WO2010060392A1

WO2010060392A1 - Method and apparatus for joining workpieces

Info

Publication number: WO2010060392A1
Application number: PCT/DE2009/001324
Authority: WO
Inventors: Thorge Hammer; Matthias Graul; Marc Michaelis
Original assignee: Volkswagen Ag
Priority date: 2008-11-25
Filing date: 2009-09-24
Publication date: 2010-06-03
Also published as: DE102008058917A1

Abstract

The invention relates to a method for joining, wherein the workpieces (1, 2, 3) to be joined to each other and disposed so as to overlap each other are heated at a joining site (7, 8, 9) by non-contact heat supply until the workpieces (1, 2, 3) exhibit deformability that is sufficient for joining and are then locally plastically deformed by way of an apparatus comprising a joining tool and using a joining element (4). It is the object of the invention to provide a method by which a rigid connection of workpieces (1, 2, 3) can be created, wherein the necessary joining force and the warpage of the workpieces (1, 2, 3) are as low as possible. The object is achieved by a method in which the workpieces (1, 2, 3) are heated by a laser beam (5).

Description

Method and device for joining workpieces

The invention relates to a method for joining, in which the overlapping arranged to be joined together workpieces are heated at a joint by non-contact heat, until the workpieces receive a sufficient for the joining formability and then using a joining tool having a device and using a Joining element locally plastically deformed. Furthermore, the invention relates to a device for joining, to be joined, overlapping arranged workpieces at a joint with a trained for introducing a joining element into the workpieces joining tool, wherein the device is movable relative to the workpieces.

From EP 1 754 896 B1, a method is known in which a nail-like joining part accelerates to high speed and is driven into the non-pre-punched workpieces which are to be joined together and overlapped.

A similar method is known from the document DE 10 2006 002 238 A1. The pointed joining part displaces the material, which locally experiences a strong increase in temperature, whereby higher degrees of deformation are possible. In this method, the joining element is fired with pure force through the joint. The clamping of the joining element is due to the springback of the so-called statement on the exit side of the joint connection. Furthermore, a so-called head entry occurs at the point where the head of the joining element strikes the sheet metal surface. This head feeder is due to the high impact force of the joining tool. The impact hammer of the joining tool must apply a minimum impact energy in order to drive the joining element through the joint connection. When breaking through the workpieces, the joining process no longer opposes the percussion hammer so that the residual impact energy set the head of the joining element on the workpiece from this must be cushioned. This residual impact energy leads to deformation of the joining joint and also to the loosening of the joint connection just produced.

In order to reduce the necessary minimum impact energy and thus also the unwanted residual impact energy, the joint can be heated prior to the introduction of the joining element. A method in which the joint is heated before the introduction of the joining element is known from DE 196 30 488 A1. In this method, the workpieces are heated at the joining surfaces by contact with preheated parts of the joining tool. A contactless heat supply by means of integrated in the joining tool, inductive heating elements describes the cited document. By heating the workpieces, the ability to change the shape of the workpieces is adjustable. Thus, the joining of brittle materials is possible.

In order to avoid component distortion, the residual energy must be cushioned by the component stiffness, especially in the case of unilaterally acting methods such as those mentioned above, without any component distortion occurring. Therefore, it is important to minimize the joining force.

This is possible, for example, by introducing the joining element as a screw rotating in the locally heated workpiece. Such a method is described in the document DE 103 48 427 A1.

A similar method, in which locally heated workpieces are connected without a joining element only by a brief penetration of the joining tool into the workpieces, is shown in DE 101 33 292 A1.

By heating the workpieces, the deformability of the workpieces is adjustable, however, the heat can be introduced in the known method only in the outer workpiece. The other workpieces to be joined are heated only indirectly by the transfer of heat through the outer workpiece. In this case, heat spreads in all workpieces in all directions, whereby the rigidity of the workpieces is reduced over a large area. Against this background, the invention has the object to perform a method of the type mentioned in such a way that a firm connection of workpieces can be produced, in which the necessary joining force and the delay of the workpieces are minimized. Furthermore, the invention has for its object to provide a device of the type mentioned, with a firm connection of workpieces can be generated, in which the necessary for the introduction of the joining element joining force and the delay of the workpieces are minimized.

The first object is achieved by a method according to the features of claim 1. The subclaims relate to particularly expedient developments of the invention.

