KR900003081B1 - Process for the butl-welding of especially deepdrawable steel sheets or steel strips galvanized at least on one side - Google Patents

Abstract

A butt welding process of deep-drawing steel sheets or strips with rectangular cut edges and with at least a zinc coating on one side is based on the use of a laser beam. The cut edges should have a longitudinal ripple of not more than 0.04 mm and are kept in contact along these edges. The laser beam which has a focal spot of max. 0.2mm diameter fuses these edges together without reducing the thickness at the joint noticeably.

Description

Butt welding of dip-drawn steel sheets or strips galvanized on at least one side

1 and 2 are cross-sectional views of butt-welding apparatus showing an embodiment of the invention.

* Explanation of symbols for main parts of the drawings

1,2: plate 3: base

4: support surface 5: long groove

7: welded joint 8, 9: clamping jaw (clamping jaw)

10-13: channel 14: laser gun

15: laser beam

The present invention relates to a method for butt welding a deep-drawable steel sheet or steel sheet galvanized on at least one side and having a substantially rectangular cut surface such that the welding seam is not corroded by a laser beam. will be.

Manufacturers of galvanized sheets often require plates with a width that is not designed for special purposes, such as molded plates produced by deep drawing, which are not currently designed in galvanizing plants available. In this case, they have used two or more plates by butt welding. If the plate is manufactured by a normal butt welding method, a welded joint having the same plane as the plate can be obtained so as to be suitable for the following process (Deep drawing process), and no corrosion preventing means is provided on the welded joint. It is not necessary to rework the welded joint. In particular, the thickness of the welded joint obtained by the conventional method is not uniform.

Such plates are not suitable for forming by direct dip drawing or pressurizing because the plates produced by such conventional methods cannot be carried out with damage to the tool or with the precision required for the molding operation.

One of the known methods for butt welding a galvanized sheet is a method of forming a welded joint by applying a filler (welding wire) by an electron beam. This method required the welding seam to be flattened by grinding means in order to obtain a quality suitable for subsequent processing. In addition, in the electron beam welding, zinc is evaporated due to the high welding temperature, so that the corrosion is not prevented in the welded joint and the relatively large area adjacent to the welded joint. Therefore, it is necessary to apply anti-corrosion coating not only to the welded joint but also to the part where zinc is peeled off after welding. This type of treatment is simple but does not satisfy manufacturers who need a metal plate that is corrosion resistant and suitable for deep drawing throughout the entire surface.

Another well-known method of butt-welding galvanized plates or pieces by laser beam is to place the rectangular cut surfaces at a constant distance from each other so that a continuous weld gap is formed and the weld gap is melted additive (welding wire). As a charging method (see EP-A 0,098,306 and EP-A 0,117,751). This method has the feature that the laser beam can be projected more precisely than the butt welding by the electron beam. Thus, in this method the laser beam can only be used directly on welding wires having a diameter larger or smaller than the weld joint. As a result, the plates to be welded to each other are melted only by the heat of welding of the molten weld wire. The disadvantage of this method is that the welded joints which are not corrosion-proof are formed considerably wide, so the plate and the welded joints should be flattened by mechanical surface treatment, and then the corrosion-preventive treatment should be performed.

SUMMARY OF THE INVENTION The present invention aims to provide a deep-drawable plate or body which is wider at least at a minimum cost and in particular flat and corrosion-protected from at least two galvanized plate or pieces by butt welding.

In a butt welding method, in which a welded joint is prevented from corrosion by a laser beam on a steel plate or steel plate having a galvanized plate on one side and having a substantially rectangular cross section, the purpose is to provide a corrugation of up to 0.04 mm in the longitudinal direction on the steel plate or steel plate. This is achieved by making the formed cut faces and moving the steel sheet or steel piece so that these cut faces are in mutual contact with each other by means of a laser beam having a diameter of 0.2 mm or less and a focus covering the cut face.

The method according to the present invention not only provides the plate body and the substantially flat welded seam directly but also provides the welded seam which is prevented from corrosion. Therefore, it is not necessary to rework the welded joint after welding to make it flat or to prevent corrosion. By using a laser beam, direct heat is confined to very narrow areas, leaving only zinc-free zones in very narrow areas where corrosion is prevented. This is due to the long-term protective effects known to be caused by zinc in the areas adjacent to both sides. Throughout the entire length, the welded joint at some points has a maximum width of only 2 × 0.04 mm, so that the method of the present invention can be performed without additives (filler wire). The amount of material needed to fill the remaining tiny holes and provided from the adjoining portion of the plate does not reduce the thickness of the steel sheet even ten times thicker than the gap. This means that the sheet can be shaped into a deep drawing or pressurized shape without mechanical fabrication for further processing. As regards the use of the plate, it has no disadvantages in terms of corrosion protection compared to the plate which prevents corrosion by uniform zinc coating. This is because of the long-term protective effect exerted by zinc on the zinc-activated welded joint. An advantage of the method according to the invention for producers is that they produce a wide range of plates or pieces from the plates or pieces obtained from the usual galvanized sheet they hold without compromising the quality at the weld seam. It can be done.

