TWI532577B - Method for evaluating polishability of steel material for mold and method for evaluating polishability of mold - Google Patents

Description

Method for evaluating the abrasiveness of steel for molds and the abrasiveness of the mold evaluation method

The present invention relates to a method for evaluating the abrasiveness of a steel material by measuring the waviness of the surface of the steel material used for the grinding of the working surface, and measuring the waviness of the surface after the grinding process. Alternatively, there is a method of evaluating the abrasiveness of the mold by measuring the waviness of the working surface of the mold after the grinding process, which is an actual mold obtained by grinding the working surface.

A work surface in which a mold having a high-quality surface property, such as a plastic product, is formed, requires a mirror-finished surface. Further, such a working surface is prepared, for example, by a prehardening steel material which is previously adjusted to have a hardness, and the surface thereof is cut into a predetermined shape, and then subjected to a grinding process to be finished into a mirror surface.

The above-described grinding process is usually carried out in the final step of mold making. The step of the grinding process is generally carried out in the order of coarse grinding by grindstone, followed by semi-finishing of the abrasive paper, and finally by fine polishing of diamond paste. Further, the abrasive grains contained in the grindstone, the abrasive paper, and the diamond abrasive paste respectively have specifications corresponding to the average particle diameter. For example, an abrasive having an average particle size of about 15 μm The pellets are referred to as "#1000" in accordance with the specifications of JIS R 6001 (particle size of grinding stone for grinding) or JIS R 6010 (particle size of abrasive material for polishing cloth).

However, when a mold which is finished by mirroring the working surface into a mirror surface by the above-described polishing processing is used, for example, plastic molding is actually performed, and unevenness (plaque; shadow) may be generated on the surface of the molded article obtained thereby. (shading))". This unevenness is a surface property defect due to the difference in the degree of reflection of light on each surface of the molded article, and is a factor that deteriorates the appearance quality of the molded article. In addition, it is confirmed that the cause of the unevenness is "waviness" existing on the working surface of the mold which is the source of the property of transferring the molding surface (Patent Documents 1 to 2). The waviness is a periodic fluctuation of the surface caused by an interval larger than the surface roughness as defined in JIS B 0601:2001 (ISO 4287:1997) (Non-Patent Document 1).

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 01-212789

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2010-242147

[Non-patent literature]

[Non-Patent Document 1] JIS B 0601:2001 "Geometry Specifications (GPS) - Surface Properties: Contour Curve Method - Terminology, Definition, and Surface Property Parameters", JIS Handbook, 2005

The waviness generated when the mold is polished with steel is determined by the quality of the molded article. Therefore, before processing the mold steel into the actual mold, if By grasping the degree of waviness of the steel material for a mold, that is, the degree of waviness generated during the polishing process according to a predetermined condition, it is possible to determine whether the steel material for the mold is a suitable material or to judge the mold. The best use or grinding conditions for steel. Further, even in the state of the mold after the production, if the degree of waviness generated on the working surface can be quantitatively evaluated, the degree of unevenness of the surface of the molded article can be predicted without using the mold. And can evaluate the soundness of the mold.

However, there are actually cases in which a plurality of steel materials for a mold having the same degree of waviness value after the polishing process are present in a molded article obtained by using a mold obtained by processing the steel materials for these molds. The degree of unevenness produced is divided into the degree of pass or fail. Therefore, the evaluation of the abrasiveness of the steel for the mold ultimately has to rely on the experience and the feeling of the method, that is, the working surface of the mold at the time of obtaining a good molded product, and the surface after the grinding and the surface to be evaluated are visually observed. Or the photos are compared (Patent Document 2), so that the results of the evaluation differ.

An object of the present invention is to provide a method for evaluating the abrasiveness of a steel material for a mold or a mold, which can be quantitatively measured at an optimum measurement condition at a time before the steel material for a mold is processed into an actual mold or at a time of the mold after the production. The surface properties of the molded article obtained by the mold were predicted.

The inventors of the present invention have conducted research on the degree of waviness measured on the working surface of the polished mold and the degree of unevenness of the molded article obtained by the mold. As a result, it is known that the grinding process is performed by grinding particles. The surface property of the working surface of the mold removes the element corresponding to the surface roughness of the size of the abrasive grain, and only the element of the waviness is evaluated, and the correlation between the waviness value and the degree of unevenness at this time can be confirmed. . Further, as long as the correlation can be grasped, the degree of occurrence of the unevenness can be quantitatively predicted by the measured waviness value. Therefore, the present invention has been completed by achieving the measurement conditions of the waviness associated therewith.

