Temperature and Load Measurement Method for Friction Stir Welding and Measurement Device for Friction Stir Welding Used Therein

Abstract

To provide a temperature / load measurement method for friction stir welding that can measure variations in temperature and load in actual processing of friction stir welding with time simultaneously in real time, and a measurement device for friction stir welding used therefor.SOLUTION: The present invention relates to a temperature / load measurement method for friction stir welding that measures a temperature and a load during friction stir welding of a joined member in real time, and that comprises: outputting, as a load signal, an electric resistance variation of an electric resistance strain gauge mounted at a position apart from a rotary tool that a tool holder coupled to a main spindle of a friction stir welding device grips; outputting, as a temperature signal, electromotive force of a thermocouple in the rotary tool that the tool holder grips; and outputting the load signal of the electric resistance variation and the temperature signal of the electromotive force in real time on the same time base. The load signal is output after linear power conversion of an output voltage from the electric resistance strain gauge, and transmitted simultaneously with the output signal from the thermocouple.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for measuring temperature and load for friction stir welding, which can simultaneously and real-time measure the temporal changes of temperature and load during actual processing of friction stir welding, and a measuring device for friction stir welding used therefor.

Background Art

[0002] In recent years, as one of joining techniques, friction stir welding (hereinafter, also referred to as "FSW"), which reduces the deformation resistance of a member to be joined by frictional heat and then stirs (plastic flow) to achieve joining, has been developed. This friction stir welding is different from ordinary welding that melts the joint part. Since it is a solid-phase joining, the structure of the joint part is refined and has excellent mechanical properties, so it has been put into practical use especially in high-precision joining and dissimilar material joining.

[0003] The joining conditions of friction stir welding generally consist of the load of the rotating tool, the rotational speed of the rotating tool, the moving speed of the rotating tool, and the plunge angle of the rotating tool. By adjusting each of these parameters, the desired joining is achieved. In friction stir welding, it is important to control the appropriate plastic flow of the joint part by stirring. When considering the joining conditions, it is to detect whether the member to be joined is placed under a deformation resistance suitable for joining.

[0004] Temperature and load are important conditions for controlling the plastic flow of the member to be joined. The applicant has already developed and provided a tool holder type temperature measuring device that can detect the temperature change of the rotating tool (probe) during joining in real time for temperature (Patent Document 1). As a result, it has become possible to detect the heat input near the joint part that directly affects proper joining, estimate an appropriate decrease in the deformation resistance of the joint part, and perform real-time control of high-precision plastic flow.

[0005] On the one hand, as described above, it has been found that load conditions are also important for controlling the plastic flow of the joined member. Conventionally, however, after joining, measurement and verification have been performed using a dynamometer or load cell (load sensor) provided in a friction stir welding device or the like (Patent Document 2). However, in order to control the plastic flow of the joint portion with high precision, it is necessary to detect and analyze the load in real time during joining. While the applicant measures the temperature at the tip of the rotating tool during joining using the tool holder type temperature measuring device exemplified in Patent Document 1 above, the load is measured using a dynamometer or load cell provided in the friction stir welding device, and the bending load, uniaxial load, and torsional force are evaluated on an external PC using individual software from the measurement data of temperature and load respectively.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, even in the case of further measuring both temperature and load as in the case of the conventional applicant, when performing the measurement of each of temperature and load using individual software as described above, it has been substantially difficult to evaluate the correlation between temperature and load in detail in real time during joining. This has made it difficult to develop a technique for automatically determining appropriate joining conditions based on the correlation between temperature and load and detecting abnormalities in the joint portion. In addition, many of the load sensors such as load cells provided in friction stir welding devices are of the wired type, and although it is possible to apply them as load measurement tools at the laboratory level because handling is troublesome, it has been difficult to apply them at the mass production site.

[0008] Therefore, the present invention was created to solve the above problems, and aims to provide a temperature and load measurement method for friction stir welding that can simultaneously measure the temperature and load during actual friction stir welding, and can detect abnormalities and defects on the workpiece side and abnormalities on the tool side with high precision and high sensitivity in real time from the changes in temperature and load over time, as well as a measurement device for friction stir welding used therefor.

Means for Solving the Problems

[0009] The present invention provided to solve the above problems provides a temperature and load measurement method for friction stir welding that measures the temperature and load during joining of workpieces in friction stir welding in real time.

