Base plate, motor, disk drive device, and manufacturing method of base plate

Abstract

To provide a base plate capable of preventing deterioration in assembly accuracy of mounted components, and a motor and a disk drive device equipped with the base plate.SOLUTION: A base plate serves as a part of a housing of a disk drive device and is made of a metal die-cast member. The base plate includes a bottom wall part and a peripheral wall part. The bottom wall part extends perpendicularly to a rotation axis of the disk extending in a vertical direction, extends upward in an axial direction from a peripheral edge part, surrounds the bottom wall part, and has a screw hole 416. The screw hole is recessed upward in the axial direction from the peripheral edge part of a lower end surface of the bottom wall part 411. The screw hole has an inclined part 416a and a columnar part 416b. The inclined part has an inner diameter formed smaller as progressing toward the upper side in the axial direction from a lower end of the screw hole, the columnar part extends upward in the axial direction from an upper end of the inclined part, and a threaded part 416c screwed with a screw is formed, and the inclined part inclines at an inclination angle of 25° or more and 35° or less with respect to a centerline in a cross section including the centerline extending in the axial direction through the center of the columnar part.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a base plate, a motor, a disk drive device, and a method for manufacturing the base plate. [Background technology]

[0002] A base plate, which is a part of the housing of a conventional disk drive device, is made of a die-cast metal member and has a bottom wall that extends perpendicular to the rotation axis of the disk, which extends in the vertical direction (see, for example, Patent Document 1).

[0003] The lower surface of the bottom wall portion is provided with a screw hole for fixing a circuit board or the like with a screw. The screw hole is arranged on the peripheral portion of the bottom wall portion and extends axially upward from the lower end surface. The screw hole is tapped (rolled) to form a screw-threaded portion that screws into the screw. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-190510 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the base plate disclosed in the above Patent Document 1, when tapping, there is a possibility that a rolling tool may come into contact with the inner peripheral surface of the lower end of the screw hole. At this time, the lower end of the formed screw part may protrude from the inner peripheral surface of the lower end of the screw hole, causing burrs. In addition, when tapping, stress may be applied to the peripheral portion of the lower end of the screw hole, causing a part of the inner peripheral surface of the lower end of the screw hole to rise up, causing burrs. In addition, if a burr is formed protruding axially downward from the lower end of the bottom wall part, the base plate placed on the workbench may rattle, and the assembly accuracy of the parts mounted on the base plate may decrease.

[0006] An object of the present invention is to provide a base plate capable of preventing a decrease in the assembly accuracy of mounted parts, and a motor and a disk drive device including the base plate. [Means for solving the problem]

[0007] An exemplary base plate of the present invention is a part of a housing of a disk drive device, and is made of a die-cast member made of metal. The base plate includes a bottom wall portion and a peripheral wall portion. The bottom wall portion extends perpendicularly to a rotation axis of the disk extending in the up-down direction. The peripheral wall portion extends from a peripheral portion of the bottom wall portion to the axially upward direction and surrounds the periphery of the bottom wall portion. The bottom wall portion has a screw hole. The screw hole is recessed from a peripheral portion of a lower end surface of the bottom wall portion to the axially upward direction. The screw hole has an inclined portion and a columnar portion. The inclined portion is formed so that the inner diameter becomes smaller from the lower end of the screw hole toward the axially upward direction. The columnar portion extends from the upper end of the inclined portion to the axially upward direction, and a screw-engaging portion that screws with a screw is formed. The inclined portion is inclined at an inclination angle of 25° to 35° with respect to the center line in a cross section including a center line extending in the axial direction through the center of the columnar portion. Effect of the Invention

[0008] According to an exemplary embodiment of the present invention, it is possible to provide a base plate capable of preventing a decrease in the assembly accuracy of mounted parts, and a motor and a disk drive device including the base plate. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a vertical cross-sectional view of a disk drive device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view showing a schematic view of the periphery of a disk in the disk drive device according to the embodiment of the present invention. [Diagram 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. [Figure 4] FIG. 4 is a perspective view showing a schematic view of a base plate according to an embodiment of the present invention. [Diagram 5] FIG. 5 is a perspective view showing a schematic view of a base plate according to an embodiment of the present invention. [Figure 6] FIG. 6 is an enlarged vertical cross-sectional view showing a screw hole of a base plate according to an embodiment of the present invention. [Figure 7] FIG. 7 is an enlarged vertical cross-sectional view showing a screw hole of a base plate according to an embodiment of the present invention. [Figure 8] FIG. 8 is an enlarged vertical cross-sectional view showing a screw hole of a base plate according to an embodiment of the present invention. [Figure 9] FIG. 9 is an enlarged perspective view of a portion of the base plate according to the embodiment of the present invention. [Figure 10] FIG. 10 is an enlarged top view of a portion of the base plate according to the embodiment of the present invention. [Figure 11] FIG. 11 is a cross-sectional view taken along line BB in FIG. [Figure 12] FIG. 12 is a flow chart showing the steps of manufacturing a base plate according to an embodiment of the present invention. [Figure 13] FIG. 13 is an explanatory diagram illustrating a manufacturing process of the base plate according to the embodiment of the present invention. [Figure 14] FIG. 14 is an explanatory diagram illustrating a manufacturing process of the base plate according to the embodiment of the present invention. [Figure 15] FIG. 15 is an explanatory diagram illustrating a manufacturing process of the base plate according to the embodiment of the present invention. [Figure 16] FIG. 16 is an explanatory diagram illustrating a manufacturing process of the base plate according to the embodiment of the present invention. [Figure 17] FIG. 17 is an explanatory diagram illustrating a manufacturing process of the base plate according to the embodiment of the present invention. [Figure 18] FIG. 18 is an explanatory diagram illustrating a manufacturing process of the base plate according to the embodiment of the present invention. [Figure 19] FIG. 19 is an explanatory diagram illustrating a manufacturing process of the base plate according to the embodiment of the present invention. [Figure 20] FIG. 20 is an explanatory diagram illustrating a manufacturing process of the base plate according to the embodiment of the present invention. [Figure 21]FIG. 21 is an enlarged longitudinal sectional view showing a screw hole according to a modified example of the base plate according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the drawings. In this specification, the direction parallel to the rotation axis J of the disk 50 is referred to as the "axial direction", the direction perpendicular to the rotation axis J is referred to as the "radial direction", and the direction along the arc centered on the rotation axis J is referred to as the "circumferential direction". In addition, in this application, the shape and positional relationship of each part will be described with the axial direction being the up-down direction and the cover 42 side being the upper side with respect to the base plate 41. However, this definition of the up-down direction is not intended to limit the orientation of the base plate 41 and the disk drive device 1 according to the present invention when used.

