load spreading metal plate, at least one composite panel and a second sheet metal part d) a first sheet metal part in the form of a washer or a load spreading metal plate, at least one composite panel and a second sheet metal part in the form of a washer or load spreading metal plate

e) a first metal part, optionally in the form of a washer and a load spreading plate, a second panel in the form of a sandwich panel having first and second skins and a core disposed there-between, the skin of the sandwich panel remote from the head portion of the press-in element forming the second panel, the material of which is brought into engagement with the circumferentially extending grooves, the core being of any desired material such as a honeycomb material of card or metal, a porous plastic core, a solid plastic core or plastic membrane, a fiber reinforced plastic core or membrane or a metal foam material.

f) a combination as set out at e) above with an additional washer or load spreading plate forming the second panel member.

The element of the present invention is distinguished from the rivet element known from the document WO2012113463 in that it is a press-in element and not a rivet element. Persons skilled in the art distinguish between these two types of element. A rivet element is understood to mean an element which is intentionally deformed when connecting two panels together, i.e. by the beading over or upsetting of the foot end of the rivet. A press- in element on the other hand is understood to be an element provided with features defining undercuts, in the present case the circumferential grooves, with panel material being deformed and caused to flow into the undercuts. With press-in elements it is usual to speak of clinching rather than riveting.

Importantly the provision of a shaft portion having a larger diameter portion and a smaller diameter portion defining a shoulder means that the degree of compression applied to the panel assembly during clinching is limited by the presence of the shoulder thus protecting the panel assembly from unwanted damage. Despite the fact that the shoulder is of fixed position it can nevertheless limit the panel assembly to a certain degree of compression during assembly irrespective of the panel thickness by utilizing a spacer (such as a washer) to compensate for difference in height of different assembles. Thus fewer elements are required in practice, only a few different sizes need to be stocked to cope with a range of panel thicknesses.

The press-in element of the present invention is also used differently from the known rivet element.

The idea behind the present invention is to provide a press-in element which can be used to form panel assemblies by clinching to form a permanent bond between panel assemblies. However, in the pursuit of better performance with reduced weight, vibration and noise transmission, there are a range of emerging panel construction materials that cannot straightforwardly be clinched or otherwise joined. For example, such emerging panel construction materials include stacked multiple-dissimilar panel materials, sandwich panel constructions and composite panels such as carbon fibre reinforced materials. It will be noted that most of these panel assemblies cannot be welded as the materials and material combinations are not suited for this purpose. The use of adhesives is frequently possible but curing times are long relative to other fastening methods and often clamping or loose fastener assemblies are needed to provide temporary support. Rivet elements are also inherently soft and this gives rise to difficult handling and greater assembly process time. Sandwich materials and composites often need a greater surface area to spread the clamping load over a larger bearing surface.

These problems are overcome by using the press-in element of the present invention in a component assembly as defined in claim 6. Thus the component assembly comprises a stack of at least first and second panels, and a press-in element in accordance with the invention as defined above, the shaft portion of the press-in element extending through a hole in said stack of panels, with the head portion being one of recessed into or bearing against a first panel of the stack at one side of the stack, when the first panel is a metal panel, or, if the first panel is a composite material, being one of recessed into or bearing against a load spreading plate, with material of a second panel of the stack at an opposite side of the stack from the first panel being displaced into at least some of the plurality of circumferentially extending grooves when the second panel is a metal panel, or, when the second panel of the stack is of composite material, with material of a metal load spreading plate being displaced into at least some of the plurality of circumferentially extending grooves.

The present invention is highly adaptable - it is possible to clinch multiple panel stack- ups, of metals, metals and composites, and composites and the press-in element can be combined with clamping spreader plates of metal for sandwich and composite panels. The following advantages result:

- The parts can be simply pressed together - no clean-up or waiting time.

- Thicker metal panels can engage with more than one clinch ring - thus enhancing strength of joint.

- Separate fastener components can be partially assembled off-line - i.e. stud and bottom plate - resulting in an easier final assembly. This is advantageous for supply into high- volume applications.

- A complete set of separate parts can be installed on-line in one press stroke. This is advantageous where customers want control of the full assembly or want flexibility to substitute stud sizes etc.

