Numerical Simulation and Experimental Investigation of the Viscoelastic Heating Mechanism in Ultrasonic Plasticizing of Amorphous Polymers for Micro Injection Molding

Jiang, Bingyan; Huajian, Peng; Wu, Wangqing; Jia, Yunlong; Zhang, Yingping

doi:10.3390/polym8050199

Cited by 37 publications

(46 citation statements)

References 21 publications

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“…Ultrasonic processing technology, as a novel molding processing technology, has been widely used in recent years for the injection molding, extrusion molding, and compression molding of polymers [9,10]. Despite different ways of applying ultrasonic energy, studies have found that ultrasounds can affect the microstructure filling performance [11], change the material properties [12], affect the extrusion swelling [13], improve the weld line strength of the plastic parts [14], and reduce the interface friction during ejection [15].…”

Section: Introductionmentioning

confidence: 99%

Micro-Ultrasonic Viscosity Model Based on Ultrasonic-Assisted Vibration Micro-Injection for High-Flow Length Ratio Parts

Lou

Xiong

2020

Polymers

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A micro-ultrasonic (MU) viscosity model based on ultrasonic-assisted vibration micro-injection for high- flow length ratio polymer parts was established. This model considered the effects of ultrasonic energy and the characteristic microdimension. Ultrasonic energy parameters (such as the ultrasonic amplitude, frequency, and ultrasound velocity), the characteristic microdimension, and the molecular chain length (MCL) were introduced into the MU viscosity model. An ultrasonic micro-injection experimental platform was built on an injection molding machine. Polypropylene (PP) filling experiments were carried out using microgrooves with different flow length ratios (depth-to-width ratios of 3:1, 5:1, and 10:1). The validity and accuracy of the MU viscosity model were examined through a filling experiment with polypropylene (PP) microgroove injection molding and by a flow pressure difference experiment with polystyrene (PS). The results showed that the MU viscosity model was in better agreement with the experimental results compared to other models. The maximum error of the MU model was 4.9%. Ultrasound-assisted vibration had great effects on the filling capacity for microgrooves with high flow length ratios (depth-to-width ratios greater than 5:1). The filling capacity increased as the ultrasonic amplitude increased.

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Section: Introductionmentioning

confidence: 99%

Micro-Ultrasonic Viscosity Model Based on Ultrasonic-Assisted Vibration Micro-Injection for High-Flow Length Ratio Parts

Lou

Xiong

2020

Polymers

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“…By changing the time to strain, there were only slight changes in the maximum temperatures, but the polymer was still able to relax to approximately the same state during each pre‐strain sequence. These effects are similar to the initial temperature‐ and frequency‐dependent heating effects seen in ultrasonic plasticization, in which rapid heating occurs near T g . In all cases presented here, the viscoelastic stress relaxation during pre‐strain was accelerated due to the internal temperature rise that resulted from viscous heating.…”

Section: Resultsmentioning

confidence: 60%

“…The greatest increase in temperature corresponded to χ = 1. The rapid rise in temperature was consistent with experimental observations and computational results of temperature rise near or slightly above the T g in studies of polystyrene and other polymers acted upon by ultrasonic waves . In those studies, oscillating pressure waves interact with polymer chains which dissipate the mechanical energy through viscous shearing and relaxation .…”

Section: Resultsmentioning

confidence: 99%

“…This heating effect is significant in many polymer systems during the transition from glassy to rubbery behavior and is prevalent near the glass transition temperature, T g . Viscous heating, in response to ultrasonic waves, has been shown to have a significant effect during the unfolding of polymer sheets, drug delivery, and polymer plasticization during injection molding . Additionally, viscous heating affects rubber dampers, which dissipate energy from cyclic mechanical loading .…”

Section: Introductionmentioning

confidence: 99%

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A fully coupled thermo‐viscoelastic finite element model for self‐folding shape memory polymer sheets

