EP1793960A1

EP1793960A1 - Method of welding a holder to a metal sheet, including removal of some holder material and deposition thereof on the metal sheet

Info

Publication number: EP1793960A1
Application number: EP04764193A
Authority: EP
Inventors: Ivan Zilic
Original assignee: Individual
Current assignee: ZILIC, IVAN
Priority date: 2004-05-27
Filing date: 2004-08-17
Publication date: 2007-06-13
Also published as: WO2005118200A1

Abstract

The invention relates to a method for welding a holder (20) comprising a narrow surface, the holder (20) being joined to a metal sheet by means of said narrow surface. According to the inventive method, the narrow surface of the holder (20) is retained at a free distance from the metal sheet (24), a voltage is applied between the holder (20) and the metal sheet (24), and an electric arc (42) burns between the narrow surface and the metal sheet (24). Some material is removed from the narrow surface because of the electric arc and is applied to the metal sheet (24) as a deposited melt (46). The holder (20) is then brought in contact with the metal sheet (24), the narrow surface of the holder (20) being dipped into the deposited melt (46). The melt crawls up along the holder (20) and a concave welding seam or filling is formed. The voltage is switched off and the electric arc (42) is extinguished. The welding process is rendered more stable by using inert gas.

Description

METHOD FOR WELDING A BRACKET TO A SHEET WITH REMOVAL OF SOMETHING BRACKET MATERIALS AND DEPOSITING ON THE SHEET

The condition relates to a method for welding a holder with a narrow surface stump to a metal sheet, in particular a body panel.

The stud welding method is known for connecting stud-shaped or pin-shaped holders to a sheet. An arc is generated between the end face of the holder and the sheet, both parts are melted and brought together under slight pressure, they are connected to each other.

In drawn arc stud welding, a stud is brought into contact with the sheet by a lifting mechanism and a tension is applied between the stud and the sheet. The bolt is lifted slightly from the sheet, a pilot arc with low current is ignited. A main arc is then ignited between the tip of the stud and the sheet metal. The bolt and workpiece are melted in the process. After a set welding time has elapsed, the stud is immersed in the workpiece melt. The resulting melted workpiece forms an outwardly convex weld. The power source is switched off, the melt solidifies and cools down. A seam connection that breaks the flow of force is created. The workpiece structure in the pin insertion area becomes inhomogeneous.

The stud welding process is used in the automotive industry, among others. It has the advantage that the surface of the sheet metal facing away from the bolt is influenced as little as possible, so that it can form the outer surface of a body. However, it has been found that stud welding does not always lead to sufficient results. In particular, automobile manufacturers have to determine that studs fall off due to weakness in the material structure in the area of the stud head or that rust forms, in particular due to trapped condensation water at weld transitions. This is where the invention begins. It has set itself the task of modifying the welding process and designing it in such a way that a more reliable connection takes place between the holder and the sheet metal and preferably the surface of the sheet metal facing away from the holder is influenced even less than before. ferrATiGUNGSKOPiE This object is achieved by a method for welding a holder, which has a narrow surface, with this narrow surface to a sheet metal, in particular to a body panel, in which method the holder is held at a free distance from its narrow surface to the sheet metal, between the holder and sheet metal is subjected to an electrical voltage and an arc burns between the narrow surface and sheet metal, some material is removed from the narrow surface due to the arc and is applied to the sheet metal as a deposited melt. The holder is then brought into contact with the sheet, the holder dipping into the deposited melt with the narrow surface, the voltage being switched off and the arc extinguishing.

In contrast to the stud welding process, this method does not weld stud-shaped or stud-shaped holders, but holders that have an elongated narrow surface. The holders are essentially flat sheet metal pieces that are welded on with a narrow side. The sheet metal pieces can also be shaped as desired, for example bent. However, the essentially elongated narrow side remains.

Under the effect of the arc, the holder is slightly removed in the area of the narrow surface and the removed material is applied to the sheet as a deposited melt. Only the holder is slowly melted, the sheet is heated and combines with the gradually deposited melt. The surface of the sheet facing the holder is built up by the self-melt applied by the holder and thereby reinforced. After a fixed melting time, which can be, for example, 30 to 200 milliseconds and which essentially corresponds to the duration of the arc, the holder is brought into contact with the sheet metal, immersing it in and practically force-free in the deposited melt, which is largely molten can hit the surface of the sheet. It can now be seen that the deposited melt moves towards the holder and is pulled up a little on it, as is also the case with different materials, such as glass and water. This subsequent cohesion effect creates a force-flowing seam connection. Molten material that (still) adheres to the narrow surface 22 also contributes to the weld seam located. Since the deposited melt consists of the material of the holder, the present method is also referred to as cohesive welding. In any case, it is crucial that it takes place without filler materials, as in the arc welding process, as with the stud welding process, only between the holder and the sheet metal.

