WO2007006669A1

WO2007006669A1 - Friction stir welding tool and method and assembly for the real-time control of a friction stir welding process

Info

Publication number: WO2007006669A1
Application number: PCT/EP2006/063758
Authority: WO
Inventors: Jean Pierre Bergmann; Johannes Wilden; Frank BARTHELMÄ; Bernd Aschenbach
Original assignee: Technische Universität Ilmenau
Priority date: 2005-07-09
Filing date: 2006-06-30
Publication date: 2007-01-18
Also published as: EP1901875A1; DE102005032170A1

Abstract

The invention relates to a friction stir welding tool and to a method and an assembly for the real-time control of a friction stir welding process. The aim of the invention is to provide a compact friction stir welding tool for universal application and a method and an assembly for the real-time control of a friction stir welding process, in order to produce a weld seam that conforms to quality standards without the need for subsequent finishing and to minimise the stress exerted on the friction stir welding installation. To achieve this, the oscillations of a friction stir welding tool are recorded in the x-, y- and z-directions and the processing forces that emanate from the friction stir welding tool, together with the working temperatures that occur directly at the welding point, are recorded during the friction stir welding process with the aid of appropriate sensors. The recorded data is then telemetrically transmitted to an evaluation unit, where said data is prepared by computer. The process parameters processing speed, processing force and working temperature are regulated by a control unit.

Description

ROUGHBED WELDING TOOL AND METHOD AND ARRANGEMENT FOR REAL-TIME CHECKING OF AN ERROR WRITING PROCESS BY DETECTING THE ACCELERATOR AND / OR VIBRATION TO THE TOOLBODY

The invention relates to a friction stir welding tool and a method and an arrangement for real-time control of a friction stir welding process.

Friction welding has been used industrially for a number of decades for a variety of joining tasks in which rotationally symmetric or flat workpieces are joined. In conventional friction welding, the heat is generated by friction of the joining surfaces, which is generated by the relative movement of the joining partners to each other.

Friction Stir Welding (FSW) is a further development of friction welding technology and was patented in the early 1990s (GB 2 270 864). This method is due to the low joining ^¬ temperatures and the excellent property profile of the compounds of. In the FSW, both the frictional heat and the pressure are generated by wear-resistant tool stir bolts. These consist of a shoulder and a pin and are pressed in rotation in the joining area in the workpiece material until the shoulder is in contact with the workpiece surface ^¬ piece. The friction between the workpiece material and the shoulder produces the required heat for plasticizing the workpiece material. During the movement of the friction stir tool along the joining area, the plasticized material is stirred by the pin inside the seam and transported to its rear side. Basic explanations of this technique can be found in Dalle Donne, C; Braun, R .; Staniek, G .; Jung, A .; Kaysser, WA: Micro- structural, mechanical and corrosive properties of friction-welded butt welds in aluminum alloys; in: Mat.-wiss. u. Werkstofftech. 29, (1998), 609-617.

However, the forces occurring during friction stir welding in the diving phase make special demands on the used machine tools and systems. These must be sufficiently rigid because vibrations occurring during Rührreibschweißprozesses to irregular Nahtaus- lead education and process reliability as well as its reproduction ^¬ ibility be greatly affected. In Blach, 0 .; Senne, F .: friction stir welding from the perspective of a user in rail vehicle construction; in: 2. GKSS Workshop, (2002), 85-94; the reason given for the lack of reproducibility is the overloading of the machining centers used. Despite the displayed constant values of the height position (z position) of the tool stir pin, fluctuations in the immersion depth can be recognized on the seam surface. Due is insufficiently ^¬ reaching rigidity of the machine occur during the process sequence to the "jerk". In addition, axial forces cause the processing process occurring in the machining of up to 30 kN, a reduction in service life of the rolling bearing and the Werkzeugrührbolzen of the welding system.

