Cavity Pressure Sensors Research Articles

Recurrent neural networks as virtual cavity pressure and temperature sensors in high-pressure die casting

High-pressure die casting (HPDC) is a permanent mold-based production technology that facilitates the casting of near net shape components from nonferrous alloys. The pressure and temperature conditions within the cavity impact the cast product quality during and after the conclusion of the die filling process. Die surface cavity sensors can deliver information describing the conditions at the die-casting interface. They are associated with high costs and limited service lifetimes below the achievable total cycle count of the die inserts and therefore ill-suited for industrial use cases. In this work, the suitability of long short-term memory (LSTM) recurrent neural networks (RNN) for substituting physical cavity temperature and pressure sensors virtually after the production ramp-up or at the end of the sensor service life is investigated. Training LSTMs with data of 233 casting cycles with different process parameters provides networks which are then applied to 99 further cycles. The prediction accuracy is investigated for different time interval lengths in the solidification and cooling phase. For longer time intervals, the cavity pressure prediction deteriorates, potentially due to a highly individual and hardly ascertainable buildup of casting distortion and internal stresses. Overall, however, the accuracy of the developed LSTMs is excellent for the cavity temperatures and good for the cavity pressures.

Surface Modified Optical Fiber Fabry–Perot Cavity Pressure Sensor With Carbon Film

By the method of pulsed laser deposition of a Ni/C bilayer precursor films and annealing in air, amorphous carbon films were prepared on the surface of the capillary used for fabrication of optical fiber Fabry-Perot (FP) cavity pressure sensors. The surface morphologies of the coated and annealed carbon films were investigated through scanning electron microscopy. The images reveal that surface modification smoothes the irregular particles on the capillary surface and releases the stress induced by carbon and nickel deposition and oxy-hydrogen flame welding. Performance tests showed that the surface modified pressure sensors have good linearity for pressure response and the cavity length variations during the full cycle of pressure change is within 31 nm. Furthermore, thanks to the introduction of carbon films, the long-term stability of the cavity length can be kept within 10 nm during the tested 150 days.

Micro-Bubble F-P Cavity and FBG Cascade Structure-Based Pressure Sensor With Temperature Self-Compensation for Minimally Invasive Surgery.

This paper presents a high-sensitivity optical fiber pressure sensor with temperature self-compensation for pressure measurement in minimally invasive surgery through a cascade structure of Fabry-Perot (F-P) interferometer and fiber Bragg grating (FBG). A micro-bubble is configured at the tip of the fiber to form an F-P cavity that is sensitive to pressure. A loose optical fiber inscribed with an FBG element is cascaded with the F-P cavity leading to temperature compensation for the designed sensor. The sensing theoretical model has been derived and combined with the finite element method (FEM) simulation the sensor structure has been determined as well. Fabrication processing of the designed sensor has been optimized and explored by experiments. Calibration experiment results indicate that the pressure sensitivity of the designed sensor is 8.93 pm/kPa, which is consistent with the simulated value. The temperature coupled error is less than 3.89% leading to a capability for temperature self-compensation. Several heart-vascular simulation experiments have been carried out to investigate the dynamic performance of the designed sensor, which shows the measured pressure errors within this confidence interval of [-2.56%, 2.54%] correspond to high confidence of 0.95. An in-vivo intracranial pressure (ICP) measurement experiment on the rat brain has been conducted to further validate the feasibility and effectiveness of the designed sensor.

