JP2016078534A - Manufacturing method of torsion beam and torsion beam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a torsion beam using an electroseamed steel pipe without seam buckling and deterioration of appearance by the same, and deterioration of fatigue characteristic.SOLUTION: In a manufacturing method of a torsion beam where an electroseamed steel pipe is pressed so that a cross-sectional shape becomes V-shaped, press working is performed while a seam position of the electroseamed steel pipe is a range: 15-25° relative to a V-shape apex of 0°. Therefore, the torsion beam is provided in which seam buckling can be suppressed and fatigue characteristic can be improved compared with a conventional torsion beam where the seam position is 45°.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a torsion beam for an automobile using an electric resistance welded steel pipe, and a torsion beam manufactured by the method.

  As a torsion beam that constitutes a suspension of an automobile, as shown in Patent Document 1, an ERW steel pipe that has been pressed into a V-shaped cross section is used. As a material for the electric resistance welded steel pipe, a steel sheet having a tensile strength of 590 MPa or more is widely used.

  The ERW steel pipe is manufactured by gradually bending a steel plate into a circular shape by a group of rollers and continuously welding the end surfaces thereof. Therefore, a welded seam is formed on the electric resistance steel pipe in the axial direction of the pipe. Patent Document 1 describes a method of manufacturing a torsion beam in which a seam position of an electric resistance welded steel pipe is set to a V-shaped apex, and a welding burr formed at the seam position is engaged with an opposing inner wall surface and fixed. In addition, it is also customary to press the seam position of the ERW steel pipe at a 45 ° position when the V-shaped apex is 0 °.

  According to the inventor's investigation, there has been no example in which the relationship between the position of the seam portion and the internal buckling has been studied in detail. For example, the 45 ° seam position that has been conventionally adopted is a position where the distortion during press molding is small and the stress is low when an external force is applied to the center position of the V-shaped flat part after molding. It has been thought and adopted. However, when the present inventor examined, the seam portion of the ERW steel pipe was often softened inevitably compared with other parts due to the influence of welding heat, and the seam position of the ERW steel pipe was set to 45 °. It has been found that when pressed, the seam softened portion deforms and buckles out of the tube to the inner surface side, resulting in unevenness after pressing, deteriorating the appearance, and reducing the performance of components such as fatigue characteristics.

JP 2009-132249 A

  Accordingly, an object of the present invention is to solve the above-mentioned conventional problems, and torsion beam manufacturing method and method for manufacturing a torsion beam without buckling or deterioration of fatigue characteristics using seam-softened ERW steel pipe It is to provide a manufactured torsion beam.

  The torsion beam manufacturing method of the present invention, which has been made to solve the above problems, is a torsion beam manufacturing method in which an ERW steel pipe is pressed so that its cross-sectional shape is V-shaped. , When the vertex of the V-shape is 0 °, the press working is performed in a range of 15 to 25 °.

  The torsion beam of the present invention made to solve the above problems is a torsion beam obtained by pressing an electric resistance steel pipe so that its cross-sectional shape is V-shaped, and the seam position of the electric resistance steel pipe is V-shaped. It is characterized in that it is in the range of 15 to 25 ° when the vertex of is 0 °.

  As in claim 3, the electric resistance welded steel pipe can have a tensile strength of 590 MPa or more. Further, it is preferable that the residual strain at the seam position is 2% or less.

  As will be described in detail below, according to the present invention, it is possible to manufacture a torsion beam without buckling or deterioration of fatigue characteristics using an electric resistance steel pipe having an inevitable seam softened portion as a base pipe. Moreover, since only the seam position is changed, there is no need to change the manufacturing equipment.

It is drawing which shows the positional relationship before shaping | molding and after shaping | molding. It is a graph which shows the result of the numerical analysis of distortion. It is a distribution map which shows the generated stress at the time of receiving the residual stress after shaping | molding of a torsion beam, and a load. It is a graph which shows hardness distribution near the seam position of an electric resistance steel pipe. It is a graph which shows the relationship between a seam position and seam buckling depth.

Embodiments of the present invention will be described below with reference to the drawings.
First, the present inventor numerically analyzed the presence / absence of out-of-plane deformation in each section of the torsion beam in order to search the position in the torsion beam section where the seam position of the ERW steel pipe should be set. The positional relationship before and after molding is shown in FIG. The angles are values when the V-shaped apex is 0 °. In this numerical analysis, a steel pipe having a tensile strength of 780 MPa, an outer diameter of 101.6 mm, and a thickness of 3.4 mm was used as a raw pipe. Unlike the ERW steel pipe, the strength distribution of the raw pipe was uniform in the circumferential direction. The results are shown in the graph of FIG. The vertical axis represents the surface strain, the horizontal axis represents the machining stroke, and a number of lines represent the data at each angular position from 15 ° to 75 °.