The targeted melting of some material from the holder and the transfer or application of this material to the sheet metal, where it forms the deposited melt, are particularly crucial. The sheet itself is heated significantly, but is not otherwise affected. The direct influence on the or even destruction of the sheet metal structure, as often occurs in stud welding, is prevented. In contrast to stud welding, where there is an outwardly bulging (convex) bead around the stud in the area of the connection point, in the welding method according to the invention an inwardly bulging (concave), in any case not bulging outwards (convex) Night or stuffing. When there is contact between the holder and the sheet metal at the end of the welding process, the material from the deposited melt pulls up to the adjacent surface of the holder and forms this concave seam or filling.

The connection of the welded-on holder to the sheet is extremely good, very high strengths are achieved. In particular, however, no voids are left behind when painting over later. The bursting of layers of paint, under which condensation was trapped, while drying the paint in an oven is not observed. It has proven to be advantageous to ignite a precursor arc, also called a pilot arc, in front of the actual arc. This creates the conditions for the main arc to ignite stably, burn well and be localized. The precursor arc can be maintained by a small, preliminary current that is significantly smaller than the actual welding current. However, the precursor arc can also be generated in another way, for example by a plasma discharge or by a higher electrical voltage which ignites an arc directly over a greater distance.

In the method according to the invention the holder becomes shorter when it is welded on. This is also observed in the stud welding process. Part of the material of the Narrow area is required for the welding process. The holder is typically at least 1 mm shorter in the welded-on state, usually 2 to 3 mm shorter than before welding.

The method is suitable for electrically conductive holders and sheets, in particular sheets and holders made of steel, alloyed and unalloyed. It can also be used for other metals, for example aluminum.

The narrow surface of the holder is preferably not flat before welding, but is slightly curved, has a blunt or sharp tip, a tip or a curvature. In the following we generally speak of a protrusion on the narrow surface. The arc ignites at this projection. It is located the smallest distance from the flat sheet. The projection is advantageously in the middle of the narrow surface. The main arc extends over the entire end face of the holder in the area of its narrow surface, so the main arc is not located in any way. The narrow surface runs essentially parallel to the sheet.

The narrow surface has a length that is significantly larger than its width. The narrow surface is therefore essentially elongated. It preferably has a constant width, so it is a narrow rectangular area. It can be bent as desired, e.g. S-shaped, L-shaped or in the form of a tube. The holder can also be a closed tube itself. It is crucial that the narrow surface is relatively long, in particular at least four times, preferably at least ten times larger, than the width, so that the narrow surface has a relatively large extension compared to the compact end surface of a prior art bolt.

The method is by no means limited to the connection of brackets and body panels, rather it can be used wherever the stud welding method, in particular the drawn arc ignition method, is used today. The holder itself can have any shape, provided that it only has the elongated geometry in the area of the narrow surface. At a distance from the narrow surface and in the area in which no material is removed from the holder, the holder can have any shape, for example expand greatly, be relatively long and the like. The only thing that is important for the welding process is the formation of the narrow surface and its immediate surroundings, so to speak, the immediately adjacent approx. 5 mm.

The sheet must also meet certain conditions. It must be ensured that the deposited melt is adequately bonded to the sheet under the effect of the arc. The sheet must be able to reach a sufficient temperature in the area where the deposited melt is located. Body panels from the motor vehicle sector generally meet this condition, they have a thickness of approximately 0.6 to a maximum of 5 mm, for example 1.6 mm. The distance d between the holder and the sheet is also important.

It seems to be advantageous to adapt the material thickness of the holder in the area of its narrow surface to the thickness of the body panel. This favors the erosion of the material of the holder according to the invention and the application of this material as a deposited melt to the sheet metal. So you should use thin holders for thin sheets and vice versa. If possible, the material thickness of the holder in the area of its narrow surface should not differ from the thickness of the sheet by more than a factor of 5. It is advantageous if the width of the narrow surface is not very different from the thickness of the sheet, for example at most half to twice the thickness of the sheet. The differences should be less if possible.

