RU2123918C1 - Method for laser welding of thin-sheet cylindrical products and apparatus for performing the same - Google Patents

Abstract

FIELD: production of cans, aerosol bottles, different-designation tubes and so on. SUBSTANCE: laser welding of materials is realized in range of thickness with deep fusion. As welded cylindrical blank is rolled out between rolls until necessary thickness values. Deep-fusion laser welding allows to eliminate incomplete fusion, undercuts, burnouts, drop like bulges that are typical for laser welding of thin-wall products. It enhances quality of welded joint and operational reliability of products. Article is finally rolled out by means of rolls and mandrel. It allows to use tube rotation around its own axis simultaneously for several processes such as tube shaping, welding, finish rolling out, cutting by separate portions. EFFECT: enhanced quality of welded joint. 4 cl, 2 dwg, 2 ex

Description

 The proposed method, as well as a device for its implementation, can be used for laser welding of products for various purposes from sheet materials in the food, chemical, electronic and radio industries, as well as in the production of pipes.

 In the vast majority of cases, laser welding is divided into two directions: laser welding of flat sheet materials - mainly products of the electronic and radio engineering industries and laser welding of cylindrical products - food, chemical, industrial products: aerosol cans, cans, etc., as well as pipes for various purposes.

Depending on the subsequent specific application, the thickness of the materials to be welded can vary widely. The general technological cycle of creating cylindrical welded products is as follows (see [1], p. 29):
FIG. 1.

 The notation in FIG. one.

P ₁ , P ₂ , ... P ₃ - sequential rolling of the material in rolling mills to operational thicknesses;
F - the process of forming a cylindrical workpiece;
L _with - laser welding process;
P - the process of coating the product with food, protective or other coatings (if necessary);
R _l - the process of cutting a workpiece of cylindrical shape to the required length.

 Steel ingots (castings) are repeatedly rolled in rolling mills. In this case, the thickness of the disc is gradually reduced. After reaching the required operational thicknesses, the resulting sheets (tin) are cut into the required sizes and stored in a bundle.

 There are two fundamentally different methods for manufacturing pipes.

 1. Longitudinal pipes. The technological process for the production of such pipes is as follows: sheets with an operational thickness are fed from the bundle to production, where they are molded with special devices - rollers into cylindrical billets and welded with a longitudinal seam (see [1], p. 198).

 2. Spiral pipes. The sheet is rolled to a predetermined thickness, cut into a tape, molded into a pipe, welded, and then pipes are cut to a predetermined length (see [1], pp. 206–207).

 A known method and device for laser welding of metal can cases made by running rectangular plates with two joined edges, chamfers and clearance [2]. When welding, the laser beam is directed into the gap. To improve the quality of the weld, the body is compressed on both sides by a device with a certain force and is connected without a gap.

 A known installation for laser welding of longitudinal seams of cans of steel with or without coating, which uses two-sided welding [3]. The use of special guiding devices and spring grips mounted on a caterpillar conveyor allows to achieve high precision welding of butt joints and thereby improve the quality of the welded joint.

 A known method of laser butt welding of longitudinal seams of tube blanks for can cases [4], wherein the abutting edges of the parts are assembled using special equipment at a small angle so that the ends of the edges touch each other only with their inner surface and become open towards the laser beam. This arrangement of the edges provides a more stable melting of the metal and the formation of the weld.

All of the above methods of device and installation for them have the main drawback - the formation of low-quality welded joints, which leads to [5]:
1. Unstable weld formation.

 2. To lack of fusion, undercuts, burnouts.

 3. Teardrop-shaped formations on the surface of the seam.

 4. Buckling the seam.

 The poor quality of the welded joint does not allow widespread use of the most productive welding method - laser (welding speed 30-60 m / min) in the production of mass-produced products, for example, cans or spray cans, which also work under excessive internal pressure, which further worsens the prospect of using laser welding.

 The main reason for the poor-quality formation of a welded joint is that welding is performed according to the method of welding materials of small thicknesses (see [6], p. 37, Fig. 2.1 "Classification of laser welding methods" and p. 110), i.e., with a thickness the materials being welded is less than 1 mm, which is caused by the fields of application, at a high welding speed (30-60 m / min). As a result, during the welding process, high temperature gradients arise of heating and cooling the processed material, as well as using thin-walled materials (in the case of food products h = 0.08 - 0.25 mm), at which the volume of the weld pool is very small and necessary for high-quality formation the weld processes in the weld pool - melting, mixing, crystallization, cooling do not occur sufficiently.

