JP7701588B2 - Temperature and load measurement method for friction stir welding, and friction stir welding measurement device used therefor - Google Patents

Description

The present invention relates to a method for measuring temperature and load for friction stir welding that can simultaneously and in real time measure the changes over time in temperature and load during actual friction stir welding processing, and a measurement device for friction stir welding used therefor.

In recent years, friction stir welding (hereinafter also referred to as "FSW") has been developed as a joining technology in which frictional heat is used to reduce the deformation resistance of the parts to be joined, and then the parts are stirred (plastic flow) to achieve a joint. Unlike regular welding, in which the joint is melted, friction stir welding joins the parts in the solid phase, resulting in fine structure at the joint and excellent mechanical properties, and therefore it has been put to practical use particularly in high-precision joining and joining of dissimilar materials.

The joining conditions for friction stir welding are generally composed of the load of the rotating tool, the rotation speed of the rotating tool, the moving speed of the rotating tool, and the advance angle of the rotating tool, and the desired joining is achieved by adjusting each of these parameters. In friction stir welding, it is important to control the appropriate plastic flow of the joint caused by stirring, and when considering the joining conditions, it is important to detect whether the parts to be joined are in a state where they are subjected to a deformation resistance suitable for joining.

Temperature and load are important conditions for controlling the plastic flow of the parts to be joined, and the applicant has already developed and provided a tool holder type temperature measurement device that detects the temperature change of the rotating tool (probe) during joining in real time (Patent Document 1). This makes it possible to detect the heat input near the joint, which directly affects proper joining, estimate the appropriate reduction in the deformation resistance of the joint, and perform highly accurate control of the plastic flow in real time.

On the other hand, as mentioned above, it is known that the load conditions are also important for controlling the plastic flow of the welded parts, but in the past, measurements and verifications were made after welding using a dynamometer or load cell (load sensor) equipped on the friction stir welding machine or the like (Patent Document 2). However, in order to control the plastic flow of the weld with high precision, it is necessary to detect and analyze the load in real time during welding as well. The applicant measured the temperature of the tip of the rotating tool during welding using a tool holder-type temperature measurement device as exemplified in Patent Document 1 above, while measuring the load using a dynamometer or load cell equipped on the friction stir welding machine, and evaluated the bending load, uniaxial load, and torsional force from the measurement data for temperature and load using separate software on an external PC.

International Publication No. WO2016/111336 JP 2009-269077 A

However, even if the applicant goes one step further and measures both temperature and load as described above, if the temperature and load measurements are performed using separate software, it is practically difficult to evaluate the correlation between temperature and load in detail in real time during welding. This makes it difficult to develop technology that automatically determines appropriate welding conditions based on the correlation between temperature and load and detects abnormalities in welds. In addition, many of the load sensors, such as load cells, that are equipped in friction stir welding equipment are wired, which is cumbersome to handle, and therefore difficult to use at the mass production site, even if it is possible to use them as a load measurement tool at the laboratory level.

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 processing and detect abnormalities and defects in the workpieces to be joined and abnormalities in the tool in real time with high accuracy and high sensitivity from changes in temperature and load over time, and a friction stir welding measurement device used for this.

The present invention, which is provided to solve the above-mentioned problems, provides a temperature and load measurement method for friction stir welding that measures the temperature and load of the workpieces being joined in real time during friction stir welding.

Specifically, in this temperature/load measurement method for friction stir welding, the change in electrical resistance of an electrical resistance strain gauge attached at a position away 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 electrical resistance change and the temperature signal of the electromotive force are output in real time on the same time axis.

The load signal can be output by linearly converting the output voltage from the electrical resistance strain gauge into a load signal, and can be transmitted simultaneously with the output signal from the thermocouple.

In the present invention, in addition to the temperature inside the rotating tool that was previously measured during actual friction stir welding, the load calculated from a strain gauge attached to the spindle side of the tool holder can be output simultaneously. Therefore, abnormalities and defects on the workpieces to be joined can be detected in real time from the changes over time in temperature and load.

