JPH0972799A - Method and device for testing press forming property of metal plate surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To objectively evaluate the lubrication characteristics of a material surface in a press forming where plastic deformation and slide are repeated without being affected by the difference in the material deformation force by performing the plastic forming of bending, bending return, and slide to a metal plate and measuring the friction coefficient of the surface of the metal plate which is subjected to plastic forming. SOLUTION: The lubrication characteristics of a surface can be objectively evaluated without being affected by the strength of a material and the influence of a plate thickness by independently damaging a material (metal plate) to be tested due to bending/bending return deformation and slide and measuring slide resistance. Further, by comparing the difference between an evaluation value and a friction coefficient due to flat-plate slide, namely the difference between friction coefficient before and after receiving damage on the surface, the degree of surface damage can be quantitatively evaluated. Namely, as the difference of the friction coefficient is larger, the surface damage is judged to be larger.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for testing the press formability of the surface of a metal plate, which evaluates the lubricating characteristics of the surface of the metal plate during press forming.

[0002]

2. Description of the Related Art As shown in FIG. 5, a press die used for producing automobile parts is composed of a punch 16, a die 18, a wrinkle holding plate 17, etc.
A draw bead 19 is provided between the die 18 and the wrinkle holding plate 17.
Is provided. The material (metal plate) 20 is the die 18
While being restrained by the crease presser plate 17 and the drawing bead 19, they flow into the mold and are processed. At this time, if the constraint of the material is too weak, the inflow becomes excessive and wrinkles occur in the product. On the other hand, if the constraint is too strong, the strain applied to the material will be large and the product will break. Therefore, in order to obtain a good product, the balance between the restraint of the material and the inflow is important.

Of the factors that influence the ease of flow into the mold, the most influential factor is the lubricity of the surface of the material. The lubricity of the surface of the raw material varies depending on the performance of the press oil, and also greatly varies depending on the type of raw material and the state of the surface. Among them, it is known that surface-treated steel sheets, which are widely used as automobile steel sheets, have a large difference in surface lubricity depending on the type of plating. Such superiority or inferiority of lubricity directly affects the press formability, and changing the type of press oil or the type of plating tends to cause defective molding such as wrinkles and breakage. Therefore, in order to satisfactorily mold the material, it is important to accurately evaluate and grasp the lubrication characteristics of the surface.

As a method for evaluating the lubrication characteristics of the material surface,
The most reliable method is to perform molding using a real press die, but it is not rational because it requires a lot of labor and cost to operate the press machine and adjust the press die. Further, it has been found that a simple sliding test cannot evaluate the lubrication characteristics of the material surface in press molding. The reason is,
This is because a complicated sliding phenomenon occurs during press molding.

Against this background, various test methods have been proposed for the purpose of simulating sliding during press molding.

For example, a flat plate sliding test has been conducted.
This test uses a friction coefficient measuring device as shown in FIG.
This is a method in which a material to be tested pressed by a tool is drawn at a certain speed, changes in the drawing force and the pressing force at that time are measured, and the friction coefficient is obtained from the ratio of the drawing force and the pressing force.
In FIG. 2, 8 is a sliding tool, 9 is a material to be tested, 10 is a drawing load cell, and 12 is a load cell. At this time, the sliding state of the bead portion, the wrinkle holding portion, the die shoulder portion, and the like can be simulated by changing the shape and pressing force of the tool (hereinafter referred to as "prior art 1").

A draw bead test is conducted as an evaluation of the lubrication characteristics of the squeezing bead portion. This exam is
This is a method of measuring the resistance when the material under test is pulled out while restraining the material under test with a tool simulating the drawing bead portion as shown in Fig. 1. The lubrication state when the drawing bead portion is bent and bent back. Can be simulated. In FIG. 1, 1 is a load cell, 2 is a chuck, 3
Is a load device, 4 is a drawing device, 5 is a material to be tested, and 6 is a bead (hereinafter referred to as "prior art 2").

Further, as a technique developed from this draw bead test, a method of simultaneously simulating the lubrication state of the squeezing bead portion and the die shoulder portion is disclosed in JP-A-60-25083.
No. 5 proposes this. This method is to measure the pulling force of the material by simulating bending / bending back deformation and sliding at the radius of the bead drawing and the die radius (hereinafter referred to as "Prior Art 3").

