JP7765964B2 - Stretch molding device and stretch molding method - Google Patents

Description

The present invention relates to a stretch forming device and a stretch forming method.

For example, when manufacturing an aircraft frame or a reflecting surface of a parabolic antenna, a plate-shaped workpiece made of metal or the like is formed into a curved surface.
As described above, a stretch forming apparatus is known as an apparatus for forming a plate-shaped workpiece into a curved surface.

For example, in the stretch forming device described in Patent Document 1, the workpiece is clamped in a direction perpendicular to the surface direction of the workpiece, and the leading end of the workpiece is pulled.
Then, a curved mold is pressed against the part of the workpiece being pulled, and the workpiece is pulled in that state, thereby forming the plate-shaped workpiece into a curved surface.

Japanese Patent Application Publication No. 4-300033

In conventional stretch forming devices, the workpiece is bent (curved) by pressing a curved mold against it, as described above, but it can also be bent in a direction perpendicular to the direction in which the mold extends, i.e., in the direction in which the workpiece is pulled. This is achieved by changing the distance between the position where the workpiece is clamped and the position where the mold is pressed against them, or by changing their relative heights.
However, conventional stretch forming devices have sometimes been unable to accurately form a workpiece into a curved surface.

The present invention was made in consideration of the above points, and aims to provide a stretch forming device and stretch forming method that can accurately form a workpiece into a curved surface.

The stretch forming device according to the present invention comprises:
a clamping mechanism including a first frame and a second frame that clamp a portion of a workpiece, a movement mechanism that moves at least one of the first frame and the second frame in a clamping direction, and a constraint force variable mechanism that makes it possible to change the constraint force applied to the workpiece by the first frame and the second frame, and causing the workpiece to slide between the first frame and the second frame ;
a pulling mechanism that pulls another portion of the workpiece while the workpiece is clamped by the clamping mechanism;
a forming unit that forms the workpiece between the clamping mechanism and the pulling mechanism;
Equipped with.

Further, the stretch molding method according to the present invention includes the steps of:
In the stretch forming method using the stretch forming device,
When the workpiece is shaped in the shaping section while the first frame and the second frame of the clamping mechanism are clamping the workpiece and the pulling mechanism is pulling the workpiece, the workpiece is shaped while the restraining force applied to the workpiece by the first frame and the second frame is changed by the restraining force variable mechanism of the clamping mechanism.

This invention makes it possible to precisely shape a workpiece into a curved surface.

FIG. 1A is an image diagram for explaining the stretch forming device according to the present embodiment, and FIG. 1B is an image diagram as seen from the side. FIG. 10 is a diagram illustrating the amount of reduction of the workpiece. FIG. 1A is a perspective view showing an example of a compound curved surface formed on a workpiece, and FIG. 1B is a side view. 1 is a schematic side view showing the configuration of a stretch molding device according to an embodiment of the present invention. 1A and 1B are diagrams showing the configuration of the clamping mechanism according to the present embodiment, in which FIG. 1A shows a state in which the first frame is brought close to the third frame, and FIG. 1B shows a state in which the first frame is moved away from the third frame. 10A is a graph showing the relationship between the amount of reduction G and the tension T, and FIG. 10B is a graph showing the relationship between the amount of reduction G and the restraining force F. 3A and 3B are diagrams illustrating a configuration of a tension mechanism according to the present embodiment. (a) A graph showing the relationship between the radial distance r from the center of the parabolic antenna and the radius of curvature R on the reflecting surface of the parabolic antenna, and (b) a graph showing the relationship between the pulling stroke Sx of the workpiece and the reduction amount G when forming the shape of (a). FIG. 10 is a diagram illustrating a configuration example of a tension mechanism of a conventional stretch forming device. 10A is a graph showing the change over time in the pulling stroke of the workpiece, and FIG. 10B is a graph showing the change over time in the absolute value of the current flowing through the servo motor of the pulling mechanism. (a) is a graph showing the change over time in the pulling stroke of the workpiece; (b) is a graph showing the change over time in the absolute value of the current flowing to the servo motor of the pulling mechanism; and (c) is a graph showing the change over time in the amount of pressure reduction in the clamping mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a stretch forming apparatus and a stretch forming method according to the present invention will be described with reference to the drawings.
In the following description, the X direction shown in Fig. 1 etc., which will be described later, of the stretch forming device, may be referred to as the pulling direction of the workpiece W or simply as the pulling direction, and the Z direction may be referred to as the up-down direction or the clamping direction of the workpiece W. In addition, the following description will be given of a case where the workpiece is a plate material with a substantially triangular shape, but the workpiece may be rectangular or the like, and the shape of the workpiece is not limited to a substantially triangular shape.

FIG. 1(a) is an image diagram for explaining the stretch forming device according to this embodiment, and FIG. 1(b) is an image diagram seen from the side.
1(a) and 1(b), the direction indicated by the arrow X is the direction in which the workpiece is pulled, and will be referred to as the X direction or pulling direction hereinafter. The direction indicated by the arrow Y in the figures is the direction perpendicular to the pulling direction, and will be referred to as the Y direction hereinafter. The direction indicated by the arrow Z in the figures is the direction perpendicular to the plate-shaped workpiece, and will be referred to as the Z direction hereinafter.