All these negative phenomena occur more frequently when working on tough material classes, such as steels or mixed compounds. Therefore, in order to be able to produce FSW connections of identical and / or different materials to a greater extent in a process-reliable manner, a real-time process control is required. In order to be able to guarantee constant stirring conditions, the wear of the tool stirring pin (pin and shoulder) must be be constantly monitored. The control of the welding process is very problematic because the joint is very difficult to access. The literature occasionally reports on online process control systems. For example, in Kailee, S .; Nicholas, DE; Thomas, W .: Friction Stir Welding: Invention, Innovations and Applications; in: 2. GKSS Workshop, (2002), 9-22; the forces occurring detected by a dynamometer and a load cell, with a feedback with the machine control does not occur. This measurement allows only the detection of the force components F _x , F _y and F _z and can be used to monitor the immersion depth at the beginning of the process.

In Kleiner, D .; Bird, CR .: Signal Processing for quality assurance in friction stir welds; in: 42nd Annual British Conference on NDT, (2003), 169-174; Sound emissions are measured and evaluated during the ongoing process. By transforming these signals, it is possible to perform a control of the process. For example, can be safely discharged, the occurrence of cavities and irregularities in the weld seam (Kissing bonds) with the aid of a proces ^¬ tung algorithm from these thus obtained signals. However, the monitoring of sound emissions is greatly impaired by the background noises occurring in a production hall.

Another arrangement for controlling the FSW process with a double-shouldered bolt is shown in WO 00/2699 A1. Also in this case, only integrated information about path change and pressurization are determined. The regulation then takes place via an actuator. In WO 03/064100 Al, the force is assumed between the shoulders as prozessregelnde size and measured over the Antriebsmo ^¬ ment.

DE 101 39 687 C1 describes a solution for measuring the temperature in the tool and thus for determining the auftre ^¬ border time-temperature regime in the process.

A significant further development of this control process is provided by the patent DE 10 2004 030 381 B3, published on January 12, 2006. Here, the use of suitable measuring methods and arrangements for determining the pressurization (eg by means of strain gauge, piezoelectric or magnetostrictive element or by means of a printing foil) as well as the occurring oscillations (microwave sensor) is presented. In particular, the vibrations are measured via the change in position of the machine parts involved in the process with a laser or microwave sensor. These measuring elements can be mounted externally or on the holder (tool chuck). The solution illustrated is a deve ^¬ development of the hitherto known prior art. The disadvantage of this solution, however, is that in all cases the information about the processes from the state of the stirring ^¬ bolt, so below the contact surface shoulder / component is determined. It is not possible with this method, for example, specifically the flow of material around the pin, as well as wear of the pin itself to ermit ^¬ stuffs. The process safety as well as the occurrence of sogenann ^¬ th Kissing bonds during friction stir welding, however, are largely determined by the flow of material around the pin. If this is continuous, then it is a matter of uniform mixing (in the solid state, similar to kneading) between the joining partners to close (see Fig. 1). If this occurs a discontinuity, such as the short-term

Peeling off a film of material in the rotating motion around the

Pen around, then results in a time-limited speed change. This can with the in DE 10 2004

030 381 B3 are not precisely recorded, as this is always one of several influencing factors

(Compliance of the materials, the stirring pin, transmission at the interface in the case of measuring the strain and the change in position) dependent information is determined. A direct determination of the velocity field changing in the material flow is not realized. A clear statement about the material-specific conditions of the joint seam is thus not possible. In addition, it is precisely in the case of heterogeneous material pairings that the situation arises that an untypical velocity field exists due to the different flow properties. This can not be reliably defined by the current sensor technology.

The process control systems available in the prior art are therefore only of limited suitability for one-off production on CNC universal machines and for series production. In particular, the known measuring methods provide no useful information about the tool wear and changes in the material flow at the interface pin / plasticized workpiece material, which is decisive for the quality of the connection and for the design of the pin and the process.

It is therefore an object of the present invention to provide a compact, universally applicable friction stir welding tool as well as a method and an arrangement for real-time control provide a Rührreibschweißprozesses with which it is possible the joining process mieren easy and inexpensive to opti ^¬ so that in its result, the quality requirements ^¬ stakes corresponding joint seam without the need for post-processing occurs and the load on the friction stir welding mini ^¬ mized is.

According to the invention, the solution of this problem succeeds with the features of the first, ninth and twelfth claims.

