US3760496A - Panel mounted electrical terminal - Google Patents

Abstract

A method and article for mounting electrical contacts in a panel is disclosed which features a headed metal tubular element carrying a spring contact adapted to be inserted in an aperture of a panel. The tubular portion of the element is dimensioned to be symmetrically compressed longitudinally by tooling to develop an outward annular bulge capable of locking the element tightly into panels of different thicknesses. Bulging of the contact element is controlled to permit large numbers of contacts to be mounted in a plastic panel without causing panel growth and incident misalignment of elements. The tubular element is of a configuration to assure adequate deformation without damage to a preassembled spring contact carried therewithin.

Description

United States Patent [191 Douglass [451 Sept. 25, 1973 PANEL MOUNTED ELECTRICAL TERMINAL Inventor: Frank Irvin Douglass,

Mechanicsburg, Pa.

[22] Filed:

- 21 Appl. No.: 62,770

Related US. Application Data [52] US. Cl. 29/629, 29/630 D [51] Int. Cl H0lr 9/00 [58-] Field ofSearch 29/522, 523, 630 D,

[56] References Cited UNITED STATES PATENTS 2,464,405 3/1949 Knauf, Jr. 29/509 2,673,336 3/1954 Peters 29/630 D X 2,670,021 2/1954 Torresen et al 29/509 2,667,688 2/1954 Winter, Jr 29/509 3,286,539 11/1966 Loper et a]. 29/509 2,846,659 8/1958 Hinspater et a. 29/522 3,069,490 12/1962 Polizzano 29/522 X 3,183,394 1 5/1965 Hipozer et a]. 29/630 D 2,278,025 3/1942 Sadoski 29/522 2/1966 Grabbe 29/630 1) 5/1969 Tally et al 29/522 x Primary Examiner-Charles W. Lanham Assistant Examiner-James R. Duzan Attorney-Curtis, Morris and Safford, Marshall M. Holcombe, William J. Keating, Frederick W. Raring, John R. Hopkins, William l-lintze, Adrian J. La Rue and Jay L. Seitchik [5 7] ABSTRACT A method and article for mounting electrical contacts in a panel is disclosed which features a headed metal tubular element carrying a spring contact adapted to be inserted in an aperture of a panel. The tubular portion of the element is dimensioned to be symmetrically compressed longitudinally by tooling to develop an outward annular bulge capable of locking the element tightly into panels of different thicknesses. Bulging of the contact element is controlled to permit large numbers of contacts to be mounted in a plastic panel without causing panel growth and incident misalignment of elements. The tubular element is of a configuration to assure adequate deformation without damage to a preassembled spring contact carried therewithin.

PATENTED SEP25 K175 sum 1 m2 PATENTED SEF25 I975 SHEET 2 [IF 2 PANEL MOUNTED ELECTRICAL TERMINAL CROSS REFERENCE TO RELATED APPLICATION This application is a divisional application of application Ser. No. 756,809 filed Sept. 3, 1968, now abandoned, and refiled as a continuation application Ser. No. 64,139, now U.S. Pat. No. 3,704,441.

BACKGROUND OF THE INVENTION The need for precision placement of electrical con- ---taets-arises in many instances. In connection matrices wherein a relatively large number of terminal posts are secured in a panel in an array adapted for wiring by automatic machinery each terminal must be placed within a given close tolerance of a center referenced to the overall dimension of the panel. In other instances terminal matrices are interconnected by multiple connectors carrying an array of contact springs in a plastic housing on fixed centers which require a rather exact placement of panel-carried terminals mated therewith. In still another example, a matrix of terminal receptacles mounted in a panel are engaged by the multiple leads of circuit modules, each having a number such as 14 or 16 individual terminals which must be plugged into the terminal receptacles. Misalignment of receptacles results in considerable hand labor, and possible damage to the assembled elements. g

A constant problem faced in the foregoing applications is one of a phenomena termed panel growth." This phenomena is caused by the incremental build-up of stresses in a panel due to wedging terminals through panel apertures. Panel growth may result in a panel becomingwarped or cracking or fracturing, or in perhaps a greater problem resulting in misalignment of terminals. For example, in a panel having an array of 100 terminals in a line across a given dimension, specified to be on, for example, 0.100 of an inch centers, the individual stresses created by wedge-fitting terminals into the panel will cause a gradual off-centering of terminals as more and more terminals in a given line are inserted. This may occur even though the apertures are drilled in a precise center-to-center spacing.

