Means For Fastening Overlying Metal Sheets

Abstract

A longitudinally extending pierce and forming punch having a free end face is mounted on the base of a double-acting press that has first and second independently actuatable rams. Rigidly mounted on the first ram is a pierce and forming die having a punch receiving aperture into which the pierce and forming punch is receivable when the first ram is actuated. De-actuation of the first ram clears the die from the pierce and forming punch exposing its free end face. A flattening punch rigidly mounted on the second ram is slideably mounted in the punch receiving aperture in the die and is cooperable with the end face of the pierce and forming punch when the second ram is actuated.

Description

DETAILED DESCRIPTION

This invention relates to a method and means for fastening overlying metal sheets utilizing a punch and die set mounted in a double-acting press having two separately actuatable rams.

It is conventional to fasten overlying sheets by partially piercing and deforming sections of the sheets. Such a process eliminates the need for a separate fastener and is adequate for sheet metal joints used in forming ducts or the like. So simple is this integral connection to fabricate that many such connections can be made to provide a joint of adequate strength against both tension and torsion.

In making this integral connection, overlying sections of superposed metal sheets are displaced out of the plane of the sheets by piercing a portion of the periphery of the sections and bending or forming the remainder thereof. The displacement is such that the lower surface of the displaced section is even with the upper surface of the top of the two sheets. By swaging and or flattening the displaced section, the resultant lateral growth of the section causes its pierced edges to overlie the edges from which the section was pierced.

Conventionally, this type of connection is achieved using a process that requires two stations, one to pierce and displace the section, and one to swage the displaced section. Apparatus is known, however, in which all of the steps take place at one station. This latter apparatus includes a punch and die set wherein, in a single stroke, initial movement achieves the piercing and displacing of the section, and final movement achieves the swaging. To accommodate the resultant lateral growth of the section, the die must be provided with an expandable portion that is initially set to provide sufficient clearance for the piercing operation. As the swaging begins, the growth of the section forces the movable portion of the die to expand against a spring load. An example of this design is shown in U. S. Pat. No. 2,811,880, issued Nov. 5, 1957.

While the conventional apparatus may be adequate for many purposes, the expandable feature of the die is a possible source for maintenance problems when volume production is required. Accordingly, it is the primary object of the present invention to achieve a fastener of the type described at one station without the necessity for having a die requiring a movable section operated by the lateral growth of the section of the fastener as such section is swaged or flattened.

Briefly, this and other objects of the invention are achieved by employing a double acting press having two separately actuatable rams. Rigidly attached to the base of the press is a pierce and forming punch having a free end face. A cutting and forming die is rigidly mounted on one of the rams and has a punch receiving aperture therein into which the pierce and forming punch is receivable when the one ram is actuated.

The periphery of the pierce and forming punch surrounding its free end face has a first portion that closely matches a corresponding portion of the punch receiving aperture of the die to provide a fixed die clearance that achieves a piercing of a portion of the periphery of the section that is displaced from the plane of the sheets by actuation of the first ram. A second portion of the periphery of the pierce and forming punch is relieved and widely spaced from a corresponding relieved portion of the punch receiving aperture of the die. Such second portion causes bending and stretching of the portion of the periphery of the displaced section that is not pierced. The design is such that the section is displaced beyond the plane of the sheets and held there by the pierce and forming punch. The stresses in the bent and stretched portion of the displaced section resiliently urge the displaced section toward the sheets.

Rigidly mounted on the other ram is a flattening punch that is slideably received in the punch receiving aperture in the die. After the first ram is actuated to achieve the desired piercing and displacing of a section of the overlying sheets, it is then deactuated or moved clearing the die from the punch receiving aperture and freeing the displaced section for lateral expansion. Such expansion occurs when the second ram is actuated swaging and flattening the section between the flattening punch and the end face of the pierce and forming punch. In addition, the release of the displaced section by the pierce and forming punch permits the residual stresses in the bent and stretched portion of the displaced section to resiliently urge the laterally expanded section toward the sheets forming a secure connection therewith. This arrangement thus produces the desired integral fastener at one station by a two-step process that eliminates the special type of die required by the prior art.

