JP6704319B2 - Steel pipe expansion method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a steel pipe expanding method in which a punch is pushed into a pipe end of a steel pipe to expand the pipe in stages.

A fuel filler pipe that guides fuel for an automobile from a fuel filler port to a fuel tank is manufactured by expanding a pipe end on the fuel filler port side of a steel pipe. In this case, it is necessary to expand the pipe end to about twice the diameter of the raw steel pipe. However, if the pipe is rapidly expanded at one time, the steel pipe may be cracked or buckled. For this reason, conventionally, a punch having a tip angle of 20° to 25° was used, and the pipe end was gradually expanded in 6 steps (6 steps).

However, in such a pipe expanding method, the thinning rate of the steel pipe end portion during the process becomes as large as about 20 to 22%, and a pipe expanding defect such as a crack may occur. Further, since there are many processes and six types of punches are required, there is a problem that the pipe expansion cost also becomes high. The above-mentioned wall thinning ratio is a value defined as a ratio (T/t) between the wall thickness T of the steel pipe after pipe expansion and the wall thickness t of the steel pipe before pipe expansion.

In order to solve such a problem, there is a method of expanding the pipe in one step by using a punch having a tip angle of 30° to 60° while restraining the outer circumference of the steel pipe using an outer die (Patent Document 1). Proposed. However, this method requires an external mold, which causes a problem that the equipment configuration becomes complicated. Further, since the pipe is rapidly expanded, there is a risk that the pipe end may buckle.

Japanese Patent No. 4442973

Therefore, the object of the present invention is to solve the above-mentioned conventional problems, it is possible to expand the pipe end of the steel pipe at low cost without complicating the equipment structure and without causing expansion defects such as cracks. It is to provide a method for expanding a steel pipe.

The method for expanding the steel pipe of the present invention made to solve the above problems is to expand the pipe end stepwise by pressing a punch having a tapered tip into the pipe end of the steel pipe without restraining the outer circumference of the steel pipe. A method for expanding a steel pipe, in which a punch with a tip angle of 35° to 55° is used and the first tube expansion is performed without using an outer die, and the tip angle is smaller than the punch used in the first time after the second time. It is characterized by using a punch having a tip angle and expanding the pipe without using an outer die .

The first tube expansion is preferably performed so that the tube expansion ratio (D1 is the diameter after the first tube expansion and d is the diameter before the tube expansion) defined as (D1-d)/d is 45 to 55%. .. In addition, it is preferable that the above-mentioned punching-in is performed in four steps while sequentially increasing the diameter of the punch. Further, the pipe expansion ratio after the second pipe is preferably 10 to 20%, and the wall thickness reduction is defined as the ratio (T/t) between the wall thickness T of the steel pipe after pipe expansion and the wall thickness t of the steel pipe before pipe expansion. The rate is preferably less than 18% in each step.

According to the steel pipe expanding method of the present invention, the first pipe expansion is performed by using the punch having the tip angle of 35° to 55° without restraining the outer periphery of the steel pipe, and thereafter, the punch whose tip angle is the first time is used. Expand with a punch having a smaller tip angle. Thus, when a punch having a large tip angle is first pushed into the pipe end of the steel pipe to expand the pipe so that the expansion ratio is 45 to 55%, a large compressive force in the axial direction acts on the pipe end. This compressive force has the effects of shortening the length of the raw material steel pipe and increasing the wall thickness of the pipe end by the amount of compression. Therefore, the thinning rate of the pipe end portion in the first pipe expanding step, which was about 20 to 22% in the conventional method using the punch with the tip angle of about 20 to 25°, is 18% according to the present invention. Less than Further, since the initial pipe expansion ratio is increased to 45 to 55%, the pipe expansion ratio in the subsequent pipe expansion step can be reduced to 10 to 20%, and the wall thinning ratio can be set to less than 18%.

Therefore, according to the present invention, the pipe end of the steel pipe can be expanded at low cost without causing a pipe expansion defect such as a crack. Further, according to the present invention, since the outer circumference of the steel pipe is expanded without being restricted, an outer mold is not required, and the equipment structure is not complicated. Moreover, the number of steps can be reduced from the conventional 6 steps to 4 steps.

It is process explanatory drawing of the steel pipe expansion method of this invention. It is sectional drawing explaining the first pipe expansion process. It is a top view which shows the state after completion|finish of pipe expansion.

Embodiments of the present invention will be described below.
FIG. 1 is a process explanatory view of the steel pipe expanding method of the present invention. The material steel pipe shown in (a) is a steel pipe made of ordinary steel, and its pipe end is expanded in four steps (b) to (e). The material steel pipe is not particularly limited, but in this embodiment, an electric resistance welded steel pipe having a tensile strength of 300 N/mm ² is used.

In the first tube expanding step shown in FIG. 1B, as shown in FIG. 2, the tapered punch 1 having a tip angle α of 35° to 55° is pushed into the tube end to expand the tube. At this time, the outer circumference of the steel pipe is not restrained. The tube end is plastically deformed along the outer shape of the punch 1 and expanded until the outer diameter D1 of the punch 1 is reached. The first tube expansion is preferably performed so that the tube expansion ratio (D1 is the diameter after the first tube expansion and d is the diameter before the tube expansion) defined as (D1-d)/d is 45 to 55%. The expansion ratio is determined by the outer diameter D1 of the punch 1.

