基于石墨烯镀层快速热循环的熔体充填及纤维分布

基于石墨烯镀层随形快速热循环高比率纤维超薄制件的注塑成型,应用Moldflow软件对不同模具温度下的短玻纤维增强复合材料的快速热循环注塑成型过程进行了数值模拟,分析了不同纤维含量的熔体进入模腔后的填充行为,通过对模型内部的纤维取向张量、壁上剪切应力及冷冻因子的分析,从流动受力方面解释了高比率纤维超薄制件中纤维的分布。将单侧模具快速热循环注塑成型(RHCM)的试样在液氮条件下脆断,通过SEM观察微观结构形态,验证了模拟结果的正确性。     

快速加热条件下注塑模具温度场分布研究

基于传热数值传热学,采用Fluent在快速加热条件下研究了电加热棒功率、组间距离以及纵向距离等因素对型腔表面温度响应速率及表面温度均匀性的影响规律。结果表明,型腔表面温度响应速率随加热功率显著提高,但表面温度均匀度会变差;型腔表面温度响应速率随加热棒的组间距缩短,而略有提升但型腔表面温度均匀度会发生明显恶化;模具型腔表面温度响应速率随加热棒与型腔表面的距离减小显著提高,且对表面温度均匀度影响较小。     

快速热循环工艺对玻纤增强注塑制品表面质量的影响研究

提出将快速热循环方法辅助注塑成型工艺,探究不同型腔温度对薄壁玻纤增强制品的表面质量的改善情况。结果表明:制品表面光泽度随着型腔温度的升高也有所提高,表面的"浮纤"缺陷得到明显的改善,但是制品表面粗糙度则随着型腔温度的升高而增大。通过提高型腔表面质量的同时辅助快速热循环工艺,可以明显改善制品的表面质量。     

温度外场对注塑制品微观结构调控的数值模拟研究

利用数值模拟软件重点研究了由快变模温工艺提供的不同温度外场对注塑制品微观结构的影响规律。对结晶型聚丙烯注塑成型的模拟结果表明:提高模具型腔表面温度能有效减薄冷凝层,并降低注射压力;残余应力则随之呈现先降后升的趋势,其分布更均匀。结晶分析模块的结果表明:制品的结晶取向因子整体上随模具型腔表面温度的升高而下降;模具型腔表面温度的升高有利于增大制品晶体的平均粒径,但模具表面温度过高会导致制品晶体的平均粒径减小。     

快速热循环成型技术研究进展

综述了快速热循环成型技术在模具成型领域的研究进展，简要介绍了其不同于传统注塑成型技术的原理及其优点，同时详细介绍了几种加热方式不同的快速热循环成型技术，包括蒸汽加热、电加热、感应加热和辐射加热，说明了各自的优缺点并且总结了数值模拟软件在快速热循环成型技术上的应用，分析表明感应加热作为一种新型的加热方式，是未来快速热循环成型技术发展的一个重要方向。最后对快速热循环成型技术目前存在的问题及未来发展趋势进行了展望。     

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。     

RHCM成型制品高光面形成微观机理研究

根据快速冷热成型技术(RHCM)成型塑料熔体在型腔内的填充流动规律,在普通注射成型机理研究基础上,从微观角度对RHCM技术在提高制品对模具的复原性,消除熔接痕、凹痕、银丝纹、流纹、表面浮纤等表观缺陷以及改善制品表面色差等方面的成型机理进行研究。结果表明,正是由于RHCM高温快速成型这一工艺特点,一方面确保熔体在型腔内的充分扩展与汇合,另一方面最大程度的限制制品的成型收缩,从而确保制件的最终成型品质。     

注射压缩成型和注射成型平板的光学性能对比研究

研究了注射成型和注射压缩成型平板的光学性能特点,然后对两者光学性能的差异进行了分析.结果表明,注射成型平板的光学畸变和角偏差大,与其残余应力大且分布范围宽有关;而注射压缩成型平板的残余应力相对较小且分布范围较窄,型腔压力分布更为均匀,从而成型平板具有更低的光学畸变和角偏差.     

联机连帮注射模具结构优化

建立联机连帮注射模具型腔的力学模型,采用Moldflow软件对其注射成型过程进行模拟分析,以确定型腔受力,并将其作为刚度和强度分析的输入载荷;运用ANSYS workbench软件分析模具型腔的应力和应变,以优化模具结构。结果表明,该分析方法能够较全面地反映注射模具型腔在成型过程中的受力和变形,为模具设计提供了参考依据。     

液体硅橡胶的最新应用开发

液体硅橡胶的注射成型方法(LIMS)已得到广泛普及。该文介绍了液体硅橡胶的镶嵌件成型及与塑料的二元成形。镶嵌件成型用材料的特点是，当型腔未充满时，胶料不会发生固化；而型腔一旦被充满，便会快速固化，实现无废胶边、无流道、无公害及短时间成型。在二元成型方面值得注意的是对被粘物具有选择性的粘合材料，即对金属(模型)无粘接性，但对塑料却具有良好的粘接性的材料。采用选择性粘合材料能实现短时间整体注射成型。     