In addition to the foregoing problem, many applications call for connections which may be readily disconnected and replaced, which practice leads to the use of spring contact members associated with panel mounted terminals. A frequent configuration finds a panel carrying on one side an array of terminal posts which may be interwired by automatic machinery or by hand through a variety of techniques with such postsconnected to contact spring mounted in receptacles in the panel accessible from the other side. A number of prior art terminal structures have been devised for this type of application whichare either quite complex in terms of number of parts or assembly steps required or functionally limited in terms of providing a stable interconnection which can be repeatedly made and broken without deterioration ofcontact interface. In applications wherein the terminal dimensions are very small, as on the order of tenor twenty-thousandths of an inch in cross-section, the use of elements which must be hand assembled in a panel becomes so impractical as to preclude any use in matrix type terminal applications.

SUMMARY OF THE INVENTION The present invention relates to a method and article for mounting electrical contacts in panels.

It is an object of the invention to provide a method of mounting very small electrical contacts in the form of terminals, receptacles and the like, which is simple and inexpensive in terms of elements employed and steps required. It is another object to provide a method, article and tooling which facilitates mounting of arrays of relatively large numbers of electrical contacts in panel structures of different thicknesses without causing panel growth. It is a further object to provide an electrical contact article which facilitates a mounting in a panel which is sufficient to withstand both torque and axial stresses incident to various termination techniques presently being employed. It is still a further object to provide an electrical contact spring receptacle of a configuration permitting deformation for mounting in panels of different thicknesses in preassembled form.

The foregoing objects are attained by the invention through anelectrical terminal and contact structure including a headed metal tubular element carrying a contact spring therewithin which is preassembled in terms of being mechanically and electrically connected thereto. The walls of the element and the exterior configuration are arranged so that the element may be compressed in a longitudinal sense to be plastically deformed presenting an outwardly directed annular bulge of the wall material locking the element within a panel by engagement of opposing surfaces of the panel. In accordance with the method of the invention and the structure of the article, the annular bulge occurs essentially outward of the panel aperture to prevent loading of the panel material in a radial sense causing panel growth. The method of the invention contemplates control of the dimensions of the element and application tooling to assure the plastic deformation but at the same time precluding interference with the contact spring disposed within the element. In one embodiment the contact article includes a terminal post extended from the tubular portion. At another embodiment the invention contemplates a socket adapted to be interconnected to a panel by such techniques as flow soldering or the like.

Referring now to the drawings:

FIG. I is a perspective view in partial section of a portion of a panel, considerably enlarged from actual size;

. FIG. 2 is a sectional view showing one of the contacts of FIG. 1, further enlarged, with a compressing tool disposed thereon just prior to deformation of the contact;

FIG. 3 is a view similar to that of FIG. 2, but at a point after the application of compressive forces and initial deformation of the contact;

FIG. 4 is a view similar to FIG. 3, showing deformation of a contact in an intermediate stage;

FIG. 5 is a view similar to FIG. 4 showing deformation of a contact in a final stage, just prior to removal of the compressing tool;

FIG. 6 is a view of the final stage of deformation of a contact in use with a panel of lesser thickness than that shown in FIGS. 2-5;

FIG. 7 is a sectional view of the head end of a contact in conjunction with a support plate of an alternative configuration; and

FIG. 8, is a sectional view showing an alternative contact construction in the final stage of compression by a compressing tool.

Referring now to FIG. 1, a portion of a terminal matrix is shown to include apanel 12 containing a series of apertures such as 14, each having anelectrical contact 16 fitted thereto and locked to the panel. Thepanel 12 is typically of a plastic sheet material such as is used to make printed circuit boards. Each contact includes aterminal post 18 supported to extend upwardly from a surface of the panel with thevarious posts 18 disposed in a parallel line or row relationship. Theposts 18 serve to provide terminations for the contacts which may be made in any number of ways, including the well-known techniques of wrapping wires thereabout and forcing wires into engagement through the use of clips or the like applied over a post, or through engagement with multiple connectors carried in a common block, commonly mounted on a given row or line. Each of thecontacts 16 is made to extend through thepanel 12 and each includes in an illustrative embodiment a contact spring as shown in FIG. 1, adapted to receive a lead or conductive strip or member inserted therein. Typically, a number of leads extended from a given component module may be inserted in portions of two rows of contacts.

