EA028399B1 - Method for laser welding of parts made of dissimilar metals - Google Patents

Abstract

The invention is related to a method of welding dissimilar metals by laser radiation and can be used, among others, in the fields of motorcar manufacture and mechanical engineering. The objective of the invention consists in higher welding speeds, an increase of ratio of weld depth to weld width, reduction of welded joint strength variation in different directions. The objective is attained by provision of a method for laser welding of dissimilar metals comprising laser radiation focusing on the more refractory metal at a distance from the abutting surface, wherein welding modes ensuring knife-like melting and weld cross-section configuration are previously determined, and in accordance with said determinations edge preparation is performed, then welding is carried out while focusing laser radiation at a distance from the abutting surface that provides melt bath adjoining to the butt.

Description

The invention relates to methods for welding dissimilar metals by laser radiation and can be used, inter alia, in the fields of automobile and mechanical engineering.

A known method of welding metal sheets of various thicknesses [1], in which metal plates are installed end-to-end and welded with a laser beam. During welding, the laser beam moves along a path that is offset relative to the joint towards a thick sheet. The offset value is 0.1 ... 0.4 mm from the junction of the sheets. In the laser welding process, at the first stage, the edge of the thicker sheet is melted, and the edge of the thin sheet serves as a cushion for the melt for a short time and can be used to press it into the melt, which reduces the requirements for the accuracy of cutting (fitting) the edges of the sheets to be welded.

This method cannot be used when welding sheets of dissimilar metals of the same thickness, since with a shift of the focus point from the weld, uneven heating of the weld zone occurs due to different heat removal conditions in the depth and on the surface of the welded sheets. This, as a rule, leads to overheating of individual zones of the weld, the formation of a non-optimal structure, the formation of pores and other defects that reduce the strength of the welded joint.

Closest to the claimed is a method of laser welding of parts of dissimilar metals [2], in which the butt joint plane is oblique tangentially to the segment of the heat affected zone of the weld, and the laser radiation is focused on a more refractory metal at a distance from the butt plane, while the angle the inclination of the plane of the butt joint and the focusing distance are calculated from the condition of evaporation of the low-melting metal and the metals are welded in conduction welding mode.

The disadvantage of the prototype is that when implementing the method, laser welding is carried out in the conductivity welding mode, which is characterized by reduced welding speeds, and the resulting seams have a small ratio of depth to width. In addition, the inclined plane of the weld can lead to different strengths of the welded joint in different directions.

The problem solved by the invention is to increase the welding speed, increase the ratio of depth to width of the weld, reduce the strength of the welded joint in different directions.

The problem is achieved in that in the method of laser welding of parts made of dissimilar metals, in which the laser radiation is focused on a more refractory metal at a distance from the butt surface, the welding modes that provide dagger penetration, the configuration of the weld in the cross section are determined on a sample of refractory metal, according to which the edges are cut, then welding is carried out, focusing the laser radiation at a distance from the butt surface, ensuring the adjoining bath asplava to the joint.

The invention is illustrated by the drawing, which shows the welding circuit.

When implementing the inventive method in a laser welding process in the dagger mode, the melt bath 1 is formed in the focus area of the laser beam 2 on the refractory metal 3. The melting bath is adjacent to the melting zone of the fusible metal 4. Due to the thermal conductivity, the fusible metal 4 is melted, partial mixing melt and during crystallization the formation of a durable weld. The configuration of the melt zone in the cross section under optimal conditions is straightforward in the central part with expansion in the lower and upper zones, which is associated with a deterioration in heat removal in these areas.

If the butt joint is not equidistant to the molten bath, in different zones of the welded joint of dissimilar metals there is a significant difference in thermal cycles, which reduces the quality of the welded joint. So, with the rectilinear shape of the joint and with its position corresponding to adjoining the melting zone in the central part, there is an overheating of the welded joint zones in the upper and lower parts (the overheating of the low-melting metal 4 is most severe), which can lead to defects in the weld in these zones, for example, increased porosity, increased stress, which can lead to the formation of cold and hot cracks. If the rectilinear joint is in the area adjacent to the bath 1 of the melt of the upper and lower parts, then the connection in the middle part will occur in the soldering mode of the liquid low-melting metal 4 to the solid refractory metal 3 or with minimal mixing of the melts. This leads to an increased gradient of properties in the joint zone and, as a consequence, the appearance of a high level of residual stresses, which, in turn, helps to reduce the strength of the welded joint or cracking.

