JPH0638963B2 - Method for manufacturing metal substrate for memory disk - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a metal substrate for a memory disk whose surface is ultra-flat and ultra-smooth from a metal blank material. The metal blank material referred to here is aluminum, aluminum alloy, copper, copper alloy, magnesium, magnesium alloy, titanium, titanium alloy,
It means a non-magnetic metal blank material made of an austenitic stainless steel material or the like or a composite material thereof, and a metal substrate has the same meaning.

[Prior art and its problems]

Conventionally, a memory disk that stores and reproduces various kinds of information (characters, voices, images, etc.) is usually a donut disk-shaped metal substrate, for example, an aluminum alloy substrate (substrate) whose surface is ultra-precision finished, coated with a magnetic substance. It has a structure. The memory disk is required to have a high level of flatness and smoothness in order to accurately store and reproduce data on the magnetic head, but the surface condition of the memory disk depends on the surface condition of the metal substrate. Requires extremely high dimensional accuracy (flatness such as waviness and warpage) and high quality surface condition (mirror-like surface without defects, smoothness).

Conventionally, as a method for producing such a metal substrate for a memory disk, a metal such as an aluminum alloy blank is used.
There are (a) a method of ultra-precision cutting with a natural diamond bite, (b) a method of simultaneously polishing both sides with a grindstone, (c) a method of simultaneously polishing both sides with abrasive grains and warm water using a lapping machine, etc. Also, since it is processing by cutting or grinding, processing takes time, productivity is poor,
Moreover, there was a problem that many equipments were required.

[Means for solving problems and their effects]

In view of the problems of the prior art as described above, the present invention provides a highly versatile metal substrate for a memory disk, which has a very high productivity using coining by a press and the quality thereof is at least as good as that of the conventional production method. It provides a method.
The coining process is a technique that is usually used in the manufacture of coins, and the general method is to press the material with a die that has an uneven pattern on the pressing surface to form the uneven pattern on the material surface. . The present invention is different from the formation of such a concavo-convex pattern, and a metal substrate for a memory disk that simultaneously and super-precisely finishes both surfaces of a substrate by imprinting a smooth surface on a metal blank material using a die with a smooth pressing surface. The present invention provides a method for manufacturing the same.

That is, according to the manufacturing method of the present invention, as shown in FIG. 1, the metal blank material 6 is placed in the mold ring 3 and the core metal 4 for controlling the spread limit of the material, or as shown in FIG. Then, the mold ring 3 is sandwiched between two dies 1 and 2 having a smooth pressing surface, and the pressing force P (kg / mm ² ) of the dies is set to the tensile strength σ _B (kg / mm ² ) less than 5 times
The plate thickness reduction rate of the metal blank material is 4% or less, the surface roughness Rmax of the metal blank material is 20 μm or less, the lubricant application amount on the surface is 1000 mg / m ² or less, and the pressing surface of the die is Surface roughness Rmax of 0.20
When the thickness is less than or equal to μm, coining is performed to manufacture a metal substrate for memory disk having excellent surface characteristics.

In the method of the present invention, the reason for coining the blank material in the mold for controlling the spread limit of the material is to regulate the flow of the material to easily transfer the precisely finished die surface to the surface of the molded product. This is because it is possible to obtain a molded product having excellent surface accuracy (roughness). Further, by coining in this way, it is possible to obtain an outer diameter and an inner diameter with good dimensional accuracy.

Also, the reason why the pressing force P (kg / mm ² ) of the die is 5 times or less of the tensile strength σ _B kg / mm ² ) of the metal blank material is that when the pressing force exceeds 5 times, the pressing force becomes excessive. "Waviness" of metal substrate
This is because the flatness such as “warpage” and the “plate thickness difference” become large, and the dimensional accuracy is impaired. Since it is coining, as a matter of course, the pressing force of the die needs to be at least large enough to transfer the smoothness of the die pressing surface to the metal blank material. The lower limit of this pressure is usually the elastic limit (0.
It is about half of the proof stress of blank material in the area exceeding 1% elongation).