[0011] (1. Configuration of Disk Drive Unit) A disk drive device 1 according to an exemplary embodiment of the present invention will be described below. Fig. 1 is a vertical cross-sectional view of a disk drive device 1 according to an embodiment of the present invention.

[0012] The disk drive device 1 is a hard disk drive and includes a spindle motor (motor) 2, a disk 50, a head 31, an arm 32, a swing mechanism 33, a ramp , and a housing .

[0013] The housing 40 accommodates therein the spindle motor 2, the disk 50, the head 31, the arm 32, the swing mechanism 33, and the lamp .

[0014] The inside of the housing 40 is filled with a gas having a lower density than air. This reduces the airflow resistance inside the housing 40, thereby reducing the vibration of the disk 50. Specifically, the housing 40 is filled with helium gas. Note that hydrogen gas or the like may be filled instead of helium gas.

[0015] The housing 40 is formed of a die-cast member made of an aluminum alloy, although the die-cast member may be made of a metal other than an aluminum alloy.

[0016] The housing 40 has a base plate 41 and a cover 42. That is, the base plate 41 is a part of the housing 40 of the disk drive device 1, and is made of a metal die-cast member. Inside the housing 40, the disk 50, the spindle motor 2, and the rocking mechanism 33 are arranged on the base plate 41. The upper opening of the base plate 41 is closed by the cover 42. The base plate 41 will be described in detail later.

[0017] The spindle motor 2 supports the disk 50 and rotates the disk 50 about a rotation axis J. That is, the disk 50 is rotated by the spindle motor 2 about the rotation axis J extending in the vertical direction. The spindle motor 2 has a stationary part 10 and a rotating part 20. The stationary part 10 is stationary with respect to the housing 40. The rotating part 20 is supported rotatably with respect to the stationary part 10.

[0018] The stationary part 10 has a shaft 14 and a stator 12. In addition, a part of a base plate 41 constitutes the stationary part 10. The base plate 41 is a part of the spindle motor 2 and also a part of the housing 40. In other words, the spindle motor 2 includes the base plate 41. The stator 12 and the bearing unit 13 are fixed to the base plate 41.

[0019] The shaft 14 is a columnar metal member extending in the axial direction. The lower end of the shaft 14 is fixed to a base plate 41.

[0020] The stator 12 has a stator core 121, which is a magnetic body, and a plurality of coils 122. The stator core 121 has an annular core back 121a and a plurality of teeth 121b. The core back 121a is arranged to surround the rotation axis J, and the teeth 121b, which are fixed to the base plate 41, protrude radially outward from the outer circumferential surface of the core back 121a and are arranged in a circumferential direction. The plurality of coils 122 are formed by conductive wires wound around the teeth 121b.

[0021] The bearing unit 13 is disposed on the outer periphery of the shaft 14, and rotatably supports a hub 22 on the rotating part 20 side. The bearing unit 13 uses, for example, a fluid dynamic bearing mechanism.

[0022] The rotating part 20 has a hub 22 and a magnet 23. The hub 22 has a top surface part 22a and a cylindrical surface part 22b. The top surface part 22a is disposed on the outer periphery of the bearing unit 13 and expands radially outward. The cylindrical surface part 22b is formed in a cylindrical shape extending in the axial direction and has a flange part 22c extending radially outward from the lower end part. A plurality of discs 50 are arranged side by side in the axial direction on the outer periphery surface of the cylindrical surface part 22b.

[0023] Magnet 23 is fixed to the inner circumferential surface of cylindrical portion 22b, and is disposed facing and spaced a predetermined distance from the radially outer side of stator 12. Magnet 23 is annular, and its inner circumferential surface is magnetized with N poles and S poles alternately arranged in the circumferential direction.

[0024] When a driving current is supplied to the coil 122, magnetic flux is generated in the multiple teeth 121b. At this time, the magnetic flux interacts between the teeth 121b and the magnet 23, generating a circumferential torque. This causes the rotating part 20 to rotate about the rotation axis J relative to the stationary part 10. The disk 50 supported by the hub 22 rotates together with the rotating part 20 about the rotation axis J.

