MXPA98005340A - Method of manufacturing fasteners - Google Patents

Abstract

The invention relates to a method of manufacturing fasteners such as self-piercing rivets, self-piercing studs, plugs, inserts, etc.. In such method a blank is provided and said blank is subjected to a rolling process causing material of the blank to flow radially towards said central axis and axially so as to axially lengthen the blank, with said predetermined geometry of said finished fastener being formed by said rolling process. In addition, a mandrel can be used to precisely define the geometry of the fastener. Fasteners made by the method of the invention are much cheaper than fasteners made by conventional upsetting and extrusion processes. Furthermore, the fasteners made by the method of the invention generally have the advantage of superior grain flow and closer manufacturing tolerances.

Description

A METHOD FOR MANUFACTURING FASTENERS Field of the Invention This invention relates to a method for manufacturing fasteners, in particular fasteners having an inner cavity of a predetermined geometry. Typical examples are self-drilling rivets, self-drilling bolts and screws, self-drilling nuts, plugs and threaded inserts with both internal and external threads, expandable inserts, plugs with internal threads and external grooves and similar small parts, having an inner cavity; the cavity can be a blind hole or a hollow hole.

Background and Brief Compendium of the Invention According to the prior art, such fasteners are conventional by means of being manufactured in several steps, by stressing and extruding the length of a wire rod. This technique requires a large number of tools and dies, in addition to which the transfer of the piece worked from one step to the next, requires time. Moreover, the tools are locally subject to very high stresses, which can detrimentally affect their useful life. In addition, the notches REF: 27792 radial, such as the external grooves and grooves, or internal threads, require additional operations, in many cases, a more expensive machinery. Moreover, conventional technology has many limitations, particularly in the case of deep cavities of small diameter or cross-section, especially conical cavities with a small included angle, since the cavity has to be formed by a needle. side die Because of a self-blocking effect caused by friction, it is difficult to remove from the needle, the finished parts and the needles having a substantial length, generally lack the strength and stability required for the production process. Experience has shown that cavities made in a multi-step extrusion process, generally have small breaks in its lower part and the rod of the fastener, will not have at its end a "sharp edge" or a well-defined plane, due to the limitations of production techniques currently used. This results in poor processing performance and thus in poor joint properties, in terms of both appearance and strength. Finally, due to the limitations exposed by current production techniques, it is not possible to economically manufacture such fasteners, from materials such as austenitic stainless steel, by means of cold forming.

It is an object of the present invention to provide a method for manufacturing fasteners, which do not suffer from the above-mentioned disadvantages and limitations. Said method should allow the elaboration of fasteners and similar parts, which considering the depth and geometry of the central cavity, do not have the limitations mentioned above. In addition, the production process will be simplified, the production output per unit of time will be increased and both the economy of the method, as well as the quality of the products, will be improved. Additionally, the method of the invention, should allow, to produce economically, fasteners of materials that are difficult to process, by means of the use of conventional methods of reinforcement and extrusion. Up to this point, the present invention provides a method for manufacturing a fastener, of a predetermined geometry and having a central axis and a central cavity, method in which an unprocessed element is provided, which is subject to a rolling process, causing the material of the unprocessed element to flow radially about the central axis and axially, such that the unprocessed element is axially stretched, with the predetermined geometry, of said finished fastener, by the rolling process. According to the invention, the raw element is generally constituted of a length of unthreaded wire rod. The extreme faces of the raw element can be flat; alternatively an end face may be provided with a groove, obtained by means of upsetting and / or extrusion. Subsequently, the unprocessed element is formed in a finished fastener, by means of a rolling process. Said rolling process causes the material of the unprocessed element to flow radially towards the center of the unprocessed element and axially, in such a way that the length of the unprocessed worked element is increased and thus, the required geometry of the finished fastener is obtained . The result is a fastener with a cavity of a desired geometry, even when starting from an unprocessed element with flat end faces. If, on the other hand, the unprocessed element is worked in such a way that it has a hole in one of its extreme faces, the rolling process causes the material of the unprocessed element to flow from an area radially outward and from the cavity radially inward, in an axial direction, until the final shape of the fastener is obtained. The rolling process is a one-step operation, that is, a single step in which the rolling dies form the finished fastener, from the raw element. A prerequisite for this is that the profile of the rolling dies continuously changes, along the length of the rolling dies, from a profile corresponding to that of the unprocessed element and that of the finished fastener. Various types of rolling tools are suitable for performing the rolling process, such as those having flat rolling dies, which are linearly movable with respect to each other, rolling dies with cylindrical rolls and rolling dies with roller segments . In each of the cases, the tools are provided, on their opposite exterior surfaces, with a continuously changing profile. When a pair of cylindrical rollers or roller segments are employed, a stationary straight edge is used to support and guide the unprocessed element during lamination. In another version, three rollers are used, to provide the fasteners, with a predetermined external profile, by means of stamping. Said rolling tools are known in the art and have been conventionally used, for example, to form threaded rods into bars, bolts and bolts. A major difference between the prior art and the invention is that in the case of the latter, the rolling process is used to produce hollow or semi-hollow parts, of defined interior and exterior geometries. The method of the invention can be practiced with or without a mandrel. As already mentioned, a central cavity in the fastener can be obtained, simply by means of rolling. In spite of this, a precisely defined geometry must be obtained, within the central cavity, it is preferable to use a rotary mandrel, which is axially mounted in spring and which is inserted in the hollow of the unprocessed element. Since the material flow is radial from the outside to the inside, there is no tendency to self-block; Because the mandrel is spring mounted, there will be a space between the clamp and the mandrel, which facilitates the removal of the finished fastener from the mandrel. On the other hand, the method of the present invention allows fasteners with hollow holes to be made. In this case, it is suggested to use an unprocessed element, with a hole. Again, the rolling process causes the material to flow in both radial and axial directions, until the desired geometry is obtained. The use of a mandrel is suggested to produce a cylindrical perforation. The mandrel can be provided threaded, such that the fastener is provided with internal threads, by means of the rolling operation. The exterior of the fastener may be of a cylindrical or polygonal shape. In particular, to make the self-drilling rivets and the self-drilling nuts, the volume of the unprocessed element must be greater than that of the calculated volume of the finished fastener, with the excess volume, being dependent on the diameter of the length of the unprocessed element. The excess volume must be between approximately 0.5% and 2% of the finished fastener volume. The excess volume ensures that the length of the fastener can be maintained, substantially constant, while the excess volume of the unprocessed element can result in a slight excess of volume in the finished fastener, for example, in the head of the fastener, where precise dimensions are not required. This allows to accurately design the self-drilling terminations of the spindles of the self-drilling rivets, in such a way that they are particularly suitable for performing the self-piercing operation, in a forming process.

Brief Description of the Drawings Preferred embodiments of the invention will be described in more detail with reference to the accompanying drawings and in which: Fig. IA is a longitudinal section of a die for the extrusion of an unprocessed element; Fig. IB is a view similar to Fig. IA, after the extrusion operation; Fig. 2A is a longitudinal section of an unprocessed element, for a self-drilling rivet, with the self-drilling rivet being indicated with dotted lines; Fig. 2B is a view similar to Fig. 2A of a finished self-drilling rivet; Fig. 3A is a longitudinal section of an unprocessed element, for a self-drilling rod, with the self-drilling rod being indicated with dotted lines; Fig. 3B is a view similar to Fig. 3A of a finished self-drilling rod; Fig. 4 is a perspective view of a roller die; Fig. 5 is a cross-sectional view of a pair of roller dies, for making a self-drilling rivet, according to Fig. 2B; Fig. 6 is a cross-sectional view of a pair of roller dies, for making a self-drilling rivet, from an unprocessed element without cavity; Fig. 7 is a cross-sectional view of a pair of roller dies and a rotating mandrel for making a self-drilling rod, as shown in Fig. 3B; Fig. 8A is a cross-sectional view of an unprocessed element, for an insert; Fig. 8B is a cross-sectional view of an insert, made of the unprocessed element of Fig. 8A; Figs. 9A and 9B are lateral elevations of self-drilling rivets, with different external profiles; Fig. 10 is a sectional view, in the direction of arrow B in Fig. 9A, to show the external profile of a self-drilling rivet.

Description of the Preferred Modalities Fig. IA shows a die 1, including a punch 3, movable within a perforation 2. The length of the wire rod 4 is inserted in the die 1, which includes a propeller together with a mandrel 5, at its bottom. By moving the punch 3, it causes the length of the wire rod 4 to deform from its shape in Fig. IA to the shape in Fig. IB; the mandrel 5 helps to form a cavity 11, which is arranged centrally, with respect to the cylindrical perimeter 12 of the unprocessed element. A flange 14 extends from the cylindrical perimeter 12 The result is an unprocessed element 10, as shown in Fig. 2A, the central axis, which has been designated as 15. Consequently, the unprocessed element 10 is subject to a rolling process, for deforming the unprocessed element, in a self-drilling rivet 16, as shown in Fig. 2B. a comparison of the geometry of the finished fastener 16 of Fig. IB, with that worked unprocessed element of Fig. IA, shows that the rolling process makes the material radially outwardly of the cavity 11, to flow radially inwardly. in an axial direction, such that the hollow rod 17 is formed, as shown in Fig. 2B. In Fig. 2A the hollow rod 17 is indicated with dotted lines, with the aim of facilitating a comparison of the shapes, before and after the rolling process. The decisive factors for the final interior geometry of the cavity 18 are the shape (profile) of the rolling dies and the geometry of the worked raw element. A rolling tool for making a self-drilling rivet 16 is shown in Figs. 4 and 5. In Fig. 5, a lower rolling die 41 is mounted on a support 42, such that it is stationary and an upper rolling die 40, is mounted in such a way that it is movable linearly, forwardly. and backwards, by means of locomotion, not shown, in such a way as to perform reciprocal movements in a direction perpendicular to the plane of the drawing. Both rolling dies 40 and 41, are provided with lamination profiles 43 and 44, extending longitudinally and continuously. Fig. 4 is a perspective view of a lower lamination die 41, with its profiles 44 and 44 ', on its upper surface. The profile 44 continuously changes from the geometry 44A, at the corresponding starting point of the raw element 10, to the geometry 44B at the corresponding termination of the 16. The upper rolling die 40, not shown in Fig. 4, is made up of a matt lamination profile. Moreover, Fig. 4 shows that each rolling die 40 and 41 can be provided with two, or even more, profiles 44 and 44 '. From the foregoing, it continues that the external geometry of the self-drilling rivet 16, is defined by the profiles of the rolling dies, in their termination. The internal geometry of the hollow rod 18 depends on the geometry of the unprocessed element 10 and on the shape of the profiles of the rolling dies. The rolling dies have profiles of identical geometry in their termination, however, the different geometries along their length, will produce hollow spindles 18 with different internal geometries. In order to produce a finished fastener of predetermined dimensions, it is necessary to use an unprocessed element with an excess volume, of the theoretical volume required, for a finished fastener. The excess volume should be between 0.5% and 2.0%. this allows the sharp and precise edge 19 (Fig. 2B) to be obtained at the end of the hollow rod 17. The rolling dies shown in Fig. 5 allow to form a 16, having a hollow rod 17, which increases towards the head 14. The sharp edges 19, are formed with precision and sharp, in such a way that they can cut through the upper sheet, during the process of self-drilling riveting, with a minimum of distortion and warping. FIG. 2A shows an unprocessed element 20 of another cross-sectional shape, ie, a raw element having a collar 24 at its outer periphery and a cylindrical portion 22 forming radially inwardly therein, with a shape cavity. Transverse 21. The raw element 20, furthermore, is provided with a portion of the rod 23. The central axis, and the axis of rotational symmetry of the raw element 20, is designated 25. FIG. 3B shows a finished fastener , which is a self-drilling rod 26, which includes a head 27, formed by a rolling process. The sharpened end bottom of the hollow rod 28 is being indicated by the reference numeral 29. Fig. 7 shows a pair of rolling dies 50, 51, being of a respective profile to form self-drilling rivets, as shown in Fig. 3B. the two lamination dies 50, 51 are operable in such a way that they perform a linear reciprocal movement, with respect to each, along an axis normal to the plane of the drawing. A mandrel 52, which is mounted on a support 53, so as to be displaceable and non-rotatable, in the cavity 21 of the raw element 20. The support 53 is rotatably mounted on the support 54. The mandrel 52 is pressed towards the cavity 21, by means of the spring 55. During the rolling operation, the material flows from the cylindrical portion 22 of the raw element 20, into the space between the rolling dies 50, 51 and the mandrel 52. As a result, the geometry of the perforation of the self-drilling rod is determined by the geometry of the mandrel 52. The longitudinal displacement required for the mandrel 52 can be driven by an impeller, or it can result from the friction forces that occur when the material flows to the core. along the mandrel 52, during the rolling operation. As shown in Fig. 7, the mandrel 52 is cushioned by means of the spring 55, such that it can be displaced during the progression of the rolling operation, because the spring is being compensated. Fig. 6 is a longitudinal sectional view of a pair of rolling dies 60, 61. The stationary lower rolling die 61 has a profile 64 and the upper movable rolling die 60 has a matte roller profile 63. This a pair of lamination dies 60, 61, allows forming a self-drilling rivet 66, from a cylindrical unprocessed element 4, comprised by a length of wire rod 4, as shown in Fig. IA. Again, a finished fastener 66, having a cavity capped, as shown in Fig. 6, by means of dotted lines, is obtained by laminating an unprocessed element 4, having a flat end face 13. Fig. 8A shows an unprocessed element 30, for making an insert 36, as shown in Fig. 8B. In this case, the cavity 31 is of the shape of a hollow hole. By forming the insert 36 from the unprocessed element 30, it is obtained, again by a rolling process, using a mandrel, which is provided with external threads. The mandrel is inserted into the cavity 31, before the rolling operation. During the rolling operation, the material flows between the mandrel and the rolling dies. In this way, the insert 36 will be provided with an internal thread 37, with the grooves 38 on the outer periphery thereof and with, for example, a hexagonal peripheral portion 39, for fitting the tool. The rolling tool can be of the type shown in Fig. 7. The mandrel 52 shown in Fig. 7 will then be replaced by a threaded mandrel. It is possible to locally laminate locally on the outer surface of the hollow rod 17 (Fig. 2B) or 28 (Fig. 3B), a profile P is whatever, for example, polygonal or grooved, with the aim of reducing stresses in the communication areas greater efforts. Thus, the strength of the rod can be improved in the areas where greater efforts occur, during the formation process, due to the riveting of the rivet. This allows to reduce the pressure, per unit area and thus, improve the behavior of the fatigue of the riveted joints. The modification of the outer surface may be locally limited. Figs. 9A and 10 show a fastener, with a non-circular profile P, under the head 14, while Fig. 9B shows a fastener having a fluted profile R. In a similar manner, various exterior and interior profiles can be produced. of the hollow stem. For example, it is possible to produce notch profiles. Such a profile is shown, for example, in the H of FIG. 9B. It is noted that, with regard to this date, the best method known by the requested, to carry out the present invention, is that which is clear from the present, discovering the invention. Having described the invention as above, the content of the following is claimed as property.