First, looking at the horizontal load during friction stir welding, as can be seen from the formula F = TA/σ in the right column of Figure 10, the limit load F at a given temperature depends on the shear deformation resistance of the probe at that temperature and is therefore determined by the temperature of the rotating tool. In other words, the horizontal load (= limit load) at which 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, it is possible to calculate the limit value of the safe welding speed at each time with high accuracy in real time.

Furthermore, as will be described in detail later, it was found that the voltage output of the electrical resistance strain gauge can be linearly converted into force both when the rotary tool is loaded and when it is unloaded, and that the sensitivity to welding abnormalities of the welded parts (formation of cavities, void entrapment, etc.) is greater to force than to temperature. Therefore, by measuring the horizontal load calculated from the electrical resistance strain gauge during welding, sensitive and highly accurate abnormality detection can be performed in real time. Therefore, by measuring the temperature and load using the temperature/load measurement method for friction stir welding of the present invention, the conditions for the fastest and safest friction stir welding can be obtained.

The present invention also provides a specific friction stir measurement device used in the above-mentioned friction stir welding temperature/load measurement method. In detail, the friction stir measurement device measures the temperature and load of the workpieces during friction stir welding in real time. The friction stir measurement device is equipped with a tool holder that rotates around the axis of the main shaft of the friction stir welding device body and holds the rotating tool at its tip. The tool holder is equipped with a thermocouple that is disposed in an axial channel provided in the rotating tool that contacts the workpieces during welding and outputs an electromotive force, an electric resistance strain gauge that is attached to a position on the outer peripheral wall of the tool holder (such as the surface of the housing part 5 in the covering part 6 described later) separated from the rotating tool except for the connection part with the spindle and outputs the deformation of the tool holder as a change in electric resistance value, and an electronic board that receives the electromotive force output from the thermocouple and the change in electric resistance output from the electric resistance strain gauge and outputs digital signals of temperature information and load information, respectively.

In addition to measuring the temperature using thermocouples in one or more channels installed in the rotating tool, this friction stir measuring device also uses a configuration in which an electrical resistance strain gauge is attached to the outer periphery of the tool holder away from the rotating tool to detect deformation of the tool holder as a change in electrical resistance value and calculate the load.

When measuring horizontal loads (bending forces), it is advantageous to attach the electric resistance strain gauge to a part far from the processing point (rotating tool) so that the moment is large, preferably to the part farthest from it (excluding the gripping part 7 that connects to the spindle). Here, the electric resistance strain gauge is attached to a part on the outer wall of the tool holder far from the rotating tool other than the part connected to the spindle. Also, since a rise in temperature due to frictional heat causes a drift in the output value of the electric resistance strain gauge, it is advantageous to attach it away from the processing point from the viewpoint of preventing this. It is also known that the sensitivity of the electric resistance strain gauge is not significantly affected by the attachment position when detecting tensile and compressive loads (uniaxial loads) in the vertical direction (z direction) and torsional forces, as long as it is not at the part connected to the spindle or the gripping part of the rotating tool.

The friction stir measuring device preferably also includes a transmitting means for simultaneously transmitting digital signals of the temperature information and load information output from the electronic board, and a display means for receiving the temperature information and load information transmitted from the transmitting means and displaying them on the same time axis.

Conventionally, temperature and load were measured using separate software, but with this friction stir measuring device, temperature and load are measured using the same tool holder-type measuring device and simultaneously transmitted as digital information via wireless communication, etc., and the signals are displayed on the same time axis on the display of an external PC, etc.

As a representative example, the electric resistance strain gauge measures bending strain by forming a bridge circuit with electric resistance strain gauges Rg1 and Rg3, which detect a pair of compressive or tensile strain along the axial direction on the outer peripheral wall of the tool holder, and electric resistance strain gauges Rg2 and Rg4, which detect a pair of 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 each other.

