Dimension Sensor

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Backgound There has been increasing recognition that the measurement and control of the polymer state within the mold cavity is vital for maintaining product dimensions and quality.  In-mold shrinkage is the major driver of the final molded parts dimensions. It is primarily a function of cavity pressures, mold and melt temperatures, cycle times, and material properties amongst other factors. The control of shrinkage can be difficult, especially in tight tolerance and multi-cavity applications. To improve the capability of the in-mold sensors to predict quality, sensor fusion approaches have incorporated multiple sensor streams with on-line and/or post­ molding analyses to predict the molded parts dimensions. However, till date no single control strategy or system design has been universally successful, and defective components are likely to be manufactured in high volume production. Further, there have been significant increases in molded part complexity due to the development and widespread implementation of design for manufacturing and assembly (DFMA) guidelines that leverage the capabilities of the injection molding process. Given such potential functionality arising from complex molded parts, it is currently not uncommon for a molded part to be specified with several critical dimensions with tight tolerances. Thus, there is a critical need for further development of improved process sensors, real time sensor fusion and control architectures directed to shrinkage prediction and control in order to produce molded parts with desired precise dimensions reproducibly. Technology UMass Lowell professor, Dr. David Kazmer and his team has developed a method for use in forming a molded part which enables the measurement of the molded part dimensions in situ, prior to ejection from the mold. The invention provides a high fidelity system for controlling molded part dimensions by integrating appropriate shrinkage instrumentation, analysis and controls. The key components of the system include: A dual-mode sensor utilizing strain gages and piezoelectric elements to monitor both in-mold part dimensions and melt pressure A shrinkage analysis to use the sensed dimensional and pressure date with transient heat analyses to predict the final molded part dimensions after cooling and annealing An auxillary controller to track the consistency of the molding process, perform control actions given the part quality requirements, and recommend alternative process set-points Applications High fidelity system for dimensional control of injection molded products leading to production of molded parts with desired precise dimensions and quality reproducibly Sensors designed to measure in-mold part dimensions and cavity pressures System for controlling the formation of a plurality of molded parts in a cavity of a mold Measure the size and shrinkage of molded parts in commercial molding applications accurately Advantages Dual mode size/pressure measurement sensor provides more information than a conventional cavity pressure sensor, potentially leading to dynamic control of molded part formation Sensor is of acceptable size and usage leading to precise measurement of molded part dimensions in situ prior to ejection from the mold Low cost sensor, leading to substantial savings in manufacturing molded parts