[0009]

Since the prior art 1 does not involve plastic deformation of the material, it is not possible to completely evaluate the lubrication characteristics during press forming.

The methods of the prior art 2 (draw beat test) and the prior art 3 can simulate the sliding phenomenon during press molding to some extent, but the evaluation method has the following problems.

Since the pull-out resistance, which is a combination of the sliding resistance of the material and the deformation resistance of bending / unbending, is evaluated, it is possible to avoid the influence of the deformation force of the material when the materials have different thicknesses and strengths. Absent. It is difficult to make the material thickness and strength uniform, and it is necessary to compare the lubrication characteristics between various types of materials. From such a background, there has been a demand for a method of objectively evaluating only the lubrication characteristics of the material surface by eliminating the influence of the difference in material deformation force.

Therefore, the present invention has been made in view of the above problems, and an object thereof is to improve the lubrication characteristics of a material surface in press molding in which plastic deformation and sliding are repeated, and An object of the present invention is to provide a press formability test method and apparatus for the surface of a metal plate, which can be objectively evaluated without being affected by the difference.

[0013]

According to the method of the present invention, a metal plate is subjected to plastic working such as bending, unbending and sliding, and the friction coefficient of the surface of the metal plate subjected to the plastic working is measured. It is characterized by doing.

The apparatus of the present invention comprises means for subjecting a metal plate to plastic working such as bending, unbending and sliding.
And a means for measuring the friction coefficient of the surface of the metal plate after the plastic working.

[0015]

According to the present invention, the application of damage (plastic working) to the material under test (metal plate) due to bending / bending back deformation and sliding and the measurement of sliding resistance are independent. By doing so, without being affected by the strength and thickness of the material,
The surface lubrication properties can be evaluated objectively.

[0016]

Next, the present invention will be described with reference to examples.

Based on the test method of the present invention, a draw bead device and a flat plate sliding device were used to evaluate the lubrication characteristics and press formability of the surface of the material to be tested. The raw materials (metal plates) subjected to the test are hot-rolled steel plates, cold-rolled steel plates and various surface-treated steel plates shown in Tables 1 to 3. The material to be tested was prepared by shearing the above material into a strip shape having a width of 30 mm and a length of 250 mm, degreasing it, and then applying a prescribed oil.

A tool for the draw bead test is shown in FIG.
An apparatus having a bead convex mold 13 and a bead concave mold 14 having a triangular bead shape with a tip of 0.5R and a height of 4 mm as shown in FIG. The test material was restrained with a pressing force of 500 kgf by the tool, and then pulled out at a speed of 0.2 m / min. The pulling force at this time was measured, and the ratio between the pressing force and the pulling force was evaluated as a friction coefficient. Next, the test material damaged by the bead pulling out was subjected to a flat plate sliding test as it was. The flat plate sliding test was carried out by using a sliding tool 15 having a contact surface of 3 mm × 10 mm as shown in FIG. 4 under the conditions of a pressing force of 400 kgf and a drawing speed of 1 m / min. Measure the pulling force at this time, evaluate the ratio of the pressing force and the pulling force as a friction coefficient,
The results are shown in Tables 1 to 3 as “μ after Draw” of the test method of the present invention.

For comparison, the evaluation of the results of the above-mentioned flat plate sliding test or draw bead test independently performed on the test material is also shown in Tables 1 to 3 as a conventional method.

In the press forming test, the test material of the hot rolled steel sheet is molded by a mold that models an automobile suspension, and the test material of the cold rolled steel sheet and the surface treated steel sheet is the door panel of the automobile. Molding was performed by using a chamfered die having a size of 350 mm × 350 mm, which simulates a part. Evaluation is wrinkle holding force (BH
By changing F), the BHF region in which a good product can be molded is defined as the moldable range, and the larger the range, the better the moldability.

Tables 1 to 3 summarize these results. Table 1 shows the effects of material strength and hot dip coating on hot rolled steel sheets. Tables 2 and 3 investigate the effects of material strength, surface roughness, plate thickness, lubricating oil, and surface treatment film on cold-rolled steel sheets and surface-treated steel sheets.

