DE2647082A1 - LASER WELDING - Google Patents

Description

PATENT ADVOCATE

DiPL-ING. G

HELMUT GÖRTZ

^ ί ^ October 18, 1976

Gzm / Wa.

Union Carbide Corporation, 270 Park Avenue, New York, N.Y.

Laser welding

The invention relates to a method for the continuous seam welding of strips of plate-shaped! Material at high speed using a laser beam as a power source for welding; the invention relates also on the welded structure that is manufactured using this process.

Two conditions must be met for a seam welding on plate-shaped! Material at high uniform speed can be carried out. The welding energy must be supplied to the workpieces in a concentrated manner, so that the Heating is local; in addition, the weldment must be formed quickly before the heat builds up in the mass of the metal spreads. So far, the composition of the material has been particularly significant in controlling welding speed, especially when it is conductive Metal acted like aluminum. In conventional oxy-fuel welding and electric welding, the welding speed is even for light metallic calibration material (gage metal material) to less than 12 m / min, because the heating

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tion is not sufficiently local, with a substantial part of the heat being lost in the bulk of the metal and the surrounding area. With high-frequency resistance welding, a speed of 90 m to 120 m / min is achieved, but only in one limited number of configurations where the contact area is tight and the welding energy is concentrated on the contact area is. An electron beam is a high density energy source, but vacuum equipment is necessary to make a beam high energy density is obtained over an acceptable distance. Accordingly, all known welding processes are either actually Sense unsuitable for welding workpieces at a reasonably high speed of at least 30 m / min., Especially for workpieces made of aluminum, or they are more inexpedient due to configuration limitations Unsuitable requirements for the holding device.

It has been found that a continuous seam weld between moving workpieces made of plate-shaped! material with the help of a laser beam as an energy source for welding can be established if certain critical conditions are met. Laser beams have been successful so far used as sources of high density energy for deep penetration welds and spot welding. In all previous applications of lasers in the field of welding, the goal has been to use higher energy for the deeper Provide penetration. The method according to the invention is not limited to a specific minimum energy density. In the method according to the invention, the penetration through the cross section of the workpieces is undesirable and in certain cases Applications even detrimental. In other words, the invented

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method according to the invention results in a welded seam between the strip of plate-shaped! Material that is not visible except at the ends of the seam. Any laser can be used although a compromise has to be made in terms of welding speed with reduced laser energy. With the aid of a 1 kW (^ -continuous laser, welding speeds of up to 150 m / min were achieved, whereby excellent welding qualities were achieved.

It has also been found that using the present Invention produced weldment is a "fusion weld" which is defined herein as coalescence between the Base materials resulting from being molten in the melting zone; the welded structure is further characterized by the fact that in the surrounding base material there is a zone influenced by the heat is missing. The term "heat affected zone" denotes that part of the base metal which is the melting zone is adjacent but has not been melted, however the mechanical properties or the microstructure has been reduced by the Changed heat when welding. If with the help of an ordinary light microscope at a magnification of a hundred times there are no changes the microstructure can be detected, then the heat affected zone near the melt zone is missing. Under under these circumstances the changes in the microstructure would be less than 10 mm. All previously known welding processes result in a weldment with a clearly visible zone that is affected by the heat and visible to the naked eye can be seen. Conventional laser and electron beam welding leads to welded structures with a significant zone, which is affected by the heat and which can be viewed at 50x magnification with the aid of a light microscope *

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can be observed.

The method for the continuous seam welding of moving strips of plate-shaped material consists of the following
Steps:

At least one of the moving strips is moved against the other, with a converging one between the moving strips V trains;

a force greater than zero pond is applied to a point adjacent to the point at which the moved Stripes converge so that the moving stripes are at the point of convergence overlap in intimate contact;

a laser beam is directed towards the converging V, so
that a continuous, welded seam is created between the moving, overlapping strips.

In addition, there is a continuous finishing construction
consisting of a fusion weld nugget between the two base materials, which are characterized by the absence of a heat affected zone.

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AO

In accordance with the present invention, it has been observed that the laser beam is within the plane of symmetry and a narrow focal area that extends only from the point of convergence extends downwards, must be focused if the laser beam is to be used optimally.

In the context of the present invention, "optimal use of laser beam energy" "means continuous Welding construction can be achieved, at the highest possible speed and lowest Laser beam energy. The ability to keep the laser beam energy as low as possible and still weld quickly, should not be underestimated, because it represents a significant economic advantage over a system which otherwise depends very much on high laser beam energy, in order to create a continuous welded construction at high speed to achieve.

