Strain Gauge Virtual Sensor for Injection Molding Pressure Control
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Solution Overview
Problem
Current indirect sensors for measuring pressure within a mold cavity during injection molding, such as strain gauge sensors, often require downtime for installation, are expensive, and may not be optimally placed, leading to suboptimal pressure monitoring and potential mold damage due to excessive pressure.
Innovation Solution
Mounting strain gauge sensors on the exterior of a mold surface adjacent to the parting line, in conjunction with a virtual cavity sensor, to approximate pressure conditions within the mold cavity and adjust the injection molding process when pre-set trigger points are exceeded, ensuring optimal pressure control without direct contact with the mold cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct sensors are placed within the mold cavity to measure pressure, then measurement precision is improved, but the high gloss finish of the parts is marred and manufacturing precision deteriorates
Solution Approach 1:
The patent uses an intermediary indirect sensing system that measures mold cavity pressure without direct contact with the part surface. The sensor system includes a sensor positioned outside the mold cavity that detects pressure through the mold wall or via strain measurements on the mold, thereby preserving the high gloss finish while still providing accurate pressure data for process control
Solution Approach 2:
The patent creates a virtual representation of the pressure conditions inside the mold cavity by measuring external parameters (such as strain on the mold or pressure at accessible locations) and using these measurements to infer the internal pressure state. This copying approach allows pressure monitoring without physical intrusion into the cavity that would mar the part surface
2Manufacturing precision
If indirect sensors are used to avoid maring the part surface, then surface finish quality is improved, but sensor placement options are limited and installation requires downtime
Solution Approach 1:
The patent segments the sensing function from the mold cavity interior, placing sensors on external surfaces or at accessible locations on the mold. This segmentation allows the sensing system to be installed independently without requiring mold disassembly or downtime, while still providing the needed pressure measurement capability through indirect detection methods
3Ease of operation
If strain gauge sensors are mounted on the exterior of the mold adjacent to the parting line, then ease of installation is improved and surface finish is preserved, but measurement precision for cavity pressure is reduced
Solution Approach 1:
The patent implements a feedback-based virtual sensing system where external strain gauge measurements are continuously monitored and processed to infer internal cavity pressure conditions. The system uses algorithms that correlate external strain patterns with internal pressure states, providing real-time feedback control that compensates for the indirect measurement approach and maintains effective measurement precision for process control
Solution Approach 2:
The patent changes the measurement parameters from direct pressure sensing inside the cavity to external strain measurement on the mold. By measuring strain (deformation) on the mold exterior and using the known mechanical properties of the mold material, the system calculates the internal pressure state, transforming the measurement approach while maintaining operational effectiveness
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 solution allows for real-time pressure monitoring and adjustment, preventing mold damage by approximating pressure conditions and maintaining optimal pressure levels, even in molds with high L/t ratios, thereby improving the quality and efficiency of the injection molding process.
Implementation Method 1
The strain gauge sensor or sensors measures surface strain of the mold
Data Source
AI summary
A injection molding method involves measuring, using at least one strain gauge sensor, a change in strain in a mold side of a mold cavity, approximating a pressure within the mold cavity based on the change in strain, comparing the approximated pressure to a pre-set trigger point, and if the approximated pressure equals or exceeds the pre-set trigger point, activating a virtual cavity sensor having an optimal pre-defined pressure-time curve, wherein upon activation, the virtual cavity sensor tracks approximated pressures calculated from the change in strain measurements measured by the at least one strain gauge sensor over time and compares the results of the approximated pressure tracking to the optimal pre-defined pressure-time curve.