Reinforced Plastic Gear Rim Layout to Prevent Sinks and Voids
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Solution Overview
Problem
Molded plastic gears face challenges with resin shrinkage leading to voids and sinks, particularly in thicker regions, which compromises strength and accuracy, making it difficult to manufacture large gears with sufficient tooth depth.
Innovation Solution
The design incorporates a ring-shaped outer rim with tooth portions and reinforcing ribs spaced by thinning portions, where the ribs are positioned at tooth grooves, enhancing strength and accuracy without increasing rim thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the rim thickness is increased to ensure gear strength, then the gear strength is improved, but voids and sinks occur due to resin shrinkage in thicker regions
Solution Approach 1:
The rim is segmented into multiple regions with different thicknesses by providing reinforcing ribs that extend from the inner circumferential surface to the outer circumferential surface. The rim thickness varies between regions adjacent to tooth portions and regions adjacent to tooth grooves, allowing optimized strength and precision without uniform thickness increase
Solution Approach 2:
Different rim thicknesses are provided at different locations: thicker regions adjacent to tooth portions for strength, and thinner regions adjacent to tooth grooves to prevent voids and sinks. This local variation in quality resolves the contradiction between overall strength and manufacturing precision
2Strength
If the tooth depth is increased to increase tooth size, then the gear strength is improved, but the rim thickness must be increased which causes voids and sinks
Solution Approach 1:
The rim is divided into multiple thickness regions through reinforcing ribs, allowing large tooth depth while maintaining manageable rim thickness in specific areas. This segmentation enables large tooth size without uniformly increasing the entire rim thickness
Solution Approach 2:
The rim thickness is locally optimized: thicker where needed for tooth support and thinner where it would cause manufacturing defects. This allows large tooth depth to be achieved without the moldability issues that would result from uniform rim thickness increase
3Strength
If the rim thickness is increased to satisfy strength specifications, then the gear strength is improved, but the wall thickness becomes large causing sinks
Solution Approach 1:
The rim is segmented into multiple thickness zones using reinforcing ribs, creating a non-uniform thickness distribution. This allows strength to be maintained in critical areas while avoiding excessive thickness that would cause sinks in other areas
Solution Approach 2:
Different rim thicknesses are provided at different locations: thicker regions adjacent to tooth portions for strength, and thinner regions adjacent to tooth grooves to prevent sinks. This local variation resolves the contradiction between strength and surface flatness
Data Source
AI summary
A gear includes: an outer circumferential rim provided integrally with a plurality of tooth portions disposed side-by-side in a circumferential direction on an outer circumferential surface; and a plurality of reinforcing ribs disposed inside the outer circumferential rim to be spaced from each other in the circumferential direction by thinning portions, wherein a position where each of the plurality of reinforcing ribs and the outer circumferential rim are joined corresponds, in the circumferential direction, to a position of a tooth groove between the plurality of tooth portions.