JP2014240774A - Membrane appearance deformation prediction method, manufacturing method, and press molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology capable of quantitatively evaluating and predicating a whitening phenomenon (appearance deformation) of a membrane 3 at the time when a surface coated metal plate 1 is subjected to press molding.SOLUTION: In an appearance deformation prediction method of a membrane 3 that predicts appearance deformation of the membrane 3 generated by performing press molding to a surface coated metal plate 1 in which the membrane 3 is formed on at least one surface of a metal plate 2, the relationship of degree of appearance deformation of the membrane 3 formed in the metal plate 2 with respect to distortion generated on the metal plate 2 is obtained in advance, and on the basis of the relationship and distortion estimated to be generated in the metal plate 2 by performing press molding to the surface coated metal plate 1, appearance deformation of the membrane 3 on a surface membrane 3 metal is predicted.

Description

  The present invention relates to a technique for deforming a surface-coated metal plate having a film provided on at least one surface of a metal plate by press forming such as drawing or stretch forming into a processed product. The present invention relates to a technique capable of suppressing the appearance deformation beyond a predetermined value from occurring on the surface film. Here, the appearance deformation of the surface film is a phenomenon that the surface is whitened (whitened), for example.

  The surface-coated metal sheet is used after being processed into a desired shape in various industries, such as containers represented by automobiles, home appliances, building materials, cans, and the like. Here, the surface-coated metal plate imparts a film to the surface of the metal plate to give the metal plate as a substrate functions such as corrosion resistance, fingerprint resistance, and design properties such as gloss and color tone.

  When processing a surface-coated metal sheet into a part, press work with excellent productivity such as drawing, overhanging, and bending is often used. If the surface coating has characteristics that are harder or less likely to deform than the underlying metal plate, when the surface coated metal plate is press-molded, the coating cannot follow the deformation of the metal plate, so cracks in the coating It is known that peeling or whitening may occur. When a crack or peeling occurs in the film, corrosion proceeds from there, and the peeled film enters between the mold and the metal plate, thereby causing problems such as wrinkling the metal plate. In addition, when the film is more than predetermined whitened, the appearance quality of the product is impaired, resulting in a defective product.

For this reason, in order to prevent a crack, peeling, and whitening from generating in a film, the component and manufacturing method of a film suitable for press molding have been examined conventionally.
In patent document 1, the method of prescribing | regulating the gel fraction of the resin film at the time of a heating is proposed for the precoat aluminum plate. Patent Document 1 describes that by increasing the adhesion between the film and the aluminum plate, the film does not peel or whiten even when deep drawing or ironing is performed.

  Moreover, there exists a technique of patent document 2 as a technique which evaluates peeling and adhesiveness of a film | membrane quantitatively. In Patent Document 2, there is a method of measuring the strain of the film on the surface of the substrate with a laser beam and evaluating it as the limit at which the film does not follow the distortion of the substrate. On the other hand, as a technique for evaluating the whitening of the film, there is a method of visually determining the degree of whitening of the film by performing cylindrical drawing or tensioning as in Non-Patent Document 1, but conventionally, it has been quantitatively evaluated. There is almost no technology to do.

Japanese Patent No. 4783051 Japanese Patent Laid-Open No. 11-142319

"Whitening Phenomenon and Drawing Mechanism in Drawing of Pre-Coated Aluminum" Light Metal, Vol. 57, No. 6 (2007) pp.228-233

When press-molding a surface-coated metal sheet, various deformations are applied to the metal sheet, but it is unclear how much the whitening phenomenon of the film will occur when the metal sheet and the film are deformed. . Further, it is considered that the degree of whitening of the film varies depending on the deformation characteristics of the metal plate and the film.
As described in Patent Document 1, it is important to produce a surface-coated metal plate that does not cause whitening of the film, but when deformation is small or when deformation that is difficult to cause peeling or whitening of the film occurs. The production conditions for the surface-coated metal sheet may be excessively limited.

