Patent Description:
Conventionally, as a step of hemming, there is known a step in which an edge portion of a plate-shaped workpiece is bent at an acute angle to form an upright flange (pre-hemming) and the flange is bent inward by performing finish bending (main hemming) (See <CIT>, for example). A bending method according to the preamble of claim <NUM> disclosed in <CIT> includes steps of bending a narrow sheet in a V-shape and pressing an end face of the sheet to reduce a warp. <CIT> discloses a punch for a V-shaped bending machine comprising a die having a workpiece pressing portion with a planar surface and a curved surface forming a V-shape at their joining edge.

When the finish bending is started, a thrust load in accordance with an angle of the flange bent at an acute angle acts on the workpiece. In other words, a force is generated that pushes the workpiece forward (toward a side of an operator). Particularly, the force pushing the workpiece forward becomes larger when the thrust load acting on the workpiece is increased due to the influence of the material, thickness, and the like of the workpiece. In this case, workability of the hemming may be lowered. Further, misalignment of the workpiece with respect to a die may be generated so as to lower the processing accuracy of the bending.

In addition, in order to address this problem, a method of preparing a dedicated die is conceivable so as to reduce the thrust load, that is, to reduce the bending angle when the workpiece is bent at an acute angle. However, in this case, there is a problem of increased cost as the dedicated die is prepared. Furthermore, since it is necessary to use the dedicated die for each acute-angle bending, the workability of the bending is lowered.

A bending method according to the present invention is defined by appended claim <NUM>.

According to the bending method of the invention, it is possible to provide a bending method that can improve workability of bending without using a dedicated die when the bending, which can also be used for preliminary bending and the like of hemming, is performed to the plate-shaped workpiece.

Hereinafter, an embodiment will be described based on the drawings. Note that the same or similar reference signs will be given to the same functions and configurations, and the description thereof will be omitted as appropriate.

In the present embodiment, the "lateral direction" is one of the horizontal directions and is a width direction in a state in which a die and a punch are mounted on a press brake (a direction orthogonal to a paper surface in each drawing). The "front-back direction" is a depth direction in a state in which the die and the punch are mounted on the press brake (a lateral direction of the paper surface). The "vertical direction" is a direction orthogonal to the lateral direction and the front-back direction (a vertical direction of the paper surface). Note that in the drawings, the forward direction is described as "FR", the backward direction as "RR", the leftward direction (the front side of the paper surface) as "LH", the upward direction as "UP", and the downward direction as "DN".

<FIG> is a side view illustrating a state in which a die and a punch used in a bending method according to the present embodiment are attached to a press brake device.

As shown in <FIG>, the press brake <NUM> used in the bending method according to the present embodiment is a press brake for bending a workpiece W of a sheet metal, which can be used for preliminary bending and the like of hemming. A lower table <NUM> extending in the lateral direction is provided to a lower part of a main body of the press brake <NUM>. A die <NUM> is mounted on an upper side of the lower table <NUM> via a die holder so as to be removable and installable. Further, an upper table <NUM> extending in the lateral direction is provided to an upper part of the main body of the press brake <NUM> so as to be vertically opposed to the lower table <NUM> and be vertically movable. A punch <NUM> is mounted on a lower side of the upper table <NUM> via a punch holder so as to be removable and installable.

Note that the configuration for vertically moving the upper table <NUM> may be, for example, a known configuration described in <CIT>, <CIT>, and the like. Further, a servo motor for a table or a hydraulic cylinder (not shown) may be used to move the upper table <NUM> in the vertical direction. Furthermore, instead of the upper table <NUM> being configured to be vertically movable, the lower table <NUM> may be configured to be vertically movable.

<FIG> is an enlarged cross-sectional view of a workpiece pressing portion <NUM> of the punch <NUM> and a V-groove <NUM> of the die <NUM> shown in <FIG>.

As shown in <FIG> and <FIG>, the die <NUM> used in the bending method according to the present embodiment includes, at an upper part <NUM> thereof, the V-groove <NUM> including a first groove wall surface <NUM> and a second groove wall surface <NUM>. The die <NUM> is mounted on the lower table <NUM> of the press brake <NUM>.