一种新型高光注塑模具加热方法的模拟和实验研究

采用电加热方式的高光注塑模具可以有效消除传统注塑成型过程中塑料件的熔接痕、浮纤、银纹等缺陷。然而直接将电加热棒插入模具孔中,由于间隙处的空气,大大降低了传热速度,提出一种新型电加热方法,通过在电加热棒与模具之间填充一种导热液,改变电加热棒与模具之间的接触状况,建立三维传热模型,并通过模拟和实验研究,证明了这种方法可以提高40%的加热效率,同时还能降低电加热棒内部40%的温度。     

Numerical Simulation for Injection Molding with a Rapidly Heated Mold,Part I: Flow Simulation for Thin Wall Parts

The rapid thermal response (RTR) injection molding is a novel process developed to raise the mold surface temperature rapidly to the polymer melt temperature prior to the injection stage and then cool rapidly. The resulting filling process is achieved inside a hot mold cavity by prohibiting formation of frozen layer so as to enable thin wall injection molding without filling difficulty. The present work covers flow simulation of thin wall injection molding using the RTR molding process. Both 2.5-D shell analysis and 3-D solid analysis were performed, and the simulation results were compared with the prior experimental results. Coupled analysis with transient heat transfer simulation was also studied to realize more reliable thin-wall-flow estimation for the RTR molding process. The proposed coupled simulation approach based on solid elements provides reliable flow estimation by accounting for the effects of the unique thermal boundary conditions of the RTR mold.     

Research on a New Variotherm Injection Molding Technology and its Application on the Molding of a Large LCD Panel

The polymer injection products produced by using the current injection molding method usually have many defects, such as short shot, jetting, sink mark, flow mark, weld mark, and floating fibers. These defects have to be eliminated by using post-processing processes such as spraying and coating, which will cause environment pollution and waste in time, materials, energy and labor. These problems can be solved effectively by using a new injection method, named as variotherm injection molding or rapid heat cycle molding (RHCM). In this paper, a new type of dynamic mold temperature control system using steam as heating medium and cooling water as coolant was developed for variotherm injection molding. The injection mold is heated to a temperature higher than the glass transition temperature of the resin, and keeps this temperature in the polymer melt filling stage. To evaluate the efficiency of steam heating and coolant cooling, the mold surface temperature response during the heating stage and the polymer melt temperature response during the cooling stage were investigated by numerical thermal analysis. During heating, the mold surface temperature can be raised up rapidly with an average heating speed of 5.4°C/s and finally reaches an equilibrium temperature after an effective heating time of 40 s. It takes about 34.5 s to cool down the shaped polymer melt to the ejection temperature for demolding. The effect of main parameters such as mold structure, material of mold insert on heating/cooling efficiency and surface temperature uniformity were also discussed based on simulation results. Finally, a variotherm injection production line for 46-inch LCD panel was constructed. The test production results demonstrate that the mold temperature control system developed in this study can dynamically and efficiently control mold surface temperature without increasing molding cycle time. With this new variotherm injection molding technology, the defects on LCD panel surface occurring in conventional injection molding process, such as short shot, jetting, sink mark, flow mark, weld mark, and floating fibers were eliminated effectively. The surface gloss of the panel was improved and the secondary operations, such as sanding and coating, are not needed anymore.     

Experimental investigation of infrared rapid surface heating for injection molding

A low cost and practical infrared rapid surface heating system for injection molding is designed and investigated. The system was designed to assemble on the mold and a control system was used to operate the motion of the lamp holder. Four infrared halogen lamps (1 kW each) were used as the radiative source to heat the surface of mold insert. The temperature increase is verified on the mold plate with a thermal video system. Two types of specular reflectors combined with different bulb configurations were applied to study the heating ability of radiation heating. A modified spiral flow mold was used to test the enhancing filling ability of the rapid surface heating system. Three resins, PP, PMMA and PC were molded in the spiral flow injection molding experiments. If spherical reflector and centralized lamp configuration are used, the temperature at the center of the mold surface is the highest. The temperature of mold center surface is raised from 83°C to 188°C with 15 s of infrared heating. Because the surface temperature of the mold insert is higher than the glass transition temperature of resins before filling, the flow distance of resins in the modified spiral flow mold will be increased. The location effect of the infrared surface heating system on a thin‐long cavity was studied to demonstrate the possibility of using smaller infrared heating area on a large mold surface. A microprobe cavity also demonstrated that with the assistance of infrared heating technology the formability of a microprobe can be greatly improved. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3704–3713, 2006     

高光无痕注塑成型模具热响应的研究

高光无痕注射成型技术是一种新开发的注射技术,能够消除塑件表面熔接痕等缺陷,表面可以达到镜面效果,免去二次喷涂。通过建立模具的二维几何模型,应用ANSYS模拟了加热、冷却过程,获得了模具表面及熔体中心层的热响应和温度分布情况;对比分析了常规注塑与高光无痕注塑两种成型工艺;通过加热、冷却时间及温度分布等对比,验证了高光无痕注塑的优越性。     