The features of this invention for which protection is sought are pointed out with particularity in the appended claims. The invention itself, however, both as to its organization and method of organization, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, wherein like parts in each of the several figures are identified by the same reference character, and wherein:

FIG. 1 is a top view of a fragment of a pair of superposed metal plates showing an integral connection made in accordance with the present invention;

FIG. 2 is a section taken along the lines 2--2 of FIG. 1;

FIG. 3 is a section taken along the lines 3--3 of FIG. 1;

FIG. 4 is a sectional view of a double acting press into which the novel punch and die set of the present invention has been incorporated, the parts of such set being shown just prior to the piercing and displacing step in forming the integral connection shown in FIG. 1;

FIG. 5 is a sectional view like FIG. 4 but shows the parts after the first ram has been actuated and the piercing and displacing step has been completed;

FIG. 6 is a sectional view like FIG. 4 but showing the parts after the first ram has been de-actuated and the die about to be cleared from the pierce and forming punch;

FIG. 7 is a sectional view like FIG. 4 but showing the parts after the second ram has been actuated;

FIG. 8 is a perspective view of the free end face of the pierce and forming punch; and

FIG. 9 is a perspective view of the cutting and forming die showing details of the punch receiving aperture.

Referring now to FIGS. 1 - 3, integral connection 10 is shown in superposed metal sheets 11 and 12. Connection 10 comprises a pair of overlying sections 13 displaced out of the planes of each of the sheets. This configuration is achieved by piercing opposite portions 14 and 15 of the periphery defining the sections and bending the remainder of the two opposite portions 17 and 18 of the periphery. The displacement of sections 13 is such that the lower surface 19 of sections 13 must be held above the upper surface 20 of the top sheet 11 against the stresses developed by stretching portions 17 and 18 by which the sections remain attached to sheets 11 and 12.

After this displacement has taken place, sections 13 are flattened and swaged to effect lateral growth of the sections in a direction aligned with pierced portions 14 and 15. Such lateral growth is sufficient to cause the pierced edges 21 to overlie the edges 22 from which sections 13 were pierced. Upon the release of sections 13, the residual stresses in portions 17 and 18 urge the laterally expanded pierced edges 21 into resilient engagement with the top surface of sheet 11 adjacent edges 22. As a consequence of this construction, an integral fastener is achieved because edges 21 in cooperation with edges 22 prevent separation of sheets 11 and 12.

To develop the connection shown in FIGS. 1 - 3, a double acting press 30 (shown schematically in FIGS. 4 - 7) is used in connection with the punch and die set 31 of the present invention. Press 30 includes a rigid base 32, first and second rams 34 and 33, independently actuatable by control means 35 for longitudinal movement relative to the base, and stripper table 36 resiliently mounted on base 32. Punch and die set 31 comprises three elements: pierce and forming punch 37, cutting and forming die 38 and flattening punch 39.

Considering stripper table 36 first, it comprises a planar support 40 adapted to provide a horizontal support for the metal sheets to be fastened, and a plurality of vertical round posts 41 rigidly fastened to the support on the underside thereof adjacent the periphery of the support. Posts 41 are mounted in anti-friction bearings 42 attached by blocks 43 to base 32. The bearings limit movement of support 40 to the vertical or longitudinal direction. Centrally located in support 40 is clearance aperture 44 into which forming punch 37 projects.

Punch 37 extends longitudinally upwardly from base 32 and is rigidly mounted thereon by means of holder 45 which includes block 46 attached to base 32, punch holder 47 and adjusting screw 48. Punch holder 47 is provided with a longitudinal aperture receiving one end 49 of punch 37 which is provided with a transverse recess for receiving set screw 50 that locks and orients the punch. Screw 48 can be adjusted to provide the necessary vertical positioning of end face 51 of punch 37 which is on end 52 of the punch opposite end 49. As shown in FIG. 4, coiled spring 53 surrounds punch 37 and has one end abutting holder 45 and the other end abutting the under side of support 40. By this arrangement, the top of support 40 is resiliently held above end face 51 of punch 37 which is received in aperture 44, permitting overlying sheets 11 and 12 to be placed on support 40 without being interfered with by punch 47.

Turning now to forming die 38, it is rigidly mounted on first ram 34 for movement therewith. Specifically, die 38 is cylindrical in shape having flange 54 at one end receivable into a counterbored recess in the lower face of ram 34 and held there by block 55 which may be bolted to the lower face of the ram.

Forming die 38 has a longitudinally extending punch receiving aperture 56 for receiving displaced section 13 and the top of punch 37 when the first ram is actuated. Punch 37 is essentially cylindrical, and its end face 51 is essentially dome shaped with a central flat region 57 (FIG. 8) and a pair of opposite relieved portions 58 defined by a pair of opposite longitudinal recesses 59 formed in the periphery of end 52 of the punch. Aperture 56 in die 38 closely matches the configuration of end face 51 of punch 37. Thus, aperture 56 is essentially cylindrical, but has a pair of opposite relieved portions 60 formed by longitudinal recesses 61. By means of suitable keys, relieved portions 58 on punch 37 are aligned with relieved portions 60 in aperture 56 of die 38.

