WO1998045065A1

WO1998045065A1 - Diffusion welding process and device for joining sheet metal parts

Info

Publication number: WO1998045065A1
Application number: PCT/EP1998/001970
Authority: WO
Inventors: Hanns-Peter Liebig; Jan Bober; Jens Jacobsen; Timm Kühne
Original assignee: Eckold Gmbh & Co. Kg
Priority date: 1997-04-05
Filing date: 1998-04-03
Publication date: 1998-10-15
Also published as: PT934132E; DK0934132T3; ES2179494T3; DE59804575D1; RU99100054A; CN1222872A; ATE219708T1; EP0934132A1; EP0934132B1; CA2257251A1; DE19714129A1; JP2000511470A

Abstract

In a diffusion welding process for joining superimposed sheet metal parts by welding, part of the material of the metal sheets is locally upset by means of a stamp and a die perpendicularly to the plane of the metal sheets, causing the material of the sheet metal parts to yield and diffusion welding the sheet metal parts at a weld. In order to achieve a sufficiently solid weld even when the parts to be joined are made of materials with a particular tendency to hardening at low temperatures or pre-hardened materials, the parts of the metal sheet surrounding the weld are pressed onto the die during welding with a force which is sufficient to prevent the material from yielding against the active direction of the stamp.

Description

Enforcement method and device for connecting sheet metal parts

The invention relates to a clinching method according to the preamble of patent claim 1 and to a device intended for its implementation according to the preamble of patent claim 8.

From EP 0 330 061 B1 a method and a device for pushing through two or more superimposed, flat sheet metal parts is known, in which a tool set consisting of a punch and a die is used, the die of which has a central anvil and die moldings that stand up relative to an anvil work surface preferably can escape laterally during a compression and delimit a mold cavity into which is inserted.

In the known push-through joining, the sheet metal parts to be joined are pushed through together at a selectable joining point and then cold-compressed using such pressures that a lateral tool flow of material creates a positive and non-positive interlocking of the sheet metal parts in the form of a cup-like joining element. The volume of material located at the joint under a stamping surface is initially only enforced. For this purpose, the sheet metal material is moved out of the plane of the sheet metal parts, the base thickness of the resulting joint still roughly corresponding to the total starting sheet thickness. In a further enforcement, the bowl of the joining element is clamped between a stamping surface and the anvil and an upsetting process with radial material flow in the bottom region, the so-called spreading, is brought about by an increasingly increasing stamping force. The thickness of the floor panels is reduced by upsetting compared to the original panel thickness, which is necessary in order to produce the necessary positive fit by spreading.

In order to facilitate this upsetting process, the sheet metal parts to be connected can be partially cut at the joint in the direction of penetration, since then during the upsetting process the bowl bottom of the joining element remains largely free of the bond to the other material or this bond is at least reduced. However, it is disadvantageous that a cutting portion of the joining process reduces the strength of the penetration joining and the joining is not gas-tight, so that joining elements which are produced without local cutting are preferred.

This pushing through of sheet metal parts has so far not been economically applicable to stainless steel sheet metal parts with a predominantly austenitic structure. The same applies to other metals that tend to undergo particularly pronounced strain hardening as the shape changes, e.g. high-alloy stainless steel, titanium, or for pre-consolidated metals, e.g. higher strength steels. The material-related process forces for metal-forming joining are above the load limit of the joining tool or lead to failure of the joining tool after only a few joining processes.

However, if the process forces are too low, the load-bearing behavior is the inadequacies. Furthermore, it was found that even with the greatest possible cold compression, an inadequate positive fit is achieved in the joining element. It is therefore only possible to assert such sheet metal materials at all by cutting the sheet metal parts and accepting the associated disadvantages, the reduction in process forces achieved by the cutting also not leading to any appreciable increase in the tool life.

A first object of the invention is therefore to create a clinching method of the type mentioned at the outset with which a sufficiently firm joining can be produced even in the case of joining parts from materials which tend to undergo particular strain hardening or from pre-consolidated materials.

A second object is to provide an apparatus for this method.

The first object is achieved by the features of the characterizing part of patent claim 1.

The second object is achieved by the features of the characterizing part of patent claim 8.

This creates a method in which an effective positive locking is achieved with reduced introduction of joining force. This applies in particular to the materials that tend to work harden particularly. The joining forces to be used are reduced so that the tools can withstand this load.

According to the invention, it was found that, particularly in the case of sheet metal materials with strong work hardening, the widthing is made more difficult by the fact that the material tries to evade under compressive stresses and flows back against the direction of action of the punch. By pressing the parts to be joined during the joining process, this backflow is prevented and the sheet metal Material is forced to form a form-fitting connecting element in the effective area of the die by thus initiating the spreading. In the case of the materials that tend to work harden particularly, the process therefore also leads to a good positive fit not previously achieved.

Characterized in that the sheet metal parts lying around a joint are pressed against the die with a force that is sufficient to press the material onto a base (here the die) such that the volume of material to be joined is no longer counter to the direction of action of the punch can flow back, namely it is achieved that the initiated compressive force is used in an early phase of upsetting to form an effective form fit. As a result, a sufficiently firm joint results in an advantageous manner even if, while protecting the tools, the necessary degree of deformation at the joint takes place with reduced force application. This makes enforcement joining particularly economical because the number of joining operations that can be carried out with a joining tool increases considerably.

The pressure force acting on the sheet metal parts around the joint is a passive force that must be higher than the reflux force of the material of the parts to be joined during the joining process. According to the invention, it was found that the pressure force then exceeds the return flow force of the material if the pressure force is preferably set at least so high that the sheet metal parts do not gap in the vicinity of the stamp during the joining process.

Furthermore, preferred values for the pressing force, for example for flat, flat sheet metal parts, are δ times to δ times the forces which are only required for stripping or to prevent bending of the joining parts during the enforcement phase.

Furthermore, the pressure force is preferably applied to an effective pressure surface with such a size around the joint that the pressure force to be used does not leave an impression in the metal sheets and the moldings of the die can move laterally when compressed. The contact pressure effective area can therefore be dimensioned sufficiently large so that the resulting pressure load cannot lead to plastic deformation of the clamped parts to be joined, and as small as possible so that joining can also be carried out in poorly accessible places.

It has been found that the deformation can be improved even more if the sheet metal parts are joined at a higher temperature than the environment or the tools; a temperature difference of 10 ° C to 50 ° C results in an improvement in the load-bearing behavior of the joint with the same joining force, or with the same load-bearing behavior as joining elements produced at ambient temperature, the joining force can be reduced by up to 15%. One reason for this is a reduction in strain hardening, as occurs in particular in the case of austenitic sheet materials.

With the clinching device according to the invention, sheet metal materials with a pronounced tendency to work hardening can also be clinched without causing plastic deformation of the punch and anvil or failure of the basic tool body. The modular stamp and die-side structure enables the tool set to be more resilient because cracks are anticipated. The tool set can therefore accommodate higher joining pressures.

Preferred materials of high strength for the stamp and anvil are hard metal and high-strength ceramic.

To support the stamping pin and anvil pin in accordance with the load, they can each be supported on a flat base plate.

The anvil surface preferably has a design in accordance with the flow of material in the form of a circumferential, flat chamfer, with which a better positive fit is achieved with the same sheet metal base thickness. At the same time, such a chamfer relieves pressure on the edge, which amount is increased.

The active surfaces of the stamp and anvil pin can have a star-shaped grinding pattern, which further increases their tool life and improves the material flow.

Further refinements of the invention can be found in the following description and the subclaims.

The invention is explained in more detail below on the basis of the exemplary embodiments illustrated in the attached figures.

1 schematically shows a partially sectioned side view of a first embodiment of a clinching device,

2 shows a partially sectioned side view of a stamp with pressure element according to a further exemplary embodiment of a clinching device,

3 shows a top view of an active surface of a stamp according to FIG. 2,

4 shows a side view of an anvil according to a further exemplary embodiment of a clinching device,

5 shows a plan view of an active surface of an anvil pin according to FIG. 4,

6, 7 and 8 are enlarged side views of others

Embodiments of the area marked with a dash-dotted circle in FIG. 4.

9a shows in partial section a connection made with the device according to FIG. 1,

9b shows a partial section of a connection made with a device without a pressing element with the same bottom thickness of the joining element as in FIG. 9a,

10a shows the connection produced according to FIG. 9a, FIG. 10b shows a partial section of a connection made with a device without a pressure element with a bottom thickness of the joining element reduced by greater joining force as in FIGS. 9a, 9b and 10a.

1 shows a first exemplary embodiment of a device for clinching from a tool set with a punch 1 and a die 2, which are each arranged in a clinching tool holder 3, 4.