Accordingly, it is the primary object of the present invention to provide a method of welding moving plates of strip-shaped Develop material at high speed, using a laser beam to create a welded Establish a seam between the moving strips.

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Another object of the present invention is to provide a Specify weldment made from a fusion weld nugget characterized by the absence of a heat affected zone.

Other objects and advantages of the present invention will become apparent from the following detailed description and drawings attached drawings.

Show it:

Fig. 1 shows the preferred device for carrying out the invention Procedure in plan view,

Figure 2 is a graph of the quality of the weldment as a function of the position of the focal point, using two different lenses Focal lengths, whereby the other process parameters are specified,

Fig. 3a

to 3e an enlarged view of the converging V that forms between the pressure rollers around the To clarify the effect of the following parameters on welding: position of the focal point, focal length and Diameter of the pressure rollers,

Fig. 4a-b

and Figures 5a-b include photographs of the welded seam, magnified 100 times, between two strips of aluminum panels a speed of 120 m and 150 m / min.

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1 shows the apparatus for carrying out the present invention. Two strips of plate-shaped Material 10 and 12 are fed from supply rolls 14 and 16 in Direction towards each other drawn so that a converging V forms, in which the strips 10 and 12 at the point of convergence 18 are on top of each other. The strips 10 and 12 are brought into contact with each other by the pressure rollers A and B, so that the The point of contact between the pressure rollers corresponds to the point of convergence 18. Idler rollers 20 and 22 can be used to handle strips 10 and 12 and to maintain tension in the strips as they are pulled. Though each Plate material 10 and 12 according to FIG. 1 consists of a wound strip of continuous length, of course It goes without saying that the strips of sheet material 10 and 12 are not limited to strips of continuous length are. When the strips of sheet material have a having a predetermined limited length, another output device would be required to process the strips, and although preferably one after the other by the pressure rollers A and B. There are known unwinding devices that use a conventional one Equipment can be used continuously or intermittently and at controlled time intervals to introduce strip-shaped material of limited length according to the method according to the invention.

To carry out the method according to the invention, the strips 10 and 12 can be made of any metal or plastic, although the composition of each material must be compatible. The properties of the plate material, e.g. its conductivity and its thermal diffusivity

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do not mean any restriction. Accordingly, the method is particularly suitable for welding conductive metals such as Aluminum and copper. In addition, the thickness of the material is only limited by aspects of practical handling and the speed. Board material with a thickness of only 0.25 mm up to a board thickness of 6 mm can be produced with the help of the erfin-r easily welded according to the method.

The strips 10 and 12 are driven by the pressure rollers A and B. pulled by the gripping devices 24 and 26, which the Draw strips below the point of convergence 18 and also along a predetermined and preferably unchangeable one Travel in the direction of the arrow in Fig. 1. Although it is preferable to pass the strips 10 and 12 through the pressure rollers To pull A and B from below, the strips can also be fed from a point above the pressure rollers; alternatively, the pressure rollers can be driven themselves. The speed at which the strips pass through rollers A and B drawn is a process variable that is affected in a manner to be discussed.

A conventional source 30 of laser energy generates a laser beam 32 which is optically passed through a lens 34 or some Another optical medium is focused on the converging V formed from the moving strips 10 and 12 is. The energy of the laser beam 32 is not a critical factor in creating a welded seam between the moving strip; however, it is one of the regulating variables in determining the maximum speed with which one continuous welding can be carried out. For any-

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A laser of given energy exists an optimal relationship between focal length, position of the focal point, diameter of the Beam, beam orientation, pressure roller diameter and welding speed, which make a weld more acceptable Quality creates. Properly focusing the laser beam 32 on the converging V is essential, if at all wants to get a weld apart from the energy of the laser. In addition, a correct focus can be used accordingly the method according to the invention an optimal utilization the laser energy can be achieved. The focusing of the laser beam is detailed in connection with FIGS. 2 and 3 discussed.

The pressure rollers A and B have a critical function in connection with properly focusing the laser beam in practicing the present invention. It was found that strips 10 and 12 must be in intimate contact at convergence point 18; moreover must at this Place at least a nominal compressive force against the strips. The complete lack of a compressive force leads to ensure that a continuous weld between the moving strips even at reduced speeds and other optimal process variables cannot be performed can. The magnitude of the compression force does not appear to be significant, provided that at least some positive one Pressure is applied. Too much pressure is disadvantageous and can lead to deformation.

