WO2001089735A2

WO2001089735A2 - Joining sheet metal

Info

Publication number: WO2001089735A2
Application number: PCT/AU2001/000599
Authority: WO
Inventors: Steven Bas Vanderpeet
Original assignee: Bhp Steel (Jla) Pty Ltd.
Priority date: 2000-05-24
Filing date: 2001-05-23
Publication date: 2001-11-29
Also published as: WO2001089735A3; AUPQ773900A0

Abstract

Method and apparatus for joining overlapping metal sheets. Handheld apparatus has a body structure (21) formed with a slot (26) between upper and lower plates (24, 25) to receive overlapped sheets (28, 29). A square (37) is moved upwardly by pneumatic punch actuator (35) to penetrate the sheets (28, 29) and force portions of the sheets to be folded out to either side of a square opening formed in the sheets. A die (38) is then moved downwardly by a pneumatic die actuator (36) to engage and squash the outwardly folded portions of the sheets. The formation of the out turned and squashed flanges of the parent sheet metal produces a strong joint without the need for separate fasteners or other consumables.

Description

JOINING SHEET METAL

TECHNICAL FIELD

This invention provides a novel method and apparatus for joining pieces of sheet metal together. It has particular, but not exclusive application to the joining of ends of metal sheet strips in continuous strip processing lines .

In continuous strip processing lines, for example strip coating lines, strip ends are normally joined to maintain continuity by welding or by use of a stitching machine which stitches the ends of the sheets together by studs or wires or by a pressing operation. These tend to be cumbersome fixed installations and need to be supplied with consumables. They cannot be conveniently used to deal with unplanned breaks which may occur anywhere in the process line. The present invention provides an effective manner of joining pieces of sheet material without the use of consumables and it enables the use of equipment which may be readily transportable.

DISCLOSURE OP THE INVENTION

According to the invention, there is provided a method of joining a plurality pieces of sheet metal together, including the steps of holding the pieces together face to face and at a plurality of locations in the region where the pieces are to be joined, moving a punch transversely of the general plane of the sheets and from one side of the sheets so as to penetrate the sheets to form an opening through them and to fold portions of the sheets outwardly from the opening as folded out flanges, moving a die from the opposite side of the overlayed sheets and in a direction counter to the direction of punch movement so as to engage and squash the folded out flanges against the sheets adjacent the perimeter of the opening. The sheet metal may be sheet steel . The die may be formed with a die cavity to receive the leading end of the punch when it is moved to squash the folded out flanges back against the sheets.

The pieces of sheet material may consist of or include end pieces of sheet strips to be joined end to end. In this case, the end pieces of the strips may be overlapped and said locations may be disposed in linear arrays of spaced openings extending longitudinally of the strips .

Preferably, the punch has a rectangular stem and a wedge shaped head having a pair of side flanks tapering inwardly and forwardly to a sharp linear leading edge, whereby, on penetration of the sheets, the leading edge severs the sheets along a straight line and the flanks of the punch fold back two portions of the overlapped sheets one to each side of the leading edge to create a rectangular opening and a pair of said folded back flanges, disposed at mutually opposite sides of the rectangular opening.

The term "rectangular" is used herein to include the specific case of a square shape as well as the case of an elongate rectangular shape. Accordingly, the rectangular openings may be square or of elongate rectangular shape.

Preferably, the folded and squashed flanges at each location are spaced laterally of the strips.

The invention also provides apparatus for joining two pieces of sheet material together comprising: a body structure defining a slot passage to receive a pair of sheets to be joined in face to face relationship; a punch actuator mounted on the body structure to one side of the slot passage; a punch actuable by the punch actuator to move from said one side of the slot passage and transversely through that passage to penetrate the sheets so as to form an opening through them and to fold portions of the sheets outwardly from the opening as folded out flanges; a die actuator mounted on the body structure to the other side of the slot passage; a die actuable by the die actuator to move from said other side of the slot passage and in a direction counter to the direction of punch movement so as to engage and squash the folded out flanges against the overlapped sheets adjacent the perimeter of the opening.

The slot passage may be defined between a pair of closely spaced parallel plates forming part of the body structure and provided with aligned openings to receive and guide the punch and the die.