- Component parts in stock allow flexibility - plain washers with holes could be used with multiple stud lengths etc. - Here sandwich or composite panels are elastically deformable - so that one can obtain pre-load clamp, especially in combination with a compression limiter such as the aforementioned ring shoulder.

- The design allows potential rotation of assembled panels to perhaps make a subassembly more compact for transport etc.

- The stud part, i.e. the press-in element, can be cold-headed and multi-clinch profile can be rolled using existing Penn Engineering technologies. Flat washers can be blanked and punched per existing Penn Engineering criteria and meet existing performance specifications.

- The press-in element component can be auto-fed and load spreading plates can be supplied separately for greater flexibility at customer assembly site.

- An assembly of a new special multi-clinch stud design and companion plates each prepared with a central hole, to allow clinching of multiple panels at variable stack-up heights.

- The invention simplifies assembly of dissimilar metal, metal-skinned sandwich and composite panels. The fastener assembly is simply pressed in to place without curing time, clean-up or cross threading risks. In addition, the individual fastener part construction is easier to manufacture and offers increased flexibility in assembly and automatic feeding options

The diameter D3 of the larger diameter portion of the shaft portion is greater than the diameter D2 of the smaller diameter portion of the shaft portion by a factor in the range from 1.1 x D2 to 2 x D2, i.e. D3 > 1.1 x D2 but≤ 2 x D2. This is a useful range of sizes that result in shoulders having a radial width suitable for use with a variety of panel materials to control the degree of compression of the clamped panel assembly. The invention also contemplates the use of a press-in element, wherein the head portion is received in or against a load spreading plate such as a metallic washer, the load spreading plate optionally being provided with a plurality of shaped apertures. This design can be used to provide a large area load spreading plate for use with composite panel materials where good load spreading is desired to prevent undue compression of the panel material. The apertures are used to lighten the design of the load spreading plate or washer without significantly detracting from its load carrying ability. This design also only requires the head portion to have a fractionally larger size than the diameter of the shaft portion so that it is easy to manufacture by cold heading but still has a head portion of a size which enables easy handling of the press-in element. If Dl is the diameter of the head portion and D2 is the diameter of (the smallest portion of) the shaft portion, then Dl is preferably greater than 1.1 x D2 but less than 1.5 x D2. As an alternative to the above design a press-in element in accordance with the invention can be made with a significantly larger diameter Dl of the head portion. Thus the Dlof the head portion can be is at least twice the diameter D2 of the shaft portion (of the smaller diameter of the shaft portion). In accordance with a particularly preferred embodiment of a press-in element of the present invention it can have

a) a head portion,

b) a shaft portion of smaller diameter than the head portion,

c) a plurality of circumferentially extending grooves provided at said shaft portion and disposed to receive material from one or more panel members, when the material is displaced into at least some of the circumferentially extending grooves , for example by the action of a plunger or setting head and d) a threaded portion being either an internal thread formed in at least one of the shaft portion and the head portion or an external thread formed on a thread carrier extending from at least one of the shaft portion and the head portion. This design has the special advantage that a further component can be joined to a component assembly formed using the press in element in at least first and second panels as described above to form a component assembly, the further component being clamped to the component assembly by a bolt engaging through a hole in the further component into the internal thread or by the thread carrier extending through a hole in the further component which is then retained on the component assembly by a nut engaging on the thread carrier.

Preferred embodiments of the component assembly of the present invention are set forth in claims 7 to 12 and preferred methods of making the component assembly are set forth in claims 13 to 15.

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings which show: Fig. 1 a perspective view of a press-in element having a head portion engaged in a metal washer and showing also a washer for clinching to the circumferentially grooved shaft of the press-in element,

Fig. 2A a perspective view of a component assembly having two different press-in ele- ments joining two composite panels together, Fig. 2B a side view of a component assembly similar to Fig. 2A but with the two composite panels being joined by a single press-in element with the press-in element and the two associated metal washers being shown separately in a perspective view, Fig. 3 a perspective view of a plunger used for clinching together a component assembly such as that of Fig. 2A or Fig. 2B or in Fig. 4,

Fig. 4 a schematic drawing showing a partly cut away side view of a component assembly such as is shown in Fig. 2B but illustrating the use of the plunger of Fig. 3 and an anvil,