It will be understood that the weld formed between the moving strips as the strips advance must be continuous. A lack of

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Continuity of the seam means that no weld has been made at all. The continuity of the weld can be achieved with free Eye or by pressing on the seam leaks are checked. Obviously, the quality of the weld depends on at least certain minimum Pressure requirements are met which depend on the application of the welded strips.

Pressure rollers A and B are preferably conventional nip rollers with a circular periphery. Others too Devices can be used provided that these devices assume a curved contour once they have the Reach the point of convergence. For bilateral welding symmetry, the diameters of pressure rollers A and B are the same.

Figs. 2 and 3 illustrate the importance of focusing and the diameter of the pressure rollers A and B for quality the weld.

To achieve a weld, the laser beam must be focused on the converging V, substantially above the point of convergence. The width taken for focusing depends mainly on the focal length, the diameter of the beam, the diameter of the squeegee roller and the speed to be achieved. Figures 2 and 3a to 3e contain the results of a number of experiments carried out with a 1 kW continuous CC ^ laser of wavelength 10.6 microns; the output _{beam (TEM 00} mode) has a diameter of 1.25 cm; this beam was through optical lenses of focal length 6.25 cm and

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9.37 cm to a focal point about the diameter of 0.1 mm focused at the focal points f1, f2 and f3. One another number of focal points with respect to the point of contact were used to make up the graph in FIG obtain. Extrapolation of the data in Figs. 2 and 3 shows the importance of the following criteria for continuous, fast seam welding, at a speed of at least 30 m / min:

a) the laser beam should essentially be along the "plane of symmetry" which is defined as the plane passing through the point of contact 18 between the pressure rollers A and B goes and which is parallel to their longitudinal axes. If the laser beam is outside the Plane of symmetry lies, but in a plane parallel to If the plane of symmetry is a non-symmetrical weld formed between the strips. The extent of the asymmetry is directly proportional to the deviation from the plane of symmetry. But the position of the ray within the plane of symmetry can be adjusted over a wide range up to at least + 30 °, provided that the focal point is relatively accurate is maintained as explained below j

b) when optimal utilization of the laser beam is not required and the laser beam contains sufficient energy, then the focal point can be substantially above the convergence point 18 lying. However, if optimal utilization is desired, the focus of the laser should be within one can be maintained in a narrow focal area, essentially from the convergence point to a point downward

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that's enough. The term "optimal use" denotes the ability to achieve a continuous weld at the highest possible speed and with the lowest possible laser beam energy. The position of the focal point with respect to the point of contact as a function of pressure is shown in FIG. 2 for a lens of focal length 6.25 cm and 9.37 cm, the diameter of the beam being 1.25 cm. The focal range within which an acceptable, continuous, uninterrupted welded seam is made between moving strips will vary according to changes in the other process parameters. For the 1 kW CO ₂ laser described here, which is focused on two moving aluminum strips (speed at least 120 m / min., Pressure rollers A and B with a diameter of 2.8 cm) within the plane of symmetry, the acceptable focal point range is only approximate 1.75 mm wide for the 6.25 cm focal length lens and about 3.25 mm for the 9.37 cm focal length lens. It is interesting and surprising that the area of focus only extends downward from the point of contact. The area of the focal point can be expanded by reducing the diameter of the pressure rollers A and B and / or increasing the operating speed and / or the energy of the laser beam or the focal length or both factors. It is believed, however, that at a high speed of operation, an acceptable weld between the strips cannot be made without focusing the beam on a focal point substantially at or beyond the point of convergence, ie

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downwards, even with a laser beam, is much higher Energy;

c) the entry of a laser beam of conical geometry into a converging V from the preceding strips of the material 10 and 12 can adjust the beam depending on the size of the converging light beam, i. the focal length, the position of the focal point and the diameter of the pressure roller. For those identified above At the focal point, a shortening of the laser beam by the pressure rollers was unavoidable. Under certain In some circumstances, shortening may even be desirable. When the laser beam hits the pressure roller, it will part of the laser energy is reflected into the converging V and therefore also into the active welding zone Part is absorbed by the moving stripes and appears as heat and a part is diffusely scattered and is thus lost. The further away from the point of convergence the shortening occurs, the more laser energy is lost.

