JPH0642967B2 - Bending method of circular pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a circular tube in which a straight tubular material circular tube is bent into a bent tube by using a floating plug mounted in a floating state on a mandrel. It relates to a bending method. The method of bending the circular pipe according to the present invention is referred to as "floating plug method".

[Conventional technology]

It is very difficult to bend a circular pipe into a bent pipe without impairing the roundness, and if the circular pipe is simply bent, it will be crushed or buckled.

As a bending process to make a straight tubular pipe into a bent pipe, a circular pipe is made plastic by inserting a spherical plug having a diameter larger than the inner diameter of the circular pipe into the straight tubular pipe and allowing it to pass. A method of bending at the plug portion while deforming and expanding the tube is known.

As a method of using this plug, there are a method of using a fixed plug (hereinafter referred to as “fixed plug method”) and a method of using an eccentric plug (hereinafter referred to as “eccentric plug method”).

In the former "fixed plug method", a technique similar to this is described in Japanese Patent Laid-Open No. 53-142964, and as shown in FIG. 2, the center (C ₁ ) of the plug 11 and the core The plug 11 is integrally attached to the mandrel 12 so that the axial center (C ₂ ) of the gold 12 coincides, and a bending force (F) is applied to a portion of the raw material circular pipe P immediately after the expansion by the pressing tool 13 while directly applying the bending force (F). This is a method in which the plug 11 is inserted into and passed through the tubular material circular pipe P to form the straight tubular material circular pipe P into a bent pipe P ′. In this fixed plug method, the center of the plug 11 (C _1), since the axis of the mandrel 12 (C ₂₎ and match, there is a disadvantage of reduced thickness at the outer bending is large.

The latter “eccentric plug method” is also described in Japanese Patent Publication No. 51-7151, and as shown in FIG.
The center of the _{(C 1),} by eccentric by (e) with respect to the axis of the mandrel 22 _{(C 2),} integrally attached to the plug 21 to the mandrel 22, a plug 21 which is eccentric relative to the mandrel 22 Is inserted into the material circular pipe P and passed therethrough, whereby the straight tubular material circular pipe P is bent toward the eccentric side of the plug 21 to form a bent pipe P ′. In the eccentric plug method, the curvature of the bent pipe P ′ is determined by the eccentricity (e) of the plug 21, and the curvature cannot be changed freely, and the material properties are not uniform or lubrication is difficult. There is a drawback that the curvature of the bending partly changes due to a defect, and therefore, it cannot be bent with a large curvature. Furthermore, this "eccentric plug method"
Then, it is not possible to perform bending processing while leaving the straight pipe portion partially.

[Problems to be Solved by the Invention]

An object of the present invention is to make it possible to change a bending direction and a curvature freely and to process a bent pipe having a complicated shape with a small thickness strain distribution (uneven thickness) with high accuracy. It is a thing.

[Means for Solving the Problems]

In the method for bending a circular pipe according to the present invention, the center of a spherical floating plug having a diameter larger than the inner diameter of a straight tubular material circular pipe is arbitrary within a certain range with respect to the axis of a round bar-shaped mandrel. The floating plug is attached to one end of the mandrel, and the bending plug is applied to a portion of the raw material circular pipe immediately after the pipe is expanded, so that the floating plug is inserted into the raw material circular pipe. The floating plug is eccentric with respect to the mandrel, and the floating plug and the material circular pipe are relatively moved.

[Operation of the invention]

Since the plug is attached to one end of the mandrel in a floating state, the bending plug is inserted into the material circular pipe while passing it while applying bending force to the portion of the material circular pipe immediately after expansion. The force causes the floating plug, which is mounted in a floating state with respect to the mandrel, to be eccentric to the side on which the bending force is applied, and is in a state similar to that of the eccentric plug.