[0025] The disks 50 are circular information recording media having a hole in the center. The disks 50 are attached to the spindle motor 2 and are arranged in parallel to each other and at equal intervals in the axial direction via the spacers 24.

[0026] The head 31 magnetically reads and writes information from and to the disk 50. The arm 32 is attached to the tip of the pivot post 413 via a bearing (not shown). The head 31 is disposed at the tip of the arm 32.

[0027] The pivot post 413 is formed in a cylindrical shape and protrudes upward from the upper surface of a bottom wall portion 411 of the base plate 41, which will be described later, along the oscillation axis H. The pivot post 413 has a post step portion 413a (see FIG. 4). The post step portion 413a is formed in an annular shape and protrudes radially outward from the outer circumferential surface of the base portion of the pivot post 413. The bottom portion of the post step portion 413a is formed integrally with the upper portion of the bottom wall portion 411. By providing the post step portion 413a, the base portion of the pivot post 413 is reinforced. This makes it possible to prevent the pivot post 413 from tilting with respect to the oscillation axis H.

[0028] The swing mechanism 33 is a mechanism for swinging the arm 32 and the head 31. When the swing mechanism 33 is driven, the head 31 swings about the swing axis H via the arm 32. At this time, the head 31 moves relatively to the disk 50 and approaches and accesses the rotating disk 50.

[0029] FIG. 2 is a plan view showing the periphery of the disk 50, and FIG. 3 is a cross-sectional view taken along line AA in FIG. 2. The ramp 34 is placed on the bottom of a second recess 418 (described later) of the peripheral wall 412 (see FIG. 4), and has a plurality of guide portions 34a arranged in the axial direction. The guide portions 34a sandwich the disk 50 in the axial direction and are disposed close to the disk 50. When access to the disk 50 is completed, the head 31 is moved by the swing mechanism 33 away from the disk 50 and toward the ramp 34. At this time, the head 31 is held within the ramp 34 via the tip of the guide portion 34a. That is, the ramp 34 holds the head 31 which reads or writes information from or to the disk 50.

[0030] (3. Detailed configuration of the base plate) 4 and 5 are perspective views showing the base plate 41, with Fig. 4 showing the base plate 41 from an axially upper side and Fig. 5 showing the base plate from an axially lower side. The base plate 41 includes a bottom wall portion 411, a peripheral wall portion 412, and a pivot post 413.

[0031] In this embodiment, the bottom wall portion 411, the peripheral wall portion 412, and the pivot post 413 are an integrally formed casting. Although the bottom wall portion 411 and the peripheral wall portion 412 are an integrally formed casting, the base plate 41 may be configured by assembling the bottom wall portion 411 and the peripheral wall portion 412 that are each cast as separate members.

[0032] The bottom wall portion 411 has a rectangular shape when viewed in the axial direction, and extends perpendicular to the rotation axis J and oscillation axis H that extend in the up-down direction. The bottom wall portion 411 has a shaft through hole 415 and a screw hole 416. The shaft through hole 415 passes through the bottom wall portion 411 in the axial direction along the rotation axis J. The lower end of the shaft 21 is press-fitted into the shaft through hole 415 and fixed to the bottom wall portion 411.

[0033] The screw hole 416 is recessed axially upward from the peripheral edge of the lower end surface of the bottom wall portion 411. A circuit board (not shown) connected to the coil 122 of the spindle motor 2 is disposed on the lower surface of the bottom wall portion 411. The circuit board has a board through hole (not shown) that penetrates in the axial direction.

[0034] A screw (not shown) is inserted into the board through hole and screwed into the screw hole 416. This fixes the circuit board to the bottom wall portion 411. In this embodiment, the screw hole 416 is used to fix the circuit board, but the present invention is not limited to this. For example, the screw hole 416 may be used to fix a component other than the circuit board to the base plate. The shape of the screw hole 416 will be described in detail later.

[0035] The peripheral wall portion 412 extends axially upward from the outer periphery of the bottom wall portion 411 and surrounds the periphery of the bottom wall portion 411. The cover 42 is screwed to the upper end surface of the peripheral wall portion 412. The peripheral wall portion 412 has a first recess 417 and a second recess 418. The lamp 34 is placed on the bottom of the second recess 418. The first recess 417 and the second recess 418 will be described in detail later.

[0036] The pivot post 413 protrudes upward from the upper surface of the bottom wall portion 411 along the pivot axis H. The swing mechanism 33 is supported by the bottom wall portion 411 via the pivot post 413.

[0037] (5. Detailed configuration of screw holes) 6, 7, and 8 are vertical cross-sectional views showing the screw hole 416 in an enlarged manner, and FIG. 6 shows the state before tapping. FIGS. 7 and 8 show the state after tapping. The screw hole 416 has an inclined portion 416a and a columnar portion 416b. The inclined portion 416a is frustum-shaped, and is formed so that the inner diameter becomes smaller from the lower end toward the axially upward direction. The columnar portion 416b is cylindrical, extends axially upward from the upper end of the inclined portion 416a, and has a screw portion 416c that screws with a screw (not shown). The screw portion 416c is a female screw formed by tapping (rolling) the screw hole 416.