Fiber-Tip Fabry–Perot Cavity Pressure Sensor With UV-Curable Polymer Film Based on Suspension Curing Method

We investigate a novel and compact fiber-tip pressure sensor based on Fabry-Perot interferometer (FPI). The proposed device is fabricated by welding a Section of hollow silica tube (HST) on the end of single mode fiber (SMF) and then coating with ultraviolet (UV) curable polymer film at the tip of HST. A simple suspension curing method is introduced to control the formation of the UV curable polymer layer. Therefore, different thicknesses of the polymer film can be easily controlled. The pressure sensing mechanism is based on the cavity length change induced by ambient pressure. The sensor characteristics are studied theoretically and experimentally. The proposed fiber-tip pressure sensor with polymer film thickness of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.7\,\, \mu \text{m}$ </tex-math></inline-formula> exhibits a pressure sensitivity of 396 pm/kPa in the range of 0–30 kPa based on wavelength shift of the interference dip. Moreover, temperature crosstalk is measured, and the thermal-induced deformation of the polymer film is simulated using the Finite Element Analysis method. The proposed fiber-tip Fabry-Perot cavity pressure sensor has advantages of high sensitivity, fast response, excellent repeatability, compact size, cost effectiveness and easy fabrication, which makes it suitable for high sensitivity pressure detection in a limited space.

Number of Times Recycled and Its Effect on the Recyclability, Fluidity and Tensile Properties of Polypropylene Injection Molded Parts

The ease with which modern plastics can be injection molded makes them very suitable for the production of many different products and, today, plastics are often used as substitutes for metal. Polypropylene (PP) is one of the most widely used thermoplastics globally since it is very useful, cost-effective and flexible for molding. However, the amount of harm to the environment caused by plastic waste has become phenomenal and the recycling of plastics has become a serious aspect of environmental protection. PP, as the most commonly used plastic material, was selected for use in this study. It has a melt flow index of 15 g/min and its recyclability, fluidity, and physical properties, as well as manufacturing conditions, were explored in relation to the number of times the material could be recycled (TR). A cavity pressure sensor was used to measure the viscosity index of the recycled plastic after multiple cycles of plasticizing and injection, part molding, scrap-recycling, and crushing. A paperclip-shaped test specimen was used to determine PP fluidity and crystallinity of specimens with different TRs. Tensile tests were used to detect differences in the tensile strength between specimens made from Raw-PP and recycled PP. The results showed that PP that had been recycled several times had a higher melt flow index, material fluidity, melting peak area, crystallinity, crystallization rate, and crystallization temperature. Repeated injection and recycling of the material had reduced the length of the molecular chains and broadened the molecular weight distribution. This improved the fluidity and increased crystallinity. The increase in fluidity made cavity filling easier, reducing the cavity pressure as well as the viscosity index. The results of this study showed that the recycling of the PP could improve the physical properties of the products to a degree and also went some way to further the benefits of a circular economy. The recycling of injection-molded PP material can be added to renewable energy technologies and used in environmental impact assessment.

Rapid heating injection moulding: An experimental surface temperature study

Rapid heat cycle moulding (RHCM) is a recent set of injection technologies that allow a full temperature control in a mould.Between all technologies available in terms of heating and cooling, electrical resistance heating and water cooling were chosen for this study.The mould design has a capital importance in terms of process efficiency. Thermal and mechanical key points must be addressed together. Temperature distribution in moulding cavity and quality part run together.Before mould machining, a full mechanical, thermal and rheological simulation was carried out. Due to transient thermal complexity, thermal simulation was validated using infrared thermography on a dummy tool fitted with both heating and cooling devices.All this previous work is usual for each new tool. When a new process is suggested for new part requirements, it is necessary to understand injection physical bases in order to prevent unexpected failures. This work introduces the mould temperature curve to realize how RHCM works, and compare its results with conventional moulding.The influence of cavity temperature map was studied with a cavity pressure and temperature sensor helped with near infrared thermography. At the same time, the relationship with parameters which control both heating and cooling periods was considering.Simulation and experimental results are compared, and RHCM process highlights could be well understood to improve future new injection parts development.

Tie-Bar Elongation Based Filling-To-Packing Switchover Control and Prediction of Injection Molding Quality.

Filling-to-packing switchover (also called V/P switchover) is critical for assuring injection molding quality. An improper V/P switchover setting may result in various defects of injection-molded parts, such as excessive residual stress, flash, short shot, and warpage, etc. To enhance a consistent molding quality, recent V/P switchover approaches adopt cavity pressure profiles requiring sensors embedded in mold cavities, which is invasive to mold cavities and more expensive. Instead of using cavity pressure sensors, by working with the most popular screw position switchover control, this study hereby proposes a novel approach of tuning V/P switchover timing using a tie-bar elongation profile. In this investigation, a dumbbell testing specimen mold is applied to verify the feasibility of the method proposed. The results show that the mold filling and packing stages can be observed along the tie-bar elongation profile, detected by mounting strain gauges on the tie bars. Also, the characteristics of the cavity pressure are similar to those of the tie-bar elongation profile under a proper clamping force condition. Moreover, the varying process parameter settings which include injection speed, V/P switchover point, and holding pressure, can be reflected in these profiles. By extracting their characteristics, the application of the V/P switchover is proved to be realistic. This research conducted an experiment to verify the proposed V/P switchover decision method based on the tie-bar elongation profile. The result showed that the fluctuation of the part’s weight corresponding to a slight change of the barrel’s temperature from 210 °C to 215 °C can be successfully controlled with this method. Besides, the maximum clamping force increment extracted from the tie-bar elongation profile was found to be a good indicator for online monitoring of the reground material variation.

Forming characteristics during the high-pressure resin transfer molding process for CFRP

The high-pressure resin transfer molding (HP-RTM) process has potential applicability to the mass production of lightweight vehicles made of carbon fiber-reinforced plastic in the automotive industry. In recent years, the development of robust equipment, new processes, and fast cure matrix systems have significantly reduced the cycle time to less than 5 min. In this study, the cavity pressure of the HP-RTM process was monitored to analyze the molding characteristics. The mold was equipped with two cavity pressure sensors and three temperature sensors. The cavity pressure characteristics during the HP-RTM injection, pressurization, and curing processes were studied. Selected process parameters such as the mold cap size, maximum pressing force, and injection volume were analyzed. The results demonstrated correlations between the selected process parameters and final forming characteristics.

Effects of ultrasonic injection molding conditions on the plate processing characteristics of PMMA

Abstract Polymer processing is a crucial and diverse field in the manufacturing industry. We investigated the process characteristics and effects of injection molding using ultrasonic vibration. An ultrasonic device was installed in an injection mold; polymer was directly vibrated during injection. An ultrasonic oscillation device 45 mm in diameter was placed in the cavity and used to vibrate a poly(methyl methacrylate) melt at 19 kHz. The amplitude of the acoustic unit was set at 15 μm for the measurements. Moreover, cavity pressure sensors were positioned at the front and rear sides of the vibration region to determine the melt flow behavior under ultrasonic-assisted injection molding conditions. Because of the absorption of ultrasonic energy, local heat was generated inside the resin, thus improving the flow characteristics of the melt. Moreover, the melt flow behavior around the skin layer was changed; the molecular orientation and high shear effect were reduced. Furthermore, the freezing rate of the melt was reduced; thus, the amount of melt pressure lost through the cavity was decreased and the residual stress inside the injection-molded component generated during the photoelastic stress analysis was lower.

Application of ultrasonic-assisted injection molding for improving melt flowing and floating fibers

Abstract In this study, we investigated the use of ultrasonic technology in assisted injection molding and mold designs. We used an ultrasonic device installed in a mold to vibrate a melt directly, thereby converting kinetic energy into thermal energy. In addition, we developed three flat specimens of different thicknesses (3, 1, and 3-1-3 mm) produced by ultrasonic-assisted injection molds. An ultrasonic oscillation device 45 mm in diameter was placed in the cavity and used to vibrate a polycarbonate or a polycarbonate with 30% glass fiber melt at a frequency of 20 kHz. Furthermore, cavity pressure sensors were positioned at the front and rear of the vibration region for analyzing the melt flow behavior under ultrasonic-assisted injection molding conditions. Because of the absorption of ultrasonic energy, local heat was generated inside the resin, thus forming an oscillatory flow during the packing and holding stages, improving the flow characteristics of the melt, and changing the melt flow behavior around the skin layer to reduce the molecular orientation and high shear effect. The freezing rate of the melt was also reduced to eliminate the glass fiber streaks, floating fibers, and fiber orientation, particularly for thinner parts; the hesitation phenomena were then improved to increase the weld line strength.

