[成形过程仿真优化与集成计算材料工程]限定加热管布局的快速热循环注塑成形模具电加热系统优化

针对管道布局、最大允许能耗给定条件下快速热循环注塑成形（RHCM）注塑模具型腔表面快速均匀加热的问题，提出以单根加热棒热流密度为设计变量，以模具型腔表面升温效率和温度分布均匀性为目标，结合有限元模拟、响应面设计以及多目标粒子群优化技术来优化RHCM模具电加热系统。与优化前相比，加热系统优化后，模具型腔表面最大温差降低63.4%，加热系统总能耗降低9%。对比了不同注塑成形工艺条件下成形的平板塑件表面质量，结果表明，相对传统注塑成形（CIM）工艺，RHCM工艺将制品表面粗糙度Ra从320 nm降低到118 nm，并有效抑制了制品表面熔接痕、缩痕等缺陷；发现制品表面粗糙度与型腔表面对应点温度成负相关，说明优化后的型腔表面温度分布更有利于提升制品表面质量。     

蒸汽辅助注射成型技术的现状与发展

介绍了蒸汽辅助注射成型技术的基本原理与特点,利用它可以很好地解决传统注射成型塑件的一些缺陷,如熔接痕、表观质量差、翘曲变形等,探讨了该技术需要研究的主要内容,并提出一些解决方案。该技术的推广应用对提升注塑行业的水平将会有积极的作用。     

Research of thermal response simulation and mold structure optimization for rapid heat cycle molding processes, respectively, with steam heating and electric heating

The dynamic mold temperature control system is the key of rapid heat cycle molding (RHCM) technology because it significantly affects the stability of the process, productivity and the quality of the final polymer part. For this reason, the approaches and techniques for dynamic mold temperature control were discussed in this study and two different dynamic mold temperature control methods, respectively, with steam heating and electric heating were found to be very feasible in mass production. The methods and principles of mold design for the two RHCM technologies were also discussed and then several different kinds of mold structures were designed. By constructing the corresponding thermal response analytical models for these RHCM molds, the temperature responses of the molding systems in the heating and cooling process of RHCM were simulated and studied. The effects of the mold design parameters such as the insulation layer between mold plate and mold inert, and mold material, on thermal response efficiency and temperature uniformity of the two RHCM processes were analyzed based on the simulation results. The results show that the insulation layer can increase the upper limit temperature of RHCM with steam heating and improve the heating speed of RHCM with electric heating. It can also greatly decrease the energy consumption of the two RHCM processes. The heating efficiency of RHCM with steam heating can be effectively improved by increasing the thermal conductivity of the cavity/core material, while the situation is diametrically opposite for RHCM with electric heating. Therefore, we acquired an optimized mold design principle and method for RHCM with steam heating and electric heating, respectively. Finally, a new electric heating mold with a cooling plate was proposed to enhance the cooling efficiency. The thermal response of this new electric heating mold was also simulated. The simulation results show that the cooling plate can significantly improve the cooling and heating efficiency.     

Three‐dimensional thermal response and thermo‐mechanical fatigue analysis for a large LCD TV frame mould in steam‐assisted rapid heat cycle moulding

Rapid heat cycle moulding (RHCM) is a newly developed moulding technique to improve the surface appearance of plastic parts and eliminate the polluting secondary operations such as primers and painting. In steam‐assisted RHCM, the mould surface temperature should be thermally cycled by alternatively cycling the high temperature steam and cooling water in the heating/cooling channels of the mould. The mould design is of great importance for RHCM because it not only has a great effect on the heating/cooling efficiency and hence the productivity but also directly affects the mould surface temperature uniformity and accordingly the final part quality. Furthermore, the service life of the RHCM mould with steam heating is also very much dependent on the mould structure or the layout of the heating/cooling channels as the fatigue crack is likely to occur at the wall of the heating/cooling channels under combined thermal cycling and mechanical loading. In this study, an RHCM mould for a type of 52‐inch LCD TV frame was designed. A three‐dimensional (3D) transient thermal analysis was performed to determine the thermal response efficiency of the designed RHCM mould cavity and investigate the factors affecting the heating efficiency. Then, by using the results obtained from the heat transfer simulation, the thermal‐structure coupling analysis comprehensively considering the cavity pressure and clamp force was conducted to analyse the stress distribution in the mould cavity, which is helpful to find the weak position in the mould cavity. We found that the spots where the maximum stresses occur are similar to the region where fatigue cracks come into being in the actual RHCM mould. Based on the simulation results, the mechanism of the cavity cracks formation on the cavity surface was proposed. Finally, the fatigue analysis was conducted to predict the fatigue life of the RHCM mould. The analysis results show that the regions at the top edges of the heating/cooling channels have the lowest fatigue life and safety factor. The discrepancy between the available life predicted by simulation and the actual service life of the RHCM mould is also discussed.     

