FASTENER AND METHOD OF ATTACHMENT TO SHEET MATERIAL

Abstract: A fastener (2) and method of attachment of such fastener to sheet material to provide attachment of a tubular fastener to the sheet material by extruding, without severing, portions of the sheet material completely through openings on the base portion of the fastener. In one embodiment of the invention, the extruded material is clinched on the top surface (8) of the base portion (6) by clinch members (12) integrally formed with the base portion. The fastener is internally threaded (16), lightweight and preferably heat-treated prior to attachment to the sheet material to provide fastener strength equivalent to or greater than that of much heavier nuts. Two types of such fasteners may be attached by a method which opens up a hole in the sheet material of a larger diameter than the major diameter of the threads (16) in the fasteners while simultaneously clinching the fastener in place. This elimi­ nates the need to use thread-cutting bolts. The fasteners (2) may be connected together to form a strip to be fed into an automated assembly unit from a dispenser. In another embodiment of the invention, the extruded material is clinched on the top surface (8) by extruding it through clinch openings into the cavities of a die member that is brought into contact with the top sur­ face of the fastener, each such cavity being aligned with and being somewhat larger than the clinch opening of the fastener that it is adjacent to.

Description: This invention relates to a method of attaching at least one fastener to sheet material according to the features in the preamble of claim 1 and to a fastener according to the features in the preamable of claim 10. In the manufacture of automotive products it is often necessary to join component parts, one of which is a panel, to one another by the use of threaded fasteners. Bolts or screws are commonly threaded into suitable nuts secured to the panel. The prior art in methods of attachment encompass various types of fasteners including nuts, clinch nuts and pierce clinch nuts. They are attached by welding or by a variety of mechanically clinched, extruded, or swaged techniques whereby the nut body or a portion thereof, cooperating with a die member, effects an attachment. Clinch nuts are most commonly attached to sheet material by one of two methods. In the first method the nuts are punched through the sheet material, clinching the nut around the periphery of the hole punched out by the nut according to U.S. Patent No. 3315 345 the nut is provided with a pair of reentrant grooves into which portions of the sheet material are extruded for attachment. Using this method of attachment reduces the load bearing surface area of the nut abutting against the sheet material. When power tools are used to insert a bolt or screw into the attached nut, there is a tendency to dislodge the nut from the panel because of the low push-off strength of these fasteners. In the second method the nuts are clinched onto the surface of the sheet material while simultaneously having a punch in the bore of the nut punch out a slug in the sheet material. This method of attachment offers an increased area of load bearing surface abutting against the sheet material. It also necessitates the use of a thread cutting bolt with the fastener, because the diameter of the punch in the bore of the nut cannot be larger than the minor diameter of the threaded bore. The use of thread cutting bolts is shown by the U.S. Patent Nos. 3,829,957, 3,926,236, and 3969809 and Russian Patent 506,317. The use of thread-cutting bolts, however, reduces the performance of the nut because of the relatively low push-off strength it exhibits. Also, the use of such bolts is more costly and it is more difficult to control tolerances of the fastener. In either method, the nuts are relatively heavy, making their use undesirable in automotive assembly where there has been an effort to reduce weight to increase fuel economy. With the quest for lighter weight vehicles, thinner sheet panels are being used. Inadequate pull-through strength has been cited as a weakness of clinch and pierce and clinch type fasteners. The prior art patents of Schleicher, U.S. Patent No. 3,900,937; Marquis, U.S. Patent No. 4,059,897; Williams. U.S. Patent No. 2,254,558; Double, U.S. Patent No. 3,299,500; Double et al, U.S. Patent No. 3,315,345; Grube, U.S. Patent No. 3,704,507; and Steward, U.S. Patent No. 3,878,598 all teach methods of attachment wherein first a panel of material is severed by punching, shearing, or lancing and then a nut body is deformed. However, any fastener attachment which causes the panel material to be severed increases the potential for seepage of corrosive liquids through the severed panel. Barrel-type, clip-on fasteners have been used as a lightweight, low-cost alternative to clinch nuts. The present clip-on method for mounting these fasteners, however, restricts their application to holes near the edge of the sheet material. Furthermore, the clip-on mounting method does not provide as secure a mount as the clinch nuts. An object of the present invention is to provide a lightweight fastener which is equal in strength to current fasteners and which lends itself to a simple fastening operation for securing it to sheet metal panels and certain co-polymers and plastic panels, which is adapted for assembly to sheet panels of varying