In other words, the present invention relates to a method for evaluating the polishing property of a steel material for a mold, wherein the surface of the steel material for a mold is polished by abrasive grains, and the waviness of the surface after the processing is measured, thereby evaluating the polishing property of the steel material for the mold. The method for evaluating the abrasiveness of the steel material for a mold is characterized in that the waviness is measured by using a cut-off value λc to satisfy (average particle diameter of the abrasive grains used in the polishing process × 10) < The waviness curve obtained by the value of the relationship of λc < (the average length WSm of the elements) was measured. Preferably, the measurement of the waviness is performed by using the average height Wc as an index.

Moreover, the present invention is a method for evaluating the polishing property of a mold, and a mold obtained by polishing a surface of a steel material for a mold by polishing grains to form a working surface of the mold, and measuring the mold after the production. The waviness of the working surface is used to evaluate the abrasiveness of the mold, and the method for evaluating the abrasiveness of the mold is characterized in that the waviness is measured by using the cut value λc to be satisfied (grinding used in the polishing process) The waviness curve obtained by the value of the relationship between the average particle diameter of the particles × 10) < λc < (the average length WSm of the elements) was measured. Preferably, the measurement of the waviness is performed by using the average height Wc as an index.

According to the present invention, the previously used mechanical properties of the steel for the mold or the actual mold can be evaluated by an appropriately processed value. Further, even if an actual mold is not used, and a small test piece is collected from a steel material before the mold is processed into the mold, the polishing property can be evaluated, and therefore, the polishing performance can be evaluated easily and at low cost.

1 is a cross-sectional curve measured on the surface of a steel material for a mold after finish polishing by a diamond slurry of #3000 in Example 1, and a waviness curve when the cutoff value is 0.160 mm. .

Fig. 2 is a metal photomicrograph showing the surface of a steel material for a mold after the finish grinding process by the #3000 diamond abrasive paste in the first embodiment.

Fig. 3 is a metal photomicrograph showing the surface of a steel material for a mold after finish polishing by a #2000 abrasive paper in Example 2.

4 is a metal photomicrograph showing the surface of a steel material for a mold after finish polishing by a #5000 diamond polishing paste in Example 2. FIG.

Fig. 5 is a metal photomicrograph showing the surface of a steel material for a mold after finish polishing by a diamond paste of #14000 in Example 2.

The present invention is characterized in that, by appropriately measuring the surface of the steel material for the mold before the processing into a mold, or the working surface when the original mold is processed (hereinafter referred to as "surface") Waviness, but can be set The degree of unevenness produced by the molded article was quantitatively evaluated. In other words, when the waviness is measured in accordance with JIS B 0601:2001, the cross-sectional curve to be measured is also an element corresponding to the size of the abrasive grains and the "surface roughness" irrespective of the occurrence of unevenness. Therefore, the waviness measured without excluding the element is that the unevenness of the molded article cannot be evaluated in a correlated manner. Therefore, in the present invention, by extracting the element of the surface roughness from the profile curve in the surface property after the polishing process, only the profile of the waviness element having a large relationship with the unevenness is appropriately extracted. From this curve, the "true" waviness value is determined.

The method for evaluating the abrasiveness of the steel material for a mold or the mold of the present invention will be specifically described. In the surface of the steel material for the mold after the grinding process or the actual mold (hereinafter referred to as the "steel material for the mold"), the waviness which is a factor causing the unevenness of the molded product is mainly due to the hardness of the steel material for the mold. Both, the undulation formed by the portion that is easy to grind and the portion that is difficult to grind. Further, since the period of the undulation is substantially larger than the abrasive grains used in the polishing process, the waviness is large, and the unevenness to the extent that can be visually confirmed is transferred to the molded article.

On the other hand, the abrasive grains used for the polishing process form a grinding mark on the surface of the steel material for a mold. The grinding marks are fine, that is, the elements of the surface roughness specified in JIS B 0601:2001. Further, the grinding marks also form undulations on the surface, but they are not so large as to cause unevenness in the molded article. In addition, when the element of the surface roughness is added to the measurement of the waviness for predicting the unevenness of the molded article, even if the above-mentioned undulation is the same level (even if the molded article is not equal) Degree), in the case of grinding more marks and grinding marks In the case of a small amount, the values of the measured waviness are different, and the quantitative relationship with the unevenness generated cannot be grasped.