Specifically, the die <NUM> includes the groove <NUM> extending laterally (in the direction orthogonal to the paper surface of <FIG>) at the upper part <NUM> thereof. As shown in <FIG>, the V-groove <NUM> includes the first groove wall surface <NUM> and the second groove wall surface <NUM>. The V-groove <NUM> further includes a groove bottom <NUM> that connects the first groove wall surface <NUM> and the second groove wall surface <NUM> and whose cross-sectional shape perpendicular to the lateral direction is an arch shape.

Further, the first groove wall surface <NUM> and the second groove wall surface <NUM> of the V-groove <NUM> are symmetrical with respect to a first perpendicular plane CP. Here, the first perpendicular plane CP is a perpendicular plane passing through an intersect position CL at which imaginary planes extending downward along the respective groove wall surfaces <NUM> and <NUM> of the V-groove <NUM> intersect with each other. In other words, in the present embodiment, the groove wall surfaces <NUM> and <NUM> of the V-groove <NUM> are inclined such that an angle formed between the first groove wall surface <NUM> and the first perpendicular plane CP and an angle formed between the second groove wall surface <NUM> and the first perpendicular plane CP are equal. In the present embodiment, since the cross-sectional shape of the groove bottom <NUM> perpendicular to the lateral direction is an arc shape, the first perpendicular plane CP is a perpendicular plane that passes through the arc-shaped center of the groove bottom <NUM>.

In the present embodiment, an angle θv formed between the first groove wall surface <NUM> and the second groove wall surface <NUM> of the V-groove <NUM> is an acute angle. Specifically, the angle θv of the angle formed between the first groove wall surface <NUM> and the second groove wall surface <NUM> of the V-groove <NUM> is <NUM>°. At this time, an angle formed between the first groove wall surface <NUM> and the first perpendicular plane CP and an angle formed between the second groove wall surface <NUM> and the first perpendicular plane CP are each <NUM>° (θv/<NUM>).

However, this angle θv may be set in accordance with the material and thickness of a workpiece to be bent, or the purpose of the bending. The angle θv may be in a range of, for example, <NUM>° or more to <NUM>° or less.

As shown in <FIG> and <FIG>, the first groove wall surface <NUM> and the second groove wall surface <NUM> of the V-groove <NUM> are flat on a side of the groove bottom <NUM> of the V-groove <NUM> and are curved as a ridge line R on a side of the upper part <NUM> to be smoothly connected to the upper part <NUM>.

The punch <NUM> used for the bending according to the present embodiment is mounted on the upper table <NUM> of the press brake <NUM> so as to be able to advance to the V-groove <NUM> of the die <NUM>, as shown in <FIG>.

As shown in <FIG> and <FIG>, the punch <NUM> includes the workpiece pressing portion <NUM> that advances to the V-groove <NUM>. Specifically, the punch <NUM> is configured to advance to and retreat from the V-groove <NUM> in a state of being mounted on the upper table <NUM> when the upper table <NUM> is vertically moved.

As shown in <FIG>, in the state of being mounted on the upper table <NUM>, the workpiece pressing portion <NUM> of the punch <NUM> includes a first surface <NUM> and a second surface <NUM> positioned on an upper side thereof, and a distal end <NUM> that is positioned on a lower side thereof and is continuous to respective lower ends of the first surface <NUM> and the second surface <NUM> at a predetermined position L1 in the vertical direction.

In the state of being mounted on the upper table <NUM>, the first surface <NUM> is positioned on a first side FS (a left side of the first perpendicular plane CP in <FIG>) with respect to the first perpendicular plane CP. The second surface <NUM> is positioned on a second side SS (a right side of the first perpendicular plane CP in <FIG>) with respect to the first perpendicular plane CP.

As shown in <FIG>, at the workpiece pressing portion <NUM> of the punch <NUM>, the first surface <NUM> is parallel to the first groove wall surface <NUM> of the die <NUM> mounted on the lower table <NUM>. An angle θ<NUM> formed between the second surface <NUM> and a perpendicular plane that is parallel to the first perpendicular plane CP including the lateral direction is different from the angle θv/<NUM> formed between the second groove wall surface <NUM> and the first perpendicular plane CP. Note that an angle θ<NUM> formed between the first surface <NUM> and the perpendicular plane including the lateral direction is naturally equal to the angle θv/<NUM> formed between the first groove wall surface <NUM> and the first perpendicular plane CP (θ<NUM> = θv/<NUM>).

