US3702085A

US3702085A - Method of rigidly securing members with a recessed fastener

Info

Publication number: US3702085A
Application number: US37249A
Authority: US
Inventors: Hershel E Hicok
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-05-14
Filing date: 1970-05-14
Publication date: 1972-11-07
Anticipated expiration: 1989-11-07

Abstract

An elongated strip of bead stock is secured to a sheet metal draw die by first punching longitudinally spaced tapered holes within the strip with a punch having a diameter substantially smaller than the opening within the punch die. The strip is shaped and inserted within a groove formed within the draw die, and a pin-like fastener is inserted through each tapered hole and into a correspondingly aligned blind bore formed within the draw die. The outer end of each fastener is peened so that it expands both within the bore adjacent a hardened ball placed within the bore, and also within the tapered hole to effect a rigid and positive connection between the bead stock and the forming die. A punch tapered hole and a recessed tapered head fastener are also disclosed for rigidly connecting other adjacent members.

Description

United States Patent Hicok Nov. 7, 1972 Hershel E. Hicok, 4636 Pine Village Drive, Orchard Lake, Mich. 48033 Filed: May 14, 1970 Appl. No.: 37,249

Inventor:

References Cited UNITED STATES PATENTS 5/1905 Dodge ..29/522 UX 3/ 1942 Leighton ..29/522 UX 9/1970 Pipher ..29/522 X 10/1932 Groehn ..72/350 10/1940 Oeckl et al ..29/522 UX FOREIGN PATENTS OR APPLICATIONS 934,615 5/1948 France ..29/522 Primary Examiner-Charlie T. Moon Attorney-Marechal, Biebel, French & Bugg [57] ABSTRACT An elongated strip of bead stock is secured to a sheet metal draw die by first punching longitudinally spaced tapered holes within the strip with a punch having a diameter substantially smaller than the opening within the punch die. The strip is shaped and inserted within a groove formed within the draw die, and a pin-like fastener is inserted through each tapered hole and into a correspondinglyaligned blind bore formed within the draw die. The outer end of each fastener is peened so that it expands both within the bore adjacent a hardened ball placed within the bore, and also within the tapered hole to effect a rigid and positive connection between the bead stock and the forming die. A

punch tapered hole and a recessed tapered head fastener are also disclosed for rigidly connecting other adjacent members.

6 Claims, 7 Drawing Figures PATENTEDnuv 1 ma 4 3,702,085

IN VE N TOR HERSHEL E. HICOK MM, M7843 A TTOR/VE Y5 METHOD OF RIGIDLY SECURING MEMBERS WITH A RECESSED FASTENER BACKGROUND OF THE INVENTION In the art of constructing a die for drawing sheet metal, as for example, a die which is used for producing an automobile panel, it is common to mount a shaped strip of head stock on either the female die or on the blank holding die which surrounds the punch or male die. The strip extends generally arOund the die cavity and has a rounded projecting surface which is adapted to extend into a complementary shaped recess or groove formed within the opposing die. The bead material is usually formed of steel having a hardness range that could vary from soft to harder than that of the die proper and functions primarily t minimize wear on the dies and to minimize the formation of wrinkles within the metal sheet aS it is being drawn.

Sometimes a rounded bead strip is formed as an integral part of the female die or blank holding die, but usually the strip is formed from bead stock having a D- shaped cross-sectional configuration. After the strip of bead stock is formed to the desired configuration corresponding to the shape Of the die cavity, the strip aS inserted into a correspondingly shaped groove and is secured by a series of longitudinally spaced fasteners.

The fasteners may comprIse cap screws which extend through holes drilled and counterbored within the bead stock and are threaded into corresponding holes formed within the die. It is also common to drill a series of holes within the bead stock and then taper ream each hole for receiving a pin-line fastener which is inserted into a correspondingly aligned hole within the die. The outer end portion of the pin-like fastener is peened to expand the fastener within the tapered hole in the bead stock, after which the fastener is ground or filed so that its end surface is flush with the curved or rounded surface of the bead stock.