[0010] Specifically, in this temperature and load measurement method for friction stir welding, the change in electrical resistance of a strain gauge mounted at a position separated from the rotating tool held by a tool holder connected to the spindle of a friction stir welding device is output as a load signal, the electromotive force of a thermocouple in the rotating tool held by the tool holder is output as a temperature signal, and the load signal of the change in electrical resistance and the temperature signal of the electromotive force are output in real time on the same time axis.

[0011] Also, the load signal can be output as a load signal by linearly power-converting the output voltage from the strain gauge and transmitted simultaneously with the output signal from the thermocouple.

[0012] In the present invention, in addition to the temperature inside the rotating tool that has been conventionally measured during actual friction stir welding, the load calculated from the strain gauge attached to the spindle side of the tool holder can also be output simultaneously. Therefore, abnormalities and defects on the workpiece side can be detected in real time from the changes in temperature and load over time.

[0013] First, focusing on the horizontal load during friction stir welding, as can be seen from the formula F = TA / σ in the right column of FIG. 10, the critical load F at a given temperature depends on the shear deformation resistance of the probe at that temperature and is thus determined by the temperature of the rotating tool. That is, the horizontal load (= critical load) when the rotating tool breaks is determined by the temperature of the rotating tool. Therefore, if the temperature during welding is measured in real time using the temperature / load measurement method for friction stir welding of the present invention, the limit value of the joining speed with high accuracy and safety can be calculated in real time at each moment.

[0014] Furthermore, although details will be described later, it has been found that the voltage output of the strain gauge can be linearly converted into force both during loading and unloading of the rotating tool, and regarding the sensitivity to joining abnormalities (such as formation of cavities and entrainment of voids) in the workpiece, force is more sensitive than temperature. Therefore, if the horizontal load calculated from the strain gauge during welding is measured, sensitive and highly accurate abnormality detection can be performed in real time. Thus, by measuring temperature and load using the temperature / load measurement method for friction stir welding of the present invention, the conditions for performing friction stir welding at the highest speed and safely can be obtained.

[0015] The present invention also provides a specific measurement device for friction stir welding used in the above temperature / load measurement method for friction stir welding. Specifically, it is a measurement device for friction stir welding that measures the temperature and load during welding of the workpiece in friction stir welding in real time. The measurement device for friction stir welding includes a tool holder that is connected to the spindle of the friction stir welding device main body and rotates axially, and grips the rotating tool at its tip. The tool holder is disposed in an axial channel provided in the rotating tool that contacts the workpiece during welding and is provided with a thermocouple that outputs an electromotive force, and an electrical resistance strain gauge that is mounted at a position on the outer peripheral wall of the tool holder (such as the surface of the accommodating portion 5 within the covering portion 6 described later) separated from the rotating tool except for the connecting portion with the spindle, and outputs the deformation of the tool holder as a change in electrical resistance value, and an electronic board that receives the electromotive force output from the thermocouple and the electrical resistance change output from the electrical resistance strain gauge, and outputs them as digital signals of temperature information and load information, respectively.

[0016] In addition to measuring the temperature with a thermocouple in one or more channels provided in the rotating tool, this measurement device for friction stir welding employs a configuration in which a strain gauge is attached to the outer peripheral side of the tool holder away from the rotating tool to detect the deformation of the tool holder as a change in the electrical resistance value and calculate the load.

[0017] Also, the position where the strain gauge is attached (the strained portion) is preferably a portion separated from the processing point (rotating tool) so that the moment becomes large when measuring the horizontal load (bending force), and more preferably the most separated portion (excluding the gripping portion 7 connected to the main shaft) is the strained portion. Here, the strain gauge is attached to the position of the outer peripheral wall of the tool holder separated from the rotating tool except for the connecting portion with the main shaft. Also, since the temperature rise due to frictional heat causes drift in the output value of the strain gauge, it is advantageous to be separated from the processing point from the perspective of preventing this. It should be noted that regarding the detection of the tensile / compressive load (uniaxial load) in the vertical direction (z direction) and the torsional force, it is known that the sensitivity of the strain gauge is not much affected by its mounting position as long as it is outside the connecting portion with the main shaft and the gripping portion of the rotating tool.

[0018] Moreover, it is preferable that the measurement device for friction stir welding includes a transmitting means for simultaneously transmitting the digital signals of the temperature information and the load information output from the electronic substrate, and a display means for receiving the temperature information and the load information transmitted from the transmitting means and displaying them on the same time axis.