Fig. 5 a view similar to that of Fig. 4 but showing a preferred design of the press-in element with a shaft portion having a shoulder,

Fig. 6 a view closely similar to that of Fig: 5 but showing a press-in element having a head portion of enlarged diameter,

Fig. 7 a view similar to that of Fig. 6 but showing an alternative design of the head portion of the press-in element for use adjacent a softer metal panel such as one of aluminum,

Fig. 8 a view similar to that of Fig. 7 but illustrating the use of the press-in element to join a panel of softer material such as aluminum to a panel of sandwich material or composite material, Fig. 9 a view similar to Fig. 7 but showing the press-in element used with a three panel assembly, Fig. 10 a view similar to Fig. 9 but showing the use of the press-in element of Fig. 9 to join a metal panel of harder material such a steel to a sandwich material comprising two skins and a core disposed between the skins, Fig. 11 a view similar to Fig. 7 but with only two panels secured to the press-in element by clinching and with the shaft portion of the press-in element being extended by a threaded portion enabling another component to be secured by a nut to the component assembly formed by the press-in element and the two panels clinched to it, Fig. 12 an alternative design of a press-in element similar to Fig. 11 but with the threaded portion for securing a further component extending away from the head portion of the press-in element,

Fig. 13 a view similar to Fig. 6 but with the press-in element being hollow and having an internal thread enabling a further component to be secured by a bolt to the component assembly of Fig.6,

Fig. 14 a view similar to Fig 13, but with the further component being attached to the other side of the component assembly,

Fig. 15 is a view similar to Fig. 5 but showing increased bearing area using load spreading plates for sandwich materials and composite materials,

Fig. 16 a drawing similar to Fig. 11 but with the element having a ring shoulder similar to Fig. 5 and

Fig. 17 a drawing similar to Fig. 12 but with the element having a ring shoulder similar to Fig. 5. In all embodiments common reference numerals are used for parts of the same design or having the same function. The description of such parts will not be unnecessarily repeated in the interest of brevity and it will be understood that a description once given for any part in relation to a specific figure applies also to a part having the same reference numeral in another figure but not specifically described unless something is stated to the contrary.

Turning now to the drawings Fig. 1 shows a fastener element 10 having:

a head portion 12, a shaft portion 14 of smaller diameter than the head portion 12 and a plurality of circumferentially extending grooves 16 provided at said shaft portion 14. The grooves can have a variety of profiles ranging from semicircular to rectangular or grooves with tapering flanks, optionally with different taper angles. They preferably have the same contour as the single groove to be found in so-called PEM fasteners. More specifi- cally this groove can be described as a "c-shaped" annular groove, but grooves can also be considered with square undercuts and offset diameters.

In the embodiment shown in Fig. 1 the head portion 12 is countersunk within a metal washer 18 and is passed in use through a preformed hole in the panel assembly which is to be clinched together. Above the press-in element of Fig. 1 there is shown one form of a metal washer, i.e. a circular metal plate 20 which is used in a panel assembly comprising at least two layers of composite panel materials 22, 24 as shown in Fig.2A to clamp the composite material panels 22, 24 between the washer 18 at the head portion of the press-in element and the further washer 20. This is shown at the left hand side of Fig. 2A. Instead of using a relatively small diameter washer 20 a larger washer 20' shown at the right hand side of Fig. 2A can be used for improved load spreading. The washer 20' in Fig. 2A is optionally provided with an array of equi-angularly spaced apertures 26 which are used to lighten the washer 20' and which can also provide a degree of torque resistance if this is required (for example in an embodiment such as is shown in any of the Figures 11 to 14). This torque resistance is achieved because the clamping load applied to the washer to clamp the panel assembly causes the washer to form a slight depression in the adjacent composite panel and the composite panel forms slightly raised portions located in the apertures 26 of the further washer or load spreading plate 20'. A similarly designed metal washer 18' which can be seen in Fig. 2B can also be provided at the head portion 12.