According to the invention, therefore, a method is provided in which the workpieces are heated by a laser beam. This makes it possible that the workpieces are heated without contact by absorbing the energy of the laser beam. It is favorable that for the heating of the workpieces by means of a laser less energy must be applied than in conventional non-contact heat sources and that the energy emitted by the laser beam is easier to control. By using a laser beam, it is also possible to introduce the heat into the workpieces at high speed in a spatially limited area. In this case, the heat generated in the workpieces can increase in the short term in such a way that the yield strength of the workpiece in the effective range of the laser beam is greatly reduced and thus the penetration of the joining element counteracting resistance and thus the necessary joining forces are small. If the material of the workpieces is heated in such a way that it becomes almost molten in the short term, the material can flow around the barbs and / or cavities attached to the joining element. Thus, a particularly firm connection of the workpieces is achieved with the joining element. Such a joint connection can transmit higher forces. The material therefore flows because the kinetic energy with which the joining element is driven into the workpieces is converted into heat and the melting temperature of the material of the workpiece is briefly exceeded with the heat already placed by means of the laser beam. The material flowing around the barbs and / or cavities of the joining element forms a metallurgical bond. In the conventional joining method, the joining element is shot with pure force through the joint. The clamping of the joining element is due to the springback of the so-called statement on the underside of the joint connection. Furthermore, a head entry occurs at the point where the head of the joining element strikes the sheet surface. The head feed is due to the high impact force of the joining tool. In order to drive the joining element through the workpieces, a minimum impact energy must be applied by the joining tool. When breaking the joining element, however, the workpieces then no longer resist the joining tool, so that the residual impact energy when placing the head on the workpiece must be cushioned by this. This residual impact energy leads to deformation of the joining joint and also to the loosening of the joint connection just produced. By preheating the joining area, the impact energy to be applied can be substantially reduced so that the residual impact energy does not lead to a deformation of the workpieces. Especially in the case of one-sided acting processes, the residual energy has to be cushioned by the component stiffness, without causing any component distortion. Therefore, it is important to reduce the necessary joining force and to maintain the component rigidity as far as possible. The latter is achieved by heating a spatially narrow range of workpieces.

It is particularly favorable that a particularly tubular zone is produced by means of the laser beam in the workpieces. This makes it possible that by means of a so-called deep-welding effect, the temperature can be easily and quickly passed into the depth of the workpieces. At high beam intensities of a laser beam, a vapor capillary - a tubular zone filled with metal vapor or partially ionized metal vapor, also called a keyhole - forms in the jet direction in the jet direction in the depth of the workpiece. The material is also melted in the depth, the zone can be deeper than wide. The vapor capillary increases due to multiple reflections on the walls of the absorption of the laser radiation in the material, whereby a large melt volume can be generated. The energy introduced into the depths of the workpieces and the heat generated from them make it possible to further reduce the necessary joining force. By changing the laser parameters, the amount of heat introduced can be precisely controlled. This can produce a desired heat field and adjust the material properties of the workpieces, for example, the hardness. The material properties change to the extent that with warm materials, the yield strength is reduced. The reduction of the yield strength is inversely proportional to Temperature of the material - the warmer the lower the yield strength. The temperature in the cylindrical heating field decreases after the end of the laser action, depending on the material properties and the elapsed time. Shortly after the pretreatment of the workpieces by the laser beam, the yield point is the lowest. By means of the laser beam, the temperature is increased in the workpieces in a, in particular tubular and / or cylindrical zone and thus generates a zone with a low yield strength.

The heat-affected zone forms in a cylindrical shape in the workpieces to be joined, wherein in the heat-affected zone the material has a low yield strength and at the edges of the heat-affected zone is harder material. It is particularly favorable that the joining element is guided by the zone during penetration into the workpieces. This makes it possible to further reduce the necessary joining force. The risk of evasion of the joining element and / or a misfeed is low in such a trained zone.

It is advantageous that the workpieces are completely penetrated by the joining element. This makes it possible that of the materials that do not exceed the melting limit, a part of the joining element is pushed through the workpieces and form an extract similar to a volcanic cone at the exit from the workpieces. During the cooling of the workpieces a material shrinkage takes place, so that the extract is applied more tightly than in the prior art to the joining element and thus creates a firm connection.

It is further advantageous that initially the laser beam acts on the workpieces at a joint, then the action of the laser beam on the joint is terminated, then the joining tool is positioned over the joint and then the joining element is inserted into the workpieces by means of the joining tool. This makes it possible to use the joining element in the workpieces in succession at individual joints according to the invention. For this purpose, a movement unit moves the joining tool designed as a shooting device into a position above the joint previously heated by the laser beam and inserts the joining element into the workpieces. For preheating, the laser beam is directed onto the joint for 20 to 2,000 milliseconds. The joining tool us then proceed within 100 to 1,000 milliseconds. For setting the joining element, a period of 1 to 100 milliseconds is required.

