JPS6330095B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for upsetting the end of a tube, and more specifically, it eliminates all dents and scratches on the inner circumferential surface of the tube, which occur when upsetting products with a large wall thickness increase ratio, and improves the quality of the product. The present invention relates to a method for upsetting the end of a tube to improve the yield.

There are three types of upset products, as shown in FIG. 1a, b, and c, depending on their use, such as oil drilling, casing, and tubing. Here, Fig. 1a shows an internal upset product;
FIG. 1b shows an outer upset product, and FIG. 1c shows an inner and outer upset product. When manufacturing such a processed product, the wall thickness to of the raw pipe performed in one shot upset processing and the wall thickness after upset processing t ₁
The ratio, that is, the thickness increase ratio t ₁ /to, varies depending on the type of upset processing, but it is said to be about 1.4 at most. A desired upset product is obtained by processing multiple shots.
Conventionally, for example, for an upset-processed product on the inner and outer surfaces as shown in Fig. 1c, a two-shot process is used. Using a mold, the first shot is formed to increase the thickness on the inner side to obtain an intermediate product 3 for internal upset processing, and then the second shot is performed using the mold shown in Fig. 2b to further increase the thickness on the inner side. At the same time, the outer surface is also subjected to thickening molding to produce a final product 4 with upset processing on the inner and outer surfaces. According to this method, as shown in Figure 3, along the inner circumference at a position several tens of mm from the tube end,
There was a problem that dent defects 5 of about 0.3 to 1.5 mm often occurred, making it impossible to obtain stable products and greatly reducing the yield.

SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned drawbacks of the prior art, and specifically, to provide a method for upsetting a tube end, which can reduce dent defects at the tube end and advantageously improve the yield. purpose.

That is, in the method of the present invention, after upsetting the inner surface of the tube, the inner diameter of the tube is enlarged and the end of the tube is upset into a desired shape by expanding the inner diameter of the tube and upsetting the end of the tube toward the outer surface. It is characterized by adjusting the inner diameter expansion to 1.05 to 1.25 times the inner diameter during the previous inner surface upsetting process.

Therefore, in the present invention, various studies have been carried out regarding the process of expanding the inner diameter toward the outer surface in the final shot when manufacturing a product with internal and external upsets using multiple shots, and as a result, the process is carried out under the optimum conditions obtained. ,
The inner diameter is enlarged toward the outer surface, and even when the thickness increase ratio is large, upset processing is possible with almost no defects such as dents at the tube end.

Therefore, the present invention will be explained in detail as follows.

Generally speaking, when increasing the wall thickness by upsetting the heated end of a tube in a mold consisting of a pair of dies and a punch, the rate of increase in thickness per process is Although it varies depending on the type, the thickness is increased toward the inner side as shown in Figure 2a.
The upset process on the inner surface of the tube as shown in Fig. 2b is the largest, followed by the thickening on the inner and outer surfaces at the same time.
The inner and outer surface upset processing shown in FIG.

Incidentally, upset-processed products with a large thickness increase ratio require processing of multiple shots, resulting in an increase in manufacturing costs. From this,
In order to minimize the number of heating and shot times,
It is important to optimize the thickness increase direction and the thickness increase ratio for each shot. For example, when producing a two-shot product with internal and external upsets, the appropriate direction for increasing the thickness is to take advantage of the above-mentioned advantage of upsetting the internal surface, that is, the large thickness increase ratio. Upsetting the inner surface with the first shot and enlarging the inner diameter with the next shot,
Although it has been found that the desired upset product can be obtained by increasing the thickness toward the outer surface, the above-mentioned defects are likely to occur.

From this point of view, in the present invention, we went further and examined the conditions for removing the above defects, and in particular, focused on the fact that the ratio of the depth of denting to the inner surface has a close relationship with the expansion rate of the inner diameter, and clarified the appropriate inner diameter expansion rate. I made it. Incidentally, this relationship is clarified using the example shown in FIG. 4 as follows.

That is, the outer diameter of the original tube D ₀ = 114.3φ, the wall thickness t ₀ =
In order to obtain an intermediate product like the dotted line section 6 in Figure 4 in the first shot of a 6.85 mm piece, the inner surface was upset-processed, and the diameter d ₀ of the inner surface at that time was changed as appropriate. Prepare the workpiece, and at the second shot, use a punch 2 with a fixed punch diameter d ₁ (corresponding to the finished inner diameter of the upset product) to perform upset processing between the upper and lower dies 1 and 1', and form the part shown by code 7 (solid hatched part). The final product has been processed with internal and external upsets. As a result, the relationship between d ₁ /d ₀ and the inner recess depth ratio δ/t ₀ was as shown in FIG. From this, it can be seen that as the expansion ratio of the inner diameter is increased, the dent depth ratio decreases, and in particular, when d ₁ /d ₀ is in the range of 1.05 to 1.25, there is no dent at all, and a high-quality upset product can be obtained.

Therefore, in the present invention, when the inner diameter is expanded toward the outer surface in the final shot, the value of d ₁ /d ₀ is 1.05 to 1.25.
Perform upset processing by adjusting to the range of . At this time, the lower limit of d ₁ /d ₀ is set to 1.05 because if it is smaller than this, dents will occur and the product will be defective, and the upper limit is set to 1.25 because this value is the same as when the outer circumference of the tube end is rounded. This is because this is the permissible limit that causes

Next, examples will be described.

First, when upsetting the inner and outer surfaces of a 60.3φ
A semi-finished product of 8.95mm was obtained. Next, change this to the punch diameter
Using a 46.2φ punch, enlarge the inner diameter and make an upset on the outer side, and finally the outer diameter is 73.7φ and the inner diameter is 73.7φ.
An upset product with a diameter of 46.2 mm and a wall thickness of 13.75 mm was obtained with a wall increase ratio of 2.8. This processed product had no dents and was a good upset product, and when processed as described above, this processed product was stably obtained.

As described above, it has become possible to stably manufacture high-quality upset products with no internal dent defects even with a large thickness increase ratio, and the product yield has improved dramatically.

[Brief explanation of the drawing]

Figures 1a, b and c are cross-sectional views of various upset products, Figures 2a and b are explanatory diagrams of each process of upsetting in the conventional method, and Figure 3 is an example of an internal dent defect that occurs after upsetting. FIG. 4 is an explanatory diagram of an upset processing method according to one embodiment of the present invention, and FIG. 5 is a graph showing the relationship between the inner diameter enlargement ratio and the recess depth ratio. Code 1, 1'...Upper die, lower die, 2
... Punch, 3, 6 ... Intermediate product of inner surface upset processing, 4, 7 ... Final product of inner and outer surface upset processing, 5 ... Inner surface dent defect, t ₀ ... Wall thickness of raw pipe, t ₁
...Wall thickness after upset, δ...Depth of inner recess.

Claims (1)

[Claims] 1 After performing upsetting on the inner surface of the tube, the inner diameter of the tube is enlarged and the end of the tube is upset into the desired shape by expanding the inner diameter of the tube and upsetting it toward the outer surface. A method for upsetting an end of a tube, characterized by adjusting the inner diameter to 1.05 to 1.25 times the inner diameter during internal upsetting.