超声外场对微通道中熔体黏性耗散效应的影响

针对聚合物熔体在微尺度通道中流动时的黏性耗散效应对其流动行为的影响,通过自行构建的带有温度传感器和超声振子的微注塑成型试验系统,采用单因素成型试验方法,对聚丙烯(Polypropylene, PP)和高密度聚乙烯(High-density polyethylene, HDPE)两种聚合物材料在不同工艺参数和超声外场作用下,流经矩形截面微通道时由黏性耗散效应引起的通道出口熔体温升进行试验测量。结果表明,微通道中熔体的黏性耗散效应随注射速度的增加而增强,随入口熔体温度和模具温度的升高而减弱;与不加超声振动相比,施加超声振动使两种材料的微通道出口熔体温升值明显升高;但材料自身的微观分子结构及其热物理性能不同,其温升增幅差别较大。试验注射速度下,施加超声振动比不加超声振动时的PP熔体温升增幅高出34.7%,而HDPE熔体的温升增幅则高达71.7%。当超声频率和工艺参数一定时,增大超声功率使PP熔体的微通道出口温升增加了24.8%,HDPE熔体的温升增加了83.6%。可见施加超声外场作用能使微通道中聚合物熔体的黏性耗散效应明显增强。     

Comparison of crystallization characteristics and mechanical properties of polypropylene processed by ultrasound and conventional micro-injection molding

Ultrasound injection molding has emerged as an alternative production route for the manufacturing of micro-scale polymeric components, where it offers significant benefits over the conventional micro-injection molding process. In this work, the effects of ultrasound melting on the mechanical and morphological properties of micro-polypropylene parts were characterized. The ultrasound injection molding process was experimentally compared to the conventional micro-injection molding process using a novel mold, which allows mounting on both machines and visualization of the melt flow for both molding processes. Direct measurements of the flow front speed and temperature distributions were performed using both conventional and thermal high-speed imaging techniques. The manufacturing of micro-tensile specimens allowed the comparison of the mechanical properties of the parts obtained with the different processes. The results indicated that the ultrasound injection molding process could be an efficient alternative to the conventional process.     

Micro-injection moulding: Factors affecting the achievable aspect ratios

Micro-injection moulding is one of the key technologies for micro-manufacture because of its mass-production capability and relatively low component cost. The aspect ratios achievable in replicating micro features are one of the most important process characteristics and constitute a major manufacturing constraint in applying injection moulding in a range of micro-engineering applications. This research studies the effects of five process and one size factors on the achievable aspect ratios, and the role they play in producing micro components in different polymer materials. In particular, the following factors are considered: barrel temperature, mould temperature, injection speed, holding pressure, the existence of air evacuation and the sizes of micro features. The study revealed that the barrel temperature and the injection speed are the key factors affecting the aspect ratios of micro features replicated in PP and ABS. In case of POM, in addition to these two factors, the mould temperature is also an important factor for improving the replication capabilities of the micro-injection moulding process. For all three materials, an increase of feature sizes improves the melt flow. However, the melt fill of micro features does not increase linearly with the increase of their sizes.     

Optimal injection molding conditions considering the core shift for a plastic battery case with thin and deep walls

The objective of this paper is to examine the influence of injection molding parameters on the core shift to obtain the optimal injection molding conditions of a plastic battery case with thin and deep walls using numerical analyses and experiments. Unlike conventional injection molding analysis, the flexible parts of the mold were represented by 3-D tetrahedron meshes to consider the core shift in the numerical analysis. The design of experiments (DOE) was used to estimate the proper molding conditions that minimize the core shift and a dominant parameter. The results of the DOE showed that the dominant parameter is the injection pressure, and the core shift decreases when the injection pressure decreases. In addition, it was shown that the initial mold temperature and the injection time hardly affect the core shift. The results of the experiments showed that products without warpage are manufactured when the injection pressure is nearly 32 MPa. Comparing the results of the analyses with those of the experiments, optimal injection molding conditions were determined. In addition, it was shown that the core shift should be considered to simulate the injection molding process of a plastic battery case with thin and deep walls.     

