METHOD FOR HOMOGENEOUS WELDING OF FLAT-CURVED STRUCTURES BY FRICTION STIR WELDING

Description

[0001] The invention relates to a method for using a device for homogeneous welding of flat, curved structures by friction stir welding.

[0002] The prior art includes, among others, EP 2 027 962 A1, which relates to a welding device and a welding method for orbital welding of pipes. This document identifies several disadvantages of the known prior art, the elimination of which is the objective of this application. According to the information in claim 1, this is an arc welding device comprising a welding head for applying a welding arc with a welding power to a joint between a first and second workpiece to create a weld pool, wherein the welding arc is movable relative to the first and second workpieces.The invention claimed here in the characterizing part of claim 1 is that the welding device comprises a temperature measuring device for measuring a temperature in the area surrounding the weld pool and a control device, wherein the control device is designed to generate at least one signal as a function of the measured temperature, which signal serves to control at least one welding parameter. It is further claimed that the temperature measuring device is preferably designed as a pyrometer and / or the temperature measuring device is arranged such that the temperature is measured at at least one temperature measuring point in front of, next to and / or behind the weld pool, wherein the temperature measuring device is preferably arranged such that it encompasses a region whose temperature allows a conclusion to be drawn about the weld pool temperature.

[0003] In general, orbital welding of tubular components using conventional welding processes such as MIG or MAG welding requires considerable effort in terms of process control due to the effects of gravity on the melt and the shielding gas. When used in the field, for example, for buried power lines and pipelines, conventional orbital welding processes are also highly susceptible to environmental conditions.

[0004] From the document DE 20 2015 000 949 U1, which forms the preamble of patent claim 1, a device for the homogeneous welding of flat, curved structures in the form of at least two joining partners by friction stir welding is known, wherein a sliding surface of a transverse web of the welding shoe is adapted in its curvature to the surface curvature of the two joining partners.

[0005] Regarding the prior art, reference is further made to EP 2 561 948 A1, which relates to a method and system for producing a flange-pipe-flange element by friction stir welding. The objective of such a system is to simplify the centering of the flange and pipe and to utilize the weld pool support not only to support the area softened by friction stir welding, but also to absorb the contact forces during friction stir welding and to center the pipe along the longitudinal axis of the flanges, eliminating the need for measuring and setting processes while simultaneously reducing production times, saving material, and ensuring economic benefits.In this case, the weld pool retainer is designed as a pneumatically clampable and detachable clamping and support disk for centering the pipe on the axis of rotation of the flanges and for absorbing the contact forces during friction stir welding, wherein a sensor is provided for scanning the butt joints between pipe and flange, and furthermore a device is provided for moving a shaped wedge towards and away from the tangential plane lying horizontally above the axis of rotation and running through the butt joint in order to move the friction stir welding probe of the friction stir welding tool out of the friction stir welded butt joint without leaving any holes, wherein the sensor and the device for moving the shaped wedge towards and away from the butt joint are connected to the control system.

[0006] In friction stir welding, frictional heat is generated in the joining area of the materials to be welded by the friction between a rotating tool that simultaneously moves in a translational motion and applies pressure. This heat transforms the materials to be welded into a plasticized state. The tool is moved along the joining area and stirs the plasticized material inside the seam of the abutting materials to be joined. At the end of this seam, the tool is withdrawn from the joining area, and the weld seam is immediately ready for loading.

[0007] DE 20 2014 003072 U1 discloses a device suitable for the homogeneous welding of straight structures. It features strain gauges spaced 120 degrees apart around the circumference of the tool holder cone.

[0008] Furthermore, from the document DE 20 2014 000 747 U1 a device for friction stir welding of materials of different thicknesses and for fillet welds is known, wherein a welding shoe has a shoe sliding surface and a shoe smoothing surface as a crossbar, which is acute-angled for fillet welds and bevelled for different material thicknesses.

[0009] Finally, from the document DE 20 2012 005 397 U1, a device for improving the quality of a weld seam in friction stir welding is known, wherein the welding shoe has a flat sliding surface and two adjoining, curved sliding surfaces inclined thereto.