The assembly of Figs. 2A and 2B is clamped together by material of the washer 20 or 20' being deformed or clinched to engage those ones of the circumferentially extending concentric grooves 16 that are present in the vicinity of the rim of the central hole of the washer 20 or 20'. These grooves 16 are thus disposed to receive material from the washer 20 or 20' (if used), or from one or more panel members (if metal panel members are to be used), the respective material being displaced into at least some of the circumferen- tially extending grooves, for example by the action of a plunger of a setting head pressing against the washer 20 or 20' in Fig. 2A or 2B while the washer 18 or 18' and/or the head portion 12 of the press-in element 10 is supported on an anvil (36 in Fig. 4), which in this case can simply comprise a flat tool. Fig. 3 shows a typical plunger 28 for indenting the metal washer 20, 20' around the protruding circumferentially grooved portion to cause metal of the washer to flow into the adjacent circumferential grooves 16. The plunger 28 has at its end face a central bore 30 to accommodate the protruding end of the shaft portion of the press-in element and a ring nose 32 surrounding the central bore 30. The ring nose 32 forms a ring shaped de- pression 34 of complementary shape to the ring nose 32 in the exposed surface of the washer 20, 20' as can be seen in Figs. 2A and 4. Thus the metal of the washer 20, 20' which is displaced during formation of the ring recess flows radially into the adjacent circumferential grooves 16, thus locking the washers 18 and 20, or 18' and 20' together by clinching and clamping the composite panels 22, 24 between them. It can be seen that the ring nose has, facing the washer 20, 20' a diverging, radially inwardly inclined flank forming an included angle of approximately 90deg. with the central longitudinal axis of the plunger or of the press-in element, and an outer flank which lies on the surface of a right cylinder. The two flanks are preferably joined by a circularly extending flat land. It will be understood that the flat land or rather its radial width provides stability and increases the volume of metal that can be displaced and that the inclined flank favors the radially inwardly directed movement of metal by cold deformation. It will be appreciated that by providing a plurality of circumferential grooves 16 along an elongate shaft portion 14 the axial height of the panel assembly (the height in the axial direction of the shaft portion 14 of the press-in element 10) can vary within wide limits with more or less of the shaft portion 14 projecting beyond the washer 20 or 20' and the appropriate ones of the circumferentially extending grooves being used to accommodate the radially displaced material.

It can be seen from the foregoing that the clinching action used to secure the panels 22, 24 between the washers 18 and 20 or 18' and 20' involves only deformation of the metal washer 20 or 20' so that metal of the washer flows into undercuts of the fastener element, the concentric circumferential grooves 16, and that no intentional deformation of the fastener element takes place. Alternatively if the upper panel 24 is a metal panel the washer 20 or 20' can be omitted and the clinching effected by cold deformation of the uppermost panel. Thus the element is a press-in element rather than a rivet element.

Although it is possible and indeed within the scope of the present invention to control the preload applied to the panels 22, 24, for example by use of a hold down member (not shown, but taking the form of a spring loaded ring surrounding and axially slidable relative to the plunger 28) and/or by suitable sizing of the washers 18 and 20 or 18' and 20', it is easier to control the preload by a different technique, namely by the design shown in Fig. 5.

In Fig. 5 the shaft portion 14 has a larger diameter portion 38 adjacent the head portion 12 and a smaller diameter portion 40 provided with the circumferentially extending grooves 16, with the larger diameter portion 38 forming a shoulder 42 axially spaced from the head portion 12, the shoulder 42 being positioned to restrict compression of the panel material on deforming the washer 20 or 20' (or the metal of the uppermost panel if this a metal panel) into at least some of the circumferentially extending grooves 16. With this design the preload which can be applied to the stack of panels is controlled by the position of the shoulder 42 which limits the downward movement (downward in the geometrical representation shown) of the washer 20, 20' and thus the preload. For example, the shoulder 42 could be positioned to permit a maximum compression of the undamped panel height of 5%.

In Fig. 5 the diameter D3 of the larger diameter portion of the shaft portion is typically greater than the diameter D2 of the smaller diameter portion of the shaft portion by a factor in the range from 1.1 x D2 to 2 x D2, i.e. D3 > 1.1 x D2 but≤ 2 x D2. It can be seen from the representations of the head portion 12 of the press-in element 10 so far discussed that this is only slightly larger by say 10 to 20% than the diameter of the shaft portion and has alternating depressions and noses or lugs which dig into the metal of the washer 18 or 18' (or of a metal panel if this is disposed adjacent the head portion 12 and of adequate strength). It is, however, also possible to make the head portion sub- stantially larger as shown in Fig. 6.

