外文翻譯---通過微注射成型復(fù)制聚合物微小結(jié)構(gòu)的實(shí)驗(yàn)和分析（英文）

1、This content has been downloaded from IOPscience. Please scroll down to see the full text.Download details:IP Address: 128.250.144.144This content was downloaded on 10/03/2015 at 05:42Please note that terms and condition

2、s apply.Implementation and analysis of polymeric microstructure replication by micro injection moldingView the table of contents for this issue, or go to the journal homepage for more2004 J. Micromech. Microeng. 14 415(h

3、ttp://iopscience.iop.org/0960-1317/14/3/015)Home Search Collections Journals About Contact us My IOPscienceY-C Su et al2bxyzy z Velocity profilePolymer meltPressure and material supplyFigure 1. Schematic of polymer melt

4、flowing in a thin cavity.these strategies are applied in mold trials to evaluate their validity.2. Theoretical modelsBecause most injection molded polymeric parts have complicated three-dimensional (3D) configurations an

5、d the rheological response of polymer melt is generally non- Newtonian and non-isothermal, it is extremely difficult to analyze the filling process without simplifications. The generalized Hele-Shaw (GHS) flow model intr

6、oduced by Hieber and Shen [17] is the most common approximation that provides simplified governing equations for non-isothermal, non-Newtonian and inelastic flows in a thin cavity, as shown in figure 1. The assumptions o

7、f the GHS flow model are(1) The thickness of the cavity is much smaller than the other dimensions. (2) The velocity component in the direction of thickness is neglected, and pressure is a function of x and y only. (3) Th

8、e flow regions are considered to be fully developed Hele-Shaw flows in which inertia and gravitational forces are much smaller than viscous forces. (4) The flow kinematics is shear-dominated and the shear viscosity is ta

9、ken to be both temperature and shear rate dependent.The detailed derivations have been developed by Hieber and Shen, and these assumptions apply well for the micro injection molding process. In view of these assumptions

10、and neglecting compressibility during the filling stages, the momentum equation in the Cartesian coordinate system reduces to [17]??z?η?vx?z?= ?P?x??z?η?vy?z?= ?P?y (1)where vx and vy are velocity components in the x and

11、 y directions, respectively; P(x, y) is the pressure, η(γ ?, T ) is the shear viscosity, γ ? is the shear rate and T is temperature. Under the present assumptions, γ ? is given byγ ? =???vx?z?2 +??vy?z?2?1/2. (2)Applying

12、 the lubrication approximation, the thickness- averaged continuity equation results in?(b¯ vx)?x + ?(b¯ vy)?y = 0 (3)where ¯ vx and ¯ vy are averaged velocities over z, and b is half of the thickness.

13、 After several derivative steps, the governing equation for the flow of the polymer melt can be reduced to the celebrated Reynolds equation:??x?S ?P?x?+ ??y?S ?P?y?= 0 (4)where S is the flow conductance which is defined

14、asS =? b0z2η dz. (5)The velocities and shear rate can be obtained asvx = ?x? bzz1 η dz1 vy = ?y? bzz1 η dz1 γ ? = z?η(6)where?x = ??P?x , ?y = ??P?y and ? = ? ?2 x + ?2 y ?1/2.Because of the temperature difference betwee

15、n mold and polymer melt and the viscous heating inside the flow, the filling process should be treated as a non-isothermal case. Heat conduction in the direction of flow is neglected based on the assumption that the thic

16、kness 2b is much smaller than the other two dimensions. The energy equation in the melt region becomesρcp??T?t + vx ?T?x + vy ?T?y?= k ?2T?z2 + ηγ ?2 (7)where the ηγ ?2 is the viscous heating term, and ρ, cp and k are de

17、nsity, specific heat and thermal conductivity, respectively. For simplicity, it is assumed that the velocity and temperature are symmetric in the z direction, the velocities of polymer melt on the mold surfaces are zero

18、and the temperature of mold remains at Tw during filling. The boundary conditions are given byvx = vy = 0 at z = b ?vx ?z = ?vy?z = 0 at z = 0T = Tw at z = ±b ?T?z = 0 at z = 0.(8)As can be seen, the equations of th

19、is model are nonlinear and coupled. It is difficult to solve these equations analytically. In this paper, simulation software C-MOLD that employs numerical solvers based on a hybrid finite element/finite difference metho

20、d is used to solve the pressure, velocity and temperature fields of the GHS model. Because of these approximations, a GHS model cannot predict the exact flow field near the advancing flow front or at the edges of the mol

21、d. This might cause errors in predicting the flow behavior near microscale mold cavities.3. Design and fabrication of molding apparatusAn aluminum mold is manufactured for the replication process. The schematic diagram a