Overmolded Base Stress Relief for Disc Drive Distortion
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Solution Overview
Problem
The challenge in manufacturing small form factor disc drives is the base distortion caused by residual stress between the metal stamped section and the overmolded plastic section, due to their differing heat coefficients, which leads to performance and functional issues, especially at low environmental temperatures.
Innovation Solution
Incorporating stress relief features in the overmold section with thinner sidewall thicknesses to alleviate the residual stress exerted on the metal stamped section, thereby reducing distortion and maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the base thickness is reduced to meet smaller form factor requirements, then the disc drive thickness is reduced, but base distortion increases due to residual stress
Solution Approach 1:
The base is divided into multiple sections with varying wall thicknesses. The sidewalls include stress relief features such as recesses or reduced thickness regions that segment the continuous structure, allowing differential contraction between the metal stamped section and overmolded plastic section without causing distortion to the mounting surfaces.
Solution Approach 2:
Different portions of the base have different thickness characteristics. The mounting surfaces maintain sufficient thickness for stability, while the sidewalls incorporate stress relief features with reduced thickness to accommodate thermal expansion differences. This local variation in quality allows the base to meet overall thickness requirements while preventing distortion in critical areas.
2Volume of moving object
If the base is made thinner, then the disc drive form factor is reduced, but residual stress between metal and plastic sections increases
Solution Approach 1:
The base structure is segmented with stress relief features that create regions of reduced thickness in the sidewalls. This segmentation allows the metal stamped section and overmolded plastic section to contract at different rates during cooling without generating excessive residual stress, while maintaining adequate thickness in critical mounting areas.
3Ease of manufacture
If the base thickness is reduced, then manufacturing cost is reduced, but manufacturing precision deteriorates due to distortion
Solution Approach 1:
The base incorporates local variations in thickness through stress relief features. Critical mounting surfaces maintain sufficient thickness to ensure manufacturing precision and prevent distortion, while non-critical sidewall regions have reduced thickness to lower overall material cost and meet form factor requirements.
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
The implementation of stress relief features significantly reduces base distortion during the overmolding process and at low temperatures, ensuring improved performance and reliability of the disc drive base.
Implementation Method 1
The metallic section of the base deforms because it has a different heat coefficient than the overmolded plastic section of the small form factor disc drive. The overmold plastic material is injected into the base mold at a high temperature (200 to 300° C.) and cooled quickly to room temperature. Once the base is cooled, both the metallic stamped section and the plastic section will contract. However, the contraction of the plastic section is much larger than the metallic stamped section because the heat coefficient of the plastic section is much higher than that of the metallic stamped section.
Implementation Method 2
The overmold section includes at least one stress relief feature for eliminating distortion stresses exerted on the metal stamped section by the overmold section.
Data Source
AI summary
A base assembly for use in an airtight enclosure. The base assembly includes a metal stamped section and an overmold section formed adjacent to the metal stamped section. The overmold section includes at least one stress relief feature for eliminating distortion stresses exerted on the metal stamped section by the overmold section.