Friction stir welding device

Abstract

Provided is a friction stir welding device that has a simplified device configuration and thus can reduce the load of both assembly work and maintenance work. This friction stir welding device 100 comprises a processing head 101 having a joining tool 103 that is pressed against laminated workpieces WK1, WK2 while being rotationally driven. A Z-axis driving motor 109 is connected to the processing head 101 through a ball screw mechanism 107, and the joining tool 103 is pressed against the workpieces WK1, WK2. The Z-axis driving motor 109 is operated and controlled by a control device 130. When the joining tool 103 is being pressed against the workpieces WK1, WK2, the control device 130 executes constant pressing force control for controlling the operation of the Z-axis driving motor 109 so as to constantly press the joining tool 103 against the workpieces WK1, WK2 with a constant pressing force regardless of changes in the magnitude of a reaction force.

Description

Friction stir welding equipment

[0001] The present invention relates to a friction stir welding apparatus that uses frictional heat to weld stacked or butted workpieces by pressing a welding tool against the stacked or butted workpieces while being driven to rotate.

[0002] Conventionally, friction stir welding (FSW) machines have been known that use frictional heat to weld stacked or butted workpieces by pressing a welding tool against the stacked or butted workpieces while rotating and driving the tool. For example, Patent Document 1 listed below discloses a friction stir welding machine that controls the pressing load with which the friction stir welding tool presses the workpieces by providing a load cell in a ball screw mechanism that displaces a spindle unit that holds the friction stir welding tool in the vertical direction.

[0003] Patent No. 6372615

[0004] However, in the friction stir welding apparatus shown in Patent Document 1, the load cell is disposed between the nut in the ball screw mechanism and the mounting member extending from the moving table that supports the spindle unit, resulting in a complex apparatus configuration, which results in problems such as complicated assembly and maintenance work and a heavy workload.

[0005] The present invention has been made to address the above-mentioned problems, and its object is to provide a friction stir welding apparatus that can simplify the apparatus configuration and reduce the workload of each assembly and maintenance work.

[0006] In order to achieve the above object, a feature of the present invention is a friction stir welding apparatus for joining stacked or butted workpieces, comprising: a processing head having a welding tool that is pressed while being rotationally driven against stacked or butted workpieces; Z-axis displacement means that has a prime mover to reciprocately displace the processing head in the Z-axis direction to move it closer to or away from the workpieces and to press the welding tool against the workpieces; and a control device that controls the operation of the prime mover, wherein the Z-axis displacement means comprises a ball screw that is rotationally driven by the prime mover, and a displacement body that is threadably fitted into the ball screw and displaces in the axial direction by the rotational drive of the ball screw, thereby reciprocatingly displacing the processing head in the Z-axis direction, and the control device performs constant pressing force control that controls the operation of the prime mover so that when the welding tool is pressed against the workpieces, the welding tool is always pressed against the workpieces with a constant pressing force regardless of changes in the magnitude of the reaction force from the workpieces.

[0007] According to the features of the present invention configured as described above, in the friction stir welding apparatus, the Z-axis displacement means for displacing the processing head in the Z-axis direction is configured as a so-called ball screw mechanism, and the control device performs constant pressing force control, controlling the operation of the prime mover so as to press the welding tool against the workpiece with a constant pressing force regardless of changes in the magnitude of the reaction force from the workpiece. Therefore, in the friction stir welding apparatus, the ball screw mechanism operates in the forward or reverse direction in response to changes in the magnitude of the reaction force from the workpiece, causing the welding tool to approach or move away from the workpiece, thereby maintaining a constant pressing force with which the welding tool presses the workpiece. In other words, the friction stir welding apparatus according to the present invention can maintain a constant pressing force with which the welding tool presses the workpiece without using a load cell for detecting the pressing force with which the welding tool presses the workpiece, as in the prior art. This simplifies the apparatus configuration and reduces the workload of assembly and maintenance.

[0008] Another feature of the present invention is that in the friction stir welding apparatus, the Z-axis displacement means further includes a reaction force detector which detects the magnitude of the reaction force from the workpiece when the welding tool is pressed against the workpiece and outputs the detected magnitude to the control device, and the control device selectively executes, when the welding tool is pressed against the workpiece, the constant pressing force control and a constant pressing force control which controls the operation of the prime mover based on the detection signal from the reaction force detector so that the welding tool is always pressed against the workpiece with a constant pressing force.

[0009] According to another feature of the present invention configured in this manner, the friction stir welding apparatus is provided with a reaction force detector that detects the magnitude of the reaction force from the workpiece when the welding tool is pressed against the workpiece. Therefore, it is possible to select and execute constant pressing force control using a ball screw mechanism or constant pressing force control that controls the operation of the prime mover based on the detection signal from the reaction force detector so that the welding tool is always pressed against the workpiece with a constant pressing force, as appropriate depending on the specifications of the welding process.

[0010] In order to achieve the above object, the present invention is characterized by a friction stir welding apparatus for welding stacked or butted workpieces, comprising a processing head having a welding tool that is pressed against stacked or butted workpieces while being rotationally driven, a work table that supports the workpieces, Z-axis displacement means having a prime mover that reciprocates and displaces the processing head in the Z-axis direction to move the processing head toward or away from the workpieces and presses the welding tool against the workpieces, and a control device that controls the operation of the prime mover, the Z-axis displacement means comprising a ball screw that is rotationally driven by the prime mover, and a screw threadedly fitted to the ball screw to which the processing head or the work table is connected. and a reaction force detector that detects the magnitude of the reaction force from the workpiece when the welding tool is pressed against the workpiece and outputs the detection signal to the control device. The reaction force detector is provided on a bolt that connects the machining head or the work table to the displacement body, and outputs a detection signal corresponding to the distortion of the bolt to the control device. When the welding tool is pressed against the workpiece, the control device performs constant pressing force control, which controls the operation of the prime mover based on the detection signal from the reaction force detector so that the welding tool is always pressed against the workpiece with a constant pressing force.