The stretch forming device 1 includes a clamping mechanism 2 including a first frame 21 and a second frame 22 that clamp the workpiece W, a pulling mechanism 4 that pulls the workpiece W in the X direction, and a forming section 3 that forms the workpiece W between the clamping mechanism 2 and the pulling mechanism 4.
The specific configurations of the clamping mechanism 2, the forming unit 3, and the pulling mechanism 4 will be described later.

The configuration of the clamping mechanism 2 is not limited to a specific configuration as long as it can clamp the workpiece W between the first frame 21 and the second frame 22 in a direction perpendicular to the plate-shaped workpiece W, i.e., in the Z direction.
In this embodiment, the lower surface of the upper mold 21a of the first frame 21 extending in the Y direction has a central portion in the X direction that protrudes downward, forming a convex portion that extends in the Y direction. Also, the upper surface of the lower mold 22a of the second frame 22 that extends in the Y direction corresponding to the first frame 21 has a central portion in the X direction that is recessed downward, forming a concave portion that extends in the Y direction corresponding to the convex portion of the upper mold 21a.

The downward protrusion distance of the convex portion of the upper die 21a of the first frame 21 of the clamping mechanism 2, or more precisely, the depth of the recess into which the workpiece W is pressed down when the upper die 21a and the lower die 22a are close to each other as shown in Figure 2, will be referred to as the pressing amount G hereinafter.
In addition, the convex portion formed on the upper mold 21a of the first frame 21 and the concave portion formed on the lower mold 22a of the second frame 22 do not have to have a single line, and for example, it is possible to provide multiple lines.

In this embodiment, the molding section 3 has a second stage 31 extending in the Y direction and having a mold 31a that is curved downwardly convexly at its lower end, and the second stage 31 is positioned so as to press the mold 31a against the workpiece W from above.
In addition, when viewed from the clamping mechanism 2 side, the molding section 3 has a third stage 32 extending in the Y direction at the rear side of the second stage 31, which has a mold 32a that is curved downwardly convexly at its upper end, and the third stage 32 is positioned so that the workpiece W pressed down by the second stage 31 is pushed up from below by the mold 32a.

When viewed from the clamping mechanism 2 side, the workpiece W is pulled in the X direction by the pulling mechanism 4 with its end held by the clamp portion 41 of the pulling mechanism 4 located at the rear side of the forming section 3.
The clamping portion 41 of the pulling mechanism 4 pulls the workpiece W while gripping the end of the workpiece W and moving in the X direction, i.e., in the direction away from the clamping mechanism 2 .

In the stretch forming device 1, the workpiece W is clamped by the clamping mechanism 2 as described above, and in this state is pulled in the X direction by the tensioning mechanism 4. Then, while sliding between the first frame 21 and the second frame 22, the workpiece W is pressed against the dies 31 a, 32 a from above and below in the forming section 3 with tension applied in the X direction.
In this manner, in the stretch forming device 1 according to this embodiment, the workpiece W is formed by the forming unit 3 between the clamping mechanism 2 and the pulling mechanism 4. By forming the workpiece W in this manner, the workpiece W is formed into a curved state in the Y direction, as shown in Fig. 3(a), for example.

Furthermore, while the workpiece W is being pulled, the distance L1 between the clamping mechanism 2 and the second stage 31 and the distance L2 between the second stage 31 and the third stage 32 can be changed, or the second stage 31 and the third stage 32 can be moved vertically to change the amount by which the second stage 31 presses the workpiece W downward and the amount by which the third stage 32 presses the workpiece W upward, thereby forming the workpiece W into a curved shape in the X direction as well, as shown in Figures 3(a) and (b), for example.
In this way, the stretch forming device 1 according to this embodiment is capable of forming a compound curved surface having a three-dimensional curvature in the X and Y directions of the workpiece W. This point will be explained again later.

FIG. 4 is a schematic side view showing the configuration of the stretch forming device according to this embodiment.
The workpiece W is inserted between the first frame 21 and the second frame 22 of the clamping mechanism 2 from the left side in the figure, passed under the mold 31a of the second stage 31 of the molding section 3, and passed over the mold 32a of the third stage 32.
The workpiece W is then clamped between the first frame 21 and the second frame 22 of the clamping mechanism 2, pushed down by the mold 31a of the second stage 31, and pushed up by the mold 32a of the third stage 32, and its end is gripped by the clamp portion 41 of the pulling mechanism 4 at the position indicated by A in the figure.
This state corresponds to the state immediately before the start of forming of the workpiece W. Hereinafter, the position indicated by A in FIG.

