JP2007061894A - Method for ironing metal tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for ironing a metal tube where, even in the case a metal tube in which thickness deviation in the circumferential direction of the tube is relatively large is used as a tube stock, the roundness of the metal tube after one process ironing with one die is not reduced. <P>SOLUTION: In the method for ironing a metal tube where a metal tube 3 is pushed through a die 1 by a punch 2 with a columnar shape inserted into the inner face side of the tube, so as to be subjected to ironing, using a die provided with two step ironing faces, the second step ironing ratio (=(gap A-gap B)/gap A×100(%)) is controlled to ≥0.5%; wherein, the gap A and the gap B are spacing distances between the first and second step ironing faces respectively from the inlet side of the die and the outer circumferential face of the punch coaxially arranged with the die. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for ironing a metal pipe.

  For example, mechanical structural parts such as a power steering motor cover that require high-precision roundness are manufactured by ironing a metal pipe (for example, a steel pipe). For ironing a metal tube, a punch is inserted from the rear end of the tube into a metal tube with a punch locking part at the tip, the punch locking part is pushed by the punch tip, the metal tube is passed through a die, and the inner surface of the tube is contacted. The tube is squeezed between the punch and the inner surface of the die hole contacting the outer surface of the tube. Normally, the punch has a cylindrical shape, and the die hole has a tapered hole portion with a wide entrance opening and a narrow back portion, and a cylindrical hole portion with a constant inner diameter connected to this, and the inner surface of this cylindrical hole portion is the outer periphery of the punch. In cooperation with the surface, the tube becomes a squeezed surface, ie a squeezed surface. In a normal die, the ironing surface of one die is only one step in the die axis direction.

In addition, in order to form a thick short tube into a thin long tube, a punch and die sleeve replacement work is performed in a pipe ironing device that is configured so that a plurality of dies are arranged concentrically in series and can be sequentially ironed. Patent Document 1 discloses an apparatus in which a punch is fixed to a support frame or a die sleeve is fixed in a taper fitting form so that centering accuracy can be easily performed. In Patent Document 1, there is no particular description about the hole shape of each die, and also from the die cross-sectional shape illustrated in the document, the ironing surface of one die is in the direction of the die axis as usual. It is estimated that there is only one stage.
JP-A-9-174168

  In the conventional ironing process using one die with only one ironing surface and a punch, when using a metal pipe with a relatively large thickness deviation in the pipe circumferential direction, such as a seamless steel pipe, There is a problem that the roundness of the metal tube after processing may decrease, and the yield of processed products is poor. Although it is possible to improve the roundness of the metal tube by preparing a plurality of dies having different hole types and performing ironing in a plurality of processes, the equipment becomes large and the processing cycle time becomes long. An object of the present invention is to solve the above problems, even when a metal pipe having a relatively large thickness deviation in the circumferential direction of the pipe is used as a base pipe, the trueness of the metal pipe after the ironing process is performed in one step with one die. An object of the present invention is to provide a method for ironing a metal pipe in which the circularity does not decrease.

The present invention is a method of ironing a metal tube in which a metal tube is pushed through a die with a cylindrical punch inserted on the inner surface side of the tube, and is defined by the following formula using a die having two stages of ironing surfaces. This problem is solved by setting the second stage ironing rate to 0.5% or more.
2nd stage ironing rate = (Gap A−Gap B) / Gap A × 100 (%)
However, the gap A and the gap B are distances between the first and second ironing surfaces from the die entry side and the outer peripheral surface of the punch arranged coaxially with the die.

  According to the present invention, even if the uneven thickness of the pipe in the pipe circumferential direction is relatively large, the roundness after ironing by the cooperation of one die and the punch is stabilized at a high level, and the processed product yield is improved. improves.

First, the background to the present invention will be described. The inventors of the present invention have found out the cause of the processing shape defect that occurred in the steel pipe that was ironed by the ironing method (conventional method: see FIG. 6) by the cooperation of one die having a one-step ironing surface and a punch. I studied.
FIG. 3 is a distribution diagram showing an example of the result of examining the pipe wall thickness distribution in the pipe circumferential direction, the inner diameter distribution after ironing, and the residual stress after ironing for a steel pipe ironed by the conventional method. Note that the raw pipe wall thickness distribution and the inner diameter distribution after ironing indicate the deviations from the target values. The residual stress after ironing shows a distribution of σo−σi (σo: outer surface residual stress (tensile), σi: inner surface residual stress (compressed)). As shown in the figure, the pipe wall thickness, the inner diameter after ironing, and the residual stress after ironing are similar to each other in the distribution pattern. And the residual stress after ironing is large. This phenomenon is considered to occur by a mechanism as shown in FIG.

  FIG. 2 is a conceptual diagram showing a mechanism for generating a machining shape defect according to a conventional method. If the uneven thickness of the blank tube is large, the pipe 3a being ironed has a reduction in area on the equivalent side of the blank tube thicker than that on the equivalent side of the blank tube. The difference (σo−σi) between the outer surface residual stress σo (tensile) and the inner surface residual stress σi (compression) is larger than that on the side corresponding to the thin tube portion. Due to the difference in the inner and outer surface residual stress differences depending on the pipe circumferential direction part, in the pipe 3b after the ironing, a relatively large bending moment M is applied to the side corresponding to the high-thickness portion, which corresponds to the raw pipe thick portion. In response to this, it is displaced in the diameter expansion direction, and the side corresponding to the thin tube portion is displaced in the diameter reduction direction in balance with this, and as a result, the cross-sectional shape changes to a substantially elliptical shape.