[0011] According to the features of the present invention configured in this manner, the friction stir welding apparatus has a reaction force detector that detects the magnitude of the reaction force from the workpiece when the welding tool is pressed against the workpiece, which is provided on the bolt that connects the processing head or work table to the displacement body.This means that the reaction force detector can be installed or replaced without disassembling the ball screw mechanism, simplifying the apparatus configuration and reducing the burden of each assembly and maintenance work.

[0012] Another feature of the present invention is that in the friction stir welding apparatus, the reaction force detector is provided inside the bolt.

[0013] According to this, in the friction stir welding apparatus, the reaction force detector is provided inside the bolt, so that the reaction force detector can be prevented from being soiled or damaged.

[0014] Another feature of the present invention is that in the friction stir welding apparatus, the reaction force detector is disposed between the bolt and an object to be fastened by the bolt.

[0015] According to this, since the friction stir welding device has a reaction force detector positioned between the object to be tightened and the bolt, no processing or work is required to attach the reaction force detector to the bolt itself, and commercially available bolts can be used, making it easier to obtain bolts.

[0016] Another feature of the present invention is that in the friction stir welding apparatus, a plurality of bolts are provided, and the reaction force detector is provided on at least two of the plurality of bolts.

[0017] According to this, the friction stir welding apparatus has reaction force detectors provided on at least two of the multiple bolts, thereby improving the reliability of detecting the magnitude of the reaction force from the workpiece. In this case, the at least two reaction force detectors provided on at least two bolts can be provided in a state where one is connected to the control device and the other reaction force detector is a spare and not connected to the control device. Furthermore, the at least two reaction force detectors are each connected to the control device, and the control device can control the operation of the prime mover by simultaneously or selectively using the at least two connected reaction force detectors.

[0018] Another feature of the present invention is that the friction stir welding apparatus further comprises a Z-axis position detector that detects the position of the welding tool in the Z-axis direction and outputs the detected position to the control device, and when the control device detects that the position of the welding tool in the Z-axis direction has reached a predetermined limit position, it interrupts the constant pressing force control by the prime mover.

[0019] According to this, the friction stir welding device is equipped with a Z-axis position detector that detects the position of the welding tool in the Z-axis direction, so when the position of the welding tool in the Z-axis direction reaches a predetermined limit position, the constant pressing force control by the prime mover is interrupted, thereby preventing the continuation of abnormal processing and preventing damage to the welding tool or workpiece.

[0020] 1 is a perspective view schematically showing an outline of the external configuration of a friction stir welding apparatus according to a first embodiment and a second embodiment of the present invention. FIG. 2 is a front view schematically showing a state in which a processing head in the friction stir welding apparatus shown in FIG. 1 is lowered to perform welding. FIG. 3 is a side view of a left linear guide from a right linear guide in FIG. 2 to explain details of a ball screw mechanism on the back surface of the processing head in the friction stir welding apparatus shown in FIG. 2. FIG. 4 is a block diagram of a control system for controlling the operation of the friction stir welding apparatus shown in FIG. 1. FIG. 5 is a side view of a left linear guide from a right linear guide in FIG. 2 to explain details of a ball screw mechanism on the back surface of the processing head in a friction stir welding apparatus according to a second embodiment of the present invention. FIG. 6 is a side view of a left linear guide from a right linear guide in FIG. 2 to explain details of a ball screw mechanism on the back surface of the processing head in a friction stir welding apparatus according to a modified example of the present invention.

[0021] First Embodiment A first embodiment of a friction stir welding apparatus according to the present invention will now be described with reference to the drawings. FIG. 1 is a perspective view schematically illustrating the overall external configuration of a friction stir welding apparatus 100 according to the present invention. FIG. 2 is a front view schematically illustrating a state in which the processing head 101 of the friction stir welding apparatus 100 shown in FIG. 1 is lowered to perform welding. FIG. 3 is a side view of the linear guide 105a viewed from the linear guide 105b side in the friction stir welding apparatus 100 shown in FIG. 2 to explain the details of the ball screw mechanism 107 on the back surface of the processing head 101. FIG. 4 is a block diagram of a control system for controlling the operation of the friction stir welding apparatus 100 shown in FIG. 1. Note that the figures referred to in this specification are schematic, with some components exaggerated, to facilitate understanding of the present invention. Therefore, the dimensions and ratios of the components may differ.

[0022] (Configuration of friction stir welding apparatus 100) This friction stir welding apparatus 100 is a computer-controlled (NC-controlled) processing apparatus that joins the workpieces WK1 and WK2 to each other by plastic flow by displacing a rotationally driven welding tool 103 while pressing it against one surface of the workpieces WK1 and WK2 that are stacked or butted together and made of metal. The friction stir welding apparatus 100 includes a processing head 101.

[0023] The machining head 101 has the function of gripping and rotating the welding tool 103, and is mainly equipped with a spindle 101a, a spindle drive motor 101b, and a spindle housing 102. The spindle 101a is a component that detachably holds and rotates the welding tool 103, and is made of a metal material formed into a round bar. In other words, the spindle 101a is a so-called spindle. One end (not shown) of the spindle 101a (upper side in the figure) is connected to the spindle drive motor 101b, and the other end is supported within the machining head 101 in a state where it hangs down in the figure. Here, the vertical direction in the figure, in which the spindle 101a extends, is the Z-axis direction.