[0010] The invention is based on the object of providing a method for using the device according to the preamble of patent claim 1, wherein hole formation in the exit area of the welding pin is further reduced.

[0011] According to the invention, this object is achieved by the characterizing features of the new patent claim 1.

[0012] An advantageous embodiment of the invention is characterized in subclaim 2.

[0013] The device according to the invention is described in more detail below.

[0014] They show in detail: Fig.1 : a side view of an arrangement for friction stir welding, Fig.2 : the representation of a preferred welding shoe, Fig.3 : the sectional view of a pin exit, and Fig.4 : Details of the measured value recording in a holding cone 3

[0015] In the Fig.1 A side view of an arrangement for friction stir welding on a flat, curved structure is shown. A support plate 1, which can be guided by a robot arm (not shown here), carries a drive head 2 with a tool bell 3 for holding a welding shoe. The welding shoe with its pin bearing 5 is fastened to the retaining cone 3 by a retaining ring 4. The component of the curved structure of the two joining partners, shown in cross-section, that can be seen from the front is designated 6.

[0016] The Fig.2 : shows the representation of a preferred welding shoe.8. Here, in the Fia.2a) a welding shoe 8 is shown transversely to the direction of movement of the welding process over the two flat, curved joining partners, which are shown here in cross-section. Furthermore, the sliding surface of the welding shoe 8 is essentially adapted to the curvature of the surface of the joining partners 6. In the Fig.2b) The same welding shoe can be seen directly in the direction of movement of the welding process, with the two joining partners being seen in a linear form transverse to their curved surface. The pin shaft 7 of the welding shoe 8 with its pin bearing 5 can be seen differently in both figures due to its holding mechanism. Fig.2a) the material exit area 10 and the welding pin 11 are designated.

[0017] The welding shoe (8) has a circular basic shape, on which, running across the cross-section and at right angles to this basic shape, there is a crossbar which has a width of approximately 1 / 4 to 1 / 5 of the diameter of the basic shape and has an arcuate shoe sliding surface and shoe smoothing surface, with a small flat surface in the form of a notch-like taper, a chip guide step 9, being located on the front side of this surface in the area of the edge of this surface.

[0018] On the front side of the welding shoe 8, which can be identified by the arrow shown to indicate the direction of movement of the welding process, the chip guide step 9 is shown. The respective joining partner 6 is in the Fig.2a) in a curved form. In the representation of the Fig.2b) Additionally, the rear joining partner is designated with 13 and the front joining partner with 14.

[0019] The Fig.3 : shows a cross-sectional view of a pin exit. The two concentric circles shown here represent the cross-section of a joining partner 6, which in this case, for reasons of simplified representation, represents a tube with a small diameter compared to the welding shoe 5 with its welding pin 11. In particular, the friction pin can have a conical shape at the end located in the material in order to keep the volume change linear during a retraction movement.

[0020] On the left, the welding pin 11 can be seen in a position where it is beginning to complete the friction stir welding process and is preparing to reduce the pressure on the joining partners and withdraw from contact with them. Since the welding shoe 5 continues to move in the direction of the arrow during this withdrawal of the welding pin 11, the superposition of the movements shown creates the exit curve 15 shown.

[0021] This movement consists of two components. The pin is retracted in the true sense, meaning the rotating element is also axially displaced. Furthermore, the static, non-rotating shoulder is advanced while the rotating pin is not longitudinally adjusted. This results in the position control of the friction pin and the force control of the shoe. Both control processes are synchronized according to the invention.

[0022] In all cases, the compaction process must be ensured by appropriate contact pressure conditions, i.e., maintaining certain pressure conditions is essential.

[0023] The Fig.3 The illustration shown is only an example. Instead of the continuously running exit curve 15 shown, a stepped exit curve may also prove useful in individual cases. However, for all of the processes described, it is important to know the temperature of the welding pin 11. For this purpose, a special temperature sensor, in particular an infrared sensor, is provided (not shown in any figure). The type of this temperature sensor depends on the specific task and can either determine the temperature of the welding pin directly or indirectly by measuring the ambient temperature of the welding process in question.

