Low Constant Pressure Injection Molding for Thin-Walled Parts
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Solution Overview
Problem
Conventional injection molding processes face challenges in reducing wall thickness of injection molded parts without increasing capital expenses and often result in parts with undesirable warping, sink, and reduced mechanical properties due to premature hardening and stress retention in the mold.
Innovation Solution
A method of injection molding at low, substantially constant melt pressures, allowing for efficient filling of mold cavities without premature hardening, using a system with a manifold, injection nozzle, actuator, and valve pin to control material flow, enabling the use of unheated mold cavities and reducing sensitivity to thermoplastic material variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional injection molding processes are used to reduce wall thickness, then material usage and cost are reduced, but the material freezes prematurely on the mold walls causing flow path closure and preventing complete cavity filling
Solution Approach 1:
The patent changes the pressure parameter from conventional high pressure to low, substantially constant pressure during injection. This parameter change allows the material to flow at a controlled rate that prevents premature freezing on the mold walls while still enabling complete cavity filling, thus resolving the contradiction between reducing material usage and ensuring complete filling.
2Manufacturing precision
If injection pressure is increased to force material into thin-walled areas, then cavity filling is improved, but equipment cost and complexity increase significantly
Solution Approach 1:
The patent applies low, substantially constant pressure instead of high pressure to achieve complete cavity filling. This parameter change eliminates the need for expensive high-pressure equipment while still enabling material to flow into thin-walled areas, thus resolving the contradiction between filling completeness and equipment cost.
3Manufacturing precision
If conventional high pressure injection is used to fill thin-walled parts, then cavity filling is achieved, but molded-in stresses cause warping and reduced mechanical properties
Solution Approach 1:
The patent uses low, substantially constant pressure during injection instead of high pressure. This parameter change allows the material to flow and fill the cavity without retaining high molded-in stresses, thereby preventing warping and maintaining mechanical properties while still achieving complete filling of thin-walled parts.
4Productivity
If mold cooling is applied to reduce cycle time, then productivity increases, but material freezing on mold walls is exacerbated
Solution Approach 1:
The patent changes the injection pressure parameter to low, substantially constant pressure, which compensates for the cooling effect on the mold walls. This allows the material to maintain flow capability even when the mold is cooled for reduced cycle time, thus resolving the contradiction between productivity and material flow.
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 method produces high-quality thin-walled parts with reduced material usage and cost, minimizing warping and stress retention, and allows for the use of recycled plastics and low-cost, high thermal conductivity mold materials, while maintaining part quality across varying temperature and viscosity conditions.
Implementation Method 1
injecting the shot comprising molten thermoplastic material into the mold cavity to fill the mold cavity while maintaining the melt pressure of the shot comprising molten thermoplastic material at a substantially constant pressure within the range of 1000 psi to less than 6000 psi
Data Source
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AI summary
Disclosed herein is a method of injection molding at low, substantially constant melt pressures. Embodiments of the disclosed method now make possible a method of injection molding that is more energy-and cost-effective than conventional high-velocity injection molding processes. Embodiments of the disclosed method surprisingly allow for the filling of a mold cavity at low melt pressure without undesirable premature hardening of the thermoplastic material in the mold cavity and without the need for maintaining a constant temperature or heated mold cavity. Heretofore, it would not have been expected that a constant pressure method could be performed at low pressure without such premature hardening of the thermoplastic material when using an unheated mold cavity or cooled mold cavity.