As described above, conventionally, a punch having a tip angle of about 20° to 25° was used, whereas in the present invention, a punch 1 having a tip angle α of 35° to 55°, which is twice as large, is used. Expand. Therefore, a larger compressive force than the conventional one acts in the axial direction of the steel pipe. This compressive force acts to compress the steel pipe and at the same time increase the wall thickness. In the present invention, since the outer circumference of the steel pipe is not constrained, the increase in wall thickness is not hindered. Therefore, according to the present invention, it is possible to suppress the metal thinning rate to less than 18% even though the diameter is increased by 45 to 55%.

If the tip angle of the punch 1 used in the first tube expansion is less than 35°, the compressive force in the axial direction is insufficient, so the effect of increasing the thickness is reduced, and the thickness reduction rate cannot be suppressed to less than 18%. On the contrary, if the tip angle of the punch 1 is larger than 55°, buckling occurs and the tube cannot be expanded properly.

Since the electric-welded steel pipe has a weld bead in the electric-welded portion and the hardness of the electric-welded portion is higher than that of the other portions, it is difficult to reduce the thickness of the electric-welded portion, and the electric-welded portion is 20° to 90° away Positional thinning rates tend to be maximized. Therefore, in this specification, the average value of the metal thinning rate at the position 20° to 90° away from the electric seam portion is used as the value of the metal thinning rate.

After the first tube expansion is performed in this manner, the second tube expansion is then performed as shown in FIG. The second expansion is performed using the punch 2 having a tip angle of less than 25°. The outer diameter of the punch 2 is set to be 10 to 20% larger than that of the punch 1.

Similarly, the third and fourth expansions shown in (d) and (e) of FIG. 1 are performed using the punch 3 and the punch 4 whose outer diameters are successively increased by 10 to 20%. The punch 3 and the punch 4 are also performed using the punch 2 having a tip angle of less than 25°. Since the pipe expansion ratio of the second to fourth pipe expanding processes is as small as 10 to 20%, the wall thinning ratio of each process can be suppressed to less than 18%.

As described above, since the electric resistance welded portion of the electric resistance welded steel pipe is hardened, the protrusion 5 is formed at the pipe end as shown in FIG. However, this part is cut and becomes a product.

As described above, according to the present invention, the pipe end of the steel pipe can be expanded at a low cost without causing a defective expansion. Examples of the present invention will be shown below.

An electric resistance welded steel pipe having an outer diameter of 25.4 mm and a wall thickness of 0.8 mm was used as a raw material steel pipe and expanded by the conventional method and the method of the present invention until the outer diameter became 48.4 mm. The material of the material steel pipe is STKM11A.

In the conventional example, a pipe having a tip angle of 25° was used to perform tube expansion in the first three steps, and a punch having a tip angle of 19° was used in the latter three steps. Table 1 shows the pipe expansion ratio in each process and the wall thickness reduction ratio as a result of processing. Thus, in the conventional method, the metal thinning rate exceeded 20%.

Examples 1 to 3 shown in Tables 2 to 4 are examples in which the tip angle of the punch used for the first tube expansion was 35° to 55°. In both cases, the rate of thinning is low and there is no risk of cracks. The comparative example shown in Table 5 is an example in which the tip angle of the punch used for the first tube expansion was set to 65°, and the thickness reduction rate exceeded 20% and buckling occurred. In all cases, the total number of steps was four.

As described above, according to the present invention, the number of steps is reduced as compared with the conventional one, and the pipe end of the steel pipe is expanded without cracking or buckling by a simple equipment configuration without using an outer die. can do.

1 Punch used for the first tube expansion 2 Punch used for the second tube expansion 3 Punch used for the third tube expansion 4 Punch used for the fourth tube expansion 5 Projection

Claims (5)

A method for expanding a steel pipe, in which a punch having a tapered tip is pushed into the pipe end of the steel pipe and the pipe end is expanded in stages without restraining the outer circumference of the steel pipe, and a punch having a tip angle of 35° to 55° is used. using performs initial tube expansion without using an outer die, the second and subsequent use of a punch having a smaller tip angle than punch the tip angle was used for the first time, to pipe expansion without the outer die that A method for expanding a steel pipe. The first expansion is characterized in that the expansion ratio (D1 is the diameter after the first expansion and d is the diameter before the expansion) defined as (D1-d)/d is 45 to 55%. The method for expanding a steel pipe according to claim 1. The method for expanding a steel pipe according to claim 1, wherein the pressing of the punch is performed in four stages while sequentially increasing the diameter of the punch. The steel pipe expanding method according to claim 2 or 3, wherein the pipe expanding ratio after the second time is set to 10 to 20%. The thinning rate defined as a ratio (T/t) between the wall thickness T of the steel pipe after pipe expansion and the wall thickness t of the steel pipe before pipe expansion is set to be less than 18% in each step. The method for expanding the steel pipe according to any one of to 4.