[0024] The spindle drive motor 101b is an electric motor for driving the spindle 101a to rotate, and is attached to the spindle housing 102 of the machining head 101. The operation of this spindle drive motor 101b is controlled by a control device 130, which will be described later.

[0025] The spindle housing 102 is a metal component for supporting the spindle 101a and the spindle drive motor 101b, and is configured as a rectangular box extending in the Z-axis direction in the figure. In this case, the spindle housing 102 houses the spindle 101a with its bottom end exposed, and supports the spindle drive motor 101b on its upper surface. In addition, the spindle housing 102 has a mounting portion 102a formed on its back surface, which is the surface opposite to the front surface.

[0026] The mounting portion 102a is a portion to which a displacement body 107b (described later) is connected, and is formed in the shape of a plate that protrudes horizontally from the back surface of the spindle housing 102. A slider that slides on a linear guide (described later) is attached to the back surface of the spindle housing 102. This machining head 101 is held by the head base 104 via linear guides 105a and 105b.

[0027] The joining tool 103 is a tool for joining the workpieces WK1 and WK2. More specifically, the joining tool 103 is formed into a cylindrical shape from a material that has excellent strength, impact resistance, and wear resistance, such as carbon steel, such as tool steel or tungsten steel, or alloy steel. The joining tool 103 is held by the spindle 101a at one end (the upper end in the figure) while hanging down from the spindle 101a. When the joining tool 103 is not held by the spindle 101a, it is held by a tool magazine 121 (described later) while hanging down.

[0028] The head base 104 is a component for reciprocatingly displacing the machining head 101 in the Z-axis direction and the X-axis direction. Specifically, the head base 104 is made of a metal material formed into a plate shape extending in the Z-axis direction, and is supported by a column 110 via linear guides 111a and 111b. The head base 104 includes linear guides 105a and 105b, a Z-axis position detector 106, a ball screw mechanism 107, and a Z-axis drive motor 109.

[0029] The linear guides 105a and 105b are components for guiding the machining head 101 in the Z-axis direction in the drawing, and are composed of two metal rods extending like rails. These linear guides 105a and 105b are attached to the head base 104, arranged parallel to each other in the Z-axis direction in the drawing, on both left and right sides of the machining head 101 when viewed from the front. Sliders are fitted to these linear guides 105a and 105b, respectively, so that they can slide freely in the Z-axis direction in the drawing, and the machining head 101 is connected via these sliders.

[0030] The Z-axis position detector 106 is a measuring device that detects the position of the machining head 101 in the Z-axis direction and outputs a detection signal to the control device 130, and its operation is controlled by the control device 130. In this embodiment, the Z-axis position detector 106 is configured as a linear scale. This Z-axis position detector 106 is attached to the head base 104 along the linear guides 105a and 105b.

[0031] The ball screw mechanism 107 is a group of parts that cooperate with the linear guides 105a and 105b to guide the machining head 101 in the Z-axis direction in the drawing. Specifically, the ball screw mechanism 107 is mainly composed of a feed screw 107a and a displacement body 107b.

[0032] The feed screw 107a is a component for supporting the displacement body 107b and displacing it back and forth along the Z-axis direction, and is configured by a metal rod having a male thread formed on its outer surface. The feed screw 107a is disposed so as to extend in the Z-axis direction, with one end (the upper end in the figure) connected to the Z-axis drive motor 109 and the other end (the lower end in the figure) slidably held on the head base 104 via a bearing.

[0033] The displacement body 107b is a component that reciprocates along the axial direction of the feed screw 107a while connected to the machining head 101, and is configured as a metallic cylindrical body with a female thread that engages with the feed screw 107a by a small ball screw (not shown). The displacement body 107b is connected to the mounting portion 102a provided on the back surface of the machining head 101 via bolts 108. Note that three of the four bolts 108 are shown in Figure 3.

[0034] The Z-axis drive motor 109 is an electric motor for rotating the ball screw mechanism 107 to reciprocate and displace the machining head 101 in the Z-axis direction in the drawing, and its operation is controlled by the control device 130. Therefore, the machining head 101 is reciprocally displaced in the Z-axis direction in the drawing along the ball screw mechanism 107 by the rotation of the Z-axis drive motor 109. In other words, the ball screw mechanism 107 and the Z-axis drive motor 109 correspond to the Z-axis displacement means according to the present invention. Furthermore, the Z-axis drive motor 109 corresponds to the prime mover according to the present invention.

[0035] The column 110 is a component for supporting the machining head 101. Specifically, the column 110 is formed in a gate shape in which both ends of a bridge portion 110a extending in the X-axis direction in the drawing are supported by legs 110b that extend upright in the Z-axis direction in the drawing, and the column 110 is fixed in an upright position on a bed 115. The column 110 includes linear guides 111a and 111b, an X-axis position detector 112, a ball screw mechanism 113, and an X-axis drive motor 114 on the bridge portion 110a.

[0036] The linear guides 111a, 111b, like the linear guides 105a, 105b, are components for guiding the machining head 101 in the X-axis direction in the drawing, and are composed of two metal rods extending like rails. These linear guides 111a, 111b are attached to the bridge portion 110a, arranged parallel to each other in the X-axis direction in the drawing, on both sides in the vertical direction of the machining head 101 when viewed from the front. Sliders are fitted to these linear guides 111a, 111b so as to be slidable in the X-axis direction in the drawing, and the head base 104 is connected via these sliders.

