SE1830299A1 - Method and apparatus for joining two or more overlapping material members - Google Patents

Abstract

The present invention concerns a method and an apparatus for joining of two or more overlapping material members. Two or more punches work essentially parallelly and are driven essentially perpendicularly through the overlapping material members, while interacting with one or more dies. The punches have an offset between them in time and thus position with respect to the material members, in such a way that they non-simultaneously will cut out groups of tabs or tongues from the overlapping material members. One or more swaging elements are then activated so that each group of tabs or tongues are bent over and compressed against the overlapping material members, whereby the overlapping material members through the swaging are joined mechanically and locked together.

Description

Technical FieldThe invention concerns a method and an apparatus forjoining two or more overlappingmaterial members.

Background Art Joining two or more overlapping material members, in metal as well as in othermaterials is a recurring task in virtually all industrial sectors, from the automotive andappliances to HVAC and the construction area. The material members are oftensheets but can also typically be profiles having more or less complex shapes.

Classical methods for joining such overlapping material members include spot orresistance welding. However, welding suffers from numerous drawbacks. Amongother things, it is difficult to measure the strength of a weld joint in a non-destructiveway. Welding is also linked with considerable health hazards for the operators fromthe sparks, smoke and poisonous gases that are created by the welding process.Furthermore, welding destroys generally speaking the coating of material membersthat are pre-coated or feature other types of surface finish.

The overlapping material members may also be joined using added fasteners, suchas screws, both classical as well as self-tapping, or rivets both classical and self-piercing or pop rivets. Main drawbacks of these assembly methods are the costsassociated with the purchase and sorting of the fasteners as well as the unavoidablecomplications and costs linked with the feeding of the fasteners, regardless if theyare in bulk or strip mounted. l\/lechanical joining methods such as clinching are growing rapidly in importance. lnclinching a rivet-like joint is formed from the overlapping material members through acold flow process between a punch and an anvil, Fig. 1 and Fig. 2. As clinching is ajoining method without added fasteners, it is also easier to apply in many situations,particularly automated or robotized, than when the assembly requires addedfasteners.

Stitchfolding is another mechanical joining method. ln stitchfolding a staple-like jointis created from the overlapping material members, Fig. 3. This method is knownsince some 30 years in a shape which has remained unchanged ever since.

Two punches cut out tabs or tongues in the overlapping material members and thesecut-out tabs are then bent over by a folder resulting in a staple-like joint.

Since the two punches work simultaneously, the stitchfolding equipment will facestrong limitations from the point of view of material thicknesses that can be stitchfolded with hand-held equipment, as relatively low weight is particularlyimportant to enable the equipment to be used efficiently and ergonomically.

The folder geometry which so far has been used, essentially a concave cylindricalshape, acts in such a way that the cut-out tabs are only partially bent over and this ina way that the outer tab often presents a sharp edge which easily can cause handinjuries on the operator or later on the user of the stichfolded product. lt would mean an important innovative step if a mechanical joining method based onthe swaging of the cut-out tabs with significantly increased capacity than today”sstitchfolding, but without a higher weight and reduced workability, and that theproblem with insufficiently bent-over tabs could be resolved simultaneously andthereby significantly reduce the risk for hand injuries.

Technical Solution The main objective of the present invention, called stitchswaging, is to offer a methodand an apparatus for mechanically joining two or more overlapping material memberswithout added fasteners and where the joining process can be realized with lowweight, handheld equipment and where the joint presents minimal risks for handinjuries.

The present invention solves the problems linked with the current technology as ithas the characteristics of the subsequent patent claims.

Description of Drawings Fig. 1 shows how clinching works Fig. 2 shows a resulting clinch joint Fig. 3 shows how stitchfolding works and an idealized illustration of a stitchfold jointFig. 4 shows how a punch cuts out a tab in one material member and the associatedshearing process Fig. 5 shows the situation when two overlapping material members are present Fig. 6 shows how the force depends on the penetration of the punch in the overlappingmaterial members Fig. 7 shows how the necessary force can be reduced in the present invention Fig. 8 shows how the present invention allows joining of thicker/harder materialmembers without increase of the necessary force Fig. 9 shows a classical folder geometry Fig. 10 shows an example of the geometry of the swaging elements in the presentinvenüon Fig. 11 shows examples of apparatus through which the present invention easily canbe realized Mode for the lnvention Method The current description of the present invention is illustrated as a situation in whichtwo overlapping material members are joined. That the method can be applied also tosituations where the number of overlapping material members is greater than two isself-evident and is not described in detail here.

The joining method in the present invention can be seen as consisting of threephases: 1. The initial punching of the overlapping material members through aninteraction between punch and die 2. The subsequent penetration of the overlapping material members by thepunch, so that groups of tabs or tongues are formed from the overlappingmaterial members 3. Bending over and compression, in other word swaging, of the cut-out tabs ortongues so that the overlapping material members are joined and lockedtogether ln order to facilitate the understanding, the notion of punch and punching are used asillustration and designation for an element that through interaction with a die willcreate tabs or tongues in the overlapping material members.

Fig. 4 first shows the principle when a punch works in a single material member.

When the punch (4.1) penetrates the material member from the front face (4.2) a tabwill be cut out through an interaction with a die (4.4) held against the back face (4.3).

The necessary force will depend on the shear strength of the material member andthe area over which the shearing will take place.

This area consists of a rectangular area (4.5) having a width equal to the thickness ofthe punch and will grow as the punch penetrates the material member until themember is broken through. Additionally, the sheared area will consist of triangularparts (4.6) each on either side of the punch.

The situation with two overlapping material members A and B is analogous, Fig. 5.

The punch penetrates from the front face (5.1), that is the free face of materialmember A, with a die (5.4) held against the back face (5.2), that is the free face ofmaterial member B, whereby tabs are cut out of the overlapping material members(5.3).

Fig. 6 shows how the force (6.3), represented along the vertical axis (6.1) is related tothe penetration and subsequent break-through of the overlapping material members,represented along the horizontal axis (6.2).

As is shown in Fig. 6, the force will reach a maximum, designated F1, when thepunch breaks through the overlapping material members (6.4) and will then decreasesignificantly as the punch continues its motion. lf two punches work simultaneously, the total force required (6.5) will be twice that ofa single punch as is shown in Fig. 6. The maximum force is designated F2 and will beequal to 2xF1. ln the present invention, the punches are made to work with an offset in time andtherefore in position with respect to the material members.

Fig. 7 shows as an illustration the required resulting force F2 when two punches worksimultaneously. Punch number one designates the punch first reaching the front face(5.1). As a comparison the required resulting force (7.1) when punch number two isactivated in a position (7.4) when punch number one has reached a point which issituated 1.5 times the thickness of the overlapping material members away from thefront face (5.1). ln this example the maximum required force is designated (7.5).

Comparing the necessary force when the punches work with an offset in time andtherefore in position with respect to the material members with the necessary forcewhen they work simultaneously F2, is also illustrated in Fig. 7. The maximumrequired force (7.5) is significantly lower than F2, as in this example (7.5) is just overhalf of F2.

As the maximum necessary force is the main dimensioning parameter for theapparatus through which the described method can be realized, the same joiningresult can be obtained with an apparatus which is smaller and lighter than anapparatus where the punches work simultaneously. This means an importantinnovative step.

Alternatively, an apparatus capable of reaching a maximum force equal to F2, butworking with punches according to the present invention, namely with punchesworking with an offset in time and therefore position with respect to the materialmembers, can be used to join thicker and/or harder overlapping material membersthan an apparatus using simultaneously working punches. Also this aspect means animportant innovative step.

This is illustrated in Fig. 8. The maximum force required to join 2x1.5 mm (8.3) withpunches offset in time and therefore in position with respect to the material members corresponds roughly to the force F2 required to join 2x1 mm with two simultaneouslyworking punches.

The described method of the present invention is not significantly influenced by thebending back and compression, that is the swaging, of the cut-out tabs, as the forcesrequired in this phase are just a fraction of the forces needed for the initial punching.

The other main aspect of the present invention concerns the geometry of the elementor elements that as far as possible shall favour such a bend-back and compression,that is the swaging, of the cut-out tabs that the risk for hand injuries is minimized. Fig.9 shows the situation when two punches (9.1) through interaction with two dies (9.2)have generated groups of tabs or tongues of the overlapping material members (9.4).

The folder geometry (9.3) which is used today in stitchfolding is certainly simple, butin no way optimal, a concave cylindrical surface with a radius of curvature of thesame order of magnitude as the width of the folder.

This geometry has as a consequence that the play between the folder and theoverlapping material members is greatest on the centre line of the folder which in noway contributes to the swaging of the cut-out tabs that should be of main concern.

On the contrary, the present invention uses a swaging element with process parts(10.3) which work on each group of cut-out tabs, Fig 10. When the process parts areactivated, each group of cut-out tabs will specifically be bent over and compressedstrongly against the back face (5.2) of the overlapping material members, wherebypossible sharp edges from the punching will be compressed and thus the risk forhand injuries will be radically reduced.

Apparatus Obviously, the punches in the present invention can be activated by various distinctdrive functions, such as mechanical, electromechanical, electromagnetic, pneumatic,hydraulic etc.

A simple way of realizing the intended offset in time and thereby in position withrespect to the material members between the punches (11.1) and (11.2) is to let thembe carried by an element (11.3) with one and the same drive functions mentionedabove and where the length of the punches is different, Fig. 11, so that they will workwith an offset in time and therefore in position with respect to the material members.Alternatively, an element (11.4) can be so designed that punches of same length(11.5) and (11.6) can be used and the desired offset is realized.

Analogously the present invention”s swaging element with distinct process parts(11.7) and (11.8) can be activated separately by mechanical, electromechanical,electromagnetic, pneumatic, hydraulic etc. means.

A simple way of activating the distinct swaging process parts is to let them be carriedby an element (11.9) driven separately or by the same function that drives thepunches.

Claims (5)

Claims

1. Method for joining of two or more overlapping material members, where firsttwo or more groups of overlapping tabs are cut out of said overlappingmaterial members, where after said cut-out overlapping tabs are bent over andcompressed against said overlapping material members, whereby saidoverlapping material members are joined and locked together mechanically characterized in that said cut-outs of said overlapping material members willtake place with an offset in time and thereby in position with respect to saidmaterial members.

2. l\/lethod for joining of two or more overlapping material members, where firsttwo or more groups of overlapping tabs are cut out of said overlappingmaterial members, where after said cut-out overlapping tabs are bent over andcompressed against said overlapping material members, whereby saidoverlapping material members are joined and locked together mechanically characterized in that each said group of cut-out overlapping tabs will be bentover and compressed by a distinct swaging function.

3. Apparatus according to claim 1characterized in that said cut-outs of said overlapping tabs will be created bytwo or more punches working with an offset in time and thereby in positionwith respect to said material members.

4. Apparatus according to claim 2 characterized in that said distinct swaging function will be realized by distinctswaging elements.

5. Apparatus according to claims 2 and 4 characterized in that said distinct swaging elements work offset in time andthereby in position with respect to said material members.