Low Constant Pressure Injection Molding System
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Solution Overview
Problem
Conventional injection molding processes face challenges in reducing wall thickness of injection molded parts, leading to inefficient plastic use, high costs, and potential warping or reduced mechanical properties due to high pressures and mold material limitations.
Innovation Solution
Implementing a low constant pressure injection molding system that maintains melt pressure around 6000 psi or lower, using a pressure regulating mechanism to ensure consistent flow and reduce shear stress, allowing for the use of more machineable mold materials and simpler cooling systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If high pressure is used to force liquid plastic into thin-walled molds, then wall thickness can be reduced, but equipment cost and capital expenses increase significantly
Solution Approach 1:
The patent changes the pressure parameter from conventional high pressure to low pressure injection molding. By using a reciprocating piston mechanism that delivers controlled low pressure injections, the system achieves thin-walled part formation without requiring expensive high-pressure equipment, thus reducing capital expenses while maintaining the ability to produce parts with wall thicknesses less than 1.0 millimeter
Solution Approach 2:
The patent replaces the conventional high-pressure mechanical injection system with a low-pressure reciprocating piston system. This substitution uses a multi-stroke injection process where the piston reciprocates to deliver material in controlled increments, achieving thin-wall formation through cumulative low-pressure injections rather than single high-pressure bursts
2Productivity
If high pressure is applied to fill the mold, then material flow is improved, but molded-in stresses increase causing warping and reduced mechanical properties
Solution Approach 1:
The patent changes the pressure parameter from high to low, and the injection pattern from single-shot to multi-stroke. The reciprocating piston delivers material in multiple low-pressure increments, allowing the material to flow gradually and cool progressively, which reduces molded-in stresses while maintaining adequate material flow to fill the mold cavity completely
Solution Approach 2:
The patent employs periodic reciprocating injections where the piston moves back and forth multiple times to deliver material in controlled increments. This periodic action allows the material to flow and cool in stages, preventing excessive stress accumulation that would occur with continuous high-pressure injection, thereby improving mechanical properties and reducing warping
3Productivity
If conventional high pressure injection is used, then mold filling is achieved, but special hard materials are required for the mold increasing cost
Solution Approach 1:
The patent changes the injection pressure parameter from high to low, which allows the use of softer, more machineable mold materials. The reciprocating piston delivers material in controlled low-pressure increments that are sufficient to fill the mold cavity without requiring the extreme pressures that would necessitate expensive hard materials like tool steel
Solution Approach 2:
The patent enables the use of softer, less expensive mold materials that can be easily machined and modified. While these materials may have shorter service lives under extreme conditions, the low-pressure process extends their usable life significantly, providing a cost-effective alternative to expensive hard materials for many applications
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 results in uniform parts with improved mechanical and optical properties, reduced manufacturing costs, and increased efficiency by maintaining a continuous flow front and minimizing mold material stress, while allowing for more flexible mold designs and production processes.
Implementation Method 1
a low constant pressure injection molding system that maintains melt pressure around 6000 psi or lower, using a pressure regulating mechanism to ensure consistent flow and reduce shear stress
Implementation Method 2
the plastic resin freezing on the walls of the mold is exacerbated when the molds are cooled, a technique used to reduce the cycle time of each part
Implementation Method 3
heating the plastic in the injection molding machine to allow it to flow under pressure
Data Source
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AI summary
A melt pressure regulating mechanism for an injection molding apparatus having a melt holder for pressurizing molten plastic prior to injection into a mold, the molten plastic having a melt pressure, and an injection element for advancing the molten plastic from the melt holder into the mold, the melt pressure regulating mechanism comprising: a pressure regulating device disposed between the melt holder and the mold, the pressure regulating device maintaining a substantially constant melt pressure within a mold cavity, the pressure regulating device comprising one of a fluid pressure regulating valve and a pressure relief valve. The injection molding machine forms molded parts by injecting molten thermoplastic material into a mold cavity at low constant pressures of 6,000 psi and lower.