  Moreover, as in Non-Patent Document 1, it is simple to apply a deformation close to the actual press forming to the surface-coated metal plate and visually evaluate it. However, since this method is a sensory evaluation method, the results may vary depending on the measurer and measurement conditions, and the reliability is poor. As a quantitative evaluation method, there is a technique described in Patent Document 2 that measures the amount of deformation (strain) at which the film peels off, but even if the metal plate and the film are not completely peeled off, fine cracks have occurred in the film. Since the whitening phenomenon occurs even at the stage, it is considered that detailed evaluation of the whitening phenomenon is difficult.

If the whitening phenomenon cannot be evaluated quantitatively, it is impossible to set production standards such as how much whitening is acceptable as a product. As a result, there has been a problem that it is impossible to predict whether a whitening phenomenon will occur in the film at the preparation stage for manufacturing a product using the surface-coated metal plate, for example, at the design stage of a mold or product shape.
The present invention has been made paying attention to the above points, and provides a predictable technique by quantitatively evaluating the whitening phenomenon (appearance deformation) of a film when a surface-coated metal sheet is press-formed. For the purpose.

In order to solve the above-mentioned problems, an appearance deformation prediction method according to one aspect of the present invention is the appearance deformation of the above-described film produced by press-forming a surface-coated metal plate having a film formed on at least one surface of the metal plate. Is a method of predicting the appearance deformation of the film, and obtaining a relationship between the degree of appearance deformation of the film formed on the metal plate in advance with respect to the strain generated in the metal plate,
The deformation of the coating on the surface coating metal is predicted based on the strain estimated to be generated in the metal plate by press-molding the surface-coated metal plate and the above relationship.

The strain may be specified by using two parameters, minimum strain and maximum strain.
The above relationship is obtained, for example, by actually generating strain on the surface-coated metal plate and evaluating the degree of external deformation of the film with respect to the generated strain.
For example, the appearance deformation uses, as an index, any one of the color, color difference, gloss, and light reflectance of the film.
Based on the above-mentioned relationship and the strain estimated to occur in the metal plate by press-molding the surface-coated metal plate into the target shape, the coating position where the degree of appearance deformation exceeding the preset threshold value is predicted Anyway.

  Moreover, the manufacturing method which is one aspect | mode of this invention manufactures a process component by press-molding the surface coating metal plate by which the film | membrane was previously formed in at least one surface of the metal plate to the preset target shape. In the manufacturing method, for each of a plurality of coating materials, a relationship of a degree of external deformation of the coating formed on the metal plate with respect to a strain generated on the metal plate is obtained in advance, and press-molded into the target shape. Based on the strain generated in the metal plate and the relationship described above, a coating material that does not generate a degree of appearance deformation exceeding a preset threshold value is selected, and one of the selected coating materials is coated on the surface of the metal plate. To form the surface-coated metal plate.

  The press forming method according to one aspect of the present invention is a press forming method for press forming a surface-coated metal plate having a film formed in advance on at least one surface of the metal plate, and is generated in advance on the metal plate. A relationship between the degree of external deformation of the film formed on the metal plate with respect to strain is obtained, and based on the relationship, a limit strain at which the film has a preset degree of external deformation is determined, and the above-described determination is performed by press molding. The shape after pressing is set so that a strain equal to or less than the limit strain is generated.

The above limit strain may be obtained for each deformation mode generated in the metal plate.
Here, the inventors observed a sample of a surface-coated metal sheet that had been whitened by press working, and only when the film appeared to be white because the film was peeled off and the metal plate or base immediately below the surface film was exposed. In addition, it was confirmed that cracks generated in the film sometimes scattered the light and made the film appear white. Therefore, it has been found that it is not sufficient to evaluate only whether the film peels.

  Therefore, a plurality of samples were prepared by variously changing the conditions of deformation (strain ratio) and deformation (strain), and the whitening phenomenon occurring in each sample was investigated in detail. As a result, the exfoliation of the film and the occurrence of cracks in the film have a strong correlation with the state of strain of the metal plate (for example, the amount of strain), which is further influenced by the strain ratio (deformation form of the metal plate). (Degree) was found to be different. Furthermore, it was discovered that the degree of whitening of the film (the degree of external deformation) can be quantified by measuring whiteness, color, color difference, gloss, light reflectance, etc. It was found that the degree of whitening can be related to the ratio and the amount of strain.

