JPH0262723A - Production of aluminum substrate for memory disk - Google Patents

Abstract

PURPOSE:To produce the aluminum substrate for memory disks having high flatness by using an aluminum blank material having slight bulge from the surface edge to the surface central part of the surface to be pressurized. CONSTITUTION:The aluminum blank material 1 having the slight bulge from the surface edge part to the surface central part on the surface F to be pressurized is used in the method of producing the aluminum substrate for memory disks by holding the aluminum blank material in place between two dies 3 and 4 having smooth pressurizing surfaces and coining the material in a die ring 3 for regulating the spread limit of the material. The coining from the surface central part where the deformation resistance is high to the surface edge part where the deformation resistance is low according to this method and, therefore, the warpage of the formed aluminum substrate and the difference in the sheet thickness thereof are eventually decreased. The aluminum substrate for memory disks having the small warpage and the difference in the sheet thickness and the good quality is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of manufacturing an aluminum substrate for a memory disk with a smooth surface from an aluminum blank material.

The term "aluminum blank material" as used herein refers to a blank material made of aluminum, aluminum alloy, or a composite material thereof, and also includes an aluminum substrate.

[Conventional technology and its issues]

Memory disks used in external storage devices for electronic computers usually have a structure in which the surface of an aluminum substrate is coated with a magnetic material.

Memory disks require a high level of flatness and smoothness in order to accurately read and write with a magnetic head, but the surface condition of a memory disk depends on the surface condition of the aluminum substrate, so the aluminum substrate has extremely high dimensions. Precision and high quality surface condition are required.

Conventionally, methods for manufacturing such aluminum substrates for memory disks include (a) ultra-precision cutting of an aluminum blank using a natural diamond cutting tool, (b) polishing both sides simultaneously using a grindstone, and (Cl lapping machine). A method of simultaneously polishing both sides with abrasive grains and hot water using
However, since all of these processes involve cutting or grinding, they have the problem of being time-consuming and low productivity.

[Means for solving problems and their effects]

For this reason, recently, a method of manufacturing aluminum substrates for memory disks by coining has been studied.

In this method, as shown in Figure 1, aluminum blank material 1
is sandwiched between two dies 3 and 4 with smooth pressing surfaces in a die ring 2 that regulates the spread limit of the material, and pressurized.
An aluminum substrate for a memory disk is manufactured by coining the smooth surfaces of the dies 3 and 4 onto an aluminum blank material 1. Since this method is a press method, it has the advantage of being much more productive than cutting or grinding.

When manufacturing aluminum substrates for memory disks using this method, various experiments have shown that the pressurized surface has a slight bulge from the edge to the center of the surface, rather than using an aluminum blank with a uniform thickness. It has become clear that it is possible to manufacture an aluminum substrate for a memory disk with a high degree of flatness by using an aluminum blank material having the following properties (that is, the thickness gradually increases from the edge of the surface to the center of the surface).

That is, in the manufacturing method of the present invention, as shown in FIG. 1, an aluminum blank material 1 is sandwiched between two dies 3 and 4 with smooth pressurizing surfaces in a die ring 2 that regulates the spread limit of the material. In the method of manufacturing an aluminum substrate for a memory disk by performing a coining process, the aluminum blank material 1 has a pressurized surface F with a slight pressure from the edge to the center of the surface, as shown in Figure 2 or Figure 3. It is characterized by having a bulge.

FIG. 2 shows a case where the aluminum blank material 1 is a simple disk, and FIG. 3 shows a case where the aluminum blank material 1 is a perforated disk with a shaft hole 5 in the center. When coining a perforated disk, one of the two dies has a mandrel in the center, and the other has a recess into which the mandrel is inserted.

The reason why an aluminum substrate for a memory disk with high flatness can be manufactured by this method is considered to be as follows. In other words, when an aluminum blank material with a completely flat pressurized surface is coined, the parts with low deformation resistance (closer to the edge of the surface) are deformed first in the initial stage of processing, and as a result, the aluminum blank material There is a difference in the contact state with the pressurizing surface of the die in the radial direction, which tends to cause warpage and thickness differences in the formed aluminum substrate. On the other hand, in the case of an aluminum blank material with a bulge in the center of the surface, the coining process progresses from the center of the surface where the deformation resistance is high to the surface edge where the deformation resistance is low. It is thought that the warpage of the board and the difference in board thickness are small.

In order to create a bulge on the pressurized surface of an aluminum blank, it is necessary to remove the surface layer of the aluminum blank by some method to create a bulge. Eliminate scars,
This also has the effect of preventing defects that occur on the surface of the aluminum substrate after surface treatment such as nickel plating before coating the surface with a magnetic material. This pretreatment can be performed by any appropriate method, such as mechanical treatment of scraping off the surface layer of the aluminum blank material, chemical treatment of dissolving it with a chemical, or a combination of both.

Note that the height H of the bulge of the aluminum blank material needs to be set to an optimal value depending on the material of the die used, the size of the aluminum blank material, and the type of lubricant, but according to experiments,
The value of the height H is on the order of 100 μm or less. Exceeding this tends to worsen the warping of the aluminum substrate and the difference in thickness.

〔Example〕

The present invention will be explained in detail below.

A circular blank material was made from a JIS5086 (At-Ag alloy)-〇 material (tensile strength e -27Kg/mm") and a thickness of 1.51. The surface of this blank material is shown in Figure 2. As shown, the pressurized surface F was machined so as to have a slight bulge from the edge to the center of the surface, thereby preparing various aluminum blanks having different heights H of the bulge.

For comparison, an aluminum blank material with a flat pressurized surface was also prepared.

Coining was performed using these aluminum blanks using a die with a flat and smooth pressing surface. The diameter of the die ring is 65III11.

The results were as shown in Table-1.

Table-1 The measurement conditions are as follows.

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

Warpage was measured at four locations in the radial direction (45
The fluctuation value of the measurement length 551) was recorded, and was determined as the distance from the reference line connecting the measurement start point and end point, and was expressed as the average value of the four points.

The plate thickness difference was determined by measuring the plate thickness at nine locations and expressed as the difference between the maximum value and the minimum value.

As is clear from Table 1, it is better to use an aluminum blank whose pressurized surface has a slight bulge from the edge to the center than to use an aluminum blank whose pressurized surface is flat. We can manufacture high quality aluminum substrates for memory disks.

In the above embodiments, the case where the aluminum blank material is a disc is described, but the same applies to the case where the aluminum blank material is a perforated disc with a shaft hole in the center.

〔Effect of the invention〕

As explained above, according to the present invention, when manufacturing an aluminum substrate for a memory disk by coining with a press, an aluminum blank material whose pressurized surface has a slight bulge from the edge to the center of the surface is used. By using this method, there is an advantage that it is possible to manufacture a high-quality aluminum substrate for memory disks with extremely small warpage and plate thickness difference.

[Brief explanation of the drawing]

FIG. 1 is an explanatory view showing a method for manufacturing an aluminum substrate for a memory disk by coining, and FIGS. 2 and 3 are a front view and a sectional view, respectively, showing an aluminum blank material used in the manufacturing method of the present invention. 1 Ni aluminum blank material, 2: die ring, 3 and 4: dies, F pressurized surface of Ni aluminum blank material, H: swelling height. Figure-1 Figure-2 Figure-3

Claims (1)

[Claims] 1. In the method of manufacturing an aluminum substrate for a memory disk by sandwiching an aluminum blank material between two dies with smooth pressurizing surfaces in a die ring that regulates the spread limit of the material, and performing a coining process, the above-mentioned aluminum A method for manufacturing an aluminum substrate for a memory disk, characterized in that a blank material whose pressurized surface has a slight bulge from the edge to the center of the surface is used.