Effect of process conditions on birefringence development in injection‐molded parts. I. Numerical analysis

Chen, Shia Chung; Chen, Yung Cheng

doi:10.1002/app.1995.070551306

Cited by 17 publications

(15 citation statements)

References 15 publications

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“…Similar formulation has been derived and reported for CIM based on Leonov viscoelastic model in previous study. 32 Simulations of ICM process using viscous fluid model are reported elsewhere. 33,34 By assuming the no-slip boundary condition on the cavity wall of the steady platen, λ 1 can be calculated by…”

Section: Modeling For Melt Filling During Compression Stagementioning

confidence: 99%

Simulation of injection‐compression molding process, Part 3: Effect of process conditions on part birefringence

Chen

Peng

et al. 2002

Adv Polym Technol

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ABSTRACT:Simulations of the injection-compression molding (ICM) process based on a Leonov viscoelastic fluid model has been employed to study the effects of processing conditions on the birefringence development and distribution in injection-compression molded parts. A numerical algorithm combined with a modified control-volume/finite-element method is developed to predict the melt front advancement and the distributions of pressure, temperature, and flow velocity dynamically during the injection melt-filling, compression melt-filling, and postfilling stages of the entire process. Part birefringence was then calculated from residual stresses following the thermal-mechanical history of the entire molding process. Simulations of a disk part under different process conditions including compression speed, switch time from injection to compression, compression stroke, packing pressure, and postfilling time were performed to understand their effects on birefringence variation. The simulated results were also compared with those required by conventional injection molding (CIM). It has been found that an ICM part shows a significant reduction of part birefringence near the gate area as compared SIMULATION OF INJECTION-COMPRESSION MOLDING PROCESSwith CIM parts. However, ICM parts exhibit higher birefringence values near the rim of the disk. The minimum birefringence occurs around the location where injection is switched over to compression. Although longer postfilling time and higher packing pressure result in higher birefringence values, their effects are not very significant. On the other hand, higher compression speed, larger compression stroke, and shorter switch time exhibit greater effects on the increase of part birefringence. Flow-induced residual stress is the major origin of birefringence formation in the present case. The simulated birefringence for both ICM and CIM parts show good coincidence with those obtained from measurements by using a digital photoelasticity technique.

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Section: Modeling For Melt Filling During Compression Stagementioning

confidence: 99%

Simulation of injection‐compression molding process, Part 3: Effect of process conditions on part birefringence

Chen

Peng

et al. 2002

Adv Polym Technol

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“…Generally, specimens with a structure of co‐continuous microlayers are fabricated by injection molding. The melt complexly flows during injection molding, which is critical in determining morphology . The molten polymer flows from the middle of the cavity towards the wall and is subjected to extensional deformation.…”

Section: Introductionmentioning

confidence: 99%

Effect of melt flow on morphology and linear thermal expansion of injection-molded ethylene-propylene-diene terpolymer/isotactic polypropylene blends

et al. 2015

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An ethylene–propylene–diene terpolymer/isotactic polypropylene blend with a structure of co‐continuous microlayers was fabricated by injection molding and was then investigated. The blend exhibited an extremely low coefficient of linear thermal expansion (CLTE) in the directions of the length and the width. As the thickness of the oriented portion increased, the CLTE was further reduced. The morphology of the co‐continuous microlayers and the thermal expansion behavior varied with the sampling positions on the injection‐molded sheets. To study the relationship between the morphology and the melt flow, the melt flow behavior during injection molding was simulated using Moldflow. Orientation of the microlayers was determined using shear flow. When the shear rate increased, the orientation state increased and the CLTE decreased. © 2015 Society of Chemical Industry

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“…Thus, it is desirable to predict and investigate the residual stresses and birefringence in the products obtained at different processing conditions. Although much progress has been made in the simulation of polymer processing, the problem of modeling the residual stress and molecular orientation is still in the developing stage being one of the most challenging tasks in polymer processing, in general, and in injection molding, in particular 1–21…”

Section: Introductionmentioning

confidence: 99%

“…In the melt state, the flow‐induced birefringence is related to the flow stresses through the well‐known linear stress‐optical rule,4 and the problem of flow‐induced stresses and orientation is modeled on the basis of the nonlinear viscoelastic constitutive equation 5–14. Typically, the residual flow stresses are one order of magnitude smaller than the residual thermal stresses 5, 18, 19.…”

Section: Introductionmentioning

confidence: 99%

Photoviscoelastic behavior of amorphous polymers during transition from the glassy to rubbery state

Shyu

Isayev

2001

J Polym Sci B Polym Phys

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Tensile stress‐relaxation experiments with simultaneous measurements of Young's relaxation modulus, E, and the strain‐optical coefficient, Cϵ, were performed on two amorphous polymers—polystyrene (PS) and polycarbonate (PC)—over a wide range of temperatures and times. Master curves of these material functions were obtained via the time‐temperature superposition principle. The value of Cϵ of PS is positive in the glassy state at low temperature and time; then it relaxes and becomes negative and passes through a minimum in the transition zone from the glassy to rubbery state at an intermediate temperature and time and then monotonically increases with time, approaching zero at a large time. The stress‐optical coefficient of PS is calculated from the value of Cϵ. It is positive at low temperature and time, decreases, passes through zero, becomes negative with increasing temperature and time in the transition zone from the glassy to rubbery state, and finally reaches a constant large negative value in the rubbery state. In contrast, the value of Cϵ of PC is always positive being a constant in the glassy state and continuously relaxes to zero at high temperature and time. The value of Cσ of PC is also positive being a constant in the glassy state and increases to a constant value in the rubbery state. The obtained information on the photoelastic behavior of PS and PC is useful for calculating the residual birefringence and stresses in plastic products. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2252–2262, 2001

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Effect of process conditions on birefringence development in injection‐molded parts. I. Numerical analysis

Cited by 17 publications

References 15 publications

Simulation of injection‐compression molding process, Part 3: Effect of process conditions on part birefringence

Simulation of injection‐compression molding process, Part 3: Effect of process conditions on part birefringence

Effect of melt flow on morphology and linear thermal expansion of injection-molded ethylene-propylene-diene terpolymer/isotactic polypropylene blends

Photoviscoelastic behavior of amorphous polymers during transition from the glassy to rubbery state

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