Effects of polymer melt compressibility on mold filling in micro-injection molding

The flow behaviors for polymer melt at the filling stage in micro injection molding are different from those in conventional injection molding due to the miniaturization of plastic parts. This paper focuses on the study of the effects of three main influencing factors, including the microscale viscosity and wall slip, on melt filling flow in microscale neglected those in conventional injection molding process. The theoretical models and the interrelation of these factors in microscale channels were constructed by means of the model correction method. Then, the micro melt flow behaviors were investigated with comparisons of the available experimental data. The results indicate that the dimensions affect the shear rates and viscous dissipation, which in turn affects the apparent viscosity. Finally, the conclusion is that the melt flow behaviors in microchannels are different from those in macrochannels owing to these significant influencing factors.

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Effects of Wall Slip on Filling Flow for Polymer Melt in Micro Injection Molding

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.609-610.617 ◽

2014 ◽

Vol 609-610 ◽

pp. 617-622 ◽

Cited By ~ 1

Author(s):

Jian Zhuang ◽

Ya Jun Zhang ◽

Da Ming Wu ◽

Li Zhu Liu ◽

Cheng Jun Sun ◽

...

Keyword(s):

Injection Molding ◽

Slip Velocity ◽

Polymer Melt ◽

Wall Slip ◽

Diameter Ratio ◽

Micro Injection Molding ◽

Slip Mechanism ◽

Inlet Flow Rate ◽

Section Size ◽

Slip Coefficients

Effect of wall slip on melt filling flow behaviors in micro injection molding are investigated based on analysis of wall slip mechanism for polymer melt flowing at filling stage. By means of comparisons, slip coefficients in different microchannels are confirmed. With finite element method, the relationship between slip velocity and inlet flow rate or length-diameter ratio is analyzed. The results indicate that the wall slip happen for polymeric melt in microchannels, and slip coefficients are related with the size characteristics of microchannels. Moreover, wall slip velocity has the size effect and increase with the decrease of the section size of microchannels, which cause melt velocity distribution to smooth. At the same time, slip velocity is proportional to length-diameter ratio of microchannel, namely when wall shear stress is uniform, the slip velocity rises with increasing length-diameter ratio of microchannel.

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The Method of Improving Precision of Micro Injection Molding Machine Temperature Control

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.372.354 ◽

2013 ◽

Vol 372 ◽

pp. 354-359

Author(s):

Sheng De Tang ◽

Hong Xu ◽

Da Ming Wu ◽

Ya Jun Zhang

Keyword(s):

Injection Molding ◽

Temperature Control ◽

Control Method ◽

Polymer Melt ◽

Molding Machine ◽

Micro Injection Molding ◽

Injection Molding Machine ◽

Mathematical Algorithm ◽

Accurate Temperature ◽

Accurate Temperature Control

the temperature control accuracy of polymer melt is the main factor affecting quality precision of final products. In this paper, we study the method of improving the precision of temperature control based on control system of micro injection molding machine. In order to avoid big overshoot in the traditional PID control, we use gradual approximation control method based on gradual approximation mathematical algorithm to realize fast and accurate temperature control of the micro injection molding machine. Experiment results show that effective combination of the traditional PID and gradual approximation method can realize accurate temperature control of micro injection molding machine, and precision of temperature control can be improved up to±0.5°C.

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Mold surface roughness effects on cavity filling of polymer melt in micro injection molding

The International Journal of Advanced Manufacturing Technology ◽

10.1007/s00170-007-1060-6 ◽

2007 ◽

Vol 37 (11-12) ◽

pp. 1105-1112 ◽

Cited By ~ 27

Author(s):

H. L. Zhang ◽

N. S. Ong ◽

Y. C. Lam

Keyword(s):

Surface Roughness ◽

Injection Molding ◽

Polymer Melt ◽

Mold Surface ◽

Roughness Effects ◽

Micro Injection Molding ◽

Cavity Filling

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Injection Molding

Rheology and Processing of Polymeric Materials: Volume 2: Polymer Processing ◽

10.1093/oso/9780195187830.003.0013 ◽

2006 ◽

Author(s):

Chang Dae Han

Keyword(s):

Injection Molding ◽

Cooling Water ◽

Polymer Melt ◽

Mold Temperature ◽

Mold Filling ◽

Injection Rate ◽

Mold Cavity ◽

Complex Nature ◽

Almost All ◽

Cavity Cooling

Injection molding is one of the oldest polymer processing operations used to produce goods from thermoplastic polymers. Today, almost all commercial injection molding machines have a reciprocating single screw for softening (or melting) under heat a thermoplastic polymer, and polymer melt is then injected into an empty mold cavity, as schematically shown in Figure 8.1. In the injection molding operation, the mold is first closed and then a predetermined amount of polymer melt from the screw section is injected into an empty mold cavity. Pressure is maintained for some time after the mold cavity has been filled to permit the build-up of adequate pressure in the mold cavity. Cooling water is circulated through channels in the mold so as to keep the mold cavity walls at a temperature usually between room temperature and the softening (or melting) temperature of the polymer. Thus, the hot polymer begins to cool as it enters the mold cavity. When it is cooled to a state of sufficient rigidity, the mold is opened and the part is removed. Some of the important variables in the operation of an injection molding machine are: (1) pressure applied by the screw, (2) temperature profile of the screw section, (3) mold temperature, (4) the screw forward time, (5) the mold closed time, and (6) the mold open time. Relationships between these variables are very complicated. In general, one would like to know the pressure, temperature, and density of the polymer in the mold cavity as functions of time during and after the mold is filled. In principle, these quantities can be calculated, via a mathematical model, during the entire period of mold filling and subsequent cooling when information on the geometry of the mold cavity, the rheological properties of the polymer, the temperature at which the polymer enters the mold cavity, and the mold temperature is available. However, in practice it is not easy to develop a rigorous theory because of the geometrically complex shapes of mold cavities, the complex nature of mold filling patterns (i.e., jetting) at normal injection speeds of industrial practice, and the highly viscoelastic nature of polymer melts, which varies with temperature, pressure, and injection rate (i.e., shear rate in the runner).

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