The invention concerns a blind rivet, in particular for joining components made of plastic, having a hollow rivet body that has an elongated shank that extends coaxially to a longitudinal center axis of the blind rivet and has a bore, having a flange extending radially at one end of the shank for contact with an accessible side of a component, and having, at the opposite end of the shank, a foot end that is passed through openings in the components, and having, located in the bore of the rivet body, a mandrel that has a mandrel shank, a drawing end projecting out of the flange of the rivet body that can be separated from the mandrel shank, and a mandrel head that stands in operative connection with the foot end of the rivet body in order to transmit a force to the rivet body during setting of the blind rivet. The invention additionally concerns a fastening arrangement with such a blind rivet.
A blind rivet of the specified type is known from WO 2009/098,431 A1. Such blind rivets are used to permanently join workpieces that are in contact with one another. The workpieces typically have bores or holes passing through them that are brought into alignment with one another and into which the blind rivet is placed and then fastened by deformation. A fastened blind rivet usually results in a clearance-free seating of the rivet body in the holes of the workpieces and clamps the workpieces together.
In the automotive industry, uses of blind rivets include fastening attached parts such as power-window motors, loudspeakers, and other parts, to a component support, such as a door module support, using one or more blind rivets. In many cases, the mounting portions of the attached parts and component supports are made of plastic, with the result that the fastening with blind rivets was only satisfactory with the use of additional components made of metal to reinforce the plastic parts. Without metal reinforcing parts, setting of the rivet joints can occur that could lead to a detachment of the joint under load. The settings are caused by the customary formation of the blind head during setting of the blind rivet. Furthermore, under certain circumstances the mounting hole in the plastic component may split due to the radial expansion of the rivet shank during setting of the rivet.
The object of the invention is to create a blind rivet of the initially mentioned type and a fastening arrangement with such a blind rivet that permit improved joining of components made of plastic. According to the invention, the blind rivet comprises a hollow rivet body that has an elongated shank that extends coaxially to a longitudinal center axis of the blind rivet and has a bore, a flange extending radially at one end of the shank for contact with an accessible side of a component, and, at the opposite end of the shank, a foot end that is passed through openings in the components, and additionally has, located in the bore of the rivet body, a mandrel that has a mandrel shank, a drawing end that projects out of the flange of the rivet body and can be separated from the mandrel shank, and a mandrel head that stands in operative connection with the foot end of the rivet body in order to transmit a force to the rivet body during setting of the blind rivet, wherein the shank of the rivet body has a first section adjoining the flange and, adjacent thereto and extending to the foot end, a second section, and the second section is designed such that, as a result of a process in which the flange is pressed against one side of the components and the foot end is simultaneously drawn toward the other side of the components with the aid of the mandrel, a flange forms that lies flat against the component located on the inaccessible side, and wherein the strength of the first section of the shank is increased with respect to the strength of the second section in such a manner that the outside diameter of the first section does not increase or increases only slightly as a result of the process.
The blind rivet according to the invention is distinguished from prior art blind rivets in that the first section of the shank of the rivet body adjoining the flange is hardened in such a manner that it is not expanded or is expanded only slightly during setting of the blind rivet. Consequently, the hardened section of the blind rivet can be placed in a component hole with a slight oversize without having an increased radial pressure arise between the rivet section and the wall of the bore during setting, which could cause damage to the component. The blind rivet according to the invention is thus suitable for fastening components made of lower strength materials such as plastic, with it being possible to dispense with additional metal reinforcing parts, such as washers or tubular rivets. The elimination of additional reinforcing parts made of metal also results in cost advantages during assembly, and expands the range of application possibilities for the blind rivet according to the invention.
According to another proposal of the invention, the increase in strength of the first section of the rivet body is accomplished through plastic deformation. The plastic deformation can be accomplished in that the first section has multiple radial indentations, compressions, or crimps, which extend over a substantial part of its length. As a result of the plastic deformation, the first section may also be provided with multiple longitudinal ribs. The plastic deformation produces work hardening in the region of the first section, causing the deformation resistance of the first section to be significantly increased as compared to the second section. The first section can thus better withstand the forces occurring during deformation of the second section of the rivet body, so that no radial deformation, or at most minor radial deformation, of the first section occurs during setting of the blind rivet. Additionally, the strengthening of the first section by plastic deformation has the advantage that the diameter of the first section can correspond essentially to the diameter of the second section, and the rivet body is easy to manufacture. The foot end of the rivet body also can have an increased strength brought about by plastic deformation so that it can better withstand compressive forces acting during the setting process.
According to another proposal of the invention, provision can be made for the mandrel shank to have at least one constriction and/or projection in the region of the foot end and for the foot end to be brought by plastic deformation into a shape that engages in the constriction and/or engages around the projection. By this means, the rivet body is joined to the rivet mandrel in an interlocking manner so that the two parts form an easy-to-manage structural unit. During setting of the blind rivet, the mandrel shank with the attached mandrel head is held securely by the rivet body as a result of this interlocking connection. By this means, disadvantages resulting from a released mandrel head and mandrel shank are avoided. The constriction and/or projection can be designed in an annular form and can accomplish an improved sealing of the mandrel shank with respect to the rivet body in conjunction with the plastically deformed foot end.
According to the invention, the mandrel shank and the drawing end are joined by a constricted parting section, which is arranged in the bore of the rivet body such that the end of the mandrel shank adjacent to the parting section is recessed within the bore of the rivet body. The danger of injury by the sometimes sharp-edged broken end of the mandrel shank is avoided by this means. A fastening arrangement with at least two components that are joined together by the setting of a blind rivet according to the invention comprises an accessible first component and a second component located inaccessibly behind the first component, wherein the two components have bores that are aligned with one another through which the blind rivet passes, wherein the flange of the blind rivet rests against the first component, the first section of the rivet's shank extends through the first component, and the second section of the shank forms a flange that lies flat against the back of the second component, and wherein the outside diameter of the first section of the shank is equal to or smaller than the original inside diameter of the bore in the first component.
In the fastening arrangement according to the invention, the two components are clamped together between the flange and the second section that has been formed into a flange. However, the expansion of the first section of the blind rivet is reduced enough that its outside diameter essentially does not increase beyond the inside diameter of the bore in the first component. Overstressing of the component through expansion of the blind rivet during setting is avoided, so that splitting of the component also cannot occur. Consequently, the first component can be made of plastic and does not require any reinforcements made of metal.
If both components are made of plastic, it is advantageous for the length of the first section of the shank to be essentially equal to the sum of the thicknesses of the first and second components in the region of the bores that the blind rivet passes through, or to be smaller than the said sum. The reduction in the expansion of the blind rivet is then effective for the second component as well. For tight sealing of the fastening arrangement, according to the invention the mandrel shank is enclosed in an interlocking manner by the foot end of the rivet body, by which means it forms a seal together with the mandrel head for the blind-side end of the bore of the rivet body.