As shown in FIG. 4, the clamping mechanism 2 is provided with an oil plate 23 for applying lubricating oil to the upper and lower surfaces of the workpiece W.
The clamping mechanism 2 is movable in the X direction relative to the base 5, i.e., in the direction in which the workpiece W is pulled, and the stretch forming device 1 is provided with a moving device 24 including a motor 24a for moving the clamping mechanism 2 in the X direction. In this embodiment, the clamping mechanism 2 moves in the X direction relative to the base 5, thereby changing the distance L1 between the clamping mechanism 2 and the second stage 31.

The configuration of the clamping mechanism according to this embodiment will be described in detail with reference to FIGS.
As described above, the clamping mechanism 2 comprises a first frame 21 having an upper die 21a at its lower end and a second frame 22 having a lower die 22a at its upper end, and is configured to clamp a portion of the workpiece between the first frame 21 and the second frame 22.

In this embodiment, a third frame 25 is disposed above the first frame 21, that is, on the opposite side of the second frame 22 with the first frame 21 in between.
The first frame 21 and the third frame 25 are connected by a link mechanism 63 of the movement mechanism 6, which will be described later, in a state in which the first frame 21 and the third frame 25 are relatively movable in the Z direction.

In addition, a lifting guide frame 27 is arranged on the side of the first frame 21 and the third frame 25, standing upright from the lower frame 26 to which the second frame 22 is fixed, and the first frame 21 and the third frame 25 are connected by a link mechanism 63 so that they can move as a whole in the Z direction along the lifting guide frame 27, i.e., rise and fall.
The lift guide frame 27 is provided with a position sensor 28 including a linear encoder or the like for detecting the position of the first frame 21 in the Z direction.

The clamping mechanism 2 includes a moving mechanism 6 that moves at least one of the first frame 21 and the second frame 22 in the clamping direction, i.e., the Z direction.
5(a) and 5(b), the workpiece W is not shown. In the following, a case where the first frame 21 is moved in the Z direction will be described, but instead of this configuration, it is also possible to configure the second frame 22 to move in the Z direction, or it is also possible to configure both the first frame 21 and the second frame 22 to move in the Z direction.

In this embodiment, the moving mechanism 6 is configured to move the first frame 21 relative to the third frame 25, thereby moving the position of the first frame 21 in the Z direction, i.e., the clamping direction relative to the workpiece W.
The movement mechanism 6 includes a lifting actuator 61 and a link mechanism 63. The lifting actuator 61 is attached to the upper surface of the third frame 25.

Although Figures 5(a) and (b) show the case where the lifting actuator 61 is configured as a fluid cylinder, it is also possible to use, for example, an electric actuator driven by a ball screw that operates linearly.
The lifting actuator 61 extends and retracts the connecting rod 62 to rotate the members of the link mechanism 63, thereby moving the first frame 21 in the Z direction relative to the third frame 25.

That is, as shown in Figure 5(a), when the lifting actuator 61 contracts the connecting rod 62, the movement is transmitted to the first frame 21 via the link mechanism 63, and the first frame 21 moves in a direction approaching the third frame 25, i.e., upward.
In this embodiment, the moving mechanism 6 contracts the connecting rod 62 in this manner to bring the first frame 21 closer to the third frame 25, thereby moving and raising the position of the first frame 21 in the Z direction.

Also, as shown in Figure 5 (b), when the lifting actuator 61 extends the connecting rod 62, the movement is transmitted to the first frame 21 via the link mechanism 63, and the first frame 21 moves in a direction away from the third frame 25, i.e., downward.
In this embodiment, the movement mechanism 6 extends the connecting rod 62 in this manner to move the first frame 21 away from the third frame 25, thereby moving the position of the first frame 21 in the Z direction and lowering it. As a result, the workpiece W is sandwiched between the first frame 21 and the second frame 22, as shown in FIG. 1(b).

In this embodiment, a fall prevention device 7 is provided to prevent the first frame 21 from falling.
As shown in FIG. 5B, the fall prevention device 7 is disposed on the upper surface of the third frame 25 and has an engagement portion 71 that can be extended and retracted in the X direction.

A hole is provided in the link mechanism 63, which swings on the X-direction side of the fall prevention device 7 when the first frame 21 moves in the Z-direction relative to the third frame 25. As shown in Figure 5(a), when the first frame 21 is in a position closest to the third frame 25, the engagement portion 71 protruding from the fall prevention device 7 engages with the hole provided in the link mechanism 63.

In this manner, in this embodiment, the fall prevention device 7 prevents the first frame 21 from falling when the first frame 21 is closest to the third frame 25 .
For example, when the first frame 21 is moved to a raised position to perform work, such as when replacing the upper mold 21a at the bottom of the first frame 21, the work is performed with the first frame 21 prevented from falling in advance by the fall prevention device 7 for safety reasons.

On the other hand, the clamping mechanism 2 is provided with a restraining force variable mechanism 8 that enables the restraining force F applied to the workpiece W by the first frame 21 and the second frame 22 to be changed.
Here, the restraining force F applied to the workpiece W by the first frame 21 and the second frame 22 will be described.

