JP7764262B2 - Base member and manufacturing method thereof, spindle motor, and hard disk drive - Google Patents

Description

The present invention relates to a base member for an electronic device such as a hard disk drive, and in particular to a technique for forming protrusions that stand on the base member for mounting components. The present invention also relates to a spindle motor and a hard disk drive that use the base member.

Hard disk drives are equipped with various components such as pivot bearings, voice coil motors, and ramps, and their base members often have protrusions formed integrally with the base member by casting to allow for the assembly of these components. After the base member is cast, the outer periphery of the protrusion and the component mounting surface are simultaneously finished using, for example, a forming tool.

The forming tool has a cylindrical tip and is equipped with cutting tools on its tip surface and inner peripheral surface. An arc-shaped R-chamfer is formed where the cutting tools on the tip surface intersect with the cutting tools on the inner peripheral surface. Dedicated forming tools are prepared for each dimension of the protrusion.

US2019-348071 publication

However, due to the R-chamfered portion on the forming tool, the lower end of the outer peripheral surface of the protrusion is formed with an R-shape that follows the shape of the cutting tool after finishing. If the part comes into contact with this R-shape, the assembly accuracy of the part will decrease.

Furthermore, in finishing processes using forming tools such as those described above, the forming tool must be raised and lowered for each protrusion. As a result, the height of the component placement surface on which the components for the protrusions are placed is affected by the height positioning accuracy of the forming tool for each protrusion. Hard disk drives require further improvements in precision, such as reducing air resistance by sealing in low-density gas. Against this background, improvements in the assembly precision of each component inside the device are also required.

Furthermore, because the forming tool, which rotates around the central axis of the protrusion, is pressed against the part-mounting surface during processing, chatter vibrations are likely to occur due to resistance from the cutting surface. As a result, undesirable cutting marks are formed on the part-mounting surface after finishing, raising concerns that this could adversely affect height accuracy due to increased surface roughness.

The present invention was made in consideration of the above circumstances, and aims to provide a base member that eliminates the effect of the R-shape formed at the bottom end of the outer peripheral surface of the protrusion after finishing, thereby improving component assembly accuracy as well as the height accuracy of the component mounting surface.

The present invention is a method for manufacturing a base member that forms part of the housing of a hard disk drive device, and includes a molding process in which a base body having a protrusion that protrudes upward is formed by casting; a first machining process in which an undercut portion is formed by digging out a portion from the outer circumferential surface of the protrusion to the radially outward direction; and a second machining process in which the undercut portion or an area outside the area where the undercut portion is to be formed is cut by moving a rotary tool having a cutting tool on its lower end surface relatively in the horizontal direction.

The present invention also provides a base member that forms part of the housing of a hard disk drive device, comprising a base main body, a protrusion erected on the base main body, an undercut portion dug out at the base of the protrusion, and a machined portion on the outside of the undercut portion, wherein the machined portion has cutting marks formed in the shape of a continuous arc that is not centered on the central axis of the protrusion.

According to the present invention, the R-shape formed at the lower end of the outer peripheral surface of the protrusion after finishing is located at the bottom of the undercut portion, which not only improves the assembly accuracy of components, but also provides a base member, spindle motor, and hard disk drive that can improve the height accuracy of the component mounting surface.

1 is a perspective view showing a hard disk drive device according to an embodiment of the present invention; 1 is a cross-sectional view showing a hard disk drive device according to an embodiment of the present invention. 1 is a cross-sectional view showing a spindle motor according to an embodiment of the present invention. FIG. 2 is a plan view showing a base member according to the embodiment of the present invention. FIG. 4 is a rear view showing the base member according to the embodiment of the present invention. 1A and 1B are cross-sectional views showing machining steps for a protrusion, in which (A) is a machining step using a conventional forming tool, (B) is a first machining step in an embodiment of the present invention, and (C) is a second machining step in an embodiment of the present invention. 1A and 1B are cross-sectional views showing machining steps for a protrusion, in which (A) is a machining step using a conventional forming tool, (B) is a first machining step in an embodiment of the present invention, and (C) is a second machining step in an embodiment of the present invention. 1A and 1B are cross-sectional views showing machining steps for a protrusion, in which (A) is a machining step using a conventional forming tool, (B) is a first machining step in an embodiment of the present invention, and (C) is a second machining step in an embodiment of the present invention. 1A and 1B are cross-sectional views showing the machining process of the protrusion portion in an embodiment of the present invention, in which (A) shows the second machining process, (B) shows the state after electrolytic coating, and (C) shows the first machining process. 1A to 1D are cross-sectional views showing the machining process of a protrusion in an embodiment of the present invention, where (A) is a first machining process, (B) is a second machining process, (C) is a second machining process, and (D) is a first machining process.

