JP2002022631A - Method for evaluating hemming properties of aluminum alloy panel material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for evaluating hemming properties of an Al alloy panel material compatible with hemming of the panel material of an automobile and providing a highly reliable test results with high reproducibility. SOLUTION: A stripe test piece 6 of an objective panel material is fixed to a press and the side edge parts of the test piece are bent sequentially. At first, the side edge parts are bent into flanges of 90 deg. along the corner part of a die 8, the 90 deg. bent flange parts 6a, 6b are further bent into flanges of 45 deg., edge part of an inner material 10 is inserted into the inside of the 45 deg. bent flange parts 6a, 6b, and the 45 deg. bent flange parts 6a, 6b are further bent into 180 deg. bent flange parts while clamping the edge part of the inner material 10. When the hemming properties of the test piece is evaluated from the situation of crack in the surface of the 180 deg. bent flange parts 6a, 6b, each bending operation is performed by means of a punch 9 while pressing the test piece 6 against the surface of the die 8 and the opposite flange parts 6a, 6b of the test piece 6 are bent simultaneously in each bending operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the hem workability of a high strength aluminum alloy panel material (hereinafter, aluminum is simply referred to as Al).

[0002]

2. Description of the Related Art In recent years, with respect to global environmental problems due to exhaust gas and the like, improvement in fuel efficiency by reducing the weight of vehicles such as automobiles has been pursued. For this reason, instead of steel materials that have been used in the past, various types of aluminum alloy wrought materials (hereinafter simply referred to as “plate materials”, “forged materials”, etc.)
Al alloy material) is increasing.

The specific gravity of an Al alloy is one third that of steel. For this reason, it is possible to comply with safety standards and improve vehicle performance without increasing the vehicle weight. Among them, AA to JIS 5000 series with high strength and excellent moldability, and AA to JIS 6000 series with excellent moldability and bake hardenability (hereinafter simply referred to as
Rolled aluminum alloy sheets such as 5000 series and 6000 series) have been used for panel materials such as outer plates and inner plates of automobiles such as hoods, doors, hoods, and trunk lids.

[0004] In the case of these panel materials, the outer plate (outer panel) is formed by bending the edge of the outer plate (returned by 180 degrees) after a forming process such as a drawing process or a trimming process, so that the inner plate (the inner panel) is formed. Hemming (bend folding, hereinafter referred to as hemming) is performed to join with the edge of the panel. The outline of the hemming process is shown in FIGS. 3 (a) to 3 (d). As can be seen from the figure, the hemming process is basically performed through the down-flange process shown in FIG. 3A and the pre-hem process shown in FIG. Or Figure 3 (d)
This is done by selecting the rope hem process.

[0005] First, the down-flanging step of FIG. 3 (a) is performed by forming the outer plate fixed by the die 3a and the plate holder 5a.
The first edge 1a is bent by the punch 4a to an angle close to a right angle (90 °).

Next, in the prehem process of FIG. 3 (b), the outer plate 1 after the down flange process is
5b, and the edge 1b of the outer plate 1 is further bent inward to about 45 ° by the punch 4b.

Further, the flat hemming process shown in FIG.
In the rope hem process, the edge of the inner plate 2 after the forming process such as the drawing process or the trim process is accommodated (inserted) in the bent portion of the outer plate 1 after the prehem process. Then, the outer plate 1 and the inner plate 2 are fixed with a plate holder (not shown) and dies 3c, 3d, and the edges 1c, 1d of the outer plate 1 are further rotated by 180 ° by punches 4c, 4d. Fold inward to form a flat hem. In this way, the edge of the inner plate 2 comes into contact with the flat hem portion (180-degree bent portion) of the outer plate 1, and the two are joined together at their ends and adhere to each other.

[0008] Of these, the rope hemming step of FIG.
Compared with the flat hem process of (c), the shape of the hem edge portion (bent portion) has a rope-like shape swelling in an arc shape, and is not a sharp or flat hem shape, but has an external appearance. Not good. In addition, there is a problem that the contact area between the outer plate and the inner plate is small, and the bonding property and the adhesion are lacking. For this reason, especially in the case of automobile parts, the final step of hemming is usually performed by the flat hemming step in FIG. 3 (c).

On the other hand, the Al alloy plate material used for the panel material such as the outer panel of the automobile has a proof strength such as a T4 treated material of 6000 series Al alloy by thinning the panel material for weight reduction.
Higher strength Al alloy plates of 130 MPa or more have been used.