[0019] Conventionally, the measurement of temperature and load was carried out using separate software, but in this measurement device for friction stir welding, the temperature and the load are measured with the same tool holder type measurement device, and simultaneously transmitted as digital information via wireless communication or the like, and the signals are displayed on the display of an external PC or the like on the same time axis.

[0020] Also, as a representative example, the electric resistance strain gauge forms a bridge circuit with a pair of two electric resistance strain gauges Rg1 and Rg3 that detect compressive or tensile strain along the axial direction on the outer peripheral wall of the tool holder, and a pair of two electric resistance strain gauges Rg2 and Rg4 that detect tensile or compressive strain along the axial direction on the outer peripheral wall of the tool holder at a position shifted by approximately 180° in phase with respect to the former, to measure bending strain.

[0021] That is, it is preferable to form a so-called four-active method bridge circuit in which two pairs of two gauges are arranged from the viewpoints of increasing the output potential difference and improving the sensitivity and temperature compensation of the electric strain gauge. When measuring a horizontal load (bending force), two strain gauges Rg1 and Rg3 are respectively attached along the axial direction to the outer peripheral wall of the tool holder where axial tensile or compressive strain acts due to the bending force, and strain gauges Rg2 and Rg4 with compressive or tensile strain opposite to that of strain gauges Rg1 and Rg3 are attached on the radially opposite side (position shifted by approximately 180° in phase). Tensile and compressive strains generated due to temperature changes are both measured, and then a voltage converted to the effective value (RMS) is output. According to this strain gauge arrangement, since the bending force acts and tensile strain and compressive strain on the opposite side are measured, the output becomes four times, and the sensitivity can be increased.

[0022] Also, as another representative example, the electric resistance strain gauge forms a bridge circuit by mounting two pairs of an electric resistance strain gauge Rg1 along the axial direction on the outer peripheral wall of the tool holder and an electric resistance strain gauge Rg2 along the direction orthogonal to the electric resistance strain gauge, and electric resistance strain gauges Rg3 and Rg4 with the same positional relationship, to measure tensile and compressive strains on the tool holder.

[0023] That is, when measuring uniaxial stress (uniform tensile or compressive force) by forming a bridge circuit of the so-called four-active method, it is preferable to attach a total of two pairs (Rg1, Rg2, Rg3, Rg4) of two strain gauges Rg1 and Rg2 along the direction in which the tensile or compressive force acts and the direction orthogonal to it.

[0024] As yet another representative example of the electric resistance strain gauge, the electric resistance strain gauge forms a pair of electric resistance strain gauges Rg1 and Rg2 that face each other in opposite directions along one axial rotation direction or along a direction inclined at a predetermined angle on the outer peripheral wall of the tool holder, and a pair of electric resistance strain gauges Rg3 and Rg4 that face each other in opposite directions along the opposite axial rotation direction or along a direction inclined at a predetermined angle on the outer peripheral wall of the tool holder. By mounting two pairs to form a bridge circuit, the torsional strain on the tool holder is measured.

[0025] When measuring torsional force by forming a bridge circuit of the so-called four-active method, a pair of two strain gauges Rg1 and Rg2 that are preferably inclined at approximately +45° and -45° respectively with respect to one axial rotation direction and face in opposite directions are attached, and a pair of two strain gauges Rg3 and Rg4 that are preferably inclined at approximately +45° and -45° respectively with respect to the other axial rotation direction and face in opposite directions are also attached.

Advantages of the Invention

[0026] According to the temperature and load measurement method for friction stir welding and the friction stir measurement device used therefor of the present invention, the temperature and load can be measured in order to appropriately control the plastic flow of the members to be joined. By simply replacing the tool holder type of this friction stir measurement device with a general friction stir welding device, abnormalities and defects on the member side to be joined and abnormalities on the tool side can be detected with high precision and high sensitivity in real time from the changes over time of the temperature and load, and it becomes easier to search for joining conditions that can improve the joining efficiency.

