METHOD FOR PRODUCING A JOINING CONNECTION BETWEEN METAL SHEETS

Abstract

A method for producing a joining connection between at least two metal sheets or at least two components made of hot-workable sheet metal with a scaling-resistant coating, comprising is provided. The method includes at least one step in which a connection is produced between the at least two metal sheets or sheet-metal components by hot-press soldering, wherein the surface of the metal sheets or components to be connected is pretreated in order to break up the coating.

Claims

1. A method for producing a joining connection between at least two metal sheets or two components made of hot-workable sheet metal, wherein at least one of the metal sheets is provided with a scaling-resistant coating, comprising at least one step in which a connection is produced between the at least two metal sheets or sheet-metal components by hot-press soldering, wherein at least one of the surfaces of the metal sheets or components to be connected is pretreated in order to break up the coating and roughen the surface of the metal sheet, wherein the coating is broken up over the entire thickness of the coating down to the surface of the metal sheet.

2. The method according to claim 1, wherein the coating is broken up using a mechanical tool.

3. The method according to claim 2, wherein the tool is a die.

4. The method according to claim 1, wherein the coating is broken up and/or the surface of the metal sheet is roughened using a laser.

5. The method according to claim 1, wherein the coating is broken up only in the subregion which is used for the subsequent connection.

6. The method according to claim 1, wherein a solder or a solder with flux is applied in the subregion.

7. The method according to claim 1, wherein a brazing solder is applied to the subregion.

8. The method according to claim 1, wherein the at least two metal sheets are fixed to one another and are then fed to the hot-working process.

9. The method according to claim 1, wherein the energy input for the hot working is sufficient for soldering the metal sheets.

Description

DESCRIPTION OF THE FIGURES

[0026] The invention is described below by way of example with reference to the attached drawing, in which:

[0027] FIG. 1 is a schematic representation of a side part blank in the prior art;

[0028] FIG. 2 schematically shows a sheet metal arrangement according to the invention;

[0029] FIG. 3 shows a section through a coated metal sheet;

[0030] FIG. 4 shows a section through an uncoated metal sheet with a roughened surface;

[0031] FIG. 5 shows a section through a coated metal sheet with ablated regions.

[0032] Blanks made of hot-workable steels are provided as the starting material. These materials are a common starting product for lightweight construction.

[0033] As a result of the hot working, the required forming forces are low, and springback does not occur, as in the case of the deep-drawing of high-strength and ultra-high-strength steels. For example, a 22MnB5 steel is used both for supporting components and for crash-related components which do not have to withstand significant deformation. Typical applications are therefore components that serve as ingress protection, such as A and B pillars, bumpers, transverse and roof rails, but also center tunnels.

[0034] Austenitization is usually carried out in continuous furnaces, but also in induction furnaces or multi-chamber furnaces. The presence of oxygen in the furnace atmosphere leads to scaling and edge decarburization of the semi-finished product. Although the heating can also take place in an inert atmosphere, the oxygen exposure and thus the metal loss occur at the latest during transfer into the press-hardening tool.

[0035] This not only leads to a reduction in the tool life, but also to a deterioration in the heat transfer between the part being formed and the tool. Therefore, the metal sheets are frequently provided with a scaling-inhibiting coating. Of the various possible coatings, hot-dip aluminizing, i.e., an aluminum-silicon coating, which was developed first, is at present used most frequently.

[0036] For a planar connection, according to the invention, a first component 1 having an AlSi coating is connected to a second component 2 via a brazing solder 5. In preparation, the subregion 1a of the first component 1 is treated using a tool which breaks up the coating 6 in a targeted manner.

[0037] Since this break-up takes place shortly before the metal sheets are connected, no problems with oxidation arise.

[0038] For example, a die is used which mechanically perforates the surface 6a of the coating in the subregion 1a of the connection. FIG. 2 shows this as a wafer pattern 4. In the example, a circular impression can be seen, but other contours are also possible. Due to the perforation, the AlSi surface is broken up in a targeted manner in order to create an optimal connection between the steel, aluminum, and solder.

[0039] This means that the grooves and channels formed in the coating 6 extend down to the surface 7a of the steel blank 7. The depth corresponds to the thickness 6b of the coating 6. Subsequently, the brazing solder 5 is applied to the subregion 1. The brazing solder 5 may also be replaced with another solder material and a flux.

[0040] The second component is likewise prepared as described above.

[0041] Subsequently, the two components 1 and 2 are fixed and fed to the hot-working process in order to form the sheet stack. The hot-working process provides the temperature required for the planar connection. Subsequently, the sheet stack is mechanically formed in the press in the hot-working tool and cooled.

[0042] The method can be used for all hot-working steels, examples being USI-BOR or DUCTIBOR. The coating is, advantageously, AlSi, but may also be a different coating.

[0043] The break-up of the coating occurs on all components which are to be connected to one another.

[0044] As an alternative to the mechanical break-up of the coating, a laser tool may be used to break up the coating using the laser beam.

[0045] The AlSi coating is perforated in a punctiform manner by means of the laser, wherein a region 1a in which the solder connection is to be produced is preselected in this case, too. The distances between the perforations can vary as required. The perforations allow for punctiform exposure of the steel blank, with local removal of the AlSi coating down to the surface 7a of the steel blank.

[0046] By adjusting the laser power, the penetration depth is defined, and the material of the coating 6 having the thickness 6b can be removed easily and very precisely down to the surface 7a.

[0047] In another embodiment, the surface 7a of the steel blank 7 is also roughened, as is shown in FIG. 5, in addition to the removal of the coating 6. Here, the laser power is set such that the laser, in addition to the thickness 6a of the coating, also removes material from the steel blank 7 to the depth 7b.

[0048] In another embodiment, the surface 7a of an uncoated steel blank 7 is provided with peaks and troughs in the subregion la by means of a separate laser pulse method. As a result, the surface 7a acquires a very rough character. As indicated in FIG. 4, the surface 7a has indentations, and thus constitutes a good connection surface.

[0049] By means of the connection method according to the invention, coated metal sheets can therefore be connected to one another or to an uncoated metal sheet.

[0050] Depending upon the demands made of the connection, the pretreatment of the metal sheets in subregion 1a, which is used for the connection, is performed on the coating surface 6a, on the steel blank surface 7a, or on both.