Metal-Ring Plastic Transmission Gear for Shrinkage Control
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Solution Overview
Problem
Plastic gears produced by injection molding often suffer from dimensional accuracy defects due to material shrinkage, which existing methods to address, such as adjusting process parameters or mold size, are time-consuming and require significant manufacturing experience.
Innovation Solution
A transmission gear comprising a metal ring coaxially wrapped around a plastic gear member, with the metal ring serving as a support to minimize radial shrinkage and enhance dimensional accuracy, strength, and rigidity, and featuring a locating portion for precise placement in the injection mold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a plastic gear is made by injection molding, then mass production and cost reduction are achieved, but dimensional accuracy deteriorates due to material shrinkage
Solution Approach 1:
The patent uses a composite structure combining a metal ring and plastic gear member. The metal ring provides dimensional stability and prevents shrinkage during injection molding, while the plastic gear member maintains mass production advantages. This composite approach resolves the contradiction by integrating materials with complementary properties.
Solution Approach 2:
The gear is divided into two functional segments: a metal ring for structural support and shrinkage prevention, and a plastic gear member for cost-effective mass production. This segmentation allows each part to optimize its specific function, maintaining dimensional accuracy while enabling high-volume manufacturing.
2Manufacturing precision
If process parameters or mold size are adjusted to compensate for shrinkage, then dimensional accuracy is improved, but manufacturing time and experience requirements increase
Solution Approach 1:
The metal ring is pre-installed in the mold before injection molding to establish a fixed reference framework. This preliminary action prevents shrinkage during the molding process itself, eliminating the need for post-processing adjustments and reducing manufacturing time while maintaining high dimensional accuracy.
3Manufacturing precision
If a metal ring is embedded in the plastic gear member, then radial dimensional shrinkage is reduced and strength is improved, but device complexity increases
Solution Approach 1:
The metal ring is nested within the plastic gear member during injection molding, with the plastic material flowing around and bonding to the metal ring. This nesting approach integrates two components into a single unified structure, minimizing the increase in device complexity while achieving the desired dimensional stability and strength enhancement.
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 solution significantly reduces radial dimensional shrinkage, improves the accuracy and strength of the transmission gear, and allows for convenient, low-cost mass production by embedding a metal ring within the plastic gear member, preventing axial bending and ensuring precise installation.
Implementation Method 1
the metal ring serving as a support to minimize radial shrinkage and enhance dimensional accuracy
Implementation Method 2
a plastic gear member integral with the metal ring by injection molding
Data Source
AI summary
Embodiments of the present disclosure relate to a transmission gear and a deceleration mechanism including the same. The transmission gear includes a metal ring; and a plastic gear member integral with the metal ring by injection molding, the metal ring is coaxially wrapped in the plastic gear member and provided with a locating portion for locating the metal ring in an injection mold, the plastic gear member having an outer circumference that is tooth-shaped, and the plastic gear member being formed with an input hole thereon through which an input shaft passes, an outer ring surface of the metal ring being adjacent to the outer circumference, and an inner ring surface of the metal ring having a diameter greater than or equal to that of the input hole. Since almost no shrinkage occurs to the plastic gear member during injection molding, such a transmission gear has good dimensional accuracy, strength and rigidity.