Birefringence measurement for validation of simulation of precision glass molding process

During fabrication of glass lens by precision glass molding (PGM), residual stresses are setup, which adversely affect the optical performance of lens. Residual stresses can be obtained by measuring the residual birefringence. Numerical simulation is used in the industry to optimize the manufacturing process. Material properties of glass, contact conductance and friction coefficient at the glass‐mold interface are important parameters needed for simulations. In literature, these values are usually assumed without enough experimental justifications. Here, the viscoelastic thermo‐rheological simple (TRS) behavior of glass is experimentally characterized by the four‐point bending test. Contact conductance and friction coefficient at P‐SK57? glass and Pt‐Ir coated WC mold interface are experimentally measured. A plano‐convex lens of P‐SK57? glass is fabricated by PGM for two different cooling rates and whole field birefringence of the finished lens is measured by digital photoelasticity. The fabrication process is simulated using finite element method. The simulation is validated, for different stages of PGM process, by comparing the load acting on the mold and displacement of the molds. At the end of the process, the birefringence distribution is compared with the experimental data. A novel plotting scheme is developed for computing birefringence from FE simulation for any shape of lens.     

Experimental investigation of contact heat transfer coefficients in nonisothermal glass molding by infrared thermography

Nonisothermal glass molding has recently become a promising technology solution for the cost-efficient production of complex precision glass optical components. During the molding process, the glass temperature and its temperature distribution have crucial effects on the accuracy of molded optics. In nonisothermal molding, the glass temperature is greatly influenced by thermal contact conductance because there is a large temperature difference between the glass and mold parts. Though widely agreed to be varied during the molding process, the contact conductance was usually assumed as constant coefficients in most early works without sufficient experimental justifications. This paper presents an experiment approach to determine the thermal contact coefficient derived from transient temperature measurements by using infrared thermographic camera. The transient method demonstrates a beneficially short processing time and the adequate measurement at desirable molding temperature without glass sticking. Particularly, this method promises the avoidance of the overestimated contact coefficients derived from steady-state approach due to the viscoelastic deformation of glass during the inevitably long period of holding force. Based on this method, the dependency of thermal contact conductance on mold surface roughness, contact pressure, and interfacial temperature ranging from slightly below-to-above glass transition temperature was investigated. The results reveal the dominance of interfacial temperature on the contact conductance while the linear pressure-dependent conductance with an identical slope observed for all roughness and mold temperatures. The accurate determination of the contact heat transfer coefficients will eventually improve the predictions of the form accuracy, the optical properties, and possible defects such as chill ripples or glass breakage of molded lenses by the nonisothermal glass molding process.     

玻璃纤维毡增强聚丙烯在压缩模塑流动过程中的纤维分布

通过测定玻璃纤维毡增强聚丙烯经挤压流动后不同区域的纤维含量,研究了基体树脂,增强材料的结构与性质,坯料设计,模具温度及坯料的预热温度等对玻璃纤维毡增强聚丙烯在压缩模塑流动过程中纤维发布的影响。结果表明,适当提高基体的粘度及采用多层坯料叠层的坯料设计方法,有利于制品内纤维的均匀分布;针刺密度适当的连续针刺毡及由短切纤维组成的复合针刺毡与聚丙烯形成的复合材料（GMT0,在压缩模塑的流动过程中纤维分布的均匀性较好,随着针刺密度的增加,纤维分布的均匀性下降;用粘结剂粘结而成的连续原丝毡与聚丙烯复合得到的GMT材料,纤维分布的均匀性较差,经适当针刺以后,纤维分布的均匀性得到一定程度的改善,过低的模具温度及坯料预热温度,会引起材料充模流动能力下降,但模具温度及坯料预热温度过高时,流动前沿区域的树脂富集现象将加剧。     

Influence of oxygen incorporation on infrared transmission of ternary Ge-Sb-Se chalcogenide glass in the compositional range for use in infrared-imaging applications

Optical transmission window of ternary Ge-Sb-Se glass extends up to ∼15 μm, thus being transparent across the long-wavelength infrared (LWIR; 8–12 μm) range. Along with its superior thermal stability as to the precision glass molding (PGM) process, this Ge-Sb-Se glass is most well-known as the material of choice for LWIR-imaging lens applications. Presence of oxygen atoms on the surface and/or in the interior of LWIR-transmitting chalcogenide glass needs to be allowed to a tolerable amount; otherwise, its LWIR transmittance is deteriorated due to the vibrational excitations of oxygen-related bonds. In this study, we take into consideration ternary Ge-Sb-Se glasses as an exemplary case to get a clear grasp on correlations between oxygen incorporation and LWIR transmittance of chalcogenide glass: Surface oxidation turns out to be insignificant to the LWIR transmittance, but presence of oxygen inside the glass is reconfirmed to exert a strong influence. It is verified that the oxygen-related absorption peak located at ∼800 cm^-1 is mainly dominated by Ge–O vibrations; however, its position tends to redshift with increasing Sb content, implying indirect involvement of Sb atoms. Also verified is that the surface of Sb powders chosen as a starting material is more vulnerable to oxidation than the surface of Ge powders. This observation makes it reasonable to assume that Ge–O bonds are preferentially formed, at the expense of Sb–O bonds, during melting of the starting materials.     