In the present embodiment, the angle θ<NUM> of the first surface <NUM> is <NUM>°, and the angle θ<NUM> of the second surface <NUM> is <NUM>°. In other words, in the state in which the punch <NUM> is mounted on the upper table <NUM>, the first surface <NUM> is inclined by <NUM>° to the first side FS with respect to the first perpendicular plane CP. Therefore, the first surface <NUM> is parallel to the first groove wall surface <NUM> of the V-groove <NUM>. The second surface <NUM> is connected to the distal end <NUM> on the second side SS and is a surface parallel to the first perpendicular plane CP.

In the present embodiment, the distal end <NUM> of the punch <NUM> is formed symmetrically with respect to the first perpendicular plane CP in the state in which the punch <NUM> is mounted on the upper table <NUM>.

Specifically, as shown in <FIG>, the distal end <NUM> of the workpiece pressing portion <NUM> is provided, at a lower end thereof, with a tip <NUM> whose cross-sectional shape of a cross section perpendicular to the lateral direction is an arc shape. Then, the distal end <NUM> includes planar portions <NUM> and <NUM> smoothly continuous in a tangential direction of the arc-shaped tip <NUM> on the first side FS and the second side SS with respect to the first perpendicular plane CP, respectively.

As shown in <FIG>, in a state in which the punch <NUM> is advanced to the V-groove <NUM>, the planar portions <NUM> and <NUM> are opposed to and parallel to the first groove wall surface <NUM> and the second groove wall surface <NUM> of the V-groove <NUM>, respectively. In the distal end <NUM>, an upper end of the planar portion <NUM> and an upper end of the planar portion <NUM>, which are also upper ends of the distal end <NUM>, are connected to the first surface <NUM> and the second surface <NUM>, respectively, at the predetermined position L1 in the vertical direction of the workpiece pressing portion <NUM>.

Note that in the present embodiment, at the predetermined position L1 at which the planar portion <NUM> of the second side SS and the second surface <NUM> are connected, the angles formed between the respective surfaces and the perpendicular plane parallel to the first perpendicular plane CP are changed from <NUM>° to <NUM>°. Note that on the first side FS, since the angle formed between the planar portion <NUM> and the first perpendicular plane CP and the angle formed between the first surface <NUM> and the first perpendicular plane CP are the same, the planar portion <NUM> and the first surface <NUM> extend across the predetermined position L1 to form a single surface. Note that the predetermined position L1 is set in consideration of the thickness of the plate-shaped workpiece W and a desired bending angle of the workpiece W.

<FIG> is a diagram showing a state in which the plate-shaped workpiece W is positioned and placed on the die <NUM> for the bending. <FIG> is a diagram showing a working process of the bending of the plate-shaped workpiece W. <FIG> is a diagram showing a completed state of the bending of the plate-shaped workpiece W.

As shown in <FIG>, in the bending method of the plate-shaped workpiece W according to the present embodiment, the die <NUM> and the punch <NUM> for the bending are used. Then, the plate-shaped workpiece W to be bent is placed on the upper part <NUM> of the die <NUM>. As shown in <FIG>, the plate-shaped workpiece W placed on the upper part <NUM> of the die <NUM> is pressed by the punch <NUM> from an upper surface side thereof. When the plate-shaped workpiece W is pressed by the punch <NUM>, as shown in <FIG>, the punch <NUM> advances to the V-groove <NUM> up to a position at which the plate-shaped workpiece W comes in contact with the first groove wall surface <NUM> of the V-groove <NUM> and the first surface <NUM> of the punch <NUM>. Thereby, the plate-shaped workpiece W is bent in a state of being sandwiched between the first groove wall surface <NUM> and the first surface <NUM>.

Specifically, as shown in <FIG>, the plate-shaped workpiece W is placed on the upper part <NUM> of the die <NUM>. Then, the punch <NUM> is lowered to and pressed against the plate-shaped workpiece W. At this time, in the plate-shaped workpiece W, the bending is started from a state in which a bottom surface thereof shown in <FIG> comes into contact with the upper part <NUM> of the die <NUM> and the upper surface thereof comes into contact with the tip <NUM> of the punch <NUM>.

