BASE PLATE, MOTOR, AND DISK DRIVE DEVICE

A base plate includes a bottom wall and a peripheral wall. The peripheral wall extends from the bottom wall to an axially upper side. The bottom wall includes a screw hole recessed from a peripheral edge of a lower end surface of the bottom wall to the axially upper side. The screw hole includes an inclined part and a column body. The inclined part is defined to have an inner diameter that decreases from a lower end toward the axially upper side. The column body extends from an upper end of the inclined part to the axially upper side and is defined with a threaded part. In a cross section including a center line that passes through a center of the column body in an axial direction, the inclined part is inclined at an inclination angle of 25° or more and 35° or less with respect to the center line.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention claims priority under 35 U.S.C. § 119 to Japanese Application No. 2023-106231 filed on Jun. 28, 2023 and Japanese Application No. 2024-069885 filed on Apr. 23, 2024, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to a base plate, a motor, a disk drive device, and a method for manufacturing the base plate.

BACKGROUND

A conventional base plate serving as a portion of a housing of a disk drive device is defined by a die-cast member including metal and includes a bottom wall. The bottom wall extends perpendicularly to a rotation axis of a disk extending in an up-down direction.

A screw hole for fixing a circuit board or the like with a screw is provided at a lower surface of the bottom wall. The screw hole is disposed at a peripheral edge of the bottom wall and extends from a lower end surface to an axially upper side. The screw hole is subjected to tapping (rolling) to define a threaded part to be screwed with the screw.

However, in the conventional base plate, a rolling tool may contact an inner circumferential surface at a lower end of the screw hole during tapping. At this time, a lower end of the defined threaded part may protrude from the inner circumferential surface at the lower end of the screw hole to generate a burr. Further, during tapping, a stress may be applied to a lower end circumferential edge of the screw hole, and the inner circumferential surface at the lower end of the screw hole may be partially raised to define a burr. In the case where a burr is defined protruding to the axially lower side compared to a lower end of the bottom wall, the base plate placed on a work table may rattle, and assembly precision of components mounted on the base plate may decrease.

SUMMARY

An exemplary base plate of the present disclosure is a portion of a housing of a disk drive device and is defined by a die-cast member including metal. The base plate includes a bottom wall and a peripheral wall. The bottom wall extends perpendicularly to a rotation axis of a disk extending in an up-down direction. The peripheral wall extends from a peripheral edge of the bottom wall to an axially upper side and surrounds a periphery of the bottom wall. The bottom wall includes a screw hole. The screw hole is recessed from a peripheral edge of a lower end surface of the bottom wall to the axially upper side. The screw hole includes an inclined part and a column body. The inclined part is defined to have an inner diameter that decreases from a lower end of the screw hole toward the axially upper side. The column body extends from an upper end of the inclined part to the axially upper side and is defined with a threaded part to be screwed with a screw. In a cross section including a center line that passes through a center of the column body and extends in an axial direction, the inclined part is inclined at an inclination angle of 25° or more and 35° or less with respect to the center line.

DETAILED DESCRIPTION

An exemplary embodiment of the present disclosure will be described in detail with reference to the drawings. In the present specification, a direction parallel to a rotation axis J of a disk50will be referred to as an “axial direction”, a direction orthogonal to the rotation axis J will be referred to as a “radial direction”, and a direction along an arc centered on the rotation axis J will be referred to as a “circumferential direction”. In the present application, shapes and positional relationships of each part will be described with the axial direction taken as an up-down direction and a cover42side as an upper side with respect to a base plate41. However, the definition of the up-down direction is not intended to limit orientations during use of the base plate41and a disk drive device1according to the present disclosure.

A disk drive device1according to an exemplary embodiment of the present disclosure will be described.FIG.1is a longitudinal sectional view of a disk drive device1according to an embodiment of the present disclosure.

The disk drive device1is a hard disk drive. The disk drive device1includes a spindle motor (motor)2, a disk50, a head31, an arm32, a swing mechanism33, a ramp34, and a housing40.

The housing40accommodates therein the spindle motor2, the disk50, the head31, the arm32, the swing mechanism33, and the ramp34.