[0038] In this embodiment, the inclined portion 416a is inclined at an inclination angle θ1 of 25° to 35° with respect to the center line L in a cross section including the center line L extending in the axial direction through the center of the columnar portion 416b. If the diameter D of the lower end of the inclined portion 416a is kept constant and the inclination angle θ1 of the inclined portion 416a is reduced, the stress applied to the periphery of the lower end of the inclined portion 416a during tapping can be reduced. This can prevent the periphery of the lower end of the inclined portion 416a from swelling up in part to generate burrs 416d. Therefore, when the base plate 41 is placed on the workbench, the burrs 416d can be prevented from coming into contact with the workbench and causing the base plate 41 to rattle. This can prevent the assembly accuracy of the parts mounted on the base plate 41 from decreasing.

[0039] In addition, when the axial length of the screw hole 416 is fixed, if the diameter D of the lower end of the inclined portion 416a is kept constant and the inclination angle θ1 of the inclined portion 416a is reduced, the axial proportion of the inclined portion 416a in the entire screw hole 416 increases. This reduces the axial proportion of the columnar portion 416b in which the screw-engagement portion 416c is formed. Therefore, the fastening strength of the screw decreases. In this embodiment, the inclination angle θ1 of the inclined portion 416a is set to 25° or more. This can suppress the decrease in the fastening strength of the screw.

[0040] Furthermore, when burrs 416d occur on inclined portion 416a, if the diameter D of the lower end of inclined portion 416a is kept constant and the inclination angle θ1 of inclined portion 416a is increased, burrs 416d will incline downward in the axial direction (see FIG. 8). Therefore, by setting the inclination angle θ1 of inclined portion 416a to 35° or less with respect to center line L, it is possible to prevent the tip of burrs 416d from protruding downward in the axial direction from the lower end of bottom wall portion 411. This makes it possible to prevent a decrease in the assembly accuracy of components mounted on base plate 41 even if burrs 416d occur on inclined portion 416a. Furthermore, even if a rolling tool comes into contact with inclined portion 416a and a screw-type portion 416c is formed on inclined portion 416a, by keeping the diameter D of the lower end of inclined portion 416a constant and setting the inclination angle θ1 of inclined portion 416a to 35° or less with respect to center line L, it is possible to prevent the lower end of screw-type portion 416c from protruding from inclined portion 416a and becoming a burr, and thereby preventing it from protruding axially downward from the lower end of bottom wall portion 411.

[0041] Moreover, the diameter D of the lower end of the inclined portion 416a is preferably 4.0 mm or more and 4.6 mm or less. When the axial length of the screw hole 416 is fixed, if the diameter D of the lower end of the inclined portion is increased while keeping the inclination angle θ1 constant, the axial ratio of the inclined portion 416a to the entire screw hole 416 increases. This reduces the axial ratio of the columnar portion 416b in which the screwing portion 416c is formed. Therefore, the range occupied by the screwing portion 416c becomes smaller in the axial direction, and the fastening strength of the screw decreases. In this embodiment, the decrease in the fastening strength of the screw can be suppressed by setting the diameter D of the lower end of the inclined portion 416a to 4.6 mm or less.

[0042] Furthermore, if the diameter D of the lower end of the inclined portion 416a is made larger than 4.6 mm, the area of ​​the lower end surface of the bottom wall portion 411 that axially overlaps with the screw head becomes narrower, making it difficult to stably screw a component screwed into the screw hole 416.

[0043] Furthermore, if the diameter D of the lower end of inclined portion 416a is made larger than 4.6 mm, the distance between the periphery of bottom wall portion 411 and screw hole 416 becomes narrow, making the periphery of bottom wall portion 411 more susceptible to deformation and chipping.

[0044] Furthermore, when the axial length of the screw hole 416 is fixed, if the diameter D of the lower end of the inclined portion is made small while keeping the inclination angle θ1 constant, the stress applied to the periphery of the lower end of the inclined portion 416a during tapping increases. In this embodiment, by setting the diameter D of the lower end of the inclined portion 416a to 4.0 mm or more, it is possible to suppress the generation of burrs 416d on the inclined portion 416a.

[0045] Moreover, burrs 416d occurring on inclined portion 416a preferably protrude in the radial direction, and the lower end of burrs 416d is preferably located axially above the lower end of bottom wall portion 411 (see FIG. 8). This makes it possible to prevent a decrease in the assembly accuracy of components mounted on base plate 41 even if burrs 416d occur on inclined portion 416a.

[0046] (6. Detailed configuration of the first recess and the second recess) 9 is an enlarged perspective view of the periphery of the second recess 418 of the base plate 41, and FIG. 10 is an enlarged top view of the periphery of the second recess 418 of the base plate 41. FIG. 11 is a BB cross-sectional view of FIG. 10. The first recess 417 is formed such that the inner peripheral edge of the upper end surface of the peripheral wall portion 412 is recessed axially downward. The second recess 418 is formed such that the inner peripheral edge of the bottom surface of the first recess 417 is further recessed axially downward, and the lamp 34 is placed thereon. The entire bottom of the first recess 417 is located axially above the bottom of the second recess 418.

[0047] By forming the first recess 417, the peripheral wall 412 is thinned in the radial direction around the second recess 418 on which the lamp 34 is placed. Shrinkage cavities are generated when molten metal is cooled and solidifies and shrinks during casting. By thinning the peripheral wall 412 in the radial direction, the solidification time of the peripheral wall 412 is shortened, and the occurrence of shrinkage cavities can be reduced. This makes it possible to reduce the occurrence of shrinkage cavities in the peripheral wall 412 around the second recess 418. Therefore, it is possible to suppress a decrease in the dimensional accuracy of the base plate 41 around the second recess 418. This makes it possible to improve the positional accuracy of the lamp 34.