When ram 34 is actuated by control means 35, die 38 descends, and end face 61 thereof engages top sheet 11 as shown in FIG. 4. Thereafter, continued longitudinal movement of ram 34 imparts longitudinal movement to sheets 11, 12 and support 40 against the resistance of the sheets to piercing and bending, and against the resilient force of spring 53. At the end of the stroke of ram 34, displaced section 13 is removably received in aperture 56 of die 38. During the final movement of ram 34, the cylindrical portions of punch 37 between relieved portions 58 cooperate with the cylindrical portions of die 38 between relieved portions 60 and achieve the desired bending and stretching of the sheets as indicated by numerals 17 and 18 in FIG. 1. At this stage, the bottom edges of displaced section 13 are shown in the drawing as being aligned with the top surface of sheet 11. Actually, the bottom edges of displaced section 13 are slightly above the top surface being held against the residual stresses in portions 17 and 18 by punch 37.

After ram 34 completes its stroke, ram 33 is actuated by control means 35 and ram 34 is de-actuated. Rigidly attached to ram 33 is flattening punch 39 which is slideably received in aperture 56 for movement relative to die 38. Punch 39 is provided with a longitudinal peripheral slot 62 into which key 63 projects to maintain the alignment of die 38.

The timing of the actuation of ram 33 and the de-actuation of ram 34 by control means 35 is such that end face 61 of die 38 begins to clear top sheet 11 as the concave surface 64 of punch 39 begins to engage section 13 as shown in FIG. 6. This arrangement permits support 40 to remain depressed and for section 13 to remain engaged with end face 51 of punch 37.

By the time ram 33 reaches the end of its stroke, as shown in FIG. 7, section 13 atop face 51 is cleared from aperture 56 in die 38. Section 30 is then swaged between concave surface 64 of punch 39 and end face 51 of punch 37 as ram 33 reaches the end of its stroke. The curvature of dome 51 is somewhat less than the curvature of surface 64 and the flattening and swaging of section 30 results in its lateral growth as shown in FIGS. 2 and 3 until the pierced edges of the section overlie the edges of the sheets from which the section was pierced.

The timing of the actuation of ram 33 and the de-actuation of ram 34 is important because it is essential that the stripper table not release the sheets from punch 37 until the swaging operation is completed and ram 33 is de-actuated. Control means 35 in a conventional manner exerts the necessary dynamic control on rams 33 and 34.

After the swaging operation is complete, ram 33 is deactuated and the rams then return to a position at which the resilient mounting of stripper table is effective to remove punch 37 from section 30. In this condition, punch 37 releases section 13 as previously described, and the sheets can be indexed to place another portion over punch 37, in preparation for making another integral fastener.

Claims

The following is claimed:

1. Punch and die set means to fasten overlying planar metal sheets using a double acting press having separately actuatable longitudinally movable first and second rams mounted on a rigid base, comprising:

a. a longitudinally extending pierce and forming punch rigidly mounted on said base and having a free end face with diametrically opposed relieved portions therein;

b. a cutting and forming die rigidly mounted on said first ram for movement therewith and having a longitudinally extending punch receiving aperture into which said piercing and forming punch is receivable when said first ram is actuated;

c. a flattening punch rigidly mounted on said second ram for movement therewith and longitudinally slideably received in said punch receiving aperture; and

d. said flattening punch being cooperable with the end face of said pierce and forming punch when said second ram is actuated.

2. Punch and die set means according to claim 1 including means to sequentially operate said first ram and then said second ram.

3. Punch and die set means according to claim 1 including a stripper table adapted to support said sheets and resiliently mounted on said base for limited longitudinal movement, and having a clearance aperture for said pierce and forming punch.

4. Punch and die set means according to claim 3 wherein said pierce and forming punch as a periphery comprising a piercing edge and a bending edge whereby actuation of said first ram causes said die to clamp said sheets to said table and said pierce and forming punch to pass through the aperture in said table and displace a section of said sheets out of the plane thereof and into said punch receiving aperture by piercing a portion of the periphery of said section and bending the remainder thereof.

5. Punch and die set means according to claim 4 wherein de-actuation of said first ram causes said die to be retracted until the displaced section of said sheets is clear of said punch receiving aperture.

6. Punch and die set means according to claim 5 wherein actuation of said second ram causes the displaced section of said sheets to be swaged between said flattening punch and the free end face of said pierce and forming punch whereby the pierced portion of said section is laterally moved and caused to overlie the edge of said sheets from which said pierced portion was severed.

7. Punch and die set means according to claim 6 wherein the free end of said pierce and forming punch is curved, and the free end of said flattening punch is curved to a lesser extent than the curvature of the free end face of said forming punch.

8. Punch and die set means according to claim 6 wherein de-actuation of said second ram releases the swaged section to effect removal of said sheets.