JP5541684B2 - Press bending method of aluminum alloy hollow extruded shape - Google Patents

Description

The present invention relates to a press bending method for a hollow extruded shape made of an aluminum alloy , and more particularly to a press bending method capable of reducing a residual stress generated in a hollow extruded shape after bending.

  Aluminum alloy hollow shapes (extruded shapes) are increasingly applied to parts and frames that absorb load and absorb energy, such as automotive door reinforcement, bumper reinforcement, and roof reinforcement. Among them, JIS 6000 (Al—Mg—Si— (Cu)) and 7000 (Al—Zn—Mg— (Cu)) aluminum alloys have high material strength and are expected as high-strength energy absorbing parts.

Aluminum alloys often suffer from stress corrosion cracking depending on conditions. In particular, the 6000 series or 7000 series aluminum alloy has a problem that this stress corrosion cracking is likely to occur.
Stress corrosion cracking depends on the residual stress generated when the material is processed, and is more likely to occur as the tensile residual stress is higher than the material strength. Aluminum alloy hollow shapes often require bending when applied to body frames, reinforcements, etc., and stress corrosion cracking occurs due to stress remaining after the bending There is.
There are similar problems with other metal materials such as steel and copper alloys.

In the 7000 series or 6000 series aluminum alloy, development of a material composition or manufacturing method for the purpose of improving the stress corrosion cracking property has been performed (see Patent Documents 1 to 3).
However, even if these materials are used, depending on the processing conditions, tensile stress may partially remain and stress corrosion cracking may occur. On the other hand, there is a measure to reduce the residual stress by performing shot peening on the surface (see Patent Document 4), but there is a problem of cost increase due to post-processing addition.

In general, countermeasures against stress corrosion cracking by heat treatment after processing are also performed. For example, if the material strength is increased by performing T5 or T6 treatment (aging treatment) after processing in a T1 tempered state with low yield strength, the ratio of the tensile residual stress to the material strength can be reduced. .
However, since the T1 tempered material is naturally aged even at room temperature, the material characteristics are likely to change, the amount of springback changes depending on the processing timing, and the product shape varies. In particular, a product with a large bending radius has a problem that the amount of springback itself is large, and it is difficult to ensure product shape accuracy.

  On the other hand, when bending a T5 or T6 tempered material, whose material characteristics are easy to stabilize, it is easy to ensure product shape accuracy, but the problem of high residual stress tends to occur. In addition, in the case of aluminum alloy hollow shapes formed by hot working (extrusion), T5 and T6 tempered materials are likely to vary in material, and it is necessary to reduce variations in product shape by adjusting processing conditions Often becomes.

  There are various methods for bending extruded shapes such as press bending, pressing bending, tensile bending, and roll bending. Each of these bending methods has its characteristics, and there are some processing condition adjustment methods in the case where the above-described material characteristic variation occurs (Patent Documents 5 and 6). Various proposals (see Patent Documents 7 and 8) have also been made regarding the cross-sectional shape of an extruded profile used for bending.

  In the case of press bending or pressing bending in which a material is pressed against a bending mold, the tool itself is formed of a rigid body. For this reason, when material variation arises at the time of mass production, it can adjust with the pushing amount or bending angle of a punch tool. Although mold cost is high, there is an advantage that residual stress after bending is small.

  In tension bending, in which bending is performed while applying tension to a material, there is an advantage that the amount of spring back itself is small by applying tension and it is easy to ensure dimensional accuracy. Further, when the material characteristics vary, it is possible to obtain a predetermined product by adjusting the springback amount by changing the tension applied during processing. However, the end portion clamped to apply tension to the material needs to be cut and discarded after bending, which causes problems such as a decrease in the yield of the material and an increase in cost due to the addition of processing steps.

  In the case of roll bending, it is possible to produce different R products by changing the push amount of the roll tool. That is, even when the material characteristics and shapes vary, it is possible to obtain a product with a predetermined shape accuracy simply by changing the pushing amount of the roll tool. For this reason, it is particularly advantageous for application to products with a large springback condition such as a large-R bent product. However, the roll bending process has a problem that the stress remaining in the product after the bending process is higher than that of other bending processes such as a press bending process, particularly when a hollow shape is a target.

