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0第 0 页 共 7 页Modeling and Analysis of Process Parameters for Evaluating Shrinkage Problems During Plastic Injection Molding of a DVD-ROM CoverPlastic injection molding plays a key role in the production of high-quality plastic parts. Shrinkage is one of the most signicant problems of a plastic part in terms of quality in the plastic injection molding. This article focuses on the study of the modeling and analysis of the effects of process parameters on the shrinkage by evaluating the quality of the plastic part of a DVD-ROM cover made with Acrylonitrile Butadiene Styrene(ABS) polymer material. An effective regression model was developed to determine the Mathematical relationship between the process parameters (mold temperature, melt temperature, injection pressure, injection time, and cooling time) and the volumetric shrinkage by utilizing the analysis data. Finite element (FE) analyses designed by Taguchi (L27) orthogonal arrays were run in the Moldow simulation program. Analysis of variance (ANOVA) was then performed to check the adequacy of the regression model and to determine the effect of the process parameters on the shrinkage. Experiments were Conducted to control the accuracy of the regression model with the FE analyses obtained from Moldow. The results show that the regression model agrees very well with the FE analyses and the experiments. From this, it can be concluded that this study succeeded in modeling the shrinkage problem in our application.Keywords：plastic injection molding, regression modeling andANOVA,shrinkage1、IntroductionInjection molding is one of the most efcient processes in mass production of manufactured plastic part with thin-shell features. The quality of the plastic part depends on the material characteristics, the mold design, and the process parameters, one of which is more important. Several studies found that the injection molding process parameters have crucial effects on the quality of the plastic parts. They investigated the problems of the injection molding part such as the shrinkage,warpage, weld line, sink marks, and residual stress generated by the process parameters. Their studies also show that the most important parameters affecting the quality of the plastic parts are packing pressure, melt temperature, and moltemperature. However, these studies did not examine in sufcient depth the effect of the other process parameters including injection time and cooling time. Further, Demirer et al. have conducted an experimental research that evaluates the shrinkage and the warpage 1第 1 页 共 7 页causing to the problems of the part quality . This research also explained that the shrinkage and the warpage increased with increasing the process temperature, decreased with increasing the injection pressure . In this research ,although experimental conditions are enough to provide the valuable results, the major inuential process parameters consisting of the injection time and the cooling time are not considered. In the injection molding of the plastic parts as thin-shell features ,many published paper shave indicated that as tatistical relationship can be built between the process parameters and the problems associated with the shrinkage and the warpage affecting the quality of the plastic parts. In the prior studies, a number of experiments were performed to measure the values of the shrinkage and the warpage under the process parameters. The mathematical models to determine the optimum process parameters were developed by exploiting the measured values. In the similar manner, the regression analysis is utilized to derive the relationship between the process parameters and the shrinkage based on the experimental through the injection molding of thin-shell plastic part. Second-order generalized polynomial regression equations were created to derive this mathematical relationship on the shrinkage by the means of the process parameters. From these, it has also been found that the process playsstatistically a key role in determining the quality of the plastic part. On the other hand, in the studies above, it is not employed any molding simulation tool (Mold ow analysis) for comparing the experimental results.However, there are many articles investigating