GB2087284A

GB2087284A - Apparatus for and method of joining sheet metal and sheet metal so joined

Info

Publication number: GB2087284A
Application number: GB8103962A
Authority: GB
Original assignee: BTM Corp
Current assignee: BTM Corp
Priority date: 1980-09-08
Filing date: 1981-02-10
Publication date: 1982-05-26
Also published as: GB2123734A; MX174368B; GB2087284B; JPS6113889B2; GB8321311D0; GB2123734B; JPS6087935A; JPS5750224A; DE3106313A1; JPS6018259B2; MX155014A; DE3106313C2; CA1166832A

Abstract

Apparatus for joining superposed pieces of sheet metal (a, b) first draws and then laterally extrudes the material to be joined into an enlarged shape which will permanently mechanically interlock the pieces. The apparatus utilizes a die construction in which portions (38) thereof pivot laterally in response to lateral extrusion of the joining material, and is applicable to conventional "lanced" type joints as well as to a leakproof joint (as shown) with the deformed metal remaining imperforate but with interlocking projections nesting one within the other. <IMAGE>

Description

SPECIFICATION Apparatus for and method of joining sheet metal and sheet metal so joined The present invention relates generally to joining sheet metal and more especially to an apparatus for forming such joints, a method of forming such joints which preferably are leakproof, and a joint so made.

Although it is old in the art to join a plurality of pieces of sheet metal by punching or otherwise manipulating same to cause them to be deformed into an interlocking relationship in a localized area, insofar as applicant is aware such joints necessarily require the shearing of material and hence are not suitable for leakproof applications (in the absence of some sealing material), and are destructive of the corrosion resistance of coated materials. Known apparatus is also relatively complex in design, often requiring powered actuation of both a punch and portions of the die, and utilizing expensively machined sliding die portions. This complexity increases the cost of the equipment, as well as the energy required for operation.

It is therefore a primary object of the present invention to provide an improved apparatus for permanently joining sheet metal which is capable of creating leakproof joints. Additional objects reside in the provision of such an apparatus which is relatively simple in construction (only a single punch need be actuated), can utilize a standard punch, requires very little power, is compact and hence usable in many different applications, creates a minimum amount of injury to coated materials being joined, thereby increasing corrosion resistance, and is suited for use as part of a small press or in C-frames holders which can be used in a larger press.

According to the present invention there is provided apparatus for joining sheet metal, comprising: a punch having a given cross-section actuatable for reciprocating movement along a first axis; and a die mounted in fixed aligned relationship to said punch, said die including first and second die portions disposed on opposite sides of said axis means defining an opening in said die for receiving said punch when moved to said die, said opening being centered on said first axis and having a shape at least in part complementary to said cross-sectional shape of said punch, one portion of said opening being defined by one of said die portions and another portion of said opening being defined by the other of said die portions, pivot means mounting said die portions for pivotal movement with respect to one another about pivotal axes generally parallel to one another, said pivotal axes being disposed on opposite sides of and perpendicular to said first axis, and a fixed anvil disposed in said opening against which said sheet metal is adapted to be pressed by said punch.

Another aspect of this invention provides a method of joining sheet metal, comprising: assembling at least two pieces of sheet metal in overlapping relationship; positioning a die having an opening defined by a bottom surface and a laterally expansible side wall against one outside face of the sheet metal assembly; moving a punch against the opposite outside face of the sheet metal assembly in a direction toward the die opening in a manner to draw both pieces of sheet metal into the die opening and against the bottom surface thereof without shearing any portion of the sheet metal; continuing movement of the punch toward the bottom surface of the die opening to reduce the original thickness of the sheet metal pieces disposed therebetween and to extrude same in a lateral direction to form a laterally enlarged shape which will mechanically interlock the two pieces of sheet metal, said lateral extrusion occurring without fracture of any portion of the sheet metal, the wall of the opening expanding to accommodate said lateral extension; and withdrawing the punch from the opening and the joined sheet metal assembly.

A further aspect of this invention provides a leakproof joint permanently securing two pieces of overlapped sheet metal together, said joint comprising: a first projection on one of said pieces of sheet metal, said first projection being defined by a continuous, imperforate, unfractured metal portion formed integrally with said piece of sheet metal, and a second projection on the other of said pieces of sheet metal, said second projection being defined by a continuous, imperforate, unfractured metal portion formed integrally with said piece of sheet metal, one of said projections being nested within the other, and both of said projections being enlarged at the free ends thereof to form a permanent mechanical interlock between said pieces of sheet metal.