Advantageous embodiments of the invention are specified in the subclaims.

The invention will be explained in more detail below with reference to drawings. In the accompanying drawings show:

Fig. 1 - representation of the velocity field during a friction stir welding process

Fig. 2 - schematic representation of a friction stir welding tool according to the invention

Fig. 3 - schematic representation of a control loop for the friction stir welding process

Fig. 1 illustrates the components of a speed ^¬ field, as occurs in an ordinary Rührreibschweißprozess.

FIG. 2 schematically shows a friction stir welding tool according to the invention, which is attached to a non-illustrated

Machine spindle via a standard interface 1, such as a hollow shaft taper is mounted. Known friction stir welding Tools consist essentially of a tool body 2 made of tempered tool steel and a Werkzeugrührbolzen 3, the latter being composed of a shoulder and a pin, which are firmly connected together. The attachment of the Werkzeugrührbolzens 3 on the tool base body 2 ^¬ takes place in a tool holder, for example a collet or chuck for parallel according to DIN 1835 part 1 and 2. FIG.

The heat generated in the friction stir welding process is dissipated via a closed cooling system 4. The coolant is supplied to the tool via the inner coolant supply (IKZ) 5 of the machine spindle and via a radially rotatably mounted on the outer circumference of the tool coolant ring 6 derived. For spindles without ICZZ, the supply and discharge can be carried out via a modified coolant ring.

According to the invention, a correspondingly designed sensor arrangement 7 enables the detection of selected, process-related irregularities which are essentially due to changes in the material flow or in the friction behavior at the interface pin / substrate surface. This Unre ^¬ larities, which originally result from a change in the rotational speed, the acceleration occurring in the tool can be determined by the measurement. The acceleration can be multiaxial, for example, by means of a commercially available triaxial acceleration sensor based on piezos be measured. After further processing and evaluation of these measured values, it is then possible to make a statement about the vibrations occurring and loads on the machine. Further instrumentalization of the friction stir welding head, based on the already mentioned methods for determining the static and dynamic components of the force acting on the workpieces to be welded, is realized with suitable force measuring sensors, such as strain gauges or piezoelectric sensors, in a suitable arrangement. Due to the thermal characteristics of the friction stir welding process, the temperature ^monitoring required to protect the sensors can also be recorded as a process variable. In this case, the active cooling of the electronics area, which is necessary in the friction stir welding tool, is also taken into account as process parameters. For temperature measurement is a sensor with low heat capacity near the active site or near the Werkzeugrührbolzen. 3

With the solution according to the invention, a separation of the effects can take place and the weighting of the material flow change, for example due to the material-specific properties, the temperature of the materials (flow limit) but also in particular the arrangement to the pin (Positionie ^¬ tion), the geometry of the pen and its state erge ben ^¬ take place. In addition, the solution presented here offers the unique possibility of actively gaining information about the self-adjusting material flow in the case of non-similar material pairings (eg steel / aluminum, titanium / aluminum, etc.). In this case, the different flow properties of the materials used lead to an untypical velocity field, which can only be defined by measuring the resulting velocity changes (accelerations). The compact design according to the invention and the intelligent arrangement of the sensors in the friction stir welding head represent an essential feature of the invention, since thus the user can be offered a holistic, real-time process control "in one hand".

The energy for the tool-internal electronics is inductively fed via a coupling point 9.

With the help of the data collected in this way, one can conclude on changed process conditions and correlate with occurring welding irregularities.

To ensure the use of the Rührreibschweißwerkzeuges on conven- tional machining centers with automatic tool changer and to avoid collisions with this, a stator 10 has the shape of a ^¬ preferably Kreisringaus section.

In Fig. 3, the control circuit of a fiction, ^¬ friction stir welding system is shown schematically. Once occur during the welding process as a result of instabilities, such as immersion depth, tool wear, cavities, etc. changes in acceleration and / or the force profile and / or the temperature at the friction stir welding tool, the respective sensor signals via a data pre-processing and a bidirectional telemetry unit are transmitted ^¬ unit to an evaluation , There, the data is prepared and commands for controlling the action logic in the welding system are generated. The generated commands for system control are transmitted via suitable interfaces, which in turn transmit the relevant process parameters, such as processing speed. speed, processing power and working temperature. This ensures that the process parameters are adapted to the changing process conditions during the welding process and that the welding process can be carried out in a quality-oriented manner.