Brief Description of the Drawings

[0027]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Best Mode for Carrying Out the Invention

[0028] 《Overview of Friction Stir Welding Device》 FIG. 1 is a perspective view showing a schematic of the main configuration for explaining a general friction stir welding apparatus main body A (hereinafter also referred to as "apparatus main body A") when explaining the friction stir welding apparatus of the present invention. The apparatus main body A generally includes a tool holder gripping portion 40, a workpiece member installation surface 41, a work stage 42, a head support 43, a head 44, an operation panel 45 (or an external PC 46 described later), and is configured to include these components. First, a tool holder 2 that grips a rotating tool 4 that is rotationally abutted (abutting direction = arrow Z direction, rotational direction = circumferential direction around the axis of arrow Z) against two workpiece members to be joined (not shown) is attached to the tool holder gripping portion 40 (hereinafter also referred to as "main shaft 40"). As a result, the tool holder gripping portion 40, the tool holder 2, and the rotating tool 4 will rotate integrally. Further, the workpiece member is placed on the workpiece member installation surface 41 on the upper surface of the work stage 42, and is fixed to the workpiece member installation surface 41 using a fixing clamp (not shown), a fixing bolt (not shown), or the like. In this state, the user interrupts the CNC of the apparatus main body A by operating the operation panel 45 or operating an external PC described later, moves the work stage 42 in the X direction, and the workpiece member is stopped and positioned when the rotating tool 4 (see FIG. 2 described later) is positioned directly above the desired joining position.

[0029] Next, with the workpiece member stopped and positioned thereon, the operation panel 45 or an external PC described later is operated to lower the rotating tool 4, bring it into contact with the workpiece member, rotate it while pressing the joining portion, and move it in the joining direction. At this time, the user inputs in advance at least each parameter of the tool load applied to the rotating tool 4, the tool movement speed that is the joining speed, and the tool rotation speed of the rotating tool 4, and sets the joining conditions used for friction stir welding. Although not shown, in some cases, it may be preferable to incline the rotating tool 4 in the moving direction (joining direction). The setting of the tool advance angle of the rotating tool 4 is performed by changing the fitting angle between the head 44 and the head support 43.

[0030] When the setting on the operation panel 45 or the external PC described later is completed, after rotating the rotary tool 4 directly above the member to be joined and reaching the set tool rotation speed, the head 44 is moved downward in the Z direction, and the rotary tool 4 is pressed at the joint start point of the member to be joined. When the head 44 presses the rotary tool with the tool load preset for the member to be joined, the contact part (joint part) between the rotary tool 4 and the member to be joined reduces the deformation resistance of the member to be joined due to frictional heat, and agitation starts in the vicinity of the contact part by the rotation of the rotary tool 4. Then, the head support 43 is moved in the Y direction at the set tool movement speed, and the rotary tool 4 is carried from the joint start point to the joint end point to join the member to be joined. After the desired joint is achieved, while maintaining the rotation of the rotary tool 4, the head 44 is moved upward in the Z direction, and after pulling out the rotary tool 4 from the joint end point, the rotation of the rotary tool 4 is stopped. The joining is completed by this process.

[0031] Next, the tool holder 2 and the rotary tool 4 held and fixed by the tool holder gripping part 40 of the above-described apparatus main body A will be described. Fig. 2 illustrates, in (a), a parts photo before gripping the rotary tool 4 with the tool holder 2, and in (b), an assembled photo thereof. Also, the outer peripheral side of the housing part 5 of the electronic component is sealed with the covering part 6. Fig. 3 is a perspective photo showing a state where the covering part 6 is removed to expose the inside of the housing part 5 with the tool holder 2 of Fig. 2 connected to the main shaft 40 of the apparatus main body A. Further, Fig. 4 shows a schematic overview diagram schematically showing the friction stir welding measurement apparatus of the present invention constituted by the tool holder 2 connected to the main shaft 40 of the apparatus main body A and the external PC 46.

[0032] The tool holder 2 functions as a measuring device that performs joining by rotationally abutting the rotary tool 2 against the member to be joined and measures the temperature and load during joining itself. Although the detailed configuration is omitted, the substantially cylindrical tool holder 2 has a hollow hole formed axially inside, and at its lower part, the upper part of the rotary tool 4 is fitted into the hollow hole with the flange portion 4c as a stopper, and in that state, an annular fixing nut 9 is fitted from below and fixed with fixing screws 3 from the radially outer side to grip the rotary tool 4. Further, the upper part of the tool holder 2 is provided with a gripping portion 7 extending in a cylindrical shape, and the gripping portion 7 is connected to the main shaft 40 so as to be rotatable during joining in cooperation with the main shaft 40.