The present invention will become further apparent from the subsequent description given by way of example with reference to the accompanying drawings, in which: Figure 1 is a fragmentary front elevational view of an apparatus incorporating the present invention, shown in its retracted position; Figure 2 is a view similar to Figure 1 but showing the apparatus in its advanced position; Figure 3 is a view taken substantially along line 3-3 in Figure 1; Figure 4 is a fragmentary sectional view taken generally along line 4-4 in Figure 3; Figure 5 is a fragmentary sectional view taken generally along line 5-5 in Figure 3; Figure 6 is a perspective view of the die body of the apparatus shown in Figures 1-5; Figure 7 is an enlarged fragmentary sectional view illustrating the leakproof joint of the present invention at the point of completion of its formation;; Figure 8 illustrates dies for forming a plurality of different shaped joints in accordance with the present invention; Figure 9 is a partially exploded perspective view of an alternative form of a die assembly having universal applicability; Figure 10 is a view of a universal punch assembly suited for use with the die assembly of Figure 9; Figure 1 7 is a fragmentary front elevational view of another embodiment of an apparatus incorporating the principles of the present invention which is applicable to the formation of conventional "lanced" type joints; Figure 12 is a side elevational view of the apparatus of Figure 11; Figure 13 is a fragmentary enlarged sectional view of a "lanced" joint formed by the apparatus of Figures 11 and 12; and Figure 74 is a fragmentary sectional view taken generally along line 14-14 in Figure 13.

With reference to Figures 1-6, there is shown a sheet metal joining apparatus generally comprising a die assembly 10 and a punch assembly 12 for joining two pieces of sheet metal indicated ata and b, respectively.

Although only two pieces of sheet metal are shown, it is to be understood that more than two pieces may be joined, depending upon the material in question and the thickness thereof. It is envisioned that the most common materials to be joined will include such materials as aluminium, galvanized, brass, steel, and sheet stock, both coated and uncoated. The invention is particularly suitable for the joining of different materials which cannot be welded.

Punch assembly 12 is of conventional construction, including a punch body 14 mounting a circular punch 16 and having a threaded portion 18 for threadably supporting a stripper retainer 20. Disposed within retainer 20 is a stripper 22 biased to the stripping position illustrated in Figure 1 by means of coil spring 24.

Punch 16 preferably has a smooth flat tip, with a small radius at the edge as shown in Figure 7.

Die assembly 10 comprises cylindrical die body 26 mounted in the usual manner within a support structure 28 which may either be the lower leg of a conventional C-frame clamping device for use in a standard press, or the lower die supporting portion of a small press, such as a press of the type disclosed in applicant's Patent No. 3,730,044. Die body 26 is provided at its upper end (as shown) with an integral boss 30 from the opposite sides of which extend four shoulders, each indicated at 32. Die body 26 is centrally bored and at the upper end thereof is provided a bore portion 34 in which is disposed (as by press fit) a hardened pin 36 which acts as an anvil or lower die member.

Pivotally supported on each side of die body 26, by means of roll pins 40 located in apertures 42, is a die portion 38. Each die portion 38 is generally T-shaped in side elavation and is provided with two shoulders 44 engageable with two shoulders 32 on die body 26, so that vertical forces exerted on the die portions are transmitted directly to the die body and are not absorbed by pins 40. Each die portion 38 is relieved at 45 to facilitate limited rotational movement. Die portions 38 are mounted for pivotal movement between the respective positions illustrated in Figures 1 and 2, and are maintained in a normally closed position, as shown in Figure 1, by means of a coil spring 46 acting between downwardly extending integral legs 48 on die portions 38. Spring 46 passes through a suitable aperture 50 extending through boss 30.

When die portions 38 are in their closed position illustrated in Figure 1, the upper surfaces 52 thereof lie in a common horizontal plane and the abutting faces of the die portions lie in a common vertical plane indicated at 54. In this embodiment die portions 38 are each provided with a complementary semi-circular recess 56 centered on plane 54 and defining, when the die portions are in their closed position, an opening having a shape complementary to that of punch 16. Forces exerted downwardly on die portions 38 by punch 16 acting on the workpieces will not tend to pivot them away from one another because the pivotal axes defined by roll pins 40 are disposed outwardly of the edges of the opening defined by recesses 56. Thus any downward force exerted on the die portions by the punch will tend to close rather than open the die.In this embodiment the edge of the opening defined by recesses 56 should be chamfered, as indicated at 58 (Figures 1 and 7), to reduce the chance of fracturing or shearing the workpiece.