非球面玻璃模造用碳化钨模仁磁控溅射铼-铱镀膜工艺优化

通过钽过渡镀层与铼-铱复合镀层相结合的膜层结构,解决了非球面玻璃模造碳化钨模仁热压寿命短、沾黏等问题。通过离子源和镀膜层厚度参数的优化调整,得到了最佳镀膜工艺和参数,改善了模仁的表面品质,延长了模仁的使用寿命。镀钽膜层15min及铼-铱膜层21min后所得镀膜的总厚度约为270nm,模仁热压寿命可超过3000次。     

Development of stress birefringence and flow patterns during mold fillin and cooling

An experimental study was carried out to investigate the development of stress birefringence patterns of molten polymer during the mold filling and cooling operation. For this study, a rectangular mold cavity with glass windows on both sides was constructed, which permitted us to record on a movie film the changes in stress birefringence patterns in the mold cavity during the molding operation, using a circular polariscope. The mold was equipped with an automatic relay system which closes the shut-off valve when the pressure in the mold cavity reaches a predetermined value. The mold was also equipped with both heating and cooling devices, so that either isothermal or non-isothermal injection molding could be carried out. The mold temperature was controlled by thermistor regulated controllers. During the entire cycle of the molding operation, the mold cavity pressure was continuously recorded on a chart recorder, using a melt pressure transducer. The present study shows how molding conditions (namely, injection pressure, melt temperature, mold temperature) influence the distribution of stress birefringence patterns in a molten polymer while it is being injected into, and cooled in, a rectangular mold cavity.     

Precision Glass Molding: Validation of an FE Model for Thermo-Mechanical Simulation

In precision glass molding process, the required accuracy for the final size and shape of the molded lenses as well as the complexity of this technology calls for a numerical simulation. The current paper addresses the development of an FE model for thermo-mechanical simulation of the precision glass molding process including heating, pressing, and cooling stages. Temperature-dependent viscoelastic and structural relaxation behavior of the glass material are implemented through a FORTRAN material subroutine (UMAT) into the commercial FEM program ABAQUS, and the FE model is validated with a sandwich seal test. Subsequently, precision molding of several glass rings is performed at three different pressing temperatures, and the experimental deformation of the glass rings at the end of the molding is compared with the predicted ones from FE simulation. Furthermore, the transient and residual stress distribution inside the glass rings are calculated by the developed FE model, and the effects of some important process parameters such as interface friction and mold temperature on the FE results are assessed. The developed FE model can be employed to predict the deformation behavior, final size/shape, and the residual stress state inside the glass lenses in a precision glass molding process.     

Unusual Indentation Behavior of Alkali Metaphosphate Glass Above Glass Transition Temperature

The mixed alkali metaphosphate glass 12.5Li₂O–12.5Na₂O–12.5K₂O–12.5Cs₂O–50P₂O₅ (mol%) compressed under uniaxial stress shows unusually large recovery of its shape during heating above its glass transition temperature (T_g). To clarify the mechanism, the viscous, elastic, and plastic behavior of the metaphosphate glass was investigated with the depth‐sensing indentation method. From the load‐displacement (P–h) curves of the glass, a large recovery of the depth displacement was found during unloading above T_g. By analyzing the P–h curves with a viscous–elastic–plastic model, the large recovery was concluded to be due to larger elastic deformation than viscous deformation even above T_g. The phenomenon can be attributed to relaxation to the randomly oriented ‐P–O–P– chain structure from the oriented chain structure formed under stress in the metaphosphate glass .     

