JPH08243680A - Upsetting method for tube - Google Patents

Abstract

PURPOSE: To obtain an upsetting method for a tube which can obtain a prescribed increase thickness part length having large increase thickness ratio with a small number of the workings without causing the defect such as buckling, wrinkles. CONSTITUTION: In this upsetting method of the tube by heating the tube end part and holding the outer surface of the heating part at the tube end by a die 4 and pushing a mandrel 2 into the inner surface to execute plural times of workings, the initial working is executed by using the die having a recessed part 5 at the part where a tapered part 4a is crossed with a parallel part 4b3 in the inner surface of the die 4. The succeeding working is executed by using the die without recessed part to finish the part to be worked into the thickness uniform in the axial direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of upsetting a pipe.

[0002]

2. Description of the Related Art Usually, a plurality of pipes are connected by a joint and used in a long state, so that it is necessary to thread a pipe end. However, if the raw pipe is threaded, the thread portion becomes brittle due to stress concentration. Generally, after the pipe end of the raw pipe is heated, hot forging is performed to increase the wall thickness of the pipe end as shown in FIG. Processing (hereinafter referred to as upset processing) is performed to secure the strength of the screw portion.

There are three methods for this upset processing shown in FIG. In the figure, (a) is an IUE type that thickens only the inner diameter side, and (b) is an EU that thickens only the outer diameter side.
E type, and (c) shows an I & EUE type in which the inner diameter side and the outer diameter side are simultaneously thickened.

The pipe end shape after the upset process is required to have a uniform wall thickness in the axial direction (longitudinal direction). 2) (a) to (c) any of the upset processing methods or a combination thereof, and processed multiple times (multi-step processing)
Is applied.

By the way, the upset process is upsetting forging of a thin-walled circular pipe, and the thickness increase ratio in one process (the thickness after processing / the thickness before processing, hereinafter, simply referred to as the thickness increase ratio). When the (thickness increase ratio) is set to a large value, the gap between the increased thickness part of the raw tube 3 and the tool (die 1 and mandrel 2) becomes large at the initial stage of processing, and the deformation becomes unstable. This leads to the occurrence of defects such as buckling and wrinkles as schematically shown in 3. Therefore, the thickness increase ratio per upset process is naturally limited.

Therefore, in the past, in order to finish the pipe end with a large thickness and finish the pipe end to a uniform thickness in the axial direction, there is a mandrel draft gradient, but the entire thickened portion is axially changed for each machining. Has been subjected to multi-step processing to evenly increase the thickness little by little. However, such multi-step machining has a problem in productivity in addition to an increase in tool cost and machining cost.

On the other hand, for example, Japanese Patent Laid-Open No. 61-2767
Japanese Patent Laid-Open No. 32-32 proposes a method of gradually reducing the heating temperature distribution in the middle part of the pipe end from the thick part of the pipe end toward the steady part of the pipe end to perform upset processing. Although it is possible to stabilize the end-finished shape, it has not yet been possible to increase the thickness increase ratio per machining in the multi-step upset machining.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a multi-stage upset of a pipe capable of obtaining a pipe-end thickened portion with a large thickening ratio with a small number of processes without causing defects such as buckling and wrinkles. It is to provide a processing method.

[0009]

In order to solve the above problems, the present inventor has conducted a detailed investigation by analysis and experiment on the thickening deformation process in the conventional method of upsetting after uniformly heating the pipe end. The following findings were obtained.

In the I & EUE type upset process, as shown in FIGS. 4 (a) to 4 (f), the raw tube 3 first starts contact with the die taper portion 1a of the die 1. That is, the raw material pipe 3 first comes into contact with the die 1 at the portion that forms the outer surface tapered portion of the pipe, and then the raw material pipe 3 bulges outwardly so as to come into contact with the die parallel portion 1b as well, and further comes into full contact with the die 1. After this, the thickness of the raw pipe 3 is gradually increased from the pipe end, and the raw pipe 3 is successively brought into contact with the mandrel 2.

In the IUE type upset processing, since the raw tube 3 and the die 1 are in contact with each other over the entire surface from the initial stage of processing, there is no intermediate step described above, and the raw tube 3 is sequentially processed from the pipe end immediately after the start of processing. Go in contact with.

