BLIND RIVET

The present invention relates to blind rivets, and relates particularly, but not exclusively, to blind rivets for use in joining soft and or friable materials.

Fasteners known as blind rivets are commonly used to fasten together materials, particularly in plate form, and generally consist of a mandrel having a mandrel head and a pulling stem, and a hollow rivet body having a flange at one end and through which the mandrel stem passes with the mandrel head abutting the end of the rivet body remote from the flange end. In order to fasten the materials together, the rivet is inserted from one side into apertures provided in the materials to be fastened together, until the flange of the rivet body abuts the face of the materials nearest to the operator setting the rivet. A setting tool then engages the flange and pulling stem of the rivet, and a pulling force is exerted on the stem. The mandrel head transmits the pulling force to the rivet body, as a result of which the rivet body collapses to form a joint on the blind side (i.e. the side remote from that side against which the flange of the rivet body abuts), and the pulling stem subsequently breaks at a predetermined load to form the completed joint.

An example of such a blind rivet, known as a multigrip blind rivet, is shown in

Figure 1. The rivet assembly 2 has a rivet body 4 having a series of grooves 6 of generally semicircular cross section arranged along the length of the rivet body 4, so as to divide the rivet body 4 into a series of cylindrical zones 8. Regions 10 of work- hardened material are formed at the base of the grooves 6. In order to set the rivet to fasten two sheets of material (not shown) together, a pulling force is applied to a pulling stem of a mandrel 3, which causes a head of the mandrel 5 located at the end of the rivet body 4 remote from the flange end 7 to apply a downward force to the rivet body 4. Referring to Figures 2 to 4 it can be seen that this force is resisted by the work hardened zones 10 to cause, initially, the cylindrical zones 8 of the rivet body 4 between the grooves 6 to bulge radially outwards and then the grooves 6 to collapse in an axial direction in order to form an expansion or bulge of the rivet body that is in contact with the blind side of the materials to be joined. The grooves 6 therefore assist the collapsing process of the rivet body 4 during setting of the rivet assembly 2.

Rivets of the type shown in Figures 2 to 4 suffer from the drawback that the depth of the grooves 6 must be carefully controlled in order for the rivet 2 to function correctly, as is illustrated in Figure 3 and 4. Figure 4 shows a cross sectional view along the line A-A in Figure 2. If the grooves 6 are too deep, cracking of the rivet body 4 at the base of the grooves 6 can occur, and if the grooves 6 are too shallow, there may be insufficient resistance to prevent the mandrel head from being pulled into or through the rivet body 4. This can be particularly problematic if the rivet body 4 is provided at its surface with a corrosion protection coating of, for instance, a polytetrafluoroethylene based material, since the low coefficient of friction of this type of coating material increases the tendency of the mandrel head to pull through into the rivet body 4.

An attempt to overcome this problem is shown in Figures 5 to 7, and consists of a rivet 50 having a rivet body 52 provided with a series of flat bottomed indentations 54 around its circumference and at various axial locations along the length of the rivet body 52, only one such axial location being shown in Figures 5 to 7. As can be more clearly seen in Figure 7, which is a sectional view along the line B-B in Figure 5, four indentations 54 are equiangularly arranged around the longitudinal axis of the rivet body 52, which creates four thickened portions 56 between which work hardened zones 58 are formed. As a setting load is applied to the mandrel (not shown) in a similar manner to the rivet shown in Figures 2 to 4, cylindrical zones 60 of the rivet body 52 located axially between the indentations 54 bulge outwards and eventually collapse to form a joint. This type of construction has the advantage of avoiding work hardening of the material of the rivet body 52 around its entire circumference, which consequently reduces the risk of the rivet body 52 cracking under the action of the mandrel setting load.

