Visualization analysis of tiger-striped flow mark generation phenomena in injection molding

Owada, Shigeki; Yokoi, Hidetoshi

doi:10.1063/1.4942266

Cited by 5 publications

(3 citation statements)

References 6 publications

(4 reference statements)

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“…Grillet and Bogaerds et al , numerically investigated the stability of melt flow in injection molding to elucidate the mechanism of the flow marks by using a transient finite element method. Visualization analysis reported by other researchers – demonstrated that flow marks are indeed related to the unstable flow of the melt during the filling process. However, previous studies did not provide direct evidence to verify the development of unstable flow, and the relationship between the generation of flow marks and the development of unstable flow is still not clear.…”

Section: Introductionmentioning

confidence: 70%

Development of Unstable Flow and Morphological Analysis of Flow Marks in Injection Molding of Polypropylene and Polyolefin Elastomer Blend

Hu,

Zhang,

Song

et al. 2023

Ind. Eng. Chem. Res.

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The unstable flow phenomenon in injection molding and the resulting flow marks adversely affect the application of polymer products. Therefore, it is important and necessary to study the unstable flow to clarify the generation mechanism of the flow marks. In this work, the development of unstable flow in injection molding of the polypropylene/polyolefin elastomer (PP/POE) blend was investigated through short shot injection molding experiments. The results show that the melt flows stably at the early stage, and then, the flow front of the melt begins to fluctuate along the thickness direction, resulting in the formation of an unstable flow of the melt and periodic concave and convex regions on the surface of short shot samples. The relationship between the generation of flow marks and the development of unstable flow was also clarified, that is, the convex and concave regions formed during the filling process evolve into the cloudy and glossy regions of the flow marks, respectively. Since the melts in different regions experience different shear and thermal histories, the orientation degree of the dispersed phase and the crystal in the cloudy region is higher than that in the glossy region, while the glossy region has a higher crystallinity and lamellar thickness. Ultimately, a more refined unstable flow model for the generation mechanism of flow marks was proposed..

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Section: Introductionmentioning

confidence: 70%

Development of Unstable Flow and Morphological Analysis of Flow Marks in Injection Molding of Polypropylene and Polyolefin Elastomer Blend

Hu,

Zhang,

Song

et al. 2023

Ind. Eng. Chem. Res.

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“…The surfaces of all the solid samples had the same unique patterns, consisting of both smooth and dull regions, which is not as visible on the foamed MIM samples. This type of pattern could be attributed to the oscillating or snake-like melt front advancements that led to the so-called tiger stripes [ 31 ]. This surface feature that consists of alternate smooth and dull regions is known to be more common for polymer composites with a solid or rubber filler [ 32 ].…”

Section: Resultsmentioning

confidence: 99%

Conventional and Microcellular Injection Molding of a Highly Filled Polycarbonate Composite with Glass Fibers and Carbon Black

Yilmaz

Devahastin²,

Turng

2022

Polymers

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Conventional solid injection molding (CIM) and microcellular injection molding (MIM) of a highly filled polycarbonate (PC) composite with glass fibers and carbon black were performed for molding ASTM tensile test bars and a box-shape part with variable wall thickness. A scanning electron microscope (SEM) was used to examine the microstructure at the fractured surface of the tensile test bar samples. The fine and uniform cellular structure suggests that the PC composite is a suitable material for foaming applications. Standard tensile tests showed that, while the ultimate strength and elongation at break were lower for the foamed test bars at 4.0–11.4% weight reduction, their specific Young’s modulus was comparable to that of their solid counterparts. A melt flow and transition model was proposed to explain the unique, irregular “tiger-stripes” exhibited on the surface of solid test bars. Increasing the supercritical fluid (SCF) dosage and weight reduction of foamed samples resulted in swirl marks on the part surface, making the tiger-stripes less noticeable. Finally, it was found that an injection pressure reduction of 25.8% could be achieved with MIM for molding a complex box-shaped part in a consistent and reliable fashion.

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“…In addition, Owada and Yokoi found that the temperature difference of the asymmetric melt front is the cause of TS by observing the behavior of the quenched melt front. 22 As another main flow instability inducing TS, stick-slip, generally resulted from wall slip, 23,24 is marked by periodic oscillation in slip velocity and shear stress, 25 which is easy to make people associate it with TS. If the wall shear stresses exceed a second critical value, 26 stick-slip could occur within a certain range of apparent shear rates.…”

Section: Introductionmentioning

confidence: 99%

Insights into the tiger stripe phenomenon of polypropylene and its blend in injection molding with a rapid heat exchange mold

Luo,

Ou,

Peng

et al. 2024

J of Applied Polymer Sci

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To examine the formation of tiger stripes (TS) phenomenon on the surface of the injection molding parts, a home‐made injection mold with a rapid heat exchange system and in situ measurement of pressure and temperature was designed and manufactured. Based on this special mold, the TS diagrams as a function of mold temperature and injection pressure for isotactic polypropylene (iPP) and its blend with a type of polyolefin elastomer (iPP/POE) were explored for the first time. It is found that there exists a critical mold temperature and a critical injection pressure for the TS appearance or disappearance in both systems. The critical temperatures of TS disappearance for iPP and iPP/POE are ~50 and ~ 120°C, respectively. As evidenced by the correlation between melt pressure drop and TS appearance, the wall slip mechanism is regarded as the main cause of TS formation. Compared with the critical shear stress of wall slip (σw) in totally molten PP, the lower σw value in this study further indicates that the wall slip could be facilitated by the crystallization of iPP during injection. Combined with white light interferometer, micro‐area x‐ray diffraction nanoindentation and scanning electron microscopy, it is demonstrated that the cloudy and glossy region of TS in pure iPP system could be distinguished by surface crystallinity. In the blend system, however, the rubber phase orientation as a dominant factor contributes to the glossiness of TS.

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Visualization analysis of tiger-striped flow mark generation phenomena in injection molding

Cited by 5 publications

References 6 publications

Development of Unstable Flow and Morphological Analysis of Flow Marks in Injection Molding of Polypropylene and Polyolefin Elastomer Blend

Development of Unstable Flow and Morphological Analysis of Flow Marks in Injection Molding of Polypropylene and Polyolefin Elastomer Blend

Conventional and Microcellular Injection Molding of a Highly Filled Polycarbonate Composite with Glass Fibers and Carbon Black

Insights into the tiger stripe phenomenon of polypropylene and its blend in injection molding with a rapid heat exchange mold

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