玻璃纤维增强聚丙烯制品翘曲变形的研究

针对玻璃纤维增强聚丙烯(PP/GF)注射成型制品存在的翘曲变形缺陷,研究了注射工艺参数如模具温度、喷嘴温度、注射速率、保压压力和保压时间对制品成型收缩率及翘曲的影响。结果表明,随着模具温度、喷嘴温度和保压压力的降低,制品的翘曲减小;适当提高注射速率和减少保压时间也可减小制品翘曲。     

Isocyanate trimerization kinetics and heat transfer in structural reaction injection molding

Guidelines are developed for molding large composite parts via structural reaction injection molding using glass preforms and polyisocyanurate resins. These are based on numerical simulations of the simultaneous heat transfer and reaction kinetics of a commercial system during and after mold filling. Premised requirements are that resin does not gel before the mold is filled, yet, reactions are sufficiently vigorous to approach completion. An existing mechanistic kinetic model is used and material parameters found from a chemical kinetics study employing an insulated cup. It is found desirable to use a high mold temperature and a low preform temperature in molding. Nondimensionalization of the governing equations reveals the existence of a Nusselt number (N_u), which describes the relative importance of heat transfer between resin and glass relative to thermal diffusion to the mold wall. With a Nusselt number of about 50 or higher it is possible to use the cooling capacity of the preform to extend gel time. The magnitude of N_u is influenced by part thickness, glass fraction, strand diameter, and flow velocity. Thus, the effect of the preform on extending resin gel time is within control of the molder.     

汽车A柱下饰板注射成型工艺仿真分析

采用正交试验和Moldflow数值模拟相结合的方法,对汽车A柱下饰板的注射成型过程进行了分析,研究了模具温度、熔体温度、注射时间和保压压力等工艺参数对残余应力和翘曲变形的影响。通过极差分析得到,熔体温度对翘曲变形影响最大,保压压力对残余应力影响最大,最佳工艺参数组合为模具温度40 ℃,熔体温度205 ℃,注射时间5 s,保压压力45 MPa;通过仿真分析与实际成型方案进行比较,汽车A柱下饰板的翘曲变形由3.847 mm降为3.121 mm,残余应力由66.95 MPa降为65.21 MPa。     

黏弹特性对模内微装配成型热流固耦合变形的影响

建立了综合考虑二次成型黏弹性熔体充填流动约束环境影响的模内微装配成型过程黏弹性热流固耦合变形机理的理论模型,并通过有限元数值模拟,研究了二次成型熔体黏度对模内微装配成型过程黏弹性热流固耦合变形的影响规律。结果表明,黏弹性热流固耦合作用诱导的预成型微型轴变形的驱动力来源于微装配界面形成的热流固耦合压力和黏性拖曳剪应力,而二次成型熔体流动的弹性正应力对耦合变形具有抑制作用,微装配界面的热流固耦合载荷和微型轴的变形均随着二次充填熔体的黏度增大而增大,减小二次成型熔体黏度有利于提高其微装配加工精度。     

Adhesive strengths between glass fiber‐filled ABS and metal in insert molding with engraved and embossed metal surface treatments

Metal and plastic can be bonded in a single molding process by metal insert molding, in which a metal is inserted into a mold and a plastic resin is then injected. However, the adhesive strength at the interface between the metal and plastic is weakened by the difference in the shrinkage ratio and inherent differences between the materials in the metal insert molding. This study reports the treatment of a metal surface that is followed by inserting the metal into a mold to increase the adhesive strength between the metal and glass fiber (GF)‐filled acrylonitrile butadiene styrene (ABS). A laser process was used for an engraving surface treatment and a plating process was performed for an embossed surface treatment of the metal. In addition, the adhesive strength between the metal and GF‐filled ABS was evaluated after the insert molding process was completed. Particles such as glass beads, ceramic beads, artificial diamonds, and aluminum oxides were employed in the plating process. The adhesive strength varied depending on the surface treatment of the metal. In particular, the adhesive strength significantly increased when an undercut shape was formed at the metal surface. The best adhesive strength with GF‐filled ABS was found in the metal specimen plated using aluminum oxide particles. POLYM. ENG. SCI., 59:E93–E100, 2019. © 2018 Society of Plastics Engineers     

低密度长玻纤增强聚氨酯复合材料的力学性能

介绍了低密度长玻纤增强反应注射成型聚氨酯复合材料的制备工艺,研究了玻纤含量和模具温度对复合材料的拉伸性能、弯曲性能和冲击性能的影响.结果表明,当玻纤质量分数为30%、模具温度为50℃时,复合材料表现出优良的力学性能,这一结果在实际生产中也得到了验证.     