  Therefore, the strain generated on the surface-coated metal sheet during press forming is reproduced by uniaxial tension test and overhang test, and the relationship between the strain generated on the film and the degree of whitening is mapped in detail by measuring the whitening phenomenon generated on the film. And found out how to use it. Then, it was found that the degree of whitening of the film was quantified, so that it can be evaluated with higher accuracy than the conventional visual sensory evaluation and the method of evaluating the ease of peeling of the film. In addition, if the strain ratio and strain generated in each part of the molded product are predicted by press molding simulation using the finite element method, whitening will occur before the press processing (before actual whitening occurs) from the above mapping data. It was found that can be accurately predicted. Based on the above, the present invention has been conceived.

  According to the aspect of the present invention, when the target surface-coated metal plate is press-molded into a desired shape, it is possible to predict in advance how much the coating is whitened, that is, the degree of appearance deformation of the coating. For this reason, it can greatly contribute to the reduction of the defective rate of the press-formed product. In addition, it is possible to accurately predict the characteristics required for the coating of the surface-coated metal sheet at the material design stage. Therefore, the development goal of the surface-coated metal sheet can be set, which can contribute to shortening the development period. Furthermore, there is an effect that it is possible to accurately predict whether or not the selection of the surface-coated metal plate used when press-molding various parts such as electrical products and automobile panel parts is appropriate.

It is an example of a sectional view of a surface covering metal plate concerning an embodiment based on the present invention. It is a figure which shows the example of a deformation | transformation form and a shaping | molding limit line. It is a figure which shows estimation of the limit line of a film | membrane damage. It is a figure which shows the example of the relationship between the molding height and glossiness by each deformation | transformation form. It is a figure which shows the example of the contour line of glossiness. It is a figure which shows the other example of the contour line of glossiness. It is a figure which shows the structure of a whitening prediction apparatus. It is a figure which shows the example of a driving sheet. It is a figure explaining the metal mold | die used for an overhang test. It is a figure which shows the change of the glossiness in each deformation | transformation aspect. It is the figure which plotted the glossiness according to distortion. It is a figure which shows the contour line of glossiness. It is a figure which shows the difference in the change of the glossiness by the test material for every deformation | transformation aspect. It is the figure which plotted the glossiness according to distortion for every test material. It is a figure which shows the contour line of glossiness for every test material. It is a figure which shows the example which improved the whitening degree of the film | membrane for the back cover components of a thin television. It is a figure which shows the result by visual observation of the conventional method. It is a figure which shows the result by this invention method.

Next, embodiments of the present invention will be described with reference to the drawings.
(Constitution)
In the present embodiment, the surface deformation of the coating 3 will be described by taking the whitening of the surface coating as an example.
Here, the surface-coated metal plate 1 includes a metal plate 2 and a film 3 applied to the surface of the metal plate 2 as shown in FIG. In the present embodiment, the surface-coated metal plate 1 in which the film 3 is formed on one surface of the metal plate 2 will be described as an example. The metal plate 2 is, for example, an aluminum plate or a SUS plate. However, the metal plate 2 is not particularly limited as long as the metal plate 2 can be press-molded and can be provided with the coating 3. The film 3 includes, for example, a plating film, a chemical conversion film, a coating film, a film laminate film, a precoat film, or a film formed by laminating a plurality of them.

Here, basic deformation forms (strain ratio) generated by press forming the metal plate 2 are roughly classified into uniaxial tensile deformation (ε ₁ = −2 · ε ₂ ) and plane strain deformation (ε ₂ / ε _1). = 0) and three forms of equibiaxial deformation (ε ₁ = ε ₂ ). The forming limit forming limit line, which is the limit of crack deformation of the metal plate 2 due to deformation, can be represented by a curve having the maximum principal strain and the minimum principal strain as parameters, as shown in FIG. This forming limit line generally tends to be smaller in the vicinity of the plane strain state where the strain ratio (= minimum principal strain / maximum principal strain) = 0. That is, the forming limit differs depending on the deformation form of the metal plate 2.
Here, Table 1 describes the composition of each material shown in FIG.