As shown in <FIG>, the punch <NUM> is lowered via the upper table <NUM> to press the plate-shaped workpiece W by the workpiece pressing portion <NUM>. In a state shown in <FIG>, the workpiece pressing portion <NUM> is pressing the plate-shaped workpiece W while being advancing to the V-groove <NUM>. As a result of this, the bottom surface of the plate-shaped workpiece W, which has been in contact with the upper part <NUM> before the start of the pressing, is brought into a state of being in contact with the first groove wall surface <NUM> and the second groove wall surface <NUM> of the V-groove <NUM>. In other words, as the workpiece pressing portion <NUM> advances to the V-groove <NUM>, the position of the die <NUM> that supports the bottom surface of the plate-shaped workpiece W moves from the upper part <NUM> of the die <NUM> to the second groove wall surface <NUM> (or the first groove wall surface <NUM>).

Further, in a state of <FIG>, the workpiece pressing portion <NUM> is further lowered until the plate-shaped workpiece W is sandwiched between the first groove wall surface <NUM> of the V-groove <NUM> and the first surface <NUM> of the punch <NUM>, so as to press and bend the plate-shaped workpiece W.

At this time, the position at which the bottom surface of the plate-shaped workpiece W comes into contact with the second groove wall surface <NUM> is a cross section perpendicular to the lateral direction, and moves from a contact position P1 in the state of <FIG> to a contact position P2 in the state of <FIG> in which the workpiece pressing portion <NUM> is further advanced to the V-groove <NUM>.

While the upper surface of the plate-shaped workpiece W is being pressed downward by the tip <NUM> of the workpiece pressing portion <NUM> at a position on the first perpendicular plane CP, the bottom surface thereof continues to receive a reaction force in a normal direction orthogonal to the second groove wall surface <NUM> from the moving contact positions P1 and P2 with the second groove wall surface <NUM>. Therefore, on the second side SS, the plate-shaped workpiece W above the contact position P2 is separated from the second groove wall surface <NUM> and bent toward a side of the first perpendicular plane CP. In other words, the plate-shaped workpiece W is bent until the angle formed with the perpendicular plane is smaller than the angle (θv/<NUM>) formed between the first vertical surface CP and the second groove wall surface <NUM> and is larger than the angle θ<NUM> formed between the perpendicular plane and the second surface <NUM> on the second side SS.

On the other hand, on the first side FS, as shown in <FIG>, since the first surface <NUM> is parallel to the first groove wall surface <NUM>, the plate-shaped workpiece W is bent in the state of being sandwiched between the first groove wall surface <NUM> and the first surface <NUM>. Therefore, on the first side FS, even if the bottom surface of the plate-shaped workpiece W receives the reaction force from the first groove wall surface <NUM>, the plate-shaped workpiece W is abutted against the first surface <NUM> of the workpiece pressing portion <NUM>. Therefore, the plate-shaped workpiece W is not bent toward the side of the first perpendicular plane CP beyond the angle θv/<NUM> formed between the first groove wall surface <NUM> and the first perpendicular plane CP.

As a result, the plate-shaped workpiece W is bent at an angle smaller than the angle θv of the angle formed between the first groove wall surface <NUM> and the second groove wall surface <NUM> of the V-groove <NUM> of the die <NUM>. Note that when it is preferable to ensure the flatness of the first side FS of the plate-shaped workpiece W after processing, the workpiece pressing portion <NUM> may be advanced to the V-groove <NUM> up to a position at which the plate-shaped workpiece W is brought into a surface contact with the first groove wall surface <NUM> and the first surface <NUM>.

The bending method of the present embodiment utilizes the die <NUM> mountable on the lower table <NUM> of the press brake <NUM> and including the V-groove <NUM> including the first groove wall surface <NUM> and the second groove wall surface <NUM> at the upper part <NUM>, and the punch <NUM> mountable on the upper table <NUM> of the press brake <NUM> and including, at the workpiece pressing portion <NUM>, the first surface <NUM> and the second surface <NUM>, the first surface <NUM> in the state of being mounted on the upper table <NUM> being parallel to the first groove wall surface <NUM> of the die <NUM> in the state of being mounted on the lower table <NUM>, the angle θ<NUM> formed between the second surface <NUM> and the perpendicular plane being different from the angle formed between the second groove wall surface <NUM> and the perpendicular plane.

