JP2016182615A - Rotational bending method and rotational bending device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress cracking of a bent outer side and decrease of a plate thickness in rotational bending.SOLUTION: A rotational bending method for bending a metal tube 1 by use of a bending metal mold 3, a wiper 7, a side booster 5, a back booster 6 and a core grid 2, in which the core grid 2 is moved without synchronization of a travel speed of the core grid 2 with a travel speed of a neutral axis M of the metal tube 1 thereby suppressing local stretching of the metal tube 1 in the state that a specific part of the metal tube 1 on a bending outer side does not contact the core grid 2 for a long time, dispersing and averaging decrease of a plate thickness of the metal tube 1, and suppressing a remarkable decrease of the plate thickness such that said decrease occurs cracking on the bending outer side or does not satisfy an intended purpose of a finished article.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a rotary drawing bending method and a rotary drawing bending apparatus for a metal tube.

Conventionally, a roll bending method, a press bending method, a rotary pulling bending method, and the like have been put to practical use as methods for bending a metal tube. In bending of a metal tube, with the bending neutral axis as a boundary, the arc length is longer than the neutral axis on the outer side of the bending, so that it is extended in the axial direction, and the plate thickness after processing becomes thinner than the plate thickness before processing. On the other hand, the inner side of the bend is compressed in the axial direction because the arc length is shorter than that of the neutral shaft, and the thickness after processing becomes thicker than the thickness before processing.
As a result, cracks are likely to occur on the outer side of the bend, or a reduction in plate thickness that does not satisfy the intended use of the processed product, and buckling tends to occur on the inner side of the bend. Furthermore, the cross section is likely to be elliptical after bending.

The rotary pulling bending method is a method of bending while applying a tensile load in the axial direction of the metal tube. It can be widely used because it can suppress cracking, thickness reduction, buckling, and cross-sectional ovalization by the following actions. Has been.
(1) Occurrence of buckling by bending the metal tube between the wiper installed on the outer surface side of the inner side of the metal tube and the core metal inserted into the metal tube. Suppress.
(2) a side booster that is installed on the outer surface of the outer side of the metal tube and is pressed against the metal tube and moved in the axial direction; a back booster that is installed behind the metal tube and pushes the metal tube in the axial direction; Therefore, cracks and plate thickness reduction are suppressed mainly by supplying the material to the outside of the bend.
(3) The cross-section ovalization is suppressed by securing the space between the inner side and the outer side of the metal tube with a metal core inserted into the metal tube.

  However, if the material supply by the side booster or the back booster is increased, cracks on the outer side of the bend and reduction of the plate thickness are suppressed, but the material becomes excessive on the inner side of the bend, and buckling tends to occur. If the clearance between the metal core inside the metal tube and the bending die outside the metal tube is narrowed, buckling and cross-sectional ovalization are less likely to occur, but the metal tube is strongly pressed against the metal core and ironed. As a result, cracks on the outer side of the bend and reduction of the plate thickness are likely to occur. Further, when the core metal is not used or the clearance between the core metal and the bending mold is increased, cracking on the outer side of the bend and reduction of the plate thickness are suppressed, but buckling on the inner side of the bend and cross-sectional ovalization tend to occur.

  Therefore, especially when the thickness of the metal tube is thin or when the bending radius is small (for example, when the bending radius is less than 1.5 times the outer diameter of the metal tube), cracks on the outside of the bend and reduction of the plate thickness are reduced. It is difficult to balance and suppress buckling inside the bend and cross-sectional ovalization.

  As a method for suppressing cracks on the outer side of the bend and reduction of the plate thickness, for example, in Patent Document 1, the rotational speed of the bending mold and the axial push speed of the back booster are controlled synchronously, and in Patent Document 2, the back booster and side booster are controlled. Controlling the shaft pressing speed to a value larger than the rotational speed of the bending mold and Patent Document 3 propose to define the clearance between the core metal and the inner diameter of the metal tube.