It is advantageous that at a first joint initially the laser beam acts on the workpieces, then the action of the laser beam is terminated on the first joint, then the device is moved relative to the workpieces such that the joining tool is positioned over the first joint and Then, while acting on a second joint, the laser beam on the workpieces, the joining element is inserted by means of the joining tool at the first joint in the workpieces. This makes it possible that an intermittent sequence of the two processes - heating the joint and setting the joining element - is achieved. So it is possible to increase the process speed and reduce the cycle time. The laser beam warms up the second joint, while the joining element is placed on the first, already preheated joint.

It is also favorable that the laser beam acts continuously, without interruption on the workpieces, wherein the laser beam is moved relative to the workpieces while simultaneously the joining tool, the laser beam trailing, cyclically positioned over the joints and then the joining element by means of the joining tool in the workpieces are used. This makes it possible that the process speed can be increased over the above-mentioned methods. The laser beam warms up the workpieces without interruption during a continuous movement along a zone. The setting of the joining element following in the direction of travel runs cyclically and proportionally to the travel speed of the laser beam. Due to the adjustability of the setting frequency of the distance of the joining elements can be influenced. The joining element does not hit a joint with a heated area of cylindrical shape when setting, but on a zone with any number of joints, wherein the zone is formed as a gap-shaped area in the workpieces. This jointing allows as well as the zone a leadership of the joining element. The closer the two processes of heating and setting are geometrically together, the lower the necessary joining force that must be expended in order to drive the joining element into the workpieces. Furthermore, the joining force of the joining element also depends on the feed rate. The faster the process is run, the softer the material at the joint. The material of the workpieces is a natural material, such as leather or woolen fabric, a plastic or a metal, such as aluminum or iron, but preferably made of sheet steel.

The second object is achieved with a device according to the features of claim 8. The dependent claims relate to particularly expedient developments of the invention.

According to the invention, therefore, a device is provided which has a laser source for emitting a laser beam. This makes it possible to heat the workpieces to be joined by means of the laser beam before joining and thus to minimize the joining force necessary for the joining.

It is favorable that the joining tool and the laser source are movable together with the device. This makes it possible to reduce the complexity of the machine device and to achieve a lower cycle time for the entire joining process.

It is advantageous that the joining tool and the laser source on the device are movable independently of each other. As a result, a continuous and / or cyclic work of laser beam and joining tool is possible simultaneously. Moreover, it is possible to position the laser beam and the joining tool faster and more precisely than is known in the art.

The invention allows numerous embodiments. To further clarify its basic principle, one of them is shown in the drawing and will be described below. This shows in

Fig. 1 shows a joint 7, on which by means of a laser beam 5 energy in the workpieces 1, 2, 3 is entered;

Fig. 2, the joint 7, on which in the workpieces 1, 2, 3, a joining element 4 is used; 3 shows the joining parts 7 after the joining process;

4 shows the workpieces 1, 2, 3 with the joints 7, 8, 9;

Fig. 5, the workpieces 1, 2, 3 with the joints 7, 8, 9 as part of a zone. 6

Figures 1, 2 and 3 show a joint 7, at the means of the inventive method, the workpieces 1, 2, 3 are joined together. For joining, the workpieces 1, 2, 3 are arranged overlapping one above the other and connected to a joining element 4 to be introduced into the workpieces 1, 2, 3. Before the insertion of the joining element 4 in the workpieces 1, 2, 3 at the joint 7 energy is entered into the joint 7 by means of a laser beam 5. As a result, the workpieces 1, 2, 3 are heated and lowered the yield strength of the materials of the workpieces 1, 2, 3. The lower yield strength makes it possible for the joining element 4 to be inserted into the workpieces 1, 2, 3 by applying a low joining force in comparison to known methods.

The heat-affected by the laser beam 5 zone 6 is formed in a cylindrical shape in the workpieces 1, 2, 3 to be joined. The material inside the zone 6 has a low yield strength and at the edges of the zone 6 is harder material. Upon penetration of the joining element 4 in the direction of the arrow 11 in the workpieces 1, 2, 3, the joining element 4 is guided by the zone 6. This makes it possible to reduce the necessary joining force and to reduce the risk of evasion of the joining element 4 and / or a misfeed in the workpieces 1, 2, 3.