[0048] In addition, the entire bottom of the first recess 417 is located axially above the bottom of the second recess 418. As a result, a part of the mold 201 (first convex portion 2013) that forms the first recess 417 does not protrude axially downward from the bottom of the second recess 418 (see FIG. 14). Therefore, a protrusion is not formed on the part of the mold 201 (first convex portion 2013) during casting. This makes it possible to prevent melting of the protrusion. Note that if a part of the mold 201 (first convex portion 2013) that forms the first recess 417 protrudes axially downward from the bottom of the second recess 418 to form a protrusion, melting of the protrusion may occur during casting because the mold temperature of the protrusion increases. As a result, melting of the protrusion can be prevented by forming a shape that does not provide a protrusion on the part of the mold 201 (first convex portion 2013). Therefore, burrs can be prevented from occurring on the bottom of the first recess 417. This makes it possible to prevent burrs from being generated around the bottom of the second recess 418, and to further improve the positional accuracy of the lamp .

[0049] Further, the radially inner side surface of the second recess 418 has a flat surface portion 418a and a curved surface portion 418b. The flat surface portion 418a is formed parallel to the radially outer side surface of the peripheral wall portion 412. The curved surface portion 418b is formed by being curved and recessed radially outward from the flat surface portion 418a. The radially outer end of the curved surface portion 418b is located radially outward from the radially outer end of the flat surface portion 418a. By forming the curved surface portion 418b, the bottom portion of the second recess 418 expands radially outward, and the lamp 34 can be stably disposed at the bottom portion of the second recess 418. Therefore, the positional accuracy of the lamp 34 can be further improved.

[0050] The first recess 417 has a curved recess 417a. The curved recess 417a is formed such that the bottom surface connected to the curved portion 418b is recessed downward in the axial direction. By forming the curved recess 417a, the first recess 417 can be thinned in the axial direction to suppress the occurrence of shrinkage cavities. This further suppresses the deterioration of the dimensional accuracy of the base plate 41 around the second recess 418.

[0051] The bottom wall 411 has a bottom wall recess 411a recessed axially upward from the lower end face, axially below the first recess 417. By arranging the bottom wall recess 411a axially below the first recess 417, the bottom wall 411 can be thinned in the axial direction, thereby suppressing the occurrence of shrinkage cavities. This further suppresses the deterioration of the sealing performance of the housing 40 and the deterioration of the dimensional accuracy of the base plate 41.

[0052] In addition, in a cross section perpendicular to the oscillation axis H, the inclination angle θ2 of the straight line M1 extending radially from the oscillation axis H and tangent to the end of the second recess 418 on the disk 50 side with respect to the straight line M2 extending along the flat surface portion 418a is preferably 75° or more and 85° or less. In this case, by setting the inclination angle θ2 to 75° or more and 85° or less, the guide portion 34a can be disposed close to the disk 50. As a result, when the head 31 moves between the access position and the retracted position of the disk 50, the head 31 is held on the ramp 34 at a shorter distance. As a result, the time required for the head 31 to access the disk 50 can be shortened.

[0053] (7. Manufacturing method of base plate) Fig. 12 is a flowchart showing the manufacturing process of the base plate 41. Figs. 13 to 20 are explanatory views showing the manufacturing process of the base plate 41. Fig. 14 shows an enlarged view of the periphery of the first protrusion 2013 where the first recess 417 of the peripheral wall 412 is formed. Fig. 20 shows an enlarged view of the pivot post 413.

[0054] 13, in step S1, the peripheral portion of the metal mold 202 and the peripheral portion of the metal mold 201 are brought into contact with each other in the up-down direction to form a cavity 210 between the metal mold 201 and the metal mold 202. The cavity 210 has a shape corresponding to the shape of the base plate 41.

[0055] Specifically, the die 201 is formed in a rectangular parallelepiped shape and has a groove 2011 and a die protrusion 2012. The groove 2011 is formed in an annular shape with the outer periphery of the lower surface of the die 201 recessed axially upward. The die protrusion 2012 is formed on the radially inner side of the groove 2011 with the lower surface of the die 201 protruding axially downward. The lower end of the die protrusion 2012 is located lower than the lower end of the die 201 on the outer side of the groove 2011. Molten metal flows into the inside of the groove 2011 to form a peripheral wall 412.

[0056] The mold 202 is formed in a rectangular parallelepiped shape, and the mold 201 has a mold recess 2021. The mold recess 2021 is formed by recessing the upper surface of the mold 201 axially downward in a region that faces the mold protrusion 2012 in the up-down direction. Molten metal flows into the inside of the mold recess 2021 to form a bottom wall portion 411.

[0057] Furthermore, the cavity 210 communicates with a gate 214 extending along the opposing surfaces of the molds 201 and 202. The outer end of the gate 214 opens to the outside of the molds 201 and 202.

[0058] In addition, an air vent passage (not shown) for venting air from within the cavity 210 is provided on the opposing surfaces of the mold 201 and the mold 202 in addition to the gate 214. The outer end of the air vent passage is open to the outside of the mold 201 and the mold 202.

