Disk Drive Base Plate Structure for Shrinkage Cavity Control
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Solution Overview
Problem
Conventional base plates in 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 disk and head, which can cause read/write errors.
Innovation Solution
The base plate design includes an annular stepped portion with a processed surface on its outer peripheral surface, which is formed during a cutting step after casting, to prevent shrinkage cavities from forming near the shaft through hole, enhancing the rigidity and alignment of the shaft, and reducing gas leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the cylindrical wall portion is formed by conventional die-casting, then production efficiency is improved, but shrinkage cavities are generated in the cylindrical wall portion
Solution Approach 1:
The cylindrical wall portion is divided into two distinct regions: a root portion with smaller diameter and a upper portion with larger diameter. This segmentation allows the root portion to be formed with higher precision to prevent shrinkage cavities near the shaft through hole, while the upper portion can accommodate normal casting variations. The segmented structure resolves the contradiction by localizing precision requirements to where they are most critical.
Solution Approach 2:
Different quality standards are applied to different regions of the cylindrical wall portion. The root portion, which contains the shaft through hole, is manufactured with higher precision and stricter quality control to eliminate shrinkage cavities. The upper portion accepts normal casting quality. This local quality approach maintains production efficiency while ensuring critical areas meet high precision requirements.
2Reliability
If shrinkage cavities are present in the cylindrical wall portion, then gas leakage occurs, but adding preventive measures increases device complexity
Solution Approach 1:
The cylindrical wall portion is designed with a segmented structure (root portion and upper portion) before casting to prevent shrinkage cavity formation in the first place. By pre-planning the geometry with a smaller diameter root portion that solidifies first, the design prevents gas leakage pathways before they can form. This preliminary structural consideration avoids the need for additional sealing components or complex preventive measures.
3Manufacturing precision
If the shaft through hole surface accuracy is reduced due to shrinkage cavities, then shaft alignment is compromised, but improving casting precision increases manufacturing complexity
Solution Approach 1:
The cylindrical wall portion is segmented into a root portion and upper portion, concentrating precision requirements on the root portion that contains the shaft through hole. This segmentation allows the critical area to be formed with higher accuracy through optimized local casting parameters, while the rest of the structure can use standard casting processes. The segmentation resolves the contradiction by localizing precision demands rather than requiring uniform high precision throughout.
Data Source
AI summary
A base plate and a spindle motor having the same are provided. The base plate made of a metal die-cast member becomes a part of a housing of a disk drive device. The base plate includes a bottom wall portion that extends perpendicularly to a rotation axis of a disk extending in a vertical direction; and a peripheral wall portion that extends upward in an axial direction along the rotation axis from an outer peripheral edge of the bottom wall portion and surrounds the bottom wall portion. A parting line portion is configured to extend along a circumferential direction around an outer peripheral surface of the peripheral wall portion. A cutting mark is configured to extend in a band shape along the circumferential direction around the outer peripheral surface. When viewing the peripheral wall portion from outward the cutting mark has at least a portion overlapped with the parting line.