EP2747930A1

EP2747930A1 - Friction-stir welding device and method for joining workpieces using a friction-stir welding method

Info

Publication number: EP2747930A1
Application number: EP12737494.0A
Authority: EP
Inventors: Sahin SÜNGER; Franz Xaver Wirth
Original assignee: Technische Universitat Muenchen Institut fur Werkzeugmaschinen und Betriebswissenschaften
Current assignee: Technische Universitat Muenchen Institut fur Werkzeugmaschinen und Betriebswissenschaften
Priority date: 2011-08-24
Filing date: 2012-07-17
Publication date: 2014-07-02
Also published as: US9132505B2; US20150069114A1; WO2013026513A1; DE102011111750B3

Abstract

The invention relates to a friction-stir welding device for joining workpieces 1, 2, comprising a welding pin 3 that can be rotated about the welding pin central axis 9 by means of a drive and comprising at least one clamping device for clamping the workpieces 1, 2 to be joined. The invention is characterized in that the clamping device comprises at least two clamping elements 10, 11, each of which has an undercut guide track 12. The guide tracks 12 are arranged parallel to one another and parallel to a joining region 8. A sliding element 13 is arranged between the clamping elements 10, 11, said sliding element being retained against the workpieces 1, 2 by the guide tracks 12 and being movable along the guide tracks 12 in a translational manner. The sliding element 12 is provided with an opening 14 through which the welding pin 3 is passed. The invention also relates to a method for friction-stir welding using the aforementioned device.

Description

Friction friction welding device and method for joining workpieces

by means of a friction stir welding process

The invention relates to an apparatus for joining workpieces and to a method for joining workpieces by means of a friction stir welding method.

The principles of friction stir welding methods are previously known, for example, from WO 93/10935 A1.

FIG. 1 shows schematically the sequence of a friction stir welding process known from the prior art. Friction stir welding uses a wear resistant tool consisting of a welding pin 3 (pin) and a shoulder 4, contrary to the conventional friction welding process, to produce a material bond. The tool used is contoured so that solid material can be sheared in the contact area and stirred together. The plasticizing process is supported by the influence of the resulting frictional heat. The process temperatures are typically in the range of the recrystallization temperature of the base material, thus the joining partners are not melted. The friction stir tool has three primary functions to fulfill (Mishra & Mahoney 2007, "Friction Stir Welding and Processing" -1st edition, ASM International 2007, ISBN 087170840X), these are:

Heat generation by friction and shear;

Cohesive joining of the workpieces (joining partners) by stirring the plasticized material;

Sealing the seam top through the shoulder.

During the joining process, the welding pin completely dips into the joint area and is responsible for the process flow along the joint surface (abutment surface, bonding surface) and for the generation of the material bond.

The task of the shoulder 4 is primarily to complete the joining zone 8 from the seam top. For this purpose, the tool or the shoulder surface is pressed over the entire joining process away with a high contact pressure usually at an angle of 2 ° to 4 ° pungingly on the surface of the workpieces. Due to the relatively large contact surface, the shoulder 4 is able, on the one hand, to protect the still hot weld deposit from access of air and, on the other hand, to prevent excessive material leakage and thus to facilitate the compaction and consolidation of the sheared material. Furthermore, the shoulder 4, similar to the welding pin 3, contributes to heat generation and material shearing at areas near the surface. No. 6,264,088 B1 discloses a tool concept in which the welding pin can rotate independently of the shoulder.

The use of such a tool with a stationary shoulder offers the user various advantages over a conventional tool concept. These can u.a. be the following:

it forms a clean, scale-free seam surface, whose appearance resembles the unaffected base material; the thermal and mechanical influence of the base material is nearly homogeneous along the seam depth direction;

There are new fields of application for friction stir welding, for example a weld seam in the T-joint (fillet weld).