[0024] The exit curve 15 and the entire welding process are 3D-capable. This means that the entire welding process can be carried out in all spatial planes and in all spatial directions thanks to the recording of all relevant process parameters in real time. It goes without saying that the welding process leaves no trace in the joining area, and in particular, no hole formation is detectable in the exit area of the welding pin.

[0025] The Fig.4 : shows details of the measured value acquisition. In this illustration, the tool bell 3 is shown in a stylized cross-section with the tool holder cone 26.

[0026] In the longitudinal axis of the retaining cone, as shown in the Fig.1 is shown, a two-part adjusting element 16 for the axial adjustment of a shaft of the friction pin can be seen.

[0027] On the lower side of the tool bell 3, shown in section, a sensor 23 with its associated amplifier 27 and antenna can be seen. This sensor 23, for example in the form of a strain gauge (DMS) on the outside of the tool bell 3, is used to record the deformation of the tool bell 3. The DMS is an example here; it can also be a sensor 23 for determining force, pressure or displacement. This strain gauge, which is attached longitudinally to the outside of the tool bell 3, is therefore attached to the side of the tool bell 3 that is opposite the machining direction because this is where the greatest deformation of the tool bell 3 is to be expected. As already mentioned, an amplifier 27 with its antenna is used to amplify the measurement signal determined by the sensor 23.

[0028] The tool holder cone 26 shown with the shaft of the friction pin 7 reveals a tapered section 17 in its wider area, which serves to accommodate a sensor 20. This tapered section is emphasized for clarity. The mechanical cross-sectional narrowing caused by the tapered section 17 and the placement of the sensor 20 at this point enable the measurement of the axial force and torque acting on the tool holder cone 26, as well as the measurement of the bending moment occurring here. The signal transmission of the measured values determined by the sensor 20 takes place via a signal amplifier 21, which is rotatable with the tool holder cone 26, and a rotor antenna. The reception and forwarding of the measured values determined by the sensor 20 takes place via a statically fixed antenna 22.In the front area of the tool holder cone 26 there is a further, unspecified waistline which provides space for strain gauges 25 and which enables the measurement of the axial force acting directly on the pin shaft 7 and thus the welding pin tip. The strain gauges 25 consist of, for example, three strips which are distributed at a distance of 120 degrees around the circumference of the tool holder cone 26, in the illustrated waistline. More than three strips can also be distributed around the circumference. Optionally, a piezoelectric force measuring sensor 24, which also serves to measure the axial force, can also be located here in the longitudinal axis of the pin shaft 7. During operation, the measured values of the sensors 24 and 25 can be recorded simultaneously and related to one another in order to rule out measuring errors.The reception and transmission of the measured values determined by the sensors 24 and 25 also takes place via the statically fixed antenna 22. The power supply of the measuring systems described is provided by an inductive power supply, the static primary winding of which is designated 18 and the movable secondary winding of which is designated 19.

[0029] As already mentioned in the description of the Fig.3 As described above, in the welding process according to the invention, all relevant process parameters are recorded in real time using a wide variety of sensors. This essentially results in the following combinations of measured values from tools and corresponding process control actions. a) The effective force is measured at welding shoe 8 and welding pin 11. Both are subjected to a controlled pressure. b) The effective force is measured at welding shoe 8 while welding pin 11 maintains its position. The effective force at welding shoe 8 is controlled. c) The position of welding shoe 8 remains unchanged. The effective force at welding pin 11 is measured and controlled. d) The effective force at welding shoe 8 is measured, and welding shoe 8 is fed. The torque, feed, and pressure are measured at welding pin 11. e) Welding shoe 8 is operated using chip control stage 9, and the temperature of welding pin 11 is measured. The stroke of welding pin 11 is controlled depending on the transmitted torque and the effective force.

