Annular Resin Member Secondary Molding Insert Core Protection
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Solution Overview
Problem
In the manufacturing of annular resin members, the secondary molding step often results in deformation or fracture of axially thinned portions due to excessive pressure from the injected molten resin, particularly when using pin, tunnel, or side gates, which can lead to breakage of the insert core if its thickness is insufficient compared to its height.
Innovation Solution
The method involves fitting axially-projecting convex portions of the insert core into the axially thinned portions of the annular internal resin member during the secondary molding step, positioning the welds of the secondary-molding molten resin radially outside of the rib portions between adjacent thinned portions to reduce shear and bending forces on the insert core, thereby preventing breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If axially-projecting convex portions of the insert core are fitted into the axially thinned portions during secondary molding, then the molded article structural integrity is improved, but the insert core may break or fracture due to large shearing force and bending moment
Solution Approach 1:
The patent thickens the insert core at the proximal part of the axially-projecting convex portions before the secondary molding process. This preliminary structural reinforcement prevents breakage during the molding process while maintaining the necessary fitting functionality into the axially thinned portions.
Solution Approach 2:
The insert core is designed with non-uniform thickness, specifically thickening only at the proximal part of the axially-projecting convex portions where the stress concentration occurs. This localized structural modification provides strength exactly where needed without adding unnecessary weight or complexity elsewhere.
2Strength
If pressure is applied during pressure keeping after injection, then the weld joins the molten resin, but the axially-projecting convex portions experience large shearing force and bending moment that may cause breakage
Solution Approach 1:
The insert core is pre-reinforced with increased thickness at the proximal part of the axially-projecting convex portions before the pressure keeping stage. This preliminary reinforcement ensures the structure can withstand the large shearing forces and bending moments generated during weld formation without breaking.
Solution Approach 2:
The insert core thickness is locally increased at the specific location (proximal part of axially-projecting convex portions) where the maximum stress occurs during pressure keeping. This targeted reinforcement allows the weld to form with adequate pressure while preventing insert core failure.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3C
AI summary
A manufacturing method includes a primary molding step through which a plurality of axially thinned portions of an annular resin member are formed, and a secondary molding step performed in a state where axially-projecting convex portions of an insert core are fitted into the axially thinned portions. In the method, breakage or fracture of the insert core is prevented In the primary molding step, the insert core having the axially-projecting convex portions aligned apart from one another in the circumferential direction is located in a primary molding die, and the injection molding is performed for forming axially thinned portions 3A in an annular internal resin member 3. In the secondary molding step, the annular internal resin member 3 and the insert core which have undergone the primary molding step are located in a secondary molding die, and the injection molding is performed. Gates for injecting molten resin in a cavity of the secondary molding die are located in the secondary molding die so that welds W2 that are joining points of the molten resin in the secondary molding step are positioned in the radially outside of rib portions 3B.