A gas having a density lower than air is filled inside the housing40. Thus, an air flow resistance inside the housing40is able to be reduced to reduce vibration of the disk50. Specifically, a helium gas is filled. A hydrogen gas or the like may also be filled instead of the helium gas.

The housing40is defined by a die-cast member including an aluminum alloy as a material. The die-cast member may also include a metal other than an aluminum alloy.

The housing40includes a base plate41and a cover42. That is, the base plate41is a portion of the housing40of the disk drive device1and is defined by a die-cast member including metal. The disk50, the spindle motor2, and the swing mechanism33are disposed on the base plate41inside the housing40. An opening at an upper part of the base plate41is closed by the cover42. The base plate41will be described in detail later.

The spindle motor2rotates the disk50around the rotation axis J while supporting the disk50. That is, the disk50rotates by the spindle motor2around the rotation axis J extending in the up-down direction. The spindle motor2includes a stationary part10and a rotating part20. The stationary part10is stationary with respect to the housing40. The rotating part20is supported rotatably with respect to the stationary part10.

The stationary part10includes a shaft14and a stator12. A portion of the base plate41defines the stationary part10. The base plate41is a portion of the spindle motor2and is also a portion of the housing40. That is, the spindle motor2includes the base plate41. The stator12and a bearing unit13are fixed to the base plate41.

The shaft14is a columnar metal member extending in the axial direction. A lower end of the shaft14is fixed to the base plate41.

The stator12includes a stator core121, which is a magnetic body, and a plurality of coils122. The stator core121includes an annular core back121aand a plurality of teeth121b. The core back121ais disposed around the rotation axis J. The teeth121bfixed to the base plate41protrude toward a radially outer side from an outer circumferential surface of the core back121aand are disposed in the circumferential direction. The plurality of coils122are defined by conductive wires wound around the teeth121b.

The bearing unit13is disposed at an outer circumference of the shaft14and rotatably supports a hub22on the rotating part20side. For example, the bearing unit13includes a fluid dynamic pressure bearing mechanism.

The rotating part20includes a hub22and a magnet23. The hub22includes a top surface part22aand a cylindrical surface part22b. The top surface part22ais disposed at an outer circumference of the bearing unit13and extends toward the radially outer side. The cylindrical surface part22bis defined in a substantially cylindrical shape extending in the axial direction and includes a flange22cextending to the radially outer side from a lower end. A plurality of disks50are arranged in the axial direction on an outer circumferential surface of the cylindrical surface part22b.

The magnet23is fixed to an inner circumferential surface of the cylindrical surface part22band is disposed opposed to the radially outer side of the stator12by a predetermined distance away from each other. The magnet23has a substantially ring shape, and an N pole and an S pole are alternately magnetized in the circumferential direction on an inner circumferential surface of the magnet23.

Upon supply of a drive current to the coils122, a magnetic flux is generated in the plurality of teeth121b. At this time, the magnetic flux interacts between the teeth121band the magnet23, and a torque in the circumferential direction is generated. Accordingly, the rotating part20rotates around the rotation axis J with respect to the stationary part10. The disk50supported by the hub22rotates around the rotation axis J together with the rotating part20.

The disk50is a substantially disk-shaped information recording medium having a hole at a center. The disks50are mounted to the spindle motor2and are disposed in parallel with each other in the axial direction at an equal interval via a spacer24.

The head31magnetically reads and writes information from and to the disk50. The arm32is attached to a tip of a pivot post413via a bearing (not shown). The head31is disposed at a tip of the arm32.

The pivot post413is defined in a substantially cylindrical shape protruding upward from an upper surface of a bottom wall411of the base plate41(to be described later) along a swing axis H. The pivot post413includes a post step part413a(seeFIG.4). The post step part413ais defined in a substantially annular shape protruding to the radially outer side from an outer circumferential surface of a root of the pivot post413. A bottom of the post step part413ais integrally defined with an upper part of the bottom wall411. The root of the pivot post413is reinforced by the post step part413aprovided. Accordingly, the pivot post413is able to be prevented from tilting with respect to the swing axis H.

The swing mechanism33is a mechanism for swinging the arm32and the head31. Upon driving the swing mechanism33, the head31swings around the swing axis H via the arm32. At this time, the head31moves relatively with respect to the disk50and accesses the rotating disk50in close proximity.

