AU675971B2 - Clinched connections between overlapping sheets - Google Patents

Description

Is~- ID L ~LC 1 P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT ,."Invention Title: "CLINCHED CONNECTIONS BETWEEN OVERLAPPING SHEETS" lo The following statement is r full description of this invention, including the best method of performing it known to the Applicant:- This invention relates to clinched connections between a plurality .ooeo of overlapping metal sheets, overlapping sheet-like parts of a metal article, or overlapping sheet-like parts of each of a plurality of metal articles, all of which overlapping items are referred to as the "work sheets" hereinafter.

Such connections are made by a clinching tool in the nature of a press comprising a male punch and a female die. The female die comprises an anvil disposed between at least two shearing pieces, usually in the orm of blades, furnished with cutting edges and extending beyond the anvil towards the male punch. The shearing pieces are resilient, or are resiliently mounted, so that they may be spread apart by pressure acting between them. The male punch is usually a simple flat B~n I~ 11_ 2 ended punch adapted to fit neatly between the cutting edges of the shearing pieces when they are not so spread.

in other versions of the prior art, the clinching apparatus may utilise a rotary punch and die set, adapted to form a row of spaced apart clinches in elongate work sheets. In such instances the rotary punch may comprise a wheel with one or more punch elements protruding radially from its rim, and the rotary die may comprise an anvil wheel sandwiched between two co-axial shearing wheels having peripheral •margins comprising a plurality of radially projecting shearing pieces.

o The clinch is formed by placing the overlapped work sheets between the punch and die and moving at least one of those towards 0 the other, or by feeding the work sheets between the rotary punch and die, as the case may be. Initially the punch and the unspread shearing S•pieces act to slit the work sheets along lines coinciding with the cutting edges of the shearing pieces. The slits do not form a closed figure, so that there are small superimposed parts of the work sheets, referred to as "the wads" hereinafter, between the slits that are partly but not wholly separated from the main parts of the respective work sheets. The punch, assuming it is the moving item, pushes those wads ahead of it (while stretching the unslit material connecting the wads to the rest of the work sheets) until they contact the floor of the die recess or the anvil. The wads are then plastically deformed, by the pressure imposed on them by the punch and the anvil, and spread laterally, the shearing pieces of the die being able to spread apart as aforesaid to accommodate such plastic flow of the wads. In this art, that spreading process has been referred to as "lateral extrusion", and is so designated hereinafter.

Ir i _a 3 The extent to which the cutting edges of the shearing pieces initially project beyond the anvil is selected to suit the combined thickness of the work sheets, so that the wads are pushed clear of the overlapped sheets before being laterally extruded. Therefore, the laterally extruded wads cannot retract back into the space between the slits from which they were pushed, and the work sheets are permanently fastened together.

Usually the shearing pieces present two, spaced apart, parallel cutting edges so that the wads are rectangular. In this instance it is io usual for the slits to be longer than the spacing between them, so that the wads are likewise longer in one direction than the other.

United States patent specification No.4,614,017 (Eckold) describes in some detail the prior art briefly discussed above. That specification further discloses clinches having non-rectangular wads and clinches in which the depression in one surface of the clinched work sheets, caused by the displacement cf the wads from the plane of those sheets, may be filled with another piece of metal, referred to as "the slug" hereinafter.

A part of the slug is also laterally extruded in the same way as are the wads, so that the slug is retained permanently in the finished clinch.

U.S. 4,614,017 does not ascribe any functional purpose to the slug, nor does it specify any properties of the material of the slug, which would appear from that specification to be merely a cosmetic item intended to provide a smooth surface on one side of the clinched work sheets. The specification does state that the slug may be regarded as a leading or shearing part of the male punch that is left behind in the U PRQ clinch when the punch retracts therefrom. It would follow that the slug of U.S. 4,614,017 is, at least by inference, as hard as one would expect a shearing blade to be, which is usually harder than the material to be sheared.

The present invention is based on two discoveries. They are, that a relatively soft slug, indeed one that is softer than the work sheets, may nevertheless satisfactorily function as a tip of the mnale punch, and, more surprisingly, that the presence of a slug may materially strengthen the clinch, provided that the slug is appreciably softer than tile work sheets.