When a floating plug is inserted and passed through the material circular tube in such a state, the floating plug eccentric to the core metal causes the bending action and the bending force applied to the part of the material circular tube immediately after the expansion. Synergistic with the bending action, a straight tubular material circular tube is bent at the portion of the floating plug.

In this way, the bending action of the floating plug eccentric to the mandrel and the bending action of the bending force applied to the material circular pipe are synergistically bent, so that the material circular pipe can be bent with a small bending force. Can be bent greatly.

Further, the eccentricity of the eccentric plug with respect to the core metal is considered to be proportional to the magnitude of the bending force applied to the material circular pipe, so by changing the magnitude of this bending force,
The curvature of the bent pipe can be freely adjusted, and the bending direction of the circular pipe can be changed by changing the direction of the bending force. Therefore, by controlling the magnitude and direction of the bending force applied to the portion of the raw material circular pipe immediately after the pipe expansion, it is possible to process the curved pipe having a complicated shape with high accuracy.

Moreover, the bending action due to the eccentricity of the floating plug thins the inside of the bending, and the bending action due to the bending force (moment) thins the outside of the bending, and the two cancel each other out, resulting in a thickness strain distribution (deviation A bent tube with a small amount of meat can be obtained.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to examples.

In FIG. 1, the outer shape (D ₁ ) of the round bar-shaped mandrel 1 for guiding the material circular pipe P is slightly smaller than the inner diameter (d) of the straight tubular material circular pipe P. A spherical floating plug 2 is attached to one end of a mandrel 1 via a ball joint 3 in a floating state. Therefore, the center of the floating plug 2 (C ₁₎ is adapted to move in any direction within a predetermined range with respect to mandrel 1 the axis (C _2).

The diameter (D ₂ ) of the floating plug 2 is the inner diameter (d) of the material circular pipe P.
Greater than.

Then, the mandrel 1 and the floating plug 2 are inserted into the material circular pipe P, the material circular pipe P is guided by the mandrel 1, and the material circular pipe P
When the bending force (F) is applied to the portion immediately after the pipe expansion in (1) by the pressing tool 4 while the floating plug 2 and the material circular pipe P are relatively moved to pass the floating plug 2 into the material circular pipe P, the bending force (F), are moved to the side floating plug 2 is acting bending force (F), the center (C ₁₎ is eccentric to the mandrel 1 the axis (C ₂₎ [Eccentricity amount is (ex)]. The floating plug 2 which is eccentric with respect to the mandrel 1 performs the same action as the plug 21 in the above-described eccentric plug method, and the material circular pipe P undergoes plastic deformation in this portion and is expanded while being eccentric to the floating plug 2. Can be bent into.

This bending action of the floating plug 2 and the bending action of the bending force F applied to the portion of the material circular pipe P immediately after the pipe expansion synergize, so that the straight tubular material circular pipe P is formed in the floating plug 2 portion. It is bent to form a bent pipe P '. Therefore, as is apparent from FIG. 4 showing the curvature of the bent pipe (the reciprocal of the radius of curvature) with respect to the bending moment, the floating plug method according to the present invention has a smaller value than the fixed plug method. With a bending moment (bending force),
Can be bent greatly.

Further, due to the bending action due to the eccentricity of the floating plug 2, the inside of the bending pipe P ′ becomes thin, and the bending action due to the bending force (F) makes the outside of the bending pipe P ′ thin so that they cancel each other out. Therefore, a bent pipe P'having a small thickness deviation can be obtained.

The radius of curvature P of the bent pipe P'is considered to be inversely proportional to the eccentricity (ex) of the floating plug 2 with respect to the mandrel 1 as in the case of the eccentric plug method.
By changing the magnitude of the bending force (F) and changing the eccentricity (ex) of the floating plug 2, the radius of curvature R of the bent pipe P'can be adjusted freely. Further, if the direction of the bending force (F) is changed during the bending process, the floating plug 2 is eccentric in the opposite direction, so that the material circular pipe P is bent in the opposite direction or the material circular pipe P is made the same. Not only a plane but also a three-dimensional complex shape can be bent.