Even in the EUE type upset process, the raw tube 3 swells toward the die 1 side at the initial stage of deformation and there is almost no contact with the mandrel 2. Therefore, this is due to I & EU.
It can be regarded as a type of E-type upset processing.

From the above-mentioned, in any of the upset processing methods, the raw tube 3 first bulges toward the outer diameter side. Therefore, when upset processing with a large thickness increase ratio is performed, buckling occurs in the raw pipe 3 during the expansion process toward the outer diameter side,
After the upset process, the buckled part remains as a flaw.

On the other hand, as a result of various experiments in which the die shape and the mandrel outer diameter were changed, the following findings were obtained.

A small ring-shaped recess 5 is provided at the intersection of the taper portion 1a and the parallel portion 1b on the inner surface of the die shown in FIG. 1 toward the raw pipe (see FIG. 5), and the shape of this recess can be made appropriate. For example, even if the thickness increase ratio during upset processing is increased, the blank pipe will contact the die over the entire surface and buckling can be controlled.

The outer diameter of the mandrel does not directly affect the buckling during the expansion process to the outer diameter side.

The gist of the present invention based on the above knowledge is the following method of upsetting a pipe.

A method of upsetting a pipe in which a pipe end portion is heated, an outer surface of a heated portion of the pipe end is held by a die, and a mandrel is pushed into the inner surface to perform a plurality of times of processing, and a tapered portion on the inner surface of the die is used. Initial processing is performed using a die that has a ring-shaped recess at the intersection of the parallel part and
Subsequent processing is performed using a die that does not have a recess, and the processed part is finished to have a uniform wall thickness in the axial direction.

[0019]

In the upsetting method of the present invention, regarding the inner diameter shape of the die 4 at the time of initial processing in multi-step processing, a small ring shape is formed at the intersection of the tapered portion 4a and the parallel portion 4b _{3 on} the inner surface of the die toward the raw pipe. The recess 5 is provided (see FIG. 5).
reference). As a result, there is an axial distribution in the amount of increase in the thickness of the pipe end to be processed, and upset processing is performed locally with a large thickness increase ratio. Will be obtained.

The operation and effect of the present invention will be described below by taking the case of a thickness increase ratio, which has conventionally been required to be processed three times in I & EUE type upset processing.

In the method of the present invention, the die 4 shown in FIG. 5 used for the first machining has the maximum diameter portion 4b ₁ of the die near the die taper portion 4a. ) The same size as or slightly smaller than that of the die, and the length L of the maximum diameter portion 4b ₁ of the die is in the range of 5 to 9 times the wall thickness t of the raw pipe (5t
The one satisfying ≦ L ≦ 9t) is used. The length L of the die maximum diameter portion 4b ₁ is a cross section not filled meat dice maximum diameter 4b ₁ is less than 5t become bent-shaped "V". On the other hand, if the length L exceeds 9t, the die maximum diameter portion 4b
This is because buckling will occur at ₁ .

Further, in the die parallel portion 4b ₃ near the pipe end portion, the die inner diameter is made smaller than the die maximum diameter portion 4b ₁ . In this case, the inner diameter of the die parallel portion 4b ₃ was processed by the conventional method in order to obtain a pipe end thickened portion with a large thickness increasing ratio with a smaller number of machining than before without causing defects such as buckling and wrinkles. It may be determined in relation to the following outer diameter of the mandrel so that the thickness increase ratio in the range of 1.1 to 1.4 times the first pipe end thickness increase ratio is obtained. This is due to the following reasons.
The material thickness after the first processing in the die parallel part 4b ₃ is
It must be made large to some extent in order to prevent buckling and other defects from occurring in the parallel part during the second machining. In order to give the axial distribution to the thickness increase ratio without buckling in the first machining and fill the maximum diameter part 4b ₁ of the die with metal, the metal flow is controlled in the process of the material expanding to the outer diameter side, and the die parallel part is controlled. 4b
_It is necessary to give a difference in the thickness increase ratio between ₃ and the maximum diameter portion 4b ₁ of the die. In order to satisfy the above and, it is necessary to determine the inner diameter of the die parallel portion 4b ₃ as described above.