Further, in Patent Document 4, it is proposed that a core metal that is fixed and does not move in the middle of bending is lowered to a position that does not affect bending at the initial stage of bending.
In patent document 5, dividing | segmenting a bending process into a some process is proposed.

Japanese Patent No. 2544001 Japanese Patent Publication No. 2-15291 Japanese Patent No. 3974439 Japanese Patent No. 4456489 Japanese Patent No. 4680652

  However, the bending methods disclosed in Patent Documents 1 to 3 are not always sufficient, although they have the effect of suppressing cracking on the outside of the bend and reducing the plate thickness.

  In the bending method of Patent Document 4, since the effect of the core bar is not exhibited at the initial stage of bending, cracking on the outside of the bend and reduction of the plate thickness are suppressed, but buckling and cross-sectional ovalization on the inside of the bend cannot be suppressed.

  In the bending method of Patent Document 5, since the number of processing steps increases, a die corresponding to each step is required, and the processing time also increases, so that the processing cost increases.

  The present invention has been devised in order to solve the above-described problems, and particularly in a rotational pull bending method for suppressing buckling and cross-sectional ovalization inside a bend by using a wiper and a cored bar, particularly a metal tube. To provide a rotary bending method that can suppress cracking on the outer side of the bend and reduction of the plate thickness when the plate thickness is small or the bending radius is small, and a rotary drawing bending device that can realize the rotary drawing method. With the goal.

  As a result of intensive studies on the state of contact between the metal tube and the metal core during the bending process and the progress of the plate thickness reduction, the present inventors have made contact with the metal core. In the region where the metal tube is not stretched due to friction with the metal core, the plate thickness decreases slowly. On the other hand, in the region where the metal tube is not in contact with the metal core, the metal tube has a frictional force with the metal core. It was found that the progress of plate thickness reduction becomes remarkable because the film is stretched in a state in which no action occurs. Therefore, if bending is performed in a state where a specific part outside the bend is not in contact with the core metal for a long time, the reduction in thickness is concentrated on the part, and it is remarkable that the purpose of use of the processed product is not satisfied. Causes thickness reduction.

  The present invention has been developed on the basis of such knowledge, and in a rotary pull bending method for bending a metal tube using a bending die, a wiper, a side booster, a back booster, and a core metal, By moving the movement speed of the gold without synchronizing with the movement speed of the neutral axis of the metal tube, the specific part outside the bending of the metal pipe is stretched locally without being in contact with the metal core for a long time. Rotating and bending metal pipes that can suppress the reduction of the thickness of the metal tube that does not satisfy the purpose of use of the cracked or processed product outside the bend About.

  Further, the present invention provides a core metal moving mechanism for moving a core metal, and a core metal in a rotary drawing bending apparatus that bends a metal tube using a bending die, a wiper, a side booster, a back booster, and a core metal. And a controller that moves the metal tube without being synchronized with the moving speed of the neutral axis of the metal tube, so that a specific portion outside the bent portion of the metal tube is locally stretched without being in contact with the metal core for a long time. The thickness of the metal tube is dispersed and averaged, and as a result, cracks on the outside of the bend or a significant reduction in the thickness that does not satisfy the intended use of the processed product can be suppressed. The present invention relates to a rotary drawing bending apparatus.

  In the metal tube bending process, the moving speeds of the inner side and the outer side of the bending are different. Therefore, in the present invention, the moving speed of the neutral axis of the metal pipe is used as a calculation standard for the moving speed of the core metal to be loaded. . The moving speed of the neutral axis of the metal tube can be determined by a rotational speed detector attached to the bending mold or a shaft pushing speed detector attached to the back booster.

  Moreover, in the rotation drawing bending apparatus of this invention, the metal core is equipped with the control part which can control a position and a moving speed. The mandrel is adjusted and moved to a predetermined moving speed calculated based on the moving speed of the neutral axis of the metal tube.