Although the known rivets shown in Figures 1 to 7 perform satisfactorily in most applications, it is difficult to ensure that the bulged portion of the rivet joint formed after setting of the rivet is located immediately adjacent to the blind face of the materials being joined together when the blind face is located approximately axially midway between two longitudinally spaced indentations. As shown in more detail in Figures 8 to 10, with the rivet types shown in Figures 1 to 7 when the blind face 62 of the materials 64, 66 to be fastened together surrounding the rivet body 52 is located generally axially midway between indentations 54 as shown in Figure 8, bulging of the cylindrical zone

60 of the rivet body 52 immediately surrounded by the adjacent portion of the blind face 62 is impeded. As a result, the cylindrical zone 60" adjacent to and axially separated from the cylindrical zone 60' surrounded by the blind face 62 may bulge more than the zone 60' surrounded by the blind face 62, as shown in Figure 9, and prevent further bulging of zone 60' during and after setting of the rivet 2 or 50 which can give rise to an approximately cylindrical portion, or substantially un-bulged portion 60' which extends from the blind side face of the workpiece to the next bulge portion 60" formed by cylindrical zone 60. This can in turn cause the main bulged portion of the rivet body, formed by the bulge portion 60", to be spaced from the blind face of the materials being joined by the largely unbulged, or only slightly bulged, cylindrical portion 60' of the rivet body 52, known as a stalk, as shown in Figure 10. Although the formation of a stalk does not generally detrimentally affect the mechanical quality of a joint formed by the set rivet, it may have less appealing appearance to users of the rivet than a joint in which the widest part of the collapsed rivet body 52 is located immediately adjacent to the blind face of the materials 64, 66 being joined together.

It is an object of the present invention to improve the reliability with which the bulged portion of the rivet body can be located in close proximity to the blind face of the materials being joined together by the rivet.

According to an aspect of the present invention there is provided a rivet body for a blind rivet, the rivet body comprising a flange for engaging a workpiece, and a plurality of first indentations in said rivet body and inclined relative to a longitudinal axis of the rivet body; wherein the rivet body is adapted to be collapsed by means of a load applied to the rivet body in a direction towards the flange and at a location on the side of the first indentations remote from the flange.

The present invention is based on the surprising discovery that by providing a plurality of first indentations inclined relative to a longitudinal axis of the rivet body, such that the indentations can be arranged to define tapering zones around the circumference of the rivet body, this provides the advantage of enabling alternating relatively stronger and weaker zones of material to be arranged circumferentially around the rivet body, as opposed to cylindrical zones of the prior art. This in turn has the advantage of enabling a bulge to be more reliably formed on or against the blind face of the workpiece, which enables better control of collapsing of the rivet body

during setting of the rivet, and avoids the production of un-bulged approximately cylindrical portions on the blind side of the workpiece during and after setting of the rivet. The invention also provides the advantage that because the formation of cylindrical zones along the length of the rivet body is avoided, this enables the rivet to be set by means of a lower setting force than in the case of rivet bodies defining cylindrical zones, which in turn results in less radial expansion of the rivet body in holes in the workpiece. This makes the rivet suitable for setting in soft and friable materials, and therefore provides a rivet having good performance over a wider range of hole sizes, plate thicknesses and material types.

The first indentations may be arranged in an outer surface of the rivet body.

The first indentations may be arranged so as to define a plurality of tapering zones around the circumference of the rivet body.

The depth of at least one said first indentation may be 15% to 35% of the thickness of said rivet body.

The depth of at least one said first indentation may be approximately 25% of the thickness of said rivet body.

The rivet body may further comprise at least one second indentation for application of a load thereto in a direction towards the flange for causing collapse of the rivet body.

This provides the advantage of minimising the risk of the head of a mandrel of the rivet moving within the rivet body after setting of the rivet.

The first indentations may define a single band of tapering zones around the circumference of the rivet body.

This provides the advantage of minimising the setting load required to set the rivet.

The first indentations may be inclined at an angle of 10 to 20 degrees relative to the

longitudinal axis of the rivet body.

At least one said first indentation is preferably inclined at an angle of approximately 15 degrees relative to the longitudinal axis of the rivet body.

According to another aspect of the present invention, there is provided a rivet comprising a rivet body as defined above, and a mandrel having a stem and a head, wherein the head is adapted to apply a load to the rivet body towards the flange and at a location on the side of the first indentations remote from the flange to cause collapse of the rivet body when a predetermined tensile load is applied to the stem.

