【作者】 王桂龙；

【导师】 赵国群；

【作者基本信息】 山东大学 ， 材料加工工程， 2011， 博士

【摘要】 快速热循环注塑技术是一种基于模具快速加热和快速冷却的注塑成型工艺,其技术特点是在不影响注塑成型周期的前提下实现高模温注塑成型。在快速热循环注塑中,填充阶段的高模具温度可以有效避免模具型腔中塑料熔体的过早冷凝,彻底消除塑料熔体表面的冷凝层,这将显著提高塑料熔体的流动性,增强塑料熔体转印模具型腔形状的能力。因此,快速热循环注塑工艺可以有效消除常规注塑成形产品易出现的流痕、喷射痕、熔接痕、浮纤、低光泽等表面缺陷,能够注塑成形具有超高流长比的塑件,精确复制模具型腔的微细结构,有效降低注射压力、注射速率、保压压力和锁模力,减小塑件的内应力。由于快速热循环注塑成形的塑件具有极高的外观质量,无需打磨、喷涂、罩光等后续加工,所以该技术可以显著缩短高品质外观塑件的生产流程,有效降低生产成本,减小能源消耗,并避免打磨、喷涂、罩光等工序对环境造成的污染,有利于改善车间工作环境和保护工人身体健康。显然,快速热循环注塑是一种高质量、高精度而又节能减排、环境友好的绿色注塑新工艺,具有广阔的应用前景和巨大的市场潜力。本文从快速热循环注塑成型的工艺原理、工艺流程、模具温度控制系统、模具设计与制造、装备及生产线构建、模具热响应分析、模具加热／冷却系统优化设计、模具疲劳寿命分析与优化、工艺优化设计、成型机理等方面对快速热循环注塑成型工艺进行了系统研究。分析了快速热循环注塑工艺原理和模具温度控制原理,提出了蒸汽加热快速热循环注塑工艺和电加热快速热循环注塑工艺,通过对快速热循环注塑周期的深入分析,制定了合理的工艺流程。研发了基于可编程逻辑控制器和触摸屏技术的蒸汽加热和电加热动态模具温度控制系统,研制了大型液晶电视机面板用蒸汽加热快速热循环注塑模具和电加热快速热循环注塑模具,基于热响应分析和试验对模具的热循环效率进行了评估,提出了一种适合于具有三维复杂形状塑件的蒸汽加热快速热循环注塑模具结构和电加热快速热循环注塑模具结构。利用自主研制的动态模具温度控制系统和注塑模具,构建了蒸汽加热快速热循环注塑生产线和电加热快速热循环注塑生产线,实现了液晶电视机面板的高光无熔痕注塑生产,彻底消除了打磨、喷涂、罩光等二次加工工序。对快速热循环注塑成本和效益进行了对比分析,研制了不同规格不同型号的动态模具温度控制系统和注塑模具,实现了快速热循环注塑成型技术的工程化应用。分别研究了蒸汽加热和电加热快速热循环注塑过程的传热规律,推导建立了两种快速热循环注塑工艺的热平衡方程,分析了模具加热效率和冷却效率的影响因素,提出了加快模具热循环的有效措施和快速热循环注塑模具结构设计原则。构建了蒸汽加热和电加热快速热循环注塑模具的热响应分析模型,研究了两种加热方式的快速热循环注塑模具型腔表面的热响应规律,分析了模具隔热层、模具材料对模具型腔表面热响应效率和温度均匀性的影响规律,对比讨论了两种快速热循环注塑工艺的加热效率、冷却效率和能量消耗,给出了两种加热方式的快速热循环注塑模具结构设计方法。提出了一种浮动型腔式电加热快速热循环注塑模具结构,有效减小了注塑循环过程中需要快速加热和快速冷却的型腔板的热容量,显著提高了模具型腔表面的热响应效率。基于浮动型腔式模具结构,设计了大型液晶电视机面板的电加热快速热循环注塑模具,解决了与模具设计、加工和装配有关的关键技术。基于传热数值模拟技术,研究分析了加热／冷却介质类型、加热／冷却介质温度、加热冷却管道布局、模具材料以及塑件厚度对蒸汽加热快速热循环注塑模具热循环效率和温度均匀性的影响规律,建立了加热系统、冷却系统和模具结构的优化设计方法。基于响应曲面法,结合试验设计和热-结构耦合分析,研究了加热冷却管道布局和电加热元件布局对模具型腔表面的热响应效率、温度分布均匀性和疲劳寿命的影响规律,利用基于最小二乘法的回归分析,建立了模具加热时间、型腔表面最高温度和型腔板承受的最大等效应力的响应曲面模型,通过变异数分析和随机试验,验证了响应曲面模型的有效性。提出了加热效率优先、温度均匀性优先和疲劳寿命优先三种优化设计策略,基于建立的响应曲面模型分别构建了带有约束的优化函数模型,利用自主开发的优化设计程序对目标优化函数模型进行了非线性优化,获得了加热冷却管道和电加热元件的优化布局和尺寸,并模拟验证了优化设计的有效性。通过优化设计可有效提高模具的热响应效率、改善型腔表面温度分布的均匀性和减小模具承受的最大等效热应力。基于响应曲面法和开发的多目标优化设计程序,分别实现了液晶电视机面板蒸汽加热和电加热快速热循环注塑模具型腔板结构的优化设计,研究结果对提高快速热循环注塑工艺的成品率、生产效率和模具使用寿命具有十分重要的作用。以蒸汽加热快速热循环注塑模具为例,通过三维有限元传热分析和热-结构分析,研究得到了模具加热过程中型腔板内部温度场和应力场的分布规律,试验验证了传热分析结果的有效性。基于应力分析结果,对型腔板进行了疲劳模拟分析,实现了快速热循环注塑模具疲劳寿命的预测和评估,并分析讨论了模拟预测结果与实际结果之间存在一定差距的原因,结合热-结构分析结果和注塑模具的实际疲劳失效形式,揭示了模具的疲劳破坏机制。研究了模具型腔表面温度、锁模力、型腔板固定方式、模具加热系统等对快速热循环注塑模具疲劳寿命的影响规律,为快速热循环注塑工艺参数的合理控制和模具结构的优化设计提供了理论依据和科学指导。研究了快速热循环注塑工艺的模拟技术,通过对快速热循环注塑工艺和常规注塑工艺的注塑模拟,对比分析了快速热循环注塑工艺对熔体填充能力、塑件形状尺寸精度、表面缩痕、冷却时间和光学性能的影响。针对基于单侧模具快速加热和快速冷却技术的快速热循环注塑工艺存在的塑件翘曲变形问题,分析揭示了塑件翘曲变形的机理,研究了保压控制和模具冷却控制对塑件翘曲变形和缩痕深度的影响规律,提出了优化的保压控制和模具冷却策略,实现了保压参数和模具冷却参数的优化设计。基于优化的保压控制和模具冷却控制策略,进一步研究了快速热循环注塑工艺的注射速率、熔体温度、型芯侧模具温度等工艺参数对塑件翘曲变形和缩痕深度的影响规律,建立了可用于塑件翘曲变形和缩痕深度预测的数学模型,以减小塑件的翘曲变形和缩痕深度为目标,构建了有约束的优化函数模型,利用自主开发的优化设计程序,实现了快速热循环注塑工艺的优化设计。实际生产结果表明,经优化设计的快速热循环注塑工艺有效减小了塑件的翘曲变形和减轻了塑件的表面缩痕,从而显著简化了快速热循环注塑工艺的调试过程,有效提高了快速热循环注塑工艺的成品率。研制了可生产有／无熔接痕标准拉伸试样、冲击试样和热变形试样的电加热快速热循环注塑模具,对模具的加热系统和流道系统进行了优化设计,利用自主研发的动态模温控制系统,构建了电加热快速热循环注塑试验线。开发了基于薄膜热电偶、数据记录仪和计算机的模具型腔表面温度测量和采集系统,试验研究了电加热快速热循环注塑模具型腔表面的温度响应规律。通过试验设计,定量分析了模具加热时间和冷却时间对热循环过程中型腔表面最高温度和最低温度的影响,利用回归分析技术拟合建立了可用于模具型腔表面最高温度和最低温度控制的数学模型,并对构建的数学模型进行了试验验证。建立了电加热快速热循环注塑模具的热响应分析模型,对热循环过程中模具型腔板的热响应进行了模拟分析,研究了模具型腔板的温度分布规律,通过与试验结果的对比,验证了模拟分析的有效性,分析讨论了电加热元件功率密度对模具加热效率的影响和冷却水温度对模具冷却效率的影响。通过全析因试验设计,系统研究了快速热循环注塑工艺的注射压力、注射速率和模具型腔表面温度对熔体填充能力的影响规律。利用构建的电加热快速热循环注塑试验系统,系统研究了高光塑料、结晶型塑料、无定形塑料、纳米颗粒增强塑料和纤维增强塑料的快速热循环注塑工艺,探明了填充阶段模具型腔表面温度对各种材料塑件表面光泽度、表面粗糙度、熔接痕、形貌结构的影响规律,揭示了低型腔表面温度下混合型塑料和结晶型塑料塑件表面粗糙的机理、高型腔表面温度下增强塑料塑件表面浮纤或悬浮颗粒消失的机制以及玻纤增强塑件表面驼峰型熔接痕的形成机理。系统研究了快速热循环注塑工艺填充阶段的模具型腔表面温度对各种塑料有／无熔接痕塑件拉伸强度和冲击强度的影响规律。更多还原