  The present inventors consider that there is some correlation between the deformation of the metal plate 2 and the appearance deformation of the surface coating 3 on the metal plate 2, and the distortion similar to the above forming limit line as shown in FIG. It was verified by assuming that the limit line of the damage of the film 3 due to the correlated whitening could be assumed.

  Then, when the relationship between the punch stroke amount (equivalent to the molding height) and the glossiness during press working and the glossiness is obtained for each deformation mode, it is as shown in FIG. Further, when the degree of whitening is summarized using the maximum principal strain and the minimum principal strain as parameters, it is as shown in FIG. That is, it was confirmed as described later that there is a correlation between the deformation mode (strain ratio) of the metal plate 2 and the degree of whitening. The degree of whitening is evaluated by the glossiness. Moreover, as shown in FIG. 6, the position of the contour line of the same glossiness changes with film | membrane materials. However, in either case, the contour line of the glossiness has a downward slope, which is different from the tendency of the molding limit line.

  Here, as the types of deformation forms (strain ratios) increase, the contour lines of glossiness can be obtained with higher precision. In this embodiment, the three types of uniaxial tensile deformation, plane strain deformation, and equal biaxial deformation are described above. The glossiness value in the deformed form was obtained as a representative value for each material, and information on strain and glossiness was accumulated in the whitening evaluation database 5. Here, the glossiness in the deformation mode (strain ratio) between the three deformation modes is a value on a straight line connecting the same glossiness in the adjacent basic deformation modes as shown in FIG. Set. When actually obtained, contour lines are expressed by a line on a curve close to a straight line, and therefore it is estimated that the accuracy is not lowered so much even if linear approximation is performed. Since the relationship between the deformation form other than the actual deformation form (strain ratio) and the degree of whitening is an estimated value, the amount of strain corresponding to the limit value of the whitening degree set in advance with a margin for the whitening degree is provided. You may make it suppress.

The whitening prediction device 4 predicts the degree of whitening while referring to the data in the whitening evaluation database 5. As shown in FIG. 7, the whitening prediction device 4 includes an information input unit 4A, a whitening degree calculation unit 4B, and an output unit 4C.
The information input unit 4A inputs strain information and film material information.
Here, before the target surface-coated metal plate 1 is press-formed into a target shape, each strain applied to each part of the surface-coated metal plate 1 by the press-forming is publicly known, such as a finite element method. It estimates with the distortion evaluation apparatus 6 to perform. Then, the information input unit 4A inputs the strain information estimated by the strain evaluation device 6. Information on the coating material is received from, for example, a control unit of the production line of the surface-coated metal plate 1.

The strain information here is a deformation mode (strain ratio) and a strain amount. The amount of strain is represented by, for example, the maximum principal strain. Further, the strain information may be two values of the maximum main strain amount and the minimum main strain amount. In this embodiment, position information on the metal plate 2 is added as strain information.
The whitening degree calculation unit 4B refers to the whitening evaluation database 5 using the strain information and the coating material information as parameters, and obtains the whitening degree (glossiness in the present embodiment) for each strain. Each strain is tied to each position on the metal plate 2.

  The output unit 4C displays or prints the degree of whitening for each strain obtained by the whitening degree calculation unit 4B on the display unit 6 such as a display in association with the position of the metal plate 2. At this time, for example, when the limit value of the whitening degree is set, the output unit 4C emphasizes and outputs the position of the metal plate 2 that has become the whitening degree exceeding the limit value of the whitening degree, You may process so that only the location may be displayed.

(Operation)
Information on strain and whitening degree is collected in advance for each coating material and stored in the whitening evaluation database 5. In the present embodiment, for simplicity, it is represented by three deformation forms such as uniaxial tensile deformation, plane strain deformation, and other biaxial deformation, and gloss level information is collected in the three deformation forms and the whitening evaluation database 5 is collected. To accumulate. In addition, if information is individually collected for a plurality of thicknesses of a plurality of coatings 3 for the same coating material, more accurate data is obtained.