In an embodiment of the present invention, the plate or piece is cooled on both sides of the welded joint so that the effect of heat is kept as low as possible on the zinc layer in the cross section of the welded joint. Cooling can be cooled by blowing a cooling gas, for example. In particular, a good thermal protection effect can be achieved by fixing together the plates to be welded with a clamping jaw made of a thermally conductive material such as copper and cooled by circulating a cooling fluid therein if necessary. . In order to cool the surface of the plate well and to flatten it, it is advantageous to let the clamping jaws contact the plate at a position 5-10 mm away from the weld gap. In this way, the plate melts only in the focal region of the laser beam, and the molten liquid solidifies immediately after the laser beam is out of focus.

It is particularly important to cool the bottom of the plate well because it is necessary to prevent the melt from flowing out of the weld joint. The outflow of the melt can be effectively prevented by cooling the parts of the clamping jaws on the bottom of the plate particularly well.

It has proved to be beneficial to use a clamping mechanism supporting the weld and having a deep groove near the weld under the plate to be welded together to allow the inert gas to be blown so that the weld seam remains in the inert gas stream. This not only prevents oxidation of the weldment, but also helps cooling the bottom of the plate. Moreover, the excess gas pressure in the grooves prevents the melt from flowing out of the weld seam.

This welding method may be used for plates or pieces having the same or different thicknesses. When welding plates or pieces of different thickness, plates or pieces with different thicknesses, in particular thickness differences between 0.5 mm and 3.0 mm in the cutout of the plate or piece, are held in the following relative positions during welding. It is advantageous. That is, the front face of the plate or piece facing the laser beam or the back surface of the laser beam or the back plate of the laser beam is placed on substantially the same plane, or the thick plate or piece is placed on at least one edge of the front or back side of the cutout. To reduce the thickness to a thinner.

When described in more detail with reference to the accompanying drawings an embodiment of the present invention.

The method according to the invention is suitable for butt welding thin metal plates, in particular metal plates with a thickness in the range of 0.5 mm to 1.5 mm. Substantially rectangular cuts are formed to have a valley of 0.04 mm or less through the entire length. When the plates are contacted to each other for butt welding, the distance between the plates at each point may be up to 0.05 mm.

In the embodiment of FIG. 1, the plates 1, 2 to be butt welded to each other are placed in contact with each other on a base 3 having a planar support surface 4. A long groove 5 which is open toward the support surface 4 is installed in the base 3. Substantially rectangular ends (weld joints) 7 of the plates 1, 2 to be welded to each other lie at the site of the long groove 5. The plate bodies 1 and 2 are pressed onto the base 3 by means of clamping jaws 8 and 9. The bases 3 and the cranking jaws 8, 9 are provided with channels 10-13 through which the coolant passes. The inert gas is introduced into the long groove 5 closed at the top by the plate bodies 1 and 2 to cool, and generates a constant excess pressure in the long groove 5.

A laser gun 14 having a laser beam 15 directed to the welded portion is installed to be movable in the longitudinal direction of the welded portion 7. The laser beam 15 has a focus of a maximum diameter of 0.2 mm. This focal point is directed above the center line of the weld seam 7.

The traveling speed of the laser gun 14 and the welding energy applied to the welded joint after passing over the welded joint 7 depend, among other things, on the thickness of the plates 1 and 2. For example, in the case of a 0.8 mm thick galvanized steel sheet, the distance between the cooled fuselage clamping jaws 8 and 9 and the welded joint 7 is 3 mm and the focal diameter of the laser beam is 0.2 mm or less. Good results can be obtained when the traveling speed of the laser gun 14 passing over the weld joint is 2 m / min. The energy applied at this time is about 375 J / cm. The welded joint obtained in this way has no defects in corrosion protection or mechanical properties (elasticity, strength), so that the plate can be formed without any difficulty even in the part of the welded joint.

The embodiment of FIG. 2 differs from the embodiment of FIG. 1 only in the design of the base. In this case, as in the case of FIG. 1, the base is not in the form of a bridge but divided into two, and each part is fixed to the support by screws. The purpose of forming the long groove into the upper and lower beam type is to prevent the splash from being deflected toward the welded joint.

Claims (8)

A method of butt welding a steel sheet or steel sheet galvanized on at least one side and having a substantially rectangular cut portion by a laser beam, wherein the cut portion having a valley of 0.04 mm or less in the longitudinal direction is formed on a plate or piece and the plate A method of butt welding of a steel sheet or steel sheet, characterized in that the cutting parts are brought into contact with each other and then welded to prevent corrosion of the welded joint by a laser beam having a diameter of 0.2 mm or less and having a focus covering the cutting parts. 2. A portion according to claim 1, wherein, while the plates or pieces to be welded to each other are welded, the plates or pieces are cooled through both sides and the entire length of the weld seam and the portion affected by the welding has a width of 1 mm or less. How to. The method of claim 1 wherein the plate or piece is cooled on both sides. 2. A method according to claim 1, wherein the rear face (bottom face) of the weld seam is maintained in the protective gas stream. 2. A method according to claim 1, wherein the backside (bottom) of the weld joint is subjected to excessive pressure. 2. A method according to claim 1, wherein the plates to be welded to each other are held in position by a cooled clamping jaw immediately adjacent to the weld joint during welding. 2. A method according to claim 1, wherein the plates or pieces having different thicknesses are positioned such that the front of the plate or piece facing the laser beam or the back of the laser beam and the back plate or piece are in the same plane. 2. A method according to claim 1, wherein the thick plate or piece of plate or piece having a different thickness is cut by thinning at least one edge of the front or back side adjacent to the cut portion to reduce the thickness.

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