Figure 4 shows the workpieces 1, 2, 3, which are joined together by means of the method according to the invention at the joints 7, 8, 9. The joining of the workpieces 1, 2, 3 takes place as described in Figures 1 to 3. In contrast to the serial processes which have been described in FIGS. 1 to 3, FIG. 4 shows a joining process in which, while at the joint 7, the workpieces 1, 2, 3 are heated by means of the energy of the laser beam 5, simultaneously at the joint 8, the joining element 4 in the direction of the arrow 11 in the workpieces 1, 2, 3 is used. At the joint 9, an already inserted into the workpieces 1, 2, 3 joining element 4 is shown. The laser beam 5 can also generate a zone 6 in the workpieces 1, 2, 3 here. The movement of not shown here Device with the laser beam 5 and the joining tool, also not shown, takes place relative to the workpieces 1, 2, 3 in the direction of the arrow 10. This direction is also called the feed direction.

Figure 5 shows how the figures 1 to 4, the workpieces 1, 2, 3, which are arranged overlapping one another for joining. In contrast to the joining operations described above, the laser beam 5 is moved continuously in the feed direction indicated by arrow 10 here. In this case, a gap-shaped zone 6 is formed in the workpieces 1, 2, 3. The material of the workpieces 1, 2, 3 in the zone 6 has a low yield strength. At the edges of the zone 6 is harder material, so that the gap-shaped zone 6 for the joining elements 4 when inserted into the workpieces 1, 2, 3 can serve as a guide. The setting of the joining element 4 which travels in the direction of travel runs cyclically and proportionally to the travel speed of the laser beam 5. The adjustability of the setting frequency makes it possible to influence the spacing of a plurality of joining elements 4. The closer the two processes of heating and setting are geometrically together, the lower the necessary joining force that has to be expended in order to drive the joining element 4 into the workpieces 1, 2, 3. Furthermore, the joining force of the joining element 4 also depends on the feed speed. The faster the process is run, the softer the material at the joint 8.

Claims

PAT EN TA NSPR O CHE

1. A method for joining, in which the overlapping arranged to be joined together workpieces (1, 2, 3) at a joint (7, 8, 9) are heated by non-contact heat, until the workpieces (1, 2, 3) a obtained sufficient forming capacity for joining and then locally plastically deformed using a joining tool having a device and using a for holding in the workpieces (1, 2, 3) certain joining element (4), characterized in that the workpieces (1, 2, 3) are heated by a laser beam (5).

2. The method according to claim 1, characterized in that by means of the laser beam (5) in the workpieces (1, 2, 3) in a particular tubular and / or cylindrical zone (6), the temperature is increased.

3. The method according to claim 2, characterized in that the joining element (4) during penetration into the workpieces (1, 2, 3) of the zone (6) is guided.

4. The method according to at least one of the preceding claims, characterized in that the workpieces (1, 2, 3) are completely penetrated by the joining element (4).

5. The method according to at least one of the preceding claims, characterized in that at a joint (7, 8, 9) first of the laser beam (5) acts on the workpieces (1, 2, 3), then the action of the laser beam (5) is terminated on the joint (7, 8, 9), then the joining tool on the joint (7, 8, 9) is positioned and then the joining element (4) by means of the joining tool in the workpieces (1, 2, 3) is used.

6. The method according to at least one of the preceding claims, characterized in that at a first joint (7) first of the laser beam (5) acts on the workpieces (1, 2, 3), then the action of the laser beam (5) on the first Joining point (7) is terminated, then the device relative to the workpieces (1, 2, 3) is moved so that the joining tool on the first joint (7) is positioned and then, while at a second joint (8) of the laser beam (5) acting on the workpieces (1, 2, 3), the joining element (4) by means of the joining tool at the first joint (7) in the workpieces (1, 2, 3) is used.

7. The method according to at least one of the preceding claims, characterized in that the laser beam (5) continuously, without interruption on the workpieces (1, 2, 3) acts, wherein the laser beam (5) relative to the workpieces (1, 2, 3) is moved, while at the same time the joining tool, the laser beam (5) trailing cyclically over the joints (J, 8, 9) is positioned and then the joining element (4) by means of the joining tool in the workpieces (1, 2, 3) is used.

8. Device for joining overlapping workpieces (1, 2, 3) to be joined to one another at a joint (7, 8, 9), with one for introducing a joining element (4) into the workpieces (1, 2, 3) formed joining tool, wherein the device relative to the workpieces (1, 2, 3) is movable, characterized in that the device comprises a laser source for emitting a laser beam (5).

9. Apparatus according to claim 8, characterized in that the joining tool and the laser source are movable together with the device.

10. The device according to at least one of the preceding claims 8 and 9, characterized in that the joining tool and the laser source to the device are independently movable.