Therefore, in the present invention, the influence of the grinding marks, that is, the element of the surface roughness, is removed from the profile curve for measuring the waviness. Specifically, the present invention is a method for evaluating the abrasiveness of a steel material for a mold, which is obtained by grinding a surface of a steel material for a mold by abrasive grains, and measuring the waviness of the surface after the processing, thereby evaluating the steel material for the mold. The abrasiveness is measured by the waviness curve in which the cutoff value λc is set to a value exceeding the average particle diameter of the abrasive grains. The interception value refers to a predetermined wavelength removed from the profile curve. In addition, the degree of unevenness of the molded article is sufficiently represented as the number of waviness by the cutoff value of 10 times the average particle diameter of the abrasive grains used in the polishing process. Further, it is preferable that the index (parameter) of the measured waviness is an average height Wc of the fluctuation itself which can grasp the waviness as a whole. The average height is the average of the heights of the contour curve elements of the reference length. The lower the value of the waviness measured in this way, the more excellent the polishing property of the steel material for a mold at this time. In addition, for example, the value of the waviness of the working surface of the mold when a good molded product is obtained is known in advance, and then the waviness of the surface to be evaluated is measured, and the quantitative determination of the polishing property can be performed.

The average particle diameter of the abrasive grains will be described in advance. In the prior grinding process of steel for molds, fine powder for precision polishing was used as the abrasive grains. The fine powder for precision grinding is standardized in a detailed classification according to its particle size distribution (average particle diameter). Moreover, the expression method follows the above-mentioned JIS R 6001, etc., and generally uses #1000, #2000, #3000. Etc. Number (the larger the number, the finer the grain). Further, in addition to the normalized numbered abrasive grains, finer abrasive grains with larger numbers are also proposed. The average particle diameter of these abrasive grains was measured by a sedimentation test method and a resistance test method in accordance with JIS R 6002. The precipitation test method is a method of measuring the particle diameter from the precipitation rate of particles precipitated in a dispersion medium. The electric resistance test method is a method of measuring the particle diameter by using a difference in resistance value when particles in the electrolytic solution pass through the pores. Further, the relationship between the number of the abrasive grains and the average particle diameter is roughly as follows. From these abrasive grains (for example, abrasive grains of #500 to #14000), abrasive grains having a number (average particle diameter) which is in accordance with the purpose of polishing processing are appropriately selected and used.

#500:30 μm~36 μm

#1000:14 μm~22 μm

#2000: 5 μm~10 μm

#3000:4 μm~8 μm

#4000:3 μm~6 μm

#8000:2 μm~4 μm

#14000:~2 μm

Moreover, the above-mentioned interception value requires an upper limit corresponding to the average length WSm of the element which the waviness curve at the time has. The average length of the element is the average of the lengths of the contour curve elements of the reference length, that is, the period (wavelength) indicating the waviness. Therefore, if the intercept value exceeds the period of the waviness, the element of the waviness associated with the occurrence of unevenness is removed. As a result, even when the molded article is significantly uneven, the waviness curve after the truncation is flat, and it is impossible to perform or not. The degree of production is related to the quantitative assessment. Therefore, when the waviness is measured, WSm is also measured before or at the same time, whereby by setting the cut value to be smaller than the WSm, the profile curve formed only by the element of the waviness to be mainly measured can be taken out more correctly. Thus, the accuracy of the evaluation method of the present invention is improved.

Moreover, it is preferable to adjust the conditions of the grinding|polishing process performed by the steel material for molds used for evaluation to the conditions at the time of making an actual mold. In particular, it is effective when the polishing property is evaluated at the time of processing the steel material for the mold before the actual mold. Usually, the working surface of the actual mold is a curved surface. On the other hand, the sample collected from the steel material for the mold quickly and simply is mainly a flat surface. Further, in the case where the conditions of the polishing process are greatly different, even if the values of the waviness measured after the polishing process are equal, a certain degree of difference may occur in the unevenness of the molded article.

[Example 1]

P21 steel which is a specification steel of AISI and SCM440 steel which is a specification steel of JIS are prepared, and the abrasiveness of these is evaluated. These steel grades are materials which have different surface properties after processing (that is, different abrasive properties) under the usual pre-hardening hardness applied separately, even under the same conditions. P21 steel is usually made into a steel material for molds with good abrasiveness. Further, SCM440 steel is a steel material for a mold which is made into a mold which is inferior in abrasiveness to P21 steel.