[0059] The die 201 has a post recess 201a and a shaft recess 201b. The post recess 201a is formed by recessing the lower surface of the die protrusion 2012 axially upward along the oscillation axis H. The inside of the post recess 201a communicates with the cavity 210. An expanded diameter portion 201d is formed at the lower end of the inner circumferential surface of the post recess 201a. The expanded diameter portion 201d has a larger diameter than the upper end of the inner circumferential surface of the post recess 201a. Molten metal flows into the inside of the post recess 201a to form a pivot post 413. Molten metal flows into the inside of the expanded diameter portion 201d to form a post step portion 413a.

[0060] The shaft recess 201b is formed by recessing the lower surface of the mold protrusion 2012 axially upward along the rotation axis J. The inside of the shaft recess 201b communicates with the cavity 210. A protrusion 201c protruding downward is formed on the top surface of the shaft recess 201b.

[0061] When molten metal flows into the inside of the post recess 201a, a recess 414f is formed at the location where the protrusion 201c was located (see FIG. 16). The recess 414f is formed by being recessed axially downward from the upper surface of the bottom wall portion 411.

[0062] The mold 201 further has a first protrusion 2013 and a second protrusion 2014 protruding in the radial direction from the radial outer surface of the mold protrusion 2012 (see FIG. 14). The first protrusion 2013 is formed across the inner circumferential edge of the top surface of the groove 2011 and the radial outer surface of the mold protrusion 2012. The second protrusion 2014 is formed across the inner circumferential edge of the bottom surface of the first protrusion 2013 and the radial outer surface of the mold protrusion 2012. As a result, the lower end of the first protrusion 2013 is located axially higher than the lower end of the second protrusion 2014.

[0063] When the molten metal flows into the cavity 210, a first recess 417 is formed at a position corresponding to the first protrusion 2013. Also, a second recess 418 is formed at a position corresponding to the second protrusion 2014.

[0064] In step S2, as shown in Fig. 15, molten metal is injected into cavity 210 through gate 214. The molten metal is, for example, a molten aluminum alloy. When the molten metal is injected into cavity 210, the air in cavity 210 or the gas generated from the molten metal is pushed out of mold 201 and mold 202 through the air vent passage. This allows the molten metal to spread throughout cavity 210.

[0065] In step S3, after the molten metal has permeated the cavity 210, the molten metal is cooled and hardened. As a result, a base plate 41 is formed in the cavity 210. A chill layer (not shown) is formed on the surface of the base plate 41. The chill layer is formed in the area where the molten metal comes into contact with the molds 201 and 202 and hardens quickly when the molten metal hardens. The chill layer, where the molten metal hardens faster than other areas, has fewer impurities and a higher metal density.

[0066] 16, the base plate 41 is released from the pair of dies 201, 202. At this time, the peripheral wall portion 412 has a gate mark portion 41d protruding from the outer surface. The gate mark portion 41d is formed by hardening of the molten metal accumulated in the gate 214 and the air vent flow path (not shown).

[0067] In step S5, as shown in Fig. 17, the gate mark 41d is cut. In step S6, the base plate 41 is cut. More specifically, the recess 414f is cut in the axial direction to penetrate the bottom wall portion 411 in the axial direction. As a result, the shaft through hole 415 is formed by the cutting process. In addition, a mark (not shown) of the gate mark 41d is left slightly protruding from the outer surface of the peripheral wall portion 412.

[0068] Further, the radial inner surface of the peripheral wall portion 412 that faces the disk 50 in the radial direction and the upper surface of the peripheral wall portion 412 are machined.

[0069] In step S7, as shown in Fig. 18, an electrodeposition coating film 41a is formed on the surface of the base plate 41. For example, the base plate 41 is immersed in a coating material such as an epoxy resin, and an electric current is passed between the coating material and the base plate 41. This causes the coating material to adhere to the surface of the base plate 41, forming the electrodeposition coating film 41a. At this time, the outer surface of the machined surface machined in step S6 is also covered with the electrodeposition coating film 41a. By covering the base plate 41 with the electrodeposition coating film 41a, the insulation of the base plate 41 is improved and the leakage of gas that permeates the base plate 41 can be reduced.

[0070] 19, in step S8, areas of the surface of the base plate 41 that require precision are precisely shaped by cutting. Specifically, the outer peripheral surface of the pivot post 413, the upper surface of the post step portion 413a, the inner peripheral surface of the shaft through hole 415 and the periphery of the shaft through hole 415 on the upper surface of the bottom wall portion 411, the bottom surface of the second recess 418, the peripheral portion of the upper end surface of the peripheral wall portion 412, and the peripheral portion of the lower end surface of the bottom wall portion 411 are shaped. At this time, the periphery of the screw hole 416 and the periphery of a component screw hole (not shown) formed on the upper surface of the bottom wall portion 411 for fixing a component are also shaped.

[0071] By precisely machining and shaping the bottom surface of the second recess 418, the positional accuracy of the lamp 34 can be further improved.

[0072] Furthermore, by precisely machining and shaping the peripheral portion of the upper end surface of peripheral wall portion 412, cover 42 can be closely attached to the peripheral portion of the upper end surface of peripheral wall portion 412, thereby improving the sealing performance of housing 40. Furthermore, by precisely machining and shaping the peripheral portion of the lower end surface of bottom wall portion 411, it is possible to prevent the base plate placed on a workbench from rattling.