[0037] The X-axis position detector 112 is a measuring device that detects the position of the machining head 101 in the X-axis direction and outputs a detection signal to the control device 130, and its operation is controlled by the control device 130. In this embodiment, the X-axis position detector 112 is configured as a linear scale. This X-axis position detector 112 is attached along the linear guides 111a and 111b on the bridge portion 110a.

[0038] The ball screw mechanism 113 is a group of parts that cooperates with the linear guides 111a and 111b to guide the machining head 101 in the X-axis direction, similar to the ball screw mechanism 107. Specifically, the ball screw mechanism 113 is composed of a feed screw 113a and a displacement body 113b, which are similar to the feed screw 107a and displacement body 107b that constitute the ball screw mechanism 107.

[0039] In this case, the feed screw 113a is disposed so as to extend in the X-axis direction in the drawing, with one end (left side in the drawing) connected to the X-axis drive motor 114 and the other end (right side in the drawing) slidably held on the bridge part 110a via a bearing. In addition, the displacement body 113b is connected to the back surface of the head base 104.

[0040] The X-axis drive motor 114 is an electric motor that rotates the ball screw mechanism 113 to reciprocate the machining head 101 in the X-axis direction, and its operation is controlled by the control device 130. Therefore, the machining head 101 is rotated and driven by the X-axis drive motor 114, so that it reciprocates along the ball screw mechanism 113 in the X-axis direction.

[0041] Bed 115 is a component for supporting column 110, work table 120, and tool magazine 121 on the installation surface of friction stir welding apparatus 100, and is made of a casting formed in a rectangular shape in a plan view extending in the Y-axis direction, which is perpendicular to the Z-axis direction and the Y-axis direction. A groove 115a is formed in the upper surface of bed 115, in the center of the Y-axis, and is recessed along the Y-axis direction. Column 110 is provided straddling groove 115a, and linear guides 116a, 116b, a Y-axis position detector 117, a ball screw mechanism 118, and a Y-axis drive motor 119 are provided within groove 115a.

[0042] The linear guides 116a, 116b, like the linear guides 105a, 105b, are components for guiding the work table 120 in the Y-axis direction in the figure, and are composed of two metal rods extending like rails. These linear guides 116a, 116b are attached in the groove 115a, arranged parallel to each other in the Y-axis direction on both sides of the left and right direction when viewed from the front of the machining head 101. Sliders are fitted to these linear guides 116a, 116b respectively so as to be slidable in the Y-axis direction in the figure, and the work table 120 is connected via these sliders.

[0043] Y-axis position detector 117 is a measuring device that detects the position of work table 120 in the Y-axis direction in the drawing and outputs a detection signal to control device 130, and its operation is controlled by control device 130. In this embodiment, Y-axis position detector 117 is configured as a linear scale. This Y-axis position detector 117 is attached along linear guides 116a and 116b in groove 115a.

[0044] Similar to the ball screw mechanism 107, the ball screw mechanism 118 is a group of parts that cooperate with the linear guides 116a and 116b to guide the work table 120 in the Y-axis direction in the drawing. Specifically, the ball screw mechanism 118 is composed of a feed screw 118a and a displacement body (not shown) that are similar to the feed screw 107a and displacement body 107b that constitute the ball screw mechanism 107.

[0045] In this case, the feed screw 118a is disposed so as to extend in the Y-axis direction in the drawing, with one end (the front end in the drawing) connected to a Y-axis drive motor 119 and the other end (the rear end in the drawing) slidably held in the groove 115a via a bearing. The displacement body is also connected to the underside of the work table 120.

[0046] The Y-axis drive motor 119 is an electric motor that rotates the ball screw mechanism 118 to reciprocate the work table 120 in the Y-axis direction, and its operation is controlled by the control device 130. Therefore, the work table 120 is rotated and reciprocated in the Y-axis direction along the ball screw mechanism 118 by the Y-axis drive motor 119.

[0047] The work table 120 is a component for supporting the workpieces WK1 and WK2, and is made of a metal material formed into a flat plate. Clamps 120a are provided on the upper surface of the work table 120 to detachably hold the workpieces WK1 and WK2.

[0048] The tool magazine 121 is a mechanical device that detachably holds a plurality of welding tools 103 or cutting tools (such as end mills or milling cutters) and can transfer the welding tools 103 to the spindle 101a, and its operation is controlled by the control device 130. The tool magazine 121 is provided in an upright position adjacent to the column 110 on the bed 115. The tool magazine 121 is configured to move toward or away from the machining head 101 under the operation control of the control device 130.

[0049] The control device 130 is configured by a microcomputer including a CPU, ROM, RAM, etc., and comprehensively controls the overall operation of the friction stir welding apparatus 100 and performs welding processing on the workpieces WK1 and WK2 by executing a processing program (so-called NC (Numerical Control) program) (not shown) prepared by an operator. Specifically, the control device 130 controls the operation of the main shaft drive motor 101b, the Z-axis drive motor 109, the X-axis drive motor 114, the Y-axis drive motor 119, and the tool magazine 121 to press the welding tool 103 against the workpieces WK1 and WK2 and relatively displace it in three orthogonal axial directions consisting of the X-axis direction, the Y-axis direction, and the Z-axis direction, thereby welding the workpieces WK1 and WK2.

[0050] This control device 130 is equipped with an operation panel 131 which is made up of an input device consisting of a group of switches that receive instructions from the operator and input them to the control device 130, and a liquid crystal display device that displays the operating status of the control device 130. The friction stir welding apparatus 100 also includes a power supply unit that supplies electricity to operate the spindle drive motor 101b, Z-axis drive motor 109, X-axis drive motor 114, Y-axis drive motor 119, tool magazine 121, and control device 130, but a description of these configurations that are not directly related to the present invention will be omitted.