Japanese Patent Publication No. 61-28744 JP 2001-207233 A JP 2001-240930 A JP-A-5-320838 JP 2008-229643 A Japanese Patent Laid-Open No. 10-290962 Japanese Patent No. 3525979 Japanese Patent Laid-Open No. 2002-225651

In the case of aluminum alloy shaped members, especially 6000 series or 7000 series aluminum alloy members, stress corrosion cracking (SCC) is likely to occur when the residual stress is high, making it difficult to apply to the energy absorbing members and frames described above. is there. This problem of stress corrosion cracking also exists in the same way with steel, and the same with other metal materials such as copper alloys.
The present invention further reduces the residual stress after bending in the case of imparting a curvature in the longitudinal direction of a metal shaped member such as an aluminum alloy by press bending which is advantageous in terms of reducing residual stress. The purpose is to improve the SCC (stress corrosion cracking resistance) performance of the product.

According to the present invention (Claim 1), an aluminum alloy hollow extruded section is excessively bent in one direction by the first press bending, and then bent back in the opposite direction by the second press bending. the respect press bending method bent obtain a shape targeted for cylindrical workpiece, in accordance with the deviation amount from the reference value of the first press bending the bending shape of the hollow extruded shape member after processing by, the second press The pushing amount S of the bending die in the bending process is adjusted. More specifically, the height (bending height) of the central part in the length direction when both ends of the hollow extruded profile are placed horizontally is selected as an index to represent the bending shape, and the initial conditions before mass production begins. As described above, a correspondence relationship between the amount of deviation and the indentation amount of a bending die that can obtain a target bending shape by the second press bending process is obtained in advance, and after the start of mass production, individual hollow extruded profiles to be mass produced The deviation amount is measured after the first press bending process, and the bending process is performed with the pressing amount determined based on the correspondence in the second press bending process.

If the target bending shape is not obtained after the second press bending process, perform additional press bending process (bending back) one or more times to obtain the target bending shape. Also good. More specifically, the second press bending after processing, bending the shift amount from the reference value of the shape measured, determined based on the correspondence relationship in the same direction by the same bending tool and the second press-bending indentation An additional press bending process is performed in an amount ( claim 2 ). Alternatively, the additional press bending is further repeated ( claim 3 ).

INDUSTRIAL APPLICABILITY The present invention is suitable for bending of an aluminum alloy hollow extruded shape that is desired to be processed into a gentle curve (small curvature) . For example, it is hollow for both reducing the weight of the vehicle body and ensuring deformation strength. It is suitable for bending work of energy absorbing members such as automobile door reinforcing materials, bumper reinforcing materials, roof reinforcing materials, and cross members for which shape members are desired. These members are processed into relatively gentle curves according to the shape of the vehicle body.
The present invention is particularly suitable when a 6000-series or 7000-series aluminum alloy hollow extruded shape having a relatively high sensitivity to stress corrosion cracking properties is used as a raw material.

According to the method of the present invention, it is possible to produce a press-bending product having a low tensile residual stress after bending and an excellent SCC (stress corrosion cracking) performance using a hollow extruded shape of an aluminum alloy as a raw material. it can.
In addition, when the press-bending product manufactured by the method of the present invention is applied to an automobile energy absorbing member such as an automobile door reinforcement, a bumper reinforcement, or a roof reinforcement, stress corrosion cracking due to aging is prevented. By doing so, it is possible to obtain the effect of suppressing the deterioration of the collision performance accompanying the generation of cracks.

The present invention is most effective for application to a 6000 series (Al-Mg-Si- (Cu) series) or 7000 series (Al-Zn-Mg- (Cu) series) aluminum alloy having high sensitivity to stress corrosion cracking. Of course, when aging treatment (T5, T6) is performed after bending in T1 tempered condition, stress corrosion cracking resistance is improved even when aging treatment (T5, T6) material is bent. it can.

It is a schematic diagram explaining the press bending process which concerns on this invention in process order. It is sectional drawing of the hollow shape material used for the Example. It is a graph which shows the residual stress value of the press bending product shape | molded in the Example.

  The press bending method according to the present invention will be described below with reference to FIGS. In this press bending method, for example, an aluminum alloy hollow extruded member 1 having a cross section shown in FIG. 2 is given a large radius of curvature along the longitudinal direction to provide a door reinforcing material (door beam) for an automobile. To be done. The hollow extruded shape member 1 includes a flange 2 that is disposed substantially vertically on the collision surface side, a flange 3 that is disposed on the vehicle body side, and a web 4 that is substantially perpendicular to both flanges 2 and 3 by connecting both flanges 2 and 3. , 5 and bending is performed in a plane parallel to the webs 4, 5.