10 .Therefore the invention consists in a method of clinching overlapping work sheets together, of the kind comprising the steps of partially severing superimposed wads from the work sheets while displacing the wads transversely of the work sheets from the plane of the work sheets and thereby stretching unsevered sheet material joining the partially severed wads to the work sheets, inserting a slug of material into the recess in the work sheets created by the displacement of the wads, and pressing the slug and the wads against an anvil to cause the wads and at least a part of the slug to be laterally extruded, characterised in that said slug is composed of a plastically deformable material which is softer than the material of the work sheets.

The primary benefit flowing from the invention, namely the increased strength of the clinched connection, has been proved by comparative tests referred to below and demonstrated by the accompanying drawing, but a further benefit flowing from the use of relatively soft slugs is the ease with which they may be provided in preferred clinches wherein the die's shearing pieces present two, parallel, cutting edges, so that the wads are rectangular with two opposite sheared edges. In this instance it is only necessary to feed a thin strip of slug material, of a width approximating the length of the die cutting edges, transversely of those cutting edges into the path of the male die as it approaches the work sheets, to enable it to sever an appropriate length of wad material from that strip and automatically locate it correctly in the clinch, as it is formed.

The mechanism is not entirely clear, but apparently the friction between the strip of slug material and the male punch on one side of it, and between the strip of slug material and the work sheets on the other o side of it, suffices to prevent substantial spreading of the slug until it is constrained by entering the recess being formed in the work sheets by displacement of the wads. Be that as it may, it has been found that the action of the male punch, in cooperation with either the edges of the die recess or the die's shear pieces, detaches an appropriately sized slug from the strip of slug material and then presses the detached slug into the recess.

By way of example, an embodiment of the above described invention is described in more detail hereinafter with reference to the *accompanying drawings.

Figure 1 is a diagrammatic section through a clinching station.

Figure 2 is a graphical representation of the results of tests wherein galvanised steel sheet test specimens were clinched top other and then stressed in a tensile testing machine in a manner placing the clinch under shear in the plane of the clinched specimens.

The clinching station of figure 1 comprises a fixed work table 3 defining a guide way for a reciprocable punch 4 in alignment with a die comprising an anvil 5 and two shear blades 6. The blades 6 are made of spring steel and may resiliently separate to some extent.

The work table 3 also defines a passage for a strip of slug material 7.

Two sheet steel work sheets 8 and 9 are shown in position ready to be clinched.

To create a clinch the punch 4 is pressed downwardly. It first o 10 shears a slug from the end of the strip 7. That slug is pushed ahead of the punch and displaces two wads of the sheets 8 and 9 ahead of it and at the same time the blades 6 shear through the sheet metal to produce sheared edges on the displaced wads. When the wads reach the *oanvil 5 they are laterally extruded and at the same time a lower layer of the slug is laterally extruded so as to underlie the adjacent parts of the sheets 8 and 9.

S•In accordance with the invention the material of the strip 7 is softer than that of the work sheets 8 and 9.

The graphs of figure 2 show deflection in millimetres for increasing tensile loads in Newtons. Each curve shows the average values of a number of tests of each type of clinch (designated A to G respectively) tested. In each instance the wads were rectangular and of the same size and shape, namely that of a rectangle somewhat longer in one direction than in the other. In each test, two sides of the rectangle were aligned with the direction of the applied stress. In each test the work I sheets were 0.6 mm thick. In interpreting the graphs it should be borne in mind that in steel sheets of the kind from which the test pieces are made, the nominal strength of the steel is related to its hardness, such that the greater the strength of a steel the harder it is.

Curve A shows the behaviour of a standard rectangular clinch between two steel work sheets, each 0.6 mm thick and having a nominal strength of 550 megapascals. In this instance the load on the clinch was in the length direction of the clinch. It will be seen that the maximum load sustained was about 1100 Newtons, and there was .ooo io appreciable deflection at lower loads as the load was applied.