In accordance with one aspect of the invention,panel 12 might contain a large number ofcontacts 16;panels 40 inches long having posts on 0.100 of an inch centers not being unknown in the art. For those termination techniques wherein the terminal posts 18 are interwired by automatic tooling, the center-to-center spacing of the post is quite critical. The longitudinal disposition of the post is also critical, but this may be fairly easily corrected if the post is on a proper center. If the post is not on the proper center, however, bending the post will only result in a longitudinal misalignment. As previously mentioned, post misalignment can occur, due to growth of theboard 12 in turn caused by the incremental build-up of stresses created by contacts being wedge-fitted into board apertures. In accordance with the present invention, thecontacts 16 are mounted within theapertures 14 of thepanel 12 without appreciably loading the material of the panel. FIGS. 25 depict the method of the invention in the process of achieving a deformation of the contact which avoids panel growth. Before turning to a detailed description of this method, reference will be made to FIG. 2 and to the details of the contact illustrated thereby.

Thecontact 16 is comprised of two pieces; an outer metal element including an upper post portion integrally joined to a lower tubular portion, and ametal contact spring 36 fitted therewithin. Thepost portion 18 is flared outwardly as at 20 into a solid region ofmetal 22 of cylindrical outer configuration, as shown in FIGS. 1 and 2, which then joins the tubular portion which is of a larger diameter through a step forming aradial surface 26 extending around the periphery of the element. The tubular portion shown as 28 includes aninterior bore 30 extending therealong and opening opposite to the post portion in ahead portion 32, which includes aradial surface 33. Thehead portion 32 includes aflange 34, shown in FIG. 2 as being folded over and deformed inwardly to clinch thecontact spring 36 and hold such against displacement relative to the tubular portion. Clinching 36 also provides a stable electrical contact between 36 and the tubular portion and thus the post portion of the contact. Thecontact spring 36 may be of any suitable configuration, but is preferably made in the manner shown to accommodate pins or leads of different diameters inserted therein. In the embodiment shown in FIG. 2, thecontact 36 has inwardly bowedspring arms 40 which define on the inner surfaces thereof contact points for engagement with a pin or lead inserted within the spring. Thearms 40 are joined to atubular portion 42 which ties the ends of the springs together to stabilize and strengthen the contact spring. Thecontact spring 36 is made to be a little shorter in length than the length ofbore 30 for reasons which will be appreciated from the description to follow.

In accordance with the invention, as illustrated in FIGS. 25, thecontact 16 is made to have an outer diameter in the tubular portion approximately equal to the diameter of the aperture or hole which is drilled, punched or otherwise formed inpanel 12. The contact is fitted into such hole in the position shown in FIG. 2, with theradial surface 33 abutting one of the major surfaces of the panel to limit movement of the contact in an axial sense in one direction relative to the panel. The contact in such position is then caught between afixed surface 40, which may be considered as part of the tooling and a tool head shown as 42. Thetool head 42 includes aninterior bore 44 of a diameter and length to receive thepost 18 of the contact, extended freely therewithin. Thebore 44 is of a diameter to receive in a sliding fit that portion shown as 22 of the contact and thus to support the contact in a radial sense in such region. Toward the lower end of 44 is aradial surface 46 which is dimensioned to bear againstsurface 26 of the contact. Adjacent 46 is afurther bore 47 which is of a diameter to receive in a slidingfit portion 24 of the contact and to support the contact in such region against deformation. Adjacent 47 is a flared orbeveled portion 48 which serves as a relief to permit outward deformation of the contact in the region of 28. Thetool 42 ends in aflat surface 50 on the lower portion thereof. In accordance with the invention concept, thetool 42 is driven axially against the contact with theflange portion 46 bearing against 26 to an extent to cause the contact to buckle and bulge outwardly as shown by numeral 29 in FIG. 3. At this time the tool bore 47 prevents plastic deformation of the contact in the region of the contact engaged by the surface of 47 and the relief defined by 48 permits an outward bulge of the contact. I have discovered that the board aperture surface, even when defined by a plastic material, tends to restrict bulging of the contact elsewhere along the length of the contact. As can be observed from FIGS. 2 and 3, the contact is solidly formed in the region above the zone of outward bulge of deformation and above the point of application of deforming forces. The contact is also dimensioned relative to the tooling so that the forces applied to the tooling effect an outward and not inward bulge of the material of the contact.