For example, as a preliminary evaluation before manufacturing the target surface-coated metal plate 1, if the target surface-coated metal plate 1 is press-formed into a target shape based on the material information of the metal plate 2, the metal Each strain applied to each part of the plate 2 by the press molding is estimated by a known method such as a finite element method.
Next, with reference to the data of the whitening evaluation database 5, information on the degree of whitening of each part of the plate surface generated on the surface of the processed product after processing the target surface-coated metal plate 1 is obtained. For example, the location of the metal plate 2 that is greater than or equal to a preset whitening degree (in the present embodiment, less than the glossiness) is displayed in association with the position in the shape after processing or the position in the metal plate 2 before processing.

And when there exists a part which becomes more than the preset whitening degree (in this embodiment, below the glossiness), for example, the coating material to be used is changed, for example, a material having higher viscosity and viscoelasticity as the coating material. In other words, the pre-evaluation process is performed until there is no portion that is equal to or higher than the preset whitening degree (in the present embodiment, lower than the glossiness).
Alternatively, for example, as a prior evaluation before manufacturing the target surface-coated metal plate 1, if the target surface-coated metal plate 1 is press-formed into a target shape based on the material information of the metal plate 2, the metal The maximum strain generated in the plate 2 is obtained for each deformation mode. For example, the maximum value of the maximum principal strain amount is obtained for each of the three types of deformation.

  Then, referring to the data of the whitening evaluation database 5 using the maximum value of the maximum principal strain amount for each of the three types of deformation as a parameter, for example, for each of the three types of deformation for the coating material to be used The glossiness is obtained, and it is determined whether it is not more than the preset whitening degree (in this embodiment, not less than the glossiness). Alternatively, referring to the data of the whitening evaluation database 5 using the maximum value of the maximum principal strain amount for each of the three types of deformation as a parameter, the glossiness is equal to or less than the preset whitening degree (in this embodiment, the glossiness A list of coating materials is obtained. At this time, in order to select the coating 3, the strength condition of the coating 3 may be input.

  Further, as described above, with reference to the data in the whitening evaluation database 5, information on the degree of whitening occurring on the surface of the processed product after processing the target surface-coated metal plate 1 is obtained, and preset whitening is performed. When there is a portion that is greater than or equal to (in this embodiment, less than or equal to the glossiness), the composition of the metal plate 2 is changed, or the processed shape of the portion that is greater than or equal to the preset whitening degree is changed, The evaluation process is performed until there is no place where the degree of whitening is equal to or higher than the preset whitening degree (in the present embodiment, lower than the glossiness).

By carrying out as described above, it is possible to predict in advance how much the coating 3 is whitened, that is, the degree of appearance deformation of the coating 3 when the target surface-coated metal plate 1 is press-formed into a desired shape. For this reason, it can greatly contribute to the reduction of the defective rate of the press-formed product.
In addition, the characteristics required for the coating 3 of the surface-coated metal plate 1 can be accurately predicted at the material design stage. Therefore, the development goal of the surface-coated metal sheet 1 can be set, which can contribute to shortening the development period. Furthermore, there is also an effect that it is possible to accurately predict whether or not the selection of the surface-coated metal plate 1 used when press-molding various parts such as electrical products and automobile panel parts is appropriate.

  Thus, since it is rarely restricted by the material of the base metal plate 2 used as a target, the characteristics of the surface coating 3, and the manufacturing method, it can be applied to various surface-coated metal plates 1. In addition, when parts such as industrial and consumer devices and can products are produced by press-molding the surface-coated metal plate 1, the whitening of the coating 3 can be predicted in advance, so that the product shape and the characteristics of the coating 3 can be predicted. It can be selected in advance.