Further, by releasing the bending force (F) during the bending process, it becomes possible to leave the straight pipe portion, and it is also possible to form a bent pipe partially having the straight pipe portion.

In this way, since bending can be performed by freely changing the bending direction of the material circular pipe P and the curvature thereof, a complicated shape can be obtained by controlling the magnitude of the bending force (F) and its direction. It is possible to process bent pipes.

FIG. 5 shows the angle (θ) of the horizontal axis in FIGS. 6 to 8.
FIG. 4 is a diagram for defining (.degree.).

Further, FIGS. 6 to 8 show arbitrary bending from the outside to the inside of the bend of the bent pipe processed by the floating plug method, the fixed plug method, and the eccentric plug method according to the present invention using the same plug. Circumferential strain at angular position (ε
6 is a graph showing θ), longitudinal strain (ε), and wall thickness strain (εt).

As is clear from these graphs, according to the floating plug method of the present invention, the reduction in wall thickness on the outside of the bend, which was remarkable in the fixed plug method, is reduced and improved, and the circumferential strain is also improved. It can be seen that there is a slight improvement compared to the eccentric plug method.

〔The invention's effect〕

The present invention has a structure in which a floating plug attached to one end portion of a mandrel in a floating state is inserted and passed through the material circular pipe while applying a bending force to a portion of the raw material circular pipe immediately after expansion. By changing the eccentricity of the floating plug with respect to the bending pipe, the bending direction and curvature of the bending pipe can be freely changed, and by this, the bending pipe having a complicated shape with a small thickness strain distribution (uneven thickness) can be obtained. It has become possible to machine with high precision, which is a remarkable advance in the technology related to bending of circular pipes.

In addition, the bending action of the floating plug that is eccentric to the mandrel and the bending action of the bending force applied to the portion of the material circular pipe immediately after the pipe expansion synergize to bend the material circular pipe, so a small bending force is required. The material circular tube can be bent greatly.

Furthermore, by canceling the bending force applied to the portion of the material 5 circular pipe immediately after the pipe is expanded, the eccentricity of the floating plug can be made zero and the straight pipe state can be maintained. It enables the molding of tubes.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a state where a material circular pipe P is bent by the floating plug method according to the present invention, and FIGS. 2 and 3 show a material circular pipe P by a fixed plug method and an eccentric plug method, respectively. FIG. 4 is a cross-sectional view showing a state of bending, FIG. 4 is a graph showing a curvature with respect to a bending moment of a bent pipe bent by the floating plug method and a fixed plug method according to the present invention, and FIG. Curved pipe P ′ leading to
FIGS. 6 to 8 are used to identify the position of the bent pipe, which is processed by the floating plug method, the fixed plug method, and the eccentric plug method according to the present invention using the same plug. It is a graph which shows the circumferential strain ((epsilon) (theta)), the longitudinal strain ((epsilon)), and the wall thickness strain ((epsilon) t) in arbitrary angle positions from the outer side to the inner side. The explanation of the reference numerals of the main parts constituting the present invention is as follows. C ₁ : center of floating plug, C ₂ : core of mandrel P: circular pipe of material, P ': bent pipe F: bending force, 1: mandrel 2: floating plug, 3: ball joint joint 4: pressing tool

Claims (1)

[Claims] 1. A bending method for bending a straight tubular material circular tube into a bent tube, wherein a spherical floating plug having a diameter larger than the inner diameter of the material circular tube has a round bar-shaped core bar. Attaching the floating plug to one end of the mandrel in a floating state so as to move in an arbitrary direction within a certain range with respect to the axis,
By applying a bending force to a portion of the raw material circular pipe immediately after expansion, the floating plug inserted in the raw material circular pipe is eccentric with respect to the mandrel, and the floating plug and the raw material circular pipe are relatively moved. A method of bending a circular pipe characterized by: