WO2008025672A1

WO2008025672A1 - Method for the production of a double sheet metal structure

Info

Publication number: WO2008025672A1
Application number: PCT/EP2007/058413
Authority: WO
Inventors: Werner Staudinger
Original assignee: Thyssenkrupp Steel Ag
Priority date: 2006-08-30
Filing date: 2007-08-14
Publication date: 2008-03-06
Also published as: DE102006040514B4; DE102006040514A1

Abstract

The invention relates to a method for the production of a double sheet metal structure (1) by welding a first sheet metal (2) made of metal to at least one second sheet metal (3) made of metal, wherein both sheet metals are preferably made of steel or a steel alloy. The second sheet metal is provided with at least one bead (4) and is then placed with the arched section (5) of the bead onto the first sheet metal during welding and welded by a weld seam in the bead base to the first sheet metal. Furthermore, the present invention relates to a semi-finished product, comprising a double sheet metal structure and the use thereof. The task to provide an optimized production method for double sheet metal structures in regard to avoiding welding errors is solved in that at least one bead of the second sheet metal has a width of 1 mm at the most, preferably 0.8 mm at the most.

Description

Process for producing a double sheet structure

The invention relates to a method for producing a double sheet metal structure by welding a first sheet of metal with at least one second sheet of metal, wherein both sheets are preferably made of steel or a steel alloy, in the second sheet at least one bead is formed, the second sheet during the Welding with the bulge of the bead rests on the first sheet and is welded via a weld in the bottom of the bead with the first sheet. Moreover, the present invention relates to a semi-finished product comprising a double sheet structure and its use.

Many methods for the production of double sheet structures are known from the prior art. For example, double sheet metal structures are known from motor vehicle construction which have a base plate which is joined to a "patched" metal sheet by means of a reinforcing plate Corresponding "patched" metal sheets are used in particular in motor vehicle construction when local thickening of the material is required, for example by hinges for doors, hoods, etc. while providing optimized weight. A particular problem is the welding of galvanized sheets, since it must be paid attention to a good zinc degassing in order to avoid welding defects.

For example, from DE 103 46 264 Al a method for welding two sheets is known in which a the sheet is provided with a bead arranged along a line in the form of interruptions. First, the plate provided with the beads is placed on the other plate with the bulges of the beads and welded cohesively on the molded beads. Although good welding joints can sometimes be made with the method known from the cited document, the number of welding defects, especially when welding galvanized sheets, is still too great due to topping incidence, root recession, pores, cracks or holes, in order to achieve a reproducible and cost-effective result To achieve production.

Starting from this prior art, the object of the present invention is to provide a production method for double sheet structures which has been optimized with regard to the prevention of welding defects, as well as semi-finished products having a double sheet structure which are produced accordingly. In addition, it is an object of the invention to propose an advantageous use of the semifinished products produced according to the invention.

According to a first teaching of the present invention, the above-described object is achieved in that at least one bead of the second sheet has a width of at most 1 mm, preferably at most 0.8 mm.

By limiting the width of the bead in the second sheet to a maximum of 1 mm or a maximum of 0.8 mm ensures that the weld fills the entire bead width, so that the bead after the welding process is no longer or almost impossible to see. The limitation of the width of the bead ensures, especially during welding of galvanized steel materials optimum zinc degassing, due to the small contact surface of the second sheet on the first sheet. The surface areas with a joint gap of zero are therefore minimized. Due to the small width of the bead, the air gap, unlike the previously used beads, between the first and the second plate in the immediate vicinity of the weld remains constant, so that via an improved degassing, especially zinc degassing can take place.

If the bead base has at least one bead in the second sheet a radius of less than 1 mm, preferably less than 0.6 mm or less than 0.4 mm, then the bearing surface is further reduced with a joint gap of zero and the zinc degassing is further improved. This is due to the fact that correspondingly small radii in the bead base lead to a reduction in the radius at the bulge due to the bead in the second sheet, which form a zero-joint gap directly with the first metal sheet.