First, these steel materials were quenched and tempered, and the P21 steel which is a normal pre-hardened hardness was adjusted to 40 HRC, and the SCM440 steel was adjusted to 26 HRC, and a sample having a size of 10 mm × 10 mm × 20 mm was obtained. Next, one plane of these samples was subjected to grinding according to the conditions imposed by the actual mold making. work. The details of the grinding process are as follows: grinding one surface of two faces of 10 mm × 20 mm in parallel, grinding in the order of grinding stone, abrasive paper, diamond polishing paste, and finally using #3000 diamond polishing paste. Finishing. Further, in the case of the diamond slurry of #3000, the average particle diameter of the abrasive grains was about 6 μm.

Then, according to JIS B 0601:2001, the surface roughness measuring machine (Surfcom 570A manufactured by Tokyo Seimitsu Co., Ltd.) was used on the surface after the polishing, and the average height Wc of the waviness when various intercept values were applied was measured. The average length of the features is WSm. At this time, the arithmetic mean roughness Ra (cut value 0.08 mm) was also measured. The results of these are shown in Table 1. 1 is a cross-sectional curve measured on the surface of the two samples after the polishing process, and a waviness curve when the cut-off value is 0.160 mm. Further, an optical microscope photograph using the differential interference function for evaluation of Patent Document 2 was also taken, and thus is shown in Fig. 2 .

First, the Ra value measured under the condition that the intercept value is small depends on the size of the abrasive grains used mainly, so that no difference in values is observed between the two steel types. However, by observing the optical micrograph of Fig. 2, the waviness was confirmed by visual observation on the surface of SCM440 steel, and the fact that the abrasiveness of P21 steel was superior to the abrasiveness of SCM440 steel was confirmed. Further, the difference in the abrasiveness can be quantitatively confirmed by measuring the waviness according to an appropriate condition by expressing the Wc value of the P21 steel to be smaller than the Wc value of the SCM440 steel.

Therefore, when the cut-off value is set to be No. 1 which is smaller than the size of the abrasive grains to be used, since the waviness curve for measurement also includes the elements of the surface roughness, the SCM440 steel becomes a smaller Wc value without Show the correct assessment. Further, in No. 1, the reason why the WSm value of the SCM440 steel cannot be measured is that the intercept value is too small, and also includes many elements of surface roughness, and it is difficult to use the obtained value as WSm. In contrast, by setting the cutoff value to be large, the reliability of the Wc value of the two steels is improved, and these exhibit the correct relationship of SCM440 steel>P21 steel, and the intercept value is 10 times the size of the abrasive grain. After the above No. 3, the relationship was fully demonstrated.

However, if the interception value becomes too large, the element of the waviness to be measured is also removed from the waviness curve, and the value of the waviness is lost. Further, after No. 8, in the SCM440 steel, since the cutoff value at this time exceeds the WSm value, the WSm value cannot be determined, and the Wc value also indicates an inaccurate lower value. In No. 9, in the two steels, the intercept value exceeded the WSm value. As a result, the Wc value of the two steels became the relationship of SCM440 steel <P21 steel, and did not show a correct evaluation.

[Embodiment 2]

The modified steel of SUS420J2 steel which is a JIS specification steel grade, and the above P21 steel were prepared, and the abrasiveness of these was evaluated. First, these steels of size 100 mm × 100 mm × 10 mm were quenched and tempered, SUS420J2 modified steel was adjusted to 30 HRC, and P21 steel was adjusted to 40 HRC. Next, one plane (100 mm × 100 mm) of these samples was divided into three parts of area 50, area B, and area C of 50 mm × 30 mm by marking lines, and then implemented according to the actual mold making. Conditions are subjected to grinding processing for each area. The details of the polishing process were that the region A was subjected to a grinding process in the order of grindstone and abrasive paper, and finally finished by a #2000 abrasive paper (the average particle diameter of the abrasive grains was about 10 μm). The remaining areas B and C are ground in the order of grindstone, abrasive paper, and diamond paste, and area B is finished with #5000 diamond paste (average particle size of the abrasive particles is about 5 μm). C was finished with #14000 diamond paste (the average particle size of the abrasive particles was about 1 μm).