FIG.2is a plan view schematically illustrating a periphery of the disk50, andFIG.3is a cross-sectional view taken along line A-A inFIG.2. The ramp34is placed at a bottom of a second recess418(to be described later) of a peripheral wall412(seeFIG.4), and includes a plurality of guides34aarranged in the axial direction. The guides34asandwich the disk50in the axial direction and are disposed in close proximity to the disk50. When the access to the disk50is finished, the head31retreats from the disk50by the swing mechanism33and moves in a direction toward the ramp34. At this time, the head31is held in the ramp34via a tip of the guide34a. That is, the ramp34holds the head31which reads or writes information from and to the disk50.

FIG.4andFIG.5are perspective views schematically illustrating the base plate41, andFIG.4illustrates the base plate41from an axially upper side.FIG.5illustrates the base plate from an axially lower side. The base plate41includes a bottom wall411, a peripheral wall412, and a pivot post413.

In the present embodiment, the bottom wall411, the peripheral wall412, and the pivot post413are an integrally defined cast product. Although the bottom wall411and the peripheral wall412are an integrally defined cast product herein, the base plate41may also be defined by assembling a bottom wall411and a peripheral wall412respectively cast as separate members.

The bottom wall411has a substantially rectangular shape when viewed from the axial direction, and extends perpendicularly to the rotation axis J and the swing axis H extending in the up-down direction. The bottom wall411has a shaft through hole415and screw holes416. The shaft through hole415penetrates the bottom wall411in the axial direction along the rotation axis J. A lower end of the shaft14is press-fitted into the shaft through hole415and fixed to the bottom wall411.

The screw hole416is recessed from a peripheral edge of a lower end surface of the bottom wall411to the axially upper side. A circuit board (not shown) connected to the coils122of the spindle motor2is disposed on a lower surface of the bottom wall411. The circuit board has board through holes (not shown) penetrating in the axial direction.

Screws (not shown) are inserted into the board through holes and screwed into the screw holes416. Accordingly, the circuit board is fixed to the bottom wall411. Although the screw hole416is used for fixing the circuit board in the present embodiment, the present disclosure is not limited thereto. For example, the screw hole416may also be used when fixing a component other than a circuit board to the base plate. The shape of the screw hole416will be described in detail later.

The peripheral wall412extends from an outer peripheral edge of the bottom wall411to the axially upper side and surrounds the periphery of the bottom wall411. The cover42is screw-fastened to an upper end surface of the peripheral wall412. The peripheral wall412includes a first recess417and a second recess418. The ramp34is placed at the bottom of the second recess418. The first recess417and the second recess418will be described in detail later.

The pivot post413protrudes upward from the upper surface of the bottom wall411along the swing axis H. The swing mechanism33is supported by the bottom wall411via the pivot post413.

FIG.6,FIG.7, andFIG.8are enlarged longitudinal sectional views schematically illustrating the screw hole416.FIG.6illustrates a state before tapping.FIG.7andFIG.8illustrate states after tapping. The screw hole416includes an inclined part416aand a column body416b. The inclined part416ahas a substantially truncated cone shape and is defined to have an inner diameter that decreases from a lower end toward the axially upper side. The column body416bhas a substantially cylindrical shape, extends from an upper end of the inclined part416ato the axially upper side, and is defined with a threaded part416cto be screwed with a screw (not shown). The threaded part416cis a female screw defined by tapping (rolling) the screw hole416.

In the present embodiment, in a cross section including a center line L extending in the axial direction through a center of the column body416b, the inclined part416ais inclined at an inclination angle θ1of, for example, 25° or more and 35° or less with respect to the center line L. Upon keeping a diameter D at a lower end of the inclined part416aconstant and setting the inclination angle θ1of the inclined part416ato be small, a stress applied to a periphery of the lower end of the inclined part416ais able to be reduced during tapping. Accordingly, generation of a burr416ddue to a partial raise at the periphery of the lower end of the inclined part416ais able to be suppressed. Hence, when the base plate41is placed on a work table, contact between a burr416dand the work table and thus rattling of the base plate41are able to be prevented. Accordingly, a decrease in assembly precision of components mounted on the base plate41is able to be prevented.

