Extrusion Screw Heating for Injection Molding Pressure Reduction
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Solution Overview
Problem
Traditional injection molding systems face inefficiencies due to reliance on shear heat, which limits material flexibility, requires high injection pressures, and necessitates manual purging and large power sources, making them unsuitable for molding bio-based plastics and varying part sizes.
Innovation Solution
The extrude-to-fill injection molding system employs static heat conduction and a rotating extrusion screw with a shut-off nozzle to achieve homogenous melting and flexible shot sizes, reducing pressure requirements and eliminating the need for purging, while using a smaller clamp system and efficient heat conduction materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If shear heat is used to melt material in traditional injection molding, then material mixing and melting occur, but material flexibility is limited and high injection pressures are required
Solution Approach 1:
The patent changes the fundamental parameter of heat generation from shear-based to conduction-based. The heating element is wrapped around the extrusion screw, providing direct thermal conduction to the material. This parameter change enables processing of diverse materials including bio-based plastics that cannot withstand shear degradation, while simultaneously reducing the injection pressure required to 500-1500 psi from the traditional 20,000-30,000 psi range.
Solution Approach 2:
The patent replaces the mechanical shear-based melting system with a thermal conduction-based heating system. Instead of relying on mechanical friction and shear forces generated by screw rotation to melt material, the system uses an electrical heating element that conducts heat directly to the material, eliminating the need for high mechanical injection pressures.
2Reliability
If cold slug formation is used to seal the nozzle between shots, then material containment occurs, but very high pressure is required to dislodge the cold slug
Solution Approach 1:
The heating element is positioned to provide preliminary and continuous heating to the material at the screw tip and nozzle area. This prevents cold slug formation by maintaining the material in a molten state between shots, eliminating the need for high-pressure cold slug dislodging while ensuring reliable material flow and nozzle sealing through thermal maintenance rather than mechanical force.
3Strength
If thick barrel wall is used to withstand high injection pressure, then structural integrity is maintained, but heat conduction to material is reduced
Solution Approach 1:
The patent extracts the heating function from the barrel wall and places it directly on the extrusion screw. By wrapping the heating element around the screw rather than relying on barrel wall conduction, the system eliminates the need for thick barrel walls for heat conduction purposes. The barrel can be thinner since its primary function is pressure containment, while the heating function is performed by the screw-mounted element in direct contact with the material.
4Force
If large power sources are used for injection and clamp systems, then sufficient force is generated, but machine size and infrastructure costs increase
Solution Approach 1:
The patent changes the operating pressure parameter from high (20,000-30,000 psi) to low (500-1,500 psi) through the use of conduction heating. This parameter change fundamentally reduces the force requirements for both the injection system and clamp system, enabling the use of smaller power sources and reducing overall machine size and infrastructure costs while maintaining sufficient injection force for effective molding.
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 efficient molding of various materials, including bio-based plastics, with reduced pressure and energy consumption, enabling the production of parts with unlimited shot sizes and improved consistency, while minimizing machine size and infrastructure costs.
Implementation Method 1
a heating element wrapped around an extrusion screw to melt a material inside the screw
Implementation Method 2
the rotating extrusion screw pumps the molten material into the mold
Data Source
AI summary
The present disclosure provides an injection molding apparatus and a method of fabricating a component. The apparatus may include a barrel comprising a first section having an end associated with a mold through a nozzle or a gate insert, a second section coupled to a hopper configured to fill a material into the barrel, and a temperature transition section between the first section and second section. The apparatus may include an extrusion screw placed inside the barrel and rotatable relative to the barrel. The apparatus may include one or more heaters associated with the first section of the barrel to heat the material inside the barrel. Rotation of the extrusion screw relative to the barrel may continuously extrude the material into the mold.