thicknesses without the need of prior panel preparation (i.e. pre-drilled or punched holes, clips or formed tabs etc.) and which does not rely upon moving tool members to sever, lance or deform the fastener to affect an attachment. The object above referred to is solved by a method of attaching at least one fastener to sheet material according to the features of claim 1 and a fastener according to the features of claim 10. According to a first embodiment of the invention, the base portion of the fastener includes a pair of spaced clinch members integrally formed with the base portion. Each of the clinch members is displaced from the rest of the base portion to define a clinch opening in the bottom surface of the rest of the base portion and an extrusion opening in the top surface thereof in fluid communication with its clinch opening. The fastener further includes a tubular attachment portion integrally formed with the base portion between the clinch members and adapted for attachment to a separate fastener. The clinch and extrusion openings permit portions of the sheet material to be extruded through the openings, the clinch members clinching the extruded sheet material to the base portion at the top surface of the base portion. Further the method of the present invention, includes the steps of placing the fastener on the sheet material so that the bottom surface of the base portion abuts the sheet material, and punching out a slug of sheet material to leave a hole in the sheet material, the hole having its center on a line forming a vertical axis of the tubular attachment portion. The method also includes the step of extruding portions of the sheet material surrounding the hole into the clinch openings and through the openings substantially simultaneously with the step of punching to effect an attachment of the fastener to the sheet material at the top surface of the base portion without severing the portions of sheet material. In a preferred version of the fastener according to the first embodiment of the invention, the fastener is provided with a neck region and a tubular portion which has a smaller diameter than the neck region and which is separated from the neck region by an annular taper region. The fastener is attached to sheet material by placing the sheet material and the fastener in a die and compressing the die. As the die is compressed a punch in the bore of the tubular portion punches out a slug of sheet material. The sheet material is then pressed or flanged upwardly by the die against the surface of the neck region while portions of the sheet material are simultaneously extruded through the clinch members without severing the portions of sheet material surrounding the hole. One result of this method of attachment is to create a seal between the surface of the neck region and the sheet material to which the fastener is attached. The seal is important in the area of corrosion protection by preventing liquid seepage. This method also creates a bolt hole in the sheet material which is larger in diameter than the major diameter of a threaded region of the tubular portion, making use of thread-cutting bolts with the fastener unnecessary. The fastener may be heat treated to increase its strength. The relatively large, load bearing area of its base also serves to increase its strength in use. To facilitate its use in automated assembly, the fastener may be connected with other fasteners in a strip. This allows the fasteners to be fed into an automated assembly unit from a dispenser, such as a spool feeder. In carrying out the method of the invention according to a second and preferred embodiment of the invention, there is provided a fastener for attachment to sheet material, such fastener having a base portion with top and bottom surfaces, the bottom surface being adapted to abut against the sheet material. The base portion includes a pair of clinch openings through which the sheet material can be extruded into a cavity in a die that is brought to bear against the top surface of the fastener, the cavity being somewhat larger than the clinch opening, to thereby permit the sheet material to be extruded into the cavity of the die by the operation of a die tool that is brought to bear against the bottom of the sheet material and to thereby interlock the fastener to the sheet material. In a preferred version of the fastener according to the second embodiment of the invention, the fastener is provided with an internally-threaded tubular portion which is directly connected with the base portion by an annular taper region, which annular taper region tapers outwardly as it extends from the tubular portion to the base portion. The fastener is attached to sheet material by placing the sheet material and the fastener in a die and compressing the die. As the die is compressed a punch in the bore of the tubular portion punches out a slug of sheet material. The sheet material is then pressed or flanged upwardly by the die against the surface of the taper region while portions of the sheet material are simultaneously extruded through the clinch openings without severing the portions of sheet material surrounding the hole. One result of this method of attachment is to create a seal between the surface of the neck region and the sheet material to which the fastener is attached. The seal is important in the area of corrosion protection by preventing liquid