was injected into the mould。 After the cavity was filled, water was circulated with a flow rate of 1 L/min until the wall temperature cooled to the lower temperature。 During the part ejection, the heater was turned on again。 As a result, it took 60 s at maximum between 120 and
160 °C for one cycle。 The mould temperature-time profile is shown in Fig。 5。论文网
2。5 Cavity pressure characterization
Recent studies have shown that rather than using injection/ hold pressure settings, it might be more accurate to use cavity pressure for the filling of the polymer melt [25]。 Additionally, measured cavity pressure data can be used as a process variable for a numerical study。
In order to measure the cavity pressure- time profiles, a pressure transducer (Kistler 6184AA) was used, and the signal was transferred using a charge amplifier (Kistler 5073) to an oscilloscope (Tektronix TDS2001C), and recorded digitally onto a computer using the DAQ software (LabVIEW)。 Figure 6a shows the measured cavity pressure history during one cycle with an injection flow rate of 8 cm3/s, injection and
Fig。 4 Image of mould on the injection moulding machine with compo nents for temperature control
Fig。3Photograph of microcantilever cavities by micromachined metal shim Fig。 5 Experimental mould temperature profile
hold pressure of 65 MPa for 3。8 s, and cooling time of 15 s。 Once the main cavity is filled, the cavity pressure increases quickly。 On reaching its maximum point, the
Fig。 6 Experimental measurement of cavity pressure: a example of cavity pressure-time profile and b peak cavity pressure with flow rate and injection pressure
cavity pressure decreases because the gate freeze-off occurs despite the hold pressure。 In our moulding system, it was found that both injection flow rate and the injection pressure have significant effects on cavity pressure, whereas hold pressure has a negligible effect。 In particular, the cavity pressure-time profile changes according to the flow rate, relative to the peak value and rising velocity。 The peak cavity pressures were measured with the injection flow rate and the injection pressure, as described in Fig。 6b。 Using this graph, the cavity pressure was characterized in two distinct groups, as shown in Fig。 7。 One group had different flow rate conditions with constant peak cavity pressure (see Fig。 7a), and the other had different peak cavity pressure conditions with a constant flow rate (i。e。 pressure rising velocity, see Fig。 7b)。 In the experiment, the effects of flow rate and peak cavity pressure on the filling length were investigated by differentiating the pressure profiles similar to those in Fig。 7。
2。6 Injection moulding conditions
Injection flow rate, peak cavity pressure, mould temperature, and melt temperature were chosen as the process parameters。 The injection moulding tests were performed in such a way that one parameter was varied within a certain range while the others were fixed。 Two thicknesses of the microcantilevers (50 and 100 μm) were moulded by the process conditions reported in Table 2。
Under each process condition, the length of three samples was measured and averaged。 The moulded microcantilever lengths were measured by scaling the microscope images as in Fig。 8。
Fig。 7 Cavity pressure characterization according to injection flow rate and injection pressure: a different flow rate conditions and b different peak cavity pressure conditions
3 Numerical model
As shown in Fig。 9, the melt flow enters the microchannel cavities after filling the main cavity of the part。 When the main cavity is just fully filled, the flow is clogged owing to the high viscosity of the melt, and stagnation pressure develops。 The melt flow through the microchannel cavities is driven by the increasing main cavity pressure。 In the meantime, the melt solidifies quickly because the heat transfer from the melt and摘要：高纵横比微结构注射成型对于各种系统组件 的制造是重要的。微注射成型技术的成功可能取决 于一种聚合物熔体和微通道内的充填程度合理预测 充模的准确理解。到目前为止，还没有关于充型过 程中注射成型的微悬臂梁结构的充分调查。在这项 研究中，对注射成型的微悬臂梁进行了动态模具温 度控制集腔压力测量。观察了喷油流量、峰值腔压 力、熔体温度、模具温度等因素对填充长度的影响。 一个简单的一维分析模型的开发，描述了四个工艺 参数与充型长度的关系。测量腔压力分布应用于数 值分析。通过比较实验测量和仿真结果对模型进行 了验证，并显示处理工艺参数之间可以接受的协议。 注射成型的微悬臂梁结构英文文献和中文翻译(4):http://www.youerw.com/fanyi/lunwen_87354.html