Floating Core Injection Molding for Bent Pipe Uniformity
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Solution Overview
Problem
Current methods for manufacturing hollow bodies, such as pipes, from thermoplastic resin using injection molding face challenges in achieving uniform inner diameter, thickness, and smooth inner surface, especially when forming bent pipes, and lack the ability to integrate complex features like flange or attachment portions.
Innovation Solution
The method involves using a mold with a floating core that has a columnar and top portion with specific dimensions and curvature, allowing pressurized fluid to push the core through the molten resin, ensuring uniform thickness and smooth inner surfaces, and enabling the integration of complex features by injection molding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional injection molding methods are used to form hollow bodies, then the manufacturing process is simple, but the uniformity of inner diameter and thickness cannot be achieved
Solution Approach 1:
The core is designed as a floating core that can move dynamically within the mold cavity rather than being fixed. The core moves in response to fluid pressure and resin flow, adapting its position to maintain uniform thickness distribution throughout the hollow body, thereby resolving the contradiction between manufacturing precision and device complexity.
Solution Approach 2:
A fluid (gas or liquid) is introduced as an intermediary substance to interact with the floating core and molten resin. The fluid pressure drives the core movement and controls the resin flow, enabling precise control of the hollow body formation process without requiring complex mechanical mechanisms, thus achieving high manufacturing precision with relatively simple device structure.
2Manufacturing precision
If gas assist injection molding is used to form hollow pipe portions, then the hollow structure can be created, but the uniformity of inner diameter cannot be secured
Solution Approach 1:
The patent uses fluid as an intermediary to interact with the floating core, creating a coupled system where fluid pressure drives core movement that in turn controls resin flow. This intermediary mechanism provides superior control over inner diameter uniformity compared to direct gas injection, as the floating core acts as a mechanical regulator responding to fluid pressure changes.
Solution Approach 2:
The floating core automatically adjusts its position based on the distribution of fluid pressure and resin flow without requiring external control mechanisms. The core self-regulates to maintain uniform inner diameter through its movement, eliminating the need for complex control systems and simplifying the manufacturing process.
3Manufacturing precision
If water assist injection molding is used to form hollow pipe portions, then the hollow structure can be created, but the smoothness of pipe inner surface and uniformity of thickness are compromised
Solution Approach 1:
The floating core dynamically moves during the injection process, continuously adapting to maintain contact with the resin and mold wall. This dynamic movement ensures uniform thickness distribution and smooth inner surface finish, overcoming the limitations of static molding methods while keeping the process relatively simple.
Solution Approach 2:
Fluid serves as an intermediary that transmits pressure to the floating core, which then indirectly controls the resin flow and hollow body formation. This indirect control mechanism provides superior surface finish and thickness uniformity compared to direct water or gas injection methods, while avoiding the process limitations associated with assist injection molding.
4Manufacturing precision
If extrusion molding is used to manufacture pipes, then the manufacturing process is simple, but bent pipes with smooth surfaces cannot be obtained
Solution Approach 1:
The floating core moves dynamically within the mold cavity during injection, enabling the formation of bent pipe shapes with smooth surfaces. The core's movement adapts to the desired geometry, allowing complex bent shapes to be molded directly without requiring complex mold mechanisms or post-processing, thus achieving high manufacturing precision with relatively simple device structure.
Solution Approach 2:
The mold cavity is segmented into regions controlled by the floating core's movement. The core divides the molding process into phases where it moves to different positions, enabling the formation of bent shapes and complex geometries. This segmentation approach allows complex shapes to be achieved without requiring equally complex mold mechanisms.
5Manufacturing precision
If blow molding with tilting mechanism is used to form three-dimensional bent pipes, then bent shapes can be achieved, but the thickness accuracy and surface finishing accuracy do not attain satisfactory level
Solution Approach 1:
The floating core provides dynamic control during injection molding, automatically adjusting to maintain uniform thickness and smooth surface finish. This dynamic control mechanism achieves satisfactory thickness accuracy and surface finishing accuracy without requiring complex mold tilting mechanisms or swinging apparatus, thereby resolving the contradiction between manufacturing precision and device complexity.
Solution Approach 2:
Fluid acts as an intermediary that transmits pressure to the floating core, which then controls the resin flow and hollow body formation. This intermediary mechanism provides superior thickness and surface finish accuracy compared to direct blow molding with tilting mechanisms, while avoiding the complexity of mechanical tilting and swinging apparatus.
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
This approach allows for the production of hollow bodies with uniform inner diameter and thickness, excellent inner surface smoothness, and the ability to integrate complex features like attachment portions, reducing costs and improving the quality of bent pipes.
Implementation Method 1
pressure-injecting a pressurized fluid through the pressure port after the injection of the molten resin, and moving the floating core to the outlet side
Implementation Method 2
at the same time, extruding the molten resin from the outlet
Data Source
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AI summary
A hollow body formed of a thermoplastic resin and having uniform inner diameter and thickness and an excellent inner surface smoothness, and, in particular, a pipe-shaped hollow body having a bent portion is manufactured by injection molding. A method of manufacturing a hollow body includes injecting a molten resin 8 into a mold cavity 2 of a mold 1, the mold cavity 2 having on its one end a pressure port 4 provided with a floating core 6 and on its other end an outlet 5, pressure-injecting a pressurized fluid through the pressure port 4 after the injection of the molten resin 8, and moving the floating core 6 toward the outlet 5, and, at the same time, extruding the molten resin 8 from the outlet 5. In the method, the floating core 6 is constituted of a columnar portion and a top portion, which is continuously connected to one surface of the columnar portion and has a shape that a cross-sectional area perpendicular to a central axis of the columnar portion gradually decreases from one surface side of the columnar portion. When a diameter of the columnar portion is represented by A, the height of the columnar portion is 0.1 A to 1 A, and the height of the top portion is 0.3 A to 1.6 A.