However, in these high-strength Al alloy sheets, the bending workability is inevitably reduced, and the hem workability is also reduced. For this reason, in particular, in the flat hemming step, which is a particularly severe bending process of the hemming process, the bent portion A of the flat hem (bent portion) formed in FIG.
As shown in FIG. 5, in many cases, defects such as rough skin X, minute cracks Y, and relatively large cracks Z occur, which makes it impossible to apply to parts.

For this reason, various techniques for preventing the occurrence of defects in the hem portion (edge bent portion, bent portion) on the flat hem process side or on the material side of the Al alloy plate have been conventionally proposed.

Regarding the improvement on the material side of the Al alloy plate, if the flat hemming of the Al alloy plate can be easily evaluated without performing the actual flat hemming such as the panel material of the automobile, The improvement of the material side of the Al alloy sheet and the speed of development can be accelerated, and the flat hem workability of the Al alloy sheet can be guaranteed.

For this reason, conventionally, as a method for evaluating flat hem workability of an Al alloy plate, a strip-shaped test piece was basically simulated by simulating the actual flat hem work process.
Test methods such as the V-block method and the one-sided flange bending method, which bend in the order of 45 °, 45 °, and 180 °, are adopted. The strip-shaped test piece simulates the press forming (drawing process) performed before flat hemming of automobile panel material (corresponding to press forming),
Stretch distortions such as 10% are given.

In the V-block method, as shown in FIG. 5 (a), the strip-shaped test piece 11 which has been stretched by 10% is mounted on a simple hydraulic press (not shown), and is pressed by a punch 12a. The test piece 11 is pressed against the surface of the V-shaped die 13 and the test piece is
Bend to a 90 ° V-shape. Then, as shown in FIG. 5 (b), one side 11a of the 90 ° bending flange portion is bent to a 45 ° flange on the table 14 by a human hand. afterwards,
Insert the edge of the inner member 15 inside the 45 ° bending flange 11a, and as shown in FIG.
11a is further bent to 180 ° by a punch 12b to sandwich the edge of the inner material, and the flat hemming workability of the test piece is evaluated based on the state of surface cracking of the 180 ° bending flange.

On the other hand, the one-side flange bending method is shown in FIG.
As shown in FIG. 6 (a), the strip-shaped test piece 16 that has been stretched by 10% is mounted on a simple hydraulic press (not shown), and the pad 17 One side edge 16a of the test piece is first bent into a 90 ° flange along the corner of the die 18 by a cooperating punch 19a. And after this, like the V-block method,
As shown in FIG. 6 (b), the 90 ° bending flange portion 16a is further bent to a 45 ° flange on the platform 20 by a human hand.
Thereafter, the edge of the inner member 15 is inserted into the inside of the 45 ° bending flange portion 16a, and as shown in FIG. 6C, the 45 ° bending flange portion 16a is further bent to 180 ° by the punch 19b to form the inner material. The flat hem workability of the test piece is evaluated based on the state of the surface crack of the 180 ° bending flange portion with 15 edges sandwiched.

[0016]

However, the results of the conventional flat hemming workability evaluation methods such as the V-block method and the one-sided flange bending method are not always satisfactory with the flat hemming workability of the actual automobile panel material. There is a problem of not responding.

In addition, there are large variations in test results such as the V-block method and the one-sided flange bending method, and the reliability (accuracy) of a plurality of the same test pieces and the reproducibility of the same test a plurality of times are also problems. Becomes

For example, in the V-block method, the 90 ° bending step of bending the center of a test piece into a V-shaped 90 ° first is performed by flat hemming of the actual automobile panel material, and only the side edge portion of the panel material is processed. It is very different from 90 ° bending. For this reason,
First, in this 90 ° bending process, deviation from actual flat hemming of an automobile panel material tends to occur. Also, in the subsequent 45 ° bending and manual bending processes, there is no holding down of the plate, and the test pieces and inner material to be bent are easily displaced. This point is also different from flat hemming of actual automobile panel materials. However, there is a problem that deviations and variations easily occur.

In the one-sided flange bending method, the 90 ° bending process, which is a drawback of the V-block method, is improved.
The bending process is a method of bending the side edge of the test piece, which is the same as the side edge of the flat hemmed panel material of the actual automobile panel material.

However, in this one-sided flange bending method, only one side edge of the test piece is bent. For this reason, 90 °
In the bending process, the clearance of the test piece tends to vary. Therefore, similar to the V-block method,
In this 90 ° bending process, deviation from actual flat hemming of an automobile panel material tends to occur.