[0033] Also, as provided in Patent Document 1 described above, the rotary tool 4 is provided with a plurality of channels 8 extending downward from above the shoulder portion 4b to a predetermined depth inside. In the example of FIG. 4, a lower end channel 8a (preferably located near the rotation center) extending to the deepest position in the probe portion 4a, an intermediate channel 8b (preferably located radially outside the lower end channel 8a) extending from an intermediate depth in the probe portion 4a to a position near the boundary with the shoulder portion 4b, and a shoulder channel 8c located in the shoulder portion 4b and being the most radially outer among the channels 8 are provided, and thermocouples 9 are attached to the inner lower ends of the respective channels 8a, 8b, 8c. In addition, in order to obtain proper joining, it is important to detect the plastic flow state in the depth direction of the joint portion, and it has been found that it is necessary to provide at least the lower end channel 8a and the intermediate channel 8b.

[0034] The thermocouple 9 is connected to an electronic substrate disposed in the accommodating portion 5 through the hollow hole described above from the channel 8. The thermocouple 9 may be a temperature measurement element such as a thermistor and a platinum resistance thermometer, and is formed by connecting electrical wiring thereto. As shown in FIGS. 3 to 4, the temperature measurement result from the thermocouple 9 is received in the accommodating portion 5 and transmitted to the electronic substrate via electrical wiring. Generally, a potentiometer 12, an amplifier 13, an RMS converter, and an A / D converter 14 are disposed on the electronic substrate. The analog signal detected by the thermocouple 9 is digitally converted by the A / D converter 14 and wirelessly transmitted from the antenna 16 to the outside via a wireless microcomputer (transmission means) 15 together with the electrical resistance value data from the strain gauge 10 described later. The electronic substrate on which this series of electronic components are disposed is disposed in the accommodating portion 5 (see FIG. 3) located on the outer peripheral side of the tool holder 2 in consideration of the high-temperature and high-speed rotation environment. Further, the antenna 16 (wireless transceiver 16) is disposed inside the accommodating portion 5 or inside the covering portion 6.

[0035] Further, the accommodating portion 5 is provided in the gap between the covering portion 6 by reducing the diameter of the shank portion connected to the gripping portion 7, and an electronic substrate including the potentiometer 12, the amplifier 13, the RMS converter, and the A / D converter 14 described above and a wireless microcomputer 15 are disposed. An electrical resistance strain gauge 10 (hereinafter, also referred to as "strain gauge 10") used as a load measurement element is attached to the inner surface of the accommodating portion 5 (the surface of the shank portion). Although a detailed arrangement example of the strain gauge 10 will be described later, the electrical resistance value detected from the strain gauge 10 is converted into an analog voltage signal by the digital potentiometer 11, and the analog voltage signal is impedance-matched by the amplifier circuit 12 (Amplifier), and the voltage is adjusted and the gain is adjusted. The output signal from the amplifier circuit 12 is averaged by the RMS converter 13 by RMS (root mean square) to output the effective value of the voltage, and the magnitude of the voltage change is quantitatively detected. Thereafter, the effective value of the voltage of the analog signal is converted into a digital signal by the A / D converter 14, the transmission data is processed by the wireless microcomputer 15, and wirelessly transmitted to the outside by the antenna (wireless transceiver) 16 together with the temperature data described above.

[0036] The wirelessly transmitted temperature data and electrical resistance value data are received from the antenna (wireless transceiver) 17 via the transceiver 18 and processed by an external PC 46 installed with dedicated software, and are displayed on the display together with the sensor information and CNC internal information from the friction stir welding apparatus main body A on the same time axis, becoming analyzable. Also, according to the result of the analysis, it is possible to correct the CNC internal information, etc. to maintain proper plastic flow of the joint part and perform an interrupt process from the external PC to the control part in the apparatus main body A.

[0037] Hereinafter, as a typical arrangement of the strain gauges 10, a bridge circuit (4-gauge method) using 4 strain gauges 10 will be specifically described for each of the measurement of horizontal load (bending force), uniaxial load, and torsional force.

[0038] 《Typical Arrangement at the Time of Measuring Horizontal Load (Bending Force) (4-Gauge Method (Active): With Temperature Compensation, Eliminating Temperature Influence of Lead Wires, Eliminating Compressive (Tensile) Strain, Output Multiplied by 4)》 Fig. 5(a) shows the arrangement of the strain gauges 10 at the time of measuring the horizontal load (bending force (force in the direction of double arrows in the figure)), and (b) shows the circuit diagram thereof. In this arrangement of the strain gauges 10, two strain gauges Rg1 and Rg3 are attached along the direction in which tensile or compressive strain acts, and the strain gauges Rg2 and Rg4 are attached along the direction in which compression or tension opposite to that of the strain gauges Rg1 and Rg3 acts on the opposite side in the radial direction (position shifted by approximately 180° in phase), and both tensile and compressive strains generated by temperature changes are measured. In this circuit, in order to measure both tensile and compressive strains, it is output with a potential difference e0 multiplied by 4 as shown by the following formula (1). After the potential difference e0 is amplified by the amplifier 12, the voltage converted to the effective value (RMS) by the RMS converter 13 is read as a digital signal converted by the A / D conversion 14.