Experimental study of shrinkage and ejection forces of reinforced polypropylene based on nanoclays and short glass fibers

This study presents the influence of nanoclays and glass fibers on the shrinkage and ejection forces of polypropylene‐based composites for tubular parts produced by injection molding. An instrumented mold was used to measure cavity pressure, surface temperature and ejection forces in the tubular parts during the injection cycle. The materials used for the study were polypropylene homopolymer Domolen 1100L, nanoclays for polyolefin nanocomposites (P‐802 nanoMax, used in percentages of 2%, 6%, and 10%) and reinforced polypropylene homopolymer with a content of 10% and 30% glass fiber (Domolen P1‐013‐V10‐N and Domolen P1‐102‐V30‐N, respectively). Part shrinkage was measured 48 h after production. The results show that the incorporation of nanoclays reduces shrinkage and ejection forces while glass fibers decrease shrinkage and increase ejection forces due to an increase in elastic modulus. Nanoclays decrease the ejection forces when compared to glass fibers and pure PP. The effects of nanoclays are less pronounced than those of glass fibers. Moldings produced with different materials were also analyzed to assess the effect of mold temperature on the ejection forces. Shrinkage rises slightly by increasing the mold temperature while the ejection force decreases. POLYM. ENG. SCI., 58:55–62, 2018. © 2017 Society of Plastics Engineers     

玻璃纤维增强尼龙的注射成型工艺改进

分析玻璃纤维(GF)增强尼龙(PA)制件在注射成型生产中的主要参数设置,从影响注塑制件质量的材料、成型工艺、模具设计、制品设计着手,分析了GF增强PA注塑制件常见表观缺陷产生的原因并提出了相应的解决方法.     

玻璃基体化学镀镍-磷工艺研究

非晶态化学镀玻璃基体可用作计算机磁盘基板针对玻璃表面化学镀镍一磷镀层易出现剥皮、开裂等问题，研究了玻璃基材表面的性质，镍磷合金化学镀层结构、含磷量以及镀层韧性、内应力、结合力等对镀层开裂产生的影响一通过调整镀液成分，优化温度、pH值、施镀时间等工艺参数，获得了玻璃基体化学镀镍一磷的工艺配方     

半芳香族耐高温尼龙PA6T/6I基LDS功能材料制备及性能

采用半芳香族耐高温尼龙聚对苯二甲酸/间苯二甲酸己二胺(PA6T/6I)为树脂基体,铜铬氧化物为激光镭射助剂,制备了PA6T/6I基的激光直接成型(LDS)功能材料。采用扫描电子显微镜对激光镭射助剂分散状态及LDS功能材料模塑器件的表面形貌能进行了表征,使用热失重分析仪、差示扫描量热仪对LDS功能材料的热失重行为、熔融结晶性能进行了表征,研究了激光镭射助剂添加量对LDS功能材料的力学性能、热稳定性、化学镀性能的影响,同时研究了PA6T/6I熔融结晶性能和注塑模具温度对于模塑器件表面、外观的影响。结果表明,偶联剂的添加有利于改善激光镭射助剂在PA6T/6I树脂基体中的分散,其中环氧类的偶联剂KBM–403处理后的LDS镭射助剂分散效果最佳。激光镭射助剂添加量的增加,会造成LDS功能材料拉伸强度、弯曲强度、冲击强度及初始分解温度降低。激光镭射助剂添加量在8%时,预镀铜上镀时间和镀层覆盖时间最短,化学镀效果最佳。当注塑模具温度为175℃时,玻纤增强PA6T/6I基LDS功能材料模塑器件的外观最佳。     

Analysis of mold insert fabrication for the processing of microfluidic chip

The microfluidic chip has been used as an example to discuss different mold insert materials by micro hot‐embossing molding. For the mold insert, this study uses the SU‐8 photoresist to coat on the silicon wafer, then uses UV light to expose the pattern on the surface of SU‐8 photoresist, and coat the seed layer on the SU‐8 structure using thermal evaporation. The micro electroforming technology has been combined to fabricate the mold inserts (Ni, Ni‐Co) followed by replicating the microstructure from the metal mold insert by micro‐hot embossing molding. Different processing parameters (Embossing temperature, embossing pressure, embossing time, and demolding temperature) for the properties of COP film of microfluidic chip have been discussed. The results show that the most important parameter is the embossing temperature for replication properties of molded microfluidic chip. The demolding temperature is the most important parameter for surface roughness of the molded microfluidic chip. The Ni‐Co mold insert is the most suitable mold material for molded microfluidic chip by microhot embossing molding. The bonding temperature is the most important factor for the bonding strength of sealed microfluidic chip by tensile bonding test. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

微型机械运动副模内微组装成型热流固耦合变形模拟

提出了一种新型规模化高效低成本聚合物微型机械系统模内微组装成型加工技术,并针对其成型过程特点,建立了描述模内微组装成型过程成型热流固耦合变形机理的理论模型。通过有限元数值模拟,研究了模壁温度对模内微组装成型过程的影响规律。结果表明,模内微组装成型的微装配加工精度受控于热流固耦合压力场和不均匀温度场,且其热流固耦合变形随着模壁温度的升高而增大;减小模壁温度有利于提高其微装配加工精度。