However, a disadvantage is in particular the required anti-rotation, which must be realized by an additional element, often a bracket. This connects the tool housing with a fixed part of the machine. An automatic tool change, as is common in modern processing machines, involves the risk of collision with this additional device. As a rule, therefore, a previous disassembly of the tool attachment is required. Another disadvantage is the fact that the contact pressure of the stationary shoulder must be applied via the drives of the machine. The invention has for its object to provide a Rührreibschweißvorrichtung of the aforementioned type, which avoids the disadvantages of the prior art with a simple structure and simple, cost-effective manufacturability and provides a good work result. Furthermore, the invention has for its object to provide a Rührreibschweißverfahren of the type mentioned above, which provides a high-quality work product while avoiding the disadvantages of the prior art.

According to the invention the objects are achieved by the feature combinations of the independent claims, the respective subclaims show further advantageous embodiments of the invention.

With regard to the friction stir welding device according to the invention, it is thus provided that the two workpieces are positioned and clamped to one another by means of at least one tensioning device. The clamping device comprises at least two clamping elements, which may be formed like a strip. The two clamping elements are each provided with at least one guideway. The two guideways are arranged parallel to each other and have a distance to each other, in which the joining zone (joining region) is located. Between Thus, the welding pin can be sunk into the edge regions of the workpieces to be joined in order to weld these two clamping elements. The device according to the invention further provides a sliding element, which is held and guided by the guideways of the clamping elements. The sliding element is moved according to the invention in a translational movement along the guide zone, wherein only the translational movement between the sliding piece and the workpieces takes place. According to the invention the sliding element is moved non-rotating. In the solution according to the invention is thus provided that the sliding element is held and guided by the two clamping elements. The clamping elements are designed so that they hold or bias the sliding element against the surface of the two workpieces, so that the welding pin itself does not have to apply any force component for holding or pressing the sliding element.

The invention is thus based on the principle of eliminating the spatial dependence of the shoulder and welding pin on the tool side. For this purpose, the shoulder of the tool is replaced by a sliding element, which is integrated into the clamping technology of the workpiece or in additional parts, such as bars. The sliding element and the clamping jaws are for this purpose made so that the sliding element can be moved only along the welding path. Other translational or rotational degrees of freedom are limited by the positive connection between the sliding element and clamping jaws.

In the method according to the invention, the welding pin pierces through a through hole or fit, which is arranged in the center of the sliding element, in the base material. By feeding the welding pin along the welding path (joining zone), the sliding element is permanently carried along. The joining zone is sealed at the top. The sliding element should be made of a wear-resistant solid that is able to withstand the tribological loads. These result from the friction between the rotating welding pin and the cylindrical surface of a recess of the Sliding element (hole) and from the feed-induced friction between the base material surface and the clamping jaw surfaces and the sliding element.

The substitution of the tool shoulder with the sliding element results, as compared with the conventional concept of a stationary shoulder, inter alia. the following advantages are listed below: significantly lower process forces in the axial direction, because the power flow of the shoulder over the clamping device closes;

- Lesser design and manufacturing and assembly costs of the tools, since these consist only more of the welding pin;

the welding pin can move in the axial direction independently of the sliding element. As a result, endkraterfreie seams can be realized by the welding pin pulled out during the advancing movement of base material and the missing volume through

Filler metal is filled.

The invention thus provides the possibility of applying a suitable contact pressure of the sliding element to the joining region in order to recompress the joining region and to smooth the joining region. There are thus no or only minor reworking required.

Since, according to the invention, the contact force on the sliding element is applied by the clamping elements, there is a considerable reduction in the force flow to a spindle element of a machine tool, which supports the rotating welding pin. Experiments have shown that the clamping device according to the invention by means of the clamping elements allows a reduction of the contact pressure of the sliding element against the workpieces by up to 50%. According to the invention it is thus possible to produce burr-free joining areas, which often require no post-processing.

