DE112006001196B4 - Method and device for thermal joining of materials with refractory oxide surfaces - Google Patents

Abstract

A method for the thermal joining of materials (7, 8) in a joint gap (5), at least one first material (7) having an oxide layer on its surface at a joint, comprising the following steps: - providing a pulsed laser beam (4); - near the surface heating of the first material (7) at the joint by irradiation with the laser beam (4), whereby the heat input caused by the laser beam is controlled so that there is no formation of a needle hole in the first material (7), and the Laser beam (4) is directed into the joint gap (5) between the materials to be joined in such a way that it strikes the first material (7) in a laterally displaced manner, as a result of which a partial reflection (9) of the laser beam (9) on the side walls of the joint gap (5) 4) takes place, whereby the laser beam (4) is passed on in order to thermally destroy the oxide layer adhering to the side walls of the joint gap (5); - Provision of a regulated arc (6); - Melting the to ...

Description

The invention relates to a method and a device for the thermal joining of materials with at least one refractory oxide surface using a controlled short arc.

Methods for thermal joining of the same or different materials are well known in the art. However, in order to meet the increased demands on the quality and quantity of the thermal joining processes resulting from the ever increasing application needs, individual technological processes of these joining methods are combined with each other, whereby conventional arc and innovative laser beam methods are used and developed more and more frequently. This trend is due to the fact that high-power laser sources have been available for industrial use for a few years now. Until then, their safety, continuity and lifetime were not always guaranteed.

The known methods are combined with one another in order to be able to exploit their respective advantages in a process-oriented manner. On the one hand, the laser beam offers the possibility of achieving a high depth-to-width ratio and thus also of welding thicker sheet metal thicknesses in a short time. On the other hand, the tolerance in laser beam welding compared to geometric variations of the plate assemblies and offset is very low. Large gaps can be bridged only to a limited extent, for example, with the laser beam.

In contrast, the arc is characterized by wider melt baths, even if the achievable welding speed is very low.

Merging both methods combines the advantages and minimizes the disadvantages. In practice, both arc (or plasma) and laser beam are directed to the same processing point. The laser beam (which is positioned in the welding direction in front of the arc) creates the necessary stitch hole, while the arc (or plasma) provides for a wide melt pool and thus gap bridgeability.

For the surface coating, the combination of these methods is already known, with the focus here is the goal of improved energy management by preheating the base material and the filler material.

From the JP 2004298903 For example, a device for arc welding is known, which is used for welding galvanized steels with non-galvanized steels. For example, steels can be provided with a low-melting metallic coating for reasons of corrosion. As a rule, zinc is used, which has a melting temperature of 420 ° C and an evaporation temperature of 907 ° C. During welding, zinc evaporation leads to process irregularities that are detrimental to the result. In order to carry out a trouble-free welding process, the zinc coating is removed before the actual arc welding process with a strongly defocused laser radiation with low power. A brief action of the laser beam is not required in this solution, since the zinc layer melts far in front of the base material.

The JP 2002 331373 A describes a method of arc welding aluminum, which also allows stable welding when the aluminum alloy is coated with an oxide layer. The torch is preceded by a high power CO ₂ laser to destroy the oxide layer. This is separated from the welding wire by an insulating wall to prevent mutual interference.

The JP 10225770 relates to a device for welding an anodized component, in which a leading laser removes the anodized layer. The removal of the anodized layer, which has a significantly greater thickness than an oxide layer, is carried out with the aim of increasing the stability of an arc process. The document can not be found details of the arc method used. In addition, there are no indications as to whether surface areas are melted in the previously known method, which is not absolutely necessary for a subsequent welding operation.

The thermal joining of mixed compounds made of steel and aluminum as well as cladding on materials with a firmly adhering oxide layer is currently only with great effort or not possible because steel and aluminum form on cooling from the melt intermetallic phases, which contribute to the cracking and unusability of Lead component.

From the prior art, a method is known in which the steel is positioned to the laser beam side and heated until the underlying aluminum melts by heat conduction and a suitable combination of both materials can be produced by means of suitable flux.

In addition, methods for thermal joining of aluminum and steel are known in which a compatible filler material for both materials is used. In particular, are suitable zinc based alloys because they do not form intermetallic phases with aluminum and steel. However, in this process, the low melting and boiling temperature of these zinc alloys is detrimental. It quickly comes to an overheating of the melt, combined with a strong oxidation (seam appearance), and their evaporation.