【Abstract】 Rapid heat cycle molding (RHCM) is a new developed injection molding process based on rapid heating and rapid cooling technologies. Compared with conventional injection molding (CIM), the most notable feature of RHCM is that the injection mold should be rapidly heated to a high temperature before melt filling and rapidly cooled to a low temperature after melt filling. The high cavity surface temperature during melt filling can effectively prevent the premature cooling of the polymer melt and eliminate the frozen layer completely. Therefore, RHCM process can significantly improve the fluidity of the polymer melt and hence increase its transferability of the mold cavity geometry. RHCM process can effectively solve the part surface defects, such as flow mark, jetting mark, weld mark, floating fiber, low glossy, etc., usually appearing in CIM process. In addition, RHCM can be used to mold the plastic part with super-high flow length ratio, the plastic part with micro structure. Besides, RHCM can also significantly reduce injection pressure, injection velocity, packing pressure and clamping force of the molding process. This is of great significance to reduce the dependence of the molding process on large tonnage injection molding machines. Low injection pressure and low injection velocity can reduce the inner stress of the molded plastic part, which is very helpful to reduce shape distortion, improve dimension accuracy and optical performance. Since RHCM parts has extremely high surface appearance and the secondary processing operations for CIM parts, such as polishing, painting and finishing, are not needed any more, it can significantly shorten the production process, effectively reduce production cost, energy consumption and environmental pollution. Altogether, RHCM is a type of high-quality, high-accuracy, energy-saving and also environment-friendly green injection molding process, which has broad application prospects and huge market potential. In this paper, RHCM will be given a systematic and in-depth study in the aspects of technology principle, technological process, dynamic mold temperature control system, mold design and manufacture, equipment and production lines construction, mold thermal response analysis, mold heating and cooling system optimization design, mold fatigue life analysis and optimization, process optimization and experimental research.By analyzing the process principle and dynamic mold temperature control principle of RHCM, two types of new RHCM processes are presented. One based on steam heating is the so-called rapid heat cycle molding with steam heating (S-RHCM) and the other one based on electric heating is the so-called rapid heat cycle molding with electric heating (E-RHCM). The reasonable process steps for the two RHCM processes are presented by analyzing their molding cycle compositions. The corresponding dynamic mold temperature control system for the two RHCM processes are developed and manufactured based on programmable logic controller and touch panel techniques. S-RHCM mold and E-RHCM mold for a type of large LCD TV panel are also designed and manufactured. The thermal response efficiency of the two RHCM molds is evaluated by heat transfer analysis. In order to achieve uniform heating and cooling the mold cavity surface with complex geometry, a new S-RHCM mold structure with conformal heating and cooling channels and a new E-RHCM mold structure with conformal heating elements are presented. With the developed dynamic mold temperature control systems and