Characteristics analysis and mold design for ultrasonic-assisted injection molding

Abstract This study investigated the use of ultrasonic technology in assisted injection molding (AIM) and mold design. An ultrasonic device installed in a mold was employed to vibrate a melt, thereby converting kinetic energy into thermal energy. This method enabled maintaining the desired temperature in the melt flow, preventing a high level of shear and the formation of a thick frozen layer surrounding the skin layer; thus, the injection molding efficiency was enhanced and the residual stress inside the injection-molded component was reduced. In this study, a flat sample (75 mm×47 mm×1 mm) of an ultrasonic-assisted injection mold was developed. An ultrasonic oscillation device 45 mm in diameter was placed in the center of the cavity and used to vibrate a polycarbonate melt at a frequency of 20 KHz. In addition, cavity pressure sensors were positioned at the front and rear of the vibration region to analyze the melt flow behavior under ultrasonic-AIM (UAIM) conditions. The results showed that ultrasonic oscillations can reduce the amount of melt pressure lost through the cavity. The pressure loss of the flat sample used in UAIM was approximately 29% lower than that of the sample used in conventional injection molding (CIM; nonultrasonic-assisted injection); the power of UAIM did not yield substantial effects. Direct ultrasonic oscillations destroyed the melt flow and thermal stresses, therefore, the region exhibited a low stress distribution. Compared with using CIM, using UAIM reduced the average residual stress by 27%. Ultrasonic oscillation affected the surface roughness during melt solidification. When the ultrasonic power was &lt;70%, no substantial increase in surface roughness was observed; however, when the ultrasonic power &gt;70%, the surface roughness was 10 times higher compared with that observed using CIM.

Finite element method based absolute pressure sensitivity optimized membrane type double cavity vacuum sealed piezoresistive sensor

Purpose – The purpose of this paper is to use finite element method for optimizing the membrane type double cavity vacuum sealed structure for the best achievable sensitivity in a piezoresistive absolute pressure sensor and its validation using a standard complementary metal oxide semiconductor (CMOS) process. Design/methodology/approach – A double cavity vacuum sealed piezoresistive absolute pressure sensor has been simulated and optimized for its performance and an analytical model describing the behaviour of the sensor has been described. The 1×1 mm sensor chip has two membrane type 100×30×1.7 μm diaphragms consisting of composite layers of plasma enhanced chemical vapour deposition (PECVD) of silicon nitride (Si3N4) and silicon dioxide (SiO2) each hanging over 21 μm deep rectangular cavity. Potassium hydroxide (KOH) based anisotropic etching of single crystal silicon using front side lateral etching technology is used for the fabrication of the sensor. The electrical readout circuitry uses 318 Ω boron diffused low pressure vapour chemical vapour deposition (LPCVD) of polysilicon resistors arranged in the Wheatstone half bridge configuration. The sensing structure is simulated and optimized using COMSOL Multiphysics. Findings – Front-side lateral etching technology has been successfully used for the fabrication of double cavity absolute pressure sensor. A good agreement with the fabricated device for the chosen location of the piezoresistors through simulation has been predicted. The measured pressure sensitivity of two tested pressure sensors is 12.63 and 12.46 mV/MPa, and simulated pressure sensitivity is found to be 12.9 mV/MPa for pressure range of 0 to 0.5 MPa. The location of the piezoresistor has also been optimized using the simulation tools for enhancing the sensor sensitivity to 62.14 mV/MPa. The pressure sensitivity is further enhanced to 92 mV/MPa by increasing the width of the diaphragm to 35 μm. Originality/value – The simulated and measured pressure sensitivities of the double cavity pressure sensor are in close agreement. Sevenfold enhancement in the pressure sensitivity of the optimized sensing structure has been observed. The proposed front-side lateral etching technology can be adopted for making membrane type diaphragms hanging over vacuum sealed micro-cavities for high sensitivity pressure sensing applications.