[0051] (Operation of Friction Stir Welding Apparatus 100) Next, the operation of the friction stir welding apparatus 100 configured as described above will be described. First, the operator operates the operation panel 131 to turn on the power of the friction stir welding apparatus 100. As a result, the friction stir welding apparatus 100 executes a predetermined control program (not shown) that is pre-stored in the ROM of the control device 130, thereby positioning the machining head 101 and the work table 120 at their respective predetermined standby positions and then entering a standby state where it waits for instructions from the operator. Here, the standby positions are positions that do not physically interfere with the workpieces WK1, WK2 when the workpieces WK1, WK2 are attached to or detached from the work table 120.

[0052] Specifically, the control device 130 controls the operation of the Z-axis drive motor 109 to position the machining head 101 at the uppermost position (movement limit position), and controls the operation of the X-axis drive motor 114 to position it at the movement limit position on the tool magazine 121 side. In addition, the control device 130 controls the operation of the Y-axis drive motor 119 to position the work table 120 at the movement limit position on the operator side (in this embodiment, on the Y-axis drive motor 119 side).

[0053] Next, the worker sets the workpieces WK1 and WK2 in the friction stir welding apparatus 100. Specifically, the worker fixes the workpieces WK1 and WK2, which are stacked together, onto the work table 120 via clamps 120a. In this embodiment, the workpiece WK1 is set on the work table 120 in a state where it is stacked on top of the workpiece WK2.

[0054] Next, the operator operates the operation panel 131 to instruct the control device 130 to join the workpieces WK1 and WK2. In response to this instruction, the control device 130 executes a control program for joining (not shown) to perform the joining process on the workpieces WK1 and WK2. In the following explanation of the operation, it is assumed that the spindle 101a is holding the joining tool 103 required for joining the workpieces WK1 and WK2.

[0055] First, the control device 130 controls the operation of the X-axis drive motor 114 and the Y-axis drive motor 119 to position the machining head 101 at a machining start position above the workpieces WK1 and WK2, and then controls the operation of the spindle drive motor 101b to rotate the spindle 101a. Next, as shown in Figure 2, the control device 130 controls the operation of the Z-axis drive motor 109 to lower the machining head 101 and press it against the workpieces WK1 and WK2.

[0056] In this case, the control device 130 controls the operation of the Z-axis drive motor 109 so that the welding tool 103 always presses the workpieces WK1, WK2 with a constant pressing force. The pressing force with which the welding tool 103 presses the workpieces WK1, WK2 is experimentally determined in advance in accordance with the materials of the workpieces WK1, WK2, the processing path, and other processing specifications, and is set in the control program.

[0057] Next, the control device 130 controls the operation of the X-axis drive motor 114 and the Y-axis drive motor 119 so that the machining head 101 is displaced in the X-axis direction and the Y-axis direction, respectively, along a joining line that has been set (programmed) in advance by an operator. In this way, the control device 130 can weld the workpieces WK1 and WK2 along the joining line.

[0058] During such joining, the reaction force from the workpieces WK1, WK2 changes due to defects that occur during the manufacturing of the workpieces WK1, WK2 or when the workpieces WK1, WK2 are superimposed on each other, specifically, due to warpage, deformation, unevenness (variation) in plate thickness, surface roughness, etc. For this reason, the reaction force from the joining tool 103 increases when the surfaces of the workpieces WK1, WK2 are raised, and decreases when the surfaces of the workpieces WK1, WK2 are recessed.

[0059] In such a case, the control device 130 controls the operation of the Z-axis drive motor 109 so that the welding tool 103 always presses the workpieces WK1, WK2 with a constant pressing force regardless of changes in the reaction force that the welding tool 103 receives from the workpieces WK1, WK2. On the other hand, the machining head 101 that holds the welding tool 103 is supported by a ball screw mechanism 107.

[0060] Therefore, the machining head 101 is displaced in the Z-axis direction as the ball screw mechanism 107 performs forward or reverse operation depending on the magnitude of the reaction force from the workpieces WK1, WK2. Specifically, when the reaction force from the workpieces WK1, WK2 becomes smaller (decreased), the ball screw mechanism 107 performs forward operation depending on the magnitude of the reaction force, and the machining head 101 is displaced in one direction in the Z-axis direction (a direction closer to the workpieces WK1, WK2). Here, forward operation means that the displacement body 107b is linearly displaced in the Z-axis direction as a result of the rotational drive of the feed screw 107a.

[0061] On the other hand, when the reaction force from the workpieces WK1 and WK2 increases (increases), the ball screw mechanism 107 reverses its movement in accordance with the magnitude of the reaction force, displacing the machining head 101 in the other direction in the Z-axis direction (away from the workpieces WK1 and WK2). Here, reverse movement refers to the feed screw 107a being driven to rotate by the linear displacement of the displacement body 107b in the Z-axis direction. This allows the friction stir welding apparatus 100 to perform welding by constant pressure control, in which the welding tool 103 is constantly pressed against the workpieces WK1 and WK2 with a constant pressure, regardless of changes in the reaction force the welding tool 103 receives from the workpieces WK1 and WK2. It should be noted that the term "constant pressure" here naturally includes not only a single magnitude of pressure, but also a range of pressures.