  According to the present invention, in the rotary pull bending method that suppresses buckling and cross-sectional ovalization inside the bend using a wiper and a cored bar, particularly when the plate thickness of the metal tube is thin or the bending radius is small, It is possible to provide a rotary draw bending method and a rotary draw bending apparatus that can suppress cracking on the outer side of the bend and reduction in sheet thickness.

It is the side view (a) and top view (b) which show a rotation drawing bending apparatus typically, and is a figure which shows the state to which the metal pipe to be bent was attached. It is a top view which shows a rotation drawing bending apparatus typically, and is a figure which shows the state which bent the metal pipe. It is a figure which shows typically the difference in the expansion | extension of the metal pipe by the contact state with a metal core.

  A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing a rotary drawing and bending apparatus used in the method of rotating and bending a metal tube according to the present invention, and shows a state where a metal tube to be bent is attached. FIG. 2 is a view showing a state where the metal tube is bent 90 degrees from the state shown in FIG. In the top views of FIGS. 1 and 2, a cross section is shown for a metal tube portion that is not clamped.

The rotary drawing / bending apparatus 100 of the present embodiment is an apparatus for rotating and bending the metal tube 1. The rotary pull bending apparatus 100 includes a bending die 3, a clamp 4, a side booster 5, a back booster 6, a wiper 7 and a cored bar 2. In the rotary drawing and bending apparatus 100, one end of the metal tube 1 is held between the bending die 3 and the clamp 4, and the bending die 3 is rotated around the bending die rotation axis C, whereby the metal tube 1. Bending is performed while applying a tensile load in the axial direction.
At that time, the seat is obtained by bending the metal tube 1 between the wiper 7 installed on the outer surface side of the bent inner side of the metal tube 1 and the core 2 inserted inside the metal tube 1. Suppresses the occurrence of bending. Moreover, it installs in the axial direction in the state which installed in the outer surface side of the bending outer side of the metal tube 1, and pressed against the metal tube 1, and is installed in the back of the metal tube 1, and makes the metal tube 1 axial. By the back booster 6 to be extruded, the material is mainly supplied to the outer side of the bend to suppress cracking and reduction of the plate thickness. In addition, by securing a gap between the inner side and the outer side of the metal tube 1 with the metal core 2 inserted inside the metal tube 1, cross-sectional ovalization is suppressed.

Here, a conventional rotary drawing and bending method using the rotary drawing and bending apparatus 100 will be described.
In the conventional method, the position of the cored bar 2 is fixed during bending. When the bending process is started, the metal tube 1 is held and pulled by the bending mold 3 and the clamp 4 and is pushed out by the side booster 5 and the back booster 6 to move forward from the initial position of the process. At this time, since the arc length is longer than the neutral axis on the outer side of the bend, it is extended in the axial direction, and the plate thickness after processing becomes thinner than the plate thickness before processing. At that time, as shown in FIG. 3, in the region A where the metal tube 1 is in contact with the cored bar 2, the metal tube 1 is hardly stretched due to friction with the cored bar 2, and the progress of the plate thickness reduction becomes gradual. On the other hand, in the region B where the metal tube 1 is not in contact with the cored bar 2, the metal tube 1 is stretched in a free state in which the frictional force with the cored bar 2 does not act, so the progress of the reduction in the plate thickness becomes remarkable.

  Therefore, when the position of the metal core 2 is fixed, the relative speed between the metal tube 1 and the metal core 2 increases, and the position where the metal tube 1 contacts the metal core 2 is short in the axial direction of the metal tube 1. When the plate thickness reduction starts to increase at a certain part that is not in contact with the metal core 2 of the metal tube 1, even if the part comes into contact with the metal core 2, it immediately passes and passes again. Since the bending process is performed in a state where it is not in contact with the substrate, the decrease in the thickness of the portion is not suppressed, and the decrease in the thickness is concentrated or cracking occurs.