By the way, the die parallel portion 4b near the pipe end portion
Die taper section 4b from ₃ to maximum die diameter section 4b ₁
The taper angle θ of ₂ must be 10 degrees or less. This is because if the taper angle θ exceeds 10 degrees, the die taper portion 4b ₂ lacks in wall thickness and becomes defective in the next processing. The lower limit of the taper angle θ is naturally determined by satisfying the above-mentioned conditions for the inner diameters of the die maximum diameter portion 4b ₁ and the die parallel portion 4b ₃ .

As for the outer diameter of the mandrel, the thickening ratio of the die maximum diameter portion 4b ₁ is such that the pipe end thickening portion has a large thickness increasing ratio with a smaller number of machining than before without causing defects such as buckling and wrinkles. In order to obtain the above, the size of the mandrel for the first processing in the conventional method is set to be 1.3 to 2.1 times the limit value of the thickness increase ratio capable of increasing the thickness in one processing by the conventional method. It suffices to use a mandrel having a dimension between the third processing mandrel.

When the tube is first processed by using the die and the mandrel having the above-mentioned shapes, FIG.
(E), the following base tube 3 is brought into contact with the Daisutepa portion 4a, in contact with the die parallel portion 4b _3, then contact over the die 4 and the entire surface to fill the die maximum diameter portion 4b ₁ bulge outward To do. After this, the raw pipe 3 sequentially contacts the mandrel 2 from the pipe end side to complete the thickness increase.

In the present invention, after the first processing using the die 4, 4a to 4b in the vicinity of the maximum diameter portion 4b _{1 of} the die.
_In order to make the processed part in the range of ₂ as close as possible to the finished shape in the final processing, the maximum diameter part of the die 4
The cross section near b ₁ is preferably trapezoidal as shown in FIG. Here, the sectional line of the die maximum diameter portion 4b ₁ is not necessarily a straight line.

In the upset processing method according to the present invention, 1
After finishing the second processing, the second processing (finishing) is performed using the die and the mandrel having the final finished shape. In the first machining, the vicinity of the die maximum diameter part 4b ₁ (range from 4a to 4b ₂ ) has already been completed close to the final shape, so in the second finishing, pay attention mainly to the finishing of the pipe end. It will be good if you do.

At the initial stage of the second machining, which is the finishing machining, the material (meat) is immediately filled in the vicinity of the die maximum diameter portion 4b ₁ (range from 4a to 4b ₂ ), so that the restraining force against the meat flow in the axial direction is obtained. Sufficiently works to promote filling of the pipe end.

The operation and effect of the present invention have been described above by taking the case of the thickness increase ratio, which has conventionally required three times of machining in the I & EUE type upset machining, but the present invention has been conventionally performed four times or more. Of course, it can also be applied to the multi-step processing that was required. That is, the so-called "initial processing" is performed not only in the first processing but also in the second and subsequent processing by using a die having a ring-shaped recess at the intersection of the tapered portion and the parallel portion of the die inner surface, and the subsequent processing. This is because the number of times of processing can be reduced by finishing the processed portion to a uniform thickness in the axial direction using a die having no depression.

According to the method described above, the material flow is improved and the amount of thickening per machining is increased, so that the number of machining can be reduced and the defects such as buckling and wrinkle flaws which have been conventionally observed can be prevented. Upset processing can be done without looking.

[0031]

EXAMPLES The upset processing method of the present invention will be described below with reference to examples using I & EUE type upset processing as a representative example.

[Example 1] Outer diameter φ73 mm, wall thickness 5.5
Using a 1 mm medium carbon steel tube, the I & EUE type upset processing (see FIG. 2 (c)) was performed under the following conditions (a) method of the present invention, (b) comparison method and (c) conventional method. The thickness of the thickened portion was set to 140 mm and the thickness of the thickened portion was set to 15 mm.

(B) Method of the present invention: Before each upset process, the pipe end processed portion was heated to 1200 ° C., and the following processing was performed.

First processing: thickness increase ratio (upset amount /
(Outer diameter of raw pipe) = 3.3, length of thickening portion = 190 mm, thickening ratio of maximum diameter portion 4b ₁ of die = 2.6, thickening ratio of pipe end = 2.
One.

In the first machining, a ring-shaped recess (angle θ of the die taper portion 4b ₂ is formed in the die.
Is 5 degrees and the maximum diameter portion 4b ₁ of the die has a length L of 30 mm).