A preferred embodiment of the 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 a side view of a first type of known blind rivet prior to setting; Figure 2 is a side part view of the rivet of Figure 1; Figure 3 is a side view of the rivet part of Figure 2 during an early stage of setting of the rivet; Figure 4 is a view along the line A-A in Figure 2;

Figure 5 is a side part view of a second type of known blind rivet prior to setting; Figure 6 is a side view of the rivet part of Figure 5 during an early stage of setting of the rivet;

Figure 7 is a view along the line B-B in Figure 5; Figure 8 is a detailed view of part of the rivet of Figures 5 to 7 located in a workpiece prior to setting of the rivet;

Figure 9 is a detailed view of the rivet part of Figure 8 during setting of the rivet; Figure 10 is a detailed view of the rivet part of Figure 8 after setting of the rivet; Figure 11 is a front view of a blind rivet embodying the present invention in an unset condition;

Figure 12 is a side view of the unset blind rivet of Figure 11; Figure 13 is a view of tapering zones of the rivet body of Figures 1 land 12=in a flattened condition showing all of the indentations of the rivet body;

Figure 14 is an end view of the rivet of Figures 11 to 13 before setting; Figure 15 is a view along the line C-C in Figure 14 during setting;

Figure 16 is a view along the line D-D in Figure 14 during setting; Figure 17 is a view corresponding to Figure 15 at a later stage of setting; Figure 18 is a view corresponding to Figure 16 at a later stage of setting; Figure 19 is a front view of the rivet of Figures 11 and 12=when set; and Figure 20 is a side view of the set rivet of Figure 19.

Referring to Figures 11 and 12, a rivet 102 embodying the present invention has an open-ended rivet body 104 and a mandrel 106, the mandrel 106 having a pulling stem 108 and a head 110 engaging the end of the rivet body 104. The rivet body 104 is generally cylindrical and is provided with a flange 112 at one end for engaging a work piece 114 (Figures 14 and 15). Four generally straight first indentations 1 16 having a depth within the range 15% to 35%, and typically about 25%, of the thickness of the material forming the rivet body 104 are formed in the outer surface of the rivet body 104 by means of processes which will be familiar to persons skilled in the art. It is found that indentations 116 having depth in the range of 0.25 to 0.38 mm (0.010 to 0.015 inch) have acceptable performance, and a preferred depth of the indentations 116 is 0.32 mm (0.0125 inch). The indentations 116 are inclined relative to a longitudinal axis 118 of the rivet body 104 and define a single band around the circumference of the rivet body 104 of upwardly tapering zones 120 and downwardly tapering zones 122. The angle of inclination of the indentations 116 relative to the longitudinal axis 118 is between 10 and 20 degrees, and is preferably about 15 degrees, i.e. the angle θ shown in Figure 13 is between 70 degrees and 80 degrees, and is preferably about 75 degrees. The indentations 116 are separated by gaps 124 at the locations at which they are closest to each other, and the angle of inclination of the indentations 116 relative to the longitudinal axis 118 of the rivet body 104 will vary depending upon the length of the rivet body 104, which will in turn be determined by the thickness of the workpiece 114 with which the rivet 102 is to be used. The angle of inclination although generally determined by the length of the rivet body 104 may be adjusted so that the gap 124 may be larger or narrower. The gaps 124 may vary in size, although gaps 124 of about 1mm width are preferred, and the gaps 124 may be absent altogether, i.e. the ends of the indentations 116 may touch each other.

The rivet body 104 is typically 3.2mm, 4.0mm, 4.8mm, 5mm, 6mm and 6.4mm in diameter with lengths of 8 and 12mm for the 3.2mm diameter and 10 and 12mm for the remaining diameters.

Typically the flange diameters are twice or three times rivet body diameter i.e. for a 4.8mm diameter rivet body the flange diameter would be 9.6mm diameter for a standard flange or 14mm diameter for a large flange. Also, the flange thickness will vary according to diameter so for 3.2mm, 4.0mm, 4.8mm, 5mm, 6mm and 6.4mm diameters the flange thickness will be 1.1mm, 1.35mm, 1.6mm, 1.6mm, 2.1mm and 2.1mm respectively for standard flange. For large flange rivets of 3.2mm, 4.0mm and 4.8mm diameters the flange thickness is 1.5mm, 1.6mm and 2.0mm respectively. Mandrel or rivet body bore diameter for 3.2mm, 4.0mm, 4.8mm, 5mm, 6mm and 6.4mm diameters will be 1.83mm, 2.29mm, 2.64mm, 2.64mm, 3.2mm and 3.6mm respectively.

