WO1991002621A1

WO1991002621A1 - Process and device for welding by laser beam

Info

Publication number: WO1991002621A1
Application number: PCT/DE1990/000622
Authority: WO
Inventors: Axel Zwick; Ralf Imhoff
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 1989-08-15
Filing date: 1990-08-11
Publication date: 1991-03-07
Also published as: AU6158890A; DE3926781C2; DE3926781A1

Abstract

Process for welding by laser beam or similar high-energy radiation, in which two contiguous workpieces have a coating between them, the vaporization point of which is lower than the melting point of the material of the workpieces, and in which a gas flow is directed onto the weld. To improve this process so that coated workpieces can be welded without gaps and so that gas can escape through the vapour capillaries of the weld, a current of gas which promotes degasification of the vaporized coating through the vapour capillaries of the weld is used in addition to the current of protective or working gas which flows around the weld.

Description

Process for welding with laser radiation and device for carrying out the process

Technical field

The invention relates to a method for welding with laser radiation or the like. high-energy radiation, in which two workpieces lying against one another have a coating between them with a vaporization point below the melting point of the workpiece material, and in which a gas flow directed at the processing point is used.

So far it has been extremely problematic to weld surface-finished, namely surface-coated workpieces to one another. In particular, it is problematic to weld galvanized sheets together, for example in an overlap joint. The problem arises from the fact that the coating evaporates and has to escape due to its low evaporation point. When it escapes, the vaporized coating will penetrate into the melt of the processing point and into its vapor capillary and

REPLACEMENT LEAF escape from the processing point by means of their own eruption force. The eruption-like escape of the evaporated coating takes place with the entrainment of the melt. As a result, craters or holes are created in the processing area, which lead to the destruction of the weld seam. If the eruption force of the evaporated surface coating is no longer sufficient to penetrate the cooling melt, pores remain in the weld seam, which is therefore defective.

In order to avoid the above-described negative effects on the weld seam, it is known to leave a gap between the workpieces through which the evaporated coating can escape. However, such a gap is not without problems. The arrangement of a gap causes an undesirable additional effort when welding, e.g. by Spacers must be used, or by e.g. must have a special shape, such as the formation of beads in sheet metal. In addition, difficulties arise when the workpieces have a three-dimensional course. It then happens again and again, particularly in industrial manufacturing processes, that there are points with no joint gap, so that faulty welding occurs here, or that there are points with too large a joint gap, so that the design specifications are not met or a seam invasion is to be expected.

PRIOR ART From US Pat. No. 4,684,779 a method of the type mentioned at the outset is already known, in which the gas flow is directed onto the processing point coaxially with the laser radiation. With this gas flow, a positive pressure is generated from above, which should drive out the gases that develop during welding between the workpieces. A gap is therefore also required for this.

DESCRIPTION OF THE INVENTION In contrast, the invention is based on the object

To improve methods of the type mentioned at the outset so that coated workpieces can be welded gaplessly and with degassing through the steam apillary of the processing point.

REPLACEMENT LEAF This object is achieved in that in addition to a

Flushing the processing point with a protective or working gas, a gas flow promoting the degassing of the vaporized coating from the steam capillaries of the processing point is used.

For the invention, that a gas flow is used, is employed with a ^'protection or working gas additionally put into a purging the Arbeits¬ is important. This gas flow can be directed and dimensioned such that degassing of the vaporized coating or other pore-forming components present in the material is achieved from the vapor capillaries. At the same time, the gas flow, in its capacity as an additional gas flow, allows the conventional purging of the work station to continue, for example in order to influence the coupling of energy and / or to shield the work station from the ambient atmosphere.

As a result of the degassing from the steam capillaries, welding can be carried out seamlessly. According to the principle of a water jet pump, the gas flow creates a negative pressure in the region of the. Processing point so that the gases or coating vapors flowing into the steam capillary are quickly pumped off or removed. The proportion of gaseous constituents which penetrate into the melt is drastically reduced, so that an eruptive melt expulsion can be avoided.

In order to be able to use the gas flow as effectively as possible, it is directed at least essentially parallel to the workpiece surface. It is therefore not used coaxially with the laser radiation, as in the known method described above, but practically perpendicular to it.

It is particularly advantageous if the workpieces are welded through and degassed with gas flow at both ends of the steam capillaries. In this case, the vapor a pillar can be degassed at both ends and thus considerably

REPLACEMENT LEAF more effective removal of the evaporated coating can be achieved.

Since the steam capillary when welding through two workpieces is always larger on the laser radiation side because of the energy injected from there than on the side turned away from the laser beam, the procedure is expediently such that the gas flow acting on the laser beam side of the workpieces is stronger than the laser beam side. The stronger gas flow on the side of the workpiece facing away from the laser beam increases the degassing effect, which can be used to keep the degassing of the same size on both sides, for example with workpieces of the same thickness.