Advantageous here is the use of suitable compact sensors of the smallest design, for determining the acceleration, the force and the temperature. This allows the integration of these sensors preferably in the tool body, ie near the site of action. With the erfindungsge ^¬ MAESSEN friction stir welding tool changer particular Derun ^¬ can gen the flow of material and for example Verschleißerschei ^¬ voltages are detected at Werkzeugrührbolzen. The regulation of the processing force and the working temperature enables a tool and plant-saving, low-wear process flow.

Furthermore, the compact design of the friction stir welding tool according to the invention, which is compatible with various welding systems or machining centers, proves to be very advantageous since it can be used universally and, in particular, offers small companies the possibility of reacting very flexibly to corresponding market requirements.

LIST OF REFERENCE NUMBERS

1 - standard interface

2 - Tool body

3 - Tool stirring bolt

4 - closed cooling system

5 - inner coolant supply (IKZ) 6 - outer coolant ring

7 - Acceleration, force and temperature sensors

8 - Data preprocessing

9 - Coupling point

10 - Stator of the machine tool

Claims

claims

1. friction stir welding tool consisting of a tool ^¬ basic body and a Werkzeugrührbolzen with a shoulder ter and a pin, characterized in that in

Tool body at least one sensor for detecting the force acting on the tool body acceleration forces is integrated.

2. Friction friction welding tool according to claim 1, characterized in that the integrated sensor is adapted to determine acceleration forces resulting from changes in the material flow or friction behavior at the interface between the pin and workpiece surface to be welded.

3. friction stir welding tool according to claim 2, characterized in that with the integrated sensor further occurring at the interface pin / workpiece surface machining forces and / or working temperatures are determined.

4. friction stir welding tool according to one of claims 1 to 3, characterized in that the integrated sensor comprises one or more acceleration sensors, with which the vibrations of the friction stir welding tool orthogonal to one another in the x, y and z direction can be detected.

5. A friction stir welding tool according to claim 4, characterized in that the sensor is a triaxial acceleration sensor.

6. A friction stir welding tool according to one of claims 1 to 5, characterized in that the integrated sensor comprises at least one force measuring sensor, preferably as a strain gauge or piezoelectric force sensor, me the machining forces with which the friction stir welding tool acts on the workpieces to be welded, are detectable.

7. friction stir welding tool according to one of claims 1 to 6, characterized in that the integrated sensor comprises at least one temperature sensor, with which the operating temperatures that occur directly at the point of action, can be detected.

8. Rührreibschweißwerkzeug according to one of claims 1 to 7, characterized in that in the tool body (2) of the Rührreibschweißwerkzeuges means for cooling (4, 5 and 6) of the integrated sensor (7) and the Werkzeugrührbolzens (3) are provided.

9. A method for real-time control of a friction stir welding process, characterized in that the vibra ^¬ tions of a friction stir welding tool in the x, y and z direction during the friction stir welding process with sensors integrated in the friction stir welding tool are detected, transmit the acquired data to an evaluation and be processed by this and controlled by a control unit, the process parameters.

10. The method according to claim 9, further comprising detecting the machining forces with which the friction stir welding tool acts on the workpieces to be welded and the working temperatures which occur directly at the weld point with the sensors integrated in the friction stir welding tool, the detected data is transmitted to the evaluation unit and processed by the latter and regulated by the control unit as a process parameter.

11. The method according to claim 9 or 10, characterized in that at least processing ^¬ speed, processing force and working temperature are determined and regulated as process parameters, wherein the process parameters are each adapted to the changing during the friction stir welding process conditions.

12. An arrangement for real-time control of a friction stir welding ^¬ process according to a method according to any one of claims 9 to 11, characterized in that it consists of a machine tool with a friction stir welding tool according to one of claims 1 to 8, means for telemetric transmission of the collected data, a Evaluation unit for their preparation and a control unit for setting the process parameters exists.