  As shown in FIG. 2, the 35 °, 45 °, and 65 ° positions of the raw tube are deformed out of plane toward the inner surface of the tube during press molding. Therefore, seam buckling may occur when a softened seam is set at these positions. In particular, at the position of 65 °, it is considered that remarkable seam buckling occurs due to bending back after being deformed out of plane toward the tube inner surface side.

  On the other hand, the positions of 15 °, 25 °, 55 °, and 75 ° are not deformed out of the plane toward the inner surface of the tube during press molding. That is, it is considered that seam buckling does not occur even when softened seams are set at these positions. However, the 25 °, 55 °, and 75 ° positions are deformed out of plane at their neighboring 35 °, 45 °, and 65 °, so avoiding them when considering the angle error when setting the ERW steel pipe Is safe.

  As described above, from the viewpoint of suppressing seam buckling, the seam position is preferably set to 15 ° to 25 ° at which out-of-plane deformation does not occur. As shown in FIG. 1, this position is a plane portion in the vicinity of the V-shaped apex. As shown in FIG. 2, when the seam position is 15 ° to 25 °, the residual strain on the pipe inner surface at the seam position is 2% or less.

  Next, the fatigue durability of the torsion beam was examined. The fatigue durability of a torsion beam has a correlation between the residual stress after molding and the generated stress when subjected to a load. Accordingly, the residual stress after molding and the stress generated during loading when the seam position is 15 ° to 25 ° were determined by numerical analysis. The generated stress is a generated stress when one end of a single torsion beam is fixed and the other end is forcibly rotated around the tube axis by 15 °, and this test condition is a general external force condition of the torsion beam. The results are shown in FIG. 3 separately for the inner surface and the outer surface of the tube.

  As shown in FIG. 3, the residual stress is high and the generated stress is high at a position of 65 ° to 75 ° on the tube inner surface side. On the other hand, the residual stress and the generated stress are not significantly different at the position of 15 ° to 25 ° compared to the conventional 45 °, and the influence on the fatigue characteristics due to the seam position of 15 ° to 25 ° is small.

  On the tube outer surface side, the residual stress is high at a position of 25 ° to 55 °, and the generated stress is high at a position of 65 ° to 75 °. On the other hand, in the position of 15 ° to 25 °, the residual stress is greatly reduced and the generated stress is reduced as compared with the conventional 45 °. Therefore, with respect to the tube outer surface side, fatigue characteristics are improved by setting the seam position to 15 ° to 25 °. Therefore, when the inner and outer surfaces of the pipe are combined, it is considered that the torsion beam of the present invention can obtain fatigue characteristics equivalent to or better than those of conventional products with a seam position of 45 °.

  In order to demonstrate the effect of the present invention based on the above numerical analysis, an electric resistance welded steel pipe having an outer diameter of 90 mm, a plate thickness of 2.8 mm, a length of 45 mm, and a strength of 780 MPa is pressed so that the cross-sectional shape is V-shaped. The relationship between seam position and seam buckling was investigated with seam positions of 25 °, 45 °, and 65 °. The results are shown in FIG. The hardness distribution in the vicinity of the seam position of the used electric resistance welded steel pipe is as shown in FIG. 4. The raw pipe averaged 290 Hv, the seam softened portion was 250 Hv, and was softened by 40 Hv.

  FIG. 5 is a graph showing the seam buckling depth when the seam position is 25 °, 45 °, and 65 °. Here, the seam buckling depth is the depth of the buckled portion in the range of 10 mm in width including the seam. As shown in FIG. 5, in the case of the present invention in which the seam position was 25 °, almost no buckling occurred. On the other hand, buckling occurred at 45 ° and 65 °, and the buckling depth was greater at 65 °. All the measurement results are in good agreement with the numerical analysis results shown in FIG. As described above, it was confirmed that the torsion beam of the present invention in which the seam position is in the range of 15 to 25 ° does not cause seam buckling even when using the electric resistance welded steel pipe softened by 40 Hv at the seam position.

  As described above, according to the present invention, it is possible to produce a torsion beam that does not buckle, deteriorate the appearance due to the seam-softened electric resistance welded steel pipe, or deteriorate fatigue characteristics.

Claims (4)

  In the method of manufacturing a torsion beam in which an ERW steel pipe is pressed so that its cross-sectional shape is V-shaped, the seam position of the ERW steel pipe is set to a range of 15 to 25 ° when the vertex of the V-shape is 0 °. A method for producing a torsion beam, comprising pressing.   A torsion beam obtained by pressing an ERW steel pipe so that its cross-sectional shape is V-shaped, and the seam position of the ERW steel pipe is in a range of 15 to 25 ° when the vertex of the V-shape is 0 °. This is a torsion beam.   The torsion beam according to claim 2, wherein the ERW steel pipe has a tensile strength of 590 MPa or more.   The torsion beam according to claim 2, wherein the strain history of the inner surface of the pipe at the seam position is 2% or less at maximum.