Preferably, the air gap between the first and second plates is set by the bulge of the bead of the second sheet to 0.1 mm to 0.3 mm, so that a low cover layer incidence and root recession or root sag is achieved in the formation of the weld. In particular, this also ensures that, for example, in galvanized sheets degassing of the zinc layer can be done and at least in vehicle makes it possible, for example, to achieve a paint protection between the joining partners via a cathode immersion paint.

The sheets used may have a metallic coating, preferably zinc. But also conceivable are sheets with non-metallic coatings, wherein the coatings can be applied on one or both sides. The sheets can also have different thicknesses.

In a particularly simple manner, the air gap between the first and second plates can thereby be adjusted to the desired range in which the bead depth is 0.1 mm to 0.4 mm. Due to flow movements of the metal in the production of the beads, the bulge, which causes the air gap between the first and the second plate, in their height is slightly less than the bead depth. Correspondingly deep beads can be achieved by embossing tools, in particular by a contoured embossing wheel provided with a corresponding radius.

According to a next further embodiment of the welding method according to the invention, the strength of the connection between the first sheet and the second sheet is improved in that the bead has a length of at least 15 mm. The length of the bead can be adjusted according to the skill requirement.

Preferably, the weld seam is produced in the bottom of the bead by at least two partial welds whose weld points are provided off-center, preferably at the ends of the bead, wherein the welding of the partial welds takes place from outside to inside. As a result, the Ausschweißpunkt usually located in the middle can be partially filled or reduced when generating the second partial weld. The partial welds can be generated synchronously or at least partially offset in time. Preferably, the partial welds are generated at least partially overlapping, so that in particular the Ausschweißpunkt an initially generated partial weld seam can be filled when welding and almost eliminated.

In order to improve the formation of weld-in points, chamfers are preferably provided for the weld-in points at the outer ends of each bead, which allow the depth of the bead to rise in a targeted manner from the outer ends in the direction of the center. The chamfers can be either linearly rising or formed as radii.

Preferably, the weld seam is produced in the bottom of the bead with a laser welding beam, which in particular makes it possible to produce welds with extremely small dimensions, in particular weld seam widths.

A process-reliable production of a weld seam only in the region of the bead bottom of the bead is achieved in that the focus diameter of the laser welding beam in the bottom of the bead is 0.2 to 1.0 mm, preferably 0.3 to 0.7 mm.

If a process gas, in particular compressed air or an inert gas is used during welding, the welding process can be further stabilized. In this case, compressed air represents a particularly cost-effective reactive process gas. Inert gases, for example helium, stabilize the welding process by preventing or reducing the oxidation of the weld seam areas.

Particularly advantageously, the method according to the invention can be further developed in that as the first sheet a base plate and a second plate, a reinforcing plate is used. The reinforcement plate can be fixedly connected to the base plate via the weld seams in the beads and be used in particular for reinforcing areas of the base plate, which are exposed to a higher mechanical load. Due to the special bead geometry, the weld seams on the reinforcing plate are no longer visible on the outside.

Welding speeds of up to 10 m / min, in particular up to 8 m / min, particularly preferably up to 6 m / min are used in the method according to the invention, wherein the travel speeds of the welding head between the individual welds to be welded at least 80 m / min, preferably at least 100 m / min, more preferably at least 120 m / min, a particularly economical process for the production of double sheet structures can be provided. Basically, the appearance of the weld improves with the reduction of the welding speeds, however, the time required per weld increases due to reduced welding speeds. In addition, the traversing speeds of the welding head should be maximized, but taking into account the investment cost of the systems, the investment costs usually increase with increasing traversing speeds of the welding head with consistently high position accuracy.

According to a second teaching of the present invention, the above-described object by a semifinished product comprising a double sheet structure consisting of a first sheet and at least a second sheet, wherein the second sheet is welded to the first sheet using the method according to the invention, solved, wherein preferably the first sheet is a base sheet and the second sheet is a reinforcing sheet.

The base plate is usually used as a structural component, which is reinforced for weight reduction only at predetermined positions with a reinforcing plate. As already stated above, a corresponding semifinished product can not only be produced particularly economically by the method according to the invention, but also has a very high weld quality in the connection region of the reinforcement plate and the base plate.