Formula

[0039] The horizontal load (bending force (in the direction of the arrow in Fig. 5(a))) measured here is the load in the radial direction (left - right direction in Fig. 1) in the actual tool holder 2. Fig. 2 shows a state where strain gauges 10 corresponding to the two strain gauges Rg1 and Rg3 are attached to the inner wall of the housing part 5 along the axial direction (the strain gauges Rg2 and Rg4 for reference are not shown in Fig. 2).

[0040] 《Typical arrangement during uniaxial load measurement (4 - gauge method (orthogonal arrangement method): with temperature compensation, elimination of temperature influence of lead wires, elimination of bending strain, output 2(1 + ν) times)》 Fig. 6(a) shows the arrangement of the strain gauges 10 during uniaxial stress (uniform tensile and compressive forces (forces in both arrow directions in the figure)) measurement, and (b) shows its circuit diagram. In this arrangement of the strain gauges 10, a total of two pairs (Rg1, Rg2, Rg3, Rg4) of two strain gauges Rg1 and Rg2 are attached along the direction in which the tensile and compressive forces act and the direction orthogonal to it. The strain gauges 10 may be attached in two pairs of two - element (two - axis cross). In this circuit, as shown by Equation (2) below, it is output with a potential difference e0 that is 2×(1 + Poisson's ratio ν) times, and after the potential difference e0 is amplified by the amplifier 12 as in Fig. 5, the voltage converted to the effective value (RMS) by the RMS converter 13 is read as a digital signal converted by the A / D conversion 14.

Equation

[0041] The uniaxial load (uniaxial stress (in the direction of the arrow in Fig. 6(a))) measured here is the load in the axial direction (up - down direction in Fig. 1) in the actual tool holder 2, and it is attached to the inner wall of the housing part 5 along the axial direction (the specific strain gauges Rg1, Rg2, Rg3, and Rg4 are not shown in Fig. 2).

[0042] 《Typical Array during Torsion Force Measurement (4-Gauge Method (Torsional Strain Measurement Method): With Temperature Compensation, Elimination of Temperature Influence of Lead Wires, Elimination of Bending Strain, Elimination of Tension / Compression, Output Quadrupled)》 Fig. 7(a) shows a side view and a cross-sectional view of the arrangement of strain gauges 10 during measurement of the torsion force (the force in the direction of the double arrows in the figure) on the upper and lower sides respectively, and (b) shows a circuit diagram. In the arrangement of these strain gauges 10, a pair of two strain gauges Rg1 and Rg2, which are inclined at approximately +45° and -45° respectively with respect to one axis rotation direction (for example, the left arrow direction in Fig. 7(a)) and face in opposite directions, are attached, and a pair of two strain gauges Rg3 and Rg4, which are also inclined at approximately +45° and -45° respectively with respect to the other axis rotation direction (for example, the right arrow direction in Fig. 7(a)) and face in opposite directions, are attached. Note that there may be a case where the two pairs of strain gauges Rg1, Rg2 and Rg3, Rg4 are attached without being inclined with respect to the axis rotation as shown in Fig. 7.

[0043] In this circuit, as shown by Equation 3 below, it is output with a quadrupled potential difference e0. After the potential difference e0 is amplified by the amplifier 12 in the same manner as in Figs. 5 and 6, the voltage converted to the effective value (RMS) by the RMS converter 13 is read as a digital signal converted by the A / D conversion 14.

Equation

[0044] The torsion force to be measured here (in the arrow direction in Fig. 7(a)) is attached to the inner wall of the housing portion 5 in Fig. 2 by being inclined at approximately 45° with respect to the axial direction of the tool holder 2 (the vertical direction in Fig. 1) in the actual tool holder 2 (the specific strain gauges Rg1, Rg2, Rg3, and Rg4 are not shown in Fig. 2).

