应用Taguchi实验设计法最小化注塑成型制品沉降斑

基于注塑成型充填后的充填模拟，应用Taguchi实验设计(DOE)技术，采用L9(3^4)正交矩阵进行实验，并采用变量分析(ANOVA)研究了工艺参数对制品内最大沉降斑的影响，优化工艺参数以使注塑制品内的沉降斑指数最小，从而提高制品质量。     

Compression molding of sheet molding compounds in plate-rib type geometry

The flow of fiber-reinforced composite materials in a plate-rib type mold geometry during compression molding was investigated using a series of sheet molding compounds (SMC). Material anisotropy in relation to the amount and the length of reinforcing fibers was analyzed. The influence of the interfacial friction between SMC charge and the mold surface on the flow and sink mark formation was also examined. The results were explained qualitatively by computer simulation.     

Effects of Process Parameters and Two-Way Interactions on Sink Mark Depth of Injection Molded Parts by Using the Design of Experiment Method

Sink mark is one of the flaws occurring on the surface of injection-molded parts caused by inappropriate mold design and process parameters. Sink marks are often quite visible and significantly impair the surface quality of the parts. In this reports, an L27(3¹³) experimental matrix designed based on the Taguchi method was conducted to investigate the effect of process parameters and two-way interactions on sink mark depth of injection molded parts, and to minimize the sink mark depth. The relative significance of each processing parameter on the sink marks was analyzed using analysis of variance (ANOVA) and F-test. A plate cavity with bosses of various thicknesses was used in the investigation. Experiments were carried out on a CJ80E II injection-molding machine, and sink mark depths were measured by a movable bridge 3D COMERO. For the factors and interactions selected in the main experiments, the boss thickness and melt temperature were found to be the principal factors affecting sink mark formation in injection-molded parts. Experimental investigation can help to understand the formation mechanism of sink marks, and to optimize the surface quality of injection-olded parts.     

Effect of two stage pressure molding on surface quality of sheet molding compounds

The goal of this work was to investigate the effect of two stage pressure molding on the compression molding of a sheet molding compound (SMC). It has been shown in previous studies that a rapid drop in pressure during SMC curing significantly reduced severity of sink marks. This study concentrated on a method of predicting the optimum time during curing to release pressure by examining material behavior through process data from in-mold sersors. A simple control scheme was them applied for automatic pressure release at the optimum time corresponding with the peak of the material expansion and the onset of the reaction exotherm.     

Flow behavior of stampable sheet with a rib part

The effect of die design on the flow characteristics of compression molded three-layer long glass fiber reinforced polypropylene composite, known as “stampable sheet,” was investigated. The flow behavior of each layer was observed by optical and soft X-ray photographs. The fiber flow length into the rib part was measured by an image processing system. The results showed that during compression resin exudation occurred and that this depended on the die's rib width. Thus, the larger the rib width, the lower the amount of resin exuded. Resin exudation was found to occur earlier in a die with zero fillet radius. The fiber flow length into the rib part was enhanced by using a die with a large fillet radius. The results were confirmed by a short-shot molding process. In this process, the stamping operation was stopped short of making a complete part. A finite element method was used to study the flow process. The results agree with the experimental results confirmed by short-shot molding.     

Optimization of polyester sheet molding compound. Part I: Experimental study

A series of differential scanning calorimetry (DSC) and molding experiments were carried out to measure the effect of curing agents, namely initiators and inhibitor, on the SMC reaction. Results showed that the induction time, the reaction rate, and the limiting conversion of sheet molding compounds can be modified through the change of curing agents. The SMC resin with a higher concentration of low temperature initiator and molded at higher temperature may cure in a shorter period of time and reach a higher conversion. The shortened scorch time and shelf life can be balanced by adding small amount of inhibitor. Surface quality of molded SMC parts measured by solvent extraction process showed that limiting conversion is an important factor in SMC molding.     

Cure analysis of sheet molding compound in molds with substructures

The effects of material flow, heat transfer, part geometry, and curing agents on the cure of sheet molding compounds (SMC) in molds with substructures were analyzed both experimentally and numerically. It was found that heat transfer during mold filling has a profound effect on the cure pattern, especially for fastcure resins molded for parts with thin dimensions.     