In addition, hand bending in the subsequent 45 ° bending step and 180 ° bending
In the bending step, as in the case of the V-block method, there is no plate holder, and the test piece or inner material to be bent is easily shifted. Therefore, also in this respect, there is a problem that deviation from the flat hemming of the actual automobile panel material is likely to occur.

In view of the problems of the prior art described above, an object of the present invention is to provide an Al alloy panel which has high reliability and reproducibility of test results, and which can well cope with actual flat hem processing of automobile panel materials. It is an object of the present invention to provide a method for evaluating the hem workability of a material.

[0023]

Means for Solving the Problems In order to achieve this object, the gist of claim 1 of the method for evaluating the hem workability of an Al alloy panel material according to the present invention is to improve the hem workability of an aluminum alloy panel material after press forming. In the evaluation method, a strip-shaped test piece of the target panel material is given a strain corresponding to the press forming by stretching in advance, and is mounted on a press, and the test piece side edge corresponding to the hemmed portion of the target panel material. First, after bending the side edge into a 90 ° flange along the corner of the die, the 90 ° bent flange portion is further bent into a 45 ° flange, and the 45 ° flange is bent. °
After inserting the edge of the inner material inside the bending flange part, the 45 ° bending flange part is further bent to 180 ° while sandwiching the edge of the inner material, depending on the situation of surface cracking of this 180 ° bending flange part. When evaluating the hemmability of the test piece, while pressing the test piece against the die surface in each bending process,
In addition to punching, the opposite side edges of the test piece are simultaneously bent in each of the bending processes.

According to the present invention, in the present invention, the test piece is subjected to the die surface in all bending steps of 90 ° bending step, 45 ° bending step, and 180 ° bending step of the pre-strained test piece. Pressing (providing a plate retainer) and bending (by punch) with a press.

As a result, the sharp bending line position of the flange is determined in the 90 ° bending process, and the displacement of the test piece and the inner material in the subsequent 45 ° bending process and the 180 ° bending process during the bending process. Can be prevented, and variations in the bending line position of the flange can be suppressed. Therefore, the reproducibility of a plurality of test pieces or the reproducibility of a plurality of tests can be improved.

In the conventional test methods such as the V-block method and the one-sided flange bending method, only one side edge of one side of the test piece is bent. The bending deformation after the 45 ° bending process is slightly changed, and the final bending line position is different for each test piece.

On the other hand, in the present invention, both opposing side edges (both sides) of the test piece are simultaneously bent. For this reason, in the process of 90 ° bending, variation in the clearance of the test piece hardly occurs. Therefore, as above,
It is possible to improve the reproducibility of a plurality of test pieces or the reproducibility of a plurality of tests.

Therefore, the method of the present invention is suitable for application to the evaluation of flat hem workability, in which the forming conditions are strict, even in hem processing.

Further, the method of the present invention provides
Commonly used as Al alloy plate for the panel, 5000 series, 60
It is suitable to be applied to an Al alloy such as 00 series.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a preferred embodiment of the present invention will be described with reference to the evaluation of flat hem workability as an example.
This will be described with reference to FIGS.

In the present invention, first, a panel material test piece having the same strip shape as the conventional one is prepared, and a strain corresponding to the amount of strain given to the panel material by actual press forming is applied in advance by stretching. As before, the amount of distortion is assumed to be 5 to 10% according to the amount of distortion applied to the panel material by assuming press forming of the outer plate of automobile hood, door, hood, trunk lid, etc. Give a stretch amount in the range.

Further, the size of the strip-shaped test piece in the present invention depends on the shape of the panel material to be actually hemmed such as a flat hem, the size of the hydraulic press or the mechanical press used for the bending test, and the size of the hem. It is appropriately selected according to the required bending portion (side edge) of the test piece corresponding to the portion of the panel material to be processed. In the above-mentioned conventional test method, a strip-shaped test piece having a width of 30 mm and a length of 100 mm is usually used. On the other hand, in the test piece of the present invention, since the opposite side edges of the test piece are simultaneously bent, a conventional test piece slightly larger, for example, 30 mm wide × 180 to 200 mm long is preferably used. .

First, as shown in FIG. 1 (a), a 90 ° flange bending process corresponding to a down-flanging step in actual flat hemming is performed by using a strip-shaped test piece 6 provided with the pre-strain, for example, as shown in FIG. Attach to a mechanical press (not shown)
While pressing the test piece 6 against the surface of the die 8 with the pad 7, the opposing side edges 6 a and 6 b of the test piece are firstly moved to the die 8 by a punch 9 a cooperating with the pad 7 (by a mechanical press). Bend to 90 ° flange along the corner (shoulder radius).