If the reinforcing plate is a hinge reinforcement, lock reinforcement and / or a gas damper reinforcement of a base plate of a motor vehicle component, in particular a tailgate or a door of a motor vehicle, a correspondingly manufactured component can be provided in a particularly cost-effective and economical manner.

Finally, the object indicated above is achieved according to a third teaching in that the semifinished product according to the invention is used in motor vehicle construction. By using the semifinished product according to the invention, on the one hand, the weight of motor vehicles can be reduced; on the other hand, the reinforced areas of the semi-finished products can be subjected to further refining steps, such as painting, without and only with little reworking. There are now a variety of ways to further develop and design the inventive method for producing a double sheet structure and the semi-finished product according to the invention. Reference is made on the one hand to the claims subordinate to claims 1 and 14, on the other hand to the description of two embodiments in conjunction with the drawings. The drawing shows in

1 is a sectional view transverse to the longitudinal direction of the bead of an embodiment of a semifinished product according to the invention,

Fig. 2 is a plan view of the embodiment of FIG. 1 in the region of a welded bead and

Fig. 3a), b) a weld of the prior art and a weld of the embodiment of Fig. 1 in comparison in a transverse section.

1 shows, in a schematic sectional view, a double sheet structure 1 comprising a first sheet 2 and a second sheet 3, wherein the second sheet 3 is formed as a reinforcing sheet and the first sheet forms a base sheet. The section shown schematically in Fig. 1 by the

Double sheet structure 1 extends transversely to the longitudinal direction of the bead 4, which has been introduced into the second sheet 3. The bead 4 has, for example, a radius of 0.2 mm and a depth of 0.2 mm. The second sheet 3 preferably has a thickness of 0.4 to 1.5 mm, so that the bead 4 with a depth of about 0.2 mm a Bulge 5 generated on the underside of the second sheet 3, with which the second sheet 3 rests on the first sheet 2. The resulting due to the bead 4 bulge 5 is used to adjust the air gap between the first sheet 2 and the second sheet 3. The width of the bead is limited to a maximum of 0.6 mm, so that when welding the sheets 2, 3 along the bead. 4 , the bead 4 is completely filled by metal. This not only ensures that the weld in the bead bottom of the double sheet structure has a particularly good visual appearance, but is also very free of pores and cracks. In the present case, the air gap 6 has been adjusted to about 0.1 mm via the bulge 5. About the small radius of 0.2 mm of the bead bottom of the bead 4 is achieved that the bulge 5 forms only in an extremely small area a zero-joint gap, so that when welding in particular galvanized steel materials optimal zinc degassing on the one hand on the air gap, on the other hand over the extremely low surface contact 2, 3 is achieved.

When welding the two sheets 2, 3, for example, these are clamped in a device, not shown, or otherwise fixed and generates the welds using a laser welding beam.

In the plan view in Fig. 2, the bead 4 of the second sheet 3 is now shown. When welding the sheets 3 and 2 together according to the invention, the weld is produced in the bottom of the bead by two partial welds, the welds 7 and 8 off-center, as shown at the ends of the bead are provided and the welding direction A, B takes place from the outside to the center of the bead. The length of the bead 4 is 22 mm, for example that the sheet metal connection between the sheets 2 and 3 receives a particularly high strength.

Due to the small width of the bead, the welding beam can be guided along the longitudinal axis 9 of the bead 4 along. The individual partial welds, starting from the welding points 7, 8 may overlap in the area of the center of the bead 10, so that the Ausschweißpunkt is partially filled and eliminated. The partial welds can be staggered or generated simultaneously.

