Switchover Point Research Articles

A decision analysis of cancer patients and the consumption of ready-to-eat salad.

Listeria monocytogenes is a foodborne pathogen of concern for cancer patients, who face higher morbidity and mortality rates than the general population. The neutropenic diet (ND), which excludes fresh produce, is often utilized to mitigate this risk; however, an analysis weighing the theoretical listeriosis risk reduction of produce exclusion aspects of the ND and possible negative tradeoffs has never been conducted. Consequently, this work constructed decision analytic models using disability-adjusted life years (DALYs) to compare the impacts of the ND, such as increased neutropenic enterocolitis (NEC) likelihood, with three alternative dietary practices (safe food handling [SFH], surface blanching, and refrigeration only) across five age groups, for cancer patients who consume ready-to-eat salad. Less disruptive diets had fewer negative health impacts in all scenarios, with median alternative diet DALYs per person per chemotherapy cycle having lower values in terms of negative health outcomes (0.088-0.443) than the ND (0.619-3.102). DALYs were dominated by outcomes associated with NEC, which is more common in patients following the ND than in other diets. Switchover point analysis confirmed that, because of this discrepancy, there were no feasible values of other parameters that could justify the ND. Correspondingly, the sensitivity analysis indicated that NEC mortality rate and remaining life expectancy strongly affected DALYs, further illustrating the model's strong dependence on NEC outcomes. Given these findings, and the SFH's ease of implementation and high compliance rates, the SFH diet is recommended in place of the ND.

Out-of-Mold Sensor-Based Process Parameter Optimization and Adaptive Process Quality Control for Hot Runner Thin-Walled Injection-Molded Parts.

Injection molding is a highly nonlinear procedure that is easily influenced by various external factors, thereby affecting the stability of the product's quality. High-speed injection molding is required for production due to the rapid cooling characteristics of thin-walled parts, leading to increased manufacturing complexity. Consequently, establishing appropriate process parameters for maintaining quality stability in long-term production is challenging. This study selected a hot runner mold with a thin wall fitted with two external sensors, a nozzle pressure sensor and a tie-bar strain gauge, to collect data regarding the nozzle peak pressure, the timing of peak pressure, the viscosity index, and the clamping force difference value. The product weight was defined as the quality indicator, and a standardized parameter optimization process was constructed, including injection speed, V/P switchover point, packing, and clamping force. Finally, the optimized process parameters were applied to the adaptive process control experiments using the developed control system operated within the micro-controller unit (MCU). The results revealed that the control system effectively stabilized the product weight variation and standard deviation of 0.677% and 0.0178 g, respectively.

Determination of constant current to constant voltage switch-over point for health-aware fast charging using heuristic algorithm

High charging times for EVs are a hurdle to mainstream adoption since quick charging shortens battery life. The paper proposes a quick charging method that reduces charging time and battery deterioration. The proposed charging method modifies the conventional Constant Current – Constant Voltage (CC-CV) charging approach, where the switching point from CC to CV mode is altered. Sixteen charging techniques with varied CC-CV switchover points have been explored, comprising nine charging strategies with capacity switching and seven with voltage switching. The gathered data is processed using a mathematical relationship to determine the State of Health, capacity deterioration, and Internal Resistance characteristics. In addition, a Fuzzy Logic Controller is employed to determine the two effective switchover points based on the least amount of cyclic capacity deterioration, SoH, and charging time. The optimal CC-CV transition point between these two points is estimated using Genetic Algorithm Optimization. Compared with the traditional CC-CV charging approach, the effectiveness of the resulting switchover point is evaluated. The results indicate that the recommended charging approach costs an additional time of 4.22 %, and it increases the cell's cycle life by 51.77 % compared to CC-CV. Thus, the comparative analysis reveals that the proposed charge technique offers more efficient performance.

Optimize Injection-Molding Process Parameters and Build an Adaptive Process Control System Based on Nozzle Pressure Profile and Clamping Force.