As shown in FIG. 4, the tooling is further driven to cause a further collapse and outward annular bulging of the material of the contact and to shape the outward bulging by the engagement of the material of the outer wall of the contact with thesurface 48. As this occurs the forces tending to deform the contact are applied to a broader area of material. FIG. 5 shows the tooling in a position with thesurface 50 bottoming against the surface of thepanel 12 and with the material of the contact bulged and deformed outwardly and down against the upper surface of the panel. Care must be taken not to overdrive the tooling so as to shear the walls of 28 at 29.

As can be discerned from FIG. 5, the length of thecontact spring 36, relative to the length of thebore 30 in the contact is made to accommodate shortening of the contact due to the outward bulging and deformation thereof.

The contact as shown in FIG. 5 and also as shown in FIG. 1 is effectively locked against any axial displacement relative to the panel oraperture 14 thereof between theflange surface 33 of the head of the contact and the bulgedportion 29. Somewhat surprisingly, the locking action achieved through the deformation indicated in FIG. 5 has been found to also resist torque loads applied to contact through the application of wires spirally wrapped around thepost portion 18 and placed under tension. As previously mentioned, deformation of the contact indicated in FIG. 5 has been found to result in an inappreciable stressing of the panel material, notwithstanding the fact that the panels of use are typically of an insulating plastic material.

FIG. 6 shows thecontact 16 heretofore described being appliedto a panel shown as 52, which is substantially thinner than 12. In accordance with the invention, the contact is caught between asurface 60 which is part of the tool and a tool head 62 similar to the tool head 42.previ0usly described, but with aradial surface 66 spaced further away from the interiorly beveled relief shown as 68 and corresponding surfaces of the previously mentioned tool. As shown in FIG. 6, the application of compressive forces by the tooling results in an outward bulge and deformation of the wall of the contact to lock the contact into the panel. This deformation is approximately the same in extent as in the previously mentioned embodiment, only displaced downwardly to accommodate the thinner panel.

FIG. 7 shows an alternative embodiment of a part of the tooling corresponding to 40 and 60 previously described. In the embodiment of FIG. 7 the lower or fixed surface of the tooling shown as 41 is made to include a raised portion shown as 43, which has a configuration to fit within the head of the contact and increase the bearing area therewith. The tooling of FIG. 7 has been found to stabilize the compressing operation to prevent cooking of the contact and to further minimize the chance of damaging the contact and in particular the mounting of the contact spring therein. One of the more critical steps of the method of the invention is to assure that the deforming force is applied evenly or symmetrically to the contact. The embodiment of FIG. 7 also helps in this respect.

FIG. 8 shows an alternative embodiment ofcontact 70 in the process of being mounted in athin panel 52 apertured as at 54 and made to include a conductive path shown as 55, which may typically be a foil or the like, as used on printed boards. Thecontact 70 is comprised ofa thin walled metal shell having a rounded end as at 72 closing the shell at one end. At the other end the shell material is deformed inwardly as at 74 to trap and connect acontact spring 76 therewithin. The contact spring includes a plurality ofspring arms 78 extended down within the shell. The tooling shown in FIG. 8 includes an elementSO having a raisedandbeveled portion 81 to partially enter and atool head 82 similar in function to the tool heads previously described Thetool head 82 includes a bore of a length to receive the end portion of the shell of the contact ending in a relievedbeveled surface 86. It has been found that by making the bottom of the bore of the tool head to include a relieved surface like 84 (formed for example by an included angle of approximately a contact having a rounded end can be longitudinally compressed to effect the bulging shown in FIG. 8. It is felt that the shape of thesurface 84 better assures the application of forces causing a compression of the contact in the manner indicated in FIG. 8.

In an actual embodiment like that shown in FIGS. 11-7, the contact outer shell was screw-machined out of brass with the post portion thereafter being coined into a 0.025 X 0.025 of an inch square cross-section. The portion numbered 22 of the contact 'was approximately 0.040 of an inch in diameter with the tubular portion of the contact being approximately 0.050 of an inch in diameter. The tubular portion had a wall thickness of approximately 0.005 of an inch and the tubular portion was approximately 0.165 of an inch in length. The contact was staked into a phenolic board roughly 0. or 0.063 of an inch in thickness having apertures on the order of 0.052 of an inch in diameter to provide a slight interference fit when the contact was inserted therein. Tooling of the configuration shown in FIG. 2 or in FIG. 6 was driven to develop a compressive force of approximately 60 to 75 pounds to effect the deformation indicated in FIG. 5. Contacts so staked readily accepted up to 2.5 ounce inch pounds torque without twisting in the panel.