Due to the substantial number of fasteners which are required, at intervals of a few inches, to secure a-strip of bead stock to a die, it has been found that substantial time isrequired for drilling holes within the bead stock and for counterboring or taper reaming each hole. For example, it is not uncommon for the drilling and reaming operations for each hole to require 6 or 7 minutes. This time significantly increases the cost of attaching the bead stock to a die and thus significantly increases the overall cost of the die set.

SUMMARY OF THE INVENTION The present invention is directed to an improved method of securing two members together with a recessed fastener extending through or into aligned holes formed within the members. The method of the invention is particularly suited for securing a strip of head stock to a metal drawing die. According 'to the preferred method of the inVention, a series of longitudinally spaced tapered holes are punched within a strip of bead stock by successively advancing the strip between a cylindrical punch having a diameter substantially smaller than the diameter of a hole formed within the punch die. As a result of this differential diameter, a tapered hole, defined by a frusto-conical surface, is formed within the bead stock, and the larger end of the hole is located adjacent the rounded surface of the bead stock.

After the strip of bead stock is formed to the desired configuration, it is inserted within a complementary shaped groove formed within the draw die, and blind holes are drilled within the die in allgnment with the tapered holes in the bead stock. A cylindrical pin-like fastener is inserted into each of the holes after a hardened steel ball is located at the inner end of the hole. The outer end portion of the fastener is peened so that it expands into the tapered hole within the bead stock and the inner end portion of the fastener expands within the hole around the ball to form a rigid connection between the bead stock and the die. The method of the invention may also be used for forming a non-circular hole within a member to prevent rotation of a fastener which is expanded or fitted into the hole.

A primary advantage provided by the invention in the art of die making is the significant time savings in forming the tapered holes within the bead stock when compared with the prior method of drilling, taper reaming and deburring each hole. However, other advantages and features of the invention will be apparent from the following description, the accompanying drawing and the appended BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammatic fragmentary section of a draw die set incorporating a strip of bead stock formed and secured in accordance with the invention;

FIG. 2 is a view illustrating the punching of the bead stock to form a tapered hole in the stock; I

FIG. 3 is a fragmentary section of a die illustrating the assembly of the bead stock;

FIG. 4 is a view similar to FIG. 3 and showing the bead stock after it has been secured to the die;

FIG. 5 is an enlarged fragmentary section of the lower portion of the assembly shown in FIG. 4;

FIG. 6 is a fragmentary section of two adjacent members rigidly connected in accordance with the present invention; and

FIG. 7 illustrates a subsequent counterboring operation which may be performed on the bead stock in accordance with the invention.

DESCRIPTION OF THE PREFERRED METHOD OF THE INVENTION FIG. 1 shows diagrammatically a die set for drawing a blank or sheet S of metal and which generally includes a female die 10 defining a cavity 12 withln a blank supporting surface 13. A punch or male die 14, having a configuration corresponding to that of the cavity 12, is slidably supported within a blank holding die or blank holder 15 having a lower surface 16 adapted t0 move downwardly toward the surface 13 of the female die 10. An elongated strip 20 lower bead stock surrounds the punch 14 and is mounted within a corresponding groove 22 formed within the bottom surface 16 of the blank holder 15. Preferably, the strip 20 has a D-shaped cross-sectional configuration forming a rounded bottom surface 24 which is adaPted to project into a complementary shaped recess 25 formed within the upper blank holding surface 13 of the die 10 and extending around the cavity 12.

Referring to FIGS. 2-5, the strip 20 of head stock is preferably formed of cold rolled steel or SAE 10-18 or 10-20 steel having a Rockwell hardness in the low thirties, although the bead stock may be composed of a pretoughened alloy steel. A series of longitudlnally spaced tapered holes 28 are formed within the strip 20, and each hole is defined by a frusto-conical surface 30 extending from a substantially cylindrical surface 32. The tapered holes 28 are preferably spaced at intervals of between 2 and 8 inches depending uponthe particular application of the die, and have a taper angle A (FIG. 3) of between 6 and 8.