In operation, the apparatus is initially in the position illustrated in Figure 1. To join two or more metal sheets they are first placed in overlapping orface-to-face relationship and thereupon placed into the apparatus in Figure 1, with the lower surface of the sheet metal assembly disposed on surfaces 52 of die portions 38. Thereafter the press (or whatever apparatus is used) is actuated to cause the punch to move downwardly (as shown) towards sheet metal pieces a and band die assembly 10. Upon engagement of die 16 and the sheet metal, the latter is caused to be drawn downwardly toward the upper surface of anvil 36, indicated at 60. There is no fracturing or shearing of the metal because of the provision of radius 58 around the periphery of the opening defined by recesses 56 and the clearance between the latter and the punch.The drawing action results directly from the coaction of the punch and the opening in die portions 38 defined by recesses 56. As punch 16 approaches anvil 36 at a distance less than the total combined original thickness of sheet metal pieces a and b, there is a transverse or lateral extrusion of the metal, which results in the formation of a laterally enlarged shape, such as indicated at 62 in Figure 7, which defines a mechanical interlock between sheet metal pieces a and b. Figure 7 is not drawn to scale, but is intended to provide a representative illustration of the cross-sectional configuration of the metal forming the joint. The lateral extrusion of sheet material causes die portions 38 to be forced laterally outwardly whereupon they pivot outwardly as best illustrated in Figures 2 and 7. A strong, permanent and leakproof joint having been formed, the punch is then withdrawn to the position illustrated in Figure 1 and the workpiece removed. It is noteworthy that in applicant's apparatus only punch 16 requires actuation, and anvil 38 remains fixed. Upon removal of the workpiece spring 46 causes die portions 36 to move back to their closed position illustrated in Figure 1.

Shearing or lancing of the sheet metal is avoided with the aforedescribed apparatus by providing radius 58 and an appropriate clearance between punch 16 and the opening defined by recesses 56. This clearance is preferably of uniform width. Although applicant has not conducted tests for optimizing the respective dimensions of the parts, set forth below are formulae which establish dimensions which have been found to provide very satisfactory results: P = 2 (M1 + M2) (+1- 20%) D=P+0.8(M1 + M2) T=0.2(1.2(M1 + M2)) where: P = punch diameter D = die diameter M1 = top metal thickness M2 = bottom metal thickness T = total metal thickness at center of joint These relationships have been found to be a satisfactory starting point.Once the punch diameters are chosen and the apparatus assembled and tested, satisfactory results can be obtained for the materials being joined by adjusting the bottom anvil height using the standard "shut heighth" adjustment (not shown) provided on conventional small presses and C-frames (i.e., the distance between the bottom of the punch and the anvil when the press is at the end of its downward stroke).

Although the apparatus of the first embodiment illustrates the use of a circular punch other shapes may be used, depending upon the application and the strength required. For example, there are shown in Figure 8 four different configurations which might be used. Die portions 38a are provided with three circular apertures 64 for those applications in which either the anti-rotation characteristics or the strength characteristics desired require more than a single circular joint. Die portions 38b have a diamond-shaped aperture 66 which is capable of providing a joint of strength comparable to that of the first embodiment, but yielding better anti-rotational characteristics. Die portions 38c have a triangular opening 68 which should give results similar to those of the diamond-shaped opening 66.Die portions 38d have an oval shaped opening 70 providing a relatively large joint of high strength and high anti-rotational characteristics.

Regardless of cross-sectional shape, the interior wall of the drawn portion of the upper piece of sheet metal will be generally cylindrical in configuration.

In Figure 9 there is illustrated a universal type die body 26a which is virtually identical to die body 26 of the first embodiment but is provided with a plurality of parallel vertically aligned holes 72, 74 and 76 adapted to receive hardened anvil pins 78, 80 and 82, respectively, in a press fit relationship. It is envisioned that in applications where a single circular joint is sufficient, pins 78 and 82 may be removed from the die body, thus reducing energy requirements. On the other hand, if greater strength or anti-rotation characteristics are desired, then one or two more additional pins may be inserted in the proper hole to provide additional joining capability. The die portions which would be affixed to die body 26a would have a top configuration similar to that shown at 38a in Figure 8, with openings 64 being designed to cooperate with pins 78, 80 and 82.