As can be seen more clearly in Figure13, showing rivet body 102 as a developed section, i.e. in which the rivet body 102 is shown in a flattened condition in order to more clearly show the first indentations 116, when the rivet is inserted into a workpiece 114, the first indentations 116 in the rivet body 104 define a band of alternating upwardly tapering zones 120 and downwardly tapering zones 122 in the part of the rivet body 102 which projects beyond blind face 126 and outside of the workpiece 114. In the embodiment shown, the upwardly tapering zones 120 are diametrically opposed to each other, and the downwardly tapering zones 122 are diametrically opposed to each other. As a result, regardless of where the blind face shown as a line 126 of the workpiece 114 is located relative to the rivet body 104, the region of the rivet body 104 located outside of the workpiece 114 and adjacent the blind face 126 will define alternating stronger regions 128 of larger cross sectional thickness and larger developed sectional area and weaker regions 130 of smaller cross sectional thickness and smaller developed sectional area.

Referring back to Figures 11 and 12, second indentations 132 are also provided in the rivet body to push the rivet body material into recesses (not shown) beneath the mandrel head 110 to retain the mandrel head 110 in position relative to the rivet body 104 during setting of the rivet 102.

The setting operation of the rivet 102 shown in Figures 11 to 13 will now be described with reference to Figures 14 to 18.

The rivet body 104 is inserted into an aperture 134 in the workpiece 114 to be fastened, until the flange 112 of the rivet body 104 abuts the front face of the workpiece 114. A traction load is then applied to the stem 108 of the mandrel 106, as a result of which the mandrel head 110 applies an equivalent setting load to the end of the rivet body 104. As shown in Figures 14 to 16, which are respectively a plan view of the rivet 102 of Figures 11 to 13 after a setting load has been applied to the rivet 102 but before setting of the rivet has been completed, a view of the rivet body 104 along the line C-C in Figure 14 during setting, and a view of the rivet body along the line D-D in Figure 14 during setting, in the portion of the rivet body 104 outside of the aperture 134 of the workpiece 114, the stronger zones 128 bulge outwardly less than the weaker zones 130 because of their larger cross sectional thickness and larger developed sectional area.

As the rivet body 104 outside of the aperture 134 collapses further, as shown in Figures 17 and 18, the weaker zones 130 continue to bulge outwardly more than the stronger zones 128, as a result of which the angle of inclination of the portions of the first indentations 116 located outside of the workpiece relative to the longitudinal axis of the rivet body 104 becomes steeper. This results in a greater degree of collapse of the weaker zones 130 relative to the stronger zones 128, until the final condition of the set rivet 102, as shown in Figures 19 and 20, is reached, in which the rivet body 104 has collapsed in regions 136 inclined relative to the longitudinal axis 118 of the rivet body 104. This has the effect of ensuring that bulging of parts of the rivet body 104 always occurs beside the blind face of the workpiece 114 to produce a reliable fastening for a wide range of workpiece thicknesses and for a lower setting load in comparison with a rivet body defining cylindrical collapse zones around its circumference.

It can therefore be seen that the embodiment of the present invention described above has the advantage that the widest part of the fastening produced by the collapsed rivet can be reliably located immediately adjacent to the blind face of the materials being joined together, and the problem of "stalking", i.e. the formation of a cylindrical portion of the rivet body located between the widest part of the collapsed

rivet body and the blind face of the workpiece, together with the resulting reduced visual appeal to users of the rivet, is avoided.

It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. For example, although the indentations 116 of the embodiment described with reference to Figures 11 to 15 are generally straight and each indentation of a single rivet body has approximately the same angle of inclination relative to the longitudinal axis of the rivet, it will be appreciated by persons skilled in the art that under certain circumstances a single rivet body may have indentations having different angled of inclination relative to the longitudinal axis, and may have non-straight, for example curved, indentations.