Method of laser welding

Abstract

The invention relates to a method of joining first and second objects, each object having a substantially planar surface. The method comprises the steps of: - placing the objects with their surfaces in contact along an interface, their surfaces being substantially parallel, the interface having a peripheral edge, - irradiating a laser beam along the direction of the interface with a focal point located on said peripheral edge while the plates are in contact, and - moving the focal point of the laser beam along the interface in a direction transverse to the edge to a position at a distance from the edge.

Description

TECHNICAL FIELD

[0001] The invention relates to a method of laser welding a first and a second object, each object having a substantially flat surface, the method comprising the step of placing the first and the second object in such a way that the surfaces of the first object and the second object are in contact relationship along an interface. BACKGROUND

[0002] It is known to join two metal strips in contact relationship by introducing them together between two pressure rollers. The strips are spaced apart before entering between the pressure rollers, a laser beam irradiates the strips at their point of contact before they are pressed together to form a kissing weld.

[0003] The known method comprises heavy rollers for the pressing of the plates and requires a relatively large footprint. SUMMARY

[0004] It is an object of the invention to provide a method of laser welding two metal objects in contact relationship at their surfaces to obtain a strong bond. It is a further object of the invention to provide a method of laser welding two objects which requires a relatively small footprint and can easily be integrated in a production environment.

[0005] Herein, the method according to the invention comprises the steps of:

[0006] placing the objects in contact relationship along an interface, the surfaces of the objects being substantially parallel, the interface extending to a peripheral edge,

[0007] irradiating a laser beam in the direction of the interface with a focal point on the peripheral edge while the objects are in contact parallel relationship, and

[0008] moving the focal point of the laser beam along the interface in a direction transverse to the peripheral edge to a position at a distance from the edge.

[0009] It has been found that the laser beam penetrates from the peripheral edge a relatively long distance through the two metals on both sides of the interface, while forming a strong bond of the molten metals after the beam is switched off.

[0010] In one embodiment of the method according to the invention, the first object comprises aluminium and the second object comprises copper. It has been found that the welding method according to the invention achieves a strong, non-brittle copper-to-aluminium bond over a large bonding area, resulting in a strong bond. BRIEF DESCRIPTION OF DRAWINGS

[0011] Embodiments of the laser welding method will be described in detail by non-limiting examples with reference to the accompanying drawings.

[0012] In the drawings:

[0013] Figure 1 A schematic layout of the laser welding method according to the present invention is shown,

[0014] Figure 2 A side view of a laser weld joint formed between an aluminum and a copper strip is shown, and

[0015] Figure 3 An enlarged cross-sectional view of Figure 2 the weld joint in the vertical direction is shown. DETAILED DESCRIPTION

[0016] Figure 1 An aluminum plate 1 and a copper plate 2 are shown, each having a substantially flat contact surface 3, 4. The surfaces 3, 4 are placed in contact relationship along an interface 5. The plates 1, 2 can have a thickness T of e.g. 1-10 mm, and can have a larger thickness, e.g. up to 20 mm or more.

[0017] A laser source 10 generates a laser beam 8, which is focused by optics 12 in a focal point 9 at a location of the interface 5 on the periphery 7 of the plates 3, 4.

[0018] In a test setup, a copper plate and an aluminum plate were placed in contact relationship according to the invention with their flat surfaces, each plate having a thickness of 3 mm. A laser welding apparatus of the type Trudisk 6001, sold by Trumpf GmbH, Germany, was used, with a laser power of 3000 W and a focal spot diameter of 0.17 mm, the laser being directed onto the periphery 7 of the stacked plates to melt the metal surfaces on each side of the interface 5.

[0019] The focal point 9 of the laser penetrates between the plates 1, 2 over a distance D of more than 5 mm, and away from the periphery 7 along the interface 5 for several centimeters.

[0020] Figure 2 An example of a weld joint 15 formed along the interface 5 of the aluminum plate 1 and the copper plate 2 over a length D which can be several centimeters or more is shown.

[0021] Figure 3 An enlarged cross-section of the weld joint 15 in the vertical direction is shown, forming a homogeneous alloy of copper and aluminum over a large surface area along the weld joint 15 and achieving a very strong bond.

Claims

1. Method of joining a first metal sheet (1) and a second metal sheet (2), each metal sheet having a substantially flat main surface (3, 4) which is the surface of the metal sheet having the smallest aspect ratio, the method comprising the steps of: - placing the first and second metal sheets with their main surfaces (3, 4) in contact relationship along an interface (5), the main surfaces being substantially parallel, the interface extending to a peripheral edge (7), - while the first metal sheet (1) and the second metal sheet (2) are in contact parallel relationship, irradiating a laser beam (8) in the direction of the interface (5) so that a focal point (9) is on the peripheral edge (7), and - moving the focal point (9) of the laser beam (8) along the interface (5) in a direction transverse to the peripheral edge (7) to a position at a distance D from the peripheral edge (7).

2. The method of claim 1, wherein, The first metal sheet (1) comprises aluminium and the second metal sheet (2) comprises copper.

3. The method of claim 1 or 2, wherein, The size of the focal point (9) of the laser beam (8) is between 0.01 mm and 0.5 mm and the distance D from the peripheral edge (7) is between 0.5 mm and 50 mm.

4. The method of claim 1 or 2, wherein, The power of the laser beam is at least 2500 W.

5. The method of claim 4, wherein, The power of the laser beam is at least 3000 W.

6. The method of claim 5, wherein, The power of the laser beam is at least 4000 W.

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