Depending on the structure of the convex portion of the upper die 21a of the first frame 21 and the lower die 22a of the second frame 22, as well as the material of the workpiece W, when the workpiece W is clamped between the upper die 21a of the first frame 21 and the lower die 22a of the second frame 22 and pulled in the pulling direction, i.e., the X direction, by the pulling mechanism 4, the relationship between the tension T applied to the workpiece W when the workpiece W begins to slide relative to the first frame 21 and the second frame 22 and the amount of reduction G to the workpiece W can be experimentally determined, resulting in a relationship where the tension T monotonically increases with the amount of reduction G, as shown in Figure 6(a), for example.

In this case, the tension T and the restraining force F on the workpiece W by the first frame 21 and the second frame 22 have the following relationship, where μ′ is the coefficient of dynamic friction:
T = μ′F ... (1)
Therefore, the restraining force F also monotonically increases with the reduction amount G as shown in FIG. 6(b).

Therefore, in this embodiment, the restraining force variable mechanism 8 changes the restraining force F applied to the workpiece W by the first frame 21 and the second frame 22 by changing the amount of pressing down G on the workpiece W based on the relationship in Figure 6 (b).
In this embodiment, the amount G of pressing down on the workpiece W is calculated from the position of the first frame 21 in the Z direction detected by the position sensor 28. In other words, the restraining force variable mechanism 8 calculates the distance that the first frame 21 moves in the Z direction from the position where the upper die 21a of the first frame 21 abuts against the workpiece W, i.e., the distance that the first frame 21 clamps the workpiece W, as the amount G of pressing down on the workpiece W.

In this embodiment, the restraining force variable mechanism 8 is disposed on the upper frame 29 that spans the upper end portion of the lift guide frame 27, and includes a worm jack 81 and a servo motor 82. Although Figures 5(a) and 5(b) show a case where two worm jacks 81 are disposed, one worm jack, or three or more worm jacks may be disposed.
The worm jack 81 is erected so as to penetrate the upper frame 29 , and its lower end is attached to the upper end portion of the third frame 25 .

A servo motor 82 is disposed at one end portion of the upper frame 29 in the Y direction, and the output shaft of the servo motor 82 is connected to the worm jack 81 via a coupling 83 .
The worm jack 81 moves in the Z direction, that is, moves up and down, by rotational driving of a servo motor 82 disposed at one end portion of the upper frame 29 in the Y direction.

The restraining force variable mechanism 8 is configured to drive the servo motor 82 and move the worm jack 81 in the Z direction when the first frame 21 is at its farthest distance from the third frame 25 by driving the movement mechanism 6 as shown in Figure 5(b), i.e., when the first frame 21 is at its lowest point in the Z direction relative to the third frame 25 and the workpiece W is sandwiched between the first frame 21 and the second frame 22 as shown in Figure 1(b).

In this case, when the first frame 21 is moved downward, the gap between the first frame 21 and the second frame 22 narrows, so that the amount of pressing G on the workpiece W described above increases, and the restraining force F on the workpiece W by the first frame 21 and the second frame 22 becomes stronger.
Furthermore, when the first frame 21 is moved upward, the gap between the first frame 21 and the second frame 22 increases, so that the amount of pressing G on the workpiece W decreases and the restraining force F on the workpiece W by the first frame 21 and the second frame 22 weakens.

In this embodiment, the moving mechanism 6 is first driven to move the first frame 21 to the position furthest away from the third frame 25 as shown in Figure 5 (b), and the workpiece W is sandwiched between the first frame 21 and the second frame 22.
Then, the restraining force variable mechanism 8 drives the servo motor 82 to extend and retract the worm jack 81 in the vertical direction, moving the third frame 25 in the Z direction, i.e., the clamping direction of the workpiece W, and moving the first frame 21 in the Z direction, thereby changing the amount G of pressure applied to the workpiece W by the first frame 21 and the second frame 22, thereby changing and fine-tuning the restraining force F on the workpiece W.

The effects and utilization of changing the restraining force F applied to the workpiece W by the first frame 21 and second frame 22 using the restraining force variable mechanism 8 of the clamping mechanism 2 will be explained later.

Furthermore, when the servo motor 82 is driven as described above to fine-tune the amount of pressing G onto the workpiece W with the worm jack 81, if the fine adjustment is made with the link mechanism 63 of the moving mechanism 6 standing vertically as shown in Figure 5 (b), the force applied to the upper mold 21a is transmitted along the link mechanism 63 in the vertical position, so that the link mechanism 63 will not rotate even if a strong force is applied to the upper mold 21a.
This makes it possible to reduce the load on the lifting actuator 61 of the moving mechanism 6. Furthermore, since the lifting actuator 61 does not need to have the ability to prevent the link mechanism 63 from rotating when a strong force is applied to the upper mold 21a, it is possible to reduce the actuator size.

