Ultrasonic Melt Density Measurement in Injection Molding
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Solution Overview
Problem
Existing methods for online density measurement in injection molding are costly, require complex mold modifications, and can affect the product surface, while existing ultrasonic methods struggle with temperature compensation, internal drift, and reduced sensitivity due to multilayer media interactions.
Innovation Solution
An ultrasonic online nondestructive measurement method using time domain and frequency domain analysis to calculate melt density without the need for in-mold sensors, by emitting ultrasonic waves from the mold cavity wall, analyzing reflection echoes to determine propagation velocity and acoustic impedance, and calculating density based on these parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If in-mold sensors are used for online density measurement, then measurement capability is improved, but device cost increases significantly
Solution Approach 1:
The patent replaces mechanical pressure and temperature sensors with an ultrasonic measurement system. By measuring ultrasonic wave propagation characteristics (velocity, attenuation) through the polymer melt, the system indirectly determines density without direct mechanical contact. This substitution eliminates the need for expensive in-mold pressure and temperature sensors while maintaining online measurement capability.
Solution Approach 2:
The patent introduces ultrasonic waves as an intermediary to measure density. Instead of directly measuring pressure and temperature with sensors, the system uses ultrasonic wave propagation characteristics as a mediator to infer density. The ultrasonic waves interact with the polymer melt, and changes in wave velocity and attenuation provide information about density without requiring direct sensor contact with the melt.
2Measurement precision
If in-mold sensors are installed for online measurement, then process monitoring capability is improved, but mold modification complexity increases
Solution Approach 1:
The patent replaces the need for mechanical sensor installations with an ultrasonic transducer mounted on the mold exterior. This substitution eliminates the need for drilling mounting holes, creating complex sensor assemblies, and making precise H7 tolerance adjustments. The ultrasonic transducer can be mounted on the outer surface of the mold cavity, requiring minimal modification to the mold structure.
Solution Approach 2:
The patent inverts the traditional sensor mounting approach by placing the ultrasonic transducer on the exterior of the mold rather than embedding sensors within the mold cavity. This inversion allows the measurement system to function from the outside, eliminating the need for complex internal sensor installations while maintaining the ability to monitor the polymer melt properties online.
3Measurement precision
If in-mold sensors are used for direct melt contact measurement, then measurement accuracy is improved, but product surface quality deteriorates
Solution Approach 1:
The patent replaces direct mechanical contact measurement with ultrasonic wave measurement. The ultrasonic transducer measures density by analyzing wave propagation through the mold wall and polymer melt without the sensor physically contacting the melt or product. This eliminates the harmful effect of sensor traces on the product surface while maintaining measurement accuracy through non-contact ultrasonic characterization.
4Measurement precision
If traditional density measurement methods are used, then measurement capability is improved, but measurement timing is delayed to after demolding
Solution Approach 1:
The patent implements preliminary measurement action by enabling density measurement during the injection molding process itself, before demolding occurs. The ultrasonic system continuously monitors polymer melt density in-situ, providing real-time feedback that can be used for process control and optimization. This eliminates the time delay inherent in post-demolding measurement methods and allows for timely process adjustments.
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 provides accurate, non-destructive, and surface-untouched density measurements, adaptable to various process conditions and materials, facilitating online process monitoring and optimization in injection molding without the need for expensive in-mold sensors.
Implementation Method 1
emitting an ultrasonic wave toward a polymer melt in the mold cavity
Implementation Method 2
collecting reflection echoes of two surfaces of the melt in contact with a mold
Data Source
AI summary
The present disclosure discloses an ultrasonic online nondestructive measurement method for a melt density in injection molding, which solves the problems of difficult installation, high cost, influence on product surface quality, and the like existing in an existing density measurement method. According to the present disclosure, an ultrasonic velocity is obtained from a time domain signal with reference to time domain and frequency domain signal analysis of ultrasonic echo signals, an acoustic impedance is calculated by full spectrum analysis of a frequency domain signal, and the melt density is calculated from a correlation of the ultrasonic velocity, the acoustic impedance, and the density. The method has the advantages of having high measurement accuracy and being nondestructive, online and low in cost, and has a great application value in the injection molding industry.