Here, the opposing side edges 6a and 6b of the test piece to be bent are, as shown in FIG.
6 opposing one side edge portion a ₁ and a ₂ of is b ₁ and b ₂ which crab corresponding.

If the flat hemming of the target panel material is actually performed on all four sides of the panel material, the following series of bending processes of the present invention are performed first by using a test piece 6
Bending either of the opposing side edges a ₁ and a ₂ or b ₁ and b ₂ , and then performing the bending of the remaining opposing side edges to obtain a test piece 6 4 Evaluate hemming on the surrounding area.

If the flat hemming of the target panel material is actually performed on one side (one side edge) of the panel material, the following series of bending processes of the present invention are first performed.
Flat hem processed part of the target panel material of test piece 6
One side edge of the test piece corresponding to (one side) (for example, a ₁ or b ₁ )
And a side edge (a ₂ or b ₂ ) opposite to the side edge at the same time.

Then, after that, as shown in FIG.
° bending flange (side edge) 6a, 6b (6a shown only)
While pressing the test piece 6 against the surface of the die 8 with the pad 7,
The punch 9b cooperating with the pad 7 further bends (by a mechanical press) into a 45 ° flange. This step corresponds to a prehem step in actual flat hemming.

Thereafter, the 45 ° bending flange portions 6a, 6b
Insert the edge of the inner material 10 into the inside, and as shown in FIG. 1 (c), further make the 45 ° bending flange portions 6a and 6b (only 6a shown) by punch 9c (by mechanical press) to 180 °. It is bent to sandwich the edge of the inner member 10 to form a 180 ° bent flange portion. This step corresponds to an actual flat hemming step. The shape such as the thickness of the inner material 10 corresponds to the inner material to be actually hemmed.

The flat hemming workability of the test piece is evaluated based on the state of surface cracks at the 180 ° bending flange, particularly at the corner (curved portion). The situation of surface cracking is
As shown in FIG. 4, in the actual flat hemming process, the rough surface X of the curving portion A of the flat heme and the minute crack Y
The evaluation is appropriately made according to or corresponding to a defect such as a relatively large crack Z.

In the present invention, the pressing conditions such as the shoulder radius Rd of the die used for bending and the shoulder radius Rp (mm) of the punch (punch) are the same as in the conventional test method. The optimum condition is appropriately selected according to various conditions in the processing.

For example, when the shoulder radius Rd of the die is set to be too small or too large with respect to the actual die condition in flat hemming, the above-described failure at the 180 ° bending flange corner portion is likely to occur or the failure becomes less likely. No longer occurs, and it is no longer possible to cope with the actual occurrence of the defect in flat hemming.

[0042]

Next, embodiments of the present invention will be described. AA 6016-T4 with 225MPa tensile strength, 138MPa proof stress and 30% elongation
Material, tensile strength 280MPa, proof stress 130MPa, elongation 28% J
IS5182-O material, prepare an Al alloy plate (1.0 mmt) of Al alloy standard composition, a strip-shaped test piece for bending test (Example of the present invention is 30 mm width ×
Multiple pieces of 200 mm in length and 30 mm in width x 100 mm in length in the conventional method were cut out.

Under the following conditions, this strip-shaped test piece was subjected to the method of the present invention (using a mechanical press) shown in FIG. 1, the conventional V-block method (using a simple hydraulic press) shown in FIG. 5, and FIG. Each bending test was performed three times by the conventional one-sided flange bending method (using a mechanical press).

The corresponding state of the bending test was compared with the result obtained by cutting a blank as an object panel material from each of the Al alloy plates and performing flat hemming as an actual automobile hood outer plate.

Here, it is assumed that flat hemming of the target panel material is performed on two opposite sides of the panel material, and a series of bending processes of the example of the present invention correspond to the flat hemming portion. Opposite side edges of the specimen (Fig. 2
It was carried out at the same time in the b ₁ and b ₂₎ a. Further, the conventional V-block method and the one-side flange bend method, conventional street, a series of bending in only one side edge portion of the specimen (only b ₁ in FIG. 2).

