Insert Flange Protrusions Prevent Over-Rotation in Plastic Threads
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Solution Overview
Problem
Conventional metal inserts used in plastic parts can easily over-rotate during insertion, leading to stripped threads and unsatisfactory attachment of subsequent parts, especially when attaching blow molded plastic parts to other materials like metal or wood using threaded fasteners.
Innovation Solution
The design of a modified insert with an annular flange featuring alternating radial protrusions and recesses, and a larger diameter, which interlocks with complementary features in the plastic part's counter bore hole to resist over-rotation, along with coarse and discontinuous threads on the insert's longitudinal body, enhances the resistance to over-rotation and ensures secure attachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional metal inserts are used in plastic parts, then threaded fasteners can be attached to plastic parts, but the inserts easily over-rotate during insertion causing stripped threads
Solution Approach 1:
The insert features an asymmetric drive mechanism with a driven gear having asymmetric teeth that engage with a drive gear. This asymmetric engagement prevents over-rotation by providing a mechanical stop when the teeth disengage, ensuring the insert cannot rotate beyond the intended insertion depth and preventing thread stripping in the plastic part.
Solution Approach 2:
A drive gear acts as an intermediary component between the insertion tool and the insert. This intermediate gear transmits rotational motion during insertion but provides a mechanical blocking mechanism when over-rotation is attempted, mediating between the tool's rotational input and the insert's linear advancement into the plastic part.
2Adaptability or versatility
If conventional inserts are used, then plastic parts can be joined to other materials, but over-rotation strips the female threads in the plastic part opening
Solution Approach 1:
The asymmetric gear teeth provide a precise mechanical stop that limits rotation to exactly the amount needed for proper thread engagement. This prevents over-rotation that would otherwise strip the threads, ensuring consistent and high-quality thread engagement across all insertions while maintaining the ability to join plastic parts to various materials.
Solution Approach 2:
The driven gear on the insert is pre-configured with asymmetric teeth that will engage with the drive gear. This preliminary mechanical configuration ensures that during insertion, the gears automatically engage and provide over-rotation prevention, eliminating the need for additional control steps or procedures during the insertion process.
3Reliability
If the insert diameter is increased to resist over-rotation, then resistance to over-rotation improves, but the insert becomes more difficult to insert into smaller openings
Solution Approach 1:
The over-rotation resistance mechanism is segmented into separate gear components (drive gear and driven gear) rather than increasing the overall insert diameter. This allows the anti-over-rotation functionality to be added without proportionally increasing the insert's external dimensions, maintaining ease of insertion into smaller openings while providing reliable over-rotation prevention.
Solution Approach 2:
Instead of resisting over-rotation by increasing diameter in the radial dimension, the solution uses gear engagement in the rotational dimension. The asymmetric gear teeth provide mechanical blocking through angular engagement rather than radial interference, allowing over-rotation resistance without increasing the insert's outer diameter and maintaining ease of insertion.
Data Source
AI summary
A method for joining a plastic part to a second part with an insert adapted to thread into the plastic part. The insert includes a longitudinal body with outer threads, a hole in the longitudinal body with female threads, and an annular flange. Protrusions and recesses on the bottom of the annular flange alternate in a radial pattern. The insert is threaded into an opening in the plastic part. The protrusions and recesses of the insert interact with the plastic part to resist over rotation of the insert. The opening in the plastic part may include a hole and a counter bore portion. The counter bore includes protrusions and recesses. The protrusions and recesses alternate in a radial pattern. When the insert is threaded into the opening, the protrusions and recesses of the insert interact with the protrusions and recesses of the plastic part and resist over rotation.