(Effect of this embodiment)
(1) The relationship between the degree of external deformation of the film 3 formed on the metal plate 2 with respect to the strain generated in the metal plate 2 is obtained in advance, and the surface-coated metal plate 1 is estimated to be generated on the metal plate 2 by press forming. The appearance deformation of the film 3 on the surface film 3 metal is predicted based on the strain to be applied and the above relationship.
According to this configuration, it is possible to predict in advance how much the coating 3 is whitened, that is, the degree of appearance deformation of the coating 3 when the target surface-coated metal plate 1 is press-formed into a desired shape. For this reason, it can greatly contribute to the reduction of the defective rate of the press-formed product.

(2) The strain is specified using two parameters, minimum strain and maximum strain, as parameters.
According to this configuration, the appearance deformation degree of the film 3 can be evaluated with higher accuracy.
Here, the evaluation may be made more simply by one strain amount such as the maximum principal strain amount without looking at the deformation form. For example, when attention is paid only to the deformation near the plane strain deformation, the evaluation may be made using only the maximum principal strain amount.
(3) The above relationship is obtained by actually generating strain on the surface-coated metal plate 1 and evaluating the degree of appearance deformation of the coating 3 with respect to the generated strain.
Thus, the above relationship can be obtained in advance reliably.

(4) The appearance deformation uses as an index any one of the color, color difference, gloss, and light reflectance of the coating 3.
Such an index can be objectively measured and evaluated by a measuring device such as a gloss meter.
Here, in the above-described embodiment, the glossiness is exemplified as an index of the degree of whitening as the appearance deformation degree. However, an amount that can be measured by the measuring device such as a color degree or a light reflectance may be used as the index value.
Moreover, although whitening is illustrated as an external appearance deformation | transformation of the membrane | film | coat 3, this invention is applicable if it changes from the external appearance used as references | standards, such as blackening and greening, and a change in external appearance can be measured with a measuring device. .

(5) A film in which the degree of appearance deformation exceeding a preset threshold value is generated based on the strain estimated to be generated in the metal plate 2 by press-molding the surface-coated metal plate 1 into a target shape and the above relationship. Predict 3 positions.
As a result, the occurrence position of the degree of appearance deformation that becomes a problem can be predicted in advance, so that it is possible to cope in advance.

(6) For each of a plurality of coating materials, when the relationship of the degree of external deformation of the coating 3 formed on the metal plate 2 with respect to the strain generated on the metal plate 2 is obtained in advance, and press-molded into a desired shape Based on the strain generated in the metal plate 2 and the above relationship, a coating material that does not generate a degree of appearance deformation exceeding a preset threshold value is selected, and one of the selected coating materials is applied to the surface of the metal plate 2. A film 3 is formed to form the surface-coated metal plate 1.
According to this configuration, optimization of the coating 3 can be executed in advance.

(7) The relationship of the degree of external deformation of the coating 3 formed on the metal plate 2 with respect to the strain generated in the metal plate 2 is obtained in advance, and the external deformation of the limit set by the coating 3 based on the relationship is determined. The limit strain that is the degree is obtained, and the shape after pressing is set so that the strain below the limit strain obtained above is generated by press molding.
Thereby, optimization of a press shape can be implemented in advance.
(8) The above limit strain is obtained individually for each deformation mode generated in the metal plate 2.
As a result, it is possible to respond with higher accuracy.

  The metal plate 2 is processed into a JIS No. 5 tensile test piece and a 200 mm square test piece. At this time, a test piece for measuring the degree of whitening of the film 3 and a test piece for measuring strain are prepared. In addition to the measurement of glossiness, the measurement method of the degree of whitening of the film 3 can quantitatively measure changes in the film 3 such as whiteness, yellowness, blackness, lightness, color difference, or light reflectance. Any method may be used as long as it can be measured.

  The gloss of the test piece for measuring the gloss is measured in advance. The test piece for measuring strain is marked on the back surface of the contact portion with the punch 11 with a distance between the gauge points of 0.5 to 50 mm. If the distance between the gauge points is smaller than 0.5 mm, the reading error of the gauge position becomes so large that it cannot be ignored with respect to the measured strain value, which is not suitable. When the distance between the gauge points is larger than 50 mm, the strain change between the gauge points is averaged, so that the measurement accuracy of the strain may be lowered. The marking method may be any method as long as strain can be measured, such as a scribed circle, laser marking, etching, or marking. In addition, distortion may be measured using image processing such as digital image correlation (DIC).

