Cannula Manufacturing Friction Reduction via Core Pin Clearance
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Solution Overview
Problem
Existing manufacturing methods for cannula units involve complex and costly processes, leading to high rejection rates due to friction issues between the cannula, housing, and piercing needle, which can cause crumpling, rupture, or leakage problems.
Innovation Solution
A method involving injection molding of a cannula onto a molding core pin with a larger distal end diameter, followed by molding of the cannula housing around the distal end and piercing needle, which is then threaded into the cannula with a diameter smaller than the molding core pin, reducing friction forces and simplifying the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a cannula is injection molded directly onto a piercing needle, then the manufacturing process is simplified, but high friction forces cause crumpling, rupture, or leakage problems
Solution Approach 1:
A molding core pin with diameter d1 is introduced as an intermediary object during the injection molding process. The cannula is molded onto this pin, and the pin's larger diameter creates a clearance gap between the cannula inner wall and the final piercing needle (diameter d4 < d1). This intermediary pin acts as a space holder that prevents excessive friction and mechanical stress during both manufacturing and subsequent needle insertion/removal operations.
Solution Approach 2:
The invention changes the diameter parameter of the molding core pin (d1) to be larger than the final piercing needle diameter (d4). This parameter change creates a deliberate clearance gap that reduces friction forces. By controlling the relationship between d1 and d4, the invention optimizes both the mechanical integrity of the cannula and the ease of piercing needle insertion and removal.
2Manufacturing precision
If the piercing needle has the same diameter as the molding core pin, then the cannula fits tightly, but friction forces increase causing insertion and withdrawal difficulties
Solution Approach 1:
The invention deliberately changes the diameter parameter of the piercing needle (d4) to be smaller than the molding core pin diameter (d1). This creates a controlled clearance gap that reduces friction during insertion and withdrawal operations. The parameter relationship d4 < d1 is maintained throughout the process, ensuring both adequate fit and reduced friction.
3Reliability
If multiple manufacturing steps are used to assemble cannula, housing, and piercing needle separately, then quality control is improved, but the process becomes more complex and costly
Solution Approach 1:
The invention merges the manufacturing of the cannula and housing into a single injection molding operation. Both components are molded simultaneously in the same tool, with the cannula being formed onto the molding core pin while the housing is formed around it. This consolidation reduces the number of assembly steps, lowers manufacturing complexity, and reduces costs while maintaining quality control through process integration.
Solution Approach 2:
The molding core pin serves multiple functions: it acts as a support during cannula molding, defines the inner diameter of the cannula, creates the clearance gap for reduced friction, and is later removed to allow piercing needle insertion. This multi-functionality reduces the need for separate components and steps, simplifying the overall manufacturing process.
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 the static and dynamic friction forces between the cannula and housing, allowing for easier insertion and withdrawal of the piercing needle, thereby minimizing the risk of cannula crumpling, rupture, and leakage, while also reducing manufacturing costs and improving process reliability.
Implementation Method 1
injection molding of a cannula (3) onto a molding core pin (4)
Implementation Method 2
After completion of the curing, the now hollow flexible cannula is removed from the tool
Implementation Method 3
injection molding of a cannula housing (2) around the distal end (32) and a first distal section (34) of the cannula (3)
Data Source
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AI summary
Disclosed is a method for manufacturing a cannula unit (1) with a cannula housing and a cannula, comprising the steps: - injection molding of a cannula (3) onto a molding core pin with outer diameter d1, wherein the cannula has a distal end (32) with an outer diameter that is larger than the outer diameter of the remaining cannula, a first distal section adjoining the distal end, a second proximal section adjoining the first distal section, and a proximal end; - injection molding of a cannula housing (2) onto the distal end and the first distal section of the cannula; - removing the molding core pin from the cannula; and - threading a piercing needle (5) with outer diameter d4 into the cannula, wherein the diameter d4 of the piercing needle is chosen such that it is smaller than the diameter d1 of the molding core pin.