热塑性塑料微注射成型的关键技术

综述了微注射成型技术存在的问题和改进方法，探讨了微注射成型机的塑化、注射和计量等装置的结构性能改进，并提出了监测系统的改进方案。在比较微注射成型模具和常规注射成型模具基础上，介绍了微注射成型模具的特殊变模温控制方法、抽真空排气方法、模具材料选择及模芯微细加工方法。还探讨了特殊热塑性塑料材料的开发和微注射成型零件的检测和处理方法，并进一步分析了微流动特征下计算机模流分析软件适应性。     

注射成型快变模温技术研究进展

快变模温技术是新型绿色注射成型技术。通过对模温的动态控制,可以有效地消除制品熔接痕,减少制品残余应力。介绍了快变模温技术的原理,对电加热、蒸汽加热、电磁加热、红外加热等多种加热方式进行分析。最后对快变模温技术发展前景作出展望。     

蒸汽加热变模温注射成型数值模拟与结果分析

采用Moldflow软件对变模温注射成型过程进行数值模拟。利用蒸汽加热和冷却水冷却的变模温注塑工艺,研究不同蒸汽加热时间下注塑位置处压力以及制件冷凝层的变化规律,同时分析了制件表面和模具型腔表面的热响应规律。结果表明,相比于传统注射成型工艺过程,变模温注射成型通过提高注塑充填过程中模具温度,使得制件冷凝层出现在充填阶段之后;随着模具加热时间从10、15、25 s增加到40 s,注塑位置处最大注射压力从87.0608、84.6064、79.6863 MPa减小到74.4342 MPa,大大提高了熔体注塑充填过程中的充填能力;通过不同的蒸汽加热时间,制件表面和模具型腔表面可以获得不同的温度值,同时通过模拟获得了传热系数对制件表面温度的影响。     

变模温注塑技术的研究与应用分析

变模温注塑料是一种基于动态模温控制策略的注射成型技术,可根据不同工艺阶段的特点,随时调整模具温度,可在不降低生产效率的同时有效提升塑件的品质.在深入回顾变模温注塑技术研究发展的基础上,分析比较各种技术的优缺点和应用范围.构建了蒸汽辅助加热变模温注塑系统,实现了平板电视机面板的高光无熔痕注塑生产.     

变模温控制之下温度变化特性

近年来由於变模温技术的发展,射出成型在模温控制上呈现更多样的可能性,其考虑的不只是设定模温高低,也需考虑模具温度的前後状态变化,以掌握成型过程之中,模具整体温度状态。尤其是模具之中的温度控制元件,包含了加热及冷却等不同温度来源,更增添了温度操作上的变数。因此,我们藉由CAE工具研究模温变化,讨论在变模温下温度变化特性,进而协助决定最佳成型条件。     

变模温控制技术改善注塑制品熔接痕的研究

阐述了变模温技术理论,借助CAE数值模拟仿真平台对翻盖手机外壳注塑成型过程进行动态模拟,对传统注射工艺和变模温注射工艺产生的熔接痕进行了详细的比较和分析。结果表明:相比传统的恒定模温控制,变模温控制技术对塑件熔接痕的改善效果更加明显,提高了熔接强度,优化了熔接痕,在不影响生产效率的基础上,达到了提升制品品质的目的。     

基于ANSYS的LED电视面壳高光模具方案设计

基于高光成型工艺原理,为实现LED电视面壳的高光效果,提出采用油加热、油冷却方式对其型腔表面进行变模温控制。构建基于多种不同模具材料和结构变模温注塑工艺分析模型,利用ANSYS对其加热响应、冷却过程进行数值模拟。最终采用以AMPCOLOY 972作为模具材料且带隔热方式的高光模具结构方案。     

变模温注压成型对超薄导光板品质的探析与实践

超薄导光板高速高压注射成型具有残余应力集中、厚度不均、微特征转写效果差等缺陷。简述了导光板注射成型缺陷原因,重点分析了注压成型工艺对超薄导光板残余应力、厚度均匀性、微特征转写性的影响,并根据导光板设计要求选择最佳工艺方案进行实验,结果显示,与注射工艺相比,注压工艺使导光板样本点应力集中均值从9.46 MPa降为7.98 MPa、厚度均匀性均值从0.428 mm降为0.391 mm、微特征高度均值从0.022 mm提升为0.0388 mm,导光板综合性能显著提高。鉴于微特征转写性是导光板光学性能的关键因素,且其受模温影响显著,进一步将变模温技术与注压工艺相结合,使微特征高度均值进一步从0.0388 mm提升至0.0394 mm,更加接近设计值0.04 mm。     