In the examples previously given, one embodiment of theinvention has been detailed which includes a post extended from one end of the contact and another em bodiment has been detailed which includes the closed end shell having no post thereon. The invention fully contemplates applications wherein the shell may be opened-ended, as for example by changing the shape of the configuration shown in FIGS. 1 and 2 by removing the post and having an aperture extending into the shell. The invention contemplates having exteriorly therefrom contact members of other configurations extending longitudinally of the shell or exteriorly therefrom with or without a spring portion. The invention also contemplates having dielectric or insulating inserts carrying contact posts or other contacts mounted within the shell and inserted therefrom for feedthrough or shielded application; the important criteria being that the shell includes a portion shaped relative to the tooling to provide the collapsing action herein described.

Having now disclosed the invention in terms intended to enable a preferred practice thereof, claims are appended which are intended to define what is asserted to be inventive.

What is claimedis:

1'. In a method of mounting an electrical contact within a plastic insulating structure the steps comprising providing a contact element having a tubular portion of a wall thickness and material characteristics to define essentially a ductile and circumferentially closed and hollow structure and including a spring portion extended within said hollow structure, inserting said element within the aperture of said insulating structure with a portion extending exteriorly and interiorly of said aperture, positioning tooling to bear against spaced portions of said element as fitted within said aperture and applying a compressing force entirely longitudinally of said element, said force symmetrically balanced about the center line of said element to effect a bulge of the walls of the tubular portion radially outwardly to define a surface bearing against an exterior surface of said insulating structure to lock said element within said structure, said bulge being limited in axial length to preclude interference with such spring portion and to minimize stressing of the material of said insulating structure.

2. A method of mounting a metal electrical terminal in an aperture provided in a plastic panel without the need for compression between said terminal and said panel, and thereby substantially eliminating panel growth, the steps comprising: inserting a metal tubular portion of said terminal in said aperture, locating a first radially enlarged portion of said terminal against a first surface of said panel, providing an expansible resilient spring contact member internally of said tubular portion, said tubular portion being initially longer than said spring contact member, and applying an axial force on said tubular member to form an outwardly buckled portion of said tubular member at a location essentially outward of the panel aperture to prevent loading of the panel in a radial sense which causes panel growth, and engaging said outwardly buckled portion of said tubular member on a second surface of said panel, whereby said tubular member is reduced in length a limited amount so as not to compress on said spring member and said terminal is substantially locked in place on said panel by said first radially enlarged portion and said outwardly buckled portion.

3. The method as recited inclaim 2 and further including the steps of: partially enclosing said tubular portion in a tool used to apply said axial force on said tubular portion, and confining said outwardly bulged portion within a generally flared portion of said tool in order to limit the extent of outward bulging of said tubular portion.

4. The method as recited in claim 3, and further including the steps of: applying said tool axially against said outwardly bulged portion, and forcing said outwardly bulged portion into engagement on said second surface of said panel.

5. A method of mounting a plurality of closely spaced elongated electrical terminals into corresponding apertures provided in a plastic panel without causing panel growth, comprising the steps of: inserting a metal tubular portion of each terminal into a corresponding aperture provided in said panel, engaging a first surface of said panel with an enlarged head portion of each terminal, the tubular portion of each terminal projecting through a second surface of said panel, enclosing only a portion of each said tubular portion within a relatively slim sleeve of a tool, applying an axial force by said sleeve of a tool axially on each said tubular portion in a direction toward said second surface of said panel, outwardly bulging a portion of each of said tubular portions adjacent to but outwardly of said second surface of said panel, forcing each said outward bulging portion into engagement on said second surface, whereby said terminals are locked within the apertures of said panel and are mounted to said panel in closely spaced relationship without appreciable compression of the terminals in a radial sense against said panel and further including: an expansible resilient spring element internally of each said tubular portion, each said tubular portion being initially longer than said corresponding spring element, and further including the steps of: reducing the length of each said tubular element simultaneously upon outwardly bulging a portion thereof, and limiting the amount of length reduction in said tubular portions to prevent compression on said spring elements internally thereof.

