JP4442973B2 - Steel pipe end expansion method - Google Patents

Description

【００１１】
【発明の効果】
本発明では、ポンチのテーパー角度を３０°から６０°の範囲に設定することにより、拡管時にポンチのテーパー部に接触した管が直線部へ移動していく際、管端以外は、ポンチの直線部になじまず、隙間が生じることを利用し、外金型に管を接触させ、管円周を拘束することにより局部的な応力集中を抑制し、管端からの割れの伝播を抑制することが可能となる。
【図面の簡単な説明】
【図１】ポンチのテーパー角度が３０°未満の場合における拡管時の鋼管の変形挙動を表す図。
【図２】ポンチのテーパー角度が３０°から６０°の場合における拡管時の鋼管の波打ち現象を表す図。
【図３】本発明の鋼管の波打ち現象を利用し、鋼管を外金型で拘束しながら拡管する状況を示した図。
【符号の説明】
１：鋼管 ２：ポンチ ３：外金型 θ：テーパー角度[0001]
[Industrial application fields]
TECHNICAL FIELD The present invention relates to a tube expansion method that suppresses occurrence of cracks from the tube end over the entire length of a tube expansion portion in punch tube expansion.
[0002]
[Prior art]
The oil supply pipe for automobiles has an expanded pipe end in order to form an oil supply opening. In order to reduce the weight of the vehicle, a small-diameter oil supply pipe has begun to be used, but the size of the oil supply port is constant. Therefore, the expansion rate tends to be large.
As the tube expansion rate increases, that is, when the processing conditions become severe, processing cracks that have not been considered as a problem in the past may occur from the tube end to the entire expanded portion.
For this reason, a molding method for improving dimensional accuracy and preventing cracks using a bulge molding rubber and an outer mold has also been proposed (Japanese Patent Laid-Open No. 5-450). There are difficulties in adopting it.
[0003]
[Problems to be solved by the invention]
Since the welded steel pipe generally has a welded portion that is harder than the base metal part and has a different thickness depending on the bead processing method, when the pipe is expanded, the welded part differs in deformation behavior from the base metal part. For this reason, a position where stress is concentrated locally is likely to occur in the vicinity of the welded portion, and when the degree of processing is increased, thinning near the tube end increases, and cracks from the tube end may occur over the entire length of the expanded portion.
In addition, even when a pipe with a thinned part due to chamfering of the pipe end or a pipe with a burr due to cutting is expanded, cracks from the pipe end occur over the entire length of the expanded pipe from the defective part. There is a case.
In general, when used for an oil supply pipe for automobiles, after expanding the tube, the expanded tube end is cut by about 10 to 20 mm. Therefore, if the crack is several millimeters long from the tube end, there is no problem as a product. It aims at suppressing that the crack from the pipe end mentioned above generate | occur | produces over a pipe expansion part full length.
[0004]
[Means for Solving the Problems]
In order to achieve the object, the present invention uses a punch and an outer mold in which a taper angle is set in a range of 30 ° to 60 ° in order to constrain the pipe expanded at the time of expansion with an outer mold. And
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Pipe expansion is generally performed by punching at the end of the steel pipe. When the taper angle of the punch is less than 30 ° as shown in FIG. 1 and when the taper angle of the punch is 30 ° as shown in FIG. In the case of 60 °, the behavior of the steel pipe during pipe expansion differs.
[0006]
When the taper angle of the punch is less than 30 °, as shown in FIG. 1, when the tube in contact with the taper portion of the punch moves to the straight portion, the expanded tube has a shape of the straight portion of the punch. Become familiar with.
When the taper angle of the punch is 30 ° to 60 °, as shown in FIG. 2, the tube is in contact with the taper portion of the punch, and the tube end of the tube subjected to the mouth widening deformation is a single axis in the circumferential direction. Because of the tensile stress state, the mouth of the end of the tube is squeezed to the outer diameter of the straight part of the punch, but the other expanded part does not conform to the shape of the straight part of the punch, and does not fit into the expanded pipe. A so-called rippling phenomenon in which a gap is generated occurs.
Further, when the taper angle of the punch is made larger than 60 °, the end of the tube is curled and tube expansion cannot be performed.
[0007]
Therefore, in the present invention, as shown in FIG. 3, the wavy phenomenon is utilized, the pipe expanded to the outer mold is brought into contact, and the pipe is restrained, thereby suppressing local stress concentration and cracking from the pipe end. The taper angle of the punch is set from 30 ° to 60 ° in order to suppress the propagation of.
[0008]
【Example】
As a test material, STKM11A (carbon steel pipe for mechanical structure) piped by high frequency welding, outer diameter 25.4 mm × thickness 1.0 mm × length 350 mm was used. The expansion punch was used with a taper angle of 10 ° to 70 °, and coaxial expansion was performed to an outer diameter of 50.8 mm. The clearance between the punch and the outer mold was 1.0 mm, the same as the wall thickness.
[0009]
Table 1 shows the result of expanding 20 tubes for each taper angle. When the taper angle was 10 ° and 20 °, cracks sometimes occurred from the tube end to the entire expanded portion. When the taper angle was 30 ° to 60 °, some pipes were cracked several millimeters in length, but all of them could be expanded. On the other hand, when the taper angle was 70 °, the end of the tube curled and tube expansion could not be performed.
When the outer mold was not used, cracks from the tube end sometimes occurred over the entire length of the expanded portion even when the taper angle was 30 ° to 60 °.
From the above results, it was appropriate to set the taper angle of the punch from 30 ° to 60 ° and use an outer die in order to suppress cracking from the tube end in pipe expansion.
[0010]
[Table 1]

[0011]
【The invention's effect】
In the present invention, by setting the taper angle of the punch within a range of 30 ° to 60 °, when the tube that contacts the taper portion of the punch moves to the straight portion during tube expansion, the straight line of the punch except for the tube end is moved. By using the fact that a gap is created without first adapting to the part, the tube is brought into contact with the outer mold and the circumference of the tube is restrained, thereby suppressing local stress concentration and suppressing the propagation of cracks from the tube end. Is possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing the deformation behavior of a steel pipe during pipe expansion when the taper angle of the punch is less than 30 °.
FIG. 2 is a diagram showing a corrugation phenomenon of a steel pipe during pipe expansion when the taper angle of the punch is 30 ° to 60 °.
FIG. 3 is a view showing a situation in which the steel pipe is expanded while being restrained by an outer mold by utilizing the corrugation phenomenon of the steel pipe of the present invention.
[Explanation of symbols]
1: Steel pipe 2: Punch 3: Outer mold θ: Taper angle

Claims (1)

A method of push tube expansion from steel tube end using a punch having a tapered over part at the tip, by a range of punch taper angle from 30 ° to 60 °, tube punch line contact with the tapered portion of the punch at the time of pipe expansion when moves into parts, after a certain undulation shape in a state not contacting the portion of the tube to the punch linear portion, said being expanded tube to the outer die waving contacting a portion of the shape, the tube expansion by tube A method of expanding a pipe end of a steel pipe, characterized by restraining crack propagation from the pipe end to the pipe length direction by restraining with an outer mold.

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