[0062] During this welding process, the control device 130 constantly monitors the position of the welding tool 103 in the Z-axis direction using a detection signal input from the Z-axis position detector 106, and immediately interrupts the welding process when the position of the welding tool 103 reaches a lower limit position or an upper limit position preset in the control device 130. Specifically, the control device 130 moves the welding tool 103 away from the workpieces WK1 and WK2. This allows the control device 130 to prevent abnormal welding from continuing and to prevent damage to the welding tool 103 or the workpieces WK1 and WK2.

[0063] Note that the control device 130 does not control the welding tool 103 to change the pressing force against the workpieces WK1, WK2 when the position of the welding tool 103 in the Z-axis direction is within a range from the lower limit position to the upper limit position, for example, above the lower limit position and below the upper limit position. Therefore, as described above, the processing head 101 is displaced in the Z-axis direction by the ball screw mechanism 107 performing forward or reverse operation depending on the magnitude of the reaction force from the workpieces WK1, WK2. As a result, the friction stir welding apparatus 100 can perform welding using constant pressing force control, in which the welding tool 103 is always pressed against the workpieces WK1, WK2 with a constant pressing force, regardless of changes in the reaction force that the welding tool 103 receives from the workpieces WK1, WK2.

[0064] Next, when the machining head 101 is positioned at the end position of the joining line, the control device 130 controls the operation of the Z-axis drive motor 109 to displace the machining head 101 upward in the figure so as to move it away from the workpieces WK1 and WK2. Then, the control device 130 controls the operation of the main shaft drive motor 101b to stop the rotational drive of the main shaft 101a, and then controls the operation of the X-axis drive motor 114, the Y-axis drive motor 119, and the Z-axis drive motor 109 to return the machining head 101 and the work table 120 to their respective standby positions. Therefore, the operator can remove the joined workpieces WK1 and WK2 from the work table 120 by releasing the clamp 120a from the work table 120.

[0065] As can be understood from the above description of operation, according to the first embodiment, the friction stir welding apparatus 100 causes the ball screw mechanism 107 to operate in a forward or reverse direction in response to changes in the magnitude of the reaction force from the workpieces WK1, WK2, thereby moving the welding tool 103 toward or away from the workpieces WK1, WK2, thereby maintaining a constant pressing force with which the welding tool 103 presses the workpieces WK1, WK2. In other words, the friction stir welding apparatus 100 according to the present invention can maintain a constant pressing force with which the welding tool 103 presses the workpieces WK1, WK2 without using a load cell for detecting the pressing force with which the welding tool 103 presses the workpieces WK1, WK2, as in the above-mentioned conventional art, thereby simplifying the apparatus configuration and reducing the workload of each assembly and maintenance task.

[0066] Second Embodiment Next, a friction stir welding apparatus 200 according to a second embodiment of the present invention will be described with reference to Figures 1, 2, 4, and 5. The friction stir welding apparatus 200 according to the second embodiment differs from the friction stir welding apparatus 100 according to the first embodiment in that it is provided with a reaction force detector 210. Therefore, in the second embodiment, the description will focus on the parts that are different from the first embodiment, and descriptions of parts that are common to both embodiments and corresponding parts will be omitted as appropriate.

[0067] (Configuration of friction stir welding apparatus 200) The reaction force detector 210 is a component for detecting the magnitude of the reaction force from the workpieces WK1, WK2 when the welding tool 103 is pressed against the workpieces WK1, WK2 to perform welding. Specifically, the reaction force detector 210 has a piezoelectric effect element or a piezoresistive effect element that exhibits a piezoelectric effect or a piezoresistive effect attached to the inside or outer surface of a bolt 211 serving as a fastener, and is configured to output a detection signal consisting of an electrical signal corresponding to the deformation (strain) of the bolt 211. In the second embodiment, the reaction force detector 210 is provided inside the bolt 211.

[0068] This reaction force detector 210 is arranged by replacing one of the four bolts 108 that connect the displaceable body 107b to the mounting portion 102a of the machining head 101 in the first embodiment with a bolt 211. The reaction force detector 210 is electrically connected to the control device 130 so as to output a detection signal to the control device 130. The control device 130 controls the operation of the Z-axis drive motor 109 in accordance with the detection signal output from the reaction force detector 210. Note that two bolts 108 are shown in FIG. 6.

[0069] (Operation of Friction Stir Welding Apparatus 200) A description will be given of the operation of the friction stir welding apparatus 200 configured as described above. In the welding process in which the welding tool 103 is pressed against the workpieces WK1, WK2, the control device 130 controls the operation of the Z-axis drive motor 109 using a detection signal input from the reaction force detector 210, thereby performing constant pressing force control to keep the pressing force with which the welding tool 103 presses the workpieces WK1, WK2 constant.

[0070] First, when the welding tool 103 starts to press the workpieces WK1, WK2, the control device 130 controls the operation of the Z-axis drive motor 109 so that the welding tool 103 presses the workpieces WK1, WK2 with a predetermined pressing force. As a result, a force corresponding to the pressing force with which the welding tool 103 presses the workpieces WK1, WK2 acts on the reaction force detector 210, and the reaction force detector 210 outputs a detection signal corresponding to this pressing force to the control device 130.

[0071] The control device 130 constantly monitors the reaction force that the welding tool 103 receives from the workpieces WK1, WK2, i.e., the pressing force with which the welding tool 103 presses the workpieces WK1, WK2, using the detection signal input from the reaction force detector 210, and controls the operation of the Z-axis drive motor 109. Specifically, when the reaction force that the welding tool 103 receives from the workpieces WK1, WK2 becomes smaller (decreased) than a predetermined lower limit value, the control device 130 controls the operation of the Z-axis drive motor 109 in accordance with the magnitude of the reaction force, thereby displacing the welding tool 103 in a direction closer to the workpieces WK1, WK2.