Next, the reason why the thickness reduction rate of the metal blank material is set to 4% or less is that if it exceeds 4%, the flow of the material due to coining becomes too large, and the “waviness” or “sledding” of the manufactured metal substrate is also caused. This is because there will be adverse effects. The plate thickness reduction rate m is calculated by the following equation.

However, t ₀ : plate thickness before coining (mm) t: plate thickness after coining (mm) This plate thickness reduction rate is due to the diameter difference between the ring and the core metal and the metal blank when the blank is doughnut-shaped. Is determined. That is, as shown in FIG. 1, the outer diameter of the blank 6 is made slightly smaller than the inner diameter of the ring 3, and the inner diameter of the blank is made slightly larger than the outer diameter of the core metal. When processed, the area of the metal blank material 6 expands outward and inward, and the plate thickness decreases. However, since the expansion of the metal blank material 6 is restricted by the ring 3 and the core metal 4, the metal blank material 6 Is expanded to completely fill the voids inside the ring 3 and the voids outside the cored bar 4, the plate thickness no longer decreases. Therefore, in order to adjust the plate thickness reduction rate, if the inner diameter of the ring 3 and the outer diameter of the cored bar 4 are constant,
It is only necessary to change the outer diameter and the inner diameter of the metal blank material. If the blank is disk-shaped, then only the outer diameter needs to be considered.

The metal blank materials referred to here are Al, Al alloys, Cu, Cu alloys, M
It means g, Mg alloys, Ti, Ti alloys, austenitic stainless steel materials and composite materials thereof, and these applications are possible. For example, it is possible to easily obtain a highly accurate surface by coining even for a composite material obtained by cladding pure Al, Cu or the like, which is difficult to cut or grind, into a high-strength alloy. The reason why it is preferable to use a pure metal for the surface layer of the substrate is that there are no material defects and preferable results can be obtained by the subsequent Ni plating or anodizing treatment. Further, a composite material in which a hard material such as an austenitic stainless steel is clad on an Al alloy can be applied.

In the method of the present invention, the pressing force P (kg / mm ² ) of the die is set to 5 times or less the tensile strength σ _B (kg / mm ² ) of the metal blank material, but the blank material is a composite material. In some cases, the average tensile strength of the composite as a whole applies. Although the memory disk finally has a donut-shaped shape, the metal substrate in the method of the present invention may be manufactured by coining a donut-shaped blank material as shown in FIG. The blank material may be coined as shown in FIG. 2 and then the inner diameter may be punched to form a donut shape.

Further, in the method of the present invention, since the pressing surface of the die is transferred to the blank and at the same time the surface of the blank is subjected to plastic working, the pressing surface of the die is used with ultra-precision finishing.

According to the method of the present invention, by coining a metal blank material, surface accuracy (flatness,
Smoothness). Moreover, it is possible to process both sides at once.

Therefore, as compared with the conventional cutting and grinding methods, it is possible to omit a large number of steps, and it is possible to manufacture a memory disk substrate with extremely high productivity.

The metal substrate for memory disk obtained by the method of the present invention can be applied not only as a magnetic recording system but also as a disk substrate by an optical recording system.

Example An example was carried out by using the coining device and the disc-shaped blank material shown in FIG. (Preliminarily, a disc blank with the same outer diameter (about 65 mm) and a donut blank (inner diameter 15 mm) were coined and compared, but the results of the disc blank material are shown because the characteristic values do not differ greatly. ) First, 5086-O material (Al-Mg alloy, tensile strength σ _B = 27 kg /
A circular blank material was prepared from a plate material having a length of ² mm and a length of 1.5 mm. The outer diameter of the blank is 65 mm inside the ring of the coining machine.
On the other hand, the plate thickness reduction rate was set to 1%. The surface roughness Rmax of the blank material is 1.50 μm (average at 5 points). The die pressing surface is flat, and its surface roughness Rmax is 0.20 μm (5
The average of the points). 50 mg / m on both sides of the blank
^Two lubricants were applied. The lubricant is Nippon Machine Oil Co., Ltd.
G6311 (Kinematic viscosity 1.0, 20 ° C. cst, oil film strength 10 kg / cm ² ) manufactured by G6311 was used.

Table 1 shows the results of coining under different conditions by changing the pressure applied to the die.

The surface gloss of the molded products was all good.

The measurement conditions are as follows.

The pressing force P is a value obtained by dividing the pressing force at the time of imprinting by the surface area of the blank material.

The waviness was recorded as a variation value of one revolution by a film meter in a φ50 mm line of the molded product, and displayed as a difference between the maximum value and the minimum value.

The sled recorded a variation value at four points (intervals of 45 °) at a measurement length of 55 mm, calculated the distance from a reference line connecting the measurement start point and the end point, and displayed the average value at four points.

The plate thickness difference was measured as the difference between the maximum value and the minimum value by measuring the plate thickness at 10 locations.

The surface roughness is an average value of 5 points.

The surface gloss is the result of visual observation.

All of the above was done for 10 cards.

As for the number of built-ups (adhesion of material to the die pressing surface), the pressing surface was observed after every 100 continuous molding, and the occurrence of built-ups was grasped. For example, the number of built-up occurrences is 20
00 means that built-up did not occur during molding of 2000 sheets, but built-up was observed during molding of 2100 sheets.

From the above results, it is apparent that the surface state of the die pressing surface is transferred to the blank material by coining, and a molded product having good surface roughness and gloss can be obtained. Especially, when the applied pressure P is set to 5 times or less of the tensile strength σ _B of the blank material, the waviness, warpage and plate thickness difference of the molded product become small, and it is clear that it is suitable for manufacturing a metal substrate for a memory disk. It is also clear that if the number is 5 times or less, the number of sheets until the build-up occurs is large and the productivity is good.

Next, in order to investigate the influence of the change in the sheet thickness reduction rate, an experiment was performed in which the pressing force P was kept constant at 81 kg / mm ² (3 times σ _B ) and the sheet thickness reduction rate was changed. The results are shown in Table 2.

The surface gloss of the molded products was good except that Comparative Examples 8 to 10 had some cloudiness.

According to this result, it is understood that when the plate thickness reduction rate is set to 4% or less, the undulation, warpage and plate thickness difference of the molded product can be reduced.

Next, when the applied pressure P is set to 5 times the tensile strength σ _B and the plate thickness reduction rate m is set to 3.4% (Example 11), the undulation of the molded product is 19 μm, the warp is 2.2 μm, and the plate thickness is Difference of 19 μm, surface roughness R
The maximum was 0.24 μm, the surface gloss was good, and it was almost good as a whole.

By the way, according to the above results, it is apparent that the surface roughness, which is one index indicating the quality of the memory disk metal substrate, is hardly affected by the pressing force and the plate thickness reduction rate. Therefore, when further examining the factors affecting the surface roughness of the molded product, the amount of lubricant applied,
It was found that the surface roughness of the blank material and the surface roughness of the die pressing surface are related.

First, the applied pressure P is 81 kg / mm ² depending on the amount of lubricant applied.
(Three times σ _B ), 1% reduction in plate thickness, 1.50 μm blank surface roughness Rmax, and 0.5 mm die pressing surface surface roughness Rmax.
When the lubricant application amount was changed by setting the thickness to 20 μm, the results shown in Table 3 were obtained.

According to this result, the amount of lubricant applied has the advantage that the number of sheets until buildup occurs increases if this amount is increased,
When it exceeds 1000 mg / m ² , the surface roughness of the molded product deteriorates, so it is understood that 1000 mg / m ² or less is suitable for the production of the aluminum substrate for memory disk.

Next, regarding the influence of the surface roughness of the blank material,
81 kg / mm ² (3 times σ _B ), 1% reduction in thickness, 50 mg / m ² lubricant coating amount, 0.20 surface roughness Rmax of die pressing surface.
When the surface roughness of the blank was changed by setting the thickness to μm, the results shown in Table 4 were obtained.

According to this result, the surface roughness of the molded product is affected by the surface roughness of the blank material, but in order to make the surface roughness of the molded product comparable to the surface roughness of the die pressing surface, It is desirable that the surface roughness be 20 μm or less.

Next, regarding the influence of the surface roughness of the die pressing surface, the pressing force P
81 kg / mm ² (3 times σ _B ), plate thickness reduction rate 1%, lubricant application amount 50 mg / m ² , blank material surface roughness Rmax 1.50μ
When m was set and the surface roughness of the die pressing surface was changed, the results shown in Table 5 were obtained.

According to this result, it is clear that the surface roughness of the molded product is almost directly affected by the surface roughness of the die pressing surface. The shape of the die pressing surface is transferred to the surface of the molded product,
Since the surface roughness of the molded article does not become better than the surface roughness of the die pressing surface, it is understood that the surface roughness of the die pressing surface should be at least smaller than the required surface roughness of the molded article.

Although not shown in the table, it is clear that the waviness, warpage, and plate thickness difference of the molded product are hardly affected by changes in the lubricant coating amount, the blank material surface roughness, and the die pressing surface surface roughness. I'm running.

Next, 1100-O material (pure Al, tensile strength σ _B = 9 kg / mm ² ),
A circular blank material was manufactured from a plate material having a thickness of 1.5 mm, and the test was conducted under the same conditions as above. The results are as follows.

From the above results, it is found that pure aluminum has the same tendency as that of the aluminum alloy. Although not described in this embodiment, the same can be said for the above-mentioned other metal materials other than aluminum and aluminum alloy.

〔The invention's effect〕

As described above, according to the present invention, a metal substrate for a memory disk having excellent surface characteristics can be manufactured by coining with a press, which is an advantage that the production speed is remarkably improved as compared with the conventional manufacturing method by cutting and grinding. There is. Further, the die pressing force P (kg / mm ² ) for coining was set to 5 times or less of the tensile strength σ _B (kg / mm ² ) of the metal blank material, and the plate thickness reduction rate of the metal blank material was set to 4% or less. By the way,
There is an advantage that it is possible to manufacture a good quality metal disk substrate for a memory disk, in which waviness, warpage and plate thickness difference are extremely small. Further, during coining, the surface roughness Rmax of the metal blank material
Is 20 μm or less, and the amount of lubricant applied to the surface is 1000
and mg / m ² or less, by the surface roughness Rmax of the die pressing surface was less 0.20 [mu] m, an advantage of producing a metal substrate for high-quality memory disk with a smaller smooth surface of surface roughness.

[Brief description of drawings]

FIG. 1 is a sectional view showing a method for manufacturing a metal substrate for memory disk according to an embodiment of the present invention. FIG. 2 is an explanatory view of the coining machine used in the embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Upper die, 2 ... Lower die 3 ... Mold (ring), 4 ... Mold (core metal) 5 ... Recessed portion to which core head is fitted 6 ... Metal blank material

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Jun Yamazaki 1750 Kiyotaki Arasawa-cho, Nikko City, Tochigi Prefecture (56) Reference JP-A-57-185964 (JP, A) JP-A-58-141828 (JP, A) ) JP-A-62-47822 (JP, A) JP-A-61-502787 (JP, A)

Claims (1)

[Claims] 1. A metal blank material is sandwiched between two dies having a smooth pressing surface in a die for controlling the spread limit of the material, and the pressing force P (kg / mm ² ) of the die is set to the above. The tensile strength σ _B (kg / mm ² ) of the metal blank is 5 times or less, the plate thickness reduction rate of the metal blank is 4% or less, and the surface roughness Rmax of the metal blank is 20 μm or less, The amount of lubricant applied to the surface is 1000 mg / m ² or less, and the surface roughness Rmax of the pressure surface of the die is 0.20 μm.
A method for manufacturing a metal substrate for a memory disk, which comprises performing coining.