Stepped Base Member Cavity Suppression in HDD Spindle Motors
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Solution Overview
Problem
The existing techniques for forming base members in hard disk drive devices, particularly those with protrusions, often result in cavity formation during the casting process, leading to reduced stiffness and efficiency due to insufficient molten metal reaching the blind holes in the mold.
Innovation Solution
A base member design featuring a stepped portion with a uniform height difference on its lower surface, where the tangential line drawn through the stepped portion extends between the lower edge points of the protrusion's outer periphery on both surfaces, ensuring that molten metal flows effectively into the blind holes, thereby reducing cavity formation and maintaining stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a protrusion is formed in the base member by die casting with a blind hole in the mold upper half, then the protrusion can be formed integrally with the base member, but cavities are generated in the protrusion due to insufficient molten metal reaching the blind hole
Solution Approach 1:
The invention introduces a stepped portion on the lower surface of the base member that creates a three-dimensional flow path for the molten metal. This stepped structure guides the molten metal from the lower surface upward toward the blind hole, utilizing vertical dimensionality to ensure proper filling of the protrusion cavity during die casting.
Solution Approach 2:
The stepped portion is strategically positioned at specific locations on the lower surface to create localized flow channels. This local modification optimizes the molten metal flow distribution, directing it precisely toward the blind hole regions where cavities would otherwise form, without altering the entire base member structure.
2Manufacturing precision
If a protrusion is provided on the mold lower half to enable molten metal to move toward the blind hole, then cavity formation is reduced, but the molten metal flows around the periphery of the protrusion instead of moving toward the blind hole
Solution Approach 1:
The stepped portion creates localized flow channels on the lower surface that direct molten metal upward toward the blind hole. This localized structural modification ensures that molten metal flows efficiently into the protrusion regions without deviating to the periphery, optimizing both filling quality and process efficiency.
3Productivity
If the stepped portion has a uniform height difference, then the amount of flowing molten metal that deviates from the direction of the protrusion is minimized, but the design complexity increases
Solution Approach 1:
The invention specifies a uniform height difference parameter for the stepped portion, transforming a potentially complex variable geometry into a standardized design element. This parameter standardization simplifies manufacturing while maintaining effective molten metal flow control, balancing design complexity with functional performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively suppresses cavity formation in the protrusions, ensuring a sufficient amount of molten metal flows into the blind holes, thus enhancing the stiffness and reducing porosity, as demonstrated by experimental results showing a significant reduction in porosity volume compared to traditional methods.
Implementation Method 1
once the molten metal reaches the portion of the mold that forms the stepped portion, the molten metal flows in the direction of the protrusion
Data Source
AI summary
A base member of a spindle motor includes an upper surface and a lower surface, in which the base member is a casting, the upper surface includes a pin portion extending upward, the lower surface includes a first lower surface and a second lower surface positioned higher than the first lower surface, and the first lower surface and the second lower surface are adjacent to each other with a stepped portion interposed between the first lower surface and the second lower surface, the stepped portion increasing in height from the first lower surface to the second lower surface. The stepped portion has a uniform height difference, and when a tangential line is drawn to the stepped portion in a cross section passing through a central axis of the pin portion and extending perpendicular to the stepped portion in plan view, the tangential line extends through between a lower edge point of an outer periphery of the pin portion on a side of the second lower surface and a lower edge point of the outer periphery of the pin portion on a side of the first lower surface.