When the focus point of the laser beam 2 is shifted by a distance of 5 from the junction of the metals being welded, made according to the proposed configuration, less than the claimed one, the melt of the low-melting metal 4 overheats, which leads to its intense evaporation, pore formation in the welded joint, and a decrease in its strength.

When the focus point of the laser beam is shifted by a distance of 5 from the junction of the metals being welded, made according to the proposed configuration, more than the claimed one, lack of fusion occurs, and when melting the more fusible metal 4, it is soldered to the refractory metal 3, which leads to a decrease in the joint strength or cracking .

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Examples

Welding was carried out according to the claimed method and the prototype method.

For butt welding, both methods used carbon steel samples Tm = 1490 ° C and a copper-nickel alloy Tm = 1200 ° C with a thickness of 2 mm and a size of 50x50 mm.

Welding was carried out by radiation of a 1 kW fiber laser (focal length of a tinting lens 60 mm, focal length of a focusing lens 150 mm).

When welding according to the claimed method, at the first stage, a selection was made of modes that ensure stable dagger penetration of refractory metal (carbon steel) under the condition that there are no defects; for this, samples of carbon steel were welded in various modes. Further, metallographic studies were performed to evaluate the size of the melt pool. The following mode parameters corresponded to the desired penetration zone: focus deepening 0.7 mm, power 1 kW, welding speed 1600 mm / min. In this welding mode, the following weld configuration was obtained: the width in the upper and lower parts of 0.8 mm, in the central part of 0.6 mm; the length of the central part of 0.6 mm, the upper and lower parts of 0.4 mm

Then, mechanically, the joints of the refractory and low-melting metals were cut in accordance with the obtained sizes, and the samples were welded.

Welding according to the prototype method was carried out in the following modes: focus deepening 8 mm (to achieve melting by conductivity on a fiber laser), power 1 kW, speed 500 mm / min. The angle of cutting (γ = 12 °) and the distance from the focus point to the joint (1 = 1 mm) are determined in accordance with the calculation method specified in the prototype method.

The strength of the joints welded by the method of the prototype and the claimed method, was determined at kink when clamping the sample in a vise and creating a bending force using a torque wrench.

The quality of the welded joint for the absence of pores and cracks was checked metallographically using a Micro 2000 microscope.

The test results are shown in the table.

No. Thickness samples The distance of the beam focusing point from the groove, mm Breaking force, N Speed welding m / min Weld quality one 2 a / 2 311 1600 The presence of pores 2 2 6 / 2-0.15 164 1600 The presence of pores 3 2 6/2 + 0.15 350 1600 Lack of defects 4 2 a / 2 + o.zo 73 1600 Partial non-fusion 5 2 Prototype method 347 500 Lack of defects

As can be seen from the table, the strength characteristics of the seams, expressed in effort to break the sample obtained by the present method, correspond to the characteristics of the seam obtained by the prototype method. In addition, the table shows the effect of maintaining the optimal distance from the focus point to the groove on the strength characteristics and nature of the defects. It is also seen from the processing modes that, with equal powers of the laser source, the welding speed at the specified thickness for the proposed method is 3.2 times higher in comparison with the prototype method. In this case, the width of the seam and the heat affected zone is significantly smaller. In addition, the claimed method provides a reduction in the strength of a welded joint in various directions.

Information sources.

1. MeFob o £ 1a> er- \ yMTd te! A1 §Be1§ Bautd LGGegep! Fukpezz, patent No. 5250783, I8, IPC 23K 26/00, published on October 5, 1993.

2. The patent, KI, MPK V 23K 26/40, 9/23, 33/00, published on 04/20/2011.

Claims (1)

A method of laser welding of parts made of dissimilar metals, in which the laser radiation is focused on a more refractory metal at a distance from the butt surface, characterized in that previously, on the specimen of the refractory metal, welding modes are determined that provide dagger penetration, the configuration of the weld in the cross section, in accordance with which perform the cutting of the edges, then carry out welding, focusing the laser radiation at a distance from the Central part of the cutting of the edges, equal to half the sum of the diameter of the laser learning on the surface of the workpiece and the width of the Central part of the seam, defined on a sample of refractory material.