Next, the forming section 3 of the stretch forming device 1 will be described.
As shown in FIG. 4, the second stage 31 of the forming unit 3 can move only in the Z direction.
In this embodiment, the second stage 31 has a configuration similar to that of the first frame 21 of the clamping mechanism 2 and moves in the Z direction.

That is, a fourth frame 33 is disposed above the second stage 31. The second stage 31 and the fourth frame 33 are connected by a moving device 34 having a link mechanism so that the second stage 31 and the fourth frame 33 can move relatively in the Z direction.
In addition, above the fourth frame 33, there is disposed an elevator 35 equipped with a servo motor, a worm jack, etc. for raising and lowering the second stage 31 and the fourth frame 33 connected by a link mechanism.

The second stage 31 is moved in the Z direction together with the fourth frame 33 by the driving of the moving device 34 and the lifting device 35 .
By driving the moving device 34 and the lifting device 35 to move the second stage 31 in the Z direction, it is possible to adjust the amount by which the workpiece W is pushed downward by the second stage 31.

On the other hand, the third stage 32 of the forming section 3 is capable of moving not only in the Z direction but also in the X direction.
That is, a support base 36 is disposed below the third stage 32 , and the third stage 32 can be moved in the Z direction relative to the support base 36 by driving an elevator device 37 , that is, can be raised and lowered.
In addition, the support table 36 is supported by the base portion 5 of the stretch forming device 1 so that it can be moved in the X direction, and is moved in the X direction, i.e., the pulling direction of the workpiece W, relative to the base portion 5 by driving a moving device 38 equipped with a servo motor or the like.

The moving device 38 is driven to move the support base 36 in the X direction, thereby moving the third stage 32 in the X direction, thereby changing the distance L2 between the second stage 31 and the third stage 32 shown in FIG. 1.
In addition, by driving the lifting device 37 to move the third stage 32 in the Z direction, it is possible to adjust the amount by which the workpiece W is pushed upward by the third stage 32 described above.

Next, the tension mechanism 4 of the stretch forming device 1 will be described.
The pulling mechanism 4 includes a carriage 42 supported movably in the X direction by a base 5 of the stretch molding device 1 fixed to a floor surface or the like, and the aforementioned clamping section 41 is attached to the tip of the carriage 42, i.e., the end on the clamping mechanism 2 side.
In addition, a servo motor 43 is arranged on the base portion 5, and the carriage 42 and the clamp portion 41 are moved in the X direction by the rotational drive of the servo motor 43, thereby pulling the workpiece W in the X direction, i.e., the pulling direction.

As shown in FIG. 7, in this embodiment, the tension mechanism 4 has two running frames 44 extending in the X direction fixed to the underside of a carriage 42 to which a clamp portion 41 is attached.
A plurality of wheels 45 are rotatably attached to the Y-direction side of the traveling frame 44, and each wheel 45 runs on a rail 46 extending in the X-direction. In addition, a rack 47 is attached to the underside of the traveling frame 44, as shown in FIG.

As shown in FIG. 7, the rotational output of the servo motor 43 is reduced by a reducer 48, and a pinion 49 is attached to the output shaft 48a of the reducer 48 as shown in FIG.
The rotational drive of the servo motor 43 is transmitted to the running frame 44 via a rack-and-pinion mechanism consisting of a rack 47 and a pinion 49, and as the running frame 44 moves in the X direction, the carriage 42 moves in the X direction, and the clamping section 41 pulls the workpiece W in the X direction, i.e., the pulling direction.

4, before the start of forming the workpiece W, the end of the workpiece W is gripped by the clamp unit 41 at the pulling start position A. Then, by driving the servo motor 43 to move the clamp unit 41 in the X direction, the workpiece W is formed while being pulled by the clamp unit 41 in the pulling direction.
The current sensor 50 that detects the current flowing through the servo motor 43 will be described later.

Next, we will explain the operation of the stretch molding device 1 according to this embodiment. We will also explain the stretch molding method according to this embodiment.

In the stretch molding method using the stretch molding device 1 of this embodiment, as described above, the workpiece W is clamped between the first frame 21 and the second frame 22 of the clamping mechanism 2 from the clamping direction, i.e., the Z direction, while the workpiece W is pulled in the X direction by the pulling mechanism 4, and the workpiece W is molded in the molding section 3.
At this time, the workpiece W is shaped while the restraining force F applied to the workpiece W by the first frame 21 and the second frame 22 is changed by the restraining force variable mechanism 8 of the clamping mechanism 2 .

For example, when shaping the workpiece W to form the reflecting surface of a parabolic antenna, the radius of curvature R in the radial cross section extending from the center of the parabolic antenna to the outside is shaped so that it becomes larger as it approaches the outside of the parabolic antenna, i.e., as the radial distance r from the center of the parabolic antenna increases, as shown in Figure 8(a), for example.

In conventional stretch molding devices, this type of molding is performed by changing the distance L1 between the clamping mechanism 2 and the second stage 31 and the distance L2 between the second stage 31 and the third stage 32 while pulling the workpiece W with the pulling mechanism 4, or by moving the second stage 31 and the third stage 32 vertically to change the amount by which the second stage 31 pushes the workpiece W downward and the amount by which the third stage 32 pushes the workpiece W upward.
However, with such a forming method, it is sometimes not possible to form the workpiece into a curved surface with high precision.