  In order to improve the cross-sectional shape of the metal tube 1, the cored bar 2 may be moved in synchronization with the moving speed of the neutral axis M of the metal tube. In this case, the relative speed between the metal tube 1 and the cored bar 2 is small, and even if bending progresses, the contact position between the metal tube 1 and the cored bar 2 proceeds at the same speed, and the cored bar 2 of the metal tube 1 When the plate thickness reduction starts to increase at a certain part not in contact with the core, the part does not reach the core metal 2 and is bent without being in contact with the core metal 2. The reduction in thickness is not suppressed, but the reduction in thickness is concentrated or cracking occurs.

Therefore, in this embodiment, as shown in FIGS. 1 and 2, the metal tube 1 is bent by moving the moving speed of the cored bar 2 without synchronizing with the moving speed of the neutral axis M of the metal pipe 1. It is suppressed that the specific part on the outside is stretched locally in a state where it is not in contact with the metal core 2 for a long time, and the reduction in the plate thickness of the metal tube 1 is dispersed and averaged.
In addition, the rotary pull bending apparatus 100 is synchronized with a metal core moving mechanism (not shown) for moving the metal core 2 and the movement speed of the metal core 2 during the bending process with the movement speed of the neutral axis M of the metal tube 1. By including a control unit (not shown) that controls so as not to be stretched, a specific portion outside the bend of the metal tube 1 is locally stretched without being in contact with the cored bar 2 for a long time. This is suppressed, and the thickness reduction of the metal tube 1 is dispersed and averaged.

  Appropriate conditions for controlling the moving speed of the core metal 2 are the material, surface state, dimensions, cross-sectional shape, bending radius R, bending angle θ, position of the core metal 2, rotational speed of the bending mold 3, side of the metal tube 1. It is affected by various factors such as moving speed of booster 5, axial pushing force of back booster 6, or plate thickness distribution required for bent products, degree of cross-sectional ovalization, and temperature and environmental factors during processing. .

  The shape of the cored bar 2 is not limited to the universal cored bar 2 having a plurality of balls 2 a shown in FIGS. 1 to 3, and may be a spherical cored bar or a semi-cannonball type cored bar.

  A universal core 2 having a plurality of balls 2a is configured such that a plurality of core metal balls 2a are rotatably connected to the tip of a support drive shaft 2c of the core 2 via a ball connecting portion 2b. It is flexible as a whole. Therefore, the metal core 2 can be inserted to a position in the middle of the bent portion of the metal tube 1, and the metal tube 1 and the metal core 2 can be contacted at a plurality of locations. Can be effectively suppressed.

  In a preferred embodiment of the invention, the moving speed of the metal core 2 is not synchronized with the moving speed of the neutral axis M of the metal tube 1, and the moving speed of the metal core 2 is set to the moving speed of the neutral axis M of the metal pipe 1. By moving within the range of 10% or more and 50% or less, the thickness reduction of the metal tube 1 is dispersed and averaged. Can be suppressed.

  As a method for controlling the movement speed of the metal core 2 so as not to synchronize with the movement speed of the neutral axis M of the metal tube 1, for example, the movement speed of the metal core 2 input in advance as a set value and the metal tube 1. Based on the moving speed of the neutral axis M, there is a method of moving the core metal 2 and rotating the bending mold 3. Further, the control unit of the rotary drawing and bending apparatus 100 includes a detection unit that detects the rotation speed of the bending die 3, and a calculation unit that calculates a moving speed for moving the cored bar 2 from the rotation speed detected by the detection unit; A cored bar control unit that moves the cored bar 2 at the moving speed calculated by the calculating unit may be included.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[Measurement of plate thickness reduction rate 1]
Using a ferritic stainless steel pipe having an outer diameter D of 40 mm and a plate thickness T of 1.2 mm as a metal pipe 1, rotation pulling is performed so that the radius of curvature (bending radius) R of the bending neutral axis M is 48 mm (bending radius R = 1.2 D). Bending by the bending method was performed. As the core metal 2, a three-ball free core metal was used, and the clearance between the inner diameter of the metal tube 1 and the core metal 2 was 0.5 mm on one side. The bending angle was 90 degrees. The moving speed of the cored bar 2 is 0% (fixed: Comparative Example 1), 10%, 20%, 30%, 40%, 50 with respect to the moving speed of the neutral axis M of the metal tube 1 due to the rotation of the bending mold 3. % And 60% (Examples 1 to 6), respectively, were moved in the same direction as the movement of the metal tube 1 accompanying bending under the condition of a constant speed, and the plate thickness reduction rate at the plate thickness reduction maximum position outside the bend was evaluated. . The results are shown in Table 1.