In accordance with the presentinvention, each of the tapered holes 28 is formed within the strip 20 of bead stock by progressively advancing the strip 20 between a cylindrical punch 35 (FIG. 2) and a die 36 having a cylindrical opening or bore 38. The bore 38 extends downwardly from the-bottom of a cavity 39 which has a cross-sectional configuration corresponding to that of the strip 20 of bead stock. The punch 35 has a diameter substantially smaller than the diameter of the bore 38 so that when the punch 35 is pressed or forced through the strip 20, it removes a tapered slug 42by shearing the strip along a generally frusto-conical shear plane. This causes the formation of the'frusto-conical surface 30'and the generally cylindrical surface 32 within the strip. The diameter of the punch 35 and the diameter of the bore 38 are correlated according to the size or thickness of the strip 20 to produce the combination of the tapered surface 30 and the cylindrical surface 32 as well as the taper angle A of between 6 and 8. The pressing of the punch 35 into the strip 20 is also effective to form a small radius 44 at the upper end (FIG. 2) of the tapered hole 28, thereby eliminating the need for deburring the punched hole after it is formed.

Referring t FIGS. 3 and 4, after the strip 20 of bead stock is punched with a series of longitudinally spaced tapered holes 28, the strip is formed according to the configuration of the groove 22 and is inserted into the groove. A corresponding seriesvof blindbores or holes 45 are drilled into the blank holder and extend from the bottom surface of the groove 22in alignment with the tapered holes 28 within the strip of bead stock. A hardened steel. ball 46, such as a ball bearing, is placed within the bottom of each of the holes 45, and an elongated cylindrical fastener or pin 48 is inserted through each tapered hole 2 and into the corresponding hole 45 until the inner end surface of the pin contacts the ball 46 and the outer end surface projects slightly from the tapered hole 28.

The outer end portion of each pin 48 is peened with the aid of a pneumatic hammer or by hand causing the portion to expand to form a frusto-conical head portion 49 which firmly engages the frusto-conical surface 30. The peening operation is also effective to deform the inner end portion of each pin 48around the spherical surface of the ball 46 (FIG. 5) causlng the pin 48 is expand and conform to the minor irregularities of the hole. As a result, the pins 48 form a rigid and positive connection between the strip 20 of bead stock and the blank holder 15. After the outer end portion of each pin 48 is peened to form the tapered head portion 49, the head portion is ground down to a surface 51 which conforms to the surrounding cuRved rounded surface 24 of the strip 20. I

Referring to FIG.'7, when it is desired to retain the strip -20 of bead stock by a series of longitudinally spaced cap screws (not shown) having hexagonal recesses for receiving an Allen wrench, the strip 20 is first punched to form a series of tapered holes 28. Each of the tapered holes is then counterbored to form a radial annular shoulder 54 which is engaged by the head of the cap screw when it is inserted into an aligned threaded hole formed within the blank holder 15. By first punching each tapered hole 28 and then counterboring the tapered hole as shown in FIG. 7, the counterbored holes can be formed in a much shorter period oftime than was heretofore required for drilling and counterboring a hole.

In reference to FIG. 6, the method of the invention, which is described above for securing a strip 20 of head stock toa draw die, may also be used for rigidly joinlng or connecting any two adjacent members, as for example, two

metal plates

60 and 62. That is, the plate 60 is punched in a manner as Shown in FIG. 2 to form a tapered hole 64, and the late62 is similarly punched to form a tapered hole 66. A fastener in the form of a flat tapered head rivet 68 is inserted into the

holes

64 and 66 so that the head portion of the rivet is received within the tapered hOle 66. The opposite end portion of the rivet 68 is then peened vto form the expanded head portion 69 which engages the surface defining the tapered hole 64. The rivet 68 thereby forms a rigid connection between the

plates

60 and 62 without projecting above the outer surfaces of the plates. It is apparent that tapered holes need not be punched in both of the members or plates 62. For example, the plate 62 might be provided with a tapped hole, and-a screw having a tapered head would be inserted into the punched tapered holes 64 for rigidly connecting the members.

From the drawing and the above description, it is apparent that the method of securing a strip of bead stock to a die member in accordance with the invention provides desirable features and advantages. For example, by successively punching longitudinallyspaced tapered holes within the strip 20 of. bead stock, instead of drilling, taper reaming and deburring each hole, a significant amount of time is saved in forming each hole. Thus in view of the substantial number of holes required for securing the bead stock to the die, the total time saved for forming all of the tapered holes significantly reduces the overall cost of the die. As mentioned in connection with FIG. 7, the punching of each tapered hole 28 and then counterboring the larger end of the hole, also provides for significantly reducing the time for forming counterbored holes in comparison to the prior method of drilling and counterboring each hole. Another advantage of punching the tapered holes is obtained by the formation of the slight radius 44 at the outer ends of each hole. That is, the radiuS 44 eliminates the need for deburring this end of the hole to assure that the strip 20 of head stock seats within the groove 22.