In Figure 10 there is illustrated the lower portion of a punch which may be utilized with the universal die body of Figure 9. The punch body, which can be conventional in all other respects, is indicated at 84 and is provided with a plurality of press-fit hardened steel punch pins 86, 88 and 90 adapted to coact with anvils 78, 80 and 82, respectively, in the same manner that punch 16 coacts with anvil 36 in the first embodiment Suitable apertures 92 may be provided in the punch body 84 to permit removal of the punches if it is desired to replace same or reduce the number thereof for a particular application. The punch pins and anvils can be non-circular in cross-section if desired.

In Figures 11 and 12 there is illustrated a slightly modified version of the die assembly and punch which is capable of forming conventional "lanced" type joints, such as illustrated in Figures 13 and 14. The die assembly 10a of this embodiment includes die body 26b and is substantially the same as die assembly 10 of the first embodiment (the same reference numerals are used to indicate identical parts), differing in that die portions 38e are not provided with recesses to define a punch receiving opening, but instead are provided with cutting edges 94. In addition, the anvil comprises an integrally formed continuous flat generally horizontal surface 96 extending the full length of cutting edges 94. Punch 16a of this embodiment is generally spade-shaped, having a width substantially the same as the distance between cutting edges 94 and having chamfered corners 98.

In Figures 13 and 14 sheet metal pieces c and dare shown joined utilizing the apparatus of Figures 11 and 12. As the punch moves downwardly toward the die assembly, projections 100 and 102 are lanced out of sheet metal pieces c and d, respectively. These projections remain integrally attached to the parent metal at the ends thereof, as best shown in Figure 13, but are totally severed from the material along their sides as shown at 104 in Figure 14. Continued advancement of the punch toward the anvil causes a transverse or lateral extruding of projections 100 and 102 to create the enlarged section shown in Figure 14, which provides the necessary mechanical interlock to give the joint its integrity. As will be appreciated, because there is a lancing of the sheet metal a joint of this type is not leakproof. As the metal of the projections is extruded laterally it causes die portions 38e to pivot apart to accommodate the extrusion and thereby define the interlock. The use of applicant's die assembly has been found to very satisfactorily permit the formation of this type of joint without the use of moving anvils and complex sliding dies.

Claims

1. Apparatus for joining sheet metal, comprising: a punch having a given cross-section actuatablefor reciprocating movement along a first axis; and a die mounted in fixed aligned relationship to said punch, said die including first and second die portions disposed on opposite sides of said axis, means defining an opening in said die for receiving said punch when moved to said die, said opening being centered on said first axis and having a shape at least in part complementary to said cross-sectional shape of said punch, one portion of said opening being defined by one of said die portions and another portion of said opening being defined by the other of said die portions, pivot means mounting said die portions for pivotal movement with respect to one another about pivotal axes generally parallel to one another, said pivotal axes being disposed on opposite sides of and perpendicular to said first axis, and a fixed anvil disposed in said opening against which said sheet metal is adapted to be pressed by said punch.

2. Apparatus as claimed in claim 1, wherein said pivotal axes are spaced apart a distance greater than the dimension of said opening in the same direction.

3. Apparatus as claimed in claim 1 or 2, further comprising spring means for biasing said die portions toward one another.

4. Apparatus as claimed in claim 1, 2 or 3, wherein said opening is fully complementary in shape to the cross-sectional shape of said punch, and a uniform clearance is provided between said punch and said opening to prevent shearing of said sheet metal when said punch is moved into said opening, said clearance being less than the total combined thickness of said sheet metal being joined.

5. Apparatus as claimed in claim 4, wherein said clearance is approximately 40% of said total combined thickness.

6. Apparatus as claimed in any preceding claim, wherein the edge of die opening facing said punch is provided with a radius to reduce the tendency of the apparatus to shear said sheet metal.

7. Apparatus as claimed in claim 1, wherein said opening has two sides which are substantially in alignment with corresponding sides of said punch so that said sheet metal is sheared when said punch is moved into said opening.

8. Apparatus as claimed in any preceding claim, further comprising a die body for pivotally supporting said die portions, and abutment means on said die body directly engageable with said portions to absorb the loads taken by said die portion as a result of actuation of said punch, thereby relieving said pivot means of said loads.

9. Apparatus as claimed in any one of claims 1 to 7, further comprising a die body having a plurality of aligned holes disposed in perpendicular relationship to said axis, said anvil being disposed in one of said holes, the remaining holes being adapted to receive additional anvils for applications requiring multiple joints.

10. Apparatus as claimed in any preceding claim, wherein the free end of said punch and the free end of said anvil have generally flat opposed surfaces, respectively.