模板法注射成型纳米结构及其疏水特性

以不同形貌和深宽比的阳极氧化铝(AAO)模板为模芯,采用注射成型方法制备了纳米结构,分析了纳注射成型的模具温度、制件的疏水特性和模芯的使用寿命。首先,通过对比3种AAO模板的结构特征和深宽比,研究了不同模具温度下纳米结构的复制质量。然后,针对纳米阵列结构的疏水特性,分析几何结构特征与模具温度对制件静态接触角的影响,探索PC制件不同成型区域内的疏水性能。最后,对AAO模板的宏/微观质量和使用寿命进行了分析。研究结果表明:模具温度对纳米结构复制质量影响显著,且主要体现在纳米结构的成型高度上;纳注射成型制件不同区域内的疏水特性略有差异,最大静态接触角可达108.2°,比平板制件提高了31.5%;500余次的注射成型后,低深宽比的AAO模板整体质量良好,而高深宽比的模板缺陷明显,使用寿命有限。     

微细胞皿注塑模具变温系统设计

采用微细电火花技术铣削加工了细胞皿模具型腔,以聚丙烯(PP)为例进行了成形工艺数值模拟分析,结果表明,注射速率、模具温度、熔体温度对充模过程影响较大,模具温度需要达到120℃型腔才能充满。提出了油水电相结合的变模温技术,变模温实验结果表明,型腔温度从80℃变化到120℃大约需要6min。填充实验表明,油水电相结合的变模温技术对实现微注塑模具成形过程的变模温是可行的。     

薄壁塑件注塑成形特性的试验研究

设计制造了一可成形薄壁塑件的模具,利用正交试验方法(田口方法)进行充模试验,研究各工艺参数(注射速度、注射压力、熔体温度、注射量和模具温度等)对薄壁塑件注塑成形充模过程的影响。研究结果表明:模具温度对薄壁塑件的填充起决定性作用,注射压力和注射量是影响薄壁塑件成形的重要工艺参数,注射速度与熔体温度之间的交互作用对薄壁塑件成形的影响显著。     

微注塑散热器流动诱导热导率变化的多尺度数值预测

为进一步提高聚合物复合材料热导率,采用多尺度数值预测法研究了微注塑聚酰胺/碳纤维(PA66/CFs)散热器内部CF的流动诱导取向及其对制品热导率的影响规律。首先,利用Moldflow获取CF取向张量,并以Comsol Multiphysics构建与之对应的复合材料微元胞。利用正交实验法研究熔体温度、模具温度、最大注射压力及注射流率对微散热器热导率的影响。然后,对预测数据进行分析获得最优注塑参数组合。最后,对优化结果进行模拟实验,验证了多尺度数值预测法的有效性。结果显示:上述各参数重要程度由大到小依次排列为熔体温度、注射流率、最大注射压力和模具温度;最佳组合为熔体温度360℃、模具温度70℃、最大注射压力220 MPa及注射流率3×10–4 cm3/s。另外,流动诱导热导率变化最大值达0.36 W/(m·K),为基体热导率的1.5倍。得到的研究结果为从工艺调控的新角度来改善聚合物复合材料的导热性能提供了理论依据与数据支撑。     

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

Micro injection molding presents many challenges in the injection-molding community. When the dimensions of the part (and thus the cavity of the mold) are small, micro-scale factors such as mold surface roughness may play an important role in the filling of polymer melt. This paper investigates the effects of mold surface roughness on cavity filling of polymer melt in micro injection molding. A disk insert, which has two halves with different surface roughness but with the same roughness mean lines, was used in the investigations. The ratio of flow area of the rougher half with the total flow area of the molded part is used to evaluate the significance of surface roughness effect. The experimental results revealed that mold surface roughness does resist the cavity filling of polymer melt in micro injection molding. For the limited range of injection rate investigated, it is not significant on the surface roughness effects. The increase of mold temperature will decrease surface roughness effects. The change of melt temperature within the range allowed by the process is insignificant for surface roughness effects.     

超薄塑件注塑成形特性的试验研究与数值模拟

薄壁注塑成形技术具有节约材料、降低成本、减少制品重量和外形尺寸等优点,可促进移动电话等电子产品的迅速发展,特别是超薄塑件的注塑成形技术在微机电领域具有巨大的应用潜力。但随着制品厚度的减小也使注射成形难度加大,填充过程更为复杂,成形特性有待探索。设计制造出可成形超薄塑件的模具,利用正交试验方法(田口方法)进行充模试验和数值模拟技术研究各工艺参数(注射速度、注射压力、熔体温度、注射量和制品厚度等)对超薄塑件注塑成形充模过程的影响。研究结果表明,制品厚度对超薄塑件的填充起决定性作用;注射量及注射速度对超薄塑件注塑成形的填充起主导作用,提高注射速度能大幅度地提高填充率;熔体温度和注射压力相对于注射量和注射速度只起次要作用,但在填充过程中,高的熔体温度和注射压力也是必要的。     

Influential factors on the outer lens color in an industrial injection molding process

The quality and the aspect of outer lens fabricated by an injection molding process are an essential part for the optical properties of vehicular lighting system. This work is accurately addressed to identify the influential factors on the red color of the outer lens made of blends of polycarbonate and acrylonitrile butadiene styrene, which are mixed with a red masterbatch. Seven factors were investigated in this work: masterbatch concentration, mold and nozzle temperatures, holding and packing pressures, and holding and packing times. The main influential factors were found through a design of experiments in a linear approximation. The outer lens's red color is mainly influenced by the masterbatch concentration, the nozzle temperature, holding time, and the holding pressure, in a decreasing order. In contrast, the mold temperature, packing pressure, and packing time are not statically significant in the color appearance.     

