Injection-Molded Main Body and Flange Geometry to Suppress Weld Lines
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Solution Overview
Problem
Weld lines form at the design surface of injection molded products due to uneven resin flow speeds between the movable and fixed side molds, particularly at the flange portion, affecting the external appearance.
Innovation Solution
An injection molded product with a main body portion and a projecting portion where the thickness relationship A≥B is maintained, and the resin flow distance is limited to less than or equal to 600 mm, with a movable side mold opening to enlarge the cavity volume after resin filling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the width between the movable side mold and the fixed side mold at the flange portion is larger than at the main body portion, then the resin can fill the cavity properly, but the flow speed at the flange becomes higher causing weld lines to form at the design surface
Solution Approach 1:
The cavity width is designed to vary locally: wider at the main body portion (where design surface quality is critical) and narrower at the flange portion (where resin injection occurs). This local variation in geometry controls flow speed distribution, preventing weld lines at the design surface while ensuring complete cavity filling.
2Productivity
If the cavity width at the flange portion is increased to ensure proper resin flow, then filling is improved, but the resin flow speed increases causing it to move ahead and conflate with other resin flows forming weld lines
Solution Approach 1:
Different sections of the cavity have different widths optimized for their specific functions: the flange portion has a narrower width to control flow speed and prevent premature arrival at the design surface, while the main body portion has a wider width to accommodate the design features. This local differentiation resolves the conflict between filling efficiency and surface quality.
3Object-affected harmful factors
If the resin flow distance is reduced to prevent weld lines, then surface quality improves, but the cavity volume or part complexity may be constrained
Solution Approach 1:
Instead of simply shortening the flow path (one-dimensional solution), the invention modifies the cavity geometry in the width dimension. By making the cavity narrower at the flange portion and wider at the main body, it controls flow velocity through cross-sectional area variation, allowing long flow distances to be achieved without weld lines forming at the design surface.
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
Suppresses the formation of weld lines at the design surface by ensuring equal resin flow speeds and preventing resin convergence, enhancing the product's external appearance.
Implementation Method 1
the flowing speed of the molten resin that flows within the cavity is affected by the width between the movable side mold and the fixed side mold that form the cavity
Implementation Method 2
a foaming treatment is carried out in a state in which the movable side mold has been moved so as to open slightly (core-back), and a resin molded product is thereby obtained
Implementation Method 3
the portions that contact the mold for molding are cooled and hardened, and a film-like skin layer is formed
Data Source
AI summary
An injection molded product includes a main body portion having a design surface and an opposite surface; and a projecting portion provided at a peripheral edge portion of the main body portion, and projecting out toward a side opposite from the design surface in a thickness direction of the main body portion, wherein a thickness A of the main body portion and a thickness B of the projecting portion satisfy a relationship of A≥B.