[0072] On the other hand, when the reaction force that the welding tool 103 receives from the workpieces WK1, WK2 becomes larger (increases) than a predetermined upper limit, the control device 130 controls the operation of the Z-axis drive motor 109 in accordance with the magnitude of the reaction force to displace the welding tool 103 in a direction away from the workpieces WK1, WK2. As a result, the control device 130 can perform welding by constant pressing force control, in which the welding tool 103 is always pressed against the workpieces WK1, WK2 with a constant pressing force regardless of changes in the reaction force that the welding tool 103 receives from the workpieces WK1, WK2.

[0073] It should be noted that here, it goes without saying that the "constant pressing force" does not only include a pressing force of one magnitude, but also a pressing force within a certain range. Furthermore, the friction stir welding apparatus 200 is provided with the ball screw mechanism 107 of the first embodiment, but the control device 130 performs constant pressing force control using the reaction force detector 210 before the ball screw mechanism 107 operates in the forward or reverse direction.

[0074] As can be understood from the above description of operation, according to the second embodiment, in the friction stir welding apparatus 200, the reaction force detector 210 that detects the magnitude of the reaction force from the workpieces WK1, WK2 when the welding tool 103 is pressed against the workpieces WK1, WK2 is provided on the bolt 211 that connects the machining head 101 to the displacement body 107b. Therefore, the reaction force detector 210 can be installed or replaced without disassembling the ball screw mechanism 107, which simplifies the apparatus configuration and reduces the workload of each assembly and maintenance work.

[0075] Furthermore, the present invention is not limited to the first and second embodiments, and various modifications are possible without departing from the scope of the present invention. In the following description of each modification and the drawings to which reference is made, the same reference numerals are used to designate the same components as those in the above embodiments, and their description will be omitted.

[0076] For example, in the first embodiment, the control device 130 is configured to immediately interrupt the welding process when the position of the welding tool 103 in the Z-axis direction reaches a predetermined lower limit position or upper limit position using the detection signal output from the Z-axis position detector 106. However, in this case, the control device 130 can also be configured to monitor only one of the lower limit position and the upper limit position of the welding tool 103 in the Z-axis direction. Furthermore, the control device 130 can omit this monitoring control when control for monitoring the position of the welding tool 103 in the Z-axis direction is not necessary. Note that this monitoring control of the position of the welding tool 103 in the Z-axis direction using the detection signal output from the Z-axis position detector 106 may be performed or omitted in the control device 130 in the second embodiment.

[0077] Furthermore, in the second embodiment, the friction stir welding apparatus 200 is configured to always execute constant pressing force control using the detection signal output from the reaction force detector 210. However, the friction stir welding apparatus 200 can also be configured to selectively execute constant pressing force control using the ball screw mechanism 107 in the first embodiment and constant pressing force control using the detection signal output from the reaction force detector 210. In this case, the control device 130 can receive a designation for constant pressing force control from the operator before starting welding or during welding. Furthermore, when the friction stir welding apparatus 200 can selectively execute constant pressing force control using the ball screw mechanism 107 and constant pressing force control using the detection signal output from the reaction force detector 210, the reaction force detector 210 can be provided in a location other than the bolt 211 as in the conventional technology. For example, the reaction force detector 210 can be arranged to detect deformation (distortion) of the work table 120.

[0078] In the second embodiment, the reaction force detector 210 is configured by attaching a piezoelectric element or a piezoresistive element to the inside or the outer surface of the bolt 211 serving as a fastener. However, the reaction force detector 210 may be configured in any manner so long as the welding tool 103 can detect the magnitude of the reaction force from the workpieces WK1 and WK2. Therefore, the reaction force detector 210 may be disposed, for example, between the bolt 108 and an object to be fastened by the bolt 108.

[0079] 6, the reaction force detector 210 is formed in an annular shape through which the bolt 108 passes, and can be disposed between the bolt 108 and the displacement body 107b (the object to be fastened). In this way, the reaction force detector 210 can be easily removed from between the bolt 108 and the displacement body 107b by removing the bolt 108 from the displacement body 107b.

[0080] Furthermore, in the second embodiment, the friction stir welding apparatus 200 is configured to include one reaction force detector 210. However, the friction stir welding apparatus 200 may also be configured to include two or more reaction force detectors 210. In this case, in the friction stir welding apparatus 200, at least one of the three bolts 108 other than the bolt 211 can be replaced with the bolt 211 having the reaction force detector 210.

[0081] In this case, two reaction force detectors 210 for at least two bolts 211 can be selectively connected to the control device 130, so that the remaining reaction force detector 210 can be used as a spare. Also, by connecting all of the at least two reaction force detectors 210 to the control device 130, the control device 130 can perform constant pressing force control using detection signals output by each of the multiple reaction force detectors 210. In this case, the control device 130 can perform constant pressing force control using an average value of reaction forces represented by the detection signals output by each of the multiple reaction force detectors 210, and can also selectively use the multiple reaction force detectors 210 by switching them in order.

[0082] Furthermore, in the first and second embodiments, the Z-axis displacement means, which is composed of the ball screw mechanism 107 and the Z-axis drive motor 109, is configured to displace the machining head 101 in the Z-axis direction relative to the work table 120. However, the displacement relationship between the machining head 101 and the work table 120 is relative. Therefore, the Z-axis displacement means can also be configured to displace the work table 120 in the Z-axis direction relative to the machining head 101. In this case, the reaction force detector 210 in the second embodiment may be provided on a bolt connecting the work table 120 to a displacement body that constitutes the ball screw mechanism for displacing the work table 120 in the Z-axis direction.

