METHOD FOR CONNECTING AT LEAST TWO COMPONENT LAYERS BY MEANS OF PLASMA JET PRE-DRILLING OF THE COVER LAYER

Abstract

The invention relates to a method for connecting at least two component layers by means of a connection element. the invention to provide a particularly advantageous method for connecting at least two component layers lying on top of each other through the creation of a pilot hole in at least one cover layer. The pilot hole in the form of a through hole is made in the at least one cover layer using only a plasma jet, which cover layer is at least temporarily held in place on the base layer. Holding the cover layer and the base layer temporarily fixed to each other will allow the connection element to be placed at the same position in the base layer where the pilot hole is made. Sufficiently large layers can thus be kept in a fixed position relative to one another solely using their weight and friction.

Claims

1. A method for connecting at least two component layers by means of a connection element, said connection comprising at least one cover layer and at least one base layer, wherein a pilot hole in the form of a through-hole is made in the at least one cover layer, and the at least one base layer is not pre-drilled in the region of said pilot hole, with a connection element having a shoulder being connected to the base layer through the pilot hole in the cover layer, and said connection element holding the cover layer in place by means of its shoulder, characterized in that a pilot hole is made only in the at least one cover layer, which is at least temporarily retained on the base layer, and, once the pilot hole has been made in the cover layer, the connection element is guided through the cover layer and connected to the non-pre-drilled base layer, said pilot hole being formed by a plasma jet.

2. The method according to claim 1, characterized in that the plasma jet is generated by means of a non-transferred electric arc, wherein the hot plasma jet causes the cover layer to melt and the plasma pressure acts to displace the molten material, thus creating the pilot hole.

3. The method according to claim 1, characterized in that the material displaced when making the pilot hole is used to form a concentric bead during the displacement process.

4. The method according to claim 3, characterized in that the concentric bead is produced by means of a molding member which rotates when the pilot hole is made by the plasma jet.

5. The method according to claim 1, characterized in that the distance between the plasma nozzle and the cover plate is varied during hole forming.

6. The method according to claim 1, characterized in that the current used to generate the electric arc is varied over the pre-drilling period t.sub.V, which current is a pre-arc current I.sub.V over a pre-arc period t.sub.V, over a main current period it is a main arc current I.sub.H, which is higher than the pre-arc current I.sub.V, and over a post-arc period t.sub.N it is a post-arc current I.sub.N, which in particular is higher than the pre-arc current I.sub.V and lower than the main arc current I.sub.H.

7. The method according to claim 1, characterized in that the connection of the connection element to the base layer is effected using friction welding, nailing, friction nailing or hole-forming screw driving, in particular flow drilling screw driving.

8. A device for joining a component connection, comprising at least one cover layer and at least one base layer, wherein the device comprises a pilot hole forming unit and a joining unit, which interact to join the component layers by means of a connection element, and wherein the pilot hole forming unit makes a pilot hole in the at least one cover layer and the joining device connects a connection element to the still complete base layer via said pilot hole, characterized in that said pilot hole making unit comprises a plasma jet pre-drilling unit comprising a plasma nozzle having a nozzle orifice from which a hot plasma jet can be ejected.

9. The device according to claim 8, characterized in that the plasma jet pre-drilling unit generates a plasma jet solely by means of a non-transferred arc.

10. The device according to claim 8, characterized in that a molding element is arranged concentrically to the plasma nozzle, which element in particular spaces the plasma nozzle from the cover layer.

11. The device according to claim 10, characterized in that the molding element is designed in such a way that it limits the displacement of the melt at least in the radial direction, in particular also in the axial direction.

12. The device according to claim 10, characterized in that the molding element is formed from a high-temperature-resistant metal or a ceramic material.

13. The device according to claim 10, characterized in that the molding element is designed to be rotatable.

14. The device according to claim 10, characterized in that the molding element has at least one hole which is oblique, in particular perpendicular, relative to a central hole of the molding element and serves as a vent hole.

15. The device according to claim 10, characterized in that the plasma nozzle and the molding element are designed as a structural unit, in particular as a combination element.

16. The device according to claim 10, characterized in that the molding element has a coating/an alloy.

17. The device according to claim 8, characterized in that the nozzle orifice has a central circular cutout.

18. The device according to above claim 8, characterized in that the nozzle orifice has a plurality of circular cutouts lying on the circumference of a circle.

19. The device according to claim 8, characterized in that a hold-down device is provided which is used to apply a hold-down force to the component layers during the pilot hole making operation and during the joining operation.

20. The device according to claim 8, characterized in that the joining unit and/or the pilot hole making unit are provided with a hold-down device.

21. The device according to claim 8, characterized in that a control unit is provided that interacts with a parameter memory which stores operating parameters depending on the material properties of the component layers to be joined.

22. The device according to claim 21, characterized in that the operating parameters are dependent on the size of the pilot hole.

23. A component connection, comprising at least one cover layer, wherein said cover layer has a bead surrounding a pilot hole, with the shaft of a connection element extending through said pilot hole, which shaft is connected to a base layer, said connection element having a head with a shoulder, said head of the connection element is designed such that a groove provided on the underside of the head accommodates the bead surrounding the pilot hole.

Description

[0058] In the drawings:

[0059] FIG. 1 is a schematic view of a plasma jet pre-drilling unit in the process of making a pilot hole using a concentrically arranged molding element;

[0060] FIG. 2 is a 2D sectional view of a pilot hole made in the cover layer;

[0061] FIG. 3 is a schematic view of the joining step;

[0062] FIG. 4 is a view of a connection made according to the method;

[0063] FIG. 5a is a view of a device according to the invention in the process of making of the pilot hole; and

[0064] FIG. 5b is a is a view of a device according to the invention in the process of making the connection;

[0065] FIG. 6 is a view of a molding element with a vent hole integrally formed with a plasma nozzle;

[0066] FIG. 7 is a view of the electric arc current curve during the pre-drilling process.