In the stretch molding device 1 of this embodiment, when molding the workpiece W, as described above, the workpiece W is pulled by the pulling mechanism 4, while the distance L1 and the distance L2 are changed, and the amount by which the workpiece W is pushed down by the second stage 31 and the amount by which the workpiece W is pushed up by the third stage 32 are changed.
At the same time, the workpiece W is shaped while the restraining force F applied to the workpiece W by the first frame 21 and the second frame 22 is changed by the restraining force variable mechanism 8 of the clamping mechanism 2 as described above.

In this case, in this embodiment, as described above, the restraining force variable mechanism 8 changes the restraining force F on the workpiece W by changing the amount of pressing G on the workpiece W by the first frame 21 and the second frame 22.
Furthermore, the greater the restraining force F applied to the workpiece W by the first frame 21 and the second frame 22, i.e., the greater the amount of pressing G applied to the workpiece W, the greater the tension T, and the smaller the springback after forming, so the curvature of the curved surface formed on the workpiece W becomes larger and the radius of curvature R becomes smaller.

For example, when forming the reflecting surface of a parabolic antenna as shown in FIG. 8(a), immediately after the pulling mechanism 4 starts pulling the workpiece W, that is, at the point when the pulling stroke Sx in the X direction from the starting position A of pulling the workpiece W by the pulling mechanism 4 is short, the part that is far from the center of the parabolic antenna in FIG. 8(a) in the radial direction by the distance r is formed.
In this case, in the part that is far from the center of the parabolic antenna in the radial direction r, the radius of curvature R is large and the curvature of the curved surface formed on the workpiece W can be small, so as shown in Figure 8 (b), the restraining force F, i.e., the amount of pressing down G, on the workpiece W by the first frame 21 and the second frame 22 can be small.

As the pulling stroke Sx of the workpiece W by the pulling mechanism 4 increases, the distance r from the center of the formed parabolic antenna in the radial direction becomes shorter, and the radius of curvature R becomes gradually smaller.
That is, the curvature of the curved surface formed on the workpiece W gradually increases, and the curve becomes sharper.

Therefore, as shown in Figure 8 (b), the larger the pulling stroke Sx of the workpiece W by the pulling mechanism 4, the larger the restraining force F, i.e., the amount of pressing down G, applied to the workpiece W by the first frame 21 and the second frame 22 can be, thereby gradually increasing the curvature of the curved surface formed on the workpiece W.
Therefore, as shown in FIG. 8A, a curved surface is formed on the workpiece W such that the radius of curvature R decreases as the radial distance r from the center of the parabolic antenna decreases.

Furthermore, in this embodiment, as described above, the restraining force F applied to the workpiece W by the first frame 21 and the second frame 22, i.e., the amount of pressing G onto the workpiece W, can be appropriately changed, thereby improving the accuracy of curved surface forming in the direction perpendicular to the X direction, i.e., the Y direction.
Therefore, in this embodiment, the workpiece W can be formed into a curved surface with high precision.

As described above, according to the stretch molding apparatus 1 and stretch molding method of this embodiment, when molding the workpiece W, while the workpiece W is being pulled by the pulling mechanism 4, it is possible to change the above-mentioned distances L1 and L2, or the amount by which the workpiece W is pushed down by the second stage 31 and the amount by which the workpiece W is pushed up by the third stage 32, and at the same time, change the amount G of pressure applied to the workpiece W by the first frame 21 and the second frame 22, thereby changing the restraining force F on the workpiece W.
Therefore, it is possible to precisely form a curved surface in the X direction, i.e., the pulling direction, of the workpiece W, and also to precisely form a curved surface in the direction perpendicular to the X direction, i.e., the Y direction. Therefore, according to the stretch forming device 1 and stretch forming method of this embodiment, it is possible to precisely form the workpiece W into a curved shape.

Furthermore, by using the stretch molding device 1 and stretch molding method according to this embodiment, the following beneficial effects can be obtained.
In conventional stretch molding devices, there are various configurations for the clamping mechanism, but for example, as shown in Figure 9, similar to this embodiment, the clamping mechanism 100 may be configured such that a first frame 101 arranged above a second frame 102 and a third frame 103 arranged above that are connected by a link mechanism 104, and the first frame 101 is moved in the Z direction by driving a moving mechanism 105.

In such a case, the moving mechanism 105 is driven to move the first frame 101 to the farthest position relative to the third frame 103, i.e., to the lowest position, and then the workpiece W (not shown) is sandwiched between the first frame 101 and the second frame 102.
However, in the above configuration, there is no mechanism for raising and lowering the first frame 101 and the third frame 103 as a whole, so the amount of pressing G onto the workpiece W by the first frame 101 and the second frame 102 cannot be changed.