To avoid this disadvantage, methods have been developed in which the arc burns only for a short time and thus the energy input into the materials to be joined is significantly minimized. However, it is problematic here that although the so-called "cold arc" produces a molten bath, the flow of the melt into the gap between the materials to be joined due to the existing oxide layer on the aluminum which has not been molten is made more difficult. In addition, the solder seam thus produced has an overhang, which requires a subsequent processing (finishing in the field of view).

To avoid these disadvantages, fluxes are used, for example, which destroy the oxide skin, favor a flow of the melt and thus give rise to an attractive seam. However, the use of flux is not always desirable in mass production.

The object of the present invention is therefore to propose a method and a device of the type described at the outset, with which it is possible to overcome the listed disadvantages and to provide a cost-effective method for thermal joining of materials, of which at least one has a refractory oxide-bearing surface , which meets the requirements in quality and quantity of modern mass production.

According to the invention, the solution of this problem succeeds with the features of the first and fourth claims.

For thermal joining of materials with at least one refractory surface covered with oxide, a controlled short arc is thus used by the device according to the invention. In the region of the joint or weld, the adhering oxide topcoat is destroyed with a pulsed laser prior to melting the materials to be joined. For this purpose, a laser with average power (100-500 W) is used, which heats the oxidized surface only briefly, so that it does not come to the formation of a stitch hole.

Advantageous embodiments are specified in the subclaims.

In order to bond materials with a firmly adhering oxide covering layer (eg aluminum) by means of thermal joining processes or otherwise to thermally process them (eg build-up welding or coating), this firmly adhering oxide covering layer must be destroyed. Only then can a metallurgical connection of these materials take place. However, it must be taken into account that the thermal load is as low as possible, so that a low mixing of these materials can be ensured.

Therefore, according to the invention, a controlled short arc (eg ColdArc) is combined with a pulsed laser. The leading laser thermally destroys the oxide layer by a small surface heat input, while the trailing low-heat short arc creates the molten bath or melt layer. In contrast to the known from the prior art method, the laser power is to be selected so that it does not come to the formation of a stitch hole, but only for short-term heating of the surface (average power range 100-500 W). Due to the multi-reflection of the laser beam in the gap between the surfaces to be joined, the oxide layer is destroyed to the depth, so that a continuous connection is made possible.

The offset between laser and arc is at least half of the nozzle diameter, so that an active influence of the arc by the laser does not occur. The inclination of the laser beam to the arc or gap is variable in the range between 0 ° and 80 °, wherein it should impinge laterally displaced on the material with the adherent high-melting oxide topcoat.

Further advantages, details and developments will become apparent from the following description of a preferred embodiment of the invention, with reference to the drawings. Show it:

1 a schematic diagram of a device according to the invention in a side view;

2 a detailed view of the device according to the invention in a perspective view.

Based on 1 and 2 , in which a device for the thermal joining of materials with high-melting surface oxide surfaces is shown in principle, the most important features of this device are explained below. At the same time, the process steps that are performed during the operation of this device to perform the thermal joining of materials.

The device comprises a laser beam generating means 1 and an arc generating means 2 , To form a weld or a flat bonding layer, these two means are moved together, as by a movement arrow 3 is symbolized. During the welding process, the distance of the laser beam generating means 1 to the arc generating means 2 are not normally changed unless this is required due to structural conditions on the workpiece to be welded or to change the angle of incidence of the laser beam in order to achieve the desired processing points. The advantages of an angular change are described below.

The laser beam generating means 1 throws a laser beam 4 on a weld gap 5 , In this case, a pulsed laser beam is used, which is dimensioned in terms of its performance so that the oxide layer adhering to the material surface is thermally destroyed, without resulting in a complete material liquefaction in the entire material thickness. The laser beam penetrates only in a superficial region of the material and generates there a targeted heat input. A stitch hole should just not be formed in the workpiece by the laser beam.

The laser beam 4 or its focal spot rushes during the welding process an arc 6 preceded by the arc generating means 2 along the weld gap 5 is produced. Preferably, a controlled short arc is formed. The laser beam 4 is positioned so that only a small distance to the arc 6 but no laser radiation into the arc 6 incident. In this way, the actual welding process is performed by the short arc, without laser power affects the welding process.