  The prepared specimens are processed with different strain ratios (ratio of maximum and minimum principal strains) and strain amounts. Here, in order to produce test pieces having different strain ratios, a uniaxial tensile test and a frustoconical overhang test of FIG. 9 using the driving sheet 10 having different plate widths W shown in FIG. 8 are performed. The structure of the mold is not particularly limited, but it is preferable that the evaluation position has a sufficient width in order to measure the degree of whitening of the film 3 at the top of the punch 11 as described later. If the degree of whitening of the film 3 can be measured, the tip of the punch 11 may be spherical. Since the test piece is deformed following the deformation of the driving sheet 10, the driving sheet 10 is preferably made of mild steel having better deep drawability (higher Rankford value) than the test piece. Lubricating oil is applied to the interface between the driving sheet 10 and the punch 11 and does not need to be applied to other portions. By changing the width W of the driving sheet 10 in a range that is larger than the hole diameter D at the center and smaller than the distance between the beads (Φ180 mm), a wider strain ratio can be added to the test piece.

The amount of strain is changed by changing the tensile distance in the uniaxial tensile test and the molding height in the truncated cone test. By changing the tensile distance and the overhang height, the glossiness of the coating 3 at the center of the top of the punch 11 can be measured for each deformation mode as shown in FIG.
Next, for a test piece to which various strains are applied, if the strain is measured from a scribed circle, the relationship between the strain and the glossiness can be measured as shown in FIG. The horizontal axis is the minimum principal strain, and the vertical axis is the maximum principal strain. If the glossiness at each strain ratio is connected by contour lines, the relationship of the degree of whitening of the film 3 to the strain applied to the surface-coated metal plate 1 can be quantitatively evaluated as shown in FIG.

  In addition, when evaluating in more detail, what is necessary is just to measure the whitening degree of the membrane | film | coat 3 by adding distortion ratios other than biaxial deformation, such as uniaxial tension deformation and plane strain deformation, to a test piece. In particular, since the unequal biaxial deformation region between plane strain deformation and equal biaxial deformation is a strain ratio that is likely to occur in press forming, it is preferable to evaluate the strain ratio of the unequal biaxial deformation region in detail. Moreover, if the strain ratio generated at the time of press molding is known in advance, it is efficient to evaluate the degree of whitening of the coating 3 with respect to the strain around the strain ratio. The method of applying the strain is not limited to the above, and an overhang molding or a bending molding using hydraulic pressure may be used.

  By performing a press molding simulation using the finite element method, it is possible to predict the strain generated when the press molded product is molded. Therefore, the whitening degree of the film 3 generated in the press-formed product can be predicted by comparing with the relationship of the degree of whitening of the film 3 to the strain applied to the surface-coated metal plate 1. If a certain degree of whitening of the film 3 is provided as an acceptable standard for a molded product, the presence or absence of whitening of the film 3 can be predicted in advance at the production preparation stage.

This will be described more specifically.
Three types of metal plates 2 shown in Table 2 were prepared.
The characteristics of the film of each test material are as shown in Table 2, and the film is mainly composed of a polyester resin, a curing agent, and carbon black. Further, the hardness of the film is a hardness in a state where it is coated on a metal plate, and was measured by a Fischer hardness meter (manufactured by Fischer Instrument Co.). As the curing agents, Cymel 327 and Cymel 701 (both registered trademarks, Mitsui Cyanamid Co., Ltd.) were used. Carbon black is added to complement the bridging action by being added simultaneously with the curing agent.