1. Hard Disk Drive Device FIG. 1 is a schematic perspective view showing the overall configuration of a hard disk drive device 10 according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along a plane including the rotation axis. As shown in these figures, the hard disk drive device 10 includes a base member 400 and a housing 402 formed by a recess 401 having a bottom surface 404. The housing 402 includes a spindle motor 100 and multiple hard disks 13 attached to the spindle motor 100 for rotation. The hard disk drive device 10 also includes a swing arm 11 supporting multiple magnetic heads 12 facing the hard disks 13, a pivot bearing 19 rotatably supporting the swing arm 11, an actuator 14 driving the swing arm 11, and a control unit 15 for controlling these components. The hard disk drive device 10 includes a housing formed by the base member 400 and a cover (not shown) attached to the base member 400 to seal the housing 402. The height of the housing (the dimension from the back surface of the base member 400 to the axial top of the front surface) is 1.5 inches or more and less than 2 inches, and a gas with a density lower than air, such as helium, is sealed inside the housing.

3 is a cross-sectional view of the spindle motor 100 according to the embodiment, taken along a plane including the rotation axis. The spindle motor 100 includes a base member 400 and a shaft 20 fixed to the base member 400. Conical bearing members 201 and 301 are fixed to the shaft 20 and spaced apart from each other in the axial direction, forming bearings 200 and 300.

The base member 400 has a cylindrical portion 101a that extends axially upward on the shaft 20, and a stator core 103 is fixed to the outer periphery of the cylindrical portion 101a. The stator core 103 is made by laminating multiple thin, annular sheets of soft magnetic material (e.g., electromagnetic steel sheets) in the axial direction, and has multiple pole teeth that protrude radially outward. The multiple pole teeth are arranged at equal intervals along the circumferential direction, and each has a coil 104 wound around it.

The rotating part of the spindle motor 100 includes a rotor 110. The rotor 110 includes a cylindrical portion 111, with an annular rotor magnet 113 fixed to the inner surface of the cylindrical portion 111. The rotor magnet 113 is magnetized so that adjacent portions along the circumferential direction, SNSN..., alternately have opposite polarities. The inner periphery of the rotor magnet 113 faces the outer periphery of the pole teeth of the stator core 103 with a gap between them. Supplying a driving current to the coil 104 generates a driving force that rotates the rotor magnet 113, causing the rotor 110 to rotate around the shaft 20 relative to the shaft 20 and base member 400. This principle is the same as that of a normal spindle motor.

A flange portion 114 extending radially outward is formed on the periphery of the lower end of the cylindrical portion 111. The flange portion 114 functions as a disk mounting portion for stacking multiple hard disks 13. As shown in FIG. 2, hard disks 13 are mounted on the flange portion 114, and hard disks 13 are stacked one after another with spacers 16 interposed between them, for a total of seven or more hard disks 13 (21 in this example). Note that the number of hard disks 13 does not have to be 21, and may be more than 21. The top hard disk 13 is fixed to the rotor 110 by a clamp 18 attached to the top surface of the rotor 110 with screws 17.

3. Base member
The base member 400 of this embodiment will be described with reference to Figures 4 to 10. Figure 4 is a plan view of the base member, and Figure 5 is a rear view. The base member 400 is manufactured by die-casting of aluminum. Various pin portions (protrusions) are formed integrally with the base member 400 on the bottom surface 404 of the base member 400. The various pin portions and their manufacturing methods will be described below.

In Figure 4, reference numeral 410 denotes the pin portion (protrusion) for attaching the aforementioned pivot bearing 19, and Figure 6 shows a cross section taken along line A-A in Figure 4. As shown in Figure 6(C), an undercut portion 411 is formed around the pin portion 410 by carving out a predetermined area radially outward from the outer peripheral surface, and a component placement portion 412 is formed around the undercut portion 411 and is positioned higher than the bottom surface 404 of the base member 400. The depth to which the undercut portion 411 is carved out from the component placement portion 412, i.e., the difference in height between the bottom of the undercut portion 411 and the component placement portion 412, is smaller than the axial height of the component placement portion 412 relative to the bottom surface 404.