It has been found that the eruptive effect of the evaporated coating is reduced particularly when the gas flow takes place in the direction of the relative advance of the workpieces. This is probably due to the fact that the gas flowing in the feed direction avoids a dragging effect of the coating steam into the larger melt mass on the back of the steam capillary.

It has also proven to be particularly advantageous if the gas of the gas flow has a flow velocity which causes the steam capillary to expand. The gas flow tears open the steam capillary, in particular on the side of the workpieces facing away from the jet, or, due to its flow behavior, contributes to faster removal by the melt, particularly on the side of the workpieces facing away from the jet.

An essential further procedural measure, in particular in connection with the use of the gas flow promoting the degassing, is that the surface tension of the melt is reduced by means of increased energy coupling and / or by chemical gas reaction and / or the diameter of the steam capillary is increased. The reduction in the surface tension of the melt promotes segregation of the gases which have penetrated into the melt and thus a reduction in the entrainment effect of the gases when they escape from the melt. The Increasing the diameter of the steam capillary also increases the degassing rate. In order to bring about the increased energy coupling which serves to increase the temperature of the melt and / or to increase the diameter of the steam capillaries, it is possible, for example, to increase the distance energy and at the same time to select an appropriately suitable position of the focal point in the workpiece. However, it is also possible to use chemical gas reactions, for example the gas reactions of the gases oxygen or hydrogen. Oxygen can be used to form oxides of the surface coating that only evaporate at higher temperatures, for example in the case of galvanizing to form zinc oxide.

A device for carrying out one of the above-described methods is characterized in that during welding there is at least one nozzle which is directed at a flat angle to the workpieces and has an end which is exactly parallel to the workpiece surface. With the help of the surface-parallel end, a very precisely directed gas flow parallel to the workpiece surface can be generated, so that the desired degassing effect is optimal.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is explained in more detail with reference to welding arrangements given in the drawing. It shows:

1 shows a cross-sectional view through two workpieces to be welded to one another in the region of a processing point,

Fig.2 is a plan view of the processing point of Fig.l, and

3, 3a the production of an overlap seam on two galvanized sheets.

BEST WAYS OF IMPLEMENTING THE INVENTION The workpieces 1 and 2 shown in FIG. 1 are sheets which are coated on their outer sides, for example galvanized. This results in a coating 3 located between the workpieces 1, 2 arranged without gaps

REPLACEMENT LEAF The outer sides 10, 10 'of the workpieces 1, 2 are each provided with layers 3''.

There is a processing point 4 to which a laser beam 11 is directed. This causes the material of the workpieces 1, 2 located in the area of the processing point 4 to melt, a steam capillary 7 being formed. As a result of the relative movement between the laser beam 11 on the one hand and the workpieces 1, 2 on the other hand, this causes a comparatively narrow melting front 12 in the direction 8 and a bath of melt 9 which is comparatively larger in the direction 8 of the melting front 12. In Figure 2, the area 9 'of the melt 9 is shown in dash-dot lines.

It can be seen from FIG. 1 that the steam capillary 7 has ends 1 ', 1' 'which are open to the outside because the workpieces 1, 2 are welded through. Because of the energy coupling with the laser beam 11 mainly in the area of the end 7 'of the steam capillary 7, this end 7' is larger in diameter than the opposite end 7 ''.

In the area 13, the melt 9 has solidified and a weld seam has formed. Furthermore, FIG. 1 also shows a nozzle 14 with which a protective or working gas 6 can be fed to the processing point 4, for example in order to influence the coupling of energy or to shield the processing point 4.

Arrows 5, 5 'indicate that a gas flow is used in the welding process which is directed parallel to the workpiece surface. There is a gas flow 5 and 5 'on both sides 10, 10', which covers the ends 7 ', 7' 'of the steam capillaries 7.

It can be seen from FIG. 2 that a region 15 of the coating 3 is melted or evaporated by the laser beam 11, which region is substantially larger than the region 9 'of the melt 9. The coating steam or the evaporated coating 3' flows according to the arrows 16 through the narrow melting front 12 into the steam capillary 7 or into the

REPLACEMENT LEAF according to arrow 17 moving around the steam capillary 7

Melt 9. The gas flow 5.5 'now has the effect that degassing of the latter takes place at the ends 7', 7 '' of the steam capillaries 7 because the gas flow 5,5 'there acts like a water jet pump and pumps off the steam capillary 7 , so that no excess pressure can arise which would help to drive the vaporized coating 3 'into the melt 9 or to keep it there, so that undesirable eruptions would occur.

The setting of the strength of the gas flow 5, 5 'is matched to the respective requirements, for example to the thickness of the coating and thus to the steam quantities of the coating 3' or the feed rate and the material of the coating 3.