  Fig.1 (a) shows the straight hollow extrusion shape material 1 as a raw material. FIG. 1 (b) schematically shows the first step of press bending (first press bending), in which the two extruded rollers 6 and 6 support the vicinity of both ends of the hollow extruded profile 1. The bending die 7 located at the center is brought into contact with the flange 3 and pushed between the support rollers 6 and 6 (see the white arrow), and the hollow extruded profile 1 is bent with a curvature (long) of the molding surface of the bending die 7. It is not necessary to be constant over the entire length in the vertical direction) and is bent into a predetermined bending shape corresponding to the pushing amount of the bending die 7.

The pushing amount of the bending die 7 at this time is set to be larger than the appropriate pushing amount for obtaining the target bending shape. That is, in the first step, the pushing amount of the bending die 7 is increased from an appropriate value, and the hollow extruded shape member 1 is bent excessively (to a curvature radius smaller than the target).
FIG. 1C shows a hollow extruded shape member (hereinafter referred to as an intermediate member 1A) in which the bending die 7 is retracted to be in an unloaded state and a spring back is generated. The intermediate material 1A has a radius of curvature considerably larger than that of the state shown in FIG. In addition, 8 and 8 are support rollers in the press bending process in the second step described later.

Here, as an index characterizing the bending shape (arc shape) of the intermediate material 1A, the height d _{1 of the} central portion in the length direction when both ends are horizontally placed for ease of measurement (see FIG. 1C). ) Is selected. When the reference value of the bending height of the final bent product is d ₀ and the dimensional tolerance is α, the target bending height of the bent product is (d ₀ −α) to (d ₀ + α). The bending height d ₁ of the intermediate material 1A is intentionally set so as to be out of the above range (d ₁ > d ₀ + α).
The height _{d 1} bent intermediate members 1A, the difference between the reference value _{d 0} of the bending height of the bent product, a deviation amount _{Δd (= d 1 -d 0)} . The magnitude of the amount of deviation Δd may be set as appropriate in the initial determination of conditions, but in the case of an aluminum alloy profile, it should be set in a range of about 0.1 ≦ (Δd / d ₀ ) ≦ 0.25. Thus, good results can be obtained in terms of residual stress reduction and productivity. That is, if Δd / d ₀ is too small, the residual stress reduction effect is small, and if it is too large, the stroke of the bending die 7 (and the stroke of the second bending die 9, 9 described later) becomes large, and the productivity is increased. Decreases (more time for press bending).

FIG. 1 (d) schematically shows a second step of press bending (second press bending), in which the vicinity of both ends of the intermediate material 1A is supported by two support rollers 8 and 8, and the center A pair of semi-cylindrical bending dies 9 and 9 that are symmetrically positioned at two nearby locations are brought into contact with the flange 2 and pushed between the supporting rollers 8 and 8 (pushing amount S), and the intermediate material 1A. Is bent (returned) in the opposite direction.
FIG. 1 (e) shows a hollow extruded shape member (hereinafter referred to as a bent product 1 </ b> B) in which the bending dies 9, 9 are retracted to be in an unloaded state and a spring back is generated. The bent product 1B has a radius of curvature considerably smaller than that of FIG.

Bending height _{d 2} bending processed products. 1B, of course smaller than the bending height _{d 1} of the intermediate material 1A _(d 2 _<d 1). In the second press bending process, the bending height d ₂ of the bent product 1B is within the target bending height (d ₀ −α ≦ d ₂ ≦ d ₀ + α) of the bent product. The pushing amount S of the bending dies 9, 9 is adjusted.
In the present invention, by performing two-stage press bending (press bending and unbending) in this way, a bent product is obtained as compared with the conventional method in which a predetermined bending shape (bending radius) is obtained by one press bending. The residual tensile stress of 1B can be greatly reduced.

On the other hand, with extruded profiles, even if the same material is used, there is a large change in the material cross-sectional shape due to wear of the extrusion die and the variation in mechanical properties of the material. Even if the amount of pressing of the mold 7 is constant, the bending height deviation amount Δd (= d ₁ −d ₀ ) varies for each extruded shape (particularly for each production lot). This is particularly noticeable in the case of large R bending (bending to a large radius).
A second press bending after working bent product height d ₂ bending 1B, the obtained stabilized within the target bending height _{(d 0 -α ≦ d 2 ≦} d 0 + α) , the first In accordance with the amount of deviation Δd (= d ₁ −d ₀ ) of the bending height of the intermediate material 1A after the press bending, the pressing amount S of the bending dies 9 and 9 in the second press bending is set. It is desirable to adjust.

When the magnitude of the shift amount Δd (= d ₁ −d ₀ ) changes, the push amount S that provides the target bending height (d ₀ −α ≦ d ₂ ≦ d ₀ + α) also changes. Accordingly, for example, before the start of mass production, the amount of deviation Δd of the bending height of the intermediate material 1A after the first press bending process and the pressing amount S of the bending dies 9, 9 for the second press bending process are preliminarily determined. (The indentation amount S that provides the target bending height (d ₀ −α ≦ d ₂ ≦ d ₀ + α)) is obtained, and after mass production starts, the actual bending height is obtained after the press bending process in the first step. The amount of deviation Δd is measured, and the indentation amount S corresponding to the measured amount of deviation Δd in the bending height is obtained based on the correspondence, and the second press bending process is performed with this indentation amount S. A bent product 1B having a target bending height (d ₀ −α ≦ d ₂ ≦ d ₀ + α) is obtained.

The correspondence relationship can be basically obtained by using an aluminum alloy hollow extruded material for mass production and experimenting with an actual machine for mass production, but it can also be obtained by partially using FEM analysis as necessary. it can.
In addition, as the pushing amount S, for example, the entire stroke of the bending dies 9 and 9 in the second press bending process (the moving distance from the standby position (fixed position) at the upper end until the machining is stopped), or the bending mold It is possible to select a stroke from when 9, 9 comes into contact with the hollow extruded shape member 1 until the pushing is stopped.

For example, the correspondence relationship is expressed by the table shown in Table 1 with the numerical value of the bending height deviation amount Δd and the numerical value of the pressing amount S, or the pressing amount S as a function of Δd (S = f (Δd ))be able to. It is desirable to store this correspondence in the memory of the control device so that the push amount S can be calculated immediately from the numerical value of the measured bending height deviation Δd. In the table of Table 1, when the measured deviation amount Δd is a value between, for example, Δd ₃ and Δd ₄ in the table, the value between S ₃ and S ₄ is handled by a known interpolation method. What is necessary is just to calculate as pushing amount S to perform. The control device controls a drive source of the bending dies 9, 9, for example, a servo motor, according to the calculated push amount S.

In the above example, as an index characterizing the bending shape (arc shape) of the intermediate material 1A and the bent product 1B, the height of the central portion in the length direction when both ends are placed horizontally is easy to measure. (Bending height) was selected .
In the above example, the press bending process in two steps was performed to obtain a bent shape within a predetermined dimensional tolerance range (bending height d ₀ ± α) from the target value. After the second press bending process, bending when measuring processed products 1B bending height d ₂ of the unlikely event the height d ₂ bending is not within the range of the target bending height _{(d 2> d 0 + α} ), again, bending molds The press bending process (the third press bending process) by 9, 9 can be performed. The pushing amount S of the bending dies 9, 9 at this time may be calculated based on the correspondence relationship. The same applies to the case where the fourth and subsequent press bending processes are required.

  A 7000 series aluminum alloy extruded material having a cross-sectional shape (unit: mm) shown in FIG. 2 is cut to a length of 1020 mm (the end is obliquely cut), and the radius of curvature is set to 10000 mm by a press bending apparatus. The bending process was performed. In addition, No. 1-3 are the same extrusion lot. Nos. 4 to 6 were cut from the same extrusion lot. 1 to 3 and no. 4 to 6 have different lots.

  No. 1 and 4 are examples of the present invention. As the first press bending process, both ends are supported by support rollers in the form shown in FIG. 1B, and a molding surface is formed with a predetermined curvature at the center. The bending mold was pushed in and bending was performed. Subsequently, as the second press bending process, in the embodiment shown in FIG. 1 (d), both ends are supported by support rollers, and a pair of bending dies are pushed in the vicinity of the center in the length direction to perform the bending process in the opposite direction. went. No. For both No. 1 and No. 4, the push amount of the first press bending process (forward bending) was 35 mm, and the push amount of the second press bending process (bending return) was 20 mm. The pushing amount here is a stroke after the bending mold hits the shape member.