the simulation of the plastic injection molding which are inuenced by the process parameters on the quality problems. One of the most signicant of these articles is successfully applied by Chen et al. This article deals with the application of computer-aided engineering integrating with statistical technique to reduce the warpage based on the plastic injection parameters. For this purpose, a number of Moldow analyses dependent on the Taguchi orthogonal arrays, the regression equations, and analysis of variance(ANOVA) have been coupled to predict the warpage at various injection parameters. But, this article only summarizes the results of the warpage without those of the shrinkage during the plastic injection molding. Nevertheless, another article performed by Chen et al. has employed for analysis and modeling of effective parameters on the shrinkage variation of injection molded part by exploiting a number of Moldow analyses. In contrast to the mentioned investigations, a different study 2第 2 页 共 7 页was executed by Altan to reduce the shrinkage in Injection molding using Taguchi method, ANOVA, and Neural network. Twenty-seven injection molding experiments were performed to obtain the shrinkage values for two different polymer materials of Polypropylene (PP) and Polystyrene (PS). From this study, it can be seen that an integrated approach is presented to obtain minimum shrinkage corresponding to the best process conditions. As different from the literature above, some researchers only focused on the machining processes which are the Electric Discharge Machining (EDM). In summary, even though these researchers work the different elds, they have employed the similar methods as well as the plastic injection molding. In this study, an effective regression model based on FE analyses obtained from Moldow simulations was created to model the mathematical relationship between the plastic injection process parameters (the mold temperature, melt temperature, injection pressure, injection time, and cooling time) and the volumetric shrinkage using ABS polymer material. Most of the studies in the literature have not considered to all these process parameters. The ranges of the process parameters also differ from the studies in the literature. ANOVA analysis was performed to identify the most significant process parameters and to evaluate the adequacy of the regression model for the shrinkage of the plastic injection molding. Additionally, the experiments for four plastic injection moldings of the plastic part of a DVD-ROM cover were carried out to compare the shrinkage results of the simulated values with the measured values and to prove the accuracy of the regression model created.2. Experimental Methodology2.1 Taguchi Orthogonal Array Design of ExperimentsThe design of experiments utilizing the orthogonal arrays is, in most cases, efficient and easy to use when compared to the traditional experimental design methods. It is necessary to reduce and to control the number of experiments. Furthermore, a large number of experiments have to be performed when the number of process parameters increases. In this study, 27 FE analyses based on Taguchi (L27) orthogonal arrays were run by utilizing plastic injection process parameters such as the mold temperature (T mold), melt temperature (T melt),injection pressure (P inj),injection time(I time),and cooling time (C time) as shown in Table1. The shrinkage parameter corresponds to the response value in developing the regression model. The shrinkage results obtained from FE analyses in Moldow simulations are provided in Table 2. 3第 3 页 共 7 页2.2 Mold Design and ManufacturingWhen producing a plastic part, the molds must be designed and manufactured using various machines. In this study, the steps applied for manufacturing the plastic product of the DVD-ROM cover are described and shown in Fig. 1. In the plastic injection molding, the CAD model of the plastic product of the DVD-ROM cover was designed in the Pro/Engineer Wildfire CAD/CAM program. Also, the mold designed for the DVD-ROM cover consisted of two clamping plates, a core plates, and pins. In fabricating the mold components, some machines such as CNC milling, EDM machining, drilling, and grinding were employed. The material utilized for