Fig.l also shows that the strength of the gas flow, in particular the gas flow 5 'can be adjusted so that the steam capillary 7 is expanded. The extension in question is designated 18. The strength of the gas flows can be different on the lo, lo 'sides. 1 shows a stronger gas flow 5 'on the side 10' by means of a thicker arrow, in order to degas the steam capillary more strongly through its end 7 ', which is advantageous because of its smaller diameter if the degassing through the two ends 7 , 7 'should be the same size.

The protective or working gas 6 fed through the nozzle 14 is, for example, an inert gas, such as helium, or an active gas, such as carbon dioxide. These gases can also be used for the gas flow 5.5 '. However, it is generally advisable to use an especially inexpensive gas for the gas flow 5, 5 ', since the consumption is greater as a result of the greater flow rate than when the processing point 14 is flushed with a protective or working gas 6 .

It has already been mentioned above that the gas flow 5.5 'in the region of the ends 7', 7 '' of the steam capillaries 7 can produce a negative pressure which promotes the degassing of the steam capillaries 7. On the other hand, the gas flow has 5.5 'in particular

REPLACEMENT LEAF when the flow is in the feed direction 8, in which the large area of the melt 9 is first swept over, a force acting on the substrate. The result is a surface or seam shaping which counteracts the eruptive force of the coating vapor escaping from the melt 9.

3 shows the side view of two workpieces 1, 2 designed as galvanized sheets which have bevels 1 ', 2' with which they abut one another, so that as a result there is an enclosed coating 3, which is shown in FIGS is symbolized by a reinforced line. In order to weld the two folds 1 ', 2' with a weld seam 13, a laser beam 11 is used which is directed vertically to the folds 1 ', 2' and whose beam spot width determines the width of the weld seam 13. There is a nozzle 14 for working gas 6 with which the processing point 4 is flushed. The nozzle 14 is inclined.

In addition, there are two gas flow nozzles 19 which protrude close to the folds 1 ', 2'. The ends 19 'are directed parallel to the surface of the folds 1', 2 ', so that gas flows 5, 5' parallel to the workpiece surface arise in the feed direction 8 of the workpieces 1, 2 and the effects described above in the region of the steam capillary 7, not shown here produce.

3, 3a show an exemplary embodiment of a lap joint of galvanized sheets, which is welded without a gap. Such lap joints are used, for example, in body and container construction. In the body shop there are fully galvanized engine sub-carriers, spring domes and other chassis parts or welds in the area of the gutter.

For example, carbon dioxide or a mixed gas with oxygen components is used as the gas for the gas flow 5, 5 '. Mixed gas is understood here as a mixture of inert and active gases.

REPLACEMENT LEAF Commercial recyclability

The method according to the invention is used for welding surface-coated workpieces, eg. B. galvanized sheets.

REPLACEMENT LEAF

Claims

Expectations:

1. Method for welding with laser radiation or the like. high-energy radiation, in which two workpieces (1, 2) lying against one another have a coating (3) between them with an evaporation point below the melting point of the workpiece material, and in which a gas flow (5) directed at the processing point (4) , 5 ') is used, characterized in that, in addition to purging the processing point (4) with a protective or working gas (6), degassing the vaporized coating (3') from the steam capillaries (7) of the processing point (4 ) promoting gas flow (5.5 ') is used.

2. The method according to claim 1, so that the gas flow (5,5 ') is directed at least essentially parallel to the workpiece surface.

3. The method according to claim 1 or 2, dadurchge ¬ indicates that the workpieces (1, 2) are welded through and at both ends (7 ', 7' ') of the steam capillary (7) each with gas flow (5, 5 ') is degassed.

4. The method according to claim 3, d a d u r c h g e k e n n ¬ z e i c h n e t that the averted on the laser beam. Side (10 ') of the workpieces (1,2) acting gas flow (5') is stronger than the laser beam side (5).

5. The method according to one or more of claims 1 to 3, that the gas flow (5,5 ') takes place in the direction (8) of the relative advance of the workpieces (1, 2).

REPLACEMENT LEAF

6. The method according to one or more of claims 1 to 4, so that the gas of the gas flow (5,5 ') has a flow rate which causes the expansion of the steam capillary (7).

7. The method according to one or more of claims 1 to 5, that the surface tension of the melt (9) is reduced by means of increased energy coupling and / or by chemical gas reaction and / or the diameter of the vapor capillary (7) is increased.

8. The device for carrying out the method according to one or more of claims 1 to 7, dadurchge¬ indicates that during welding at least one flat at an angle to the workpieces (1,2) directed nozzle (19) is present which a the workpiece (1st or 2) has an exactly surface-parallel end (19 ').

REPLACEMENT LEAF