The plate-shaped workpiece W is placed on the upper part <NUM> of the die <NUM> mounted on the lower table <NUM> of the press brake <NUM>.

The plate-shaped workpiece W is pressed by the workpiece pressing portion <NUM> of the punch <NUM> mounted on the upper table <NUM> of the press brake <NUM>, and is bent in the state in which the plate-shaped workpiece W is sandwiched between the first groove wall surface <NUM> of the V-groove <NUM> and the first surface <NUM> of the punch.

According to this configuration, the plate-shaped workpiece W is bent at the angle smaller than the angle θv of the angle formed between the first groove wall surface <NUM> and the second groove wall surface <NUM> of the V-groove <NUM> of the die <NUM>. In other words, it is possible to bend the plate-shaped workpiece W, without using a dedicated die or the like, to an angle smaller than the angle θv formed between the groove wall surfaces <NUM> and <NUM> of the V-groove <NUM>.

Particularly, the bending method of the present embodiment can be used in a case in which the material of the plate-shaped workpiece W is a SUS with a thickness of <NUM> or more and <NUM> or less or an SPCC with a thickness of <NUM> or more and <NUM> or less. As in the conventional art, for example, when the hemming is performed to the workpiece W after being bent at an acute angle with a bent portion of the workpiece W up to about <NUM>°, a thrust load generated to the workpiece in finish bending during the hemming, in other words, a force pushing the workpiece forward is increased if a thick plate having a high bending rigidity of the plate-shaped workpiece W is used. As a result, there is a possibility that workability of the hemming is lowered. Furthermore, there is a possibility that the workpiece may be misaligned with respect to the die during the processing, resulting in a decrease in bending accuracy.

However, if the bending method of the present embodiment is used when the plate-shaped workpiece W is bent at an acute angle, it is possible to bend the plate-shaped workpiece W at an acute angle up to an angle smaller than the angle θv formed between the groove wall surfaces <NUM> and <NUM> of the V-groove <NUM>. Therefore, this acute-angle bending can reduce the thrust load to the plate-shaped workpiece W, which is generated when the finish bending such as the hemming is performed.

Furthermore, in the present bending method, since the acute angle bending can be performed in one step without using the dedicated die, working efficiency of the bending such as the hemming of the plate-shaped workpiece W can be improved, and cost reduction can also be achieved by not using the dedicated die.

Furthermore, in the bending method of the present embodiment, the plate-shaped workpiece W is bent to the state of being sandwiched between the first surface <NUM> of the workpiece pressing portion <NUM> and the first groove wall surface <NUM> of the V-groove <NUM>. Therefore, the flatness of a plate-shaped structure of the plate-shaped workpiece W on the first side FS is stably ensured even after the bending.

In addition, in the bending method of the present embodiment, merely by setting the angle θ<NUM> with respect to the perpendicular plane of the second surface <NUM> connected to the distal end <NUM> formed symmetrically with respect to the first perpendicular plane CP, the plate-shaped workpiece W can be bent at a desired angle smaller than the angle θv formed between the groove wall surfaces <NUM> and <NUM> of the V-groove <NUM>.

In the present embodiment, in the state in which the punch <NUM> is mounted on the upper table <NUM>, the second surface <NUM> of the workpiece pressing portion <NUM> of the punch <NUM> is parallel to the perpendicular plane as shown in <FIG>. However, the configuration of the second surface <NUM> is not limited to this. In other words, the second surface <NUM> may not be parallel to the perpendicular plane.

In modified examples of <FIG> and <FIG>, the respective shapes of distal ends 37a and 37b are made similar to the shape of the distal end <NUM> of the present embodiment. Furthermore, an angle θ<NUM> of each of first surfaces 33a and 33b is the same as the angle θ1 of the first surface <NUM> of the present embodiment.

On the other hand, the angle θ<NUM> of the angle formed between a second surface 35a shown in <FIG> and the perpendicular plane including the lateral direction is set to be larger than <NUM>° and less than <NUM>°. Further, when an inclination angle of the second groove wall surface <NUM> of the V-groove <NUM> with respect to the perpendicular plane is a positive angle, the angle θ<NUM> of the angle formed between a second surface 35b shown in <FIG> and the perpendicular plane including the lateral direction is set to be a negative angle. In other words, the angle θ<NUM> is set to be less than <NUM>° and -<NUM>° or more.