seepage. This method of attachment also reinforces the taper region of the fastener, thereby increasing the strength of the fastener to compression loads applied parallel to the longitudinal axis of the tubular portion. This method also creates a bolt hole in the sheet material which is larger in diameter than the major diameter of a threaded region of the tubular portion, making use of thread-cutting bolts with the fastener unnecessary. The fastener may also be heat treated to increase its strength. The relatively large load bearing area of its base also serves to increase its strength in use. To facilitate its use in automated assembly, the fastener may also be connected with other fasteners in a strip. This allows the fasteners to be fed into an automated assembly unit from a dispenser, such as a spool feeder. For further understanding of the present invention and the objects thereof, attention is directed to the drawing, the following brief description thereof, to the detailed description of the preferred embodiment, and to the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a sectional view, taken along lines 1-1 of Figure 2, of a first embodiment of a fastener constructed in accordance with the present invention; Figure 2 is a sectional view taken along lines 2-2 of Figure 1 of the fastener; Figure 3 is a sectional view of the fastener of Figures 1 and 2 attached to sheet material; Figure 4 is a side elevational view of a second embodiment of a fastener constructed in accordance with the present invention; Figure 5 is a sectional view taken along lines 5-5 of the fastener of Figure 4; Figure 6 is a sectional view of the fastener of Figures 4 and 5, taken along lines 6-6 of Figure 5, attached to sheet material; Figure 7 is a top view of a multiplicity of fasteners according to Figures 1 and 2, connected together in a strip; Figure 8 is a top view of a multiplicity of fasteners according to Figures 4 and 5 connected together in a strip; Figure 9 is a sectional view of a fastener according to Figures 1 and 2 and sheet material positioned in a die in preparation for attachment; Figure 10 is a sectional view of the fastener of Figures 1,2, and 9 and the sheet material in the die after compression to effect attachment of the fastener to the sheet material; Figure 11 is a top plan view of a third embodiment of the fastener according to the present invention attached to sheet material; Figure 12 is a sectional view of the fastener and attached sheet material of Figure 11; Figure 13 is an enlarged, partially broken away, sectional view of sheet material and the fastener of Figures 11 and 12 in a die after compression to effect attachment of the fastener to the sheet material; Figure 14 is a view, similar to Figure 12, of a fourth and the preferred embodiment of the fastener according to the present invention attached to sheet material; Figure 15 is an enlarged fragmentary sectional view of a fastener according to Figure 14 and sheet material positioned in a die in preparation for attachment; and Figure 16 is a view similar to Figure 14 of the fastener of Figure 14 and the sheet material in the die after compression to effect attachment of the fastener to the sheet material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figures 1 through 6 and Figures 11 and 12, it will be seen that each of the fasteners designated generally at 2, 4 and 5 has a base 6 with a top surface 8 and a bottom surface 10. The base 6 has upwardly extending, spaced clinch members 12 and a tubular portion 14 therebetween. The tubular portion 14 has a threaded region 16 for engaging bolts or screws. The tubular portion 14 of each of the fasteners 2 and 5 has a neck region 18 of a substantially constant diameter which extends upwardly from the base 6 to a taper region 20. To attach each of the fasteners 2, 4 and 5 to the sheet material 22, portions 24 of the sheet material 22 are forced into clinch member openings 26, as shown in Figure 6. As the portions 24 of the sheet material 22 continue to be forced into the clinch member openings 26 they contact the underside of the clinch members 12. Continued pressure on the portions 24 of sheet material 22 causes the portions 24 to be extruded through the clinch members 12 at extrusion points 28. These extrusions effect an attachment of each of the fasteners 2, 4 and 5 to the sheet material 22. As shown in Figure 13, the extrusion is accomplished without perforating or severing the sheet material 22. Figures 9 and 10 show a method of attaching each of the fasteners 2, 4 and 5 with neck regions 18 to the sheet material 22 while forming bolt holes 30 in a single operation. One of the fasteners is placed with the sheet material 22 in a die 32 as shown in Figure 9. Then the die 32 is compressed as shown in Figure 10. Compression of the die 32 first causes a bore punch 34 of the die 32 to punch out a slug 36 of sheet material. As the die 32 is further compressed, the sheet material 22 in the area of the hole left by the slug 36 is pressed against the surface of the neck region 18 by a die ring 38 of the die 32. At the same time, the sheet material portions 24 are simultaneously extruded through the clinch members 12. The area of the hole left by the slug 36 has a center axis which lies on the longitudinal central axis of the tubular portion 14 which, in the orientation shown in Figures 9 and 10, extends vertically. Preferably, the portions 24 of