【作者】 殷素峰；

【导师】 阮锋；

【作者基本信息】 华南理工大学 ， 机械制造及其自动化， 2014， 博士

【摘要】 随着注塑产品轻、薄化的发展趋势，超薄注塑日益受到关注与青睐，它不但节省了材料，还能使产品更具美感。超薄塑件厚度小，熔体进入型腔后迅速冷却凝固，充模过程必须在极短时间内完成，以克服快速凝固而导致的填充不足。苛刻的工艺过程增加了成型的难度，也使超薄注塑具有与常规注塑不一样的特点。良好的熔体填充性、高标准的成型精度、稳定的工艺制程是产品竞争市场的先决条件。本文结合超薄导光板的生产实践，对超薄注塑的充模理论进行研究并将其结果应用于导光板的成型中，主要工作如下：（1）研究了超薄注塑成型剪切场，对超薄注塑成型“次相剪切效应”进行研究，在超薄导光板成型中利用次相剪切效应，有效提高了熔体充模性，有利于超薄注塑件的成型。超薄注塑中高射速降低了熔体充模黏度，为超薄成型提供了有利条件，但片面追求高射速也为成型过程带来诸多不利因素，如过高的射速增加了机器负载、使熔体容易剪切降解、成型过程不稳定等。基于生产实践，提出次相剪切效应概念，从理论上将超薄剪切场分为主相剪切场和次相剪切场，在分析主相剪切局限性的基础上，对次相剪切场进行了论述说明，并通过流变实验验证了次相剪切场的有效性。在理论分析的基础上，在超薄导光板设计中提出网点混排结构，利用网点混排使熔体充模产生次相剪切效应，有效提高了熔体充模性。（2）研究了注射压力对熔体黏度的影响，在黏度模型中提出“黏度当量压力影响系数”的概念，并证实了黏度当量压力影响系数对模拟结果的正确性。超薄成型注射压力可达300MPa以上，多种黏度模型中都引入黏度压力影响系数来表征黏度的压力依赖性，其值通过实验拟合为一推荐常量。超薄成型中熔体黏度对该常量极其敏感，并使数值分析结果严重偏离生产实际，如模拟中注射压力比实际成型压力大很多。基于自由体积理论，在黏度模型中提出黏度当量压力影响系数概念，认为熔体中自由体积的膨胀比与压缩比之商不为常数，压力对黏度的影响等同于将熔体玻璃化温度非线性提高，而非线性提高。在熔体P-V-T关系的基础上，研究了高压下压力与黏度的关系，推导出Cross-WLF黏度模型中黏度的当量压力影响系数，并通过短射实验证实了黏度当量压力影响系数对模拟结果的正确性。（3）研究了模具-型腔对流换热系数，测试了不同型腔厚度在不同注射速度下模具-型腔对流换热系数，证实了所测对流换热系数在超薄成型应用中的正确性。超薄件表体比大，散热边界条件对成型的影响不容忽视。本文通过狭缝流变仪和自制狭缝口模，测试了不同型腔厚度在不同注射速度下模具-型腔对流换热系数，发现超薄成型中模具-型腔对流换热系数随着型腔厚度、注射速度的不同而有较大差异。使用测试值与推荐值进行双折射模拟，将模拟所得光的迟滞带与光弹应力带对比，发现使用推荐值进行模拟时，光的迟滞带大于光弹应力带，而使用测试值进行时，光的迟滞带与光弹应力带吻合度高，证实了所测对流换热系数在超薄成型应用中的正确性。（4）探讨了基于超薄充模理论注塑参数对超薄塑件成型精度的影响。基于超薄导光板生产实践，定义尺寸精度、翘曲量、平整度为成型品质管控目标，分析了混排网点导光板与单排网点导光板成型品质的差异，分析了基于当量黏度压力系数、超薄换热系数对混排网点导光板品质的影响。通过正交试验，筛选了对成型品质影响显著的工艺参数。（5）基于超薄充模理论，对超薄导光板的成型品质进行了多目标优化研究。以尺寸精度、翘曲量、平整度为设计目标，以模具温度、保压压力、熔体温度、保压时间为响应变量，在数值模拟基础上，利用Kriging插值法拟合了三个设计目标的代理数学模型。基于NSGA-II遗传算法分析了多目标优化pareto解集。为了得到理想解，根据导光板具体设计要求，利用Vague集多目标评价模型，在考虑方案客观权重、主观权重的基础上，通过评分方法计算pareto解集中各方案相对于理想方案的适应度，根据适应度大小从pareto解集中甄选出最佳设计方案，保证了工艺过程的优化与稳健性。更多还原