the mold components was selected as DIN 1.2738 (IMPAX) steel. This materials hardness was measured to be 31 HRC with a Wolpert Instron Instrument and its chemical composition is presented in Table 3.2.3 Finite Element (FE) Analysis and Molding Cycle2.3.1 FE Pre-Processing of the DVD-ROM Cover. The 3D model of the DVD-ROM cover part was imported into the Moldflow Plastic Insight 5.0 (MPI 5.0) . The DVD-ROM cover part has dimensions of 153, 45.17, and 7 mm. The polymer material (ABS) for the DVD-ROM cover part was composed of CMOLD generic estimates, and its material properties are listed in Table 4. The ABS polymer material was also dried for 4 h using a drier before the molding cycle. The FE model of the DVD-ROM part was created by discrete geometry into the smaller simple elements. The FE fusion mesh model, as shown in Fig. 2, consisted of 2726 nodes, 69 beam elements, and 5318 triangular elements.2.3.2 Molding Cycle of the DVD-ROM Cover. The mold components were designed and manufactured to inject the plastic material of the DVD-ROM cover part, which is mounted on the front of a computer body to fix a DVD within a DVD-ROM. The plastic injection machine which is used in this study was a NETSTAL (600 H-110 60 tons 1.66 oz (25 mm) made in Switzerland. This plastic injection machine has the technical specifications of a maximum clamp force of 543 tons, a maximum injection pressure of 243 MPa, a maximum injection rate of 491 cm3/s , a screw diameter of 25 mm, and machine hydraulic response of 0.2 s. 4第 4 页 共 7 页DVD-ROM上盖的建模和注塑成型工艺对收缩率影响的分析塑料注射成型在生产高品质塑料零件中发挥着关键的作用。收缩是影响注塑成型零件质量最重要的因素之一。本文通过评估 丙烯腈-丁二烯-苯乙烯共聚物（ABS）材质的DVD-ROM上盖质量着重研究建模和注塑成型工艺对收缩率的影响。通过数据分析确定工艺参数（模具温度、熔点、注射压力、注射时间和冷却时间）与收缩率之间的数学关系开发一个有效的回归模型。有限元 (FE) 分析 (L27)田口所设计Moldow仿真程序中运行的正交数组。通过方差分析（ANOVA）校验回归模型并确定工艺参数对收缩率的影响。通过Moldow仿真分析，可获得有限元分析与控制的回归模型的准确性。结果显示回归模型与有限元分析实验的结果高度一致。由此可以得出结论这项建模的收缩问题在我们的应用程序中研究成功。关键词：塑料注塑成型，回归建模和方差分析，收缩。1 前言注射成型是批量生产制造薄壳塑料零件常用的加工方法之一。塑料部件的质量取决于材料的特性、 模具设计和最重要的工艺参数。几项研究发现，注射成型的工艺参数对塑料部件的质量都有关键的影响。他们调查注射成型工艺在生产过程中零部件的收缩、 弯曲、 熔合纹、凹陷和残余应力等问题。他们的研究还显示影响塑料部件质量的最重要参数是保压、 熔化温度和模具温度。然而，这些研究没有充分考虑到其他包括注射时间和冷却时间等工艺参数的影响。此外，德米雷尔有对收缩和翘曲变形导致部件质量问题的计算进行实验研究。这项研究还表明了收缩和翘曲变形随着温度的升高和注射压力的降低而增加。在这个研究中，虽然没有考虑到主要影响工艺参数注射时间和冷却时间，但是这些实验条件足够得出宝贵的结论。许多发表的论文指出，在薄壳塑料部件的注射成型中，工艺参数和影响零塑件质量问题的收缩与弯曲可以建立物理关系。在以往的研究中，进行一系列的试验来测量收缩和翘曲变形下的工艺参数的值。通过数学模型利用测量的值确定最佳工艺参数。以类似的方式，利用回归分析取得薄壳塑料零件注射成型工艺参数与通过实验获得的收缩率之间的关系。通过工艺参数与收缩率的数学关系式创建二阶广义多项式回归方程。由此发现，工艺对零塑件的质量起着至关重要的影响。另一方面，在上述研究中，它没有经过任何成型仿真工具（模流分析）对实验结果进行校核。然而，有许多研究工艺参数对质量的影响的仿真塑料注塑成型的文章。其中一篇由Chen et al写的文章具有典型代表性。这篇文章涉及到计算机 5第 5 页 共 7 页辅助工程结合统计技术应用，用以减少塑料注塑参数引起的翘曲变形。为此，一些依赖田口正交数组的模塑仿真分析、回归方程和方差分析(ANOVA) 可以结合预测各种注塑参数引起的翘曲变形。但是，这篇文章只是简单说明了塑料注塑过程中的翘曲变形而未提到收缩。然而，由Chen等人写的另一篇文章负责通过利用一系列模塑仿真分析研究注塑模制品收缩率变化有影响的有效参数。与上述研究结果不同的是，由阿尔坦做的一项研究使用田口方法、方差分析和模拟脑神经网络使注塑成型收缩减小。进行了二十七次注射成型试验获得的聚丙烯 (PP)、 聚苯乙烯 (PS) 两种不同的聚合物材料的收缩量。从这项研究可以看到通过综合办法可以获得最佳工艺条件对应的最小收缩量。与从上述论文不同的是，一些研究人员只研究电火花加工(EDM) 。总之，即使这些研究者工作在不同领域，但他们有采用和塑料注射成型类似的方法。从这项研究中，从模塑仿真分析模拟得到以有限元分析为基础的有效回归模型可获得塑料注塑工艺参数 (模具温度、 熔化温度、 注射压力、 注射时间和冷却时间） 和使用 ABS 高分子材料的体积收缩率之间的数学关系。大多数研究文献中没有考虑到所有这些过程参数。在不同学者的论文内工艺参数的范围也不同。方差分析是塑料注塑成型测量工艺参数和评估回归模型最有效的方法。此外，通过四次DVD-ROM上盖塑件的注塑成型实验得到的理论值和实际测量值进行比较来验证创建的回归模型的准确性。2.实验研究方法2.1田口正交数组设计实验利用正交数组的实验设计方法，在大多数情况下，高效方便的实验方法与传统的试验设计方法相比，有必要减少和控制实验次数。此外，当工艺参数增加时，必须要进行大量的实验。在此研究中，27 FE 分析基于田口正交数组(L27)对塑料注塑工艺参数的研究，包括：模具温度 （T 模） ，运行熔融温度 (T 熔体)，注射压力 （P 注射用） ，(I 时间)，注射时间和冷却时间 (C) 如表 1 所示。收缩参数值对应回归模型中的响应值。在表 2 中提供了从模塑仿真分析软件模拟有限元分析取得的收缩率结果。2.2模具设计制造当生产一个塑料部件的时候，模具必须经过各种机械设计和制造。在此研究中，适用于制造DVD-ROM上盖塑料产品的的步骤说明如图1所示。在塑料注射成型中，用Pro/Engineer CAD/CAM 程序设计DVD-ROM上盖塑料制品的CAD模型。此外，DVD ROM上盖模具设计包括了两个夹紧板、核心板和针脚。在制作模具组 6第 6 页 共 7 页件中，会用到一些机械设备，如数控铣床、电火花加工、钻和磨。DIN 1.2738 (IMPAX) 钢被选为模具元件的材料。用沃伯特英斯特朗仪器测量此材料的硬度达到31HRC，表3中列出了它的化学成分。2.3 有限元 (FE) 分析和成型周期2.3.1 FE 的预先处理， DVD-ROM盖。3D模型的DVD-ROM上盖部分被导入到Moldflow Plastic Insight 5.0（MPI 5.0）塑料仿真模拟软件。DVD-ROM上盖的尺寸为153mm45.17mm7mm。DVD-ROM上盖的材料高分子聚合物（ABS）由模流分析类似的推测而来，在表4中列出了其材料属性。在成型之前需要用干燥机烘高分子材料ABS四个小时。DVD-ROM 部件的有限元模型是利用离散几何由较小的简单元素创建的。有限元融合网格模型，如图 2 所示由 2726年节点、69 梁元素和5318三角元素组成。2.3.2 DVD-ROM上盖的成型周期。模具组件的设计和制造是为了可以注入制造 DVD-ROM 上盖部分的材料，这个上盖是安装在计算机机箱前部 DVD 安装部位。这项研究所用的塑料注塑机是瑞士制造的 NETSTAL (600 H-110 60 吨 1.66 盎司 (25 毫米)。这种塑料注塑机器技术规格最大夹紧力 543 吨、 243 MPa 的最大注射压力、 491 cm3/s 最大注射率、螺钉直径为 25 毫米和 0.2 s 的机液压响应。
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