Device for and method of establishing joints by means of laser b

Electric heating – Metal heating – By arc

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21912174, B23K 2600, B23K 2606

Patent

active

049122975

DESCRIPTION:

BRIEF SUMMARY
The invention concerns a device for establishing joints by means of laser beams, especially for welding edges, wherein the beam extends essentially parallel to the plane of the joint and perpendicular to the line of the joint.
A device of this type is known from U.S. Pat. No. 4,471,204. Two edges are positioned together to create a tapering gap. The laser beam is directed toward the gap in such a way that it will be reflected into the gap from the surfaces of the facing edges. Most of the radiation energy is absorbed in this process and accordingly does not penetrate deep enough into the tapering gap. Compression rollers are accordingly necessary to force the molten surfaces together and establish the joint. The compression leaves molten material on both sides of the gap. The drawbacks to this type of welded seam include for example its lack of uniformity and a potential for pores.
One object of the invention is to improve a device of the type initially described to the extent that the energy will be absorbed nearer the joint.
This object is attained in accordance with the invention by an improvement wherein the laser beam is polarized preponderantly parallel to the plant of the joint gap.
It is significant to the invention that the laser beam is linearly polarized parallel to the plane of the joint, meaning that no circularly polarized radiation is employed. The result is that the beam will be optimally reflected from the surfaces that are to be joined, with minimal energy being absorbed, that is. It is practically only at the joint itself that absorption is sufficient to melt the material. It is unnecessary to exert any essential transverse pressure to adequately weld the surfaces that are to be bonded together. The result will be optimal when the laser beam is polarized strictly parallel to the plane of the joint.
It is practical for the laser beam to be constructed or focused across the gap in the form of streaks that parallel the gap. The first point of reflection will accordingly be as deep inside the gap as possible and in the vicinity of the point of junction. Shaping the beam in this way will also help the beam impact in the form of a streak, maintaining the angle of the incidence as wide as possible and hence the reflection of the laser beam, which is polarized parallel to the plane of the gap as high as possible and free of absorption. The beam is shaped by focusing or, without focusing, by adjusting the cross-section of the beam to be geometry of the joint, by reducing the cross-section for example. The beam is shaped or focused by systems of mutually adapted mirrors or lenses, especially cylindrical, parabolic, or paraboloid.
The laser beam is, at the point of junction, slightly larger or smaller than the depth of the gap. If the laser beam is larger than the depth of the gap, the excess component of the beam will strike behind the point of junction at the edges of the upper and lower surface that are to be bonded. These areas will be in accordance with the entering energy be melted and evened out, improving the weld at this in itself critical region. Furthermore, the particular direction of beam polarization employed will result in optimal energy input at the upper and lower surfaces at the edges of the strip. If the laser beam is smaller than the depth of the gap, it will be possible to irradiate only a certain portion of the depth. It will accordingly be possible for example to join together two laminations in the two parts of the joint that are adjacent and at the same depth, with the beam having no effect on laminations above or below the laminations being bonded. The higher and lower laminations can then if necessary be joined together by another beam or by other means.
When the laser beam encloses the mean perpendicular to the line of the joint, the point of junction on both sides of the gap will be improved in the aforesaid sense when the beam is slightly larger than the depth of the gap.
The point of junction can additionally be heated from one or both sides of the gap with one or mor

REFERENCES:
patent: 4645256 (1987-03-01), Minamida et al.
C. M. Banas, Laser Materials Processing, Proceedings of the 5th Internatil Congress on Applications of Laser and Electro-Optics Nov. 10-13, 1986, pp. 97-104.

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