There the head portion 12 has a diameter Dl and the smaller diameter of the shaft portion has a diameter D2, such that the diameter Dl is approximately twice the diameter D2. An even larger head might be beneficial if the lowermost panel is of soft material such as aluminum or plastic, the limit is set by the technical difficulty of making a press-in element of this kind with a large diameter head portion 12 by cold heading. In Fig. 6 the head portion is not provided with alternating noses or lugs and recesses. This is not nec- essary when there is no need to prevent relative rotation of the press-in element and the adjacent panel.

Turning now to Fig. 7 there can be seen an alternative design of the press-in element with a large head, again with Dl typically being 2 x D2. Here the side of the head portion facing the lowermost panel is provided with alternating noses or lugs and recesses and it can be seen that the head portion 12 is typically only pressed into the lowermost soft metal panel 22 by the depth of the recesses, so that the noses are pressed into the panel 22 and the remainder of the head portion 12 projects below the lowermost panel 22. In the representation of Fig. 7 the uppermost panel 24 can be a metal panel used to locally stiffen the lowermost panel 22 or can be a washer such as 20 or 20' also there is no reason why an intermediate panel or panels should not be present. It is simply necessary to ensure that the shaft portion is sufficiently long to penetrate all panels and any washer such as 20 or 20' that is present and that there are circumferentially extending grooves 16 into which metal panel or washer material can be clinched to clamp the component assembly so that the panel assembly is clamped between the head portion 12 and the washer 20, 20' or the uppermost panel.

Figs 9 and 10 show two alternative embodiments in which a press-in element with a small diameter head portion 12, only fractionally larger than the diameter of the shaft portion 14, is used with a panel assembly. In Fig. 9 the panel assembly has a lower metal panel 22, which is here comparatively hard, e.g. of steel and the intermediate panel 23 of the multiple panel assembly is a softer composite panel or plastic panel, with the upper panel 24 again being of metal, i.e. no washer is used in this design. It will be noted that in this de- sign the lower end face of the head portion 12 is flush with the lower face of the panel 22 and such a flush design is possible in all embodiments (also in embodiments in which the head portion 12 engages a washer such as 18 or 18'). In Fig 10 the panel assembly again has a lower metal panel 22 which is comparatively hard, e.g. of steel, and this bears against a panel 24 made of a sandwich material, e.g. upper and outer skins of metal with a relatively soft core layer, e.g. of honeycomb material such as card or a cellular or porous material of metal or plastic. The upper metal skin of the upper panel 24 is clinched to engage some of the circumferentially extending grooves 16.

Another important embodiment of the invention is shown in Fig. 11. Here the press-in element 10, resembles a shortened version of the press-in element of Fig. 4, could however have a shaft potion 14 of any desired length. The press-in element of Fig.11 has a head portion 12, a shaft portion 14 of smaller diameter than the shaft portion 12, and a plurality of circumferentially extending grooves 16 provided at said shaft portion 14 and disposed to receive material from one or more panel members, when the material is displaced into at least some of the circumferentially extending grooves, for example by the action of a plunger and an anvil. A threaded portion 44 is formed at the end of the shaft portion 14 adjacent the circumferentially extending grooves 16. The threaded portion 44 can be used to join a further component 46 to the component assembly formed by the press-in element 10 and the panels clinched together by it. The further component 46, which may be a panel, or an instrument, or a housing of a unit of some kind, is secured to the component assembly by the use of a nut 48.

Instead of providing the threaded portion 44 at the end of the shaft portion 14 adjacent the circumferentially extending grooves 16 it could also be provided extending away from the head portion 12 as shown in Fig. 12. A threaded portion 44 for the attachment of fur- ther components could indeed be provided at both ends of the press-in element e.g. as can be understood by superimposing Figs. 11 and 12.

In similar manner the press-in element 10 could also be formed as a nut element having an internal thread 50 in at least one of the shaft portion 14 and the head portion 12, as shown in Figs 13 and 14. With such a design a further component 46 could be joined to the clinched component assembly by the use of a bolt 52, introduced into the internal thread, either from the shaft end of the press-in element (Fig. 13) or from the head end (Fig. 14).

