JPS6117323A - Production of metallic pipe - Google Patents

Abstract

PURPOSE:To obtain a metallic pipe having small residual stress and high dimensional accuracy by performing in the order of a preparatory stage, heat treatment state and bulging stage. CONSTITUTION:Two half pipe members 10A, B are made with pressing a rod material and a metallic pipe 10 having square cross section is made with the welding thereof and a welding bead 11 is made flat by cutting, plastic work, etc. At the next heat treatment stage the metallic pipe 10 is heated to about 900 deg.C by a high frequency heating device 12 and cooled rapidly with projecting a water 14 by a spraying device 13 to make the welding part in the same organization with the mother material. The bulge forming to form to the prescribed shape is then performed, with close contact of the metallic pipe 10 to the metal die by giving a load in the axial direction of the metallic pipe 10, at the same time with applying a pressure via a pressure medium from the inside of the metallic pipe 10 under the prescribed conditions, using the metal die into which the consideration of the deformation of springback, etc. of after forming and the working allowance in the following stage is taken.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for manufacturing a metal tube having a circular, rectangular, polygonal, etc. cross section, and particularly to obtain a metal tube with high cutting accuracy and low residual stress. The present invention relates to a method of manufacturing a metal tube suitable for.

[Background of the Invention] As a method for precisely manufacturing long metal tubes within strict dimensional tolerances, it has been known to use a technique called "thermal sizing." This method utilizes the difference in the coefficient of linear expansion of two types of materials, and involves inserting a mandrel with a coefficient of linear expansion larger than that of the metal tube into the target metal tube.
In this state, both are heated and the metal tube is expanded to a predetermined size due to the difference in coefficient of linear expansion.

However, in this method, when the metal tube is long, the metal tube 1 is in a deformed state due to residual stress from previous processes such as pressing and welding, as shown in FIG. When inserted into the tube, it is easy to damage the inner surface of the tube. Also,
It takes a long time to attach and detach the mandrel 2, and since the heat capacity of the mandrel 2 is large, it is necessary to heat it for a long time. There are problems such as it takes a long time to repair scratches on the inner surface of the tube.

[Purpose of the invention]

The purpose of the present invention is to form a metal tube without damaging the inner surface of the tube, with high dimensional accuracy, and with a low residual stress of /J.
It is an object of the present invention to provide a method for manufacturing a metal tube that can obtain a metal tube with a small size.

[Summary of understanding]

The present invention applies pressure to the inside of a metal tube via a pressure medium and at the same time applies a load in the axial direction of the metal tube to tightly fit the metal tube into a mold of a predetermined shape. , when forming a metal tube without scratches on the inner surface of the tube, and when processing a bulge.

If the structures of the base material of the metal tube and the welded part are different, large residual stress will occur, so heat treatment is performed to make the structures of the two the same before bulging.

[Actual side of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 6.

In the method for manufacturing a metal tube according to the present invention, a pre-process, a heat treatment process, and a bulge process are performed in this order to obtain a metal tube of a predetermined shape. In this embodiment, a long and rectangular metal tube is obtained. An example of manufacturing a metal tube with a cross section of .

In the previous step, two half-tube members were made by pressing the plate material, as shown in FIG. 1(a).

As shown in (b), the above-mentioned half pipe member 10A.

Metal tube 10 having a rectangular cross section by welding 10B together
After that, the weld bead 11 is flattened by grinding, plastic working (roll, press), etc.

In the heat treatment process, as shown in FIG. 2, after the metal tube 10 is heated to about 900'C by a high-frequency heating device 12, a water sprinkler 1 provided in the high-frequency heating device 12 is heated.
Heat treatment is performed to rapidly cool the metal tube 10 by injecting water 14 from step 3 to change the α structure of the base material of the metal tube 10 to the same β as that of the welded part.
change the organization.

This heat treatment is applied to the entire metal tube 10 by moving the high frequency heating device 12 and the water spray device 13 in the direction of the arrow shown. ``In the aforementioned metal tube 10, high dimensional accuracy could not be obtained in the aforementioned pre-process, and furthermore, due to the deformation caused by the aforementioned heat treatment, the cross section of the metal tube was moved outward by a maximum of 0.7 mm, as shown in Fig. 3. It deforms into a protruding shape, and as shown in FIG.
A bend of 0 to 15 mm occurs.