The die 2 has an anvil 5 as the central area, which forms a compression table 6 (anvil work surface) of a clinching mold cavity 7 in the die 2 on the head side. The push-through mold cavity 7 limits the penetration of a material volume by matrix elements in the form of shaped pieces 8, 9, which protrude relative to the upsetting table 6 and which can laterally deflect during an upsetting process. The pieces 8, 9 also form, with their respective head sides 10, 11, a die support for sheet metal parts 12, 13 to be joined. So that after a respective joining operation, the evaded fittings 8, 9 are reset and the die 2 close, there are preferably two Return springs 42, 43 combined in a spring bonnet. The die 2 can be fastened to the tool holder 4 by means of a fastening screw 14.

The stamp 1 has a stamp pin 15 with a stamp effective surface 16 which penetrates into the clinching mold cavity 7 with a selectable joining force for a clinching process. In this joining process, a material volume of the sheet metal parts 12, 13 located at a joining point below a stamping effective area 16 is first enforced, i.e. pushed out of the plane of the sheet metal parts 12, 13 until a bottom 17 (cf. FIGS. 9a and 10a) of the resulting joint rests on the anvil 5, and then compressed with widths.

The stamp 1 is enclosed by a pressure element 18 which applies force to the sheet metal parts 12, 13 around a joint, ie adjacent to the stamp active surface 16. For this purpose, the pressure element 18 presses the sheet metal parts 12, 13 lying around the active stamping surface 16 against the die support. The pressure element 18 is therefore intended to counteract the backward force of a material. The amount of force applied or the pressure force is controllable. This control can be separate from or linked to the introduction of the joining force.

Spring elements 19, 20 are preferably provided for applying the pressure element force. Furthermore, the pressure element 18 is preferably guided via the spring elements 19, 20 on the tool holder 3 for the stamp 1. With such a guide, the introduction of force by the pressing element 18 can be increased in a simple manner during the joining process. For this purpose, the pressing element 18 can be provided with an active surface 21 against which the plunger 1 works by compressing the spring elements 19, 20 and increasing the pressing force. The pressure element 18 is preferably designed as a pressure plate and can also be used as a stripping element at the end of a joining process.

To apply the pressure element force other pressure transmitters than springs can be used to generate the pressure forces. It is also not necessary for the pressure element 18 to be guided on the stamp. The pressure element 18 can also perform its function by means of an external guide and an external drive.

The effective surface 21 of the pressing element 18 is dimensioned sufficiently large if the resulting pressure load does not lead to a plastic deformation of the surface of the sheet metal parts 12, 13 to be joined and the shaped pieces 8, 9 of the die 2 can open during the joining process.

The stamp 1 and the die 2 are preferably of modular construction. For this purpose, the stamp 1 comprises the stamp pin 15, at the head end of which the stamp effective surface 16 is formed and which is pressed into a base body 23. For this purpose, the base body 23 preferably has one Through hole 24. This modular structure allows the use of different materials for the stamp pin 15 and the base body 23. The stamp pin 15 can consist of a first material, namely a material of higher hardness or higher strength. Preferred materials for this are hard metal and high-strength ceramics. The base body 23 can consist of a second material that is less hard, but is, for example, tougher than the first material. Tempered tool steel is preferred as the second material.

At its end facing away from the working surface 16, the stamp pin 15 is preferably supported on a plate 25, which can be made of the same material as the stamp pin 15 and which in turn is supported in the tool holder 3 of a press, not shown. The transverse dimensions of the plate 25 are chosen so that the load acting on the tool holder 3 can be absorbed by the latter without risk of breakage. The punch 1 can be fastened to the tool holder 3 by means of a fastening screw 26.

The die 2 can have a modular design like the stamp 1. The anvil 5 is then formed by an anvil pin 22 made of a first material, namely a material of higher hardness or greater strength, such as hard metal or high-strength ceramic. The anvil pin 22 is pressed into a base body 27 made of a tougher material, for which purpose it has a through hole 29. The material pairing can be chosen as for the stamp. The anvil 5 can also be supported on the tool holder 4 via a plate 28. The plate 28 can be designed corresponding to the plate 25 for the stamp 1.

2 to 5 show a second exemplary embodiment of a clinching device which differs from the exemplary embodiment described above only by the differences mentioned below. Otherwise, the above statements apply accordingly, so that the same reference numerals are used for the same parts. Fig. 2 shows a stamp 1 in a modular design with a stamp pin 15 on which the stamp effective surface 16 is formed, which is pressed into a base body 23 and is supported on a base plate. Teilu fangsnuten 30 are used for quick tool change and thus the attachment of the punch 1 to a tool acceptance. As in the exemplary embodiment according to FIG. 1, the effective end of the stamp is encompassed by a pressure element 18 which is supported on the base body 23 by means of springs 19, 20. About this pressure element 18, which surrounds the stamp 1 as closely as possible, but with a sliding fit and the springs 19, 20, the pressure forces according to the invention are now introduced, which press the pressure element 18 so strongly onto the die that the sheet metal material around the stamp 1 is firmly clamped is and so prevents that the material of the stamp-side sheet during the upsetting up, that is, against the direction of action of the stamp 1, can flow. The stamp-side sheet metal can already be pressed on before the start of the push-through, so that there is no fear of bending of the sheets during the push-through.

The pressure element 18 according to FIG. 2 differs from that of FIG. 1 in that the active surface 21 of the pressure element 18 runs continuously.

Fig. 4 shows the associated die 2 with an anvil 5, which is pressed into a base body 27 and is supported on a base plate 28. The base body 27 has on its side facing the die 1 on inclined surfaces 32, on which are supported matrix elements (not shown), which are spring-loaded against the anvil 5 and, together with the active surface 6 of the anvil, delimit the die cavity.

In order to prevent the danger that the anvil 5 and / or the stamp pin 15 break out at the edge under high pressure load, a circumferential chamfer 31 is provided, the cross-sectional shape of which, as shown in FIGS. 6 to 8, can be variable: rounded (FIG. 6 ), flat beveled (Fig. 7) or double beveled (Fig. 8). This chamfer also favors the material flow.

The facing active surfaces 16, 6 of punch 1 and / or anvil 5 are provided with a surface finish which favors the flow of the material to be joined, as can be seen from the star-shaped micrograph in FIGS. 3 and 5. Correspondingly, the active surfaces 16 and 6 can be designed in the device according to FIG. 1.

A push-through method for connecting sheet metal parts 12, 13 lying one above the other comprises a joining process in which a material volume of the sheet metal parts 12, 13 is locally penetrated at a joint by means of a stamp 1 and a die 2 and is joined under material flows by upsetting perpendicular to the sheet metal plane. The sheet metal parts 12, 13 surrounding the joint are pressed onto the die 2 during this joining process with a pressing force which is sufficient to prevent material flow against the direction of action of the punch 1.

The pressure force can be kept constant during the entire joining process. Alternatively, the pressing force can be increased during the joining process, so that at least during compression, a pressing force acts in the surrounding area of the joint, which exceeds the reflux force, while it can be selected lower beforehand. A first pressure force can also be applied around the active surface of the stamp before or shortly before the joining process.

The sheet metal parts 12, 13 are pressed onto the die 2 in a substantially stationary manner, with such a pressing force that material backflow is prevented. This applies in particular to pre-consolidated materials that tend to undergo special strain hardening.

The pressing force is chosen in particular in such a way that the sheet metal parts 12, 13 do not gap in the vicinity of the stamp 1 during the joining process, ie the sheet metal parts 12, 13 lie flat against one another. The pressure force for flat, flat sheet metal parts can also be selected such that it is δ times to δ times the forces that are only required to prevent the parts to be bent during the enforcement phase. An example of the guideline value for the force introduced with a joining element diameter of 5mm is 3000 N, if, for example, austenitic stainless steel sheets are joined.

The pressure force is preferably applied to an effective pressure surface of such a size around the joint that the pressure force to be used does not leave an imprint in the sheet metal parts and the die can open laterally.

Furthermore, the temperature of the sheet metal parts 12, 13 can be increased compared to the ambient temperature. Temperatures 10 ° C. to 50 ° C. higher than the ambient temperature are preferred.

FIG. 9a shows an example of a joint produced using the clinching devices described above, the contact pressure exerted by the pressing element 18 during the joining process being indicated by the arrows and the letter F. Sheet metal parts 12, 13 made of a particularly cold-strengthening material with an initial sheet thickness of approximately 1 mm each are positively connected by a joining element, the bottom 17 of which is compressed between the stamping active surface 16 and the anvil working surface 6 in the mold cavity 7 while reducing the overall initial thickness. A width 33 has been formed by material flows, for which the shaped pieces 8, 9 have moved outwards. The result is a joint with a good positive fit. At the end of the joining process, the sheet metal parts 12, 13 do not gap in the area surrounding the stamp, so that they lie flat against one another and without gap areas.

In comparison, Fig. 9b shows a joint with a stamp 1 and a die 2 with a stamp collar but without a pressing element. If the same base thickness is achieved, ie approximately the same joining forces, no effective positive locking is achieved. 10a and 10b serve to further clarify the method according to the invention. 10a corresponds to that shown in FIG. 9a. The joining of FIG. 10b differs from that of FIG. 9b in that increased joining forces have been used which have led to a greater compression of the bottom 17 of the joining. However, the width 34 achieved in this way does not yet show sufficient form closure.

9a, 9b and 10a, 10b illustrate that the method according to the invention allows the use of lower joining forces because the effective positive locking is achieved even with a small compression.

Claims

claims

1. enforcement method for connecting superimposed sheet metal parts by a joining process in which a material volume of the sheet metal parts is locally enforced by means of a punch and a die at a joint and joined by upsetting perpendicular to the sheet metal plane under material flows, characterized in that the sheet metal parts surrounding the joint are pressed onto the die during the joining process with a pressing force which is sufficient to prevent material flow against the direction of action of the punch.

2. clinching method according to claim 1, characterized in that the pressing force is selected such that the sheet metal parts do not gap during the joining process in the vicinity of the stamp.

3. clinching method according to claim 1 or 2, characterized in that the pressing force for flat, flat sheet metal parts is chosen such that it is δ times to δ times the forces that are used only for stripping or to prevent bending of the parts to be joined during the enforcement phase .

4. clinching method according to one of claims 1 to 3, characterized in that the pressure force is applied to an effective pressure surface with such a size around the joint that the pressure force to be used does not leave an imprint in the sheet metal parts and the die can open laterally.

5. clinching method according to one of claims 1 to 4, characterized in that a pressure force is applied to the surrounding sheet metal parts before the start of the joining process.

6. clinching method according to one of claims 1 to 5, characterized in that the temperature of the sheet metal parts is increased compared to the ambient temperature.

7. clinching method according to claim 6, characterized in that the sheet metal parts are brought to a 10 ° C to 50 ° C higher temperature than the ambient temperature.

8. clinching device for connecting superimposed sheet metal parts with a die and a punch that can be penetrated into a hollow form of the die, the die having an anvil and protruding, laterally swiveling shaped pieces for limiting the hollow shape, into which is locally penetrated, characterized that the stamp (1) is surrounded by a pressure element (18) for applying force to the sheet metal parts (12, 13) and the anvil (5) and the stamp (1) each have a pin (16, 6) with an active surface ( 15, 22) made of a material of high strength, which is pressed into a base body (23, 27) made of another material.

9. clinching device according to claim 8, characterized in that the punch and anvil base body (23, 27) have through bores (24, 29) which receive the respective pins (15, 22) inside.

10. clinching device according to claim 8 or 9, characterized in that the pins (15, 22) are supported on the respective effective surface (16, 6) opposite end in each case on a flat washer (25, 28), via which a pressure load on the anvil (5) and the stamp (1) can be introduced into a tool holder (3, 4).

11. clinching device according to claim 10, characterized in that the washers (25, 28) consist of a high-strength material.

12. clinching device according to one of claims 8 to 11, characterized in that hard metal or high-strength ceramic can be used as the material of high strength.

13. clinching device according to one of claims 8 to 12, characterized in that the active surfaces (6, 16) of the anvil (δ) and / or the stamp (1) are provided with a peripheral chamfer (31).

14. clinching device according to claim 13, characterized in that the peripheral chamfer (31) is rounded.

1δ. Clinching device according to claim 13, characterized in that the peripheral bevel (31) has a triangular cross section.

16. clinching device according to claim 13, characterized in that the circumferential chamfer (31) has a kinking cross-sectional shape approximating a rounding.

17. clinching device according to one of claims 8 to 16, characterized in that the active surfaces (6, 16) of anvil (δ) and / or stamp (1) are provided with a surface finish favoring the material flow.

18. clinching device according to one of claims 8 to 17, characterized in that the pressing element (18) is a on the punch (1) guided press plate which is supported by one or more prestressed springs (19, 20).

19. clinching device according to one of claims 8 to 18, characterized in that the pressing element (18) on the base body (23) of the stamp (1) is guided.