The injection-molding process is a non-linear process, and the product quality and long-term production stability are affected by several factors. To stabilize the product quality effected by these factors, this research establishes a standard process parameter setup procedure and an adaptive process control system based on the data collected by a nozzle pressure sensor and a tie-bar strain gauge to achieve this goal. In this research, process parameters such as the V/P switchover point, injection speed, packing pressure, and clamping force are sequentially optimized based on the characteristics of the pressure profile. After the optimization process, this research defines the standard quality characteristics through the optimized process parameters and combines it with the adaptive process control system in order to achieve the purpose of automatic adjustment of the machine and maintain high-quality production. Finally, three different viscosity materials are used to verify the effectiveness of the optimization procedure and the adaptive process control system. With the system, the variation of product weight was reduced to 0.106%, 0.092%, and 0.079%, respectively.

Study on the evaluation and compensating strategy for the wear damage of non‐return valve during injection molding process

AbstractInjection molding (IM) is one of the most essential forming methods for plastics. However, some potential risks which influence part quality may occur in the molding process. A non‐return valve (NRV) is a major component on the screw head whose function is to seal during the injection process to prevent the backflow of the melt. The NRV will wear in this process and cause fluctuations in parameters and quality but the wear states of NRVs cannot be monitored without the disassembly of the injection barrel. In this study, we proposed an optimization method to compensate for the wear damage of the NRVs. The V/P switchover point in each molding cycle was recalculated and output to stabilize the part quality. As a result, the wear damage of the NRV on the current machine was able to be predicted and the part quality could be initially optimized in the condition that the NRV had a degree of wear. The experimental results reveal that our proposed compensation algorithm can monitor the type of wear of NRV online, and at the same time, it can compensate the axial wear of NRV and finally improve the consistency of product weight, which established a fundamental for further research in the future.

Quality Monitoring of Micro-shrinkage Defects in Thick-walled Injection Molded Components

Sink mark defects are commonly observed in thick-walled injection molded components as a result of under-packing in the hot-spot areas and an insufficient compensation of the polymer melt as the plastic begins to cool. These defects degrade the surface quality of the molded parts and are a reliable indicator of excessive volume shrinkage during the molding process. Consequently, effective methods for quantifying sink marks in thick-walled components, and predicting the occurrence of such defects as a function of the injection molding process parameters, are of significant interest in improving the molding quality. Accordingly, taking an injection molded plastic handle with an average thickness of 11.57 mm for illustration purposes, the present study proposes a method for measuring the micro-shrinkage (ΔΩ) of thick-walled injection molded components using a simple image-processing technique. Simulation and experimental trials are performed to investigate the effects of the injection molding parameters on the quality of the polymer melt (as evaluated using five quality indexes (PA, PB, ηA, ηB, and CFi,p) extracted from the pressure profiles within the chamber and the tie-bar elongation, respectively) and the quality of the final molded component (as quantified by two metrics, namely the weight variation of the molded parts and the micro-shrinkage). It is shown that the quality of the polymer melt and final thick-walled component is determined mainly by the magnitude of the holding pressure applied in the molding process. By contrast, the injection speed, V/P switchover point, and barrel temperature exert only minor effects. The experimental results obtained under various values of the holding pressure show that the five injection molding process quality indexes are all highly correlated with the micro-shrinkage. The correlation is particularly strong for the pressure-based quality indexes (PA, PB, ηA, and ηB). Hence, it is suggested that these indexes provide a viable means of predicting the formation of sink mark defects and excessive micro-shrinkage in thick-walled injection molded components.