11. Apparatus as claimed in claim 10, wherein said flat surfaces are disposed generally parallel to one another.

12. Apparatus as claimed in any one of claims 1 to 6, wherein the free end of said punch and said die opening are circular in cross-section.

13. Apparatus as claimed in claim 12, wherein the free end of said anvil is generally circular in cross-section.

14. Apparatus as claimed in claim 13, wherein the diameter of said anvil is approximately the same as that of said die opening.

15. Apparatus as claimed in claim 14, wherein the diameter of said punch is less than the diameter of said die opening.

16. Apparatus as claimed in claim 15, wherein the difference between the diameters of said punch and die opening are less than the total combined thickness of said sheet metal to be joined.

17. Apparatus for joining sheet metal, comprising: a punch having a given cross-section actuatablefor reciprocating movement along a first axis; and a die, said die including first and second die portions having generally planar surfaces engaging one another along a plane incorporating said first axis, means defining an opening in said die for receiving said punch when moved to said die, said opening being centered on said first axis and having a shape complementary to said cross-sectional shape of said punch, pivot means mounting said die portions for pivotal movement with respect to one another about pivotal axes generally parallel to one another, perpendicular to said first axis, said pivotal axes being spaced apart a distance greater than the dimension of said opening in the same direction, a fixed anvil disposed in said opening against which said sheet metal is adapted to be pressed by said punch, and spring means for biasing said die portions toward one another.

18. A leakproof joint permanently securing two pieces of overlapped sheet metal together, said joint comprising: a first projection on one of said pieces of sheet metal, said first projection being defined by a continuous, imperforate, unfractured metal portion formed integrally with said piece of sheet metal, and a second projection on the other of said pieces of sheet metal, said second projection being defined by a continuous, imperforate, unfractured metal portion formed integrally with said piece of sheet metal, one of said projections being nested within the other and both of said projections being enlarged at the free ends thereof to form a permanent mechanical interlock between said pieces of sheet metal.

19. A joint as claimed in claim 18, wherein both of said projections are circular in cross-section.

20. A joint as claimed in claim 18, wherein both of said projections are triangular in cross-section.

21. A joint as claimed in claim 18, wherein both of said projections are rectangular in cross-section.

22. A joint as claimed in claim 18, wherein both of said projections are oval in cross-section.

23. A joint as claimed in any one of claims 18 to 22, wherein said joint comprises a plurality of said projections disposed in close relationship to one another.

24. A joint as claimed in any one of claims 18 to 23 wherein said projections comprise a continuous side wall projecting generally perpendicularly from said pieces of sheet metal, and a substantially flat end disposed generally parallel to said pieces of sheet metal, the enlarged portion of each of said projections being disposed at the intersection of said wall and end thereof.

25. A joint as claimed in claim 24, wherein each said wall is of less thickness than the sheet metal from which it was formed.

26. A joint as claimed in claim 24 or 25, wherein each said end is of less thickness than the sheet metal from which it was formed.

27. A joint as claimed in claim 24,25 or 26 wherein the inside surface of said wall of said first projection is generally cylindrical.

28. A method of joining sheet metal, comprising: assembling at least two pieces of sheet metal in overlapping relationship; positioning a die having an opening defined by a bottom surface and a laterally expansible side wall against one outside face of the sheet metal assembly; moving a punch against the opposite outside face of the sheet metal assembly in a direction toward the die opening in a manner to draw both pieces of sheet metal into the die opening and against the bottom surface thereof without shearing any portion of the sheet metal; continuing movement of the punch toward the bottom surface of the die opening to reduce the original thickness of the sheet metal pieces disposed therebetween and to extrude same in a lateral direction to form a laterally enlarged shape which will mechanically interlock the two pieces of sheet metal, said lateral extrusion occurring without fracture of any portion of the sheet metal, the wall of the opening expanding to accommodate said lateral extension; and withdrawing the punch from the opening and the joined sheet metal assembly.

29. The method as claimed in claim 28, wherein said bottom surface is maintained in a fixed position.

30. The method as claimed in claim 28 or 29, further comprising the step of reducing the original thickness of both pieces of sheet metal during drawing thereof.

31. The method as claimed in claim 28, 29 or 30, further comprising the steps of simultaneously forming a plurality of closely spaced joints between the pieces of sheet metal.

32. A method of joining sheet metal substantially as hereinbefore described with reference to the accompanying drawings.

33. A joint comprising two pieces of overlapped sheet metal permanently secured together substantially as herein described with reference to and as illustrated in the accompanying drawings.

34. Apparatus for joining sheet metal, such apparatus being constructed and arranged to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.