6. The method as recited in claim 5, and further including the step of: locating each of said outwardly bulging portions along the length of corresponding tubular portions for placement outwardly ofthe thickness of said panel. 7. The method as recited in claim 5 and further including the steps of: confining only a portion of each said tubular portions within a corresponding tool used to apply said axial force, creating each said outward bulging portion externally of said corresponding tool and externally of said panel, and subsequently confining each said outwardly bulging portion of each tubular portion within a flared portion of a corresponding tool, thereby limiting the amount of outward bulging of each said tubular portion.

Claims (7)

1. In a method of mounting an electrical contact within a plastic insulating structure the steps comprising providing a contact element having a tubular portion of a wall thickness and material characteristics to define essentially a ductile and circumferentially closed and hollow structure and including a spring portion extended within said hollow structure, inserting said element within the aperture of said insulating structure with a portion extending exteriorly and interiorly of said aperture, positioning tooling to bear against spaced portions of said element as fitted within said aperture and applying a compressing force entirely longitudinally of said element, said force symmetrically balanced about the center line of said element to effect a bulge of the walls of the tubular portion radially outwardly to define a surface bearing against an exterior surface of said insulating structure to lock said element within said structure, said bulge being limited in axial length to preclude interference with such spring portion and to minimize stressing of the material of said insulating structure.

2. A method of mounting a metal electrical terminal in an aperture provided in a plastic panel without the need for compression between said terminal and said panel, and thereby substantially eliminating panel growth, the steps comprising: inserting a metal tubular portion of said terminal in said aperture, locating a first radially enlarged portion of said terminal against a first surface of said panel, providing an expansible resilient spring contact member internally of said tubular portion, said tubular portion being initially longer than said spring contact member, and applying an axial force on said tubular member to form an outwardly buckled portion of said tubular member at a location essentially outward of the panel aperture to prevent loading of the panel in a radial sense which causes panel growth, and engaging said outwardly buckled portion of said tubular member on a second surface of said panel, whereby said tubular member is reduced in length a limited amount so as not to compress on said spring member and said terminal is substantially locked in place on said panel by said first radially enlarged portion and said outwardly buckled portion.

3. The method as recited in claim 2 and further including the steps of: partially enclosing said tubular portion in a tool used to apply said axial force on said tubular portion, and confining said outwardly bulged portion within a generally flared portion of said tool in order to limit the extent of outward bulging of said tubular portion.

4. The method as recited in claim 3, and further including the steps of: applying said tool axially against said outwardly bulged portion, and forcing said outwardly bulged portion into engagement on said second surface of said panel.

5. A method of mounting a plurality of closely spaced elongated electrical terminals into corresponding apertures provided in a plastic panel without causing panel growth, comprising the steps of: inserting a metal tubular portion of each terminal into a corresponding aperture provided in said panel, engaging a first surface of said panel with an enlarged head portion of each terminal, the tubular portion of each terminal projecting through a second surface of said panel, enclosing only a portion of each said tubular portion within a relatively slim sleeve of a tool, applying an axial force by said sleeve of a tool axially on each said tubular portion in a direction toward said second surface of said panel, outwardly bulging a portion of each of said tubular portions adjacent to but outwardly of said second surface of said panel, forcing each said outward bulging portion into engagement on said second surface, whereby said terminals are locked within the apertures of said panel and are mounted to said panel in closely spaced relationship without appreciable compression of the terminals in a radial sense against said panel and further including: an expansible resilient spring element internally of each said tubular portion, each said tubular portion being initially longer than said corresponding spring element, and further including the steps of: reducing the length of each said tubular element simultaneously upon outwardly bulging a portion thereof, and limiting the amount of length reduction in said tubular portions to prevent compression on said spring elements internally thereof.

6. The method as recited in claim 5, and further including the step of: locating each of said outwardly bulging portions along the length of corresponding tubular portions for placement outwardly of the thickness of said panel.

7. The method as recited in claim 5 and further including the steps of: confining only a portion of each said tubular portions within a corresponding tool used to apply said axial force, creating each said outward bulging portion externally of said corresponding tool and externally of said panel, and subsequently confining each said outwardly bulging portion of each tubular portion within a flared portion of a corresponding tool, thereby limiting the amount of outward bulging of each said tubular portion.

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