In 2 For simplicity, only the laser beam generating means is used 1 upcoming laser beam 4 shown as he on the weld gap 5 incident. The weld can be between a first material 7 and a second material 8th be formed, wherein at least the first material 7 a metallic material to which adheres a refractory oxide-bearing surface. The second material 8th may also have an oxide surface or another material, such as steel. Due to the angled impact of the laser beam on the oxide surface, it occurs in the weld gap 5 to a reflection of the laser beam between the two materials 7 . 8th done several times and by a reflection arrow 9 is symbolized. In this way, the laser beam is deep in the weld gap 5 led in, so that even in the deeper areas, the thermal destruction of the oxide layer takes place.

The in 1 drawn angles α between the beam direction of the laser beam generating means 1 and the beam direction of the arc generating means 2 is preferably variable to suit the machining conditions of different materials and surface shapes. The angle α is between 0 ° and 80 °.

By the change in the angle of the laser beam direction can also be made to adapt to the reflectivity of the oxide surface. In particular, if a deeper penetration into the weld gap is desired, the angle of incidence must be chosen so that a part of the laser radiation thermally destroyed the oxide layer at the point of impact and a sufficiently large part of the laser radiation is reflected for forwarding to deeper gap sections.

The inclination of the laser beam is thus variable in the double sense, on the one hand relative to the arc between 0 ° and 80 ° and on the other hand to the joint gap between 0 ° and 80 °.

LIST OF REFERENCE NUMBERS

1

Laser beam generation means

2

Arc generating means

3

movement arrow

4

laser beam

5

weld gap

6

Electric arc

7

first material

8th

second material

9

reflection arrow

Claims (7)

Method for thermal joining of materials ( 7 . 8th ) in a joint gap ( 5 ), wherein at least one first material ( 7 ) has an oxide layer on its surface at a joint, comprising the following steps: - providing a pulsed laser beam ( 4 ); - near-surface heating of the first material ( 7 ) at the joint by irradiation with the laser beam ( 4 ), wherein the heat input caused by the laser beam is controlled such that it does not lead to the formation of a puncture hole in the first material ( 7 ), and wherein the laser beam ( 4 ) so in the joint gap ( 5 ) is directed between the materials to be joined, that it is based on the first material ( 7 ) laterally displaced, causing the Side walls of the joining gap ( 5 ) a partial reflection ( 9 ) of the laser beam ( 4 ), whereby the laser beam ( 4 ) is passed on to the side walls of the joining gap ( 5 ) thermally destroy adherent oxide layer; - provision of a controlled arc ( 6 ); - Melting of the materials to be joined ( 7 . 8th ) at the joint using the arc ( 6 ) after irradiation with the laser beam ( 4 ) is finished to add the materials. Method according to claim 1, characterized in that the laser beam ( 4 ) is irradiated at an angle α on the surface of the joint, which deviates from 0 ° and 80 ° from the perpendicular. A method according to claim 2, characterized in that the angle α is adapted to the machining conditions with respect to material and surface shapes. Device for thermal joining of materials ( 7 . 8th ) in a joint gap ( 5 ), of which at least one first material ( 7 ) has a refractory oxide surface, with an arc generating means ( 2 ) for the provision of a controlled arc ( 6 ) at a joint, characterized in that further comprises a laser beam generating means ( 1 ), which is a pulsed laser beam ( 4 ) provides for near-surface heating of the first material ( 7 ) at the joint by irradiation with the laser beam ( 4 ), wherein the heat input caused by the laser beam is controlled such that it does not lead to the formation of a puncture hole in the first material ( 7 ), and wherein the laser beam ( 4 ) so in the joint gap ( 5 ) is directed between the materials to be joined, that it is based on the first material ( 7 ) laterally displaced, whereby on the side walls of the joint gap ( 5 ) a partial reflection ( 9 ) of the laser beam ( 4 ), whereby the laser beam ( 4 ) is passed on to the side walls of the joining gap ( 5 ) thermally destroy adherent oxide layer; and that the materials to be joined ( 7 . 8th ) at the joint by the arc ( 6 ) of the arc generating means ( 2 ) are melted after the irradiation with the laser beam ( 4 ) is finished to add the materials. Apparatus according to claim 4, characterized in that the laser beam generating means ( 1 ) a pulsed laser beam ( 4 ) with a power of 100 to 500 W. Apparatus according to claim 4 or 5, characterized in that the inclination of the laser beam ( 4 ) to the arc ( 6 ) is variable between 0 ° and 80 °. Device according to one of claims 4 to 6, characterized in that the inclination of the laser beam ( 4 ) to the joint gap ( 5 ) is variable between 0 ° and 80 °.

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