[0067] FIG. 1 illustrates a first step in the joining method according to the invention. In accordance with this method, two superimposed component layers 12, 14 are to be connected with each other. In this embodiment, the cover layer 12 is harder than the base layer 14.

[0068] First, a pilot hole is made in the cover layer 12 using a plasma jet pre-drilling unit 16. The plasma jet pre-drilling unit 16 comprises a plasma nozzle 18 in which a plasma jet 20 is generated, with an electric arc being produced between a tungsten electrode 22 and the plasma nozzle 18. This is where the gas flowing through the plasma nozzle 18 is ionized and is then ejected onto the cover layer 12 in the form of a hot plasma jet 20. The plasma jet 20 acts to melt the cover layer 12 in the area of the pilot hole, with the plasma pressure radially displacing the molten material of the cover layer 12 from the area of the hole.

[0069] In this application, a molding element 24 is placed on the cover layer 12. This element 24 is designed as a hollow cylindrical sleeve and limits the course of the melt in the radial direction, thus creating an annular elevation in the form of a circumferential bead which is clearly delimited by the molding element 24.

[0070] The operating parameters of the plasma jet pre-drilling unit 16 are set according to the characteristics of the cover layer 12 to be pre-drilled.

[0071] FIG. 2 is an illustration of a pilot hole 30 in the cover layer 12 produced by the inventive method, which hole is surrounded circumferentially by a bead 32. The area of the base layer 14 located in the area of the pilot hole 30 has been preserved fully intact and its full material thickness can thus essentially be used for a connection with a joining element.

[0072] FIG. 3 is an illustration of the joining step according to the inventive method, in which a flow-hole forming screw 34 is inserted into the pilot hole 30 provided in the cover layer 12. As a next step, the flow-hole forming screw is screwed into the base layer 14 using pressure and rotation, in which process the screw cuts a rim hole and a thread, thus producing a screw connection as shown in FIG. 4.

[0073] FIG. 4 is a view of the component layers 12, 14 connected by the flow-hole forming screw 34, with the flow-hole forming screw 34 having been screwed into the base layer 14 and using its shoulder to press the cover layer 12 against the base layer 14 and positively locking it in the axial direction.

[0074] Provided in the underside of the head of the flow-hole forming screw 34 is an annular groove which is designed to accommodate the bead 32. This makes for an improved retaining effect in the transverse direction of the screw.

[0075] FIG. 5a is a view of a device 50 according to the invention for joining two component layers. This device 50 comprises a plasma jet pre-drilling unit 60 and a joining device 70.

[0076] As described above, the plasma jet pre-drilling unit 60 comprises a plasma nozzle 62 and a tungsten electrode 64. Using DC voltage and high current, an electric arc is generated between the tungsten electrode 64 and the plasma nozzle 62. In addition, a molding element 66 is positioned in front of the plasma nozzle 62 and is used to give the melt displaced by the plasma jet a desired contour.

[0077] Furthermore, the device 50 according to the invention comprises a control unit (not shown) which first positions the plasma jet pre-drilling unit 60 on the joint-forming layer, and subsequently, once the pilot hole has been made, positions the joining means at this site, as shown in FIG. 5b.

[0078] FIG. 5b shows the joining device 70 in place at the connection site and in the process of positioning a joining element for connection with the non-perforated softer base layer at this site.

[0079] This is a fast and inexpensive way of connecting component layers including a hard cover layer and a softer base layer by means of conventional joining processes and without having to use major process forces.

[0080] As shown as an example in FIGS. 5a and 5b, the joining device 70 and the plasma jet pre-drilling unit 60 can use a common hold-down unit 78 which will apply a hold-down force on the component layers both during the pre-drilling operation and during the joining operation.

[0081] FIG. 6 is a sectional view of a one-piece combination element 80 comprising a molding element 82 and a plasma nozzle 84. The conically tapering upper portion of the combination element forms the plasma nozzle 84, while the portion adjoining the plasma nozzle constitutes the molding element 82, with a vent hole 86 extending perpendicular to the axis of the combination element 80.

[0082] This allows the plasma gas to be guided through the plasma nozzle 84 in a bundled manner, with the counterflow reflected by the component being discharged through the vent hole 86.

[0083] The vent hole 86 in the molding element 82 largely prevents accumulation of plasma gas in the molding element, thus allowing a more precise formation of the pilot hole and of the bead surrounding the pilot hole.

[0084] The molding element 82 prevents the melt from exiting laterally, thus contributing to a more uniform formation of a bead surrounding the pilot hole made in the cover layer by the plasma jet.

[0085] FIG. 7 is an exemplary and qualitative illustration of the curve of the current I used to generate the electric arc during the pre-drilling operation. Over a pre-arc current period t.sub.V, the arc is generated using a pre-arc current I.sub.V. Over a main arc current period t.sub.H, which essentially represents the time span in which the pilot hole is made in the cover layer, the arc is generated using a main arc current I.sub.H. This is in particular 200 A. Once the pilot hole has been made in the cover layer, i.e. after the main arc current period, the arc is generated using a post-arc current IN over a post-arc current period. The post-arc current is lower than the main arc current and of an intensity that will suffice to merely displace the melt laterally without, however, making a hole in the base layer. Especially in combination with a molding element, this allows a relatively precise bead contour to be produced from the molten material of the cover layer.

[0086] The above-mentioned current periods are adapted to the materials and the thicknesses of the at least one cover layer and of the base layer.