In the following the invention will be described by means of embodiments in conjunction with the drawing. Showing: Fig. 1 is a schematic representation of the invention of the underlying

Friction stir welding method according to the prior art,

Fig. 2 is an enlarged view of the Rührreibschweißvorgangs according to the

State of the art,

3 is a simplified, perspective view of an embodiment of the device according to the invention, Fig. 4 shows an embodiment of a sliding element according to the invention in

Shape of a circular disk,

Fig. 5 is a perspective view, analogous to FIG. 4, a modified

Embodiment of the sliding element with flattening,

6 is a representation of a further embodiment of the sliding element according to the invention with flattening and cavity,

Fig. 7 shows another embodiment of an inventive

Sliding element with flattening and elevation,

Fig. 8 shows a further embodiment of an inventive

Sliding element for use in T-joints or oblique impacts, and Fig. 9 shows a further embodiment of an inventive

Sliding element for use with tubular workpieces.

Fig. 1 shows a schematic representation of the individual process steps of the friction stir welding according to the prior art. A friction stir welding tool has a welding pin 3 and is flattened at its free end, so that an annular shoulder 4 is formed. The tool is first immersed in the joint area 8 of the workpieces 1, 2. The tool rotates for a certain period of time in the joining zone 8 and is subsequently moved in a translatory manner, as shown by the arrow, for joining, wherein the tool is rotated about its central axis. In this way, both the welding pin 3 and the shoulder 4 engage with the plasticized material of the workpieces 1, 2. FIG. 2 shows an enlarged detail view of the joining region 8. A plasticizing zone 6 caused by the rotation of the welding pin 3 is shown. The reference numeral 5 shows the area heated by the frictional heat, while the reference numeral 7 represents the unaffected base material. Fig. 3 shows a schematic structure of the device according to the invention. In this case, plate-shaped workpieces 1 and 2 are shown, which are to be welded together along a joining zone 8 (joining region).

The two workpieces 1 and 2 are held and positioned by means of strip-like clamping elements 10 and 11. On the detailed design of the clamping elements 10 and 1 1 and their fixation on the workpieces 1 and 2 has been omitted for the sake of simple illustration.

The two clamping elements 10 and 1 1 each have on their sides facing each other an undercut guide rail 12, in which a sliding element 13 is displaceable.

The design of the sliding element 13 will be explained below with reference to some embodiments in detail. The sliding element 13 has a recess 14, through which a welding pin 3, which is rotatable about its central axis 9, inserted and in the material of the workpieces 1, 2 is einsteinbar, as has already been explained in connection with FIGS. 1 and 2 ,

By a movement of the welding pin 3 along the joint zone 8, the sliding element 13 is moved translationally along the undercut guide tracks 12. The sliding element 13 has no further movements relative to the workpieces 1 and 2. Hereinafter, possible shapes and profiles of the sliding element 13 will be explained with reference to schematic representations. Different combinations of the individual variants of the sliding elements 13 are always possible in order to generate the most suitable solution for the respective welding task.

The basic shape of the sliding element is shown in FIG. 4. This variant consists of a circular disk with a centrally located recess 14 (through hole) for the welding pin 3. It can be incorporated to control the flow of material and a special profiling in the cylindrical surface of the recess 14. It is thus possible, for example, to guide the material flow in the direction of the tool tip by means of a thread profile and thus to improve the sealing effect between the welding pin 3 and the recess 14. An anti-rotation is not present in this basic variant. However, the displaced by the welding pin 3 base material acts a high force in the normal direction and thus a frictional connection to the sliding element 13, which effectively affects the rotation. The circular shape has the advantage that tilting of the sliding element within the guide (guideways 12) can be virtually eliminated during the feed. The sliding element 13 shown in FIG. 5 is based on the basic shape described above and is supplemented by two parallel flattenings 15, which serve as sliding surfaces and positive rotation in the recesses of the clamping elements 10, 11 (clamping bars). The sliding element 13 can, as shown in Fig. 6, in addition to the two lateral flats 15 via an additionally incorporated cavity 16. This space offers the displaced by the welding pin 3 base material and is used during the welding process as a material reservoir. The cavity 16 can be realized in various forms such as a conical or concave recess. However, other geometric variations, in particular by profiling the Kavitätsfläche, possible.

In order to assist the compaction and consolidation of the sheared material within the joining zone 8, located in that shown in Fig. 7 Sliding element 13 an additional survey 17 (compaction lip, projecting area), which exerts local pressure on the base material and thus can promote the consolidation of the sheared material. Through various designs of the shape, position and effective length of the compression lip, the effect of the welding operations and the base materials can be flexibly adapted.