Therefore, in conventional stretch forming devices, once the amount of pressing G on the workpiece W is determined, it is not possible to change the amount of pressing G while the workpiece W is being pulled, thereby changing the restraining force F on the workpiece W by the first frame 101 and the second frame 102.
Therefore, unlike the stretch forming device 1 according to this embodiment, it was not easy to form the curved surface of the workpiece W with high precision.

Furthermore, in order to maintain a constant restraining force F on the workpiece W by the first frame and the second frame even when the thickness of the workpiece W varies, in conventional stretch forming devices, as shown in Figure 9, a spacer 107 is inserted between the first frame 101 and the lower frame 106 to which the second frame 22 is fixed, and the thickness of the spacer 107 is changed to maintain a constant restraining force F.
However, with this configuration, the spacer 107 must be replaced every time the thickness of the workpiece W changes, and it takes time to adjust the binding force F and change the setup.

In contrast, the stretch molding device 1 of this embodiment has a constraint force variable mechanism 8, so the constraint force F applied to the workpiece W by the first frame 21 and the second frame 22 can be changed simply by operating the constraint force variable mechanism 8.Therefore, even if the thickness of the workpiece W changes, it is possible to easily and quickly adjust the constraint force F and change the setup by operating the constraint force variable mechanism 8.
Furthermore, even while the workpiece W is being pulled, the restraining force variable mechanism 8 can be operated to change the amount of pressure reduction G, thereby changing the restraining force F applied to the workpiece W by the first frame 21 and the second frame 22, making it possible to precisely form the curved surface of the workpiece W, as mentioned above.

Incidentally, as is the case with conventional stretch forming devices, in the stretch forming device 1 of this embodiment, when the workpiece W is clamped between the first frame 21 and the second frame 22 of the clamping mechanism 2, pushed down by the second stage 31 of the forming section 3 and pushed up by the third stage 32, and then pulled by the pulling mechanism 4, the workpiece W may break.
Breaking of the workpiece W often occurs between the third stage 32 and the clamping portion 41 of the tensioning mechanism 4 .

When the workpiece W breaks, it is usually because the tension T applied to the workpiece W is abnormally strong.
When the tension T applied to the workpiece W increases, the absolute value I of the current flowing through the servo motor 43 of the tensioning mechanism 4 increases. The current flowing through the servo motor 43 is detected by the current sensor 50 shown in FIG.

For example, as shown in FIG. 10( a), when pulling of the workpiece W starts at a certain time ta and the pulling stroke Sx in the X direction from the starting position A of pulling of the workpiece W by the pulling mechanism 4 starts to increase, the tension T applied to the workpiece W increases simultaneously with the start of pulling.
Then, the absolute value I of the current flowing through the servo motor 43 of the tension mechanism 4 detected by the current sensor 50 increases.

In the normal case, i.e., when the workpiece W is formed without breaking, the absolute value I of the current flowing through the servo motor 43 rises once and then gradually decreases while the workpiece W is being pulled, as shown by the solid line in Figure 10 (b).
Then, when the workpiece W is pulled by a predetermined pulling stroke Sx and the pulling of the workpiece W is completed, the supply of current to the servo motor 43 is stopped and the absolute value I of the current flowing through the servo motor 43 returns to zero.

In contrast, if the workpiece W breaks, as shown by the dashed line in Figure 10 (b), when pulling of the workpiece W begins, the absolute value I of the current flowing through the servo motor 43 increases, just as in the case above. However, if the tension T becomes too large and the absolute value I of the current reaches a predetermined value Ia, causing the workpiece W to break, the absolute value I of the current flowing through the servo motor 43 suddenly drops and returns to zero.

Therefore, as is the case with conventional stretch forming devices, in the stretch forming device 1 of this embodiment, a threshold value Ith is set for the absolute value I of the current flowing through the servo motor 43, as shown in Figure 10 (b), for example.
In this case, the threshold value Ith is set to a value that is greater than the maximum value Imax of the absolute value I of the current flowing through the servo motor 43 when the workpiece W continues to be pulled without breaking, but is smaller than the predetermined value Ia of the absolute value I of the current when the workpiece W breaks.

The pulling mechanism 4 can be configured to stop the rotation of the servo motor 43 and stop pulling the workpiece W when the absolute value I of the current flowing through the servo motor 43 rises to the threshold value Ith after starting to pull the workpiece W, as shown by the dotted line in Figure 10 (b).
With this configuration, it is possible to stop pulling on the workpiece W before the workpiece W breaks, thereby making it possible to avoid breaking the workpiece W.

On the other hand, when the clamping mechanism 2 of the stretch molding device 1 is equipped with a restraining force variable mechanism 8 as in this embodiment, the restraining force variable mechanism 8 can be configured to reduce the restraining force F applied to the workpiece W by the first frame 21 and the second frame 22 when the absolute value I of the current flowing to the servo motor 43 of the pulling mechanism 4 rises to the threshold value Ith after the pulling of the workpiece W by the pulling mechanism 4 begins.
By reducing the restraining force F, it is possible to reduce the tension T applied to the workpiece W. Furthermore, in this embodiment, as described above, by reducing the amount of pressing down G on the workpiece W, it is possible to reduce the restraining force F applied to the workpiece W by the first frame 21 and the second frame 22.