陶瓷微注射成型技术的研究与进展

本文介绍了陶瓷微注射成型工艺过程的新特点和新技术;探讨了陶瓷微注射成型充模流动模拟所采用的理论模型及其应用研究现状;最终指出微注射成型技术研究应该着重于陶瓷微注射模拟新方法、微尺寸型腔内的流动机理、微型零件的质量控制方法、微注射成型工艺和设备研制上.     

注射成型模具电磁感应加热技术

阐述注射成型模具电磁感应加热技术的原理及模外感应加热和模内感应加热的实现方式,着重介绍当前常用的机械手辅助感应加热、模芯通电感应加热、感应加热管加热、模具内置线圈感应加热和模芯内嵌线圈感应加热的方法,并分析了各种方法的优缺点,展望了电磁感应加热在注射成型模具上的发展趋势。     

Construction of fast-response heating elements for injection molding applications

A new type of heating element was developed capable of changing the mold surface temperature by about 70 K in 0.2 s, thus enabling reduction of frozen-in orientation and stresses in injection molded products without undue increase in cycle time. The heater, which consists of two insulation layers with a resistance layer in between, is discussed in this paper. The thickness of this insulation layer proves to be the most important design parameter. Too thick an insulation layer increases the cooling time too much, whereas with a thin layer the surface temperatures will stay too low. Temperature measurements at the heater surface and in the mold wall are reported and demonstrate the extreme fast response characteristics.     

High‐frequency proximity heating for injection molding applications

High‐frequency proximity heating was used to rapidly heat injection molds. The principle is based on the proximity effect between a pair of mold inserts facing each other with a small gap and forming a high‐frequency electric loop. Because of the proximity effect, the high‐frequency current will flow at the inner surfaces of the facing pair, thus selectively heating the mold surface. With this method, the electrical insulation layer beneath the mold surface can be eliminated, resulting in a mold insert made of a single metal. A mold with a cavity of 25 × 50 mm² was constructed with careful design on its electrical, structural, and thermal performance. Air pockets with reinforcing ribs were embedded right beneath the mold surface for enhancing the heating performance. The resulting mold cavity can be rapidly heated from room temperature to about 240°C in 5 s with an apparent heating power of 93 W/cm². The new mold heating method was applied to thin‐wall molding and micromolding, and in all testing cases, short cycle times less than a minute were achieved. POLYM. ENG. SCI. 46:938–945, 2006. © 2006 Society of Plastics Engineers     

Thermal Runaway in Mold‐Assisted Flash Sintering

Analyzing the temperature evolution in pressureless mold‐assisted flash sintering, we found the same onset condition as in standard flash sintering: When sample's DC or AC Joule heating replaces environment's radiation heating as the dominant power input term, thermal runaway ensues. Various serial and parallel components connected to the sample, including the mold, insulation, and punches, can affect Joule heating and conduction heat loss, thus play an important role in successful mold‐assisted flash sintering.     

一种简单的用于滚塑工艺加热阶段的传热模型

对从滚塑模具开始受热到其内部粉料开始熔融之间的加热阶段建立一个简化的传热理论模型,通过混合物与模具内壁面接触时的非稳态导热方程来计算这二者之间的表面传热系数,然后采用MATLAB软件求解模型中的常微分方程组。将计算所得的内部空气温度与实验结果相比较,证明了传热模型的准确性;应用该传热模型分别研究了烘箱内加热温度、外部表面传热系数以及塑料制品的厚度对加热时间和加热效率的影响,发现加热效率随时间的延长而增大,较厚的塑料制品比较薄的塑料制品具有更高的加热效率。     

Development of rapid heating and cooling systems for injection molding applications

