JPS60130440A - Upsetting method of tubular body - Google Patents

Abstract

PURPOSE:To prevent generation of defects such as a fold, dent, fin, burr or the like in the stage of upsetting the end of a steel pipe with segmental dies and a punch by determining the required forging pressure according to the upsetting shape and thickness increase rate and determining the required upsetting load and die pressing load. CONSTITUTION:The end 4 of a steel pipe 3 which is locally heated to a high temp. is securely held by segmental dies 2 and is upset and forged by a punch 1 under the compressive force exerted in the axial direction of the pipe. The required forging pressure is set according to the upsetting shape and thickness increase rate of the tubular body 3 and the required optimum upsetting load P1 and die pressing load P2 are determined from said pressure, by which the steel pipe is upset. Generation of a dent 5 owing to deficiency of the load P1 and a burr 6 and fin 7 owing to the excessive upset load P1 in the upset part is thus prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for upsetting the end of a steel pipe, and more particularly to a method for upsetting a tubular body according to a determined value of an optimal load condition in upsetting a tubular body.

Generally, as a method of connecting long pipe bodies such as oil country tubular goods, a method is used in which the pipe bodies are connected one after another by inserting a joint or the like into a threaded part formed on the outer or inner surface of the pipe end. There is.

In the pipe body to which the above connection method is applied, it is necessary to form a thickened part at the end part in order to ensure the strength of the threaded part formed at the end part.

FIG. 1 is a schematic diagram of upset processing for forming a thickened portion at the end of the tube body.

The end portion 4 of the tube body 3, which has been locally heated to a high temperature by an induction heating method or the like, is firmly held by the splitting die 2, and then
A compressive force is applied in the tube axis direction by the punch 1, and upset processing is performed by upsetting forging. In Figure 1,
(I), (TI).

(III) shows a situation in which the end portions 4 of the tube 3 are sequentially upset-processed, and the arrow 10 indicates the forward and backward direction of the punch 1.

The quality of the upset processing part is determined by the upset load P! and is largely influenced by the die presser load P2. If the upset load P1 is insufficient, wrinkles and dents 5 will occur as shown in Figure 2, and excessive upset load P1 will increase the size of burrs 6 and fins 7 as shown in Figure 3, which will be removed in the next process. This poses a major obstacle.

Conventionally, experience in the field has given priority to setting the upset load P1 and the die presser load P2.

That is, conventionally, for the upset load P1, a value obtained by multiplying the cross-sectional area of the upset portion by a constant has been used, and finding the optimum value has caused a decrease in yield and operation rate.

Moreover, the set value of the die closing force, that is, the die holding load P2, was too high, which caused damage to the die and also caused problems in terms of protecting the machine.

The present invention sets the required forging pressure according to the upset shape and thickness increase rate of the tube body 3, determines the necessary optimum forging load P1 and die holding load P2 from this pressure, and performs upsetting without causing wrinkles or burrs. The purpose is to perform processing.

FIGS. 4(a), 4(b), and 4(c) show the state of the tube end portion 4 inside the die 2 during upset processing. (a
) is immediately before upsetting, (b) is during upsetting,
(e) shows a cross section when upsetting is completed.

FIG. 5 shows the load distribution in the longitudinal section and cross section of the tube end upon completion of upsetting, and the stress state in the die is close to the hydrostatic state with a substantially uniform pressure P. If this pressure P is defined as the forging pressure, it is equal to the load per unit area applied from the punch l.

The forging pressure P is determined by the upset shape and the degree of processing, and needs to be increased as the forging method becomes a closed type or as the degree of processing increases.

The forging method is determined by the amount of inner wall thickness increase, and the smaller the ratio of the inner wall thickness increase rate to the total wall thickness increase rate, the more closed the forging becomes. Further, the degree of processing can be replaced with the rate of increase in thickness.

Therefore, the required forging pressure P must be increased as the inner wall thickness increase rate becomes smaller and as the wall thickness increase rate increases.

Due to the forging pressure P, a force F0 that attempts to open the die acts on the upper die of the split die. This forging reaction force F() is obtained by integrating the upward component of the required forging pressure P, and is given by the following equation.

Leu+Meu π FD = fo fo Ps+nθ・r11dθ−dJ
1Leu+Meu ”fo 2Pr*dr = 2P r (Leu+Meu) ++++++++
(1) Although the Meu portion has a tapered shape, the inclination is approximately 7°, so all loads were directed upward.

here P; Required forging pressure r; outer radius of the top of the splitting die Leu: Parallel part upset part Meu; Taper length It is.

The splitting die 2 is closed with a certain set force prior to upset processing, but if this value is too small or the upset load P1 is too high, the die opens and burrs are generated in the gap between the dies.

Here, the most appropriate required forging pressure P is the upset method,
It is uniquely determined by the thickness increase rate, and when the relationship was determined through experiments, it was found that the relationship shown in FIG. 6 exists. FIG. 6 is an experimental example in which the upset load P1 shown in FIG. 1 was measured using a strain gauge, and the relationship between the upset shape and the wall thickness increase rate after being converted into a load per unit area. The smaller the rate of increase in inner surface thickness is, and the higher the rate of increase in thickness is for external and inner and outer upsets, the higher the required forging pressure is.

Looking at the relationship between upset shape and forging pressure, for example, when the thickness increase rate is around 80%, the required forging pressure is 70 kg/mrn' for external upsetting, but 25 kg/mrn' for internal upsetting.
It is about g/mm'. In addition, the dependence of forging pressure on the thickness increase rate is remarkable; in the case of external upsets, the required forging pressure is 50 kg/mm" at a thickness increase rate of 50%, but when the thickness increase rate is 10
It can be seen that 80 kg/mnf is required at 0%.

Forging reaction force FD applied to the die, that is, P in Fig. 1
2 was actually measured and calculated using the above formula (1),
FIG. 7 shows the relationship with the forging pressure calculated from the upset load P1.

From Figure 7, the two are almost equal, and it can be assumed that the inside of the die is in a hydrostatic pressure state and is isotropic.
You can check the validity of the formula.

As described above, the present invention determines the required forging pressure according to the upset shape and thickness increase rate, takes the upset load into account, and further calculates the required die presser load by assuming that the stress state within the die is equivalent to the hydrostatic pressure state. , perform the upset under those conditions. Therefore, by optimizing the load conditions, we not only prevent the occurrence of upset defects such as wrinkles and dents, but also
It can suppress the occurrence of upset burrs, and has excellent effects such as improving quality, streamlining work, and smoothing processes.

[Brief explanation of the drawing]

Fig. 1 is an explanatory drawing showing an overview of upset processing, Fig. 2 is a partially cross-sectional side view of the pipe end showing an upset defect, Fig. 3 is a partially cross-sectional side view of the pipe end showing an upset burr, 4
The figure is an explanatory diagram showing the upset deformation process, Fig. 5 is an explanatory diagram of the load distribution inside the die, Fig. 6 is a graph showing the dependence of forging pressure on the working degree, and Fig. 7 is a graph showing the isotropy of the stress inside the die. This is a graph showing. 1...Punch 2...Dice 3...Pipe body 4...For pipe end Applicant: Kawasaki Steel Co., Ltd. Agent Patent attorney: Yoshio Kosugi, patent attorney Kazunori Saito Figure 4 Figure 6

Claims (1)

[Claims] 1. A method for upsetting a tubular body, which is characterized in that the required forging pressure is calculated according to the upsetting shape and the thickness increase rate, the required upsetting load and the die holding load are determined from the pressure, and the tubular body is upset in accordance with the determination. Upset processing method for pipe bodies.