Claims (21)

1. A method for manufacturing a fastener, of a predetermined geometry and having a central axis and a central cavity, characterized the method because "a processing element is provided, which is subject to a rolling process, causing the material of the raw element flow radially towards the central axis and axially, in such a manner as to elongate axially the unprocessed element, with the determined eeometrics of the finished fastener, which has been formed by the rolling process

2. A method according to claim 1, characterized because the lamination process comprises laminating the unprocessed element in an adjacent area a flat end face thereof

3. A method according to claim 1, characterized in that the unprocessed element has a gap in the face The extreme of this and the rolling process causes the material of the raw element to flow from an area radially outward of the hollow, towards the central axis axially and radially.

4. A method according to claim 3, characterized in that the recess is in the shape of a cup.

5. A method according to claim 3, characterized in that the recess is of the shape of a flat hole.

6. A method according to claim 3, characterized in that the recess is in the form of a cylindrical perforation.

7. A method according to claim 1, characterized in that the unprocessed element is made by a process of reinforcement and / or extrusion.

8. A method according to claim 1, characterized in that the unprocessed element and / or the finished fastener includes a head.

9. A method according to claim 8, characterized in that the head comprises a flange extending radially.

10. A method according to claim 1, characterized in that the fastener is provided with a circumferential section of a polygonal shape.

11. A method according to claim 1, characterized in that the fastener is provided with grooves, by means of a rolling operation.

12. A method according to claim 1, characterized in that the fastener is a self-drilling rivet, which includes a rod and the rolling process is carried out in such a way that the rod is provided with a profiled periphery, to increase the strength of the rod.

13. A method according to claim 1, characterized in that a mandrel is used in the rolling process to form the central cavity.

A method according to claim 13, characterized in that the end of the mandrel extends into the hollow of the unprocessed element during the rolling process.

15. A method according to claim 13, characterized in that the mandrel includes external threads, to provide the fastener with an internal threading.

16. A method according to claim 13, characterized in that the mandrel is supported to be axially and elastically produced.

17. A method in accordance with the claim 1, characterized by a pair of lamination dies, which are movable linearly, in opposite directions, being used to carry out the rolling process.

18. A method in accordance with the claim 1, characterized in that the rotary rolling dies include a linear edge, in a rolling space, being used to carry out the rolling process.

19. A method according to claim 1, characterized in that the unprocessed element is of a volume exceeding the calculated volume of the fastener. A method according to claim 17, characterized in that the lamination dies are provided with two or more lamination profiles, to produce a respective number of fasteners, at the same time. A method according to claim 18, characterized in that the rolling dies are provided with two or more rolling profiles, to produce a respective number of fasteners, at the same time.