Thus the present invention can be regarded as is based on a new press-in element or stud design which extends the Penn Engineering clinch profile, in multiple rings, partially or fully along the length of the stud. A special tool can then be used to deform a metal panel or washer creating a clinch fastening at any one of the clinch ring positions allowing com- pensation for multiple panels, variable stack-up heights, dissimilar materials and varying thicknesses as shown in the Figures.

The following additional description can be given. Multi-clinch installation tooling

In all embodiments, the installation tool deforms the metal panel material into the corresponding clinch ring 16 at some distance along the stud length. The tool has a hole in the center to accommodate the stud length and a raised ring profile 32 of the form as shown in Figure 3. The profile of the raised tool is designed to displace panel material, from around the panel hole, preferentially inwardly, to form a permeant clinch with one or several concentric clinch rings 16 on the stud. Finally Fig. 16 shows a drawing similar to Fig. 11 but with the element having a small head 12 and a ring shoulder 42 similar to that of Fig. 5 as well as the threaded portion 44 and Fig. 17 shows a drawing similar to Fig. 12 but with the element also having a small head 12 and a ring shoulder 42 similar to that of Fig. 5. It will be seen that in Fig. 16 the thread portion 44 extends away from the ring grooved portion of the shaft 16, whereas in Fig. 17 it extends away from the head portion 12. Also it will be noted that the head portion 12 need not be a small head as in Fig. 5 but could be a large head as shown in Fig. 6.

Special Embodiments;

Stud: Metal-to-metal assembly.

Where two or three metal panels 22, 24 are to be assembled together, as in Fig. 7, the stud can be installed with a flush style head to provide a desirable flush finish as in Fig.10 which may be advantageous over loose fasteners or rivets. For softer panel materials, or where greater loads are expected, a full headed fastener can be used. See Figures 6, 7 and 8. This still presents a lower profile than many conventional loose fasteners due to the higher hardness and strength employed in clinch fasteners.

Multiple panel assembly

Where there are more than two panels 22, 24 in a stack-up, the stud head 12 can be clinched into the bottom panel 12 and the top panel can be clinched at any position of a concentric clinch ring. This allows adaptability to clinch many different panel stack-ups heights and allows non-metallic (non-clinchable) panels to be stacked between two metal panels. See Figure 9.

Lightweight Sandwich panel Assembly

Sandwich panels are constructed with two metal skin surfaces separated by a sandwiched material - often a rigid foam material to reduce weight or a polymer material to reduce noise. In this scenario, the stud head 12 can be clinched into the bottom skin and the top skin can be clinched at any position of a concentric clinch ring. This design is similar to Figure 10, but with the head portion bearing directly against the lower skin of the sandwich panel 24. For sandwich panels, an additional over load compression can be em- ployed during the installation stroke. Once the fastener is installed and the press force removed, the expansion of the material creates some degree of clamp load. This pre-load can be further enhanced for a fixed material thickness by adding a compression limiter shoulder to the stud. See Figures 5, 6, 13 and 14. Lightweight Composite Assembly - Large Diameter Head /Plain Washer

For non-metallic composite panels, it is typical to reduce the stress concentration around the hole in the panel by increasing the bearing surface area of the fastener. This may be achieved by using a large diameter head on the fastener (Figs. 6, 7 or 8). The top panel can then be directly clinched at any position of a concentric clinch ring. For non-metallic top panels, a plate or washer 20, 20' can be added to increase the bearing area and allow clinch (Figure 8). However, there are limits to the forge-ability of large headed fasteners. In this case a plate (e.g. a circular plain washer such as 18, 18') can be clinched onto the head 12 to expand the surface area. A similar plate (such as 20, 20') may then be clinched at any position of a concentric clinch ring on the opposite surface of the joint assembly. In Fig. 15 the bottom stud and plate 18 can be pre-assembled for convenience and the combination of the three remaining plates 22, 24, 20 (plate-stud-plate) can be installed in one stroke. Lightweight Composite Assembly - bearing spreader plate with hole pattern

To reduce weight and enhance functionality, the two bearing spreader plates 18', 20' may also have holes 26 to remove some plate material. (Figs 2A and 2B). For example, the Penn Engineering VariMount blank baseplate could be used. In this format, the holes allow possible (additional) fixing with rivets or other PEM hardware. The plate could be adhesively bonded to the surface of a composite panel, overmolded or assembled into the fiber weave during lay-up. The secondary fixing can then be achieved by clinching at any position of a concentric clinch ring on the opposite surface of the joint assembly.