Optimization process parameters and adaptive quality monitoring injection molding process for materials with different viscosity

Injection molding is a cyclic process of producing plastics products by injecting molten plastic materials. There is much complexity in the process because it is a highly non-linear process; many factors affect the product quality after long-run fabrication processes. In this study, product weight is defined as product quality, and this research aims to minimize the variation in the product weight. In this study, a standard process parameter setup procedure is proposed in order to set the process parameters in a close to optimized value based on the information collected by the sensors so the adaptive process control system can work well. Three polypropylene materials with low to high MI (melting index) values were used to verify the adaptive control system. The study with the information collected through two sensors installed in the machine—the injection nozzle pressure sensor and tie-bar strain gauge. Based on a series of results in the preliminary experiments, the appropriate V/P switchover point and clamping force could be judged from the peak pressure and clamping force peak for materials with different viscosities, respectively. The viscosity index and peak pressure strongly correlated with the weight of the injection molded parts toward the materials of different viscosity. The viscosity index, peak pressure, and clamping force peak are defined in this research as the quality monitoring characteristics used to guide the adjustment and increase the stability of the process in the presented control system. The experiment reveals that a combination of nozzle pressure curve-based adaptive process control incorporated with clamping force peak monitoring can decrease the weight variation of the injection molded parts. With this system, the coefficient of variation of product weight (Cv) of different viscosity materials from low to high can be decreased to 0.031%, 0.020%, and 0.024%, respectively.

Noncontact Monitoring of IGBT Turn-OFF Time Using PWM Switching Ringing for Inverter-Fed Machine Systems

Turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> time is an important condition parameter for insulated gate bipolar transistor (IGBT), which could provide useful information on the device junction temperature and its state of health. Currently, it is measured directly from the IGBT collector-emitter voltage <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ce</sub> or indirectly from the gate side, which may cause problems of safety and complexity for a power converter operating in a harsh electromagnetic environment. To address the challenges, this article proposes a noncontact method to monitor the IGBT turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> time from the PWM switching ringing in the converter output current. First, a phenomenon is observed that there are two switch-over points in the switching ringing current corresponding to the transition of IGBT turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> voltage. Analytical analysis is performed with a high-frequency (HF) equivalent circuit to investigate the mechanism of the one-to-one temporal relationship. Then, the noncontact condition monitoring (CM) scheme including the HF switching ringing current sensor and the framework of CM system is devised. Finally, experimental work is carried out to validate the theoretical analysis and the effectiveness of the method. Research results show that the turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> time of multi-IGBTs can be effectively extracted at the terminal of converter during system normal operation with electrically isolated safety.

Determination of process parameters based on cavity pressure characteristics to enhance quality uniformity in injection molding

Injection molding is widely used for the mass production of plastic components. However, an appropriate choice of the process parameters is essential to ensure the precision and uniformity of the molded parts. The flow length-to-wall thickness (L/t) ratio for most molded components lies in the range of 100∼200. For higher values of the L/t ratio, the flow resistance increases dramatically at the end of the molded part and the injection pressure propagates less easily through the mold cavity. Consequently, the geometric dimensions of the molded parts in the near-gate region are frequently different from those in the far-from-gate region as well as resulting in lower uniformity. In practice, the variation in the geometric dimensions is significantly dependent on the filling-to-holding (V/P) switchover point, injection speed, and holding condition. Accordingly, the present study commences by proposing a simple least-squares regression-based approach for determining the appropriate V/P switchover point based on the quality requirement for the geometric dimensions of the molded component. In addition, a multi-stage holding condition is used to improve the geometric uniformity of the molded component by minimizing the residual pressure difference between the near-gate and far-from-gate regions of the mold at the end of the packing stage. Finally, a deceleration strategy is considered for the injection screw at the end of the filling stage to further reduce the quality variation. The experimental results show that for molded components with a large L/t ratio, the V/P switchover point should be determined based on the quality requirement for the part in the far-from-gate region in order to avoid insufficient quality compensation in the early holding stage. Furthermore, compared with the single-stage holding condition, the multi-stage holding condition reduces the residual pressure difference between the near-gate and far-from-gate regions of the cavity by around 74.5% (from 48.7 to 12.5 MPa). As a result, the difference in width between the near-gate region of the molded component and the far-from-gate region is reduced by about 66.7% (0.09 to 0.03 mm), while the difference in thickness is reduced by approximately 32.1% (0.028 to 0.019 mm). The deceleration strategy for the injection screw has no noticeable effect on the quality uniformity of the molded part provided that the V/P switchover point and multi-stage holding pressure are appropriately designed.