 Another disadvantage of analogues is the high reflection coefficient of laser radiation from the surface of the material being welded, because in the vast majority of cases (food, chemical, electronic industries) we are talking about welding materials with a well-worked surface (tin), and also due to the small thickness of the material. A large reflection of radiation from the surface leads to a low efficiency of the welding process itself.

 The third disadvantage of analogues is the fact that in the welding process a longitudinal seam is formed. Meanwhile, it is known that a spiral seam has several advantages over a straight seam [1], p. 206.

 1. The use of a cheaper billet with the same pipe diameter.

 2. Spiral tubes have increased strength, because a spiral seam at the same working pressure has a lower specific load than a longitudinal one.

 3. Pipes with a spiral seam are characterized by greater rigidity than longitudinal welds.

 The fourth drawback of analogues is the need for a very fine fit of the welded ends both in height and in the gap between them (tolerance - hundredths of a millimeter).

 Taken as a prototype method and device for its implementation, described in [8] US patent N 4830.258. dated May 16, 1989, class B 23 K 26/00, 26/08, is intended for the manufacture of closed-section products from sheet blanks. The method involves feeding pre-rolled sheet blanks to operational thicknesses into the forming zone, where it is formed in cylinders in a cylindrical shape, after which a special device compresses the edges. Next, the junction is heated by laser radiation to a temperature higher than the forging temperature and get a strong connection. After that, the cylinder to be welded is calibrated with an enveloping ring.

 These method and device for it allow us to solve the problem of accurate fitting of the welded ends in height and the gap between them. However, all the disadvantages associated with the formation of a poor-quality welded joint due to welding in the field of small thicknesses, high reflection coefficient, and also the formation of a longitudinal seam remain.

 The problems solved by the invention are to improve the quality of the welded joint, increase the efficiency of the manufacturing process of a thin-walled product, as well as increase the productivity of the manufacturing process of a thin-walled product.

 In the proposed method and device for its implementation, in which a pre-rolled sheet material is fed into the forming zone, where it is formed into cylindrical rolls, then it is welded with a laser beam, then coated and cut into pieces with specific sizes, the sheet material is fed to formation in a spiral, after which it is welded in the mode of rough penetration, and then it is rolled with a mandrel and rolls to the thickness required during operation. Then it is cut with a laser cutting head, making reciprocating movements. The use of the deep penetration mode (the deep penetration mode (method) was in the Classification of laser welding methods. Fig. 21, p. 36 and described in & 3.4 p. 129 [6]) in comparison with the method of welding of materials of small thickness used in the prototype and analogues in combination with subsequent rolling to operational thicknesses, as well as the use of a spiral seam, they can dramatically improve the quality of the welded joint and the pipe's operational characteristics, since in this case the thickness of the materials being welded is significantly greater than the operational The thicknesses at which welding is performed in the prototype and analogues, the weld pool has a large volume and all the processes necessary for the high-quality formation of the seam have time to occur sufficiently, while the rotation of the pipe around its axis necessary for the processes of forming laser welding and laser cutting is created a mechanism (rolls and mandrels), rolling the pipe to operating thicknesses. These method and device can significantly simplify the process of accurate fitting of the cutting edges.

 In the proposed method, the general technological cycle for creating cylindrical welded products is as follows (Fig. 2).

Steel billets are repeatedly rolled in rolling mills (P ₁ , P ₂ ... P _hl ) to thicknesses where the deep penetration mode is realized. After this, pipe forming (F) occurs, followed by laser welding in the deep penetration mode (L _s ). Next, the pipe is rolled to operating thicknesses (P _e ), after which it is covered with coatings (P), if necessary, and cut into parts (P _l ).

 A device for implementing the above method is as follows. The sheet (tape) 1 is fed into the welding zone, where the shaping process and laser welding of the pipe by the laser head 2 take place, after which the pipe is rolled by rolls 3 and mandrel 4 to the operating thickness. Next, the pipe 5 is cut by a laser head 6 into parts.