Compression limiter

For sandwich and composite panels, an additional over-load compression can be em- ployed during the installation stroke. Once the fastener is installed and the press force removed, the expansion of the material creates some degree of clamp load. As this creates a risk of cracking or damaging the panel due to over compression, the multi-clinch stud can be manufactured with a shoulder to act as a compression limiter (as in Figs. 5, 6, 13 and 14). The shoulder provides a hard stop for the top clinch plate ensuring that the desired compression is not exceeded.

Helical thread portion

In some applications, the clinch is an interim step of a sub-assembly prior to final assem- bly to additional structure. In this case, a portion of the stud length can contain concentric clinch rings 16 with a transition point to a conventional helical thread 44 standard (e.g. metric M4). In this case, the multi-clinch stud acts to "tack" two (or more) panels together with the final clamp load being delivered by conventional torque controlled spinning of a loose nut. (See Figs. 11 and 12). Rotation

As the clinch rings are concentric, panel assemblies, i.e. stacked panels joined in accordance with the invention by a press-in element, potentially allows rotation of assembled panels, relative to each other, to perhaps make a subassembly more compact for transport etc. Thus, the clinching of the uppermost panel of the stack into the concentric circumferential grooves can be effected so that at least some of the panels of the stack are not firmly clamped together but relatively rotatable to each other, whereby the component assembly can be placed in a compact form for storage and/or transport and the panels, which may for example be bars of a linkage, are subsequently rotated relative to one another for use or installation.

In the foregoing disclosure it is clear that the tool used for clinching deforms the outermost panel and that the panel is made of metal, typically aluminium, brass, copper, steel and stainless steel. This is the usual situation. However, in practise it is possible to deform and clinch any material that cold-flows and retains the deformation. The applicants have, for example, successfully clinched polymer/ plastic panels, such as panels of ABS

Poly(Acrylonitrile Butadiene Styrene), Nylon 6, Nylon 66 and an ASA/PC blend (a blend of Poly(Acrylic Styrene Acrylonitrile) and Polycarbonate) using the described apparatus and press-in elements, although the strength of the clinched connection is significantly lower than that achieved when clinching a metal panel. The present invention contemplates that the panel that is clinched can be of any material having sufficient ductility and cold- flow properties that a clinched joint can be realised, i.e. a clinched joint in which the deformed panel material retains the deformation to which it is subjected and leads to a connection of sufficient strength for the envisaged purpose. Thus it will be appreciated that the metal panel subjected to clinching in the present specification, which can be a sheet metal part, a metal washer, a load spreading metal plate or a metal skin of a composite structure can also be replaced with a panel of the same kind but made of a differ- ent ductile material, such as a plastic or polymer part. Thus the panel subjected to clinch ing could, within the context of the present invention, be a part made of a plastic or polymer sheet, a plastic or polymer washer, a plastic or polymer load spreading plate or a plastic or polymer skin of a composite structure.

Reference numeral list

10 press-in element

12 head portion

14 shaft portion

16 circumferentially extending grooves

18 metal washer, load spreading plate

20 further washer or load spreading plate

22 composite material panel

23 intermediate panel

24 composite material panel

26 apertures of the further washer 20

28 plunger

30 central bore of plunger

32 ring nose of plunger

34 ring recess formed in washer 20, 20' by ring nose

36 anvil

38 larger diameter shaft portion

40 smaller diameter shaft portion

42 shoulder

44 threaded portion

46 further component

48 nut

50 internal thread, threaded portion

52 bolt

Dl diameter of head portion 12 D2 diameter of smaller diameter shaft portion 40 (if provided) or of shaft portion 14 if no larger diameter portion 38 is provided

D3 diameter of larger diameter shaft portion 38