Influence of V/P switchover point, injection speed, and holding pressure on quality consistency of injection‐molded parts

AbstractDuring the injection molding of molten polymers, the control strategy is switched from speed control to pressure control at the filling‐to‐packing (V/P) switchover point. V/P switchover influences part quality and process stability. V/P switchover timing traditionally depends on the degree of volumetric filling of molten polymer in the cavity and is limited to obtain a smooth and repeatable pressure curve for each injection, indicating consistent part quality. Repeatability is affected by the V/P switchover point, injection speed, holding pressure, and holding time. This study clarifies the effect of the injection speed, V/P switchover point, and first‐stage holding pressure setting on cavity pressure curves and injection molding quality. These factors were optimized and verified through the injection molding of integrated circuit trays. The experimental results indicate that adjusting the rear speed of filling stage, V/P switchover point, and first‐stage holding pressure, can yield the ideal pressure curve and improve process stability. Compared with the initial process parameter setting, part warpage was reduced by 40% from 0.042 to 0.025 mm, deviation of part width at the end of the filling pattern was reduced by 54% from 0.024 to 0.011 mm, and width range was reduced by 50% from 0.006 to 0.003 mm.

Study on Optimum Steam to Oxygen Blowing Ratio for Enhanced Chromium Recovery from Ferrochromium in Creusot Loire Uddeholm Converter

Currently, the yield of metallic chromium from ferrochromium (FeCr) in Creusot Loire Uddeholm converter (hereafter abbreviated as CLU), is below optimum, owing to poor oxidation of FeCr feed. Consequently, oxygen not only reacts with carbon but chromium too, thereby causing a reduction in yield of metallic chromium. Howbeit, the focus of this research was to determine the optimum steam to oxygen blow ratio for enhanced chromium recovery from CLU converter. The focus was achieved by determining best slag chemistry for recovery of metallic chromium and carbon level switchover for best blowing ratio. Both feed and outputs from CLU process were analyzed using the ICP AES for elemental contents. The results obtained showed an increase in chromium content by16%, and a reduction in carbon content by 71%, while change in iron content was approximately 0% after refining, at a slag basicity of 1.1 to 1.4 and slag chemistry of CaO (32.5 wt%), MgO (11.5 wt%) and SiO2 (38.7 wt%). In conclusion, the best chromium recovery at lowest carbon content was achieved at an oxygen to steam blowing ratio of 6 to 10 and critical carbon content switchover point of 2.1 wt%.

Study of an Online Monitoring Adaptive System for an Injection Molding Process Based on a Nozzle Pressure Curve.

Injection molding is a popular process for the mass production of polymer products, but due to the characteristics of the injection process, there are many factors that will affect the product quality during the long fabrication processes. In this study, an adaptive adjustment system was developed by C++ programming to adjust the V/P switchover point and injection speed during the injection molding process in order to minimize the variation of the product weight. Based on a series of preliminary experiments, it was found that the viscosity index and peak pressure had a strong correlation with the weight of the injection-molded parts. Therefore, the viscosity index and peak pressure are used to guide the adjustment in the presented control system, and only one nozzle pressure sensor is used in the system. The results of the preliminary experiments indicate that the reduction of the packing time and setting enough clamping force can decrease the variation of the injected weight without turning on the adaptive control system; meanwhile, the master pressure curve obtained from the preliminary experiment was used as the control target of the system. With this system, the variation of the product weight and coefficient of variation (CV) of the product weight can be decreased to 0.21 and 0.05%, respectively.

