Stepped Base Plate Structure for Airtight Spindle Motor Alignment
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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 is manufactured with an annular stepped portion protruding radially outward from the cylindrical wall portion, featuring a processed surface with controlled cutting to minimize shrinkage cavities and enhance rigidity, and a shaft inclined portion for precise press-fitting, along with a cutting process to ensure uniform thickness and reduce gas leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the cylindrical wall portion is formed by conventional die-casting, then the base plate can be manufactured efficiently, but shrinkage cavities are generated in the cylindrical wall portion causing gas leakage and reduced surface accuracy
Solution Approach 1:
The cylindrical wall portion is divided into multiple sections with different radial thicknesses, creating a stepped structure. This segmentation allows different regions to serve different functions: thicker sections provide structural support and control shrinkage cavity formation, while thinner sections reduce material usage and casting complexity, maintaining manufacturing efficiency while improving surface accuracy at the shaft through hole location
Solution Approach 2:
The cylindrical wall portion is designed with non-uniform radial thickness, creating local variations in material distribution. The stepped portions have greater thickness to control shrinkage behavior and provide structural integrity, while other areas maintain thinner walls. This local quality variation prevents shrinkage cavities from forming at critical locations like the shaft through hole, thereby improving manufacturing precision without sacrificing overall productivity
2Ease of manufacture
If the cylindrical wall portion is made with uniform thickness, then the manufacturing process is simplified, but shrinkage cavities form and expose at the shaft through hole reducing airtightness
Solution Approach 1:
The cylindrical wall is segmented into multiple stepped portions with different radial thicknesses. This segmentation strategically positions thicker sections to control shrinkage cavity formation and prevent them from exposing at the shaft through hole, thereby maintaining airtightness. The segmentation is integrated into the casting process, so while the geometry is more complex, the manufacturing steps remain comparable to conventional casting
Solution Approach 2:
Different radial thicknesses are applied at different locations of the cylindrical wall portion. The stepped portions have increased thickness to serve as shrinkage compensation zones, ensuring that any shrinkage cavities form in non-critical areas rather than at the shaft through hole. This local quality variation maintains reliability and airtightness while keeping the casting process relatively simple
3Manufacturing precision
If the shaft through hole peripheral surface is scraped due to shaft misalignment, then the shaft may come out from the cylindrical wall portion, but this creates shavings that cause gas leakage
Solution Approach 1:
The stepped portions with greater radial thickness provide localized structural reinforcement and improved rigidity to the cylindrical wall portion. This enhanced local structure maintains the positional accuracy of the shaft through hole and prevents shaft misalignment during operation. By preventing misalignment, the structure eliminates the harmful effect of shavings generation and subsequent gas leakage, without requiring additional components or complex assembly procedures
Data Source
AI summary
A base plate becomes 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 portion and a cylindrical wall portion. The bottom wall portion extends perpendicular to a rotation axis of a disk extending in a vertical direction. The cylindrical wall portion protrudes upward from an upper surface of the bottom wall portion along the rotation axis and has a shaft through hole through which a shaft is inserted. The cylindrical wall portion has an annular stepped portion that protrudes radially outward from an outer peripheral surface of a root portion. A processed surface is formed on at least a part of an outer peripheral surface of the stepped portion.