The degree of whitening of the coating 3 before and after applying strain was measured using a gloss meter.
A scribed circle with a distance between gauge points of 6.35 mm was transferred to the back of the contact portion with the punch 11 on the test piece, and the strain was measured from the change in the circle diameter before and after the strain was applied.
A uniaxial tensile test and a frustoconical overhang test were carried out on the test piece, and the change in glossiness was measured as shown in FIG. If the strain is measured from a scribed circle for a test piece to which various strains are applied, the relationship between the strain and the glossiness can be measured as shown in FIG. If the distribution of glossiness with respect to the maximum principal strain and the minimum principal strain is connected by contour lines, the relationship between the strain and the degree of whitening of the coating 3 of each metal plate 2 can be evaluated as shown in FIG.

Next, the degree of whitening of the film 3 is predicted for the back cover component of the flat-screen television shown in FIG.
First, press molding was performed on the test materials (1), (2), and (3), and the whiteness at three positions A, B, and C was measured. The strain generated in the specimen was obtained by performing press forming simulation using the finite element method. Here, the strain may be obtained by adding a marking to the test material, press-molding, and measuring the distance between the marking marks.

  FIG. 17 shows a comparison between the conventional method and the method of the present invention. In the conventional method, a case where the test piece was visually whitened was determined as “×”, a case where slight whitening was observed was determined as “Δ”, and a case where whitening did not occur was determined as “◯”. By the method of the present invention, the degree of whitening of the film 3 with respect to the strain ratio and the strain amount could be quantitatively evaluated. Further, when the mapping of the inventive method and the result of press molding are compared, FIG. 18 is obtained. By using the press molding simulation using the finite element method and the mapping of the present invention based on the shape of the part or mold, the degree of whitening occurring in the coating 3 could be accurately predicted.

DESCRIPTION OF SYMBOLS 1 Surface coating metal plate 2 Metal plate 3 Film | membrane 4 Whitening prediction apparatus 4A Information input part 4B Operation part 4C Output part 5 Whitening evaluation database 6 Evaluation apparatus

Claims (8)

A method for predicting the appearance deformation of a film for predicting the appearance deformation of the film produced by press-molding a surface-coated metal plate having a film formed on at least one surface of the metal plate,
Obtain the relationship of the degree of appearance deformation of the film formed on the metal plate against the strain generated in the metal plate in advance,
Deformation of the appearance of the film characterized by predicting the appearance deformation of the film on the surface film metal based on the strain estimated to occur in the metal plate by press-forming the surface-coated metal sheet and the relationship described above. Prediction method.   2. The method for predicting the appearance deformation of a film according to claim 1, wherein the strain is specified by using two parameters of a minimum strain and a maximum strain as parameters.   3. The coating according to claim 1, wherein the relationship is obtained by actually generating strain on the surface-coated metal plate and evaluating the degree of external deformation of the coating with respect to the generated strain. Appearance deformation prediction method.   The appearance of the coating according to any one of claims 1 to 3, wherein the deformation of the appearance is based on any one of color, color difference, gloss, and light reflectance of the coating. Deformation prediction method.   Predicting the film position where the degree of appearance deformation exceeding a preset threshold is generated based on the strain estimated to occur in the metal plate by pressing the surface-coated metal plate into the target shape and the above relationship The method for predicting the appearance deformation of a film according to any one of claims 1 to 4, wherein: A manufacturing method for manufacturing a processed part by press-molding a surface-coated metal plate having a film formed in advance on at least one surface of a metal plate,
For each of a plurality of coating materials, obtain the relationship of the degree of external deformation of the coating formed on the metal plate against the strain generated in the metal plate in advance.
Based on the strain generated in the metal plate during press forming into the target shape and the relationship described above, a coating material that does not generate a degree of appearance deformation exceeding a preset threshold value is selected. A method for producing a surface-coated metal sheet by forming a film on the surface of a metal sheet. A press molding method for press-molding a surface-coated metal plate having a film formed in advance on at least one surface of the metal plate,
Obtain the relationship of the degree of appearance deformation of the film formed on the metal plate against the strain generated in the metal plate in advance,
Based on the above relationship, determine the limit strain at which the coating film has a predetermined limit of external deformation, and set the shape after pressing so that a strain equal to or less than the determined limit strain is generated by press molding. A press molding method characterized by the above.   The press forming method according to claim 7, wherein the limit strain is obtained for each deformation mode generated in the metal plate.

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