Preferably, the spacing between the plates is sufficient to allow the engagement of the sheet metal and withdrawal after joining but small enough to prevent human access (such as fingers) thus providing an enclosed safe joining operation.

The punch may have a rectangular (for example square) stem and a wedge shaped head having a pair of side flanks tapering inwardly and forwardly to a sharp linear leading edge. In that case, the opening- in the slot passage plate on said one side of the slot passage may be a generally rectangular (for example square) opening within which the punch stem is a sliding fit.

The side flanks of the punch head may be flat faces meeting at the linear leading edge at an included angle in the range 20° to 50°. More specifically it is preferred that the included angle be about 41°.

The die may be in the form of a die block provided with a die cavity to receive the punch head and at least part of the punch stem on actuation of the die actuator. In that case, the opening in the plate at said other side of the slot passage may receive the die block with a sliding fit on operation of the die actuator.

The punch and die actuators may be comprised of a pair of pneumatic cylinders mounted on the body structure in opposing relationship one to either side of the sheet receiving passage. Although the presently preferred power source is pneumatic, other actuating sources, such as hydraulic or electric drives, could be employed.

The apparatus of the invention may be constructed so as to be readily transportable. The body structure may be formed with a handle portion so that it can be handheld and moved along the side margins of overlapped strip ends for successive operation at spaced locations along the overlapped strip ends.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more fully explained, one particular apparatus and its mode of operation in accordance with the invention will be described in detail with reference to the accompanying drawings in which:

Figure 1 is an elevation of a sheet joining apparatus constructed in accordance with the invention;

Figure 2 is an elevation of a body structure of the apparatus;

Figure 3 is a plan of the body structure;

Figure 4 illustrates a punch incorporated in the apparatus;

Figure 5 illustrates a die incorporated in the apparatus; .^•

Figure 6 is a plan of a bottom punch plate incorporated in the body structure;

Figure 7 is an edge view of the bottom side plate; Figure 8 is a plan of a top plate incorporated in the body structure;

Figure 9 is an edge view of the top plate;

Figures 10, 11 and 12 illustrate diagrammatically successive punch and die operations in the formation of a joint between a pair of sheet strips;

Figure 13 illustrates a sheet connection formed by the punch and die operation; and Figure 14 illustrates a completed joint between a pair of overlapped strip ends.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The illustrated apparatus includes a body structure 21 comprised of a pair of parallel side plates 22 interconnected by spacer bars 23 and a pair of top and bottom punch plates 24, 25 which are held in closely spaced parallel relationship so as to define between them a narrow slot passage 26 to receive overlapped ends of a pair of sheet metal strips 28, 29 to be joined.

The side plates of body structure 21 which are constructed of flat plate for ease of manufacture are connected by handles 32 and can be handheld and moved from one side of the overlapped strips 28, 29 in the direction of arrow 30 in Figure 1 so that the margins of the overlapped strips 28, 29 enter the slot 26. The outer edges of top and bottom plates 24, 25 are chamfered at 33, 34 to form a tapered slot entrance to facilitate entry of the strip margins into the slot.

A bottom pneumatic cylinder 35 and a top pneumatic cylinder unit 36 are mounted on body structure 21 in opposing relationship so as to serve as actuators for a bottom punch 37 and a top die 38. As shown in Figure 4, punch 37 has a square profile stem 39 extending from a cylindrical screw threaded stud 41 for attachment to the pneumatic actuator 35 and a wedge shaped head portion 42 defined by a pair of flat side flanks 43 tapering inwardly through a linear sharp leading edge 44. The punch 37 is installed so as to move vertically upwards and is a sliding fit within an elongate hole 45 formed in bottom plate 25. Upward movement of the punch causes the leading sharp leading edge 44 to penetrate the sheets and the punch to form a square opening in the overlapped sheets in the manner to be described below with reference to Figures 10 to 12.

Die 38 is in the form of a square die block 46 with a projecting screw threaded stud 47 for attachment to the pneumatic actuator 36 and formed with a rectangular die cavity 48 to receive and cooperate with the punch in the manner to be described with reference to Figures 10 to 12. Top plate 24 is provided with a generally square opening 49 to receive die block 46 with a sliding fit on actuation of the die, the corners of opening 49 being a radius ensuring free movement of the die block within the opening, ease of manufacture and elimination of potential crack propagation due to induced stresses.

The operation of the punch and die is illustrated diagrammatically in Figures 10 to 12. Figure 10 shows a pair of overlapped sheets 28, 29 disposed within the slot 26 between the upper and lower plates 24, 25 and with both the punch and die retracted. Depression of a starting switch causes the pneumatic actuator 35 for punch 37 to be actuated to move the punch vertically upwards to the position shown in Figure 11. Initial upward movement of the punch causes its sharp leading edge 44 to engage the overlapped sheets and to lift them upwardly against the upper plate 24. The leading edge of the punch penetrates the sheets and the flanks 43 then force portions of the sheets to either side of the leading edge to be folded out as outwardly projecting flanges 51 to either end of a square opening formed in the sheets corresponding with the square profile of punch shank 39. The upward movement of the punch 37 causes its upper end to enter the die cavity 48 of die 38 as shown in Figure 11. A proximity switch 52 associated with the punch actuator 35 operates at the end of the punch movement to initiate operation of the die actuator 36 to cause downward movement of the die to the position illustrated in Figure 12. The downward movement of the die causes its lower rim around the die cavity to engage and squash the out turned sheet metal flanges 51 down against the overlapped sheets, the bottom plate 25 providing an anvil abutment against which the squashing action takes place and the punch stem preventing any inward flange folding. Die cavity 48 of die 38 is of sufficient depth to receive the leading end of punch 37 during the downward movement of the die such that the leading edge 44 of the punch is clear of the upper end of the recess at the end of the downward stroke of the die, as seen in Figure 12.

When die 38 has reached the end of its downward stroke, both the die and the punch actuators retract to withdraw the punch and die to their initial positions, leaving a square opening 53 in the overlapped sheets with out-turned and squashed flanges 51 at each end of the opening as illustrated in Figure 13. The formation of the out turned and squashed flanges of the parent sheet metal in this manner produces a very strong joint without the need for any studs, wires or other consumables and no loss or discharge of the joined sheet by means of the punch.

The shaping of punch head 42 should be such as to promote clear penetration of the sheets and subsequent smooth folding back of the flanges 51. Although stepped or curved side flanks would be possible, it has been determined that optimum results can be achieved if the side flanks and flat rectangular faces meeting a the leading edge 44 at an included angle in the range of 20° to 50°. The angle must be sufficiently small to provide a sharp leading edge for penetration. However, if the angle is too narrow, the punch head is weakened structurally, the wedging action of the side flanks to fold the flanges 51 will be impaired and the stroke of the punch will need to be increased. It has been found that an angle of about 41° produces optimum results when punching thin steel strip. Figure 14 illustrates the manner in which two overlapped strip ends are joined by successive operation of the apparatus at a number of locations to form an array of openings with the formed flanges along each margin of the overlapped strip ends. Because the join relies on the lower strip folding over and clamping onto the upper strip, the strength of the join is dependent upon the strength and gauge of the strip being joined and the number of punches made on each side. It is preferred that the joins be formed so that the folded back flaps or flanges at each punch opening are spaced laterally of the strips in the manner shown in Figure 14 to provide the maximum resistance to longitudinal tension in the joined strips. In a test to destruction the joint will fail either by the folded over flap from the lower strip shearing through, or the folded flap gouging through the upper strip, or a combination of these. However, so long as the lower strip flap does not shear, the join will hold. Accordingly, when joining strips of differing gauges, it is preferred that the lower strip be the heavier of the two gauges so that the outer most of the folded back flaps is the stronger of the two. When very thin strips are to be joined, an additional short strip may be placed under both sheets along the edges at the join so as to be joined with them in the punching process thereby to increase the strength of each join. In that case each punch and die operation is carried out on three sheet pieces held in face to face relationship.

The illustrated apparatus has been advanced by way of example only and it could be modified to suit differing applications. In larger capacity apparatus there may be a plurality of punches and cooperating dies to produce a series of sheet connections simultaneously. It is accordingly to be understood that the invention is in no way limited to details of the illustrated apparatus and that many modifications and variations will fall within the scope of the appended claims.

Claims

CLAIMS :

1. A method of joining a plurality pieces of sheet metal together, including the steps of holding the pieces together face to face and at a plurality of locations in the region where the pieces are to be joined, moving a punch transversely of the general plane of the sheets and from one side of the sheets so as to penetrate the sheets to form an opening through them and to fold portions of the sheets outwardly from the opening as folded out flanges, moving a die from the opposite side of the overlayed sheets and in a direction counter to the direction of punch movement so as to engage and squash the folded out flanges against the sheets adjacent the perimeter of the opening.

2. A method as claimed in claim 1, wherein the sheet metal is sheet steel.

3. A method as claimed in claim 1 or claim 2, wherein the die is formed with a die cavity to receive the leading end of the punch when it is moved to squash the folded out flanges back against the sheets.

4. A method as claimed in any one of the preceding claims, wherein the punch has a rectangular stem and a wedge shaped head having a pair of side flanks tapering inwardly and forwardly to a sharp linear leading edge, whereby, on penetration of the sheets, the leading edge severs the sheets along a straight line and the flanks of the punch fold back two portions of the overlapped sheets one to each side of the leading edge to create a rectangular opening and a pair of said folded back flanges, disposed at mutually opposite sides of the rectangular opening.

5. A method as claimed in any one of- the preceding claims, wherein the pieces of sheet material consist of or include end pieces of sheet strips to be joined end to end.

6. A method as claimed in claim 5, wherein the end pieces of the strips are overlapped and said locations are disposed in linear arrays of spaced openings extending longitudinally of the strips.

7. A method as claimed in claim 5 or claim 6, wherein the folded and squashed flanges at each location are spaced laterally of the strips.

8. Apparatus for joining two pieces of sheet material together comprising: a body structure defining a slot passage to receive a pair of sheets to be joined in face to face relationship; a punch actuator mounted on the body structure to one side of the slot passage; a punch actuable by the punch actuator to move from said one side of the slot passage and transversely through that passage to penetrate the sheets so as to form an opening through them and to fold portions of the sheets outwardly from the opening as folded out flanges; a die actuator mounted on the body structure to the other side of the slot passage; a die actuable by the die actuator to move from said other side of the slot passage and in a direction counter to the direction of punch movement so as to engage and squash the folded out flanges against the overlapped sheets adjacent the perimeter of the opening.

9. Apparatus as claimed in claim 8, wherein the slot passage is defined between a pair of closely spaced parallel plates forming part of the body structure and provided with aligned openings to receive and guide the punch and the die.

10. Apparatus as claimed in claim 9, wherein the spacing between the plates is sufficient to allow the engagement of the sheet metal and withdrawal after joining but small enough to prevent entry of human fingers.

11. Apparatus as claimed in any one of claims 8 to 10, wherein the punch has a rectangular (elongate or square) stem and a wedge shaped head having a pair of side flanks tapering inwardly and forwardly to a sharp linear leading edge.

12. Apparatus as claimed in claim 11, wherein the opening in the slot passage plate on said one side of the slot passage is a generally rectangular (rectangular or square) opening within which the punch stem is a sliding fit. . .

13. Apparatus as claimed in claim 11 or claim 12, wherein the side flanks of the punch head are flat faces meeting at the linear leading edge at an included angle in the range 20° to 50°.

14. Apparatus as claimed in claim 13, wherein the included angle is about 41°.

15. Apparatus as claimed in any one of claims 8 to

14. wherein the die is in the form of a die block provided with a die cavity to receive the punch head and at least part of the punch stem on actuation of the die actuator.

16. Apparatus as claimed in claim 14, wherein the opening in the plate at said other side of the slot passage receives the die block with a sliding fit on operation of the die actuator. 17. Apparatus as claimed in any one claims 8 • to 16, wherein the punch and die actuators are comprised of a pair of fluid cylinders mounted on the body structure in opposing relationship one to either side of the sheet receiving passage. 18. Apparatus as claimed in any one of claims 8 to

17. which apparatus is transportable and wherein the body structure is formed with a handle portion so that it can be handheld and moved along the side margins of overlapped strip ends for successive operation at spaced locations along the overlapped strip ends.