Figure 6(A) shows a conventional machining method for finishing the pin portion 410 using a forming tool T1. The forming tool T1 has a horizontal blade C1 on the tip surface of its cylindrical tip and an inner peripheral blade C2 on its inner peripheral surface. The inner peripheral blade C2 is inclined so that its inner diameter decreases as it extends downward. When the central axis of the forming tool T1 is aligned with the central axis of the pin portion 410 and the forming tool T1 is rotated and lowered, the R-chamfered portion C3 at the intersection of the inner peripheral blade C2 and the horizontal blade C1 cuts the outer peripheral surface of the pin portion 410, and when the horizontal blade C1 reaches the component placement portion 412, the component placement portion 412 is cut by the horizontal blade C1.

In this type of finishing process, a rounded shape R is formed at the base of the pin portion 410, and when a part is attached to the pin portion 410, the rounded shape R comes into contact with the part, making it difficult to achieve the desired height accuracy for the part. Furthermore, the position of the lowering end of the forming tool T1 varies depending on the height positioning accuracy of the processing equipment, resulting in variation in the height of the part placement portion 412 for each pin portion 410.

Figures 6(B) and (C) show a machining method according to an embodiment. As shown in Figure 6(B), the forming tool T2 has a cylindrical tip end surface equipped with a horizontal blade C4 extending radially outward and an inclined blade C5 extending diagonally upward from the radially outer end of the horizontal blade C4, and an inner peripheral blade C6 on the inner peripheral surface that is inclined so that the inner diameter decreases downward.

When machining using the forming tool T2, the outer surface of the pin portion 410 is cut by the R-chamfered portion C7 at the intersection of the inner peripheral blade C6 and horizontal blade C4, and when the horizontal blade C4 reaches the component placement portion 412, the component placement portion 412 is cut by the horizontal blade C4 and the inclined blade C5. This forms the undercut portion 411. In addition, an R-shape R is formed at the base of the pin portion 410 at the undercut portion 411.

Next, as shown in Figure 6(C), the component placement portion 412 is finished using an end mill E. This finishing process involves cutting the portion above the two-dot chain line in Figure 6(B). The base member 400 is attached to the table of the processing device, and the end mill E is attached to the chuck. The table is then moved up and down and fixed to the set vertical position relative to the end mill. The end mill E is then rotated while the table is moved horizontally to approach the component placement portion 412, cutting the component placement portion 412. The movement trajectory of the end mill E relative to the table forms a circle centered on the central axis of the pin portion 410. The top surface of the pin portion 410 is then cut with the end mill E, thereby achieving height precision for the pin portion 410.

The ratio (Y/X) of the axial length Y of the pin portion 410 (the length from the component placement portion 412 to the top surface of the pin portion 410) to the maximum diameter X of the pin portion 410 is set to be 6 or greater and 11 or less. Note that when the component placement portion 412 is not formed, the axial length Y of the pin portion 410 is the length from the bottom surface 404 of the base member 400 to the top surface of the pin portion 410. The axial length Y of the pin portion 410 is smaller than the height of the housing. Specifically, the axial length Y of the pin portion 410 is, for example, 1 inch or greater and less than 2 inches.

4. Effects In the manufacturing method of the base member described above, an undercut portion 411 that is lower in height than the surrounding area is formed at the base of the pin portion 410, and therefore the R-shape R formed at the base of the pin portion 410 by the R-chamfered portion C7 of the forming tool T2 is formed at the bottom of the undercut portion 411. Therefore, even when a part is attached to the pin portion 410, it does not come into contact with the R-shape R, and the assembly accuracy of the part can be improved.

The component placement portion 412, which is radially outward of the undercut portion 411, is cut using an end mill E. Machining using the end mill E described above is less likely to cause chatter vibrations, and produces a good cut surface with fine cutting marks. These cutting marks are end mill marks that form a continuous arc around the circumference, centered on a point on the circumference centered on the central axis of the pin portion 410. This prevents the roughness of the cut surface from adversely affecting height accuracy.

In particular, in the above embodiment, after cutting the undercut portion 411, the component placement portion 412 is cut with the end mill E. This allows the end mill E to remove burrs that appear on the outer periphery when the undercut portion 411 is cut. Furthermore, the end mill E can correct deformation of the component placement portion 412 caused by pressing with the forming tool T2, thereby increasing the perpendicularity between the component placement portion 412 and the pin portion 410. Therefore, this method is applicable to base members in which the length of the pin portion 410 is increased, resulting in a housing height of, for example, 1.5 inches or more but less than 2 inches. Furthermore, in the above embodiment, because the top surface of the pin portion 410 is cut with the end mill E, the heights of pin portions of the same height can be aligned, improving the height precision of the pin portion.

Here, in hard disk drive devices equipped with seven or more hard disks, helium must be sealed inside. The present invention is applicable to hard disk drive devices equipped with seven or more hard disks, and since the hard disk drive device 10 of the above embodiment has 21 hard disks 13, a gas with a lower density than air, such as helium, is sealed inside. As a result, as the number of magnetic heads 12 increases, the axial length Y of the pin portion 410 becomes longer, and the influence of the squareness between the pin portion 410 and the component mounting portion 412 becomes more pronounced. The present invention is fully capable of meeting the extremely strict squareness required between the pin portion 410 and the component mounting portion 412.

5. Application to Other Pin Portions In the above embodiment, the present invention is applied to the pin portion 410 for attaching the pivot bearing 19, but the present invention can be applied to any pin portion that is cast integrally with the base member 400, as described below.

Figure 7 shows the pin portion 420 for mounting a voice coil motor, and shows cross sections taken along lines B-B, C-C, and D-D in Figure 4. In Figure 7, (A) shows a conventional machining method, and (B) and (C) show the machining method of the embodiment. In the finishing process of this pin portion 420, a forming tool T3 is used to cut the outer surface of the pin portion 420 and also to cut the undercut portion 421. An end mill E is also used to cut the upper surface of the component placement portion 422 and cut the top surface of the pin portion 420. In this finishing process of the pin portion 420, the same effects and advantages as those of the above embodiment can be achieved. In particular, because all component placement portions 422 of the voice coil motor pin portion 420 have the same height from the bottom surface 404, machining can be performed while maintaining the relative vertical positions of the end mill E and the component placement portions 412, thereby aligning the heights of the component placement portions 412 and improving height accuracy.

Figure 8 shows a pin portion 430 for attaching a ramp, and is a cross section taken along line E-E in Figure 4. In Figure 8, (A) shows a conventional machining method, and (B) and (C) show the machining method of the embodiment. In the finish machining of this pin portion 430, a forming tool T4 is used to cut the outer surface of the pin portion 430 and also to cut the undercut portion 431. In addition, an end mill E is used to cut the upper surface of the component mounting portion 432 and cut the top surface of the pin portion 430. In this type of finish machining of the pin portion 430, the same functions and effects as those of the above embodiment can be obtained.

Figure 9 shows the pin portion 440 for attaching the cover portion, and shows cross sections taken along lines F-F and G-G in Figure 4. In finishing the pin portion 440, first, the entire top surface of the base member 400 is cut using an end mill E. Next, the base member 400 is electrocoated for insulation, dust generation, and corrosion prevention (see Figure 9(B)). Next, the top surface of the pin portion 440 is cut using an end mill E. Then, as shown in Figure 9(C), the outer periphery of the pin portion 440 is cut using a forming tool T5, and the undercut portion 441 is also cut. Only this pin portion 440 is cut using the end mill E before electrocoating, while the other pin portions 410-430 and 450 are machined using forming tools T2-T4 and T6 and the end mill E after electrocoating. This type of finishing of the pin portion 440 also achieves the same effects and advantages as the above-described embodiment.

Figure 10 shows the pin portion 450 for attaching a connector, and shows cross sections taken along lines H-H and I-I in Figure 5. In the finishing process of this pin portion 450, an undercut portion 451 is cut using a forming tool T6 (A). Meanwhile, as shown in Figure 5, a recess 403 into which the connector fits is formed on the back surface of the base member 400. The entire recess 403 is cut using an end mill E (B), and the top surface of the pin portion 450 is cut. Conversely, the entire recess 403 and the top surface of the pin portion 460 can be cut using an end mill (C), and then the undercut portion 451 can be cut using a forming tool T6 (D).

6. Modifications The present invention is not limited to the above-described embodiment, and various modifications are possible as follows.
i) In Figures 6 to 8, the undercut portions 411 to 431 are cut first, and then the component placement portions 412 to 432 are cut. However, it is also possible to cut the undercut portions 411 to 431 after cutting the component placement portions 412 to 432.

ii) In the above embodiment, the side surfaces of the pin portions 410 to 450 are cut by the inner peripheral cutting edge C6 of the forming tools T2 to T6, but they can also be cut by the side cutting edge of the end mill E.
iii) A milling cutter may be used in place of the end mill E.
iv) The horizontal blade C4 may have a cross section that is curved outwardly convex.