The invention is explained in more detail below with reference to exemplary embodiments, which are not to be understood as restrictive. These also serve to explain the method according to the invention. The explanation is given with reference to the drawing. In this show

Fig. 1 is a basic side view of a holder which is at a distance from a sheet, Fig. 2 is a plan view of the narrow surface of the holder, Fig. 3 is a side view like Figure I, but the holder is now in contact with the sheet and it flows a provisional stream 4 shows a representation similar to FIG. 1, but a precursor arc has now been ignited. FIG. 5 shows a representation like FIG. 4, but a main arc is now ignited, which creates the conditions for the subsequent welding process, FIG with the sheet in an enlarged representation and FIG. 7 shows a compilation of the individual processes in a diagram with four partial images.

The holder 20 is a substantially flat sheet metal part made of sheet steel. Its material thickness is approximately 1.5 mm. It has a lower narrow surface 22 which lies directly opposite a sheet 24 and is largely parallel to the sheet. The distance is about 2 - 6 mm. The sheet has a material thickness of approximately 2 mm.

The holder 20 has a width of approximately 18 mm measured parallel to the sheet. The distance between the narrow surface 22 and a free, upper edge 26 is approximately 30 mm. The narrow surface 22 is rounded, there is a projection 28 in the center of the surface or in the central region of the narrow surface 22. The projection 28 is closer to the sheet 24 than the other regions of the narrow surface 22. Instead of a rounding, a tip or the like can be provided, it is preferred that the narrow surface 22 is closest to the sheet 24 at approximately its center point.

2 shows that the narrow surface 22 is essentially elongated. The rectangle length, which corresponds to the width of the holder 20, is 10 times greater than the rectangle height, which corresponds to the sheet thickness. 2 is intended to illustrate the elongated design of the narrow surface 25. Instead of the elongated design of the narrow surface 22 shown, it can also be curved, kinked, etc.

In practical use, the sheet 24 is usually somehow fixed or connected to a larger part so that it is stationary. The holder 20 is normally moved. It is held in a holding device 30, which can be moved at right angles to the sheet 24 in the direction of a double arrow 32. 3 is the Holding device 30 only indicated and any holding device 30 can be used, for example also a holding device 30, as is known from the methods for stud welding.

The holder 20 is connected to a voltage source 34 which supplies the welding current. The voltage source has an output voltage of 0.1 to 1 volt, for example 0.5 to 0.6 volt direct voltage. The positive pole is connected to the holder 20. The holding device 30 is preferably designed such that it simultaneously provides the electrical contact with the holder 20. The negative pole of the voltage source is connected to the sheet 24 over a large area via a resistor 36. The contact with the sheet 24 takes place over a large area and in such a way that no changes or influences occur on the sheet 24; it is preferably carried out on the same side of the sheet on which the holder 20 is also to be welded.

In contrast to the illustration according to FIG. I, the holder 20 is now in contact with the sheet metal 24 in the region of its projection 28. A closed circuit is thus present, the short-circuit current is limited by the resistor 36 to a small, provisional current is, for example, at 50 A.

In FIG. 4, starting from the position according to FIG. 3, the holder 20 is now moved upwards away from the sheet 24 by means of the holding device 30. A precursor arc is formed, which is fed by the voltage source 34. A current of approximately 50 A continues to flow. The precursor arc 38 has an energy which is approximately 25 watts, it is not sufficient for the welding process. The precursor arc 38 paves the way for the later actual arc 42. FIG. 4 shows the state with the precursor arc 38. The narrow surface 22 of the holder 20 is at a distance from the sheet 24, which is approximately 3 mm, typically it is between 0.5 and 6 mm.