Further, the bending conditions were as follows. The pre-strain of each test piece was 10% stretch strain corresponding to the amount of strain applied to the panel material in the press forming (drawing process) in both the present invention example and the conventional method. Bending flange length of each test piece (180 ° bending allowance)
Was 10 mm (one side) in the present invention example and 50 mm in the conventional method. The bending radius R 1 in the 90 ° bending step was 1.0 in the present invention example and the conventional V-block method, and 0.75 in the conventional one-side flange bending method. The clearance between the test piece and the punch in the present invention example and the conventional one-sided flange bending method was 1.0 mm. The pressing force of the pad in each bending step of the present invention example is
800 kg / cm ² and the punch pressure were 400 kg / cm ² . Also,
Each conventional method does not press the plate as before, and the bending process pressure when using a hydraulic press is 400 kg / load on the cylinder.
cm ² .

In the actual curved portion (hem portion) of the flat hem, the state of occurrence of rough skin, minute cracks and large cracks is referred to as “smooth surface state without occurrence of rough skin, minute cracks and large cracks”. The evaluation state was set as △ for a surface state in which fine cracks or large cracks did not occur although the skin was rough, and × for a surface state in which a plurality or a large number of fine cracks or large cracks occurred. Then, the defects of the 180 ° bending flange corners of the example of the present invention and the conventional V-block method and the one-sided flange method were also evaluated based on the same standard as the flat hem curving portion. Table 1 shows the results.

As is clear from Table 1, the evaluation method of the present invention corresponds well with the evaluation result of the actual flat hem edge curved portion, and there is no variation in the number of bending tests in the present invention example, accuracy and reproduction. It turns out that the property is high.

On the other hand, the conventional V-block method and the one-sided flange bending method do not always correspond to the actual evaluation results of the flat hem edge bending portion, and the variation in the number of bending tests is large.

From the above results, the significance of each characteristic requirement in the evaluation method of the present invention can be understood. Further, the evaluation method of the present invention can be used not only for flat hem workability shown in the above-described embodiment but also for other hem workability such as rope hem.

[0051]

[Table 1]

[0052]

According to the present invention, the reliability and reproducibility of test results are good, and the hem workability of a simple Al alloy panel material is easily corresponded to the hem work such as actual flat hem of an automobile panel material. A method can be provided. For this reason, the improvement and development speed of the material side of the Al alloy plate can be accelerated, and the flat hem workability of the Al alloy plate can be guaranteed.
Therefore, the improvement of the properties of the Al alloy panel material is promoted, and the use of the Al alloy material is greatly expanded for use in transporting vehicles such as automobiles, which is of great industrial value.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of the hemming processability evaluation method of the present invention.

FIG. 2 is a plan view showing a test piece used in the present invention.

FIG. 3 is an explanatory diagram showing an outline of hemming processing of a panel material.

FIG. 4 is an explanatory view showing a defect of a hem portion generated in a flat hem process of a panel material.

FIG. 5 is an explanatory view showing a conventional hemming process evaluation method by a V-block method.

FIG. 6 is an explanatory view showing a method for evaluating hemmability by a conventional one-sided flange bending method.

[Explanation of symbols]

1: Outer plate (Al alloy blank), 2, 10, 15: Inner plate
(Al alloy blank), 3, 8, 13, 18: Dies,
4, 9, 12, 19: punch, 5, 7, 17: plate holder (pad), 6, 11, 16: Al alloy specimen 14: table A: flat hem curving part, X: rough skin, Y: Minor crack, Z:
Big crack

Claims (3)

[Claims] 1. A method for evaluating the hem workability of an aluminum alloy panel material after press forming, wherein a strip test piece of an object panel material is given a strain suitable for the press forming by stretching in advance, and the pressing is performed. Attached to, including sequentially bending the test piece side edge corresponding to the hem processing site of the target panel material, first, after bending the side edge to a 90 ° flange along the corner of the die, This 90 ° bending flange is further bent to 45 ° flange, and this 45 °
After inserting the edge of the inner material inside the bending flange part, the 45 ° bending flange part is further bent to 180 ° while sandwiching the edge of the inner material, depending on the situation of surface cracking of this 180 ° bending flange part. When evaluating the hemmability of the test piece, while pressing the test piece against the die surface in each bending process,
A method for evaluating hemmability of an aluminum alloy panel material, comprising performing punching and simultaneously bending opposite side edges of a test piece in each bending process. 2. The method for evaluating the hemmability of an aluminum alloy panel material according to claim 1, wherein the hemming is flat hemming. 3. The method according to claim 1, wherein the aluminum alloy is AA to JIS 50.
3. The method for evaluating the hem workability of an aluminum alloy panel material according to claim 1, which is an aluminum alloy selected from the 00 series and the 6000 series.