Development of high gloss plastic for injection molding by utilizing wollastonite(CaSiO<Subscript>3</Subscript>) and talc fillers

The gloss of plastic products is an important factor with which customers rapidly and directly decide the value of product. In general, these high-gloss plastic molded parts are produced through the injection molding of glass fiber-added plastic resin using a high temperature mold with the fine surfaces like glass. However, making the mold temperature higher causes the cooling time of injection molding longer, and the prolongation of cooling time leads to the extension of whole cycle of injection molding process. In order to resolve this problem, we developed a resin which makes the high-gloss injection modeling possible at low mold temperature by replacing conventional glass fiber filler with wollastonite filler. The tensile strength, flexural strain, impact strength, flow rate, gloss level and so on of the developed resin were tested with respect to the content of wollastonite. The results show that most of the properties except for the flow rate and gloss level are reduced in the newly developed resin. However, the decline in these properties was not enough to limit the use of new resins. In the gloss level test, as for the equal gloss of injection molded parts, the mold temperature for the developed resin was 30 °C lower than the mold temperature for the conventional resin. The difference of gloss between two injection molded parts using two different resins has been confirmed from the surface inspection of injection molded parts by SEM (scanning electron microscope).     

齿轮齿条斜抽芯机构注塑模设计

根椐塑料垫的结构特点,设计了由对称布置在模具内部的四组齿轮齿条斜抽芯机构、推杆推出机构等主要部分组成的四型腔单分型面注塑模。介绍了注塑模主要零件的结构设计,注塑机的选择,模具的校核和工作原理。设计的模具结构紧凑、合理,工作可靠。     

Mold design and forming process parameters optimization for passenger vehicle front wing plate

The main objective of the present article is to solve the problems of poor molding quality, large warpage, inadequate cooling effect and unsuitable selection of process parameters, in the injection molding process for passenger vehicle front-end plastic wing plate. The thickness and parting surface of the vehicle front-end fender were determined, the injection mold and its cooling system were designed. The relevant process parameters, affecting the product molding quality, were tested, according to orthogonal experimental approach, while their influence on the warpage was obtained, by analyzing the data. Finally, the BP neural network of warpage model was established and globally optimized using genetic algorithm. The optimal parameter combination of the injection molding process was derived as: melt temperature 236 °C, mold temperature 51 °C, cooling time 32 s, packing pressure 97 MPa and packing time 16 s.

     

基于Moldflow的魔方中心轴注射分析与优化设计

应用Moldflow软件对魔方中心轴的注射成型过程进行浇口位置、充填、冷却和翘曲等模拟分析。通过在不同注射工艺条件下进行对比分析,确定了注射的最佳工艺参数:充填时间为2 s,注射+冷却时间为8 s,模具温度为40℃,熔体温度为240℃,注射压力为100 MPa。应用UG软件建立了注射模具的实体模型,解决了传统注射模具设计方法存在设计周期长、成本高且质量难以保证等问题。     

An experimental work on the effect of injection molding parameters on the cavity pressure and product weight

The injection molding process is one of the most efficient processes where mass production through automation is feasible and products with complex geometry at low cost are easily attained. In this study, an experimental work is performed on the effect of injection molding parameters on the polymer pressure inside the mold cavity. Also, the effect of these parameters on the final products' weight is studied. Different process parameters of the injection molding are considered during the experimental work (packing pressure, packing time, injection pressure, injection time, and injection temperature). Two polymer materials are used during the experimental work (polystyrene (PS) and low-density polyethylene (LDPE)). The mold cavity has a cuboidal form with two different thicknesses. The cavity pressure is measured with time by using pressure Kistler sensor at different injection molding cycles. The results indicate that the cavity pressure and product weight increase with an increase in the packing pressure, packing time, and injection pressure for all the analyzed polymers. They also show that the increase of the filling time decreases the cavity pressure and decreases the product weight in case of PS and LDPE. The results show that the increase of packing pressure by 100 % increases the cavity pressure 50 % in the case of PS and 70 % in the case of LDPE. They also show that the increase of injection pressure by 60 % increases the cavity pressure 36 % in case of PS and 90 % in case of LDPE at an injection temperature of 220 °C. The results indicate that process parameters have an effect on the product weight for LDPE greater than PS. The results obtained specify well the developing of the cavity pressure inside the mold cavity during the injection molding cycles.     