Presentation of a novel sensor based on acoustic emission in injection molding

AbstractInjection molding is the most important process to produce plastic parts. Because of increasing complexity of the plastic parts and the aim to reach zero‐defect production it is a must to control the dynamic injection molding process. Therefore information from the inside of the mold, measured with sensors, is necessary. State of the art is to implement wired mold cavity pressure sensors as well as wired cavity temperature sensors. This article presents a novel wireless measurement setup which uses structure borne sound as transport medium. The sound is generated by an acoustic actor which is activated by the passing flow front at certain predetermined positions in the cavity (or cavities). Beside the mechanical setup of the sensor proof of concept measurements with a prototype setup are shown in this article. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Feasibility Analysis of an In-mold Multivariate Sensor

Abstract The initial design of a novel multivariate sensor is described for the measurement of melt temperature, melt pressure, melt velocity, melt viscosity, and mold temperature. Melt pressure and temperature are respectively obtained through the incorporation of a piezoceramic element and infrared photodetector within the sensor head. Melt velocity is derived from the initial response of the melt temperature as the polymer melt flows across the sensor's lens. The apparent melt viscosity is then derived from the melt velocity and the time derivative of the increasing melt pressure given the cavity thickness. The feasibility of the envisioned sensor is then analyzed using a production-grade mold that is instrumented with commercial piezoelectric pressure sensors, infrared pyrometer, and thermocouples. Several predictive models of part weight are developed using multiple regression of data obtained from a design of experiments to evaluate the capability of the envisioned multivariate sensor. The results indicate a correlation coefficient, R2, of 0.79 for a model based on the machine settings, 0.80 for a model based on a cavity pressure sensor, 0.90 for a model based on the multivariate sensor, and 0.98 for a non-linear model based on the multivariate sensor. The implication is that multiple orthogonal sensing streams with high fidelity models are necessary to provide automatic quality assurance sufficient for fully automated plastics manufacturing.

사출금형 버 발생 방지를 위한 형합면압 측정에 관한 연구

The flashing reduces the part quality and the productivity of the molding process. We developed a contact pressure sensor to detect the flashing immediately. The performance of the sensor was analyzed in a simple 2D simulation. The sensor was applied to an automotive bumper mold with cavity pressure sensors. It showed sensitive output signal for the mold response by the cavity pressure change. It was confirmed that the flashing at the gate area occurred in the filling stage by the pressure increase due to growth of the melt flow length. The sensor output was correlated with the cavity pressure sensor output.

Multivariate regression modeling for monitoring quality of injection moulding components using cavity sensor technology: Application to the manufacturing of pharmaceutical device components

There is an increased demand within the moulding industry to improve the quality of moulded parts by maintaining consistent tolerances and overall dimensions. This interest is more important in areas of the moulding industry that are dedicated to pharmaceutical devices, where a quality by design approach is now expected to be adopted. A pharmaceutical device is an assembly of different plastic components which are manufactured by injection moulding; many have critical quality parameters which affect not only the device appearance but also more importantly its performance for drug delivery. Hence, the need of better understanding and control of injection moulding processes. This study presents the use of multivariate regression modeling approach to monitor the quality of the final product using cavity sensor technology (CST). The influence of the injection moulding process parameters on the quality of the final parts have been investigated using a design of experiment approach. The results demonstrate that the Partial Least Squares (PLS) regression model based on cavity pressure sensor data could be successfully used to monitor the quality (weight, dimensions) of the final product in plastic injection moulding.