the sheet material are extruded through the clinch members 12 by trapezoidal-shaped extrusion members 39 (only one of which is shown) formed on the die 32, as best shown in Figure 13. The resulting configuration of the attached fastener 2 and sheet material 22 is shown in Figure 3. The resulting configuration of the attached fastener 5 and the sheet material 22 is shown in Figure 12. The benefits of these configurations are twofold. First, pressing the sheet material 22 against the surface of the neck region 18 forms a tight seal between each of the fasteners 2 and 5 and the sheet material 22. Second, the diameter of each of the bolt holes 30 is larger than the major diameter of its threaded region 16, making the use of thread-cutting bolts with the fasteners unnecessary. When attaching the fastener 4 to the sheet material 22, the use of thread-cutting bolts is obviated by making a preformed bolt hole 40 in the sheet material 22 prior to attachment of the fastener 4. The bolt hole 40 of the fastener 4 has a larger diameter than the major diameter of the threaded region 16. In practice, each of the fasteners 2, 4 and 5 may be made out of an annealed 1050 steel. After making each of the fasteners 2, 4 and 5, they may be heat-treated to a Rockwell hardness of 46 to 48 to increase their strength. Referring to Figures 7, 8 and 11, the relatively large surface area of the base 6 of each of the fasteners 2, 4 and 5 is shown. This feature increases the strength of the fasteners 2, 4 and 5 in actual use by providing a large load bearing area for abutment against the sheet material 22. Also, as shown in Figures 7 and 8, in reference to the fasteners 2 and 4, connecting members 42 may be used to join the fasteners to one another in strips. The strips of fasteners, for example, the strips of fasteners 2 and 4, may be fed into an automated assembly unit from a dispenser, such as a spool feeder. Referring now to the embodiment of the invention shown in Figures 14 through 16, there is shown a fastener 2′ that has a base 6′ with a top surface 8′ and a bottom surface 10′. The base 6′ has spaced clinch openings 12′ therein and an internally threaded tubular portion 14′ between the clinch openings 12′. The tubular portion 14′ of the fastener 2′ is positioned above a planar portion 15′ of the fastener 2′ that contains the clinch openings 12′ and is connected to such planar portion 15′ by a taper region 20′ that extends outwardly and downwardly from the tubular portion 14′ to the planar portion 15′. The fastener 2′ is attached to a drawable sheet material 22′, such as annealed steel, by forcing portions of the sheet material 22′ through the clinch openings 12′ in a die 32′. The die 32′ is compressed, as is shown in Figure 16, to cause a punch bore 34′ of the die 32′ to punch out a slug from the sheet material, leaving a hole 36′ therein and to cause portions 24′ of the sheet material to be extruded through the clinch openings 12′ of the fastener 2′ by the operation of trapezoidal-shaped extrusion members 39′, only one of which is shown, into die cavities 42′, only one of which is shown. Each of the die cavities 42′ bears against the top surface 8′ of the fastener 2′, during the extrusion step, and each of such cavities 42′ is aligned with, and is somewhat larger than one of such clinch openings 12′ during the die compression step. Thus, when the extrusion members 39′ extrude the portions 24′ of the sheet material 22′ through the clinch openings 12 into the die cavities 42′, the portions 24′ will expand within the die cavities 42′ beyond the edges of the clinch openings 12′, thereby securing the fastener 2′ to the sheet material 22′ without forming any discontinuity in the sheet material 22′ that could permit liquid seepage therethrough and possible corrosion as a result thereof. The die 32′ also has a frustoconical portion 41′ that is axially aligned with the tubular portion 14′ of the fastener 2′. In the die pressing operation, the frustoconical portion 41′ of the die 32′ deflects the portion of the sheet material that surrounds the hole 30′ upwardly against the underside of the taper region 20′ of the fastener 2′ in surface to surface engagement therewith. This increases the inside diameter of the hole 36′ beyond the outside diameter of the punch bore 34′ that was used to form it, thereby eliminating the need for an additional piercing or other machining operation to increase the diameter of the hole 36′ as might otherwise be required to permit it to receive a threaded fastener that is to be attached to the fastener 2′. Further, the surface to surface contact between the portion of the sheet material 22′ that surrounds the hole 36′ and the underside of the taper region 20′ of the fastener 2′ reinforces the fastener against compression loads applied to the fastener 2′ in a direction parallel to the longitudinal axis of the tubular portion, thereby increasing the resistance of the fastener 2′ to collapsing under such compression loads. The fastener 2′ like the fasteners 2, 4 and 5, is preferably formed out of annealed steel, such as A.S.E. 1050 steel, and the fastener 2′ is also preferably heat-treated after its manufacture to increase its hardness to a hardness of 46 to 48 on the Rockwell "C" scale. Like the fasteners 2, 4 and 5, the fastener 2′ also has a base 6′ with a relatively large surface area to provide for a large load bearing area against the sheet material 22′.