In other words, it is preferable to form a bridge circuit called the four-active method in which two pairs of electric strain gauges are arranged in two pairs from the viewpoint of temperature compensation and amplifying the output potential difference to improve sensitivity. When measuring a horizontal load (bending force), two strain gauges Rg1 and Rg3 are attached along the axial direction of the outer peripheral wall of the tool holder where axial tensile or compressive strain acts due to bending force, and compressive or tensile strains Rg2 and Rg4 opposite to strain gauges Rg1 and Rg3 are attached on the radial opposite side (position shifted by approximately 180°), measuring both tensile and compressive strains caused by temperature change, and then outputting a voltage converted to an effective value (RMS). With this strain gauge arrangement, bending force acts to measure tensile strain and compressive strain on the opposite side, so the output is four times higher and sensitivity can be increased.

As another representative example of the electric resistance strain gauge, two pairs of electric resistance strain gauges, Rg1 along the axial direction on the outer wall of the tool holder, Rg2 along a direction perpendicular to the electric resistance strain gauge, and Rg3 and Rg4 in the same positional relationship, are attached to form a bridge circuit to measure the tensile strain and compressive strain of the tool holder.

In other words, when measuring uniaxial stress (uniform tensile or compressive force) by forming a bridge circuit using the so-called four-active method, it is preferable to attach a pair of strain gauges Rg1 and Rg2 along the direction in which the tensile or compressive force acts and along a direction perpendicular to this, for a total of two pairs (Rg1, Rg2, Rg3, Rg4).

As yet another representative example of the electric resistance strain gauge, the electric resistance strain gauge is mounted on the outer peripheral wall of the tool holder in a pair of electric resistance strain gauges Rg1 and Rg2 that face in opposite directions along one axial rotation direction or along a direction inclined at a predetermined angle, and on the outer peripheral wall of the tool holder in a pair of electric resistance strain gauges Rg3 and Rg4 that face in opposite directions along the opposite axial rotation direction or along a direction inclined at a predetermined angle to form a bridge circuit, thereby measuring the torsional strain on the tool holder.

When measuring torsional force by forming a bridge circuit using the so-called four-active method, a pair of strain gauges Rg1 and Rg2 are attached to one shaft rotation direction, preferably tilted at approximately +45° and approximately -45° and facing in opposite directions, and a pair of strain gauges Rg3 and Rg4 are attached to the other shaft rotation direction, preferably tilted at approximately +45° and approximately -45° and facing in opposite directions.

The friction stir welding temperature and load measurement method of the present invention and the friction stir measurement device used therein can measure temperature and load in order to appropriately control the plastic flow of the workpieces. By simply replacing a general-purpose friction stir welding device with a tool holder-type friction stir measurement device, abnormalities and defects in the workpieces and abnormalities in the tool can be detected in real time with high accuracy and high sensitivity from the changes in temperature and load over time, making it easy to find welding conditions that can improve welding efficiency.

FIG. 1 is a perspective view illustrating an outline of a main configuration of a general friction stir welding apparatus body. 1A is a photograph of the part before the rotary tool is gripped by the tool holder, and FIG. 1B is a photograph of the assembled part. FIG. 3 is a perspective photograph showing the appearance of the housing for electronic components with the covering removed in a state in which the tool holder in FIG. 2 is connected to a spindle. 1 is a schematic diagram showing a friction stir welding measurement device according to the present invention, which is configured with a tool holder connected to a spindle and an external PC. FIG. (a) shows a conceptual diagram of the four active gauge method as an example of an arrangement for measuring horizontal load (bending force), and (b) shows the circuit diagram. (a) shows a conceptual diagram of the four active gauge method (orthogonal arrangement method) as an example of an arrangement for measuring a uniaxial load, and (b) shows the circuit diagram. (a) shows a conceptual diagram of the four active gauge method (torsional strain measurement method) as an example of an arrangement when measuring torsional force, and (b) shows the circuit diagram. FIG. 2A is a graph showing the relationship between strain and force (calibration curve), and FIG. 2B is a graph showing time-series data of load values during actual machining converted using the calibration curve of FIG. FIG. 13A is a graph showing the time series change in temperature of a rotating tool during actual machining, and FIG. 13B is a graph showing the time series change in force of a rotating tool during the same actual machining. FIG. 11 is a graph showing the relationship between the moving speed (welding speed) of a rotary tool and a horizontal load.