While the punching of the tapered holes 28 vand the use of a tapered headed fastener is ideally suited for securing a Strip of bead stock to a draw die, as mentioned above in connection with FIG. 6, the method of the invention may also be used for joining any two members when it is desirable to recess the head portion of a fastener either flush or below the surface of one of the members. As also mentioned above, it is within the Scope of the invention to punch a non-circular tapered hole within a member for securing the member to another member with a fastener which is expanded or formed to fit within the non-circular hole so that it is prevented from rotating. Furthermore, while the method herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise method, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims. I

What is claimed is:

1. An improved method of securing a strip of bead stock having a generally D-shaped cross-section to a draw die having a groove for receiving the fiat face of said strip, comprising the steps of positioning said strip adjacent a punch die with its curved face inward, said punch die having an opening of a predetermined diameter, selecting a-punch having a cross-sectional area substantially smaller than that of said opening, pressing said punch through said strip to force a slug of the strip into said opening and to form a tapered surface defining a tapered hole with its larger diameter opening on the curved face of said strip, mounting said strip on said draw die with its curved face outward, forming a bore within said draw die in alignment with said hole in said strip, and attaching said strip to said draw die with a fastener having a tapered head portion engaging said surface defining said tapered hole and conforming the outer end of said fastener to the curvature of said strip.

2. A method as defined in claim 1 including the step of forming a generally cylindrical surface within said strip adjacent said tapered surface during 'said punchinG operation by correlating the diameter of a cylindrical said punch and the diameter of a cylindrical said opening within said punch die with the thickness of said strip.

3. A method as defined in claim 1 including the step of inserting a ball within said bore, inserting a pin-like said fastener into said bore with its inner end portion engaging said ball and its outer end portion projecting into said tapered hole within said strip, and peening said outer end portion of said fastener within said hole to effect expanding of said inner end portion of said fastener within said bore and expanding of said outer end portion to form said head portion.

4. A method as defined in claim 1 including the step of counterboring said punched tapered hole to form a hole having an internal annular shoulder for receiving a fastener having a head portion adapted to engage said shoulder 5. A method as defined in claim 1 including the step of successively advancing said strip between said punch and said punch die, and successively pressing said punch through said strip to form a plurality of longitudinally spaced said tapered holes within said strip.

6. A method as defined in claim 1 including the steps of counterboring the larger end of said punched tapered hole to form an internal annular shoulder, and attaching said strip to said die with a fastener having a head portion engaging said shoulder.

Claims

1. An improved method of securing a strip of bead stock having a generally D-shaped cross-section to a draw die having a groove for receiving the flat face of said strip, comprising the steps of positioning said strip adjacent a punch die with its curved face inward, said punch die having an opening of a predetermined diameter, selecting a punch having a cross-sectional area substantially smaller than that of said opening, pressing said punch through said strip to force a slug of the strip into said opening and to form a tapered surface defining a tapered hole with its larger diameter opening on the curved face of said strip, mounting said strip on said draw die with its curved face outward, forming a bore within said draw die in alignment with said hole in said strip, and attaching said strip to said draw die with a fastener having a tapered head portion engaging said surface defining said tapered hole and conforming the outer end of said fastener to the curvature of said strip.

2. A method as defined in claim 1 including the step of forming a generally cylindrical surface within said strip adjacent said tapered surface during said punchinG operation by correlating the diameter of a cylindrical said punch and the diameter of a cylindrical said opening within said punch die with the thickness of said strip.

4. A method as defined in claim 1 including the step of counterboring said punched tapered hole to form a hole having an internal annular shoulder for receiving a fastener having a head portion adapted to engage said shoulder

5. A method as defined in claim 1 including the step of successively advancing said strip between said punch and said punch die, and successively pressing said punch through said strip to form a plurality of longitudinally spaced said tapered holes within said strip.