Note that according to the configuration of a workpiece pressing portion 31a of the punch <NUM> shown in <FIG>, when being bent, the plate-shaped workpiece W can be prevented from being bent at an excessively acute angle in a range of an angle smaller than the angle θv formed between the groove wall surfaces <NUM> and <NUM> of the V-groove <NUM> by bringing the second surface 35a into contact with a bent portion of the workpiece W.

Further, according to the configuration of a workpiece pressing portion 31b of the punch <NUM> shown in <FIG>, when being bent, the plate-shaped workpiece W can be bent to an angle sufficiently smaller than the angle θv formed between the groove wall surfaces <NUM> and <NUM> of the V-groove <NUM>.

In addition, the distal end <NUM> of the workpiece pressing portion <NUM> of the present embodiment shown in <FIG> is formed symmetrically with respect to the first perpendicular plane CP in the state in which the punch <NUM> is mounted on the upper table <NUM>. However, as shown in <FIG>, a distal end 37c of the punch <NUM> may be asymmetric with respect to the first perpendicular plane CP.

In a modified example of <FIG>, the angle θ<NUM> of a first surface 33c on the first side FS is set to have the same shape as that of the present embodiment. On the other hand, the angle θ<NUM> formed between a second surface 35c and the perpendicular plane including the lateral direction on the second side SS is set to be larger than <NUM>° and less than <NUM>°.

Furthermore, the distal end 37c is shaped asymmetrically with respect to the first perpendicular plane CP. Specifically, the distal end 37c on the first side FS with respect to the first perpendicular plane CP is set to have the same shape as that of the present embodiment. On the other hand, on the second side SS with respect to the first perpendicular plane CP, the cross-sectional shape of a cross section perpendicular to the lateral direction of the tip <NUM> is an arc shape with a smaller radius than that of the first side FS, and the distal end 37c is smoothly continuous with the second surface 35c in the tangential direction of the arc-shaped portion of the cross section.

According to the configuration of the distal end 37c of the punch <NUM> shown in <FIG>, when being bent, the plate-shaped workpiece W can be bent to the angle sufficiently smaller than the angle θv formed between the groove wall surfaces <NUM> and <NUM> of the V-groove <NUM>. Furthermore, since a distance in the front-back direction is sufficiently ensured from a position at which the distal end 37c of the punch and one surface of the workpiece W come in contact with the second groove wall surface <NUM>, even if the length of a portion of the workpiece W to be bent is short, the workpiece W can be reliably bent to a desired acute angle.

As shown in <FIG>, the configuration of the die <NUM> in which the V-groove <NUM> is directly formed at the upper part <NUM> is described as the die <NUM> used in the bending method of the present embodiment. However, the die <NUM> for the bending that can be used in the bending method of the present embodiment is not limited to this. For example, the die <NUM> may be a double-deck die <NUM> for the hemming bending shown in <FIG>.

Specifically, the double-deck die <NUM> for the hemming shown in <FIG> includes a die base <NUM> supported by a lower table <NUM> of a press brake <NUM>, and a movable die <NUM> that can be moved vertically with respect to the die base <NUM>. The movable die <NUM> is constantly urged upward by an urging means S such as a coil spring.

At an upper part <NUM> of the movable die <NUM>, a V-groove <NUM> having an acute-angled groove bottom is formed for bending the plate-shaped workpiece W at an acute angle. Note that in the present modified example, the shape of the V-groove <NUM> is the same as the shape of the V-groove <NUM> of the present embodiment.

Then, a bottom surface <NUM> of the movable die <NUM> and a flat surface <NUM> of the die base <NUM> are provided so as to be vertically opposed to each other to crush a flange portion of the workpiece W bent at an acute angle. Note that the press brake <NUM> is configured in the same manner as the press brake <NUM> of the present embodiment except that the lower table <NUM> is configured to be able to support the double-deck die <NUM>.

When the plate-shaped workpiece W is bent by using the double-deck die <NUM> having the above configuration, the plate-shaped workpiece W is first placed on the movable die <NUM>. Then, the workpiece W is pressed by the workpiece pressing portion <NUM> of the punch <NUM>. At this time, the movable die <NUM> is lowered against the urging means S, and the bottom surface <NUM> of the movable die <NUM> and the flat surface <NUM> of the die base <NUM> come into contact with each other. Then, the workpiece W is pressed against the V-groove <NUM> so that the workpiece W is preliminarily bent at an acute angle.