No. Nos. 2 and 5 are comparative examples. 1 and 4 was used, and only the first press bending process was performed in the mode shown in FIG. No. In both 2 and 5, the amount of press bending (forward bending) was 20 mm.
No. 3 and 6 are comparative examples. Using the same press bending apparatus, the first press bending process is performed in the mode shown in FIG. 1B, and the second press bending process is also shown in FIG. 1B. Conducted in a manner. No. For both 3 and 6, the push amount of the first press bending process (forward bending) was 15 mm, and the push amount of the second press bending process (additional forward bending) (in this case, the stroke increment) was 10 mm.

  Select the bending height (height at the center in the length direction when both ends are placed horizontally) as an indicator of the bending shape, measure the bending height after press bending, and bend the bending product The amount of deviation Δd from the reference value was obtained. The results are shown in Table 2. The reference value for the bending height of the bent product is 7 mm. The dimensional tolerance was set to ± 0.3 mm. No. In all of Nos. 1 to 6, a target bending shape (bending height) was obtained.

No. 1-6, the position in the vicinity of the web of the bent inner flange 3 at the center position in the longitudinal direction of the profile and at a position of 200 mm to the left and right (locations marked with x in FIG. The residual stress value of was measured. The result is shown in FIG. In FIG. 3, the measurement position 2 means the center position in the length direction of the profile, and the measurement positions 1 and 3 mean positions 200 mm from side to side. Table 2 shows the maximum residual stress.
As a measuring method, a cutting open method using a strain gauge was used. Affix the strain gauge to the measurement position 1, 2 and 3 surface of the bending inner flange with an instantaneous adhesive, connect the strain gauge lead wire to the strain gauge, cut the periphery of the strain gauge, release the stress, and cut The difference in strain before and after was measured with a strain gauge, and the residual stress value was calculated from the measured value and the Young's modulus of the profile.

  As shown in Table 2 and FIG. 3, after the first press bending process, the second press bending process was used to perform bending back to obtain a target bent shape. Nos. 1 and 4 were obtained from No. 1 obtained as a target bending shape in the first press bending process. No. 2, 5 and No. 1 after additional forward bending in the second press bending after the first press bending. Compared with 3 and 6, the residual stress was greatly reduced.

1 Aluminum alloy hollow extruded shape 2, 3 Flange 4, 5 Web 6, 8 Support roll 7, 9 Bending mold

Claims (5)

After the cylindrical workpiece of aluminum alloy excessively bent in one direction by the first press bending performs bent back in the opposite direction in the second press bending, the target about this by the cylindrical workpiece In the press bending method to obtain the bending shape to be pressed, the amount of indentation of the bending die in the second press bending process according to the amount of deviation from the reference value of the bending shape of the hollow extruded profile after the first press bending process The height of the central part in the length direction when both ends of the hollow extruded profile are horizontally placed is selected as an index representing the bending shape, and the amount of deviation is used as an initial condition before the start of mass production. And a corresponding relationship between the indentation amounts of the bending dies that can obtain the target bending shape in the second press bending process, and after the start of mass production, for each hollow extruded profile to be mass produced, Press bending method bending the displacement amount measured after the processing, and performs the bending in pushing amount determined based on the correspondence relationship in the second press bending. A second press bending after processing, bending the shift amount from the reference value of the shape was measured and an additional press with pressing amount determined based on the correspondence relationship in the same direction by the same bending tool and the second press bending 2. The press bending method according to claim 1 , wherein bending is performed, thereby obtaining a target bending shape for the hollow extruded profile. After the additional press bending process, the measurement of the deviation from the reference value of the bending shape and the additional press bending process in the same direction by the same bending die as the second press bending process are performed based on the correspondence. 3. The press bending method according to claim 2 , wherein a target bending shape is obtained with respect to the hollow extruded profile by repeatedly performing the pressing amount determined one or more times. The press-bending method according to any one of claims 1 to 3, wherein the hollow extruded shape member is a JIS 6000 series or 7000 series aluminum alloy T5 or T6 tempered material. The reference value is d ₀ When the amount of deviation is Δd, 0.1 ≦ Δd / d ₀ 5. The press bending method according to claim 1, wherein ≦ 0.25.

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