  In the case of Comparative Example 1 in which the core metal 2 was fixed, the maximum thickness reduction rate on the outside of the bend was about 32%. As the moving speed of the cored bar 2 is increased, the sheet thickness reduction rate gradually decreases. When the moving speed of the cored bar 2 is set to 30% with respect to the moving speed of the neutral axis M of the metal tube 1, the sheet is reduced. The thickness reduction rate was about 15%, which was improved to ½ or less of the condition in which the core metal 2 was fixed. Furthermore, when the moving speed of the core metal 2 was increased, the plate thickness reduction rate gradually increased. In the present embodiment, when the moving speed of the metal core 2 is 10% to 50% with respect to the moving speed of the neutral axis M of the metal tube 1, cracks and buckling do not occur, and a local reduction in the plate thickness occurs. Especially suppressed. By defining the moving speed of the cored bar 2 within the above range, the contact position between the metal tube 1 and the cored bar 2 sequentially moves, so that the thickness reduction of the metal tube 1 does not concentrate locally and the thickness decreases. Is considered to be particularly suitably suppressed.

[Measurement of plate thickness reduction rate 2]
Using a ferritic stainless steel pipe having an outer diameter D of 35 mm and a plate thickness T of 1.0 mm as a metal pipe 1, the bending radius R of the bending neutral axis M (bending radius) R is 35 mm (bending radius R = 1.0 D). Bending by the bending method was performed. As the core metal 2, a three-ball free core metal was used, and the clearance between the inner diameter of the metal tube 1 and the core metal 2 was 0.55 mm on one side. The bending angle was 90 degrees. The moving speed of the cored bar 2 is 0% (fixed: Comparative Example 2), 10%, 20%, 30%, 40%, 50 with respect to the moving speed of the neutral axis M of the metal tube 1 due to the rotation of the bending mold 3. % (Examples 7 to 11) were moved in the same direction as the movement of the metal tube 1 during bending under the condition of a constant speed, and the plate thickness reduction rate at the plate thickness reduction maximum position outside the bend was evaluated. The results are shown in Table 2.

  In the case of Comparative Example 2 in which the core metal 2 was fixed, the maximum thickness reduction rate on the outside of the bend was about 40%, and necking, which was the stage before cracking, occurred. As the moving speed of the cored bar 2 is increased, the sheet thickness reduction rate gradually decreases. When the moving speed of the cored bar is set to 30% with respect to the moving speed of the neutral axis M of the metal tube 1, the sheet thickness is reduced. The reduction rate was about 17%, which was improved to ½ or less of the condition in which the core metal 2 was fixed. Furthermore, when the moving speed of the core metal 2 was increased, the plate thickness reduction rate increased. In this embodiment, when the moving speed of the metal core 2 is 20% to 40% with respect to the moving speed of the neutral axis M of the metal tube 1 due to the rotation of the bending mold 3, no cracking or buckling occurs. Local thickness reduction was particularly suppressed. By defining the moving speed of the cored bar 2 within the above range, the contact position between the metal tube 1 and the cored bar 2 sequentially moves, so that the thickness reduction of the metal tube 1 does not concentrate locally and the thickness decreases. Is considered to be particularly suitably suppressed. In this embodiment, the metal plate 1 has a small initial plate thickness and a small relative bending radius R compared to the above [Measurement of plate thickness reduction rate 1]. The appropriate range of position movement speed has become narrower.