In addition to the planar designs for butt joint or lap joint configurations, according to the invention also angled variants of the sliding element 13, for example for welding tasks on T joints or oblique joints with different opening angles, are possible. As an example, the sliding element 13 shown in FIG. 8 may be mentioned for a weld in the T-joint. As with the planar sliding element variants, the variations described above and their combinations can also be realized with the angled sliding elements.

The principle of the tool-side spatial separation of the shoulder and welding pin 3 can also be used for friction stir welding on curved components, such as pipes and shafts, by means of a sliding element 13 (FIG. 9). The main body of the sliding element 13 consists of a shell-shaped component, whose recess radius corresponds to the outer radius of the workpieces 1, 2 to be welded. In the center, the sliding element 13 is provided with a matching recess 14 for the implementation of the welding pin. Through the use of this element welds can be realized both in the longitudinal and in the circumferential direction. The inside of the pushing member 13 can be provided with the same modifications for improving the welding result as the sliding member 13 pushing member 13. Also here, similar to the sliding element, combinations of the various modifications are possible.

From the above description of different embodiments of the invention shows that the sliding element 13 is moved by a translational movement of the welding pin 3 along the guide zone 8. However, it is also possible according to the invention to carry out a separate drive for this purpose alternatively or in support of it. Furthermore, it is possible according to the invention to bias the sliding element 13 with a predetermined contact force against the surface of the workpieces 1, 2, for example by an intermediate elastic element or by suitable design of the clamping elements 10, 11 for applying an additional biasing force.

LIST OF REFERENCE NUMBERS

1, 2 workpiece (joining part)

3 welding pin

4 shoulder

5 frictional heat

6 plasticizing zone

7 unaffected base material

8 joining zone / joining area

9 central axis

10, 11 clamping element

12 undercut guideway

13 sliding element

14 recess

15 flattening / anti-rotation

16 cavity (conical or concave recess)

17 survey / area above

Claims

claims

Characterized in that the clamping device at least two clamping elements (10, 11) each having an undercut guide track (12), wherein the guide tracks (12) parallel to each other and parallel to a joining region (8) are arranged, that between the clamping elements (10, 1 1) a sliding element (13) is arranged, which is supported by the guide tracks (12) against the workpieces (1, 2) and along the guide tracks (12) translationally displaceable, and that the sliding element (12) with a recess (14) for carrying out the Welding pin (3) is provided.

Apparatus according to claim 1, characterized in that the clamping elements (10, 11) for applying a biasing force to the sliding element (13) are formed in the direction of the workpiece surface.

Apparatus according to claim 1 or 2, characterized in that the sliding element (13) is designed in the form of a plate or a shaped piece.

Device according to one of claims 1 to 3, characterized in that the recess (14) of the sliding element (13) is arranged substantially centrally to the sliding element (13).

Device according to one of claims 1 to 4, characterized in that the sliding element (13) is designed as a circular disc.

Device according to one of claims 1 to 5, characterized in that the sliding element (13) is provided with at least one anti-rotation device (15).

7. Device according to one of claims 1 to 6, characterized in that the sliding element (13) on its the workpieces (1, 2) facing side is at least partially concave (16).

Device according to one of claims 1 to 7, characterized in that the sliding element (13) on its the workpieces (1, 2) facing side has at least one projecting portion (17).

Method for joining two workpieces (1, 2) by means of a friction stir welding process, in which the workpieces (1, 2) are held by means of a tensioning device (10, 11) in which a welding pin (3) is rotated by means of a drive and rotated into the joining region (8) is introduced between the workpieces (1, 2) and moved translationally along the joining region (8) and in which a sliding element (13) by means of the tensioning device (10, 11) in the joining region (8) against the surfaces of the workpieces (1, 2) is biased and together with the welding pin (3), which passes through the sliding element (13), is translationally moved along the joining region (8).

A method according to claim 9, characterized in that the translational movement of the sliding element (13) by the welding pin (3) or by a separate drive is applied.