[0030] Overall, the axial force acting on the welding pin (11) is measured and controlled, as is the torque acting on the welding pin (11). Furthermore, the length of the welding pin (11) is automatically adjusted by means of one or more unspecified piezoelectric actuators, which also have sensory measuring properties, and the temperature at the welding pin (11) is measured by means of an unspecified infrared sensor or the like.

[0031] Furthermore, the pressure force acting on the welding shoe (8) is measured and controlled. According to the invention, the advance of the welding shoe (8) is dependent on the measured axial pressure on the welding shoe (8). Furthermore, the temperature of the welding shoe is measured by means of temperature sensors (not specified in more detail).

[0032] The formation of the weld seam, its quality and its progression are continuously monitored during the entire welding process both visually and by means of quality parameters corresponding to the joining partners.

[0033] The complex control of the described movement sequences requires a special control program. Bezugszeichenliste

[0034] 1 Mounting plate 2 Drive head 3 Tool bell for holding a welding shoe 4 Welding shoe - retaining ring 5 Pin bearing 6 Joining partner 7 Shaft of the friction pin (pin shaft) 8 Welding shoe with pin bearing 9 Chip - guiding stage 10 Material - exit area 11 Welding pin 12 Sliding surface of the welding shoe 13 Rear joining partner 14 Front joining partner 15 Path of a pin at exit 16 Adjusting element for the axial adjustment of the pin shaft 17 Cone - waist for holding a sensor 18 Primary winding of the inductive power supply 19 Secondary winding of the inductive power supply 20 Sensor (e.g. DMS) for the tool - holding cone 16 21 Sensor - signal amplifier and rotor antenna 22 Static antenna 23 Sensor on the welding shoe - holding cone ( DMS - pressure gauge for welding shoe) 24 Piezoelectric force - Measuring sensor 25Sensor for measuring the axial force 26Tool holder cone

Claims

1. A method of using a device for homogeneously welding flat-bent structures in the form of at least two assembly parts by friction stir welding, comprising the following characteristics: a) a receiving plate (1) guided by a guiding machine and accompanied by a drive head (2), and a tool bell (3) attached to it and accompanied by a welding shoe support (4) and a spindle bearing (5) for a welding spindle (11) of a welding shoe (8), wherein b) the welding shoe (8) has a circular basic shape, and c) the tool bell (3) includes a strip-shaped sensor (23), which is designed to determine a force, a pressure, or a displacement and is mounted on the side of the tool bell (3) opposite to the welding process flow direction, and wherein a conical profiling (17) is provided in the wider area of the tool receiving cone (26) to accommodate a sensor (20) for determining an axial force, a torque, and a bending moment on the welding spindle (11), and wherein another profiling is provided in the front area of the tool receiving cone (26) with sensors (25) for measuring the axial force acting on the welding spindle (11) and with a piezoelectric force sensor (24) in the longitudinal axis of the friction pin rod (7), also for measuring the axial force, and wherein a sensor signal amplifier is provided with a rotor antenna (21) to receive, amplify, and transmit all determined measurement values, wherein a static antenna (22) is provided to transmit these measurement values to a machine control, and wherein an inductive power supply system is provided to power the measurement system from a movable secondary winding (19) and a fixed primary winding (18), wherein a crossbar, extending over the circular basic shape of the welding shoe (8) above the cross-section and extending perpendicularly to this basic shape, is provided with a width ranging from 1 / 4 to 1 / 5 of a diameter of the basic shape and with an arc-shaped sliding and smoothing surface of the shoe, wherein a small flat surface in the form of a notch-shaped taper, as a chip guiding step (9), is located on the front face of this surface in the edge area of this surface, wherein the sliding and smoothing surface of the shoe substantially corresponds to the surface curvature of the respective assembly parts (6), characterized in that the pressure force acting on the welding shoe (8) is measured and controlled, wherein the displacement of the welding shoe (8) is carried out based on the measured axial pressure on the welding shoe (8), and a position control of the welding spindle (11) and a force control of the welding shoe (8) are carried out synchronously.

2. The method of claim 1, characterized in that a sensor determines a temperature of the welding spindle (11) and the welding shoe (8).