<Overview of friction stir welding equipment>
FIG. 1 is a perspective view illustrating a main configuration of a general friction stir welding apparatus body A (hereinafter also referred to as "apparatus body A") for explaining the friction stir welding apparatus of the present invention. The apparatus body A is generally configured to include a tool holder gripping portion 40, a workpiece mounting surface 41, a work stage 42, a head support 43, a head 44, and an operation panel 45 (or an external PC 46 described later). First, a tool holder 2 gripping a rotating tool 4 that is brought into rotational contact (contact direction = arrow Z direction, rotation direction = direction around the axis of arrow Z) with two workpieces (not shown) to be joined is attached to the tool holder gripping portion 40 (hereinafter also referred to as "spindle 40"). As a result, the tool holder gripping portion 40, the tool holder 2, and the rotating tool 4 rotate together. The workpieces are placed on a workpiece mounting surface 41 on the upper surface of the work stage 42, and are fixed to the workpiece mounting surface 41 using fixing clamps (not shown), fixing bolts (not shown), or the like. In this state, the user operates the operation panel 45 or an external PC (described later) to interrupt the CNC of the apparatus main body A, and moves the work stage 42 in the X direction, and the workpieces are stopped and positioned when the rotating tool 4 (see FIG. 2 described later) is located directly above the desired joining position.

Next, while stopped and positioned on the workpieces, the operation panel 45 or an external PC described later is operated to lower the rotating tool 4, bring it into contact with the workpieces, rotate it while pressing the joint, and move it in the joining direction. At this time, the user inputs at least the parameters of the tool load to be applied to the rotating tool 4, the tool movement speed which becomes the joining speed, and the tool rotation speed of the rotating tool 4 in advance to set the joining conditions to be used for friction stir welding. Although not shown, it may be preferable to tilt the rotating tool 4 in the movement direction (joining direction). The tool advance angle of the rotating tool 4 is set by changing the engagement angle between the head 44 and the head support 43.

After the setting on the operation panel 45 or the external PC described later is completed, the rotary tool 4 is rotated directly above the workpieces to be joined until the set tool rotation speed is reached, and then the head 44 is moved downward in the Z direction to press the rotary tool 4 at the joining start point of the workpieces to be joined. When the head 44 presses the rotary tool against the workpieces to be joined with a tool load set in advance, the contact portion (joining portion) between the rotary tool 4 and the workpieces to be joined reduces the deformation resistance of the workpieces to be joined due to frictional heat, and the vicinity of the contact portion begins to stir due to the rotation of the rotary tool 4. After that, 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 joining start point to the joining end point to join the workpieces to be joined. After the desired joining is achieved, the head 44 is moved upward in the Z direction while maintaining the rotation of the rotary tool 4, and the rotary tool 4 is pulled out from the joining end point and the rotation of the rotary tool 4 is stopped. This process completes the joining.

Next, the tool holder 2 and the rotating tool 4 that are held and fixed by the tool holder holding part 40 of the device body A will be described. FIG. 2 shows, in (a), a component photograph before the tool holder 2 holds the rotating tool 4, and in (b), an assembly photograph. The outer periphery of the electronic component housing part 5 is sealed with a covering part 6, and FIG. 3 is a perspective photograph showing the state in which the covering part 6 is removed to expose the inside of the housing part 5 while the tool holder 2 in FIG. 2 is connected to the main shaft 40 of the device body A. Furthermore, FIG. 4 shows a schematic diagram of the friction stir welding measurement device of the present invention, which is generally composed of the tool holder 2 connected to the main shaft 40 of the device body A and an external PC 46.