RHCM molds, S-RHCM production lines and E-RHCM production lines for LCD TV panels are constructed. The test production results show that the developed RHCM processes can significantly improve the surface appearance of the plastic part by eliminating weld marks and increasing surface gloss, and at the same time the molding cycle time of RHCM is very close to that of CIM. Several types and series of dynamic mold temperature control systems and RHCM molds are developed and manufactured and a large application of the developed RHCM processes are achieved.Heat transfer in the molding systems of S-RHCM and E-RHCM are investigated and the corresponding thermal balance equations are presented and deduced. Based on the developed thermal balance equations, the factors affecting the heating and cooling efficiency of the RHCM mold are analyzed and hence the design guidelines for S-RHCM mold and E-RHCM mold are proposed. The thermal response analysis models for S-RHCM mold and E-RHCM mold are constructed. Heat transfer analysis based finite element method (FEA) is performed to investigate the thermal response of the mold cavity surface. The effect of the insulation layer and mold materials on thermal response efficiency and temperature uniformity of the mold cavity surface are also investigated. According to the thermal response analysis results, the heating efficiency, cooling efficiency and energy consumption of the two RHCM processes are calculated and compared. Some useful guidelines are presented for mold optimization design and application of the two RHCM processes. A new E-RHCM mold structure with a floating cavity block or cooling plate is developed to reduce the thermal inertia of the cavity block that has to be rapidly heated and cooled. Thermal response analysis results show that the new developed E-RHCM mold structure can significantly improve the thermal response efficiency of the mold cavity surface. Based on the new E-RHCM mold structure, a new large E-RHCM mold for a type of LCD TV panel is developed. The tricks in design, manufacture and assembly of the new E-RHCM mold are also discussed and some useful guidelines are presented. The effect of different types of heating/cooling medium, heating/cooling medium temperatures, heating and cooling channels distribution, mold material and plastic part thickness on thermal cycle efficiency and temperature uniformity of S-RHCM process are also investigated by heat transfer analysis. Based on the analysis results, some guidelines for improving heating system design, cooling system design and mold design of S-RHCM process are presented. Finally, the effectiveness of heat transfer analysis is verified by comparing the analysis results with the theoretical results.The effect of the heating/cooling channels distribution on thermal response efficiency, temperature uniformity and fatigue life of the S-RHCM mold and the effect of the electric heating elements distribution on thermal response efficiency, temperature uniformity and fatigue life of the E-RHCM mold are both systematically investigated based on response-surface experimental design and thermo-structural coupling analysis. With the experimental design and analysis results, least squares regression analysis is used to fit the response surface models for the three objective variables including the required mold heating time, the maximum temperature difference of the cavity surface and the maximum von mises stress. The significance and effectiveness