Injection Molding Measurement and Analysis of a Plastic Part with Changes in Thickness Dimensions and Material Types

A plastic injection mold for injection of a 100mm long and 70mm width plane connected to a 20 mm height vertical side wall by a radius of 5mm fillet is investigated in this study. Four different part thicknesses, 2mm, 1mm, 0.75mm, and 0.5mm, respectively, are designed to study the thickness effect upon the warpages of plastics. Three different plastics, ABS(PA-756; Chi-Mei), PC(HF1110R; GE), and PP(PRO FAX 6331) are injection molded by the designed mold. Taguchi method is used to find out the optimum injection molding condition for each of the experimental measurement and the CAE analysis. Cavity pressure sensors are embedded in the mold to detect the inner pressures and temperatures of the melts. A 3D laser scanning system is used to measure the deformations of plastics after injection molding. Cavity pressures and deflections of the experimental measurement and the CAE analysis are compared to show the effects of molding parameters to deflections. The experimental measurement and the CAE simulation show some discrepancies in deformations which may attribute to the experimental errors or the theoretical assumptions in mold flow analysis and the used material models. In general, the deformations by experiment show greater values than the deformations by simulation.

Embedded micromachined fiber-optic fabry-perot pressure sensors in aerodynamics applications

Small size, high bandwidth pressure sensors are required for instrumentation of probes and test models in aerodynamic studies of complex unsteady flows. Optical-fiber pressure sensors promise potential advantages of small size and low cost in comparison with their electrical counterparts. We describe miniature Fabry-Perot cavity pressure sensors constructed by micromachining techniques in a turbine test application. The sensor bodies are 500 /spl mu/m squared, 300 /spl mu/m deep with a /spl sim/2 /spl mu/m-thick copper diaphragm electroplated on one face. The sensor cavity is formed between the diaphragm and the cleaved end of a single mode fiber sealed to the sensor by epoxy. Each sensor is addressed interferometrically in reflection by three wavelengths simultaneously, giving an unambiguous phase determination; a pressure sensitivity of 1.6 radbar/sup -1/ was measured, with a typical range of vacuum to 600 kPa. Five sensors were embedded in the trailing edge of a nozzle guide vane installed upstream of a rotor in a full-scale turbine stage transient test facility. Pressure signals in the trailing edge flow show marked structure at the 8 kHz blade passing frequency. To our knowledge, this is the first report of sensors located at the trailing edge of a normal-sized turbine blade.

Monitoring cavity pressure perfects injection molding

Only continuously monitoring cavity pressure allows the detailed recording of the injection molding process in the injection, compression and holding pressure phases. It alone correlates with all significant molding features such as weight, morphology, degree of forming, burr formation, shrink marks and cavities as well as shrinkage and deformation. The cavity pressure not only optimizes the timing of the switching point from the compression to the holding pressure phase, but also serves directly as a criterion for the switching. Molding weights and countless other quality characteristics thereby vary considerably less than with switching based on hydraulic pressure, screw travel or time. Quartz sensors have proved particularly successful for direct and indirect measurement of pressure. Advocates the use of cavity pressure sensors for monitoring and control of the injection molding process and describes commercial products that are available.

Critical processing issues for micromachined sacrificial layer etching and sealing

Integrating on-chip circuitry with micromachined devices poses many problems, from clearing of the sacrificial layer to sealing of the structural layer after sacrificial etch. In this paper, the repeatability of sacrificial etch of phosphosilicate glass (PSG) and the sealing of etch channels using different layers are investigated. The sacrificial etch rate changes with phosphorus weight percent concentration in the PSG. Thirteen typical structures in 10 different runs were monitored for etch front distance after 60 s in concentrated HF (49%). There was a maximum run to run coefficient of variance of 21%. Four different layers were investigated to determine the most effective for sealing. TEOS sealed less than 5% of 100 μm devices and 30% of 130 μm devices, LPCVD nitride sealed 25% of 100 μm devices and 55% of 130 μm devices. LPCVD polysilicon sealed all the devices. A reoxidation of the polysilicon membrane at atmospheric pressure was also investigated but the film seemed to cause the devices to lift and none appeared sealed. Scanning electron microscopy revealed the nitride and polysilicon layers to `fill in' the etch channel. The TEOS formed a `lip' over the channel and the reoxidation did not close off the etch channel gap. Characterising these stages in the process allows optimisation of the production of sealed cavity pressure sensors.