The description of the items shown in Tables 1 to 3 is as follows. Flat plate μ: Evaluation value by flat plate sliding test Draw Bead: Evaluation value by draw bead test μ: Evaluation value by the present invention Moldability: Evaluated in the formable BHF region; better as there are more ○ marks Dull: Normal dull finish Laser: Laser Texture finish Coating weight: g / m ² GA: Galvanized cold rolled steel sheet DURA: Organic coated cold rolled steel sheet

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

First, when the correspondence between the evaluation (flat plate μ) by the flat plate sliding test of the conventional method and the formability is considered, it cannot be said that the material having a low friction coefficient is excellent in the formability, and the lubrication property at the time of press forming is sufficient. It turns out that it is not possible to take a proper correspondence. For example, H material (flat plate μ: 0.080) with a small surface roughness due to the Laser Texture finish is usually Dull.
Although the coefficient of friction is lower than that of the finished material D (flat plate μ: 0.155), the formability evaluation is the same. . O material with a thick coating (coating (adhesion amount): U (1.6), flat plate μ: 0.11) is N material (coating (adhesion amount): U (0.
8), the coefficient of friction is lower than that of the flat plate μ: 0.14), but it does not match the tendency of formability.

The conventional draw bead test (Dra
Also in the evaluation by w Bead), there is some correlation with the press formability, but it is a material with different strength.
Material (Draw Bead: 0.441) and Material B (the same:
0.452), and D material (same: 0.352), F material (same: 0.373), and G material (same: 0.405), lubricity cannot be compared.

On the other hand, the evaluation according to the present invention (μ after Draw) has a good correspondence with the formability, and is sufficiently affected by the plate thickness and strength to simulate the lubricating behavior during press forming. Was confirmed. For example, in the materials D and H, which are materials having different surface roughness, the evaluation of the present invention shows the same value (μ: 0.146 and 0.148 after Draw), which is equal to the moldability. I am doing it. Also, P material (lubricating oil: S oil), H material (the same: S oil), M material (the same: M oil)
Oil) is a material in which the lubricating oil is changed, but the evaluation method of the present invention most clearly shows superiority and inferiority of moldability. Furthermore, N material (film (adhesion amount)): U (0.8), O material (same: U)
(1.6)) and P material (the same: P (1.2)) are different in film thickness and film type, but the evaluation value of the present invention corresponds to the formability. highest. In particular, the above N material, O
The effectiveness of the present invention was confirmed in the evaluation of the lubrication characteristics of the steel sheet having a coating that is susceptible to sliding damage, such as the steel material and the P material.

Furthermore, the degree of surface damage is quantified by comparing the difference between the evaluation value of the present invention and the friction coefficient due to flat plate sliding, that is, the difference between the friction coefficient before and after the surface is damaged. Can be evaluated. For example, O
The difference between the friction coefficients of the materials is 0.05, the difference between the friction coefficients of the P materials is 0.02, and the difference between the friction coefficients of the O materials is larger than that of the P materials. When the film state after the test was observed, the degree of damage to the O material was large, and this was in agreement with this difference. From this, it can be evaluated that the larger the difference in friction coefficient, the larger the surface damage.

[0030]

As described above, according to the present invention, even when the strength and the plate thickness of the material are different,
It is possible to simulate the sliding phenomenon in the damaged state due to the sliding of the bending-back deformation, and to grasp the surface lubrication characteristic value that is necessary for good press deformation of the material. , Industrially useful effects are brought about.

[Brief description of drawings]

FIG. 1 is a front view showing bending / unbending and sliding / processing means.

FIG. 2 is a front view showing a friction coefficient measuring device.

FIG. 3 is a front view showing an example of a draw bead tool.

FIG. 4 is a front view showing an example of a flat plate sliding tool.

FIG. 5 is a front view showing an example of a pressing die.

[Explanation of symbols]

 1 Load Cell 2 Chuck 3 Loading Device 4 Pulling Device 5 Test Material 6 Bead 8 Sliding Tool 9 Test Material 10 Pulling Load Cell 12 Load Cell 13 Bead Convex Model 14 Bead Concave Model 15 Sliding Tool 16 Punch 17 Wrinkle Holding Plate 18 Die 19 Drawing Bead 20 material (metal plate)

Claims (2)

[Claims] 1. A metal plate characterized by subjecting a metal plate to plastic working such as bending, unbending and sliding, and then measuring the friction coefficient of the surface of the metal plate subjected to the plastic working. Test method for press formability of the surface of. 2. A means for subjecting a metal plate to plastic working such as bending, unbending and sliding, and means for measuring the friction coefficient of the surface of the metal plate after the plastic working. A press formability testing device for the surface of a metal plate, comprising: