JPH0264502A - Production of precision member having specular surface - Google Patents

Abstract

PURPOSE:To obtain the precision member which is smaller in specular surface roughness than heretofore by forming a casting stock having a unidirectionally solidified structure, subjecting the stock to working at a low reduction ratio to form the worked stock and subjecting the stock to mirror finishing. CONSTITUTION:The melt of an Al-Mg alloy is poured as a magnetic disk material into a casting mold 1 and is heated to 750 deg.C by a heater 3. On the other hand, cold water is passed into a cold water pipe 4 of a holder 2 and is drawn relatively with the casting mold 1 by the holder 2, by which the cast stock having the unidirectionally solidified structure is obtd. The stock is then subjected to the working of the low reduction ratio of <=50% plastic deformation working to form the worked stock. Such worked stock has no change in the orientation between the crystal grains and does not form the aggregate of the crystal grains having various orientations even if the crystal structure changes. The steps of the grain boundaries are, therefore, slight and the specular surface having 0.02mum roughness is obtd.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is applicable to precision members that are required to have high dimensional accuracy and mirror surfaces with particularly low surface roughness, such as magnetic disks, molds, and reflectors. Concerning new manufacturing methods for mirrors, etc.

(Prior Art) A precision member having a mirror surface of this type is manufactured in the following manner in the prior art.

Taking an aluminum alloy magnetic disk as an example, (i) as shown in FIG. 6(a), a cast material (b) is produced by continuous casting from a molten aluminum alloy (a) of a predetermined composition. The structure of this casting material (b) is such that solidification starts from the part where the molten metal contacts the surface of the mold (C) and is cooled, so the outer surface layer has columnar crystals (d) that develop perpendicularly to the casting direction. It is occurring.

(ii) Cutting the surface of the casting material (b) to remove the surface segregation layer and care for it.

(iii) This treated casting material is hot roughly rolled as shown in Figure 6 (B), and further hot finished rolled as shown in Figure 6 (C) to a thickness of 2 to 3 mm. The plate material (e) has a predetermined thickness. After rolling, the sheet material has a structure consisting of an aggregate of crystal grains with various orientations.

(iv) As shown in FIG. 6(d), a disk material (f) having a predetermined shape accuracy is punched out from the plate material.

(v) Heat treatment is applied to the disc material to remove distortion.

(vi) The disk surface of the strain-removal disk material is mirror-finished by ultra-precision cutting with a diamond cutting tool.

When the precision member is a reflective mirror, the mirror surface is mirror-finished by ultra-precision cutting through the same process as above.

When the precision component is a mold, the mold surface of the cast and heat-treated mold material is mirror-finished by mirror-finishing methods such as lapping and boring.

(Problems to be Solved by the Invention) A precision member having a mirror surface manufactured by the process of the above-mentioned prior art is an aggregation of crystal grains having an arbitrary orientation in the structure of a processed material that has been processed to a predetermined dimensional accuracy. Based on the fact that it is a polycrystalline body, the mirror-finished surface is shown in the photograph in Figure 7, and grain boundaries are clearly recognized.
A step occurs at this grain boundary, and the step is 0.02 to 0.03 μm.
reach even.

Even if various improvements are made to mirror finishing methods such as ultra-precision cutting, lapping, and polishing, as well as electrolytic composite polishing, it has not been possible to make the surface roughness of the mirror surface smaller than this grain boundary step.

This is because the crystal grains that sandwich the grain boundaries have different orientations and the deformability of each grain differs, so it was virtually impossible to avoid being affected by the grain boundary step due to the difference in processing sensitivity. This is thought to be due to.

Another method of manufacturing is to use a single-crystal material from the standpoint of avoiding the effects of crystal grains with various orientations, but this reduces mechanical strength and increases cost. Many new problems will arise that require solutions. It is also possible to cover the crystalline surfaces of the material with an amorphous coating, but amorphous plating for this purpose lacks heat resistance, and its high hardness causes significant tool wear, making it difficult to achieve shape accuracy. occurs separately.

On the other hand, from the standpoint of the use of precision members having mirror surfaces, it is known that in the case of magnetic disks, the smaller the surface roughness, the better the storage density. In the case of molds, the problem is that grain boundary steps are transferred to the product. Further, in the case of a reflective mirror, there is a problem in that it may cause diffused reflection. In order to meet these demands, it is desirable to further reduce the surface roughness of the mirror surface by minimizing the influence of grain boundary steps in the material.

(Means for Solving the Problems) The present invention has been made in order to overcome the limitations of surface roughness of mirror surfaces caused by conventional manufacturing methods and to improve the functions of precision members having mirror surfaces. , a cast material having a unidirectional solidification structure is created, and processed including plastic deformation processing at an allowable degree of processing to obtain a processed material with the shape and dimensional accuracy of a finished precision part, and then a predetermined surface is Give it a mirror finish.

In other words, in other words, by reversing the process order, in order to perform mirror finishing based on a finished precision part, a workpiece having the shape and dimensional accuracy of a precision part is transformed from a casting material to a casting material. Hot and cold plastic deformation processing, machining processing such as cutting, polishing, and punching, and heat treatment such as strain relief annealing shall be applied to the extent necessary, but the plastic deformation processing included in these shall be kept below a certain level, and The shape of the casting material having a unidirectional solidification structure is given to match this.Thus, a manufacturing plan for the series is formulated and construction conditions are determined so that the number of processing steps is minimized.

In this way, the surface roughness will be 0.02μm Rmax
A new precision component with a smaller mirror surface is obtained. In addition, for that purpose, the plastic deformation processing rate mentioned above must be 50 at the total processing rate.
It is best to keep it below %.

If the precision member is a plate material such as a magnetic disk or a reflective mirror having a flat mirror surface, the total reduction ratio of hot or cold rolling applied as plastic deformation processing should be 50% or less.

That is, the method for manufacturing a precision member having a mirror surface according to the present invention is as follows:
The structure is to create a cast material with a unidirectional solidification structure from a molten alloy of a predetermined composition, process this cast material including plastic deformation processing at a low processing rate to obtain a processed material into a predetermined member shape, and then process the processed material into a predetermined member shape. It is characterized by applying a mirror finish to a predetermined surface.

(Function) According to the method of the present invention, even if a cast material having a unidirectional solidification structure is subjected to various processing in the process of shaping into a precision member having the required dimensional accuracy, the plastic deformation processing is less than 50%. As long as the processing rate is kept low, even if the grain structure changes, there is almost no change in the orientation between grains, and the original orientation is maintained, resulting in an aggregate of grains with various orientations. Never. Therefore, when mirror-finishing is performed using ultra-precision cutting using a diamond tool, etc., the difference in machining sensitivity of each grain, and therefore the grain boundary step, will be slight even if it occurs, and the surface roughness will be less than 0.02 μm Rmax. A super mirror surface can be obtained.

This does not change even if electrolytic composite polishing, lapping, or borising is used as a mirror finishing method in addition to the above-mentioned methods.

The manufactured precision parts with mirror surfaces with small surface roughness are
A magnetic disk has a higher storage density than conventional disks, and the problems of conventional molds and reflective mirrors are reduced or eliminated.

(Example) (I) Magnetic disk (A) Using the apparatus shown in FIG. 1, the open side of the graphite inner mold (1) is closed with a holder (2) to form a magnetic disk material.
Molten f1-Mg alloy (JIS 5086/equivalent) is injected and held and heated to 750'C with a heater (3), while cooling water is circulated through the cooling water pipe (4) to the holder (2) on that side. While cooling and starting solidification, the holder (2) is retreated at a speed of 0.5 mm/min relative to the mold (1) and the solidified material is pulled out.
A cast material having a unidirectional solidification structure of 5IIIT11, a thickness of 20 mm, and a length of 250 mm was prepared.

This cast material was cold-rolled and hot-rolled at various rolling reductions ranging from the present invention example to the comparative example to create a plate-shaped material.

After heat treatment, mirror polishing was performed by ultra-precision cutting using a diamond cutting tool, and the surface roughness of the resulting mirror surface was measured.

Figure 3 shows the results, and the horizontal axis shows the total reduction rate of rolling (
%) and the surface roughness Rmax (nm) is plotted on the vertical axis, with white circles indicating cold rolling and black circles indicating hot rolling. In the range where the processing rate indicated by the total rolling reduction is 50% or less, Rma is 0.02 μm or less, which is within the range of the present invention example, and in the comparative example where the rolling reduction is above this limit, the surface roughness remains at the conventional level. known.

(n) Magnetic disk (B) A plate-shaped material obtained in the same manner as in Example (1) was subjected to electrolytic composite polishing as mirror finishing.

FIG. 4 shows the results in a similar representation to FIG. However, cold-rolled items are shown with white angle of view marks, and hot-rolled items are shown with black angle of view marks.

In this case, as in Example (1), when the total reduction rate of rolling is 50% or less, the mirror surface roughness Rmax is 0.02
It is smaller than μm.

(I [[) Magnetic disk (C) In this example, a cast material having a unidirectional solidification structure is
It was prepared using the apparatus shown in Fig. 2, which is based on Japanese Patent Publication No. 55-46265.

That is, the same ^1-Mg alloy molten metal of 690″C as described above is poured from the tundish (5) into the mold (6).

The molten metal poured into a graphite mold hole with a hole cross section of 60mm wide and 20n+m thick in the mold (5) is heated by a heater (7
) to keep the whole body warm at 660°C.

On the other hand, a nozzle (8) for spraying cooling water was provided on the outlet side of the mold, and the cooling water was supplied at a rate of 2.012/min, and the solidified casting material (9) of the above dimensions was gummy-i". (0
0) followed by pinch roll (11) grinning 40m
It is pulled out from the mold at a speed of /min.

The cast material (9) thus obtained has a unidirectional solidification structure.

This cast material was rolled under the same conditions as in Example (1), and the obtained plate material was subjected to ultra-precision cutting with a diamond cutting tool to give it a mirror finish, and the surface roughness was measured.

FIG. 5 shows the results in the same way as before.

However, cold-rolled products are indicated by a white square mark, and hot-rolled products are indicated by a black triangle mark.

It can be seen that the same surface roughness results as before can be obtained.

(rV) Mold main component C: 0.5'g, S(: 0.3XSMn:
0.1χ, Fe: bal mold steel ()! RC40
) A cast material with a unidirectionally solidified structure was created, and the mold surface was mirror-finished in the following process order.

(i) Turning, (ii) Surface grinding (WAI1120), (iii) Lapping (Persimmon #2000, WA #4000, WAI$800
0 order) (iv) Diamond lapping (diamond grain size 1 μm) (V) Diamond lapping (diamond grain size 0.5 μm) The surface roughness of the obtained mirror surface was measured and the average value of 10 points was 0. 018μva Rmax and SO
, 02 μm smaller than Rn+ax).

(Effects of the Invention) As described above, according to the method of the present invention, it is possible to obtain a precision member whose mirror surface roughness is smaller than that obtained using the conventional technique, and whose functions as a magnetic disk, a reflective mirror, a mold, etc. are improved. In addition, the number of processing steps for this purpose can be reduced, and there is no need to rely on special processing techniques.

[Brief explanation of the drawing]

Figure 1 shows one of the situations in which a specific casting material is produced in the present invention.
Fig. 2 is a side view schematically showing a vertical cross section of the device showing an example, Fig. 3 is a side view schematically showing a longitudinal cross section of the device showing another example, and Fig. 3 is a comparison example based on the relationship between the plastic deformation processing rate on the horizontal axis and the specular surface roughness on the vertical axis. Figure 4 is a diagram showing one example of the results of implementing the present invention, Figure 4 is a diagram showing other examples, Figure 5 is a diagram showing other examples, Figure 6 is the prior art, and Figure 6 (A) is the casting situation. Figure 6 showing
Figure (B) shows the rough rolling, Figure 6 (C) shows the finish rolling, Figure 6 (D) shows the disk punching situation, and Figure 7 shows the mirror finish of the conventional technology. This is a micrograph of the surface of . (1)...Mold, (2)...Holder, (3)...
Heater, (4)...Cooling water pipe, (5)...Tandish, (6)...Mold, (7)...Heater,
(8)... Cooling water nozzle, (9)... Casting material, G
O)...Dummy par, 01)...Pinch roll, (
a)... Molten metal, (b)... Casting material, (C)...
Mold, (d)...Columnar crystal, (e)...Plate material, (f)
...Disc material. 1 Figure K 21 Figure 7 I'm wearing it, and I'm totally under pressure (phantom). Figure 5: Total pressure (%) (A) Figure: Total pressure and C'l> Atsushi Figure 6 (C) Procedural amendment (method) Indication of the case Patent application No. 217975 of 1988 2゜Name of the invention Mirror surface Patent related to the case of a person making an amendment to the manufacturing method of a precision component having a 3° Applicant: 1-3-18 (119) Wakihama-cho, Chuo-ku, Kobe City, Kobe Steel, Ltd. Representative: Sokichi Kame Taka 4° Person 〒650 (Shipping date: November 29, 1988) Contents of the 7° correction

Claims (3)

[Claims] (1) Create a cast material with a unidirectional solidification structure from a molten alloy of a predetermined composition, process the cast material including plastic deformation at a low processing rate to obtain a processed material into a predetermined member shape, and process the processed material into a predetermined member shape. 1. A method for manufacturing a precision component having a mirror surface, the method comprising applying a mirror finish to a predetermined surface of the component. (2) The method for manufacturing a precision member having a mirror surface according to claim 1, wherein the processing rate of the plastic deformation processing is 50% or less. (3) The method according to any one of claims 1 and 2, wherein the plastic deformation process is performed by rolling at a reduction rate of 50% or less to form the processed material into a plate shape, in order to produce a plate-shaped precision member. A method for manufacturing precision parts with mirror surfaces.