Spindle Motor Base Plate Geometry for Shaft Hole Accuracy
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Solution Overview
Problem
Conventional base plates for disk drive devices made of metal die-cast members are prone to shrinkage cavities in the cylindrical wall portion, leading to gas leakage, reduced surface accuracy of the shaft through hole, and potential misalignment of the shaft, which can cause disk read/write errors.
Innovation Solution
The base plate design includes an annular stepped portion with a processed surface on its outer peripheral surface, formed through a casting and cutting process, which minimizes shrinkage cavities away from the shaft through hole and enhances the rigidity and alignment of the shaft, ensuring stable support of the spindle motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the cylindrical wall portion is made by conventional die-casting, then production efficiency is maintained, but shrinkage cavities are generated in the cylindrical wall portion
Solution Approach 1:
The cylindrical wall portion is divided into multiple sections with different thicknesses (first cylindrical section with smaller diameter, second cylindrical section with larger diameter). This segmentation allows the thicker second section to serve as a reservoir that absorbs shrinkage cavities during casting, preventing them from forming in the shaft through hole area while maintaining overall production efficiency through die-casting.
Solution Approach 2:
Different sections of the cylindrical wall portion are designed with different thicknesses to address local casting defects. The second cylindrical section has a larger diameter and serves as a local reservoir for shrinkage cavities, while the first cylindrical section maintains the required precision for the shaft through hole. This local quality differentiation resolves the contradiction between production efficiency and manufacturing precision.
2Reliability
If shrinkage cavities are present in the cylindrical wall portion, then gas leakage occurs, but adding structural features to prevent cavities increases manufacturing complexity
Solution Approach 1:
The cylindrical wall portion is segmented into multiple sections with varying diameters, where the thicker second section acts as a built-in reservoir to capture shrinkage cavities. This segmentation approach prevents gas leakage paths while avoiding the need for additional separate components or complex sealing structures, thus maintaining relatively simple manufacturing processes.
Solution Approach 2:
The function of preventing gas leakage is merged into the structural design of the cylindrical wall portion itself by creating a thickness variation that naturally directs shrinkage cavities away from the shaft through hole. This combines the structural support function with the gas seal function in a single integrated component, avoiding additional complexity from separate sealing elements.
3Manufacturing precision
If the shaft through hole peripheral surface is scraped due to shaft misalignment, then surface accuracy deteriorates, but preventing misalignment requires more precise casting control
Solution Approach 1:
The cylindrical wall portion is divided into sections with different thicknesses, where the thicker second section serves as a cushion that absorbs casting shrinkage and prevents misalignment of the shaft through hole. This segmentation provides a built-in compensation mechanism that maintains surface accuracy without requiring extremely precise casting control, thus balancing manufacturing precision with ease of manufacture.
Solution Approach 2:
The second cylindrical section with larger diameter is designed beforehand to serve as a cushion zone that absorbs potential shrinkage cavities and prevents them from affecting the shaft through hole area. This prior cushioning approach proactively compensates for casting variations, maintaining surface accuracy while allowing for normal casting process tolerances.
Data Source
AI summary
A spindle motor is provided. The spindle motor inclues a base plate becoming a part of a housing of a disk drive device including a bottom wall portion extending perpendicularly to a rotation axis of a disk; and a cylindrical wall portion protruding upward from an upper surface of the bottom wall portion and has a shaft through hole through which a shaft is inserted. The spindle motor further includes the shaft extending along the rotation axis and has a lower end inserting through the shaft through hole; an annular stator core; a rotor; and a bearing unit supporting the rotor to be rotatable about the shaft as the rotation axis. The shaft has a shaft inclined portion which is disposed at the lower end of the shaft and has an outer diameter decreasing toward a lower side in an axial direction.