::Curve B shows the behaviour of a clinch the same as the A clinch when loaded in the width direction of the clinch. It will be seen that the clinch in this orientation gave superior results in that it displayed a greater initial resistance to deflection, with a maximum load of about 15 1200 Newtons being sustained at a deflection of about 1mm.

Curve E should be compared with curve A. The test conditions are the same for each, but the E clinch included a 0.6 mm thick slug with a nominal strength of 550 megapascals, that is to say, the same as that of the work sheets. It will be seen that the maximum load sustained 2o by the E clinch was much the same as that of the A clinch without a slug, although the E clinch was superior in that it developed that load at a lower deflection of about 0.8 mm.

Curve C relates to a test the same as those of curves A and E, except that the clinch had a 1.2 mm thick slug having a nominal strength of 300 megapascals, that is to say, not much over half that of the slug of clinch E. It will be seen that this clinch with its softer slug shows a I L L~L~ L IC n I- 8 substantial improvement in that it sustained a maximum load of about 1700 Newtons and, importantly, did so at the low deflection of about Curve D shows a similar improvement when a clinch with a soft slug is loaded in its width direction. In this case the slug had a nominal strength of 300 megapascals, and compares favourably with the B clinch, in that its maximum load was about 1750 Newtons which was developed at as low a deflection as was the lower maximum in the case of the B clinch.

:•eooo o10 Finally it will be noticed that both of the curves C and D relate not only to clinches with relatively soft slugs but also to clinches in which the slugs were thicker than in the corresponding tests with hard slugs. In case the surprising improvement was due not to the softness but rather to the thickness of the slug, further tests were performed conforming to S° 15 tests C except for the use of hard slugs having the same thickness as the C slugs. The results of these last mentioned tests are shown by curve G, and it will be seen that these G clinches performed far worse •o than the C clinches, and even worse than the A clinches insofar as the maximum sustainable load is concerned, and no better than the S 20 C clinches insofar as the magnitude of the deflection at which the maximum load was developed is concerned.

JL3lerua i IIA

Claims (4)

1. A method of clinching overlapping work sheets together, of the kind comprising the steps of partially severing superimposed wads from the work sheets while displacing the wads transversely of the work sheets from the plane of the work sheets and thereby stretching unsevered sheet material joining the partially severed wads to the work sheets, inserting a slug of material into the recess in the work sheets created by the displacement of the wads, and pressing the slug and the wads against an anvil to cause the wads and at least a part of the slug io to be laterally extruded, characterised in that said slug is composed of a :plastically deformable material which is softer than the ma'Lerial of the work sheets.

2. A method according to claim 1 wherein the steps of partially severing, displacing and laterally extruding the wads are effected by placing the superimposed sheets between a punch and a die comprising an anvil flanked by two resiliently separable shearing pieces presenting substantially parallel, spaced apart cutting edges, and forcing the punch towards the anvil, and wherein the step of inserting the slug is effected by feeding a strip of slug material, of a width approximating the length of 20 the cutting edges, transversely of those cutting edges between the work sheets and the punch.

3. A method according to either of the preceding claims wherein the work sheets are of sheet steel having a nominal strength of 550 megapascals and the slug is of steel having a nominal strength of 300 megapascals. I LMc ~LYI L L

4. A method of clinching two work sheets together substantially as described herein with reference to the accompanying figure 1. Applicant JOHN LYSAGHT (AUSTRALIA) LIMITED Date 3 November 1993 Attorney ROBERT G. SHELSTON F.I.P.A.A. of CARTER SMITH BEADLE C C I I- I--ar MW ABSTRACT A method of clinching overlapping work sheets together, comprising the steps of parti illy severing superimposed wads from the work sheets while displacing the wads transversely of the work sheets from the plane of the work sheets, inserting a slug of material into the recess in the work sheets created by the displacement of the wads, and pressing the slug and the wads against an anvil to cause the wads and at least a part of the slug to be laterally extruded, is effected by placing the superimposed sheets between a punch and a die io comprising an anvil flanked by two resiliently separable shearing blades feeding a strip of slug material between the work sheets and the punch and forcing the punch towards the anvil According to the invention the slug is softer than the work sheets, *i whereby the strength of the clinch is increased. 15 Figure 1. 6 0 ill 'P