In the case where a length of the screw hole416in the axial direction is determined, if the diameter D at the lower end of the inclined part416ais kept constant and the inclination angle θ1of the inclined part416ais set to be small, a ratio of the inclined part416ain the axial direction to the whole screw hole416increases. As a result, a ratio of the column body416b, at which the threaded part416cis defined, in the axial direction is reduced. Thus, a fastening strength of the screw is reduced. In the present embodiment, by setting the inclination angle θ1of the inclined part416ato be 25° or more, for example, a decrease in the fastening strength of the screw is able to be suppressed.

In the case where a burr416dis generated at the inclined part416a, if the diameter D at the lower end of the inclined part416ais kept constant and the inclination angle θ1of the inclined part416ais set to be large, the burr416dis inclined toward the axially lower side (seeFIG.8). Thus, by setting the inclination angle θ1of the inclined part416ato be 35° or less, for example, with respect to the center line L, a tip of the burr416dis able to be prevented from protruding to the axially lower side of the lower end of the bottom wall411. Accordingly, even if the burr416dis generated at the inclined part416a, a decrease in assembly precision of components mounted on the base plate41is able to be prevented. Further, even in the case where a rolling tool contacts the inclined part416ato define the threaded part416con the inclined part416a, by keeping the diameter D at the lower end of the inclined part416ato be constant and setting the inclination angle θ1of the inclined part416ato be 35° or less, for example, with respect to the center line L, the lower end of the threaded part416cis able to be prevented from protruding from the inclined part416ato become a burr and protruding to the axially lower side compared to the lower end of the bottom wall411.

The diameter D at the lower end of the inclined part416ais preferably 4.0 mm or more and 4.6 mm or less, for example. In the case where the length of the screw hole416in the axial direction is determined, if the inclination angle θ1is kept constant and the diameter D at the lower end of the inclined part is set to be large, a ratio of the inclined part416ain the axial direction in the whole screw hole416increases. As a result, a ratio of the column body416b, at which the threaded part416cis defined, in the axial direction decreases. Accordingly, the range occupied by the threaded part416cin the axial direction decreases, and the fastening strength of the screw decreases. In the present embodiment, by setting the diameter D at the lower end of the inclined part416ato be 4.6 mm or less, for example, a decrease in the fastening strength of the screw is able to be suppressed.

In the case where the diameter D at the lower end of the inclined part416ais larger than 4.6 mm, for example, a region overlapping with a screw head in the axial direction on the lower end surface of the bottom wall411becomes narrow, and it becomes difficult to stably screw-fasten the component screw-fastened to the screw hole416.

In the case where the diameter D at the lower end of the inclined part416ais larger than 4.6 mm, for example, a distance between the peripheral edge of the bottom wall411and the screw hole416becomes narrow, and the peripheral edge of the bottom wall411is likely to deform or chipping is likely to occur.

In the case where the axial length of the screw hole416is determined, if the inclination angle θ1is set to be constant and the diameter D at the lower end of the inclined part is set to be small, a stress applied to the periphery of the lower end of the inclined part416aincreases during tapping. In the present embodiment, by setting the diameter D at the lower end of the inclined part416ato be 4.0 mm or more, for example, generation of a burr416dat the inclined part416ais able to be suppressed.

The burr416dgenerated at the inclined part416apreferably protrudes in the radial direction, and a lower end of the burr416dis preferably located on the axially upper side compared to the lower end of the bottom wall411(seeFIG.8). Thus, even if the burr416dis generated at the inclined part416a, a decrease in assembly precision of components mounted on the base plate41is able to be prevented.

FIG.9is an enlarged perspective view illustrating a periphery of the second recess418of the base plate41, andFIG.10is an enlarged top view illustrating the periphery of the second recess418of the base plate41.FIG.11is a cross-sectional view taken along line B-B inFIG.10. The first recess417is defined by recessing an inner peripheral edge of the upper end surface of the peripheral wall412to the axially lower side. The second recess418is defined by recessing an inner peripheral edge of a bottom surface of the first recess417further to the axially lower side, and the ramp34is placed thereon. An entire bottom of the first recess417is located on the axially upper side compared to a bottom of the second recess418.