[Measurement of plate thickness reduction rate 3]
Using a ferritic stainless steel pipe having an outer diameter D of 40 mm and a plate thickness T of 1.2 mm as a metal pipe 1, rotation pulling is performed so that the radius of curvature (bending radius) R of the bending neutral axis M is 48 mm (bending radius R = 1.2 D). Bending by the bending method was performed. As the core metal 2, a three-ball free core metal was used, and the clearance between the inner diameter of the metal tube 1 and the core metal 2 was 0.5 mm on one side. The bending angle was 90 degrees. With respect to the moving speed of the neutral axis M of the metal tube 1 due to the rotation of the bending mold 3, the moving speed of the metal core 2 is kept constant at 20% and moved in the same direction as the movement of the metal pipe 1 accompanying bending, and the bending angle is While repeatedly returning the cored bar 2 to the initial position every time it increased by 15 degrees, it was processed to a bending angle of 90 degrees, and the thickness reduction rate at the maximum thickness reduction position outside the bending was evaluated. The results are shown in Table 3.

  In the case of Comparative Example 3 in which the core metal 2 was fixed, the maximum thickness reduction rate on the outside of the bend was about 32%. In the case of Example 12 in which the core metal 2 is moved so as to return to the initial position every 15 degrees of bending angle, the plate thickness reduction rate is about 12%, which is less than 1/2 of the condition in which the core metal 2 is fixed. Improved. In this embodiment, the moving speed of the metal core 2 is set to 20% of the moving speed of the neutral axis M of the metal tube 1 due to the rotation of the bending mold 3, and the position of the metal core 2 is controlled as the bending proceeds. By doing so, cracking and buckling did not occur, and local thickness reduction was suppressed. By defining the moving speed and position of the metal core 2 as described above, the contact position between the metal tube 1 and the metal core 2 moves sequentially, and the reduction in the thickness of the metal tube 1 does not concentrate locally, It is thought that the plate thickness reduction was suppressed.

DESCRIPTION OF SYMBOLS 1 ... Metal pipe 2 ... Core metal 2a ... Core metal ball 2b ... Core metal ball connection part 2c ... Metal core support drive shaft 3 ... Bending die 4 ... Clamp 5・ ・ ・ Side booster 6 ・ ・ ・ Back booster 7 ・ ・ ・ Wiper 100 ・ ・ ・ Rotary bending bending machine C ・ ・ Bending mold rotation axis M ・ ・ ・ Neutral axis of metal tube R ・ ・ ・ Bending radius

Claims (4)

  In a rotary pull bending method for bending a metal tube using a bending die, wiper, side booster, back booster and core metal, the moving speed of the core metal is not synchronized with the moving speed of the neutral axis of the metal pipe Rotating drawing bending method for metal pipes to be moved to.   2. The metal pipe rotation drawing process according to claim 1, wherein the moving speed of the metal core is set in a range of 10% or more and 50% or less with respect to the moving speed of the neutral axis of the metal pipe due to the rotation of the bending mold. Method.   The method of rotating and bending a metal tube according to claim 1 or 2, wherein the core metal is returned to an initial position every time the bending die is rotated by a predetermined angle. A rotary drawing bending apparatus that bends a metal tube using a bending die, a wiper, a side booster, a back booster and a core metal,
A metal core moving mechanism for moving the metal core;
A controller for controlling the cored bar moving mechanism so that the moving speed of the cored bar does not synchronize with the moving speed of the neutral axis of the metal pipe during the bending process, and a rotational pulling bending apparatus for the metal pipe further provided.

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