【Abstract】 Ultra-thin plastic injection becomes increasingly popular as products are getting muchlighter and thinner. In addition to saving in material, the technique makes the finishedproducts appear more beautiful. Since the ultra-thin plastic parts have thin thickness and cooland solidify instantly upon entering into the mold cavity, mold filling must be completed invery short time so as to overcome insufficient filling as a result of instant solidification. Thedemanding craft process makes molding even more difficult and enables ultra-thin injectionmolding to have different characteristics from regular molding. Fine melt filling, high-levelmolding precision and stable craft process are the prerequisites for products to compete in themarket. The article, in line with the production of ultra-thin LGP, studies some theories ofultra-thin plastic injection mold filling and th applies them to the light guide plate moldingThe research is summarized as the following:（1） studing injection molding shear field, and first proposed the "second phase shearingeffect" study, the use of sub-phase shear effects in ultra-thin light guide plate molding,effectively improve the melt filling, is conducive to super-injection molding of thin parts.However, high rate of fire may have some negative effects on molding process such as themachine load caused by high rate of fire, melt shear degradation and instability in moldingprocess. Based on production practice, the article proposes for the first time the notion ofsecond phase shear effect, and theoretically classify ultra-thin shear field into main phase andsecond phase shear fields. The article analyses limitations of main phase shear field as well assome issues concerning second phase shear field, and proves the effectiveness of second shearfield with rheological experiments. For the first time, the research, based on theoreticalanalysis, puts forward mixed network structure in the design of ultra-thin LGP, whichimproves the melt mold filling as a result of second shear effect of mixed network structure.（2）studing the effect of the injection pressure on the melt viscosity, propose the Conceptof"equivalent pressure effect factor on the viscosity of the model and confirmed thecorrectness of effects of viscosity equivalent pressure coefficient in simulation results.The research on the impact of injection pressure on melt viscosity. The injection pressureof ultra-thin molding runs as high as300MPa. The viscosity pressure influence coefficient isintroduced in many viscosity models to indicate viscosity pressure dependency. Thecoefficient, by experiment, is a recommended constant. In ultra-thin molding, melt viscosity isvery sensitive to the constant and makes numerical analysis results deviate vastly from realproduction, for example, the injection pressure is much higher than practical molding pressure.Based on free volume theory, the article proposes the concept of equivalent pressure influencecoefficient in viscosity model, which holds that the ratio between expansion ratio andcompression ratio in free volume is not a constant. The impact of pressure on viscosity isequal to the non-linear increase of melt glass transition temperature, not linear. On the basis ofmelt P-V-T relationship, the article researches on the relation between pressure and viscosityunder high pressure, eliciting equivalent pressure influence coefficient in viscosity model andproves the validity of equivalent pressure influence coefficient to simulated results by shortshot experiment. （3）studing the mold-Cavity convective heat transfer coefficient.This paper tested themold-Cavity convective heat transfer coefficient of different thickness at different cavity moldinjection speed and confirmed the validity of heat transfer coefficient measured in ultra-thinmolding applications.The research on mold-cavity convective heat transfer coefficient. Surface-to-volumeratio of ultra-thin parts is big, so the impact of heat transmission boundary conditions onmolding is not to be ignored. The research, by using slit rheometer and self-made slit openingmold, tests mold-cavity convective heat transfer coefficient of different cavity thickness underdifferent injection speed. It finds that, in ultra-thin molding, mold-cavity convective heattransfer coefficient varies greatly with different cavity thickness and injection speed. Theresearch applies both convective heat transfer coefficient and the recommended value tobirefraction simulation, and compares simulated light hysteresis zone with photoelastic stresszone. It’s found in the research that light hysteresis zone is bigger than photoelastic stresszone for the recommended value in simulation process, while the simulated result ofconvective heat transfer coefficient coincides with photoelastic stress zone. So the validity ofthe application of tested convective heat transfer coefficient to ultra-thin molding isconfirmed.（4）disscusing the effects on ultra-thin parts molding precision of certain parameters onthe theory of ultra-thin filling.The research on molding precision of ultra-thin plastic partsbased on ultra-thin theory. It makes dimensional precision, warpage and flatness the qualitystandards for finished products based on the production practice of ultra-thin LGP. Then theresearch analyzes the quality differences of mixed network LGP and single network LGP. Andthe influence of equivalent viscosity coefficient and ultra-thin heat transfer coefficient on thequality of mixed network LGP is also discussed. By orthogonal experiment, the researchchooses the technological parameter that has obvious effects on the quality of finishedproducts.（5）The research on multi-objective optimization of the quality of ultra-thin LGP, basedon ultra-thin theory. It makes dimensional precision, warpage and flatness the designobjective, and mold temperature, dwell pressure, melt temperature and dwell time theresponse variable. And by numerical stimulation, the research over-fits the agentmathematical model of three design objectives using Kriging interpolation method. Then it,based on NSGA-II genetic algorithm, analyzes pareto disaggregation of multi-objectiveoptimization. To have ideal solution, the research is conducted in accordance with specificdesign requirements of LGP and makes use of multi-objective evaluation model of Vaguedisaggregation. Based objective and subjective weight and by method of marking to decide onthe fitness of each scheme in the pareto disaggregation to the satisfactory scheme, the researchchooses the optimal scheme, and thus guarantees the optimization and stability of the craftprocess.更多还原