Claims: A method for attaching at least one fastener (2,4,5;2') to sheet material (22), said fastener having at least a recess facing said sheet material, placing said fastener on said sheet material and extruding a portion (24;24') of said sheet metal (22) into said recess to effect an attachment of said fastener to said sheet material without severing said portion of sheet material, said method characterized by: using a fastener (2,4,5;2') including a base portion (6;6') having top and bottom surfaces (8,10;8',10'), said base portion including at least one clinch opening (26;12') in said bottom surface of said base portion and at least one extrusion opening in said top surface in fluid communication with said clinch opening said fastener further including a tubular attachment portion (14;14') integrally formed with said base portion (6,6') and adapted for attachment to a separate fastener and after placing said fastener (2,4,5;2') on said sheet material (22) extruding said portion (24, 24') of said sheet metal into said clinch opening (26;12') and through said extrusion opening, said portion (24, 24') expanding beyond the edges of said extrusion opening. The method of claim 1 including a pair of spaced clinch members (12) integrally formed with said base portion (6) to define a pair of spaced clinch openings and a pair of spaced extrusion openings. The method of claim 1 including a pair of spaced clinch openings (12') integrally formed with said base portion (6'), bringing a die (32') having a pair of cavities (42') into contact with said top surface (8') of said base portion (6') of said fastener (2'), said cavities being aligned with said clinch openings (12') and being at least slightly larger than said clinch openings and extruding said portions (24') of said sheet material through said clinch openings into said cavities. The method of one of claims 1 to 3, wherein said step of extruding said portion (24,24') of said sheet material through said clinch opening is accomplished by bringing an extrusion member (32;32') against the other of said opposed surfaces of said sheet material (22, 22') in alignment with a cavity provided in a die (32;32') being in contact with said top surface (8;8') of said base portion (6;6') of said fastener (2,4,5;2'). The method of one of claims 1 to 4 including the step of punching out a slug (36;36') of sheet material (22;22') to leave a hole (30,40) in said sheet material, said hole (30,40) having its center on a line forming a longitudinal axis of said tubular attachment portion (14;14') and extruding said portion (24;24') of said sheet material (22,22') substantially simultaneously with said step of punching. The method of claim 5 including the step of flanging second portions of said sheet material (22,22') immediately surrounding said hole (30,40) so that said second portions abut the inner surface of the tubular attachment portion (14,14'). Method of claim 6, wherein said steps of punching extruding and flanging are performed substantially simultaneously. The method of one of claims 1 to 7, wherein a strip of fasteners (2,4) is attached to sheet material (22,22') and wherein said method further includes the step of feeding said fasteners so that said fasteners are consecutively positioned immediately adjacent said sheet material. The method of one of claims 5 to 8, wherein said fastener (2') includes a tapered portion (20') connecting said tubular attachment portion (14') to said base portion (6') and further comprising: deforming a portion of said sheet material (22') around said hole to form a surface to surface contact between said portion (22') and said tapered portion (20') of said fastener (2') to increase the inside dimension of said hole, to help form a seal between said fastener and said sheet material and to increase the resistance of said fastener to collapsing under compressive loads extending parallel to said longitudinal axis of said tubular attachment portion. A fastener for performing the method according to one of claims 1 to 9, having at least a recess facing a sheet material (22,22') to which the fastener is attached by placing said fastener on said sheet material and extruding a portion (24,24') of said sheet material into said recess without severing said portion of sheet material, characterized in that the fastener (2,4,5;2') includes a base portion (6; 6') having top and bottom surfaces (6,8;6',8'), a pair of spaced clinch openings (12;12') in said base portion, a tubular attachment portion (14,14') integrally formed with said base portion between said clinch openings and a portion of enlarged diameter between said base portion and said attachment portion for receiving a flanged portion of the sheet material to which the fastener is attached.

Inventors: OAKS, DANIEL V.
Applicants: BOELLHOFF & CO, GMBH & CO KG
Application year: 1987
Main classification: F16B37
IPC codes: F16B5, B23P19, F16B37, B21D39