[0073] As shown in FIG. 20, it is preferable to use a machining tool 60 for precision machining of the outer circumferential surface of the pivot post 413 and the upper surface of the post step portion 413a. The machining tool 60 is a cylindrical body with an open bottom, into which the pivot post 413 is inserted. The machining tool 60 has a first cutting blade 61 disposed on the inner circumferential surface and a second cutting blade 62 disposed on the bottom surface. With the pivot post 413 inserted inside, the machining tool 60 rotates about a central axis C extending along the pivot post 413. This allows the pivot post 413 to be machined into a perfect circle in a cross section perpendicular to the central axis C.

[0074] The second cutting blade 62 processes the upper surface of the post step portion 413a, forming a plane perpendicular to the central axis C. At this time, the outer peripheral surface of the pivot post 413 and the upper surface of the post step portion 413a can be simultaneously processed by one processing tool 60. This allows the processing time to be shortened. When the upper surface of the post step portion 413a is processed by the second cutting blade 62, a processing mark (not shown) may be formed on the upper surface of the post step portion 413a. The processing mark may be, for example, a plurality of annular linear marks centered on the central axis C. The second cutting blade 62 may also form an annular groove portion (not shown) on the upper surface of the post step portion 413a.

[0075] When the surface of the base plate 41 is cut, the electrodeposition coating film 41a is also cut, and a non-coated region E where the electrodeposition coating film 41a is not provided is formed.

[0076] In step S9, the screw hole 416 and the component screw hole (not shown) are tapped (rolled) to form the screw-engaging portion 416c.

[0077] In step S10, the base plate 41 is immersed in an impregnating agent. This allows the impregnating agent to permeate the non-coated region E. At this time, the impregnating agent also permeates the precision machined surface shaped in step S8. The impregnating agent may be, for example, an epoxy resin or an acrylic resin. This allows minute cavities formed during casting in the non-coated region E to be sealed with the impregnating agent. This makes it possible to further prevent the gas filled inside the housing 40 from leaking to the outside.

[0078] As described above, the manufacturing method of the base plate 41, which is a casting that becomes a part of the housing 40 of the disk drive device 1, includes a casting step, a cutting step, an electrodeposition coating step, a shaping step, a tapping step, and an impregnation step, in this order. In the casting step, the bottom wall portion 411 and the peripheral wall portion 412 are cast integrally by a metal mold (steps S1 to S4). In the cutting step, the shaft through hole 415 is formed by cutting (step S6). In the electrodeposition coating step, the electrodeposition coating film 41a is formed on the surface of the base plate 41 (step S7). In the shaping step, the area of ​​the surface of the base plate 41 that requires precision is precisely machined by cutting to shape it (step S8). In the tapping step, the screw hole 416 is tapped to form the screw-engagement portion 416c (step S9). In the impregnation step, the area of ​​the surface of the base plate 41 that is exposed from the electrodeposition coating film 41a is impregnated with an impregnating agent (step S10).

[0079] (8. Others) The above embodiment is merely an example of the present invention. The configuration of the embodiment may be appropriately modified within the scope of the technical idea of ​​the present invention. In addition, the embodiments may be combined to the extent possible. For example, FIG. 21 is an enlarged longitudinal sectional view of a screw hole 416 according to a modified example, and the inclined portion 416a may be configured with a plurality of inclined surfaces 416e with different inclination angles θ1 with respect to the center line L arranged in the axial direction. This can reduce the stress applied to the periphery of the lower end of the inclined portion 416a during tapping. Therefore, it is possible to suppress the burrs 416d from being generated by a part of the periphery of the lower end of the inclined portion 416a rising up.

[0080] (9. Notes) As described above, the base plate (41) according to one embodiment of the present disclosure is a part of the housing (40) of the disk drive device (1) and is made of a metal die-cast member. The base plate has a bottom wall portion (411) extending perpendicularly to the rotation axis (C) of the disk extending in the vertical direction, and a peripheral wall portion (412) extending axially upward from the peripheral portion of the bottom wall portion to surround the periphery of the bottom wall portion. The bottom wall portion has a screw hole (416) recessed axially upward from the peripheral portion of the lower end face. The screw hole has an inclined portion (416a) whose inner diameter becomes smaller as it goes from the lower end to the axially upward, and a columnar portion (416b) extending axially upward from the upper end of the inclined portion and having a screw-threaded portion (416c) that screws into a screw. The inclined portion is inclined at an angle of 25° to 35° with respect to the center line in a cross section including the center line extending axially through the center of the columnar portion (first configuration).

[0081] In the first configuration, the diameter of the lower end of the inclined portion may be 4.0 mm or more and 4.6 mm or less (second configuration).

[0082] In addition, in the above first or second configuration, the lower end of the burr (416d) formed protruding from the inclined portion may be configured to be located axially above the lower end of the bottom wall portion (third configuration).

[0083] In any of the first to third configurations, the burrs (416d) formed on the inclined portion may be configured to protrude in the radial direction (fourth configuration).

[0084] In addition, in any of the above first to fourth configurations, the inclined portion may be configured such that a plurality of inclined surfaces (416e) having different inclination angles with respect to the center line are arranged in the axial direction (fifth configuration).

[0085] Furthermore, in any of the first to fifth configurations, the peripheral wall portion may have a first recess (417) formed by recessing the inner peripheral edge portion of the upper end surface downward in the axial direction, and a second recess (418) formed by recessing the inner peripheral edge portion of the bottom surface of the first recess further downward in the axial direction, and a ramp (34) holding a head (31) that reads or writes information from or to the disk (50) is placed on the bottom of the second recess, and the entire bottom of the first recess may be configured to be located axially above the bottom of the second recess (sixth configuration).

