Implantable Shell Weld Layout for Lower Residual Stress
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Solution Overview
Problem
Implantable medical devices face reduced longevity due to residual stresses generated during welding processes, which can occur from rapid thermal expansion and contraction, leading to tensile strain in welded joints.
Innovation Solution
The positioning of the weld line terminus on a narrow side or a rounded corner of the device shell, along with the use of laser welding and specific shell geometries, minimizes residual stresses by distributing the stress more evenly and reducing resistance during the welding process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If welding is performed to join device components, then structural integrity is achieved, but residual stresses and tensile strain are generated in the welded joint
Solution Approach 1:
The weld line terminus is specifically positioned on narrow sides or rounded corners rather than wide sides, creating localized geometric features that reduce residual stress. This local quality change at the weld terminus area distributes stress more favorably without compromising overall joint strength
Solution Approach 2:
Rounded corners are introduced at the weld line terminus positions. The curved geometry of rounded corners reduces stress concentration compared to sharp corners, thereby reducing residual stress and tensile strain in the welded joint while maintaining structural integrity
2Volume of moving object
If device size is reduced to improve patient comfort and placement flexibility, then implantable device dimensions are minimized, but welding processes generate more concentrated residual stresses
Solution Approach 1:
The patent applies specific geometric modifications (narrow sides and rounded corners) at critical weld terminus locations. These local geometric features are designed to reduce stress concentration in miniaturized devices where welding-induced stresses are more pronounced due to smaller component dimensions
Solution Approach 2:
Rounded corners at weld line termini provide curvature that distributes stress more evenly in small-scale devices. This is particularly important for miniaturized implantable devices where stress concentration can rapidly lead to fatigue failure
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 approach reduces residual stresses in the weld areas, enhancing the longevity and reliability of implantable medical devices by minimizing tensile strain and surface cracks, thereby improving their performance and durability.
Implementation Method 1
The weld line can include a laser weld line
Implementation Method 2
Residual stresses are locked-in stresses within a metal object, even though the object is free of external forces. Residual stresses can be tensile or compressive. Residual stresses can reduce the longevity of structures they are included within
Implementation Method 3
residual stresses generated during welding processes, which can occur from rapid thermal expansion and contraction
Data Source
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AI summary
Embodiments herein relate to implantable medical devices including a welded joint with reduced residual stress. In a first aspect, an implantable medical device is included having a power subunit comprising a first biocompatible electrically conductive shell, an anode disposed therein, a cathode disposed therein, and a lid. The implantable medical device can further include an electronics control subunit comprising a second biocompatible electrically conductive shell, and a control circuit disposed therein. Both of the first and second biocompatible electrically conductive shells can include first and second opposed wide sides, first and second opposed narrow sides, and four rounded corners. The first shell can be welded to the lid around a perimeter thereof forming a weld line. The weld line can have a weld line terminus and the weld line terminus can be positioned on a narrow side or a rounded corner. Other embodiments are also included herein.