Mailen

Dickey

Genzer

et al. 2017

J Polym Sci B Polym Phys

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The thermo‐mechanical response of heat activated shape memory polymers (SMPs) has been investigated using a thermo‐viscoelastic finite element analysis that accounts for external and internal heat sources. SMPs can be thermally stimulated by external heat sources, such as temperature and surface heat flux, or from internal viscous heating. Viscous heating can significantly affect the response of SMP sheets by increasing the temperature during pre‐strain, which accelerates stress relaxation. This stress relaxation results in a slower shrinking rate when the SMP is reheated. Viscous heating also causes an increase in temperatures during unconstrained recovery. The predicted results elucidate how the coupled thermo‐mechanical loading conditions affect folding and unfolding of SMP sheets in response to localized heating in a hinged region. A parametric study of sheet thickness, hinge width, degree of pre‐strain, and hinge surface temperature is also conducted. The validated results can provide guidelines for the design of functional, self‐folding structures. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1207–1219

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“…At present, researches of MIM techniques have mainly focused on specific injection machines, numerical simulation, and replicating capability analysis . Investigations of the morphology evolution mechanism, including chain orientation and crystallization, formed by MIM are relatively rare.…”

Section: Introductionmentioning

confidence: 99%

Influence of scale effect and injection speed on morphology and structure of the microinjection molded isotactic polypropylene parts

Wang

Jiang

et al. 2020

Polymers for Advanced Techs

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The morphology and microstructure as well as their forming mechanism of the parts in microinjection molding process are critical. In this work, the coupling effect of scale factor and injection speed on the morphology of the microparts was systematically investigated. Neat isotactic polypropylene parts with thicknesses of 1 mm, 200 μm, and 100 μm were molded at different injection speeds. Polarized light microscope and wide-angle X-ray diffraction were used to inspect the microstructures along the sample thickness. In this way, three kinds of typical morphology were observed in the parts, including typical skin-core structure for the parts with the thickness of 1 mm, noncore shear layer structure for the parts with the thickness of 200 μm, and special skin-core structure with large fraction of columnar crystal for the parts with the thickness of 100 μm. Most interestingly, it was intuitively and straightforward found that the wall slip occurs when the injection speed exceeds a certain value. Specifically, opposite morphological change trend can be obtained when the parts were molded at different levels of injection speeds. Based on these experimental observations, the formation mechanism was proposed to interpret the morphological evolution. Our work provides a new insight for better understanding the morphology evolution mechanism for microinjection molding parts. K E Y W O R D Scolumnar crystal structure, microinjection molding, morphology and structure, noncore structure, wall slip 1 | INTRODUCTION Microinjection molding (MIM) is currently one of the most promising processing methods for fabricating polymeric microparts, such as biochips, microgears, microheat exchangers, and so on. 1-3 MIM process not only reduces the actual dimensions of the molded products, but also involves extreme and complicated thermomechanical history, including high-temperature gradient, extremely high shear rate, high injection pressure, and so on. 4-6 These special phenomena can affect the crystallization behavior of the semicrystalline polymers during the MIM manufacturing process. It is for this reason that the morphologies of the obtained products were different from traditional injection molding. 7-10 As is known to all, morphologies and physical properties (mechanical, optical, electrical, transport, and chemical) 11-14 are closely correlated for polymeric parts. Hence, the first step toward highperformance MIM parts is to thoroughly and systematically investigate the morphology evolution mechanism.At present, researches of MIM techniques have mainly focused on specific injection machines, 13,15 numerical simulation, 16-20 and replicating capability analysis. [21][22][23][24] Investigations of the morphology

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Numerical Simulation and Experimental Investigation of the Viscoelastic Heating Mechanism in Ultrasonic Plasticizing of Amorphous Polymers for Micro Injection Molding

Cited by 37 publications

References 21 publications

Micro-Ultrasonic Viscosity Model Based on Ultrasonic-Assisted Vibration Micro-Injection for High-Flow Length Ratio Parts

Micro-Ultrasonic Viscosity Model Based on Ultrasonic-Assisted Vibration Micro-Injection for High-Flow Length Ratio Parts

A fully coupled thermo‐viscoelastic finite element model for self‐folding shape memory polymer sheets

Influence of scale effect and injection speed on morphology and structure of the microinjection molded isotactic polypropylene parts

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