In Fig. 3a), the weld joint of a double sheet metal structure with a bead geometry according to the prior art is now shown in a transverse section. In comparison, Fig. 3b) shows a welded joint of a double sheet structure prepared by the method according to the invention. Both welds were made with a 4.6 kW CO ₂ laser using a 4.5 m / min welding speed with a 0.5 mm focus diameter. However, it is also conceivable to use other laser radiation sources (YAG or fiber) and / or powers. In the present case, the second plate 3 designed as a reinforcing plate has a thickness of 0.6 mm, the air gap 6 is set by the bulging of the beads to a height of 0.1 mm and the first plate 2 designed as a base plate has a thickness of 1.2 mm. However, it is also conceivable that the second sheet 3 designed as a reinforcing sheet should be thicker than the sheet 2 formed as a base sheet. Additionally or alternatively, the reinforcing plate 3 may also consist of a higher-strength steel material than the base plate 2. As can be seen from the metallographic cross section, due to the bead geometry, the weld shown in FIG. 3b) is substantially more homogeneous and shows a more constant distance of the second sheet 3 from the first sheet 2 from the weld seam to the outside. In particular, the bead is substantially neutralized, so that it is no longer visible after welding. In comparison, Fig. 3a) shows significant fluctuations of the air gap in the region of the bead, so that it is visible from the outside. It can be seen from the welded connection produced according to the invention shown in FIG. 3b) that it has neither a cover layer incidence nor a root layer rebound or slack. As a result, it is possible to provide a double-sheet structure equipped with an optimized welded connection, which can be advantageously used in doors, tailgates and the like, for example as hinge reinforcements, lock reinforcements or gas damper reinforcements, particularly in the motor vehicle sector.

Claims

PATENT APPLICATIONS

1. A method for producing a double sheet metal structure by welding a first sheet of metal with at least one second metal sheet, wherein both sheets are preferably made of steel or a steel alloy, in the second sheet at least one bead is formed, the second sheet during welding with the bulge of the bead rests on the first sheet and is welded via a weld in the bottom of the bead with the first sheet, characterized in that at least one bead of the second sheet has a maximum width of 1 mm, preferably at most 0.8 mm.

2. Method according to claim 1, characterized in that the bead base of at least one bead in the second metal sheet has a radius of less than 1 mm, preferably less than 0.6 mm or less than 0.4 mm.

3. The method according to claim 1 or 2, characterized in that the air gap between the first and second sheet is set by the bulge of the bead of the second sheet to 0.1 to 0.3 mm.

4. A method according to any one of claims 1 to 3, wherein a depth of the bead is 0.1 to 0.4 mm.

5. The method of claim 1, wherein the bead has a length of at least 15 mm.

6. The method according to claim 1, wherein the welded seam is produced in the bead base by at least two partial welds whose weld points are provided off-center, preferably at the ends of the bead, wherein the welding of the partial welds takes place from outside to inside.

7. Method according to one of claims 1 to 6, characterized in that the partial weld seams are produced at least partially overlapping.

8. Method according to one of claims 1 to 7, characterized in that chamfers for weld-in points are provided at the outer ends of each bead.

9. The method according to any one of claims 1 to 8, characterized in that the weld is produced in the bottom of the bead with a laser welding beam.

10. The method according to claim 1, wherein the focus diameter of the laser welding beam in the base of the bead is 0.2 to 1.0 mm, preferably 0.3 to

0, 7 mm.

11. Method according to one of claims 1 to 10, characterized in that a process gas, in particular compressed air or an inert gas, is used during welding.

12. The method according to any one of claims 1 to 11, d a d u r c h e c e n e z e c h e e s, s as a first sheet a base plate and as a second sheet a reinforcing sheet is used.

13. The method according to any one of claims 1 to 12, characterized in that welding speeds up to 10 m / min, in particular up to 8 m / min, more preferably used to 6m / min, wherein the traversing speeds of the welding head between the individual to be welded beads at least 80th m / min, preferably at least 100 m / min, more preferably at least 120 m / min.

14. Semi-finished product comprising a double sheet structure consisting of a first sheet and at least one second sheet, wherein the second sheet is welded to the first sheet using the method according to claims 1 to 13, wherein preferably the first sheet a base sheet and the second sheet Reinforcing sheet is.

15. Semifinished product according to claim 14, wherein the reinforcing plate is a hinge reinforcement, lock reinforcement and / or a gas damper reinforcement of a base plate of a motor vehicle, in particular a tailgate or a door of a motor vehicle.

16. Use of a semifinished product according to one of claims 14 or 15 in motor vehicle construction and plant construction, in particular in rail vehicles, passenger cars or kitchen appliances.