FIG. 5 corresponds to the representation according to FIG. 4, but the resistor 36 is now bridged. This is done via a switch 40, which is not shown in the previous figures for reasons of simplification. Only a high current can flow, for example in the range from 350 to 2000 A, it is also referred to as welding current. As a result, a significant increase in the arc is achieved, such as Comparison of FIGS. 4 and 5 shows. The arc is now provided with the reference symbol 42 in FIG. 5 and is also referred to as the main arc. A much higher energy is now contained in this arc 42, which leads to a strong heating of the sheet 24 and the holder 20, these heats being limited locally to the immediate vicinity of the arc 42. Heat conduction does take place, given the very short period of time of the welding process, however, it can be neglected. The arc 42 leads to material of the holder 20 being removed under the very strong heating of the holder in the area of the narrow surface 22. This takes place at the points 44. The removed material is deposited on the sheet 24, more precisely on the side of the sheet 24 opposite the narrow surface, and forms a deposited melt there. This connects to the sheet 24, which is heated appropriately hot for this connection by the arc 42. After a period of 5 to 250 milliseconds, for example 90 milliseconds, in which the high current flows and the arc 42 exists, the holder 20 is again brought closer to the sheet 24 until it comes into contact with the deposited melt 46 and immerses it. The arc 42 goes out due to the short circuit. The electricity is switched off.

The holder 20 has lost some of its total length, for example at least 1 mm, typically 2 to 3 mm. When immersed in the deposited melt, he comes into contact with it and usually also with the surface of the sheet 24. The immersion takes place without force. When immersed, the material of the deposited melt 46 pulls up slightly on the hot holder 20, as is known from adhesive processes. Since this is the same material, we speak of cohesion. The result is shown in FIG. 6, which shows a section in the direction of the double arrow 32, but at right angles to the paper plane of the illustration in FIG. 5. It can be seen that the material originating from the holder 20 forms an essentially triangular seam or filling 48 that is concavely curved, in any case not convexly outwardly. Their condition is typical for a good welded joint. After the auxiliary devices have cooled and removed, the welded connection is completed.

The processes described are to be explained once again with reference to the representation according to FIG. 7, which summarizes the individual phases in a diagram which is shown as horizontal axis (x-axis) has the time axis. In the uppermost part, the holder 20 is shown in five different positions that it occupies during the course of time. Under the holder is sheet 24, which is stationary and is shown continuously.

Directly below this uppermost first partial image from FIG. 7, the distance d of the holder from the sheet 24 is shown over time in a second partial image.

Below this, the strength of the arc 42 is shown in arbitrary units D over the time t, e.g. measured optically, in particular by means of the light intensity D. First, a small arc 38 with the relative strength I can be seen, then a strong arc 42 with the relative strength 5. The fourth partial image in turn shows the course of the welding current I over time t, he takes for example the values 30 A and 2000 A.

The individual states will now be discussed in detail: before the time t = 0, the holder 20 is at a distance d of approximately 15 mm from the sheet metal 26. It is then moved to the sheet metal 24 at time 0 and makes contact with the sheet that occurs shortly after time 0. In this state, the welding voltage is now switched on, which in an alternative can also be switched on before the mechanical contact. A preliminary current I of approximately 30 A flows. It is present after approximately 80 ms. A little later, the holder 20 is lifted off the sheet 26 and then has a distance of approximately d = 6 mm from the sheet 24. When the holder 20 is lifted off the sheet 24, a precursor arc 38 is formed. At the time 120 ms, the holder 20 is at a distance d of approximately 6 mm from the sheet 24, the arc 38 burns with the relative strength I and a current of approximately 30 A flows. This state in itself can be maintained for a relatively long time. It has been shown that it is advantageous to switch on the full welding current of approximately 2000 A after approximately 180 milliseconds. As a result, the arc jumps to the relative strength 5 and is now present as the main arc 42. The distance d of the holder 20 from the sheet 24 remains 6 mm. The length of time of the large welding current and also the arc 42 is critical and important since the welding result depends on it. The full welding current is approximately 150 ms. During this time, the holder 20 is initially still at a distance of 6 mm from the Sheet 24. At time t = 260 ms, the holder 20 is approached the sheet 24. It has now become somewhat shorter because part of its material has been removed. Contact with the sheet 24 occurs at minus 3 mm, in other words the holder has lost 3 mm of its length, see melting depth in FIG. 7. When contacting the deposited melt 46 on the sheet 24, the arc 42 breaks off. The welding current can be briefly increased again or is increased by the contact or short circuit alone, see increase to over 2000 A. It is then switched off. After 350 ms the welding current is at 0. The welding process is finished.

An advantage of cohesive welding, as described above, is that the material is drawn up from the deposited melt creeping or flowing on the holder as soon as the holder comes into contact with the deposited melt 46 and is immersed in it. A flat to concave weld seam or filling 48 is formed. This creates a filled and flowing transition between the sheet 24 and the holder 20, which is ideal for the forces to be absorbed, for example tension, pressure, bending and torsion. The cohesive effect causes a smooth transition connection between the holder 20 and the sheet 24.