 Technical results obtained by carrying out the invention.

 1. The quality of the welded joint is improved and thereby the operational characteristics of the products are improved.

 2. Increases the efficiency of the laser welding process.

 3. There is no need for subsequent coating of the weld area (for example, protective food coatings).

 4. The design of the pipe making mechanism is simplified.

 Examples of specific applications of the method.

 Example 1. For the production of cans in the food industry used tin with a thickness of 0.08 - 0.25 mm The diameter of radiation focused for welding is 0.2 - 0.4 mm. The material required for welding is rolled to a thickness of 1 mm and formed into a cylindrical workpiece. After this, the welding process of the longitudinal seam is performed. Then the workpiece is rolled to the required thicknesses of 0.08 - 0.025 mm and covered with a protective coating.

 Example 2 (Fig. 3). Device for the manufacture of welded pipes. A steel strip 1 with a thickness sufficient for laser welding with deep penetration is fed into the welding zone, where it is formed and welded using a laser beam 2 with its side surface to the end surface of the pipe. During the welding process, the laser beam remains stationary. Thus, a spiral tube is obtained. After welding, the pipe is fed into the molding rolls 3, in the center of which a mandrel 4 is located. Rotating between the rolls, the pipe simultaneously moves forward. At the same time, its thickness decreases to the necessary. The mandrel gives the inner surface of the pipe a circular cross section and a smooth surface. At a certain distance from the rolls, the continuous pipe is cut into separate pieces. Thus, the proposed method allows you to weld a thin-walled tube with a laser beam with high radiation quality.

Bibliography
1. Production of steel pipes. Druyanuu V.M., Krupman Yu.G., Lyakhovetsky L.S. et al. M.: Metallurgy, 1989, pp. 102 - 108.

 2. The method and device for laser welding of metal cans. Patent application. France, N 2597378, author of Cornaud Emballage, 1986. Patent Research Report "Laser Welding of Tin", VTsPU, Rostov Branch. 1992

 3. Installation for laser welding of longitudinal seams of cans. US patent N 4713519. Applicant: Hoesch.

 4. Laser butt welding method for longitudinal seams of tube blanks for can bodies, EPO, application N 02111973, Applicant "Elpatronic", Switzerland.

 5. High Speed Laser Welding Discontinuites, Charles E. Albright and Shichan Chiiang, p. 207 - 213, Departament of Welding Egineering, Ohio State University, Columbus, Ohio / Proceeding of the 7th International Congress on Applications of Laser and Electrooptics ICALEO'88 30 Okt.-4 Nov., 1988, Santa Clara, CA, USA.

 6. Laser equipment and technology. In 7 kn. Prince 5, Laser welding of metals: Textbook. manual for universities / A.G. Grigoryants, I.N. Shiganov. Ed. A. G. Grigoryants, - M: Higher School, 1988, p. 38, 129 - 146.

 7. Obedient metal. E.V. Kuznetsov. M: Metallurgy, 1988, pp. 79 - 83.

 8. US patent N 4830258 dated May 16, 1989 MKI B 23 K 26/00, B 23 K 26/08.

Claims (4)

 1. A method of laser welding of cylindrical sheet products in which a pre-rolled sheet material is formed in rolls into a cylindrical billet, laser-welded, coated and cut into parts with a certain length, characterized in that the sheet material is rolled to a thickness greater than the operational thickness, laser welding is carried out in the deep penetration mode, and after welding roll the pipe in rolls to the operational thickness and then cut it into pieces, and the formation in a cylindrical billet, welding, rolling and cutting the pipe is performed in the process of rotating it around its own axis, which it provides the mechanism for rolling the pipe.  2. The method according to claim 1, characterized in that the pipe is cut into parts by a laser beam, while the laser cutting head is reciprocated parallel to the longitudinal axis of the pipe by a distance equal to the length of the pipe being cut.  3. The method according to claim 1, characterized in that the sheet material during shaping and welding of the pipe is fed in a spiral.  4. A device for welding thin-sheet products of a cylindrical shape, containing rolls for forming a pipe, a welding laser head and a mechanism for cutting it into parts, characterized in that it is equipped with a mechanism for rolling the pipe to operational thicknesses, consisting of rolls and a mandrel and placed between the welding head and a mechanism for cutting pipes.

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