of the constructed response surface models are then verified by ANOVA analysis and random experiments. Three different optimization design strategies including heating efficiency priority, temperature uniformity priority and fatigue life priority are proposed for optimization design of the S-RHCM mold and E-RHCM mold. The optimization function models for the three optimization strategies are built accordingly. A multi-objective particle swarm optimization algorithm (MOPSO) is then developed to solve the optimization problems. The optimization results show that heating efficiency, temperature uniformity and fatigue life of the mold can be improved significantly. Finally, the developed optimization design method based on MOPSO is used to achieve optimization design of the cavity blocks for a large LCD TV panel S-RHCM mold and E-RHCM mold. Based on the optimization design, the heating efficiency and temperature uniformity of the mold are greatly improved, which is of great significance to increase production yield, production efficiency and service life of the S-RHCM mold and E-RHCM mold.Three-dimensional finite element heat transfer analysis and thermo-structural coupling analysis are used to investigate thermal response, temperature distribution, and thermal stress distribution of the S-RHCM mold cavity block. Thermal response experiment of the S-RHCM mold is performed to verify the effectiveness of the heat transfer analysis. The fatigue analysis based on thermo-structural coupling analysis is further performed to evaluate the fatigue life of the S-RHCM mold. The reason for the difference between the estimated fatigue life and the actual fatigue life is discussed. According to the thermal stress analysis results and the actual failure mode of the S-RHCM mold, the thermal fatigue failure mechanism is proposed. Finally, the effect of the mold cavity surface temperature, clamping force, installation of the cavity block and mold heating system on fatigue life of the S-RHCM mold and E-RHCM mold is investigate by thermo-structural coupling analysis. Some useful guidelines for the process control and mold design are presented to improve the fatigue life of the S-RHCM mold and E-RHCM mold.Simulation technologies for RHCM process are investigated and Moldflow is successfully used to simulate the new molding process. Based on the simulation results of RHCM process and CIM process, the effect of RHCM process on melt filling ability, part shape and dimension accuracy, sink mark, cooling time and birefringence is investigated. The mechanism for part large warpage of the RHCM process in which only the cavity side of the mold is rapidly heated and cooled is proposed. The effect of the packing control and mold cooling control on the part warpage of the RHCM process is investigated by simulation so as to achieve optimization design of the packing process and cooling process. The optimization results show that the warpage and sink depth of the plastic part can be greatly decreased with the optimum packing and cooling control. Based on the optimum packing and cooling control, the effect of RHCM process parameters including injection velocity, melt temperature and the mold temperature of core side and packing pressure on warpage and sink depth of the molded part is further investigated. The quadratic polynomial mathematic models are developed to predicate warpage and sink depth of the plastic part. ANOVA is performed to analyze the significance of the