The hemming (the finish bending) by the double-deck die <NUM> for the hemming is performed by removing the preliminarily bent workpiece W and placing, between the flat surface <NUM> of the die base <NUM> and the bottom surface <NUM> of the movable die <NUM>, a portion (a bent portion) of the workpiece W bent at an acute angle. Then, the punch <NUM> is caused to be engaged with the V-groove <NUM> of the movable die <NUM> to press the movable die <NUM> downward. In the double-deck die <NUM>, the punch <NUM> can be directly engaged with the V-groove <NUM> of the movable die <NUM> to strongly press the movable die <NUM>.

When the plate-shaped workpiece is preliminary bent by the bending method of the present embodiment using the double-deck die <NUM> having the above configuration, as in the case of using the die <NUM> of the present embodiment, it is possible to reduce the thrust load to the workpiece that is generated during the hemming, that is, the force that pushes the workpiece forward without using the dedicated die. Furthermore, since it is possible to perform the hemming (the finish bending) without changing the die or the like, the work efficiency of crushing of the bent portion of the workpiece W is improved.

Note that the shapes of the V-groove <NUM> formed at the respective upper parts <NUM> and <NUM> of the dies <NUM> and <NUM> of the present embodiment are symmetrical with respect to the first perpendicular plane CP. However, the shape of the V-groove <NUM> is not limited to this. In other words, the groove wall of the V-groove <NUM> may be asymmetric with respect to the first perpendicular plane CP.

Claim 1:
A bending method of bending a plate-shaped workpiece (W), comprising:
with use of a die (<NUM>, <NUM>) mountable on a lower table (<NUM>, <NUM>) of a press brake (<NUM>, <NUM>) and including a V-groove (<NUM>, <NUM>) including a first groove wall surface (<NUM>) and a second groove wall surface (<NUM>) at an upper part (<NUM>, <NUM>) thereof, and a punch (<NUM>) mountable on an upper table (<NUM>) of the press brake (<NUM>, <NUM>) and including, at a workpiece pressing portion (<NUM>), a first surface (<NUM>, 33a, 33b, 33c), a second surface (<NUM>, 35a, 35b, 35c) and a distal end (<NUM>), the first surface (<NUM>, 33a, 33b, 33c) in a state of being mounted on the upper table (<NUM>) being parallel to the first groove wall surface (<NUM>) of the die (<NUM>, <NUM>) in a state of being mounted on the lower table (<NUM>, <NUM>), the distal end (<NUM>) is provided with a tip (<NUM>), whose cross-sectional shape of a cross section perpendicular to the lateral direction is an arc shape, at a lower end thereof and neighboring planar portions (<NUM>, <NUM>), and the planar portions (<NUM>, <NUM>) are continuous to the first surface (<NUM>) and the second surface (<NUM>), wherein the planar portions (<NUM>, <NUM>) are opposed to and parallel to the first groove wall surface (<NUM>) and the second groove wall surface (<NUM>) in a state where the punch (<NUM>) is advanced to the V-groove (<NUM> ,<NUM>),placing the plate-shaped workpiece (W) on the upper part (<NUM>, <NUM>) of the die (<NUM>, <NUM>) mounted on the lower table (<NUM>, <NUM>) of the press brake (<NUM>, <NUM>);
pressing the plate-shaped workpiece (W) by the workpiece pressing portion (<NUM>, 31a, 31b, 31c) of the punch (<NUM>) mounted on the upper table (<NUM>) of the press brake (<NUM>, <NUM>) so as to bend the plate-shaped workpiece (W) in a state of being sandwiched between the first groove wall surface (<NUM>) of the V-groove (<NUM>, <NUM>) and the first surface (<NUM>, 33a, 33b, 33c) of the punch (<NUM>),
characterized in that
an angle (θ<NUM>) formed between the second surface (<NUM>, 35a, 35b, 35c) and a perpendicular plane (CP) being different from an angle (θv/<NUM>) formed between the second groove wall surface (<NUM>) and the perpendicular plane (CP).