Specifically, after the pulling of the workpiece W begins and the pulling stroke Sx of the workpiece W begins to increase as shown in Figure 11(a), when the absolute value I of the current flowing to the servo motor 43 rises to the threshold value Ith as shown by the two-dot chain line in Figure 11(b), that is, at time tb in the figure, the amount of pressure G applied to the workpiece W by the clamping mechanism 2 is reduced as shown by the two-dot chain line in Figure 11(c).
When controlled in this manner, the tension T on the workpiece W decreases, and the absolute value I of the current flowing through the servo motor 43 returns to the value it would normally be, i.e., when the workpiece W is formed without breaking, as shown in FIG. 11(b).

Then, the tension T on the workpiece W is reduced, and breakage of the workpiece W is avoided.
Therefore, by configuring the restraining force F applied to the workpiece W by the first frame 21 and the second frame 22 to be reduced when the absolute value I of the current flowing through the servo motor 43 rises to the threshold value Ith as described above, it is possible to avoid breakage of the workpiece W.

It goes without saying that the present invention is not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the present invention.
For example, it is possible to provide a control unit that controls the clamping mechanism 2, the forming unit 3, and the pulling mechanism 4 as a whole.

REFERENCE SIGNS LIST 1 Stretch forming device 2 Clamping mechanism 3 Forming section 4 Pulling mechanism 6 Moving mechanism 7 Fall prevention device 8 Restraining force variable mechanism 21 First frame 22 Second frame 25 Third frame 28 Position sensor 43 Servo motor 81 Worm jack 82 Servo motor F Restraining force G Pressing amount I Absolute value Ith of current flowing to servo motor Threshold value W Workpiece

Claims (10)

a clamping mechanism including a first frame and a second frame that clamp a portion of a workpiece, a movement mechanism that moves at least one of the first frame and the second frame in a clamping direction, and a constraint force variable mechanism that makes it possible to change the constraint force applied to the workpiece by the first frame and the second frame, and causing the workpiece to slide between the first frame and the second frame ;
a pulling mechanism that pulls another portion of the workpiece while the workpiece is clamped by the clamping mechanism;
a forming unit that forms the workpiece between the clamping mechanism and the pulling mechanism;
Equipped with
Stretch forming equipment. The stretch forming device described in claim 1, characterized in that the restraining force variable mechanism changes the restraining force applied to the workpiece by the first frame and the second frame by changing the amount of pressure applied to the workpiece. a position sensor for detecting a position of the first frame in the clamping direction;
The stretch forming device according to claim 2, characterized in that the restraining force variable mechanism determines the distance moved in the clamping direction from the position where the first frame abuts the workpiece as the amount of pressing down on the workpiece. the clamping mechanism has a third frame on the opposite side of the second frame with the first frame interposed therebetween,
The stretch molding device according to any one of claims 1 to 3, characterized in that the moving mechanism moves the position of the first frame in the clamping direction by moving the first frame relative to the third frame. the clamping mechanism has a third frame on the opposite side of the second frame with the first frame interposed therebetween,
A stretch forming device described in any one of claims 1 to 4, characterized in that the restraint force variable mechanism changes the restraint force applied to the work by the first frame and the second frame by moving the third frame in the clamping direction and moving the first frame in the clamping direction. The stretch forming device described in claim 4 or 5, characterized in that the restraining force variable mechanism includes a worm jack and a servo motor, and by driving the servo motor, the worm jack moves in the clamping direction, thereby moving the third frame in the clamping direction. A stretch forming device according to any one of claims 1 to 6, characterized in that a fall prevention device is provided to prevent the first frame from falling. The pulling mechanism is configured to pull the workpiece by rotational driving of a servo motor,
A stretch forming device described in any one of claims 1 to 7, characterized in that the constraint force variable mechanism reduces the constraint force applied to the workpiece by the first frame and the second frame when the absolute value of the current flowing through the servo motor of the tensioning mechanism rises to a threshold value after tensioning of the workpiece begins. The stretch forming device described in any one of claims 1 to 7, characterized in that the pulling mechanism is configured to pull the workpiece by rotating a servo motor, and after starting to pull the workpiece, when the absolute value of the current flowing through the servo motor of the pulling mechanism increases to a threshold value, the rotation of the servo motor is stopped to stop pulling the workpiece. A stretch forming method using the stretch forming apparatus according to any one of claims 1 to 9,
When the workpiece is formed in the forming unit while the first frame and the second frame of the clamping mechanism are clamping the workpiece and the pulling mechanism is pulling the workpiece, the workpiece is formed while changing the restraining force applied to the workpiece by the first frame and the second frame using the restraining force variable mechanism of the clamping mechanism.
Stretch molding method.