[0045] 《Method for Converting Voltage Value from Strain Gauge to Load Value and Measurement Results》 FIG. 8(a) is a graph showing the relationship (calibration curve) between strain ([mV]: horizontal axis) and force ([kN]: vertical axis) from the output result of the voltage value detected by the strain gauge 10 and the output result of the dynamometer. Specifically, the rotary tool 4 is pressed against the dynamometer, and the correspondence between the output voltage from the bridge circuit of the strain gauge array and the amplifier 12 and the RMS converter 13 described above and the force indicated by the dynamometer is measured and set as the calibration curve. As shown in the graph, the relationship (calibration curve) between the output voltage from the strain gauge 10 and the force is almost linear, and it was found to have the relationship of force [kN] = -0.08759 + 0.02219 × voltage [mV]. Also, it was found that there is no influence on the calibration curve whether a load is applied or removed when pressing the rotary tool 4 against the dynamometer, and they almost coincide.

[0046] Also, FIG. 8(b) is a graph showing the time-series (time [s]: horizontal axis) data during actual machining of the load value (force [kN]: vertical axis) converted using the calibration curve of (a). Specifically, when the calibration curve of (a) is used and the voltage value from the strain gauge 10 measured during friction stir welding is converted into the load value Frms (in the graph (2)), it can be seen that the profile indicated by the maximum value side of the converted load value Frms (in the graph (2)) well matches the load indicated by the dynamometer Fy (in the graph (1)). On the other hand, when the strain gauge 10 is oriented in the direction orthogonal to the traveling direction, the bending force greatly decreases, so the output value Frms (RMS force) from the RMS converter 13 fluctuates greatly compared to the force Fy indicated by the dynamometer. The minimum value of the RMS force Frms is determined by the RMS time constant and the rotational speed. When the RMS force Frms is minimized in FIG. 8(b), Fy√(0.5(1 - 2 / π)) ≒ 0.4Fy.

[0047] 《Tool Temperature and Horizontal Load during Actual Machining (During Insertion, Joining, and Withdrawal)》 In Fig. 9, (a) in the upper part shows the change over time [s (seconds: horizontal axis)] of the temperature [°C (vertical axis)] of the rotating tool 4 during actual machining, and (b) in the lower part shows a graph showing the change over time [s (seconds: horizontal axis)] of the force Frms [kN (vertical axis)] of the rotating tool 4 during the actual machining. Note that Fig. 9(a) and Fig. 9(b) are displayed on the same time axis, and the force Frms in Fig. 9(b) indicates the output value Frms (RMS force) obtained by RMS-converting the output value from the strain gauge 10 described above. Also, the temperature in each channel 8 of the rotating tool 4 is shown in Fig. 9(a), where (1) shows the temperature of the lower end channel 8a, (2) shows the temperature of the intermediate channel 8b, and (3) shows the temperature of the shoulder channel 8c.

[0048] In the actual machining of Fig. 9, about 5 [s] after inserting the rotating tool 4 into the member to be joined, temperature measurement and force measurement (detection of the RMS output value) in each channel 8 were started, and as shown in Fig. 9(a), it can be seen that a predetermined pushing depth and joining start temperature were reached after approximately 20 [s] had elapsed. Also, the rotating tool 4 was moved horizontally to join the member to be joined, the joining was stopped at around 37 [s], the rotating tool 4 pushed into the member to be joined was raised, and it was gradually pulled out from the member to be joined. Note that the temperature [°C] and the force Frms [kN] during the above actual machining process were detected and saved simultaneously by one software installed on the external PC 46 from the data wirelessly received from the tool holder 2.

[0049] Therefore, if the temperature and load measurement method for friction stir welding and the measurement device for friction stir welding used therefor can measure the joint temperature during actual processing in real time, the critical load can be calculated from the formula in the right column of FIG. 10 described above, and the joint speed (upper limit) at the critical load can be detected from the graph in the left column of FIG. 10, enabling the calculation of a high-efficiency and safe feed speed in real time. Further, comparing the temperature [°C] and the load [Frms] at the start of joining in FIG. 9 (when about 20 [s] has elapsed), it was found that the load [Frms] responds more quickly than the temperature [°C]. Therefore, with respect to the sensitivity to joint abnormalities (formation of cavities, entrainment of voids, etc.) in the members to be joined, force is more sensitive than temperature, and highly sensitive and accurate abnormality detection can be performed in real time by detecting the force using the strain gauge 10 attached to the tool holder 2. Furthermore, using this detection result, it is possible to interrupt the internal information such as the CNC inside the friction stir welding device from the outside and perform joint control to maintain proper plastic flow.

[0050] As described above, the embodiments of the present invention have been described with reference to the drawings. However, the specific configuration is not limited to these embodiments. The scope of the present invention is indicated by the claims rather than the description of the above embodiments, and further includes all modifications within the meaning and scope equivalent to the claims.

Explanation of Reference Numerals

[0051] 2 Tool Holder 3 Fixing Screw 4 Rotating Tool 4a Probe Portion 4b Shoulder Portion 4c Flange Portion 5 Housing Portion 6 Coating Portion 7 Gripping Portion 8 Channel 8a Lower End Channel 8b Intermediate Channel 8c Shoulder Channel 9 Thermocouple (Temperature Measurement Element) 10 Electrical Resistance Strain Gauge 11 Potentiometer 12 Amplifier 13 RMS Converter 14 A / D Converter 15 Wireless Microcomputer (Transmission Means) 16, 17 Antenna (Wireless Transceiver) 18 Transceiver 40 Tool Holder Gripping Part (Spindle) 41 Joint Member Installation Surface 42 Work Stage 43 Head Support Base 44 Head 45 Control Panel 46 External PC A Apparatus Body

Claims

1. Measure the temperature and load during the joining of the members to be joined in friction stir welding in real time, Output the change in electrical resistance of an electrical resistance strain gauge mounted at a position on the outer peripheral wall of a tool holder separated from a rotating tool excluding the connection part with the main shaft of a friction stir welding apparatus as a load signal, output the electromotive force of a thermocouple in the rotating tool held by the tool holder as a temperature signal, and output the load signal of the change in electrical resistance and the temperature signal of the electromotive force in real time on the same time axis. A temperature / load measurement method for friction stir welding.

2. A measurement device for friction stir welding that measures the temperature and load during the joining of the members to be joined in friction stir welding in real time. The measurement device for friction stir welding includes a tool holder that is connected to the main shaft of the friction stir welding apparatus main body and rotates axially, and holds a rotating tool at its tip. The tool holder includes a thermocouple disposed in an axial channel provided in the rotating tool that contacts the members to be joined during joining and outputs an electromotive force, and an electrical resistance strain gauge mounted at a position on the outer peripheral wall of the tool holder separated from the rotating tool excluding the connection part with the main shaft, and outputs the deformation of the tool holder as a change in electrical resistance value. An electronic substrate that receives the electromotive force output from the thermocouple and the change in electrical resistance output from the electrical resistance strain gauge, and outputs them as digital signals of temperature information and load information respectively. A measurement device for friction stir welding.

3. Transmission means for simultaneously transmitting the digital signals of the temperature information and load information output from the electronic substrate, and display means for receiving the temperature information and load information transmitted from the transmission means and displaying them on the same time axis. The measurement device for friction stir welding according to claim 2.

4. The electrical resistance strain gauge forms a bridge circuit with a pair of two electrical resistance strain gauges Rg1 and Rg3 that detect compressive or tensile strain along the axial direction on the outer peripheral wall of the tool holder, and a pair of two electrical resistance strain gauges Rg2 and Rg4 that detect tensile or compressive strain along the axial direction on the outer peripheral wall of the tool holder at a position shifted by approximately 180° in phase with respect to this, to measure bending strain. The measurement device for friction stir welding according to claim 2 or 3.

5. The electrical resistance strain gauge forms a bridge circuit by mounting two pairs of electrical resistance strain gauges, namely, an electrical resistance strain gauge Rg1 along the axial direction on the outer peripheral wall of the tool holder and an electrical resistance strain gauge Rg2 along a direction orthogonal to the electrical resistance strain gauge, and electrical resistance strain gauges Rg3 and Rg4 having the same positional relationship, to measure tensile strain and compressive strain with respect to the tool holder. The measuring device for friction stir welding according to claim 2 or 3.

6. The electrical resistance strain gauge forms a bridge circuit by mounting two pairs of electrical resistance strain gauges, namely, a pair of electrical resistance strain gauges Rg1 and Rg2 facing each other along one axial rotation direction or along a direction inclined at a predetermined angle on the outer peripheral wall of the tool holder, and a pair of electrical resistance strain gauges Rg3 and Rg4 facing each other along the opposite axial rotation direction or along a direction inclined at a predetermined angle on the outer peripheral wall of the tool holder, to measure torsional strain with respect to the tool holder. The measuring device for friction stir welding according to claim 2 or 3.

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