Thermal response of an electric heating rapid heat cycle molding mold and its effect on surface appearance and tensile strength of the molded part

Rapid heat cycle molding (RHCM) is a newly developed injection molding technology in recent years. In this article, a new electric heating RHCM mold is developed for rapid heating and cooling of the cavity surface. A data acquisition system is constructed to evaluate thermal response of the cavity surfaces of the electric heating RHCM mold. Thermal cycling experiments are implemented to investigate cavity surface temperature responses with different heating time and cooling time. According to the experimental results, a mathematical model is developed by regression analysis to predict the highest temperature and the lowest temperature of the cavity surface during thermal cycling of the electric heating RHCM mold. The verification experiments show that the proposed model is very effective for accurate control of the cavity surface temperature. For a more comprehensive analysis of the thermal response and temperature distribution of the cavity surfaces, the numerical‐method‐based finite element analysis (FEA) is used to simulate thermal response of the electric heating RHCM mold during thermal cycling process. The simulated cavity surface temperature response shows a good agreement with the experimental results. Based on simulations, the influence of the power density of the cartridge heaters and the temperature of the cooling water on thermal response of the cavity surface is obtained. Finally, the effect of RHCM process on surface appearance and tensile strength of the part is studied. The results show that the high‐cavity surface temperature during filling stage in RHCM can significantly improve the surface appearance by greatly improving the surface gloss and completely eliminating the weld line and jetting mark. RHCM process can also eliminate the exposing fibers on the part surface for the fiber‐reinforced plastics. For the high‐gloss acrylonitrile butadiene styrene/polymethyl methacrylate (ABS/PMMA) alloy, RHCM process reduces the tensile strength of the part either with or without weld mark. For the fiber‐reinforced plastics of polypropylene (PP) + 20% glass fiber, RHCM process reduces the tensile strength of the part without weld mark but slightly increases the tensile strength of the part with weld mark. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

间隙对电热变模温高光注塑模具加热效率的影响

采用电热方式的高光注塑模具可以有效消除传统注塑成型过程中塑件的熔接痕、浮纤、银纹等缺陷。高光注塑成型技术要求对模具温度的快速动态控制,然而在电加热高光注塑成型中,电加热棒与模具安装孔之间不可避免地存在间隙,间隙层内的空气大大阻碍热量向模具传递。研究了电加热棒与模具安装孔之间的间隙对电热变模温加热效率的影响,构建了电加热高光注塑模具的三维热响应分析模型,利用有限元分析软件ANSYS进行了三维瞬态传热分析,得到了在不同间隙下的模具表面和电加热棒内部的热响应曲线,并通过大量实验证明了理论分析和模拟方法的正确性。结果表明,加热相同时间,间隙量越小,模具表面温度越高,电加热棒内部温度越低,加热效率越高,相较于间隙在0.32 mm,间隙在0.05 mm加热到60 s的模具表面温度至少高出50%,电加热棒内部的温度至少低55%。隙量对模具加热效率的影响并非成线性关系,而是间隙量在越小的区间,加热效率对间隙更加敏感,研究结果为电热变模温高光模具结构设计和电加热棒的选用提供依据。     

INCREASING FLOW LENGTH IN THIN WALL INJECTION MOLDING USING A RAPIDLY HEATED MOLD

Injection molded parts are driven down in size and weight especially for portable electronic applications. While gains are achieved via cost reduction and increased portability, thinner parts encounter more difficulty in molding due to the frozen layer problem. To increase moldability in thin wall molding, a rapid thermal response (RTR) mold was investigated. The RTR mold is capable of rapidly raising the surface temperature to the polymer melt temperature prior to the injection stage and then rapidly cooling to the ejection temperature. The resulting filling process is done inside a hot mold cavity and formation of frozen layer is prohibited. Concepts of scalable filling and low-speed filling are discussed in the article to address the benefit of this molding method. Simulation results showed that significant reduction in injection pressure and speed can be achieved in RTR molding. In contrast to the filling behavior in conventional molding, the injection pressure in RTR molding decreases as the injection speed decreases, and therefore, extremely thin parts can be molded at lower injection speeds. Filling lengths of both RTR and conventionally molded polycarbonate samples, with two levels of thickness, under two levels of injection speed were experimentally studied. The experimental results demonstrated the advantage of the new molding method.     

Experimental Results of Low Thermal Inertia Molding. I. Length of Filling

In injection molding, complete mold cavity filling is a design goal that has to be met 100% every time. Mold cavity filling is a complicated process which depends on many variables such as mold cavity surface temperature, injection pressure, injection speed, melt temperature, flow index of material being molded, etc. The aim of experimental investigation of the low thermal inertia molding (LTIM) [1] process is to demonstrate the feasibility of molding completely filled, thin parts at low injection pressure and injection speed without sacrificing part quality. The evaluation of the new molding concept consists of comparison of a conventionally molded thin rectangular part with an identical part molded by the LTIM process. The length of filling in the conventional cavity and in the LTIM cavity are compared at different injection pressures and injection speeds. The mold design, experimental procedure, and results of the molding are discussed in the following sections.