Integrated simulation of the injection molding process with stereolithography molds

Functional parts are needed for design verification testing, field trials, customer evaluation, and production planning. By eliminating multiple steps, the creation of the injection mold directly by a rapid prototyping (RP) process holds the best promise of reducing the time and cost needed to mold low-volume quantities of parts. The potential of this integration of injection molding with RP has been demonstrated many times. What is missing is the fundamental understanding of how the modifications to the mold material and RP manufacturing process impact both the mold design and the injection molding process. In addition, numerical simulation techniques have now become helpful tools of mold designers and process engineers for traditional injection molding. But all current simulation packages for conventional injection molding are no longer applicable to this new type of injection molds, mainly because the property of the mold material changes greatly. In this paper, an integrated approach to accomplish a numerical simulation of injection molding into rapid-prototyped molds is established and a corresponding simulation system is developed. Comparisons with experimental results are employed for verification, which show that the present scheme is well suited to handle RP fabricated stereolithography (SL) molds.     

Research on thermal stress, deformation, and fatigue lifetime of the rapid heating cycle injection mold

Rapid heating cycle molding (RHCM) is a novel plastic injection molding process. It can be used effectively to prevent many defects of products produced in conventional injection molding process. In this paper, the panel of large-size liquid crystal display TV was taken as an example. Thermal, deformation, and fatigue analysis models for RHCM injection mold were established. Firstly, by analyzing the heat transfer process of the RHCM mold, the temperature distributions on the mold cavity surface were studied. Secondly, through numerical simulation, the tendency of the stress and deformation of the RHCM mold was obtained. It showed that the fixing mode between the stationary mold insert and the stationary mold plate had a great influence on the thermal stress and deformation of the mold. As a result, a new fixing mode for the stationary mold insert was proposed which could effectively decrease the deformation caused by the temperature changing. Lastly, the lifetime of the mold under different fixing modes was evaluated, and reasonable suggestions which could improve the lifetime of RHCM mold were also proposed. Application in engineering proved that it was a very effective way to improve the lifetime of RHCM mold by using the suggested fixing mode.     

Microceramic injection molding of a multilayer micropatterned micropart

Microceramic injection molding (µCIM) has shown great potential in making small-scale intricate near-net-shape parts with the competitive price for mass production. In this study, multi-exposure multi-development UV-Lithographie, Galvanoformung, Abformung (LIGA), µCIM, variothermal temperature control, and Taguchi experimental method are integrated and applied to develop a multilayer micropart with zirconia (ZrO₂) feedstock. With the variothermal temperature control, a 335 μm thickness multilayer micropart having 100 microholes of 21.6 μm in diameter has been successfully molded. Optimization of the molding parameters to achieve high microhole replication quality molding was carried out with Taguchi experimental method. Results from Taguchi experiments reveal that mold temperature (40.9%), back pressure (31.8%), and injection speed (26.8%) contribute most to the replication quality, while ejection temperature has little effect on it. After further sintering processing, the thickness of the part is 200 μm, the final microhole diameter is 17.3 μm and its depth is 35.3 μm while the width of the channel is 38.5 μm and its height is 35.3 μm, and the accumulated aspect ratio of the dual layer structure is 2.95.     

Improvement of form accuracy and surface integrity of Si-HDPE hybrid micro-lens arrays in press molding

Press molding of silicon (Si)/high-density polyethylene (HDPE) composite is an important technology for producing thin hybrid infrared (IR) optics with microstructures. In this research, Si-HDPE hybrid micro-lens arrays were press molded under various conditions, and the form accuracy and surface integrity of the molded lenses were evaluated. Air trapping occurs inside the micro-lens cavities during molding in a non-vacuum environment, which leads to severe surface defects. To investigate the air trapping phenomenon, a new in-situ observation system was developed which enables real-time direct observation of the molding process. From the in-situ observations, it was found that air traps were formed among the HDPE pellets during melting, and an increase in the pressing force will increase the pressure of the trapped air, forming trenches on the lens surface. The trapped air also impacts the mold coating, causing trench formation on the coating surface. To minimize air trapping, the molding temperature, and pressing force must be strictly controlled. By performing press molding in a vacuum environment, trench formation was completely eliminated. Moreover, polymer shrinkage compensation was performed to improve the lens form accuracy.