Molded Plastic Part Rib Gate Flow Control
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Solution Overview
Problem
Molded plastic parts manufactured by injection molding often suffer from appearance defects such as flow marks and weld lines on the design surface, especially when using colored resins with added bright materials, which can lead to reduced strength and aesthetic issues due to stress concentration and uneven resin flow.
Innovation Solution
The design incorporates a reinforcing structure with transverse ribs and a longitudinal rib, where the gate is set on a transverse rib, allowing resin to flow in a divided manner, reducing inflow velocity and preventing jet-like resin arrival on the design surface, thereby minimizing flow marks and weld lines, while maintaining the structural integrity of the reinforcing structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a reinforcing structure is formed on the design back surface, then the strength and rigidity of the molded part is improved, but appearance defects such as weld lines and dents occur on the design surface
Solution Approach 1:
The reinforcing structure is divided into multiple segments (first reinforcing structure and second reinforcing structure) separated by a resin non-flow portion. This segmentation prevents continuous resin flow across the reinforcing structure, eliminating weld lines on the design surface while maintaining structural strength through the distributed reinforcement segments.
Solution Approach 2:
A resin non-flow portion is created at a specific location within the reinforcing structure to control resin flow behavior. This local modification prevents resin from flowing through the entire reinforcing structure, thereby preventing weld lines and appearance defects on the design surface while maintaining overall structural integrity.
2Manufacturing precision
If the thickness of connecting parts is reduced to prevent dents, then appearance quality is improved, but strength decreases due to stress concentration
Solution Approach 1:
The reinforcing structure is segmented into multiple parts separated by resin non-flow portions. This allows each segment to be optimized independently - the connecting parts can maintain sufficient thickness for strength while the segmentation prevents resin flow accumulation that causes dents, thus resolving the contradiction between appearance quality and strength.
3Ease of manufacture
If colored resin with bright materials is used for unpainted molding, then manufacturing cost is reduced and environmental impact is minimized, but flow marks and weld lines appear on the design surface
Solution Approach 1:
The reinforcing structure is divided into segments separated by resin non-flow portions, which prevents continuous resin flow and the formation of weld lines and flow marks. This allows unpainted colored resin with bright materials to be used without suffering from appearance defects, maintaining both manufacturing efficiency and appearance quality.
Solution Approach 2:
A resin non-flow portion is created at a specific location to control resin flow behavior locally. This prevents resin flow-related appearance defects on the design surface while allowing the use of colored resin with bright materials for unpainted molding, thus maintaining both ease of manufacture and appearance quality.
Data Source
AI summary
In a molded plastic part 1 including a body 2 constituting a design surface 2a and a reinforcing structure 3 projectingly provided on a design back surface 2b of the body 2, the body 2 and the reinforcing structure 3 being integrally molded by injection molding, the reinforcing structure 3 is formed by a combined body of a plurality of transverse ribs 7a, 7b, 7c and 7d which are arranged at appropriate intervals in the resin flow direction at the time of injection molding in the direction intersecting with the resin flow and longitudinal ribs 6p and 6q which extend at right angles to the transverse ribs and connect the transverse ribs to each other. The transverse ribs are connected to the design back surface 2b, and a gate 8 for injection molding is set on one of the transverse ribs. The longitudinal ribs are disposed so as to be separated from the design back surface 2b.