Investigation of the Effect of Molding Variables on Sink Marks of Plastic Injection Molded Parts Using Taguchi DOE Technique

The quality of an injection molded part is affected by material properties, mold geometry, process conditions etc. Obtaining optimum process conditions and mold design is the key problem to improve the part quality. Sink mark is one of several important flaws of injection molded parts. In this article, numerical simulation is combined with Taguchi design-of-experiment (DOE) technique to investigate the influence of process conditions and cavity geometry on sink mark of the injection molded part and optimize process conditions and cavity geometry. An L18(3⁷) orthogonal array based on the Taguchi method was conducted to minimize the sink marks of injection molded parts, and the significance of each factors on sink mark was investigated. For the factors selected in the main experiments, part thickness, holding pressure, melt temperature and mold temperature were found to be the principal factors affecting the sink marks of the injection molded parts.     

注塑件成型缺陷分析与解决方案

针对耳罩圈注塑件填充不足和熔接痕的缺陷问题,本文从注塑模具浇注系统分析入手,找出存在的问题,制订出改正措施,并最终解决了这些缺陷问题;在针对使用一模六腔模具成型的护盖注塑件存在缩痕缺陷的问题,通过采用了控制流入模具型腔熔体量平衡的方法,最终达到了消除注塑件缺陷的目的;针对薄壁壳体注塑件变形等缺陷的问题,则采用了脱件板方...     

Applications of flow simulation in reactive processing for cases in which the filling stage can be decoupled from heat transfer and chemical reaction

Flow simulation to predict the position of the flow front during SMC and IMC compression molding, RIM, SRIM, and RTM, is very useful in obtaining better molded parts. We have derived criteria to determine when the filling stage for these processes can be decoupled and simulated without regard to heat transfer and chemical reaction. We discuss why a Generalized Hele-Shaw model can be used to predict the flow front. Examples are given of the use of flow simulation in designing and locating SMC charges so as to reduce or eliminate knit lines, in locating IMC injection ports so as to avoid trapping air, in locating RIM injection gates to avoid trapping air and minimize knit-lines, and in locating vents to avoid trapping air in RTM or SRIM molding.     

Improving surface quality of microcellular injection molded parts through mold surface temperature manipulation with thin film insulation

Microcellular injection molding offers many advantages such as material and energy savings, reduced cycle times, and excellent dimensional stability. However, typical surface characteristics of microcellular injection molded parts—such as gas flow and swirl marks and a lack of smoothness—have precluded the process from being used for applications where surface appearance is important. This article presents an insulator‐assisted method that has been shown to improve the surface quality of microcellular injection molded parts significantly. By incorporating a thin film (75–225 μm) of polytetrafluoroethylene (PTFE) insulator on the mold surface, the polymer melt–insulator interfacial temperature can be manipulated and can be kept high enough during mold filling to reduce or eliminate swirl marks on the surface. The experimental results in terms of surface roughness and surface profile of conventional and microcellular injection molded parts with and without the insulator film are discussed. Thermal analyses of the corresponding microcellular injection molding experiments were performed to elucidate the correlation between film thickness, interfacial temperature, and the surface quality. The effect of insulator on the cooling time increase is also analyzed and presented. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

基于MPI的汽车内置储物盒注塑模具优化设计

以某汽车内置储物盒为研究对象,结合聚合物流变学的基本理论,采用Moldflow软件对汽车内置储物盒注射成型进行模流分析。针对储物盒制件在注射过程中出现的表面缩痕严重、达到顶出温度的时间长和翘曲量大等诸多缺陷,将实体模型的浇注系统和冷却系统等进行重新设计。通过对各个质量评价指标进一步分析发现,优化后储物盒制件的各种缺陷消除或减小,缩痕指数由0.638 2~4.009降低为零、零件达到顶出温度的时间由37.92~92.68 s降低到19.87~21.40 s、总翘曲量由1.166~1.782 mm降低到0.024 0~0.416 5 mm,优化效果明显。在此基础上进行汽车内置储物盒注塑模具的设计,并试模加工出了合格的制件。     

Powder coating of sheet molding compound (SMC) body panels

Sheet Molding Compound (SMC) compression molded parts are prone to porosity. During top coat baking, trapped air in the surface porosity expands and often blows through the paint leaving unacceptable craters in the final finish. The accepted solution to this problem in the SMC industry is to use a coating compound on the SMC part. The coating compound (called in‐mold coating (IMC)) is injected and cured on the SMC molding after its cure is complete, but before removing it from the mold. Another potential solution is to powder coat the parts once they have been de‐molded. While powder coating adds time to the process, it is performed outside of the mold and frees the mold for the next molding cycle earlier than if the IMC process is used. In the present paper, we develop a simplified model for the powder coating of plastic parts. We show how the model can be combined with chemo‐rheological measurements to guide the optimization of the process and material parameters. Although with the powders currently available, the surface appearance is inferior to the one obtained with IMC, this process shows potential.     