水热式RHCM成型工艺对熔接痕性能影响

根据水热式RHCM注射工艺特点,以工程应用广泛的ABS和PP为研究对象,利用Taguchi实验设计方法,研究水热式RHCM注射成型工艺对熔接痕性能影响。实验结果表明:在常规注射工艺和加热工艺中双浇口试样的拉伸强度依然比单浇口试样的拉伸强度低;模具温度的增大使单浇口试样的拉伸强度稍微降低了,使单浇口ABS试样的拉伸强度降低了0.5MPa,使单浇口PP试样的拉伸强度降低了0.27MPa。而水热式RHCM注射工艺,确使模具温度的增大使双浇口试样的拉伸强度有了明显的提升,使单浇口ABS试样的拉伸强度提升了1.57MPa,使单浇口ABS试样的拉伸强度提升了1.56MPa,这对改善熔接痕的性能具有重要的意义。     

高光泽外观部品的加工方法及应用

介绍了两种近年来比较先进的工艺方法：高光无流痕成型技术（RHCM）和可成型表面装饰技术（IMD）,并讨论了实际应用的课题和工艺要点。     

塑件收缩率测量方法及其影响因素分析

针对材料收缩率值的不确定性问题,对收缩率的测量方法及其影响因素进行了研究,对收缩率的计算方法进行了归纳,提出了基于热膨胀仪测量塑件收缩量来计算收缩率的方法,探讨了注塑成型工艺及热处理对收缩率的影响,分析了结晶度与收缩率之间的关系。选用等规聚丙烯为材料,采用不同成型工艺制备塑件,利用热膨胀仪分别测量热处理前后的塑件收缩量,分析了成型工艺与热处理对收缩率的影响。基于DSC测量塑件总体结晶度,分析了结晶度对塑件收缩的影响。研究结果表明,与工艺实验获得的收缩率进行对比和分析,可知采用热膨胀仪测量塑件收缩量来计算收缩率的方法是准确的,是一种简便易行的方法;快速变模温和热处理增大了塑件的结晶度,收缩量和收缩率随之变大,在模具设计过程中不可忽略。     

熔接痕性能评价的WSt模型及其验证

提出采用熔体汇合角度、流动前沿温度、压力三个参数来表征熔接痕,构建了评价熔接痕性能优劣的WSt模型,基于此模型对比了相同工艺参数下快速变模温成型(Rapid Heat Cycle Molding,RHCM)与普通成型的熔接痕质量,并以导风板为对象进行了生产验证.结果表明:快速变模温成型熔接痕的整体性能由普通成型的0.681提高到0.819,提高了20.3％;RHCM成型导风板熔接痕处的拉伸强度由普通成型的45.3MPa提高到53.8 MPa,强度提高了18.8％,与WSt模型所预测的20.3％接近.     

Effect of surface modifiers and surface modification methods on properties of acrylonitrile–butadiene–styrene/poly(methyl methacrylate)/nano‐calcium carbonate composites

Nano‐calcium carbonate (nano‐CaCO₃) was used in this article to fill acrylonitrile–butadiene–styrene (ABS)/poly(methyl methacrylate) (PMMA), which is often used in rapid heat cycle molding process (RHCM). To achieve better adhesion between nano‐CaCO₃ and ABS/PMMA, nano‐CaCO₃ particles were modified by using titanate coupling agent, aluminum–titanium compound coupling agent, and stearic acid. Dry and solution methods were both utilized in the surface modification process. ABS/PMMA/nano‐CaCO₃ composites were prepared in a corotating twin screw extruder. Influence of surface modifiers and surface modification methods on mechanical and flow properties of composites was analyzed. The results showed that collaborative use of aluminum–titanium compound coupling agent and stearic acid for nano‐CaCO₃ surface modification is optimal in ABS/PMMA/nano‐CaCO₃ composites. Coupling agent can increase the melt flow index (MFI) and tensile yield strength of ABS/PMMA/nano‐CaCO₃ composites. The Izod impact strength of composites increases with the addition of titanate coupling agent up to 1 wt %, thereafter the Izod impact strength shows a decrease. The interfacial adhesion between nano‐CaCO₃ and ABS/PMMA is stronger by using solution method. But the dispersion uniformity of nano‐CaCO₃ modified by solution method is worse. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

RHCM模具的三维瞬态传热建模与分析

研究RHCM模具的三维有限元瞬态传热建模,分析进入稳态工作状态的模具和熔体之间的耦合传热过程,提出了模具和熔体接触热阻计算模型。案例对比分析发现:三维模型可克服目前简化二维模型存在的加热时间预测偏短,精密模具型腔边缘与模具中心温差误差大的问题;接触热阻导致热传导效率大大降低,冷却时间增长,可通过减小热阻来解决;减少加热时间可避免冷却阶段初期型腔壁面温度继续上升。