WO2006105658A1

WO2006105658A1 - Laser welding of galvanized steel

Info

Publication number: WO2006105658A1
Application number: PCT/CA2006/000520
Authority: WO
Inventors: Cristian Golu
Original assignee: Magna International Inc.
Priority date: 2005-04-08
Filing date: 2006-04-06
Publication date: 2006-10-12

Abstract

Coated metal sheets are laser welded together forming high strength bond. A powdered flux material is applied to at least one surface of one of the coated sheets of metal. The coated sheets of metal are pressed together with the powdered flux material therebetween defining a gap. A laser beam forms a laser weld wherein a portion of the gases produced during the forming of the laser weld escape through the gap and a portion of the gases reacts with the powdered flux material. The powered flux material can be applied by first spraying one surface of the coated metal sheets with an anti-spatter spray and then coating the spray with a powdered flux material. Alternatively, the powdered flux material can be electrostatically sprayed onto the coated metal sheet.

Description

Laser Welding of Galvanized Steel Using Powdered Flux

FIELD OF THE INVENTION

[0001] The present invention relates to method of laser welding of galvanized steel. In particular, this invention relates to a process for laser welding galvanized steel with a powdered flux material.

BACKGROUND OF THE INVENTION

[0002] The automotive industry uses a variety of coated or galvanized products to increase the durability of vehicle structures. Weld joints are generally made by spot welding to join together the parts. Through the use of a high powered laser for welding, joints can be made more quickly and with better quality than other alternative joining techniques. In addition, the advantage of having a single side access, as opposed to requiring access to both sides of a work piece for conventional joining techniques, as well as no direct contact with the work piece make laser welding a desirable welding technique.

[0003] According to general laser welding practice, two sheets that are to be joined are held together contacting each other along the area to be joined. A laser beam is then energized and swept across the area to be joined welding the sheets together by smelting or melting the metal in the area swept by the laser beam.

[0004] A common problem associated with welding coated or galvanized sheet metal includes the vaporization of the zinc galvanized coating resulting in zinc gas explosion leading to a poor weld having defects or pits weakening the joints and creating a visually unacceptable part.

[0005] Removal of the protective coating in the weld joint area is an unacceptable alternative to avoid the zinc gas problem discussed above. By removing the galvanized coating, the weld joint would be susceptible to corrosion by external elements, such as the weather, resulting in a shortened life span of a part. Therefore, there is a need in the art for a method of joining galvanized or coated metals using a laser welding technique that results in robust welds without surface defects. There is also a need for a method of laser welding coated metal sheets that is economic and easy to perform without removing a substantial portion of the protective coating resulting in a less corrosion resistant part. [0006] Several solutions have been proposed with mixed success. United States Patent no. 6,479,168 has proposed the use of a copper foil to be placed between the zinc coated metal sheets acting as a spacer to set up a gap between the sheets. Copper is selected as it is has good alloyability properties with zinc.

[0007] In United States patent no. 3,881,084 has utilized a combination of iron oxide, copper oxide and nickel oxide as alloying agents. The alloying agent is painted as a small film between galvanized components to improve the laser welding process. Any other metal substances sandwiched between galvanized components that can chemically react with zinc will improve the laser welding process.

[0008] However copper and probably nickel oxide will produce brittle joints, which are not desired for automotive industry. The automotive industry requires that the welds break into the base metal. Additionally, the greater quantity of copper utilized to absorb zinc, the greater amount of laser power will be required, which is detrimental to welding speed.

[0009] In WO 2005/014215, a raised portion is provided on the inside surfaces of the coated sheets to form a gap for the gasses produced during laser welding to escape.

SUMMARY OF THE INVENTION

[0010] The present invention provides a method of laser welding utilizing a powdered flux material that is applied to the surface of the zinc coated sheets. [0011] According to one aspect of the invention, there is provided a method of laser welding coated metal sheets forming a high strength bond. A powdered flux material is applied to at least one surface of one of the coated sheets of metal. The coated sheets of metal are pressed together with the powdered flux material therebetween defining a gap. A laser beam forms a laser weld wherein a portion of gases produced during the forming of the laser weld escape through the gap and a portion of the gases reacts with the powdered flux material. The powered flux material can be applied by first spraying one surface of the coated metal sheets with an anti-spatter spray and then coating the spray with a powdered flux material. Alternatively, the powdered flux material can be electrostatically sprayed onto the coated metal sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above-mentioned features and advantages of the present invention will be more fully appreciated from the following detailed description when considered in connection with the accompanying drawings, in which the same or like reference numbers designate the same corresponding parts throughout and in which:

[0013] FIG. 1 is a perspective view illustrating the joining of two coated metal sheets having powdered flux material therebetween according to the present invention;

[0014] Fig. 2 is a top plan view of one of the coated metal sheets indicating a flow of zinc gas during a laser welding operation according to the present invention;

[0015] Fig. 3 is a side elevational view of the two coated metal sheets of Fig. 1; and

[0016] Fig. 4 is perspective view illustrating the application of the powdered flux material to the coated metal sheet according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0017] Referring to Figure 1, coated metal sheets 12, 12', each comprise a metal core

16, 16' having layers of coating 18, 18' applied to at least one side and preferably both sides of the sheets 12, 12'.

[0018] Referring to Figure 4, a powdered flux material 20 is distributed on the surface of at least one of the sheet metal parts 12, 12' to be joined. The powdered flux material

20 introduces a gap 14 between the two parts 12, 12'. In the most preferred embodiment, the powdered flux material 20 is a flux powder that is commercially available normally as a flux cored arc welding wire.

[0019] The powdered flux material 20 may be loosely blown on the surface after being coated with an anti-spatter spray or can be sprayed onto the surface of the coated sheet metal part 12, 12'. Either operation can be accomplished with the use of a spray gun 26, preferably a sand blaster type or an electrostatic type.

[0020] Referring to Figure 3, the coated sheet metal parts 12, 12' are placed in a face to face relation with the powdered flux material 20 therebetween. The parts 12, 12' are pressed together in a press, as schematically indicated by the arrows, in a manner well known in the art. The parts 12, 12' will be separated by a gap 14 approximately equal to the particle size of the powdered flux material 20.

[0021] A laser weld 24 is formed by energizing a laser 22 to locally melt the metal of the two parts 12, 12' to be joined. A portion of the zinc gas reacts with the powdered flux material 20. A portion of the zinc gas formed in the area by the laser 22 is allowed to flow between the two sheet metal parts 12, 12' thereby preventing the pressurization of zinc gas resulting in ejection through the laser keyhole area, as illustrated in Figure 2. [0022] It can thus be appreciated that the objects of the present invention have been fully and effectively accomplished. It is to be understood that the foregoing specific embodiments has been provided to illustrate the structural and functional principles of the present invention and is not intended to be limiting. To the contrary, the present invention is intended to encompass all modifications, substitutions and alterations within the spirit and scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method of laser welding a plurality of coated metal sheets, comprising the steps of: providing coated sheets of metal, applying a powdered flux material to at least one surface of one of the coated sheets of metal, pressing the coated sheets of metal together with the powdered flux material therebetween defining a gap; applying a laser beam forming a laser weld wherein a portion of the gases produced during the forming of the laser weld escape through the gap and a portion reacts with the powdered flux material.

2. A method according to claim 1 wherein said step of applying includes spraying said one surface with an anti-spatter spray and then coating the spray with a powdered flux material.

3. A method according to claim 1 wherein said step of applying includes electrostatically applying the powdered flux material to the one surface.