气体辅助注塑成型带加强筋平板的翘曲试验研究

注塑制品翘曲变形是一种严重缺陷,本文基于带加强筋平板制品实验研究了气体辅助注塑成型工艺参数对制品翘曲的影响规律及其原因,结果表明:熔体预注射量、气体压力及气体保压时间和气体压力清零时间对制品翘曲影响较大。熔体温度、延迟时间和保压压力影响较小。     

A novel method for improving the surface quality of microcellular injection molded parts

Microcellular injection molding is the manufacturing method used for producing foamed plastic parts. Microcellular injection molding has many advantages including material, energy, and cost savings as well as enhanced dimensional stability. In spite of these advantages, this technique has been limited by its propensity to create parts with surface defects such as a rough surface or gas flow marks. Methods for improving the surface quality of microcellular plastic parts have been investigated by several researchers. This paper describes a novel method for achieving swirl-free foamed plastic parts using the microcellular injection molding process. By controlling the cell nucleation rate of the polymer/gas solution through material formulation and gas concentration, microcellular injection molded parts free of surface defects were achieved. This paper presents the theoretical background of this approach as well as the experimental results in terms of surface roughness and profile, microstructures, mechanical properties, and dimensional stability.     

Study on the packing effects of external gas‐assisted injection molding on part shrinkage in comparison with conventional injection molding

Applying gas pressure on the reverse side of the part that called external gas‐assisted injection molding (EGAIM) has the potential to solve shrinkage‐related molding problems. We investigate the packing effects of EGAIM on part shrinkage and sink mark under various rib design and compare it to that of conventional injection molding (CIM). It was found that EGAIM has uniformly distributed packing pressure within the entire mold cavity. To achieve equivalent part shrinkage, CIM requires 100 MPa packing pressure from the molding machine, whereas EGAIM requires only 9 MPa. EGAIM can further reduce part shrinkage if the gas pressure and gas packing time are both increased. EGAIM can also eliminate sink marks for rib designs of an aspect ratio (rib width /part thickness) up to 1.2, whereas CIM can achieve the same sink mark level only at an aspect ratio of less than 0.5. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

优化带加强筋ABS材料制件沉降斑的气体辅助成型技术

详细介绍了气体辅助注射成型的物理过程及其关键工艺参数对成型的影响。以带加强筋的绣花机外壳为例,考察了传统注射成型与气体辅助注射成型的优缺点。针对气体辅助注射引入的新工艺参数,介绍了一种CAE技术与统计学的Taguchi正交实验相结合的方法,设计L9(34)正交实验表在可成型范围内寻求最优工艺参数。结果表明,气体辅助技术能减少原料,对有加强筋的制件能有效地去除沉降斑、减弱不均匀收缩及减少内应力,大大改善制件的表面质量,增强制件尺寸的稳定性。     

Influence of initiator on the curing of unsaturated polyester resin at 100 °C

Sheet molding compound (SMC) parts are fiber‐reinforced unsaturated polyester (UP) composites molded at 140–170 °C under a pressure of 60–100 bar. For economic and ecological reasons, the aim of this research project is to develop new SMC formulations to modify the molding conditions. For this, SMC formulations were modified and optimized to decrease the molding temperature to 100 °C. The strategy was to change the catalytic system (peroxides) in order to obtain highly reactive formulations at 100 °C. First, the temperatures of initiation of the reaction were determined by rheological and DSC measurements for each peroxide. Second, the UP resin crosslinking kinetics were measured for the various peroxides during an isothermal curing at 100 °C. The results obtained with the three experimental methods are compared and discussed. Finally, the laboratory analyses were validated by SMC molding trials. © 2019 Society of Chemical Industry     

Evaluation of molecular orientation in injection molded parts with microscale features by Raman spectroscopy

Molecular orientation of polycarbonate (PC) in injection‐molded parts with microscale features was characterized by means of polarized Raman spectroscopy, and the relationship between microstructure and replication was discussed. The microscale feature size of continuous v‐groove was 20 μm in depth and 50 μm in width. PC injection‐molded parts were molded with various molding conditions. The molecular orientation distribution along flow direction on the cross‐section of molding parts were evaluated by the intensity ratio of the bands at 635 to 703 cm^?1 (I₆₃₅/I₇₀₃) in the Raman spectra. Molecular orientation along the flow direction inside the v‐groove was higher than that of the core and the opposite surface region. In particular, the highest molecular orientation was at the surface of the v‐groove. Among the injection molding conditions, the mold temperature showed significant effect on the molecular orientation and replication. Higher mold temperature caused high replication and low molecular orientation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009