Dynamic Mould Cavity Control for Injection Moulding
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Solution Overview
Problem
Conventional injection moulding techniques face limitations in achieving optimal flow paths and wall thickness ratios, leading to in-built stresses and quality issues in plastic products, while existing variants like compression moulding lack control over material flow and pressure, resulting in uncontrolled crystallization and jetting effects.
Innovation Solution
A moulding machine design featuring a mould with moveable parts and active control of cavity pressure to manage the movement of these parts during injection, allowing for controlled expansion of the cavity and precise material flow, eliminating internal stresses and improving surface finish.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional injection moulding is used with a closed mould cavity, then the injection process is simple and fast, but the pressure builds up to high levels causing in-built stresses and quality loss
Solution Approach 1:
The patent applies the dynamics principle by making the mould cavity dynamic rather than static. The cavity expands during the injection process to accommodate the incoming material, then compresses afterward. This dynamic adjustment allows the cavity volume to change in response to material flow, reducing pressure buildup while maintaining control over the injection process.
Solution Approach 2:
The patent changes the parameter of cavity volume during the injection process. By allowing the cavity to expand (increasing volume) as material is injected, the pressure is reduced compared to a fixed closed cavity. After injection, the cavity compresses (decreases volume) to consolidate the material. This parameter change resolves the contradiction between injection speed and product quality.
2Manufacturing precision
If compression moulding with a large open cavity is used, then the flow path to wall thickness ratio is improved, but the material flows in an uncontrolled manner causing jetting effects and flow front lines
Solution Approach 1:
The patent implements feedback control by using sensors to monitor the injection process and adjusting the cavity expansion/compression accordingly. This feedback mechanism allows the system to respond to material flow conditions in real-time, controlling the material flow to prevent uncontrolled jetting effects while maintaining improved flow path characteristics.
Solution Approach 2:
The movable cavity acts as an intermediary between the injected material and the final product form. By controlling the cavity's expansion and compression, it mediates the material flow process, guiding the material smoothly into the desired shape while preventing direct uncontrolled jetting effects that would occur in a static open cavity.
3Manufacturing precision
If moveable cores are retracted to enlarge the mould cavity, then the flow path to wall thickness ratio is improved, but the process becomes more complex requiring separate compression mechanisms
Solution Approach 1:
The patent merges the cavity expansion function with the injection mechanism itself. Instead of using separate moveable cores and compression mechanisms as in traditional compression moulding, the invention integrates the cavity volume control directly into the injection system, allowing the cavity to expand and compress as part of the injection process.
Solution Approach 2:
The movable cavity structure serves multiple functions: it controls the flow path during injection, manages material compression after injection, and consolidates what would otherwise require separate mechanisms. This multi-functionality reduces overall device complexity while maintaining the benefits of improved flow path to wall thickness ratio.
4Stability of the object's composition
If high clamp force is used to maintain a closed mould, then the mould remains stable, but the machine requires heavy construction and frequent parameter resetting
Solution Approach 1:
The patent applies dynamics by making the mould cavity volume variable rather than fixed. The cavity expands during injection and compresses afterward, allowing the system to maintain stability with lower clamp forces. This dynamic adjustment eliminates the need for heavy machine construction and frequent parameter resetting that would be required with a static closed cavity system.
Solution Approach 2:
The invention changes the cavity volume parameter during the moulding cycle. By allowing the cavity to expand and compress, the system maintains mould stability through controlled parameter changes rather than relying on high constant clamp force, thereby reducing machine construction requirements and parameter resetting frequency.
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 enables the production of high-quality plastic parts with reduced internal stresses, improved surface finish, and shorter cooling times, allowing for cost-effective high-volume production with minimal machine clamp force and reduced greenhouse gas emissions.
Implementation Method 1
the core, which is held in place via an appropriate counterpressure, is slowly pushed back from its starting position resulting in the cavity space being increased in a controlled and symmetrical fashion
Implementation Method 2
During the injection of the thermoplastic resin the core, which is held in place via an appropriate counterpressure, is slowly pushed back from its starting position
Data Source
AI summary
Moulding equipment for the production of plastic parts via the injection of a molten thermoplastic resin, chiefly consisting of a mould (2) which consists of at least two mould halves (3,4), which when closed together produce a cavity (11) and a core (8), wherein at least one mould half or mould part (3 and/or 4) contains at least one moveable mould part (7) with the necessary system to control the movement of the mould part or parts (7) using the active control of the cavity (11) pressure.