Next, on the respective surfaces of the regions A to C after the polishing, the average height Wc of the waviness and the average length WSm of the elements when various cut values were applied were measured in the same manner as in the first embodiment. The arithmetic mean roughness Ra (cut value 0.08 mm) was also measured. The results of the region A (average particle diameter of the abrasive grains; about 10 μm) are shown in Table 2, and the results of the region B (average particle diameter of the abrasive grains; about 5 μm) are shown in Table 3, and the region C (abrasive grains) The results of the average particle diameter; about 1 μm) are shown in Table 4. Further, an optical microscope photograph using the differential interference function for evaluation in Patent Document 2 is also shown in Fig. 3 (area A), Fig. 4 (area B), and Fig. 5 (area). C).

In the same manner as in the first embodiment, the Ra value measured under the condition that the cut-off value was small showed no difference in value between the two steel types in all the regions A, B, and C after the polishing. However, by observing the optical micrographs of Fig. 3, Fig. 4, and Fig. 5, the waviness was confirmed on the surface of the SUS420J2 modified steel by visual observation, and it was confirmed that the polishing property of P21 steel was superior to that of SUS420J2 modified steel. fact. Therefore, as long as the cut value of the present invention is selected, the relationship between the Wc value of the P21 steel and the Wc value of the SUS420J2 modified steel can be measured, thereby confirming whether or not the above fact is expressed.

<Writing paper #2000 during finishing (average particle diameter of abrasive grains; about 10 μm)>

In No. A-1 to No. A-3 which were measured at a cutoff value of less than 10 times the average particle diameter of the abrasive grains to be used, the polishing property was excellent. The Wc value of the P21 steel is a value larger than the Wc value of the SUS420J2 modified steel, and does not exhibit a correct relationship of the Wc value. On the other hand, after performing the method of the present invention and setting the cutoff value to No. A-4 which is 10 times larger than the average particle diameter of the abrasive grains, the Wc value of the P21 steel is smaller than the Wc value of the SUS420J2 modified steel, and it is exhibited. The correct evaluation result of the abrasiveness. However, in No. A-9 in which the set intercept value exceeded the WSm value, the WSm value could not be measured in any of the steel grades.

<Diamond grinding paste #5000 during finishing (average particle diameter of abrasive grains; about 5 μm)>

In the No. B-1 and No. B-2 which were measured by the cut-off value which is less than 10 times the average particle diameter, the Wc value of the P21 steel which is excellent in the polishing property becomes the size of the abrasive grain to be used. The value of the Wc value larger than the SUS420J2 modified steel does not show the relationship of the correct Wc value. On the other hand, after performing the method of the present invention and setting the cutoff value to No. B-3 which is 10 times larger than the average particle diameter of the abrasive grains, the Wc value of the P21 steel is smaller than the Wc value of the SUS420J2 modified steel, and it is exhibited. The correct evaluation result of the abrasiveness. After No. B-8 whose intercept value exceeds the WSm value, it is difficult to measure the WSm value.

<Diamond Grinding Paste #14000 When finishing (average particle diameter of abrasive grains; about 1 μm)>

The Wc value of the P21 steel is less than that of the SUS420J2 modified steel after the method of the present invention is carried out with respect to the size of the abrasive grains used and the cut-off value is set to be 10 times larger than the average particle diameter of the abrasive grains. The Wc value, while showing the correct evaluation result of the abrasiveness. In No. C-9 where the intercept value exceeds the WSm value, it is difficult to measure Set the WSm value.

Claims (4)

A method for evaluating the abrasiveness of a steel material for a mold, wherein the surface of the steel material for a mold is polished by abrasive grains, and the waviness of the surface after the processing is measured, thereby evaluating the abrasiveness of the steel material for the mold, the steel for the mold In the method of evaluating the waviness, the waviness is measured by setting the cutoff value λc to satisfy (average particle diameter of the abrasive grains used in the polishing process × 10) < λc < (average length WSm of the element) The waviness curve obtained by the value is measured. The method for evaluating the abrasiveness of a steel material for a mold according to the first aspect of the invention, wherein the measurement of the waviness is performed by using an average height Wc as an index. A method for evaluating the polishing property of a mold, and a mold obtained by finishing a surface of a steel material for a mold by grinding with abrasive grains to form a working surface of the mold, and measuring the ripple of the working surface of the mold after the production In order to evaluate the abrasiveness of the above mold, the method for evaluating the abrasiveness of the mold is characterized in that the waviness is measured by using the cutoff value λc to satisfy the average particle diameter of the abrasive grains used in the polishing process. ×10) The waviness curve obtained by the value of the relationship of λc<(the average length WSm of the elements) was measured. The method for evaluating the abrasiveness of a mold according to the third aspect of the invention, wherein the measurement of the waviness is performed by using an average height Wc as an index.