developed mathematic models and also the design variables. Random experiments are used to verify the effectiveness and accuracy of the developed mathematic models. The optimization function model is built with the objective to reduce warpage and sink depth of the part. The developed MOPSO is then used to solve the optimization function model and acquire the optimum process parameters. Finally, actual RHCM production with the optimum parameters on the S-RHCM production line is performed to verify the effectiveness of the optimization design.An E-RHCM production line which can produce standard tensile specimens, impact specimens and heat deflection specimens with/without weld lines is constructed for experimental research of RHCM process. The heating system of the E-RHCM mold is optimized to ensure a uniform heating of the cavity surfaces and the runner system of the E-RHCM mold is also optimized to achieve balance filling of the mold cavities. A cavity surface temperature measurement and acquisition system is developed and built based on thin-film thermocouple, data logger and computer, which is then used to investigate the thermal response of the cavity surfaces. Full factorial experimental design is used to research the effect of the molding heating time and cooling time on the maximum temperature and minimum temperature of the cavity surfaces. Based on the experimental results, regress analysis is applied to develop the mathematical relationships between the design variables of mold heating time and mold cooling time and the objective variables of the maximum temperature and the minimum temperature of the cavity surfaces. The external random experiments are also performed to confirm the accuracy of the developed mathematic relationship models. Thermal response simulation based on FEA is performed to investigate the temperature variety of the cavity surfaces during rapid heating and cooling cycles. The thermal response of the cavity surface acquired by experiments is used to verify the effectiveness of the heat transfer simulation. After verification, thermal response simulation is then used to investigate the effect of power density of the electric heating elements on mold heating efficiency and the effect of cooling water temperature on mold cooling efficiency. With the E-RHCM experimental production line, the effect of injection pressure, injection velocity and mold cavity surface temperature on melt filling ability is investigated by experimental study. The RHCM processes of the high glossy plastics, crystalline plastics, amorphous plastics, nano-particle reinforced plastics and fiber reinforced plastics are systematically and in-depth researched. The effect of the mold cavity surface temperature on surface gloss, surface roughness, weld mark and structural morphology is analyzed. Based on this, the mechanisms for high roughness of the mixed plastics and crystalline plastics with a low cavity surface temperature, the elimination of the floating particles or fibers of the reinforced plastics with a high cavity surface temperature and also the hump-shaped weld mark for the fiber reinforced plastics are proposed. Finally, the effect of the cavity surface temperature in RHCM process on tensile strength and impact strength of the plastic part with/without weld lines for different plastics are systematically studied. The mechanisms for the variety of the plastic part strength with the temperature changes are in-depth analyzed and discussed.更多还原