The relationship between the shortening, if any, the location of the focal point, the diameter of the pressure roller and the focal length is shown in Figures 3a to 3e, where the diameter of the two rollers A and B is between a Value was varied from 2.8 cm and 5 cm; the optical lens was moved along the optical axis and the focal length varied from 6.25 cm to 9.37 cm with the focus at positions f1, f2 and f3. It goes without saying that the diameter of the pressure rollers A and B also

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-1A-

borrowed thickness of the strips 10 and 12 comprises. The diameter of the laser beam was 1.25 cm in each case. For the focal position f1 _f which forms a limit downwards from the point of contact 18, as can be seen from FIGS. 3a and 3b, the shortening took place at point C, with pressure rollers A and B with a diameter of 2.8 cm and a lens of the focal length 6.25 cm as shown in FIG. 3a; at point D the shortening takes place, pressure rollers A and B with a diameter of 5 cm being used and the lens of the same focal length as shown in FIG. 3b. With a focal position f2, which, as shown in FIG. 3c, forms a termination at the contact point 18, the shortening at point E was carried out using the lens with a focal length of 6.25 cm and the pressure rollers A and B with a diameter of 5 cm. The shortening took place with a beam with a diameter of 1.25 cm and a lens with a focal length of 9.37 cm, the focal point of which, as can be seen from FIG at point F, which is closer to the point of contact than points C, D and E. It follows that the shortening of the beam can be reduced by increasing the focal length. The empirical evaluation of the welds in FIGS. 3a to 4b shows that for a lens with a focal length of 6.25 cm a better quality of the weld is achieved if pressure rollers with a smaller diameter are used; for a 8.75 cm focal length lens, a superior weld resulted over a wider area when smaller diameter pressure rollers were used. All other things being equal, pressure rollers with a smaller diameter lead to better energy utilization. If the shortening is sufficiently close to the

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The V-shaped geometry directs the laser energy into the welding zone. The third focal position f3 was effected with the aid of a beam with a diameter of 1.25 cm, as can be seen from FIG. 3e, with a lens with a focal length of 6.25 cm and pressure rollers A and B with a diameter of 2.8 cm, each point £ 3 delimits a location just before the point of contact 18, ie a little upwards from the point of contact. Notwithstanding the fact that there is no shortening and the focal point is close to the contact point 18, a continuous weld could not be achieved here. Accordingly, the energy of the laser beam is not nearly as important for achieving a continuous weld as the position of the focal point, the size of the converging light cone, which is determined by the focal length, and the diameter of the beam and the diameter of the pressure rollers, which are specified in paragraphs ( a), (b) and (c) have been explained when an optimal utilization of the laser beam energy is required. In addition, the properties of the geometry of the converging V allow the laser beam energy to be absorbed more effectively, resulting in a higher welding speed and preventing the welded material from agglomerating. Aging is a problem encountered in processes for welding corners on thin material.

Photographs of the weldments made according to the method of the present invention using the 1 kW CO ₂ laser and under conditions which meet the criteria discussed above are shown in Figures 4a to 4b and 5a to 5b for aluminum strips 0.15 mm thick, FIGS. 4a to 4b showing the weld

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show which "at a welding speed of 120 m was obtained; FIGS. 5a to 5b show the welded construction, obtained at a welding speed of 150 m / min. The photographs were taken with a conventional optical microscope taken at 100x magnification. In any case, the welded construction has a microstructure, which is characteristic of all fusion welds, but at this magnification one is from the heat affected zone not visible. A heat affected zone, as noted earlier, is normal to be seen with the naked eye. Both Figs. 4 and 5 show the weldment lengthwise to show the continuity of the weld along the length of the seam; also the Cross section is shown. The cross-section of the weld obtained at a speed of 120 m / min is more uniform than the weld obtained at a speed of 150 m / min, as can be seen from the comparison 4b and 5b results. Both weldments are symmetrical and have a thickness that is only a fraction of that Thickness of the strip is. The thickness of the weldment is essentially independent of the thickness of the strip.

The examples given above relate to strip material made of aluminium. Strip material of other compositions was also tested and it was found that the method according to the invention Can also be applied to carbon steel, stainless steel, copper, brass and other materials that arise from a combination of the metals listed here; satisfactory continuous results were found in all cases Welds · Accordingly, the present invention is not

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limited to a strip material of a certain composition. Except for stainless steel and carbon steel showed no welded construction a zone affected by the heat.

It will be understood that many variations are possible in practicing the present invention. Fig. 1 describes the preferred system in which the laser beam is essentially borrowed lies within the plane of symmetry and its main vector component shows in the direction of propagation; Another embodiment would be to lay the strips so that a V-shaped configuration and to move the strips with respect to the laser beam so that the main vector component of the beam is perpendicular to the direction of propagation.

A continuous seam weld is made between two strips of sheet material while the strips are moved so that a V-shaped arrangement is made between the moved strips, at the point of convergence a pressure is applied and the laser beam is focused into the converging V.