It is advantageous if the holder 20 is located vertically above the sheet 24 during the welding process. There can also be an angle, for example the double arrow 32 can also be horizontal. However, it has been shown that material also flows somewhat downwards, in the sense of gravitation. It is therefore preferred that the double arrow 32 is parallel to the solder and that the holder 20 is perpendicular above the sheet 24.

The slow partial melting of the holder 20 has little influence on the sheet; in particular, a change in the sheet, as frequently occurs in stud welding, is largely prevented. The process works without filler materials.

If, starting from the state according to FIG. 5, the welding current is switched off in a timely manner, for example in the fourth partial image of FIG. 7, as a result of which the arc 42 is extinguished, in contrast to the sequence described above, the holder 20 is not Moved onto the sheet 24, but rather blocked the holder 20 in its position according to FIG. 5, the following was found: There was no welding process because this was deliberately interrupted. There is demonstrably a deposited melt 46 on the sheet 24, the material comes from the holder. The deposited melt 46 has a firm connection to the sheet 24 after cooling. On the holder 20 you can see worn spots 44.

LIST OF REFERENCE NUMERALS

20 holders

21 narrow area

24 sheet

25 free top edge

28 head start

30 holding device

32 double arrow

34 voltage source

36 resistance

38 precursor arc

40 switches

42 arcs

44 removed place

46 deposited melt

48 concave weld or fill

Claims

claims

1. A method for welding a holder (20), which has a narrow surface (22), with this narrow surface (22) to a sheet (24), in particular to a body panel, in which method a) the holder (20) in a free Distance is kept with its narrow surface (22) to the sheet (24), an electrical voltage being present between the holder (20) and sheet (24) and an arc (42) burning between the narrow surface (22) and sheet (24), b) due to the electric arc, some material is removed from the narrow surface (22) and applied as deposited melt (46) to the sheet (24), and c) the holder (20) is then brought into contact with the sheet (24), the Immerses the holder (20) with the narrow surface (22) into the deposited melt (46), the voltage is switched off and the arc (42) goes out.

2. The method according to claim I, characterized in that the voltage is only switched off after contact between the holder (20) and sheet metal (24).

3. The method according to claim I, characterized in that before step a) the holder (20) is held at a free distance from the sheet (24) and a small precursor arc (38) is ignited, which by itself does not yet produce a welded connection can.

4. The method according to claim 3, characterized in that the holder (20) and the plate (24) are brought into contact beforehand and an electrical voltage is present between the holder (20) and the plate (24), which leads to a small, provisional current, that the holder (20) is then moved away from the sheet (24), the precursor arc (38) forming and that the current which flows during the arc after step a) is substantially greater, at least twice as large as that Current that maintains the precursor arc (42).

5. The method according to claim I, characterized in that the holder (20) before the start of welding has a greater length L between its narrow surface (22) and a free end than after performing step c), in particular that it is at least I mm is shorter.

6. The method according to claim I, characterized in that the holder (20) and sheet (24) are made of sheet steel.

7. The method according to claim I, characterized in that the arc (42) goes out in step c) when the holder (20) touches the deposited melt (46) on the sheet (24).

8. The method according to claim I, characterized in that the welded-on holder (20) protrudes substantially at right angles (vertical) from the sheet (24).

9. The method according to claim I, characterized in that for carrying out step c) the holder (20) is connected to the sheet (24) in the region of a zone which has lateral seams or fillings which are not convexly curved towards the outside are, but are preferably concave.

10. The method according to claim I, characterized in that the welding voltage is a DC voltage and that the positive pole is preferably connected to the holder (20).

11. The method according to claim I, characterized in that the narrow surface (22) of the holder (20) is not flat before welding, but has a projection (28), which is designed in particular as a dome or tip, and that this projection ( 28) is preferably in the area of the center of the narrow surface (22).

12. The method according to claim I, characterized in that the main arc (42) burns a few milliseconds, in particular 10 to 300 milliseconds, preferably 25 to 150 milliseconds.

13. The method according to claim I, characterized in that the narrow surface (22) has a length which is at least 10 times as large as the width of the narrow surface (22).

14. The method according to claim I, characterized in that starting from the narrow surface (22) of the holder (20) has a constant cross section over a length of approximately at least 5 mm.