The injection molding process has several inherent problems associated with the constant temperature mold. A basic solution is the rapid thermal response molding process that facilitates rapid temperature change at the mold surface thereby improving quality of molded parts without increasing cycle time. Rapid heating and cooling systems consisting of one metallic heating layer and one oxide insulation layer were investigated in this paper. Design issues towards developing a mold capable of raising temperature from 25°C to 250°C in 2 seconds and cooling to 50°C within 10 seconds were discussed. To reduce thermal stresses in the layers during heating and cooling, materials with closely matched low thermal expansion coefficient were used for both layers. Effects of various design parameters, such as layer thickness, power density and material properties, on the performance of the insert were studied in detail with the aid of heat transfer simulation and thermal stress simulation. Several rapid thermal response mold inserts were constructed on the basis of the simulation results. The experimental heating and cooling response agrees with the simulation and also satisfies the target heating and cooling requirement.     

高硅氧-碳纤维增强酚醛树脂复合模压制品工艺研究

本文开发了以碳纤维酚醛树脂层为耐烧蚀层,高硅氧纤维酚醛树脂层为绝热层的模压制品。该制品为内外复合模压结构,对其模具设计、成型工艺进行了研究,确定了装料温度、加压温度、升温速率、固化温度,并对该复合制品的性能进行了测试对比。结果表明：使用该方法的制品比通过胶粘剂粘接为一体的制品界面剪切强度高。     

Dynamic mold surface temperature control using induction heating and its effects on the surface appearance of weld line

Electromagnetic induction heating combined with coolant cooling is used to achieve dynamic mold surface temperature control. A simulation tool was also developed by integration of both thermal and electromagnetic analysis modules of ANSYS, and capability and accuracy were verified experimentally. To evaluate the feasibility and efficiency of induction heating on the mold surface temperature control, a mold plate (roughly about an inset size of cellular phone housing) with four cooling channels was utilized for two demo experiments with varying mold surface temperature between 110 and 180°C, and 110 and 200°C, respectively. During induction heating/cooling, it takes 4 s to increase mold surface temperature from 110 to 200°C and 21 s for mold surface to return to 110°C. The mold plate surface temperature can be raised at about 22.5°C and cooled down at 4.3°C/s within the aforementioned temperature range. Mold plate temperature distribution exhibits good uniformity as well in all stages of the heating/cooling process. Finally, mold surface temperature of a double‐gated tensile test part mold was induction heated to above glass transition temperature for few seconds prior to melt injection. The surface mark of weld line was eliminated, and the associated weld line strength enhanced. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1174–1180, 2006     

滚塑成型工艺加热阶段的数值研究

为一个球形中空塑料制品的滚塑成型工艺的加热阶段建立了一种新的流动与传热理论模型,并采用Fluent软件对其进行数值计算。该理论模型将模具的导热、塑料层的导热和随后的熔融以及内部空气的自然对流换热耦合起来求解。数值计算所得的加热时间、模具外壁面温度和内部空气温度都与实验结果吻合较好,从而证明了本理论模型的有效性。最后采用该理论模型分别计算了在不同外部加热温度、外部对流换热系数以及塑料粉末层厚度下的加热时间,从而确定了这些参数对加热时间的影响,并得出了提高外部对流换热系数比提高外部加热温度能更有效地缩短加热时间等结论。     

Thermal and cure analysis in sheet molding compound compression molds

Sheet molding compound (SMC) compression molding growth will benefit from faster cycles and more uniform cure so as to reduce in-plane thermal residual stress and resulting warpage in the molded part. These improvements require an in-depth study of the mold thermal design. Here we use a finite element model to analyze the quasi-steady temperature distribution in a plane perpendicular to the heating channels of a representative mold, and a finite difference model to investigate the cure dynamics at critical regions. Several changes in the mold heating system and operating conditions were considered and their effects on the temperature distribution and cure time were studied. It was assumed that the steam condensate is well drained and enough steam is supplied so that the steam tube walls are kept at a constant temperature. An important conclusion of the present study is that better insulation of the mold from the press does not help much in improving the uniformity of cavity surface temperature or cure. It was also found that reducing the distance between two consecutive steam tubes beyond the distance from the steam tube to cavity surface will not yield a significant change. The most practical way to give both more uniform cavity surface temperature and faster cure is to have higher steam temperature for the region where the charge is initially placed.