The tool holder 2 rotates the rotary tool 2 against the workpieces to perform welding, and itself functions as a measuring device that measures the temperature and load during welding. Although detailed configuration is omitted, the approximately cylindrical tool holder 2 has an axial hollow hole formed inside, and the upper part of the rotary tool 4 is fitted into the hollow hole at the bottom using the flange part 4c as a stopper, and in this state, an annular fixing nut 9 is fitted from below, and the rotary tool 4 is fixed from the radial outside with a fixing screw 3, thereby gripping the rotary tool 4. In addition, the upper part of the tool holder 2 is provided with a cylindrically extending gripping part 7, which is connected to the main shaft 40 and cooperates with the main shaft 40 to enable rotation during welding.

As provided in the above-mentioned Patent Document 1, 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 center of rotation) extending to the deepest position in the probe portion 4a, an intermediate channel 8b (preferably located radially outward from 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 located radially outward of the channels 8 are provided, and a thermocouple 9 is attached to the inner lower end of each of the channels 8a, 8b, and 8c. In addition, in order to obtain a proper joint, it is important to detect the plastic flow state in the depth direction of the joint, and it has been found that it is necessary to provide at least the lower end channel 8a and the intermediate channel 8b.

The thermocouple 9 is connected to the electronic board arranged in the housing 5 from the channel 8 through the above-mentioned hollow hole. The thermocouple 9 may be a temperature measuring element such as a thermistor or a platinum resistance thermometer, and is formed by connecting an electric wire to it. As shown in Figures 3 and 4, the housing 5 receives the temperature measurement result from the thermocouple 9 and transmits it to the electronic board via the electric wire. The electronic board generally includes a potentiometer 12, an amplifier 13, an RMS converter, and an A/D converter 14, and the analog signal detected by the thermocouple 9 is converted into a digital signal by the A/D converter 14 and wirelessly transmitted to the outside from the antenna 16 via the wireless microcomputer (transmitting means) 15 together with the electric resistance value data from the strain gauge 10 described later. The electronic board on which this series of electronic components are arranged is arranged in the housing 5 (see Figure 3) located on the outer periphery of the tool holder 2, taking into consideration the high temperature and high speed rotation environment. The antenna 16 (wireless transceiver 16) is arranged on the outside of the housing 5 or in the covering part 6.

The housing 5 is provided in the gap between the shank 6 and the gripping portion 7 by reducing the diameter of the shank, and is provided with the potentiometer 12, amplifier 13, RMS converter, A/D converter 14, and a wireless microcomputer 15. An electric resistance strain gauge 10 (hereinafter also referred to as "strain gauge 10") used as a load measuring element is attached to the inner surface (surface of the shank) of the housing 5. A detailed arrangement example of the strain gauge 10 will be described later, but the electric resistance value detected by 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 (Amplifer), and the voltage and gain are adjusted. The output signal from the amplifier circuit 12 is averaged by the RMS converter 13 using RMS (root mean square), and the effective value of the voltage is output to quantitatively detect the magnitude of the voltage change. The A/D converter 14 then converts the effective voltage value of the analog signal into a digital signal, and the transmission data is processed by the wireless microcomputer 15 and wirelessly transmitted to the outside via the antenna (wireless transceiver) 16 together with the above-mentioned temperature data.

The wirelessly transmitted temperature data and electrical resistance value data are received from the antenna (wireless transceiver) 17 via the transceiver 18, processed by an external PC 46 with dedicated software installed, and displayed on the display along with the sensor information and CNC internal information from the friction stir welding device main body A on the same time axis, making it available for analysis. Depending on the results of the analysis, it is also possible to correct the CNC internal information to maintain proper plastic flow in the joint, and send an interrupt to the control unit in the device main body A from the external PC.

Below, we will explain in detail a bridge circuit (four-gauge method) using four strain gauges 10 as a typical arrangement of strain gauges 10, and how it is used to measure horizontal load (bending force), uniaxial load, and torsional force.