Enhancing the quality stability of injection molded parts by adjusting V/P switchover point and holding pressure

The injection molding process is widely used for the mass production of plastic parts. However, as product designs become lighter, thinner and smaller, and the allowable tolerances shrink, the need to improve the quality consistency of the injection molding process has emerged as a critical concern. In mass production, injection molding is typically performed using fixed settings of the machine inputs. However, in practice, the properties of the plastic melt invariably change from batch to batch and even from shot to shot. Consequently, the use of fixed parameter settings fails to guarantee the stability of the molded part quality. Existing quality monitoring and control systems for the injection molding process are often based on pressure information. However, obtaining this information generally requires the installation of pressure sensors within the molding cavity, which is not only expensive and time-consuming, but may also interfere with the injection molding process itself. Accordingly, the present study proposes a quality monitoring and control system for injection molding processes based on the tie bar elongation measurements obtained using a strain gage. In the proposed approach, variations in the tie bar strain characteristic are taken to indicate deviations in the process stability and are used to manipulate the processing parameters accordingly in order to ensure the stability and consistency of the molded part quality. The feasibility of the proposed approach is demonstrated by performing injection molding trials with a two-cavity mold designed to produce tensile test specimens. The experimental results show that the quality of the molded parts varies significantly with the injection speed, velocity-to-pressure (V/P) switchover point, holding pressure, and melt temperature. Among these four parameters, the V/P switchover point and holding pressure induce a particularly rapid dynamic response, and thus provide an effective means of compensating for process deviations from shot to shot. By changing the melt temperature to simulate environmental noise, it is shown that the two parameter settings enable the consistency of the part weight to be restored to a range of 0.01 g within six shots. Moreover, the yield rate is enhanced from 60% to 90%.

A real‐time clamping force measurement eigenvalue for prediction, adjustment, and control of injection product quality

AbstractClamping force is a crucial parameter in injection molding. Improper clamping force setting can result in poor product quality and shorter machine lifespan. The objective of this study was to establish an eigenvalue‐injection clamping force peak value by real‐time clamping force measurement with strain gage sensor for prediction, adjustment, and control of injection product quality. In this study, computer‐aided engineering (CAE) structural analysis technique was used to analyze and verify the points of measurement of the sensor. Next, the molded product was conducted using the following injection molding parameters: V/P switchover point, clamping force, injection speed, melt temperature, mold temperature, packing pressure, and packing time. The relationship between injection clamping force peak value and product quality were examined. The results showed that CAE analysis could successfully predict and provide suitable points for sensor measurement. Comparison of analysis and experiment results revealed that injection clamping force peak value and part weight exhibited identical trends. Finally, the injection clamping force peak value not only could it successfully predict product quality, but also it would achieve the purpose of optimizing and stabilizing the clamping force and part weight.

Robust parameter search for IC tray injection molding using regrind resin

Abstract Quality consistency is essential in maximizing the productivity rate of the injection molding process and minimizing the production cost. The quality consistency problem is particularly acute in the case of injection molding processes performed using regrind resin, for which the rheological properties are less uniform and more unpredictable than those of virgin material. Accordingly, the present study proposes a two-stage approach for optimizing the injection molding process parameters in such a way as to achieve a consistent molding quality over repeated injection molding cycles. In the first stage, the values of the injection speed/pressure, velocity-to-pressure (V/P) switchover point, and packing pressure are individually determined based on an inspection of the cavity pressure profile and machine parameters provided by the injection molding machine controller. In the second stage, a robust parametric search method based on a first-order regression model is employed to determine the optimal combination of the process parameter settings. Using an Integrated Circuit (IC) tray fabricated from regrind resin for illustration purposes, the results confirm that the proposed method overcomes the problem of small variations in the melt quality and therefore provides an effective technique for improving the yield rate and quality of the continuous mass production.

Energy Optimal Intelligent Switching Mechanism for Induction Motors with Time Varying Load

In medium and small process industries Induction Motor (IMs) enabled star-delta energy conservation scheme is a common practice. In such industrial applications, the Power Quality Disturbances (PQD) must be considered for hassle free operation. This paper is an attempt in the above direction on star-delta energy conservation applied to IMS (2.2 kW and 37.5 kW) operated with time varying loads. In apart to machine’s performance evaluation, variation of switchover point for uninterrupted operation and optimized energy savings under various electrical perturbations is realized. Moreover, safe restarting feature is equipped in controller for resuming the machine during unplanned shutdown or any interruption.