Second processing (finishing): thickness increase length ratio = 0.57, thickness increase portion length = 140 mm, increase in the portion increased in thickness along the die maximum diameter portion 4b ₁ in the _first processing Meat ratio = 1.05, pipe thickness increase ratio = 1.3.

(B) Comparative method: Before each upset process, the pipe end processed portion was heated to 1200 ° C., and the following processing was performed.

First machining: thickness increase ratio = 3.4, thickness increase length = 208 mm, maximum die diameter 4b ₁ thickness increase ratio =
2.6, pipe wall thickening ratio = 2.1. In this first processing, a die having a ring-shaped recess (angle θ of the die taper portion 4b ₂ is 15 degrees and length L of the die maximum diameter portion 4b ₁ is 50 mm) was used inside the die.

Second machining (finishing): thickness increase length ratio = 0.48, thickness increase part length = 140 mm, increase in the portion increased in thickness along the die maximum diameter part 4b ₁ in the _first process Meat ratio = 1.05, pipe thickness increase ratio = 1.3.

(C) Conventional method: Before each upset process, the pipe end processed part was heated to 1200 ° C. and the following process was performed.

First processing: thickness increase ratio = 2.0, thickness increase part length = 290 mm, thickness increase ratio = 1.4.

Second processing: thickness increase length ratio = 1.2, thickness increase portion length = 200 mm, thickness increase ratio = 1.4.

Third time processing (finishing): thickness increase length ratio = 0.75, thickness increase portion length = 140 mm, thickness increase ratio = 1.
4.

The number of pieces processed by the above methods (a) to (c) is 50 each.

As a result of the upset processing, when the comparative method deviating from the prescribed conditions of the present invention, the number of times of processing is reduced by one compared with the conventional method, but defects such as wrinkles and buckling are found. I was seen. However, when the method of the present invention was used, the dimensional accuracy was the same as that of the conventional method, even though the number of times of processing was reduced as compared with the conventional method, and defects such as flaws and buckling were not recognized.

As described above, according to the method of the present invention, the upset process, which has conventionally required three times of machining, requires only two processes, which also causes defects such as flaws and buckling as in the conventional method. It is clear that it can be finished in a predetermined shape, without.

[0047]

According to the method of the present invention, it is possible to carry out a stable upset process for increasing the thickness of a predetermined length with a small number of working times without causing defects such as scratches and buckling on the outer surface of the pipe. Therefore, the industrial effect is extremely large.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an outline of I & EUE type upset processing. (A) shows a state immediately before processing, and (b) shows a state immediately after processing.

FIG. 2 is a cross-sectional view showing various upset processing methods.
(A) is IUE type, (b) is EUE type, (c)
Is an I & EUE type.

FIG. 3 is a sectional view schematically showing a buckling phenomenon.

FIG. 4 is a cross-sectional view schematically showing a thickness increasing process in a conventional method of I & EUE type upset processing. (A) ~
Processing proceeds in the order of (f).

FIG. 5 is a cross-sectional view of a die having a ring-shaped recess provided inside the die used in the example.

FIG. 6 is a cross-sectional view showing the outline of the process of increasing the thickness of the initial processing in the method of the present invention of the I & EUE type upset processing. Processing proceeds in the order of (a) to (e).

[Explanation of symbols]

1: Conventional die, 1a: Die taper part, 1b: Die parallel part, 2: Mandrel, 3: Element pipe, 3a: Inner taper part of element tube, 4: Die with ring-shaped recess inside die, 4a: Die taper portion, 4b ₁ : maximum die diameter portion, L: maximum die diameter portion length, 4b ₂ : die taper portion, 4b ₃ : die parallel portion, θ: die taper angle, 5:
Ring-shaped recess

Claims (1)

[Claims] 1. An upset processing method for a pipe, comprising heating a pipe end portion, sandwiching an outer surface of a heated portion of the pipe end with a die, and pushing a mandrel into the inner surface to perform a plurality of times of processing, the method comprising: Perform initial processing using a die that has a ring-shaped recess at the intersection of the tapered part and the parallel part,
Subsequent processing is performed by using a die that does not have a recess, and the processed part is finished to have a uniform wall thickness in the axial direction.