In view of this, the present inventors have intensively studied the means for preventing the deformation as described above, and as a result, have come up with the idea of using a die having a two-step ironing surface instead of a die having a one-step ironing surface. It came to.
FIG. 1 is a schematic sectional view showing an embodiment of the present invention. The die 1 is fixed, and the punch 2 moves in the punch movement direction 2A, whereby the tube 3 is pushed into the die 1 and the punching 2 and the die 1 cooperate to perform ironing. The die 1 used in the present invention is provided with two stages of ironing surfaces 1A and 1B as cooperating surfaces with the punch 2. The two die axial portions forming the first and second squeezing surfaces 1A and 1B are separated by a portion having a larger die hole diameter (not in contact with the outer surface of the pipe). If the distance between the first and second squeezing surfaces 1A and 1B of the die 1 coaxially arranged with the punch 2 and the outer surface of the punch 2 are referred to as gap A and gap B, the squeezing process proceeds. Therefore, t0> Gap A> Gap B needs to be established between these and the tube thickness t0. Such ironing using a die having a two-step ironing surface is called two-step ironing. In addition, using a normal die having only one stage of the ironing surface, ironing performed only with the gap A is called one-stage ironing.

  By using a die with a two-stage ironing surface, the thickness distribution in the pipe circumferential direction is made uniform by the first stage ironing process, and the residual stress distribution in the pipe circumferential direction is made uniform by the second stage ironing process. Thus, the roundness can be improved. In the second stage ironing process, it is only necessary to add a strain that is small enough to yield the pipe material. As an example, Fig. 4 shows a two-stage ironing process (first and second stage target dimensions) for a pipe manufactured with the same specifications as in Fig. 3 and having a similar pipe wall thickness distribution. Shows the results of a similar investigation on a steel pipe finished to the same final target dimensions as in FIG. 3, compared with the one-stage ironing process in FIG. It is clear that the inner diameter distribution after ironing in the pipe circumferential direction and the pattern of residual stress distribution after ironing are very close to the perfect circular pattern.

  Furthermore, for a pipe that is manufactured with the same specifications as in FIG. 3 and has a thickness deviation of 0.15 to 0.24 mm as defined by the following formula (1), it is defined by the following formula (2). The second-stage ironing ratio was varied, and the second-stage ironing was performed. The inner diameter error defined by the following equation (3) was examined for the steel pipe after ironing. The results are organized and shown in FIG. In addition, the result by the conventional method (one-step ironing process) of FIG. 3 was arranged similarly, and was shown together in FIG.

Uneven tube thickness = Maximum pipe circumferential thickness-Minimum pipe circumferential thickness (mm) (1)
Second stage ironing rate = (Gap A-Gap B) / Gap A x 100 (%) (2)
Inner diameter error = Maximum inner diameter in the pipe circumferential direction-Minimum inner diameter in the pipe circumferential direction (mm) (3)
FIG. 5 is a graph showing the relationship between the inner diameter error after ironing and the second stage ironing rate. From FIG. 5, it is possible to significantly reduce the inner diameter error of the steel pipe after the second stage ironing by setting the second stage ironing ratio to 0.5% or more. Therefore, in the present invention, the second stage ironing process is performed with the second stage ironing ratio set to 0.5% or more. From FIG. 5, in order to further reduce the inner diameter error, the second stage ironing rate is preferably 1.0% or more, more preferably 6% or more. The upper limit of the second stage ironing rate is not particularly limited, but 20% or less is considered sufficient.

  Table 1 shows the results of ironing the steel pipe shown in Table 1 under the ironing conditions shown in Table 1 and investigating the inner diameter error of the steel pipe after ironing. As can be seen from Table 1, in the conventional method, when the blank thickness is less than 0.1 mm, the inner diameter error after ironing is suppressed to less than 0.1 mm, but when the blank thickness is large, Whereas the inner diameter error after ironing is 0.1 mm or more, in the example of the present invention, the inner diameter error after ironing is suppressed to less than 0.1 mm regardless of the thickness of the unbalanced tube.

It is a schematic sectional drawing which shows embodiment of this invention. It is a conceptual diagram which shows the generation mechanism of the process shape defect by a conventional method. It is a distribution map which shows an example of the result of having investigated the pipe wall thickness distribution of the pipe circumference direction, the inner diameter distribution after ironing, and the residual stress after ironing about the steel pipe ironed by the conventional method. It is a distribution map which shows an example of the result of having investigated the pipe wall thickness distribution of the pipe circumference direction, the inner diameter distribution after ironing, and the residual stress after ironing about the steel pipe ironed by the method of this invention. It is a graph which shows the relationship between the internal diameter error of the steel pipe after ironing, and the second stage ironing rate. It is a schematic sectional drawing which shows embodiment of the conventional method.

Explanation of symbols

1 Dice (two steps on the ironing surface)
1A, 1B Ironing surface (first step, second step)
2 punches
2A Punch moving direction 3, 3a, 3b pipe (metal pipe, eg steel pipe)
M bending moment

Claims (1)

In the ironing method of a metal tube, which is pushed through a die with a cylindrical punch inserted on the inner surface of the metal tube, the second step defined by the following formula using a die with two stages of ironing A method of ironing a metal tube, characterized by setting the ironing rate to 0.5% or more.
2nd stage ironing rate = (Gap A−Gap B) / Gap A × 100 (%)
However, the gap A and the gap B are distances between the first and second ironing surfaces from the die entry side and the outer peripheral surface of the punch arranged coaxially with the die.

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