[0086] Furthermore, in the above sixth configuration, the radially inner surface of the second recess may have a flat portion (418a) parallel to the radially outer surface of the circumferential wall portion, and a curved portion (418b) that is curved and recessed radially outward from the flat portion, and the radially outer end of the curved portion may be positioned radially outward from the radially outer end of the flat portion (seventh configuration).

[0087] In the seventh configuration, the first recess may have curved recess 417a, the bottom surface of which is connected to the curved portion and recessed axially downward (eighth configuration).

[0088] In addition, in any of the above sixth to eighth configurations, the bottom wall portion may have a bottom wall recess that is recessed axially upward from the lower end surface, axially below the first recess (ninth configuration).

[0089] Moreover, the motor (2) according to an embodiment of the present disclosure may be configured to include a base plate 41 having any one of the first to ninth configurations described above (tenth configuration).

[0090] In addition, a disk drive device (1) according to one embodiment of the present disclosure may be configured to include a spindle motor (2) of the above-mentioned 10th configuration, a disk (50) rotated about the rotation axis by the spindle motor, and a head (31) that reads or writes information from or to the disk (11th configuration). [Industrial Applicability]

[0091] The present invention can be used in disk drive devices such as hard disk drives. [Explanation of symbols]

[0092] 1 Disk Drive Unit 2 Spindle motor 10 Stationary part 12 Stator 13 Bearing unit 14 Shaft 20 Rotating section 21 Shaft 22 Hub 22a Top section 22b Cylindrical surface part 23 Magnet 24 Spacer 31 Head 32 Arm 33 Swing Mechanism 34 Lamp 34a Guide section 40 Case 41 Base Plate 41a Electrochemical coating 41d Gate trace 42 Cover 50 discs 60 Processing tools 61 1st cutting blade 62 2nd cutting blade 121 Stator core 121a Coreback 121b Teeth 122 Coil 201, 202 Mold 201a Post recess 201b Shaft recess 201c protrusion 201d Expanded section 210 Cavity Gate 214 411 Bottom wall 411a Bottom wall recess 412 Peripheral wall section 413 Pivot Post 413a Post step 414f Recess 415 Shaft through hole 416 Screw hole 416a Slope 416b Column body part 416c Threaded part 416d Bali 417 First recess 417a Curved concave 418 Second recess 418a Plane section 418b Curved section 2011 Mizobe 2012 Mold protrusion 2013 First Convexity 2014 2nd Convexity 2021 Mold recess D diameter E Non-coating area H Swing Axis J Rotation axis L center line M straight line θ1 Tilt angle

Claims

1. A base plate that is a part of the housing of the disk drive device and is made of a metal die-cast member, a bottom wall portion extending perpendicular to a rotation axis of the disk extending in the vertical direction; a peripheral wall portion extending axially upward from a peripheral edge portion of the bottom wall portion and surrounding the periphery of the bottom wall portion, The bottom wall portion is A screw hole is provided that is recessed axially upward from the peripheral edge of the lower end surface, The screw hole is an inclined portion having an inner diameter that becomes smaller from a lower end toward an upper side in the axial direction; a column portion extending axially upward from an upper end of the inclined portion and having a threaded portion formed thereon to be threadedly engaged with a screw; A base plate, wherein the inclined portion is inclined at an inclination angle of 25° or more and 35° or less with respect to a center line extending axially through the center of the columnar portion in a cross section including the center line.

2. The base plate according to claim 1 , wherein a diameter of the lower end of the inclined portion is not less than 4.0 mm and not more than 4.6 mm.

3. 3. The base plate according to claim 1, wherein a lower end of a burr formed protruding from the inclined portion is located axially higher than a lower end of the bottom wall portion.

4. The base plate according to claim 1 or 2, wherein a burr formed on the inclined portion protrudes in a radial direction.

5. The base plate according to claim 1 or 2, wherein the inclined portion is configured with a plurality of inclined surfaces arranged in the axial direction, the inclined surfaces having different inclination angles with respect to the center line.

6. The peripheral wall portion is a first recess formed on an inner peripheral edge portion of the upper end surface by recessing downward in the axial direction; a second recess formed on an inner peripheral edge of a bottom surface of the first recess, the second recess being further recessed downward in the axial direction; a ramp for holding a head for reading or writing information from or to the disk is placed on the bottom of the second recess; The base plate according to claim 1 or 2, wherein an entire bottom of the first recess is located axially above a bottom of the second recess.

7. The radially inner surface of the second recessed portion is A flat surface portion parallel to a radially outer surface of the peripheral wall portion; A curved surface portion that is curved and recessed radially outward from the flat surface portion, The base plate according to claim 6 , wherein a radially outer end of the curved surface portion is located radially outward of a radially outer end of the flat surface portion.

8. The first recess is The base plate according to claim 7 , wherein a bottom surface connected to the curved surface portion has a curved recess formed by being recessed axially downward.

9. The base plate according to claim 6 , wherein the bottom wall portion has a bottom wall recess that is recessed axially upward from a lower end surface, axially below the first recess.

10. A motor comprising the base plate according to claim 1 or 2.

11. A motor according to claim 10; a disk rotated about the rotation axis by the motor; and a head for reading or writing information from or to the disk.

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