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Claims (27)

Claims Process for the continuous seam welding of strips of a plate-shaped! Materials while the strip moves are characterized in that a) at least one of the moving strips is moved against the other so that between the moving strips forms a converging V, b) a force greater than zero Pond is applied at a point adjacent to the point at which the the moving strips converge so that the moving strips come to lie on top of each other, namely in the formation of close contact at the point of convergence, c) Laser beam energy is directed into the converging V so that a continuous welded seam between the overlapping strip is made. 2. The method according to claim 1, characterized in that the Laser beam is focused essentially within the plane of symmetry. 3. The method according to claim 2, characterized in that the Pressure is exerted in such a way that the moving strips are introduced between two pressure rollers, the point of convergence corresponds to the point of contact between the rollers. 4. The method according to claim 3, characterized in that the laser beam is substantially above the convergence point is judged. 709819/0639 5. The method according to claim 4, characterized in that the strips at a speed of at least 30 m / min. be moved. 6. The method according to claim 5, characterized in that the strips are made of aluminum. 7. The method according to claim 5, characterized in that the strips are made of stainless steel. 8. The method according to claim 5, characterized in that the strips are made of copper. 9. The method according to claim 5 »characterized in that the strips are made of brass. 10. The method according to claim 5, characterized in that the strips are made of carbon steel. 11. The method according to claim 5, characterized in that the strips are made of a different metal than aluminum, Copper, brass, carbon steel and stainless steel. 12. Method of fusion welding strips of flexible plate-shaped! Metal, the strips at high speed with respect to the source of welding energy, characterized in that each strip with respect to the other so that a converging V is made, a force is applied at one point 709819/063 9 - 26 - adjacent to the convergence point, a laser beam is used as energy for welding and the Laser beam is directed into the converging V, with the help of an optical medium whose focal point in is substantially above the convergence point. 13. The method according to claim 12, characterized in that the Laser beam lies essentially within the plane of symmetry between the moving strips, with its main component shows in the direction of propagation. 14. The method according to claim 13, characterized in that the Laser beam lies essentially within the plane of symmetry between the moving strips, with its main component is perpendicular to the direction of propagation, 15. A method for continuously seam welding strips of sheet material while the strip is moving are characterized in that a) at least one of the moving strips is moved against the other so that there is one between the moving strips forms a converging V, b) a force greater than zero Pond is applied at a point adjacent to the point at which the moving strips converge so that the moving strips come to lie on top of each other, namely in the training close contact at the point of convergence, q) Laser beam energy directed into the converging V in this way that a continuous welded seam is made between the overlapping strips, 709819/0 6 39 d) the laser beam is focused within the axis of symmetry, specifically within a relatively narrow focal area, which extends from the point of convergence to a point located only downstream. 16. The method according to claim 15, characterized in that the Pressure is exerted in such a way that the moving strips are introduced between two pressure rollers, the point of convergence corresponds to the point of contact between the rollers. 17. The method according to claim 16, characterized in that the strips at a speed of at least 30 m / min. be moved. 18. The method according to claim 17 »characterized in that the strips are made of aluminum. 19. The method according to claim 17, characterized in that the Strips are made of stainless steel. 20-v method according to claim 17 »characterized in that the Strips are made of copper. 21. The method according to claim 17 »characterized in that the strips are made of brass. 22. The method according to claim 17, characterized in that the strips are made of carbon steel. 709819/0639 23. The method according to claim 17, characterized in that the strips are made of a different metal than aluminum, Copper, brass, carbon steel and stainless steel. 24. Method of fusion welding strips of flexible plate-shaped material, with the strips at high speed regarding the source of the welding energy are moved, characterized in that each strip is arranged with respect to the other so "that a converging V arises when a force is applied to a point adjacent to the point of convergence, a laser beam is used as energy for welding and the laser beam is directed into the converging V, and with the aid of an optical medium whose focal area extends downward from the point of convergence. 25. The method according to claim 24, characterized in that the laser beam is essentially within the plane of symmetry lies between the moving strips, with its main component pointing in the direction of propagation. 26. The method according to claim 25, characterized in that the laser beam is substantially within the plane of symmetry lies between the moving strips, with its main component pointing perpendicular to the direction of propagation. 27. Welded construction, characterized by an autogenous fusion weld nugget, which is formed between two base metals is characterized by the absence of a surrounding heat-affected zone and the Base materials are selected from the group consisting of aluminum, copper and brass. 709819/0639