Metal-Ring Plastic Transmission Gear for Low-Shrinkage Molding
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Solution Overview
Problem
Plastic gears produced by injection molding in industrial robots 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
Incorporating a metal ring into the plastic gear member to separate the inner and outer regions radially, reducing radial dimensional shrinkage and enhancing strength and rigidity, while allowing for convenient low-cost manufacturing and mass production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a plastic gear is made by injection molding, then cost reduction and batch processing needs are met, but dimensional accuracy deteriorates due to material shrinkage
Solution Approach 1:
The patent applies composite materials by combining a metal ring (inner component) with a plastic gear member (outer component) through injection molding. The metal ring provides dimensional stability and prevents shrinkage in the radial direction, while the plastic material provides cost-effective mass production. This composite structure resolves the contradiction by integrating materials with complementary properties - the metal core maintains precision while the plastic exterior enables economical manufacturing.
Solution Approach 2:
The patent changes the physical and structural parameters of the gear by introducing a metal ring core that fundamentally alters the molding process. The metal ring serves as a rigid support structure that constrains the plastic material during curing, preventing the dimensional shrinkage that normally occurs in pure plastic injection molding. This parameter change (adding a rigid core) enables both good dimensional accuracy and plastic material benefits.
2Manufacturing precision
If process parameters or mold size are adjusted to compensate for shrinkage, then dimensional accuracy is improved, but manufacturing time increases and manufacturing experience is required
Solution Approach 1:
The metal ring is prepared and positioned in the mold before the plastic injection process begins. This preliminary placement of the support structure prevents shrinkage from occurring in the first place, rather than requiring post-manufacturing adjustments or complex process parameter optimizations. The dimensional accuracy is built into the structure during molding, eliminating time-consuming trial-and-error adjustments.
3Ease of manufacture
If a pure plastic gear is used, then manufacturing cost is low and mass production is easy, but strength and rigidity are insufficient
Solution Approach 1:
The patent uses a composite structure where the outer plastic gear member maintains low manufacturing cost and mass production advantages, while the inner metal ring provides the necessary strength and rigidity. The plastic material forms the gear teeth and external geometry, enabling cost-effective molding, while the metal core reinforces the structure to prevent bending and deformation under load, thus resolving the strength deficiency of pure plastic gears.
Solution Approach 2:
The metal ring is nested within the plastic gear member during the injection molding process. The metal core is placed first, then the plastic material is injected around it, creating a nested structure where the stronger material is embedded within the easier-to-manufacture material. This nesting arrangement allows the plastic exterior to provide cost-effective mass production while the metal interior provides structural strength.
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 metal ring arrangement significantly reduces radial dimensional shrinkage, improving the dimensional accuracy and strength of the transmission gear, making it suitable for industrial robot applications with reduced manufacturing complexity and cost.
Implementation Method 1
such defects usually result from the shrinkage of the plastic material itself during injection molding, which is typically 0.3% of the design size
Implementation Method 2
a plastic gear made by injection molding is used as a transmission component
Data Source
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Figure 5
AI summary
Embodiments of the present disclosure relate to a transmission gear and a deceleration mechanism comprising the same. The transmission gear comprises a metal ring (2); and a plastic gear member (1) integral with the metal ring (2) by injection molding, the metal ring (2) is coaxially wrapped in the plastic gear member (1) and provided with a locating portion for locating the metal ring (2) in an injection mold, the plastic gear member (1) having an outer circumference (11) that is tooth-shaped, and the plastic gear member (1) being formed with an input hole (12) thereon through which an input shaft passes, an outer ring surface (21) of the metal ring (2) being adjacent to the outer circumference (11), and an inner ring surface (22) of the metal ring (2) having a diameter greater than or equal to that of the input hole (12). Since almost no shrinkage occurs to the plastic gear member during injection molding, such a transmission gear has good dimensional accuracy, strength and rigidity.