Theoretical Research On Ultra-thin Plastic Injection And Its Application In LGP Molding

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.