The present invention can be used in electronic devices such as spindle motors and hard disk drives, as well as in base members used therein.

10...hard disk drive device, 11...swing arm, 12...magnetic head, 13...hard disk, 14...actuator, 15...controller, 16...spacer, 17...screw, 18...clamp, 19...pivot bearing, 20...shaft, 100...spindle motor, 101a...cylindrical portion, 103...stator core, 104...coil, 110...rotor, 111...cylindrical portion, 113...rotor magnet, 114...flange portion, 201, 301...conical bearing member, 200, 300...bearing, 400 ...Base member, 401...recess, 402...housing, 403...recess, 404...bottom surface, 410, 420, 430, 440, 450...pin portion (protrusion), 411, 421, 431, 441, 451...undercut portion, 412, 422, 432...component mounting portion, C2, C6...inner cutting edge, C3...R-chamfered portion, C4...horizontal cutting edge, C5...inclined cutting edge, C7...R-chamfered portion, E...end mill, R...R shape, T1, T2, T3, T4, T5, T6...forming tool, X...maximum diameter of pin portion, Y...axial length of pin portion.

Claims (16)

A method for manufacturing a base member that becomes part of a housing of a hard disk drive device, comprising the steps of:
a molding step of molding a base body having a protrusion protruding upward by casting;
a first machining step of digging down a portion from an outer peripheral surface of the protrusion to a radially outer side to form an undercut portion;
a second machining step of cutting the undercut portion or an area outside the area where the undercut portion is to be formed by relatively moving a rotary tool having a cutting tool on a lower end surface in a horizontal direction;
A method for manufacturing a base member comprising: A method for manufacturing a base member according to claim 1, wherein in the molding step, a component mounting portion is formed around the undercut portion at a position higher than the bottom surface of the base member, and in the second machining step, the upper surface of the component mounting portion is cut. The method for manufacturing a base member according to claim 2, wherein the rotary tool is moved relatively along a circumference centered on the central axis of the protrusion to cut the upper surface of the component mounting portion. A method for manufacturing a base member according to any one of claims 1 to 3, wherein the second machining step is performed after the first machining step. A method for manufacturing a base member according to any one of claims 1 to 4, wherein the top surfaces of the protrusions are machined in the second machining step. A method for manufacturing a base member according to any one of claims 1 to 5, wherein the second machining step is performed using a milling cutter or an end mill. A method for manufacturing a base member according to any one of claims 1 to 6, wherein the first machining step is performed using a forming tool having a generally cylindrical tip end, a generally horizontal blade on the tip surface, an inclined blade extending diagonally upward from the radially outer end of the horizontal blade, and an inner peripheral blade extending generally upward from the radially inner end of the horizontal blade. A method for manufacturing a base member according to any one of claims 1 to 7, wherein the height of the housing is 1.5 inches or more but less than 2.0 inches. A method for manufacturing a base member according to any one of claims 1 to 8, wherein the ratio of the axial length of the protrusion to the maximum diameter of the protrusion is 6 or more and 11 or less. A base member that is part of the housing of a hard disk drive device,
A base body,
a protrusion provided on the base body;
an undercut portion dug down at the base of the protrusion;
a machined portion outside the undercut portion;
Equipped with
The base member has a cutting mark formed in the machined portion, the cutting mark being a continuous arc that does not have its center on the central axis of the protrusion. The base member according to claim 10, further comprising a boss portion located higher than the undercut portion around the undercut portion, and a cutting mark formed on the upper surface of the boss portion that forms a continuous arc around a point on the circumference when a circumference is imagined with the center at the central axis of the protrusion. The base member according to claim 10 or 11, wherein the ratio of the axial length of the protrusion to the maximum diameter of the protrusion is 6 or more and 11 or less. A spindle motor equipped with a base member according to any one of claims 10 to 12. A hard disk drive device equipped with the spindle motor described in claim 13. The hard disk drive device of claim 14, wherein the height of the housing is greater than or equal to 1.5 inches and less than 2.0 inches. 16. The hard disk drive according to claim 14, wherein a gas having a density lower than that of air is sealed inside.