Monitoring, prediction and control of injection molding quality based on tie-bar elongation

Quality consistency is essential in the injection molding process for maximizing the yield rate and minimizing the production cost, and this issue is more concerned proceeding with recycled material. Effective methods are therefore required for performing the real-time monitoring and control of the injection molded part quality and tuning the injection molding process parameters. Accordingly, the present study proposes a real-time quality monitoring and control system based on the clamping force increment characteristic, as determined by the measured tie-bar elongation. Notably, the proposed method is applicable to both virgin raw materials and recycled plastic materials. The effectiveness of the proposed approach is evaluated for three different processing parameters, namely the barrel temperature, the back pressure and the V/P switchover point. It is shown that the three processing parameters all have a significant effect on the molded part weight and thickness. Moreover, for each parameter, the part weight and thickness are strongly correlated. The clamping force increment is also highly correlated with the molded part weight. It is hence inferred that the clamping force increment provides an appropriate quality index for monitoring the injection molding quality. Furthermore, through the integration with a V/P switchover point calibration model, the clamping force increment index can be used to control the molded part weight to within a small tolerance on a shot-by-shot basis. When performing the injection molding process with virgin raw material, the tensile strength of the molded part increases with an increasing barrel temperature due to an increasing part weight if the proposed quality monitoring and control system is not applied. However, when the proposed system is employed, the tensile strength reduces slightly at a higher barrel temperature. When using recycled material in the injection molding process, the tensile strength remains approximately constant as the barrel temperature increases, irrespective of whether or not the proposed quality control system is applied. The difference in tendencies of the two materials can be attributed to a difference in their viscosities (i.e., molecular weights).

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.

Selective laser melting raw material commoditization: impact on comparative competitiveness of additive manufacturing

The paper analyses the impact of cheaper metal powder supplies on the comparative competitiveness of additive manufacturing (AM). By utilising two case studies, we compare the economic impact of an innovative titanium extraction method on Selective Laser Melting (SLM) and conventional methods of machining and casting. A switch-over analysis identifies the production quantities above which conventional manufacturing is more cost competitive than additive manufacturing. This analysis is performed for current raw material as well as cheaper raw material supply. The results illustrate the improved comparative competitiveness of SLM as the titanium supply is commoditised and more readily available in powder form. The responsiveness of the supply chain is improved as the switch-over point between SLM and conventional methods increases. Moreover, as the raw material supply chain for titanium is transformed through the use of this novel extraction method, the manufacturing supply chain is simplified.

Statistical Properties of Round, Square, and Elliptic Jets at Low and Moderate Reynolds Numbers

An experimental study was conducted to investigate the effect of nozzle geometries on the statistical properties of free orifice jets at low and moderate Reynolds numbers. The studied cross sections were round, square, and ellipses with aspect ratios of 2 and 3. For each jet, detailed velocity measurements were made using a particle image velocimetry (PIV) system at Reynolds numbers of 2500 and 17,000. The results showed that at both Reynolds numbers, the elliptic jets had relatively higher velocity decay and jet spreading; however, the nozzle geometry effects were more pronounced at Re = 17,000 than at Re = 2500. Analysis of the swirling strength revealed that the rotational motions induced by vortices within the minor planes of the elliptic jets were stronger than observed in the major planes, square and round jets which were consistent with the relatively higher spreading observed in the minor planes. It was observed that the streamwise locations of the switchover points were independent of Reynolds number but are a strong function of aspect ratio. Based on the present results and those documented in the literature, a linear correlation was proposed for the location of axis-switching in orifice jets. Due to the axis-switching phenomena, a sign change was observed in the distribution of the Reynolds shear stress in the major planes of the elliptic jets. This results in the existence of regions with negative eddy viscosity in the near field regions, an observation that has an important implication for the predictive capabilities of standard eddy viscosity models.