[0083] In the first and second embodiments, the workpieces WK1 and WK2 are stacked on top of each other. However, the friction stir welding apparatus 100 can also weld the workpieces WK1 and WK2 at a butted portion where the workpieces WK1 and WK2 are butted against each other on the same plane on the work table 120.

[0084] In the first and second embodiments, the Z-axis position detector 106, the X-axis position detector 112, and the Y-axis position detector 117 for detecting the positions of the machining head 101 in the Z-axis, X-axis, and Y-axis directions are each configured as linear scales. However, the Z-axis position detector 106, the X-axis position detector 112, and the Y-axis position detector 117 may be configured as something other than linear scales as long as they are able to detect the positions of the machining head 101 in the Z-axis, X-axis, and Y-axis directions. For example, the Z-axis position detector 106, the X-axis position detector 112, and the Y-axis position detector 117 may be configured as encoders provided on the Z-axis drive motor 109, the X-axis drive motor 114, and the Y-axis drive motor 119, respectively.

[0085] In the first and second embodiments, the friction stir welding apparatuses 100 and 200 are configured as machine tools that can perform cutting using cutting tools such as end mills in addition to welding. However, it goes without saying that the friction stir welding apparatuses 100 and 200 may be configured as machines that perform only welding.

[0086] WK1, WK2...workpieces, 100...friction stir welding device, 101...processing head, 101a...spindle, 101b...spindle drive motor, 102...spindle housing, 102a...mounting portion, 103...welding tool, 104...head base, 105a, 105b...linear guide, 106...Z-axis position detector, 107...ball screw mechanism, 107a...feed screw, 107b...displacement body, 108...bolt, 109...Z-axis drive motor, 110...column, 110a...mounting portion, 110b...leg portion, 111a, 111b...linear guide, 112...X-axis position detector, 113...ball screw mechanism, 113a...feed screw, 113b...displacement body, 114...X-axis drive motor, 115...bed, 115a...groove portion, 116a, 116b...linear guide, 117...Y-axis position detector, 118...ball screw mechanism, 118a...feed screw, 119...Y-axis drive motor, 120...work table, 120a...clamp, 121...tool magazine, 130...control device, 131...operation panel, 200...friction stir welding device, 210...reaction force detector, 211...bolt.

Claims

1. A friction stir welding apparatus for joining stacked or butted workpieces, comprising: a processing head having a welding tool that is pressed against stacked or butted workpieces while being rotated; Z-axis displacement means having a prime mover to reciprocately displace the processing head in the Z-axis direction to approach or move away from the workpieces and to press the welding tool against the workpieces; and a control device for controlling the operation of the prime mover, wherein the Z-axis displacement means comprises a ball screw that is rotated by the prime mover, and a displacement body that is screwed into the ball screw and displaced in the axial direction by the rotational drive of the ball screw, thereby displacing the processing head back and forth in the Z-axis direction, and the control device executes constant pressing force control that controls the operation of the prime mover so that when the welding tool is pressed against the workpieces, the welding tool is always pressed against the workpieces with a constant pressing force regardless of changes in the magnitude of the reaction force from the workpieces.

2. A friction stir welding apparatus as described in claim 1, further comprising: said Z-axis displacement means including a reaction force detector which detects the magnitude of the reaction force from the workpiece when the welding tool is pressed against the workpiece and outputs the reaction force to said control device; and said control device selectively executes, when the welding tool is pressed against the workpiece, said constant pressing force control and a constant pressing force control which controls the operation of said prime mover based on the detection signal from said reaction force detector so as to always press the welding tool against the workpiece with a constant pressing force.

3. A friction stir welding device for joining stacked or butted workpieces, comprising: a processing head having a joining tool that is pressed against stacked or butted workpieces while being rotated; a work table for supporting the workpieces; Z-axis displacement means having a prime mover for reciprocatingly displacing the processing head in the Z-axis direction to approach or move away from the workpieces and for pressing the joining tool against the workpieces; and a control device for controlling the operation of the prime mover, wherein the Z-axis displacement means comprises: a ball screw that is rotated by the prime mover; a displacement body to which the processing head or the work table is connected and is screwed into the ball screw so as to be displaced in the axial direction by the rotational drive of the ball screw, thereby reciprocatingly displacing the processing head in the Z-axis direction; and a reaction force detector that detects the magnitude of the reaction force from the workpieces when the joining tool is pressed against the workpieces and outputs the magnitude to the control device, and the reaction force detector is provided on a bolt that connects the processing head or the work table to the displacement body and outputs a detection signal corresponding to the distortion of the bolt to the control device, The control device executes constant pressing force control, which controls the operation of the prime mover so that the welding tool is always pressed against the workpiece with a constant pressing force based on a detection signal from the reaction force detector when the welding tool is pressed against the workpiece.

4. A friction stir welding apparatus according to claim 3, characterized in that the reaction force detector is provided inside the bolt.

5. A friction stir welding apparatus according to claim 3, characterized in that the reaction force detector is disposed between the bolt and an object to be fastened to which the bolt is fastened.

6. A friction stir welding apparatus according to claim 3, characterized in that a plurality of bolts are provided, and the reaction force detector is provided on at least two of the plurality of bolts.

7. A friction stir welding apparatus as described in at least one of claims 1 to 3, further comprising a Z-axis position detector which detects the position of the welding tool in the Z-axis direction and outputs the detected position to the control device, and wherein the control device interrupts the constant pressing force control by the prime mover when it detects that the position of the welding tool in the Z-axis direction has reached a predetermined limit position.

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