By defining the first recess417, the peripheral wall412is thinned in the radial direction in the periphery of the second recess418in which the ramp34is placed. A shrinkage cavity is generated when molten metal is cooled, hardens, and shrinks during casting. By thinning the peripheral wall412in the radial direction, a hardening time of the peripheral wall412is shortened, and generation of a shrinkage cavity is able to be reduced. Accordingly, generation of a shrinkage cavity at the peripheral wall412is able to be reduced in the periphery of the second recess418. Thus, a decrease in dimensional precision of the base plate41is able to be suppressed in the periphery of the second recess418. Accordingly, positional precision of the ramp34is able to be improved.

The entire bottom of the first recess417is located on the axially upper side compared to the bottom of the second recess418. As a result, a portion (first protrusion2013) of a mold201defining the first recess417does not protrude to the axially lower side compared to the bottom of the second recess418(seeFIG.14). Thus, a projection is not defined at a portion (first protrusion2013) of the mold201during casting. Accordingly, melting loss of the projection is able to be prevented. In the case where a portion (first protrusion2013) of the mold201defining the first recess417protrudes to the axially lower side compared to the bottom of the second recess418and a projection is defined, melting loss may occur at the projection due to an increase in a mold temperature of the projection during casting. Thus, by defining a shape in which a projection is not provided at a portion (first protrusion2013) of the mold201, occurrence of melting loss is able to be prevented. Thus, generation of a burr at the bottom of the first recess417is able to be prevented. Accordingly, generation of a burr around the bottom of the second recess418is able to be prevented to further improve positional precision of the ramp34.

A radially inner surface of the second recess418includes a planar surface418aand a curved surface418b. The planar surface418ais defined parallel to a radially outer surface of the peripheral wall412. The curved surface418bis defined to be curved and recessed to the radially outer side compared to the planar surface418a. A radially outer end of the curved surface418bis located on the radially outer side compared to a radially outer end of the planar surface418a. By defining the curved surface418b, the bottom of the second recess418expands to the radially outer side, and the ramp34is able to be stably disposed at the bottom of the second recess418. Accordingly, positional precision of the ramp34is able to be further improved.

The first recess417has a curved surface recess417a. The curved surface recess417ais defined by recessing a bottom surface, which is continuous with the curved surface418b, to the axially lower side. By defining the curved surface recess417a, the first recess417is able to be thinned in the axial direction to suppress generation of a shrinkage cavity. Accordingly, a decrease in dimensional precision of the base plate41is able to be further suppressed in the periphery of the second recess418.

On the axially lower side of the first recess417, the bottom wall411has a bottom wall recess411athat is recessed from the lower end surface to the axially upper side. By disposing the bottom wall recess411aon the axially lower side of the first recess417, the bottom wall411is able to be thinned in the axial direction to suppress generation of a shrinkage cavity. Accordingly, a decrease in sealing property of the housing40and a decrease in dimensional precision of the base plate41are able to be further suppressed.

In a cross section orthogonal to the swing axis H, an inclination angle θ2between a straight line M1extending in the radial direction from the swing axis H to contact an end of the second recess418on the disk50side and a straight line M2extending along the planar surface418ais preferably 75° or more and 85° or less, for example. At this time, by setting the inclination angle θ2to be 75° or more and 85° or less, for example, the guide34ais able to be disposed in close proximity to the disk50. Thus, when the head31moves between an access position and a retreat position with respect to the disk50, the head31is held by the ramp34at a shorter distance. Accordingly, a time for the head31to access the disk50is able to be shortened.

FIG.12is a flowchart illustrating a manufacturing process of the base plate41.FIG.13toFIG.20are views illustrating the manufacturing process of the base plate41.FIG.14is an enlarged view illustrating the periphery of the first protrusion2013at which the first recess417of the peripheral wall412is defined.FIG.20is an enlarged view illustrating the pivot post413.

In step S1, as illustrated inFIG.13, a peripheral edge of a mold202and a peripheral edge of a mold201are brought into contact with each other in the up-down direction to define a cavity210between the mold201and the mold202. The cavity210has a shape corresponding to the shape of the base plate41.

Specifically, the mold201is defined in a substantially rectangular parallelepiped shape and has a groove2011and a mold protrusion2012. The groove2011is defined in a substantially annular shape by an outer peripheral part of a lower surface of the mold201recessed to the axially upper side. On the radially inner side of the groove2011, the mold protrusion2012is defined by the lower surface of the mold201protruding to the axially lower side. A lower end of the mold protrusion2012is located lower than a lower end of the mold201on an outer side of the groove2011. Molten metal flows into the groove2011to define the peripheral wall412.

The mold202is defined in a substantially rectangular parallelepiped shape, and the mold202has a mold recess2021. The mold recess2021is defined by an upper surface of the mold202recessed to the axially lower side in a region opposed to the mold protrusion2012in the up-down direction. Molten metal flows into the mold recess2021to define the bottom wall411.

The cavity210communicates with a gate214extending along opposing surfaces of the mold201and the mold202. An outer end of the gate214is opened to outside of the mold201and the mold202.

An air vent passage (not shown) for venting air in the cavity210is provided on the opposing surfaces of the mold201and the mold202separately from the gate214. An outer end of the air vent passage is opened to outside of the mold201and the mold202.

The mold201has a post recess201aand a shaft recess201b. The post recess201ais defined by the lower surface of the mold protrusion2012recessed to the axially upper side along the swing axis H. The inside of the post recess201acommunicates with the cavity210. A diameter-enlarged part201dis defined at a lower end of an inner circumferential surface of the post recess201a. The diameter-enlarged part201dhas a diameter larger than an upper end of the inner circumferential surface of the post recess201a. Molten metal flows into the post recess201ato define the pivot post413. Molten metal flows into the diameter-enlarged part201dto define the post step part413a.

The shaft recess201bis defined by the lower surface of the mold protrusion2012recessed to the axially upper side along the rotation axis J. The inside of the shaft recess201bcommunicates with the cavity210. A projection201cprotruding downward is defined at a top surface of the shaft recess201b.

When molten metal flows into the shaft recess201b, a recess414fis defined at a position at which the projection201cis disposed (seeFIG.16). The recess414fis defined as recessed from the upper surface of the bottom wall411to the axially lower side.

The mold201further includes a first protrusion2013and a second protrusion2014that protrude in the radial direction from the radially outer surface of the mold protrusion2012(seeFIG.14). The first protrusion2013is defined across an inner peripheral edge of a top surface of the groove2011and a radially outer surface of the mold protrusion2012. The second protrusion2014is defined across an inner peripheral edge of a bottom surface of the first protrusion2013and the radially outer surface of the mold protrusion2012. Accordingly, a lower end of the first protrusion2013is located on the axially upper side compared to a lower end of the second protrusion2014.

When molten metal flows into the cavity210, the first recess417is defined at a position corresponding to the first protrusion2013. Further, a second recess418is defined at a position corresponding to the second protrusion2014.

As illustrated inFIG.15, in step S2, molten metal is injected into the cavity210via the gate214. The molten metal is, for example, a molten aluminum alloy. Upon injection of the molten metal into the cavity210, air in the cavity210or a gas generated from the molten metal is pushed out from the air vent passage to outside the mold201and the mold202. As a result, the molten metal spreads throughout the cavity210.

In step S3, after the molten metal spreads in the cavity210, the molten metal is cooled and hardened. Accordingly, the base plate41is defined in the cavity210. A chill layer (not shown) is defined on the surface of the base plate41. When the molten metal hardens, the chill layer is defined at sites where the molten metal is contact with the mold201and the mold202and hardens quickly. The chill layer in which the molten metal hardens more quickly than the other portion has fewer impurities and a higher metal density.

As illustrated inFIG.16, in step S4, the base plate41is released from the pair of molds201and202. At this time, the peripheral wall412has a gate mark41dprotruding from the outer surface. The gate mark41dis defined by hardened molten metal accumulated in the gate214and the air vent passage (not shown).

As illustrated inFIG.17, in step S5, the gate mark41dis cut off. In step S6, the base plate41is subjected to cutting. More specifically, the recess414fis cut in the axial direction to penetrate the bottom wall411in the axial direction. Accordingly, the shaft through hole415is defined by cutting. Further, a mark (not shown) obtained by cutting off the gate mark41dis left slightly protruding from the outer surface of the peripheral wall412.

The radially inner surface of the peripheral wall412opposed to the disk50in the radial direction and the upper surface of the peripheral wall412are subjected to cutting.

As illustrated inFIG.18, in step S7, an electrodeposition coating film41ais defined on the surface of the base plate41. Regarding the electrodeposition coating film41a, the base plate41is immersed in a coating material of an epoxy resin, for example, and a current is passed between the coating material and the base plate41. Accordingly, the coating material adheres to the surface of the base plate41to define the electrodeposition coating film41a. At this time, an outer surface of the cut surface cut in step S6is also covered with the electrodeposition coating film41a. By covering the base plate41with the electrodeposition coating film41a, the insulating property of the base plate41is able to be improved, and leakage of a gas passing through the base plate41is able to be reduced.

As illustrated inFIG.19, in step S8, a region of the surface of the base plate41requiring precision is subjected to precision machining and shaping by cutting. Specifically, the outer circumferential surface of the pivot post413, the upper surface of the post step part413a, the inner circumferential surface of the shaft through hole415, the periphery of the shaft through hole415at the upper surface of the bottom wall411, the bottom surface of the second recess418, the peripheral edge of the upper end surface of the peripheral wall412, and the peripheral edge of the lower end surface of the bottom wall411are shaped. At this time, the periphery of the screw hole416and a periphery of a component screw hole (not shown) for fixing a component defined on the upper surface of the bottom wall411are also shaped.

By performing precision machining and shaping on the bottom surface of the second recess418, the positional precision of the ramp34is able to be further improved.

By performing precision machining and shaping on the peripheral edge of the upper end surface of the peripheral wall412, the cover42is able to be brought into close contact with the peripheral edge of the upper end surface of the peripheral wall412to improve the sealing property of the housing40. Further, by performing precision machining and shaping on the peripheral edge of the lower end surface of the bottom wall411, rattling of the base plate placed on the work table is able to be suppressed.

As illustrated inFIG.20, a machining tool60is preferably used for performing precision machining on the outer circumferential surface of the pivot post413and the upper surface of the post step part413a. The machining tool60is a cylindrical body with an opened bottom surface, and the pivot post413is inserted therein. The machining tool60includes a first cutting blade61disposed at an inner circumferential surface and a second cutting blade62disposed at a bottom surface. With the pivot post413inserted therein, the machining tool60rotates around a central axis C extending along the pivot post413. Accordingly, the pivot post413is able to be machined into a perfect circle in a cross section orthogonal to the central axis C.

The upper surface of the post step part413ais machined by the second cutting blade62to define a plane orthogonal to the central axis C. At this time, the outer circumferential surface of the pivot post413and the upper surface of the post step part413aare able to be simultaneously machined by one machining tool60. Accordingly, a machining time is able to be shortened. When the upper surface of the post step part413ais machined by the second cutting blade62, a machining mark (not shown) may be defined on the upper surface of the post step part413a. For example, the machining mark may be a plurality of annular linear marks defined around the central axis C. Further, an annular groove (not shown) may also be defined on the upper surface of the post step part413aby the second cutting blade62.

The electrodeposition coating film41ais also cut due to the cutting of the surface of the base plate41, and a non-coated region E in which the electrodeposition coating film41ais not provided is defined.

In step S9, the screw hole416and the component screw hole (not shown) are subjected to tapping (rolling) to define the threaded part416c.

In step S10, the base plate41is immersed in an impregnant. As a result, the impregnant is infiltrated into the non-coated region E. At this time, the impregnant is also infiltrated into the precision-machined surface shaped in step S8. The impregnant is, for example, an epoxy resin or an acrylic resin. In this manner, in the non-coated region E, the minute cavities defined during casting are sealed with the impregnant. Thus, leakage of the gas filled inside the housing40to the outside is able to be further suppressed.

The manufacturing method of the base plate41as a cast product which is a portion of the housing40of the disk drive device1sequentially includes a casting process, a cutting process, an electrodeposition coating process, a shaping process, a tapping process, and an impregnation process. In the casting process, the bottom wall411and the peripheral wall412are cast integrally by the molds (steps S1to S4). In the cutting process, the shaft through hole415is defined by cutting (step S6). In the electrodeposition coating process, the electrodeposition coating film41ais defined on the surface of the base plate41(step S7). In the shaping process, a region of the surface of the base plate41requiring precision is subjected to precision machining and shaping by cutting (step S8). In the tapping process, the screw hole416is tapped to define the threaded part416c(step S9). In the impregnation process, a region exposed from the electrodeposition coating film41aon the surface of the base plate41is impregnated with an impregnant (step S10).

The above embodiments are merely examples of the present disclosure. For example,FIG.21is an enlarged longitudinal sectional view illustrating a screw hole416according to a modification example, in which an inclined part416amay also be defined such that a plurality of inclined surfaces416ehaving different inclination angles θ1with respect to the center line L are arranged in the axial direction. Thus, a stress applied to the periphery of the lower end of the inclined part416ais able to be reduced when tapping is performed. Accordingly, generation of a burr416ddue to a partial raise at the periphery of the lower end of the inclined part416ais able to be suppressed.

As described above, a base plate (41) according to an aspect of the present disclosure is a portion of a housing (40) of a disk drive device (1) and is defined by a die-cast member including metal. The base plate includes a bottom wall (411) and a peripheral wall (412). The bottom wall (411) extends perpendicularly to a rotation axis (C) of a disk extending in an up-down direction. The peripheral wall (412) extends from a peripheral edge of the bottom wall to an axially upper side and surrounds a periphery of the bottom wall. The bottom wall includes a screw hole (416) recessed from a peripheral edge of a lower end surface to the axially upper side. The screw hole includes an inclined part (416a) and a column body (416b). The inclined part (416a) is defined to have an inner diameter that decreases from a lower end toward the axially upper side. The column body (416b) extends from an upper end of the inclined part to the axially upper side and is defined with a threaded part (416c) to be screwed with a screw. In a cross section comprising a center line that passes through a center of the column body and extends in an axial direction, the inclined part is inclined at an inclination angle of 25° or more and 35° or less with respect to the center line (first configuration).

In the first configuration, a diameter at the lower end of the inclined part may be 4.0 mm or more and 4.6 mm or less (second configuration).

In the first or second configuration, a lower end of a burr (416d) defined protruding from the inclined part may be located on the axially upper side compared to a lower end of the bottom wall (third configuration).

In any one of the first to third configurations, a burr (416d) defined at the inclined part may protrude in a radial direction (fourth configuration).

In any one of the first to fourth configurations, the inclined part may be defined by a plurality of inclined surfaces (416e) that have different inclination angles with respect to the center line and are arranged in the axial direction (fifth configuration).

In any one of the first to fifth configurations, the peripheral wall may include a first recess (417) and a second recess (418). The first recess (417) is defined by recessing an inner peripheral edge of an upper end surface to an axially lower side. The second recess (418) is defined by further recessing an inner peripheral edge of a bottom surface of the first recess to the axially lower side. A ramp (34) holding a head (31) that reads or writes information from and to the disk (50) may be placed at a bottom of the second recess. An entire bottom of the first recess may be located on the axially upper side compared to the bottom of the second recess (sixth configuration).

In the sixth configuration, a radially inner surface of the second recess may include a planar surface (418a) and a curved surface (418b). The planar surface (418a) is parallel to a radially outer surface of the peripheral wall. The curved surface (418b) is curved and recessed to a radially outer side compared to the planar surface. A radially outer end of the curved surface may be located on the radially outer side compared to a radially outer end of the planar surface (seventh configuration).

In the seventh configuration, the first recess may include a curved surface recess (417a) defined by recessing a bottom surface, which is continuous with the curved surface, to the axially lower side (eight configuration).

In any one of the sixth to eighth configurations, on the axially lower side of the first recess, the bottom wall may include a bottom wall recess recessed from the lower end surface to the axially upper side (ninth configuration).

A motor (2) according to an aspect of the present disclosure may include the base plate (41) according to any one of the first to ninth configurations (tenth configuration).

A disk drive device (1) according to an aspect of the present disclosure may include: the spindle motor (2) according to the tenth configuration; a disk (50) rotated around the rotation axis by the spindle motor; and a head (31) that reads or writes information from and to the disk (eleventh configuration).

For example, the present disclosure is applicable to a disk drive device such as a hard disk drive.