In the bulge forming process, bulge forming is performed to correct the aforementioned metal tube 10 having poor dimensional accuracy into a predetermined shape. That is, as shown in FIGS. 5 and 6, the metal tube 10 is
5, and a load P8 is applied by a mold press (not shown) to restrain the ratio mold 15. In this state, pressure fluid is introduced into the metal tube 10 from the port 17 of the pressure rod 16 to apply an internal pressure P to the metal tube 10, and at the same time, an axial compression load P is applied by the pressure rod 16, and the metal tube 10 is expanded and brought into close contact with a ratio mold 15 to correct it into a predetermined shape. The split mold 15 has a shape that takes into consideration springback and elastic deformation of the mold itself. In addition, if the metal tube 10 after bulge forming is subjected to post-processes such as pickling treatment, a metal tube whose wall thickness is increased in advance to compensate for the decrease in wall thickness due to the pickling treatment etc. is used. It is necessary to take this into account when determining the shape of the split mold 15.

In this bulging step, the metal tube 10 is molded so as to be in close contact with the proportion mold 15, so that the dimensional accuracy after molding is very high. Also, during machining, the internal pressure P of the metal tube lO
, and the axial compressive load P2 are applied to plastically deform the metal tube 0 over the entire area, so that the residual stress generated during the forming of the metal tube in the previous step is reduced.

As described above, according to this embodiment, it is possible to manufacture a metal tube with high dimensional accuracy and low residual stress without causing scratches on the inner surface of the metal tube 10. As a result, it is possible to provide high-quality metal pipes at lower costs than before.

In this embodiment, the manufacturing of a metal tube with a rectangular cross section has been described, but it goes without saying that the same effects as described above can also be achieved with metal tubes with a round or polygonal cross section. Further, although the manufacturing process is completed by performing bulge forming, autoclave treatment and annealing heat treatment may be performed for various purposes after forming.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to manufacture a metal tube that does not damage the inner surface of the tube during molding, has high dimensional accuracy, and has low residual stress.

[Brief explanation of the drawing]

1 to 6 show an embodiment of the present invention, FIG. 1 (,) is a side view of a metal tube formed in the previous step of the metal tube manufacturing method according to the present invention, and FIG. Its cross-sectional view, 2nd
The figure is a cross-sectional view of a metal tube being heat-treated, FIG. 3 is a graph showing the deformation of the cross-sectional portion of the metal tube after heat treatment, and FIG. 4 is a perspective view showing the bending of the metal tube in the longitudinal direction. FIG. 5 is a sectional view of a metal tube being bulge-formed, FIG. 6 is a cross-sectional view thereof, and FIG. 7 is a side view showing a conventional method. 10...Metal pipe, 1'OA, IOB...Half pipe member. 11... Welding bead, 12... High frequency heating device, 1
3... Water sprinkler, 15... Split mold, 16... Pressure rod, 1st mouth 2nd mouth Akira 3 mouth 4th (2) Y!J 5 Figure 71'i7 Figure

Claims (1)

[Claims] 1. Two half pipe members are made by pressing a plate material, and the half pipe members are welded together to produce a metal pipe having a circular, rectangular, polygonal, etc. cross section. A pre-process of flattening the weld bead by grinding, plastic working, etc., a heat treatment process of making the base metal of the metal tube and the welded part the same structure, and deformation such as springback after forming. By using a mold that takes into account the amount and machining allowance in subsequent processes, pressure is applied from the inside of the metal tube via a pressure medium under predetermined conditions, and at the same time, a load is applied in the axial direction of the metal tube. A method for manufacturing a metal tube, comprising a bulging step of molding the metal tube into a predetermined shape by bringing the metal tube into close contact with the mold. 2. The method of manufacturing a metal tube according to claim 1, wherein in the heat treatment step, the metal tube is heated to a temperature at which the α structure of the base material of the metal tube changes to the same β structure as that of the welded part.