<Typical arrangement for measuring horizontal load (bending force) (4-gauge method (active): with temperature compensation, temperature effect of lead wire eliminated, compressive (tensile) strain eliminated, 4x output)>
5(a) shows the arrangement of the strain gauges 10 when measuring a horizontal load (bending force (force in the direction of the double arrow in the figure)), and (b) shows the circuit diagram. 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 strain gauges Rg2 and Rg4 are attached on the radially opposite side (position shifted by approximately 180° phase) along the direction in which compression or tension acts opposite to the strain gauges Rg1 and Rg3, and both tensile and compressive strains caused by temperature changes are measured. In this circuit, in order to measure both tensile and compressive strains, a four-fold potential difference e0 is output as shown in the following formula 1, and after the potential difference e0 is amplified by the amplifier 12, the voltage converted to an effective value (RMS) by the RMS converter 13 is read as a digital signal converted by the A/D converter 14.
Gauge resistance: 120 or 350 [Ω]
E: Voltage applied to the bridge (3.3 [V])
e0: Potential difference that changes with deformation

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

<Typical arrangement for uniaxial load measurement (4-gauge method (orthogonal arrangement): with temperature compensation, temperature effect of lead wires eliminated, bending strain eliminated, output 2(1+ν) times)>
FIG. 6(a) shows the arrangement of strain gauges 10 when measuring uniaxial stress (uniform tensile and compressive forces (forces in the direction of the double arrows in the figure)), and FIG. 6(b) shows the circuit diagram. In this arrangement of strain gauges 10, a pair of strain gauges Rg1 and Rg2 are attached along the direction in which tensile and compressive forces act and along the direction perpendicular to the direction, for a total of two pairs (Rg1, Rg2, Rg3, Rg4). Two pairs of strain gauges 10 with two elements (biaxial cross) may be attached. In this circuit, a potential difference e0 of 2×(1+Poisson's ratio ν) times is output as shown in the following formula 2, and after the potential difference e0 is amplified by the amplifier 12 as in FIG. 5, the voltage converted to an effective value (RMS) by the RMS converter 13 is read as a digital signal converted by the A/D converter 14.
Gauge resistance: 120 or 350 [Ω]
E: Voltage applied to the bridge (3.3 [V])
e0: Potential difference that changes with deformation

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

<Typical arrangement for measuring torsional force (4-gauge method (torsional strain measurement method): with temperature compensation, temperature effect of lead wire eliminated, bending strain eliminated, tension and compression eliminated, 4x output)>
7(a) shows a side view and a cross-sectional view of the arrangement of strain gauges 10 when measuring torsional force (force in the direction of the double arrow in the figure) on the top and bottom, respectively, and (b) shows a circuit diagram. In this arrangement of strain gauges 10, a pair of two strain gauges Rg1 and Rg2 are attached, which are inclined at about +45° and about -45° with respect to one axial rotation direction (for example, the direction of the left arrow in FIG. 7(a)) and face in opposite directions, and a pair of two strain gauges Rg3 and Rg4 are attached, which are inclined at about +45° and about -45° with respect to the other axial rotation direction (for example, the direction of the right arrow in FIG. 7(a)) and face in opposite directions. Note that there may also be cases where two pairs of strain gauges Rg1, Rg2 and Rg3, Rg4 are attached without being inclined with respect to the axial rotation as in FIG. 7.

In this circuit, a four-fold potential difference e0 is output as shown in the following equation 3. As in the case of Figures 5 and 6, the potential difference e0 is amplified by an amplifier 12, and then the voltage is converted to an effective value (RMS) by an RMS converter 13, and the digital signal converted by an A/D converter 14 is read.
Gauge resistance: 120 or 350 [Ω]
E: Voltage applied to the bridge (3.3 [V])
e0: Potential difference that changes with deformation

The torsional force measured here (in the direction of the arrow in Figure 7(a)) is attached to the inner wall of the housing 5 in Figure 2 at an angle of approximately 45° to the axial direction of the tool holder 2 (the vertical direction in Figure 1) in the actual tool holder 2 (specific strain gauges Rg1, Rg2, Rg3, and Rg4 are not shown in Figure 2).

<<Method of converting voltage values from strain gauges into load values 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 results of the voltage values detected from the strain gauges 10 and the output results of the dynamometer. Specifically, the rotating tool 4 is pressed against the dynamometer, and the correspondence between the output voltage from the bridge circuit of the strain gauge array described above, the amplifier 12, and the RMS converter 13, and the force indicated by the dynamometer is measured, and this is set as the calibration curve. As the graph shows, the relationship (calibration curve) between the output voltage from the strain gauges 10 and the force is approximately linear,
It was found that the relationship is: Force [kN] = -0.08759 + 0.02219 × Voltage [mV]. It was also found that the calibration curve is not affected and almost coincides with the force curve regardless of whether a load is applied or removed with respect to the pressing of the rotary tool 4 against the dynamometer.

FIG. 8(b) is a graph showing the time series (time [s]: horizontal axis) data of the load value (force [kN]: vertical axis) converted using the calibration curve in (a) during actual processing. Specifically, when the voltage value from the strain gauge 10 measured during friction stir welding is converted to the load value Frms (graph (2)) using the calibration curve in (a), it can be seen that the profile shown on the maximum side of the converted load value Frms (graph (2)) closely matches the load shown by the dynamometer Fy (graph (1)). On the other hand, when the strain gauge 10 is oriented in a direction perpendicular to the moving direction, the bending force is greatly reduced, so that the output value Frms (RMS force) from the RMS converter 13 fluctuates greatly compared to the force Fy shown by the dynamometer. The minimum value of the RMS force Frms is determined by the RMS time constant and the rotation speed. When the RMS force Frms is at its minimum in FIG. 8(b),
Fy√(0.5(1-2/π))≈0.4Fy.

<Tool temperature and horizontal load during actual processing (insertion, joining, and withdrawal)>
9A is a graph showing the change in the temperature [°C (vertical axis)] of the rotary tool 4 over time [s (seconds: horizontal axis)] during actual machining, and FIG. 9B is a graph showing the change in the force Frms [kN (vertical axis)] of the rotary tool 4 over time [s (seconds: horizontal axis)] during actual machining. Note that FIG. 9A and FIG. 9B are displayed on the same time axis, and the force Frms in FIG. 9B shows the output value Frms (RMS force) obtained by RMS-converting the output value from the strain gauge 10. FIG. 9A also shows the temperature in each channel 8 of the rotary tool 4, where (1) shows the temperature of the lower end channel 8a, (2) shows the temperature of the middle channel 8b, and (3) shows the temperature of the shoulder channel 8c.

In the actual processing shown in Figure 9, approximately 5 [s] after the rotary tool 4 is inserted into the workpieces, temperature and force measurements (detection of RMS output value) are started in each channel 8, and as shown in Figure 9(a), it can be seen that the specified plunge depth and joining start temperature are reached after approximately 20 [s]. The rotary tool 4 is moved horizontally to join the workpieces, and after approximately 37 [s] the joining is stopped, the rotary tool 4 that has been pushed into the workpieces is raised, and gradually pulled out from the workpieces. The temperature [°C] and force Frms [kN] during the actual processing process are data wirelessly received from the tool holder 2 and simultaneously detected and stored by a single piece of software installed in the external PC 46.

Therefore, if the welding temperature during actual processing can be measured in real time using this friction stir welding temperature/load measurement method and the friction stir welding measurement device used therein, the limit load can be calculated from the formula in the right column of Figure 10 described above, and the welding speed (upper limit) at the limit load can be detected from the graph in the left column of Figure 10, making it possible to calculate a highly efficient and safe feed rate in real time. In addition, when comparing the temperature [°C] and load [Frms] at the start of welding (after about 20 [s] has elapsed) in Figure 9, it was found that the load [Frms] reacts more quickly than the temperature [°C]. Therefore, in terms of sensitivity to welding abnormalities (formation of cavities, porosity entrapment, etc.) of the welded members, force is more sensitive than temperature, and sensitive and highly accurate abnormality detection can be performed in real time by detecting force using the strain gauge 10 attached to the tool holder 2. Furthermore, using this detection result, it is possible to interrupt internal information such as CNC in the friction stir welding device from the outside and perform welding control that maintains appropriate plastic flow.

Although the embodiments of the present invention have been described above with reference to the drawings, 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 of the claims.

2 Tool holder 3 Fixing screw 4 Rotating tool 4a Probe portion 4b Shoulder portion 4c Flange portion 5 Storage portion 6 Covering portion 7 Grip portion 8 Channel 8a Lower end channel 8b Intermediate channel 8c Shoulder channel 9 Thermocouple (temperature measuring element)
10 Electric resistance strain gauge 11 Potentiometer 12 Amplifier 13 RMS converter 14 A/D converter 15 Wireless microcomputer (transmitting means)
16, 17 Antenna (radio transmitter/receiver)
18 Transceiver 40 Tool holder gripper (spindle)
41: Workpiece placement surface 42: Work stage 43: Head support 44: Head 45: Operation panel 46: External PC
A. Device body

Claims (6)

Measures the temperature and load of the workpieces being joined in real time during friction stir welding ,
A temperature and load measurement method for friction stir welding, comprising: outputting, as a load signal, a change in electrical resistance of an electrical resistance strain gauge attached to a position on the outer peripheral wall of a tool holder separated from a rotating tool excluding the connection portion with the spindle of a friction stir welding apparatus; outputting, as a temperature signal, the electromotive force of a thermocouple in a rotating tool held by the tool holder; and outputting in real time on the same time axis, the load signal of the electrical resistance change and the temperature signal of the electromotive force . A friction stir welding measurement device that measures in real time a temperature and a load during welding of workpieces in friction stir welding, the friction stir welding measurement device having a tool holder that is connected to a main shaft of a friction stir welding device body, rotates around the axis, and holds a rotating tool at its tip,
The tool holder is a friction stir measuring device comprising: a thermocouple disposed in an axial channel provided in a rotating tool that contacts the workpieces during joining and outputs an electromotive force; an electrical resistance strain gauge attached to a position on the outer peripheral wall of the tool holder separated from the rotating tool excluding the connection portion with the spindle and outputs 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 change in electrical resistance output from the electrical resistance strain gauge and outputs them as digital signals of temperature information and load information, respectively. The friction stir measuring device according to claim 2, further comprising: a transmitting means for simultaneously transmitting digital signals of the temperature information and the load information output from the electronic board; 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. The friction stir measuring device according to claim 2 or 3, wherein the electric resistance strain gauge measures bending strain by forming a bridge circuit with a pair of electric resistance strain gauges Rg1, Rg3 that detect compressive or tensile strain along the axial direction on the outer peripheral wall of the tool holder, and a pair of electric resistance strain gauges Rg2, 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 the electric resistance strain gauges Rg1, Rg3. The friction stir measuring device according to claim 2 or 3, wherein the electric resistance strain gauge is an electric resistance strain gauge Rg1 along the axial direction on the outer peripheral wall of the tool holder, an electric resistance strain gauge Rg2 along a direction perpendicular to the electric resistance strain gauge, and two pairs of electric resistance strain gauges Rg3 and Rg4 in the same positional relationship are attached to form a bridge circuit to measure tensile strain and compressive strain on the tool holder. 4. The friction stir measuring device according to claim 2 or 3, wherein the electric resistance strain gauges are a pair of electric resistance strain gauges Rg1, Rg2 that are arranged in opposite directions on the outer peripheral wall of the tool holder along one axial rotation direction or along a direction inclined at a predetermined angle, and a pair of electric resistance strain gauges Rg3, Rg4 that are arranged in opposite directions on the outer peripheral wall of the tool holder along the opposite axial rotation direction or along a direction inclined at a predetermined angle, to form a bridge circuit, thereby measuring torsional strain on the tool holder .