Medical Device Shaft Attachment Shrink-Fit for Gap-Free Joining
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Solution Overview
Problem
Current methods for joining medical device components, such as handholds and operating ends, are costly, time-consuming, and prone to contamination due to gaps and thermal distortion, which complicates manufacturing and compromises sterility.
Innovation Solution
A thermal shrink-fitting method where the component with lower dimensional tolerances or greater heat capacity is thermally processed to create an interference fit, eliminating the need for manual pinning and ensuring a secure, gap-free connection that meets sterility requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermal processing is applied to join two components, then the connection strength is improved, but thermal distortion outside prescribed tolerances occurs
Solution Approach 1:
The patent applies thermal processing locally to only one component (the attachment) rather than both components, creating a localized thermal field that expands only the attachment's inner diameter. This selective local heating allows the attachment to expand sufficiently for interference fit while the shaft remains dimensionally stable, resolving the contradiction between connection strength and dimensional tolerance.
Solution Approach 2:
Instead of heating both components and relying on differential cooling, the patent inverts the approach by heating only the attachment component and allowing it to cool down to create the interference fit. This reverse approach ensures predictable thermal distortion in only one component, maintaining manufacturing precision while achieving strong connection.
2Stability of the object's composition
If manual pinning and grinding methods are used to join components, then connection stability is achieved, but manufacturing cost and time increase
Solution Approach 1:
The patent replaces the mechanical joining system (manual pinning, grinding, and fitting operations) with a thermal field-based system. By using controlled thermal expansion and contraction, the attachment is shrunk onto the shaft to create a stable interference fit, eliminating the need for mechanical fasteners and post-processing operations, thereby significantly improving manufacturing efficiency.
Solution Approach 2:
The patent changes the physical parameter of temperature to achieve joining. By controlling the temperature of the attachment during processing, the inner diameter expands to allow easy insertion of the shaft, then cools to create the interference fit. This parameter-based approach replaces multiple mechanical steps with a single thermal process, enhancing both stability and productivity.
3Ease of manufacture
If compression connections with gaps are used to join components, then assembly simplicity is maintained, but contamination and corrosion occur
Solution Approach 1:
The patent utilizes thermal expansion to temporarily increase the inner diameter of the attachment during assembly, allowing simple insertion of the shaft without gaps. As the attachment cools, it contracts to form a tight interference fit that eliminates gaps, preventing contamination and corrosion while maintaining assembly simplicity through the thermal process.
Solution Approach 2:
The patent applies preliminary thermal heating to the attachment before assembly, which expands the inner diameter and facilitates gap-free insertion of the shaft. This preliminary thermal action ensures that when the attachment cools, it creates a complete interference fit without gaps, preventing harmful factors like contamination and corrosion from entering the connection.
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 method reduces manual labor and costs, enhances the connection's strength and cleanliness, and is suitable for automating the assembly process, ensuring high reproducibility and reliability while maintaining sterility and preventing contamination.
Implementation Method 1
the attachment is heated or the shaft is cooled so that it expands or shrinks due to thermal expansion or shrinkage in accordance with the material-specific expansion coefficient
Implementation Method 2
the attachment is cooled (actively or passively) in order to shrink it onto the shaft essentially without a gap
Data Source
AI summary
A joining method for a medical device, in particular a surgical instrument or implant, with a shaft and an attachment to be secured on the shaft, the method having the following steps: heating the attachment or cooling the shaft, such that an internal diameter of an opening of the heated attachment is greater than an external diameter of the shaft, then placing the shaft into the opening of the attachment, and then cooling the attachment, so as to shrink the attachment onto the shaft in a manner substantially free of gaps, or heating the shaft, such that the shaft and the opening are connected by an interference fit. A corresponding medical device is produced by the joining method.