Layered tetrahedral meshing of thin-walled solids for plastic injection molding FEM

This paper describes a method for creating a well-shaped, layered tetrahedral mesh of a thin-walled solid by adapting the surface triangle sizes to the estimated wall thickness. The primary target application of the method is the finite element analysis of plastic injection molding, in which a layered mesh improves the accuracy of the solution. The edge lengths of the surface triangles must be proportional to the thickness of the domain to create well-shaped tetrahedrons; when the edge lengths are too short or too long, the shape of the tetrahedron tends to become thin or flat. The proposed method creates such a layered tetrahedral mesh in three steps: (1) create a preliminary tetrahedral mesh of the target geometric domain and estimate thickness distribution over the domain; (2) create a non-uniform surface triangular mesh with edge length adapted to the estimated thickness, then create a single-layer tetrahedral mesh using the surface triangular mesh; and (3) subdivide tetrahedrons of the single-layer mesh into multiple layers by applying a subdivision template. The effectiveness of the layered tetrahedral mesh is verified by running some experimental finite element analyses of plastic injection molding.     

Neural‐network‐based predictive controller design: An application to temperature control of a plastic injection molding process

This paper presents a neural‐network‐based predictive control (NPC) method for a class of discrete‐time multi‐input multi‐output (MIMO) systems. A discrete‐time mathematical model using a recurrent neural network (RNN) is constructed and a learning algorithm adopting an adaptive learning rate (ALR) approach is employed to identify the unknown parameters in the recurrent neural network model (RNNM). The NPC controller is derived based on a modified predictive performance criterion, and its convergence is guaranteed by adopting an optimal algorithm with an adaptive optimal rate (AOR) approach. The stability analysis of the overall MIMO control system is well proven by the Lyapunov stability theory. A real‐time control algorithm is proposed which has been implemented using a digital signal processor, TMS320C31 from Texas Instruments. Two examples, including the control of a MIMO nonlinear system and the control of a plastic injection molding process, are used to demonstrate the effectiveness of the proposed strategy. Results from both numerical simulations and experiments show that the proposed method is capable of controlling MIMO systems with satisfactory tracking performance under setpoint and load changes. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

DETECTOR: A knowledge-based system for injection molding diagnostics

A knowledge-based system (KBS) for diagnosis of multiple defects in injection molding is presented. The general scheme for knowledge representation based on fuzzy set theory has been shown useful in representing inexact and incomplete information for developing the KBS. An optimality criterion is created for selecting a simple and best cover to explain the given problem. An efficient search algorithm for finding such cover is also discussed.     

Remanufacturability evaluation method and application for used engineering machinery parts based on fuzzy-EAHP

Remanufacturing is an important mode to promote the sustainable development of manufacturing industry. Remanufacturing mechanical components at the best recycling time can effectively reduce the remanufacturing cost and improve the remanufacturing efficiency. Therefore, the decision-making model of optimal recycling time based on full lifecycle assessment and full lifecycle cost method was firstly established to analyze and model the energy consumption, cost and emission of components in the original manufacturing, usage, remanufacturing and reuse stages. Then, a remanufacturing evaluation method based on fuzzy extension analytic hierarchy process was proposed. Considering a variety of uncertainties of waste components, a qualitative and quantitative evaluation index system was established, and the weight of each evaluation index was determined by expert evaluation and fuzzy comprehensive evaluation method. Finally, a boom cylinder of a concrete pump truck was studied. The boom cylinder recovered by the method proposed has a high recovery value, and its comprehensive score reaches 70, which verifies the effectiveness and superiority of the model.     

基于CAE和DOE技术的薄壁塑件翘曲变形分析及优化

以某型号仪表显示器外壳为研究对象,采用CAE和DOE技术对其在注塑过程中出现的翘曲变形缺陷进行数值模拟试验,研究熔体温度、模具温度、保压压力和保压时间等成型工艺参数对翘曲变形的影响,并根据试验数据进行极差分析,进而对工艺参数进行优化,获得最佳工艺参数组合.该工艺参数组合可提高塑件注塑质量和生产效率,缩短试模周期,对薄壁塑件的生产实践具有参考意义.     

Automatic layout design of plastic injection mould cooling system

This research extends our previous investigation of the automation of the preliminary design stage to the layout design stage of the cooling system design process. While the functional aspects of the cooling system are considered during the preliminary design stage, the layout design stage addresses both the functionality and manufacturability of the design. A graph structure is devised to capture a given preliminary design and a graph traversal algorithm is developed to generate candidate cooling circuits from the graph structure. Heuristic search is employed to develop the cooling circuits into the layout designs by generation of tentative manufacturing plans. A framework for fuzzy evaluation of the layout designs is developed to rate the various design alternatives generated. An experimental system is implemented to verify the feasibility of the approach, and examples generated from the system are presented to illustrate the major steps of the automatic design process.     

Multi-objective optimization of volume shrinkage and clamping force for plastic injection molding via sequential approximate optimization

Process parameters in plastic injection molding (PIM), such as the packing pressure, the mold temperature, the melt temperature, and so on, are generally determined by a trial-and error method through the experiments. Computer-aided engineering (CAE) in the PIM is an alternative approach to determine the optimal process parameters. In cap-type plastic product, large volume shrinkage makes the clamping difficult. Furthermore, small clamping force leads to high productivity as well as cost reduction. Both volume shrinkage and clamping force should then be minimized simultaneously, and a multi-objective design optimization is formulated. Inappropriate process parameters easily lead to short shot that the melt plastic is not fully filled into cavity. In this paper, short shot is handled as the design constraint. Numerical simulation of the PIM is so expensive that the response surface approach is valid. In particular, a sequential approximate optimization (SAO) that the response surface is repeatedly constructed and optimized with some new sampling points is recognized as one of the most powerful tools available. In this paper, the radial basis function (RBF) network is adopted for the SAO, and the pareto-frontier is identified with a small number of simulation runs. Numerical result shows that the pareto-frontier is well identified with a small number of simulation runs.     

Spiral and conformal cooling in plastic injection molding

Designing cooling channels for the thermoplastic injection process is a very important step in mold design. A conformal cooling channel can significantly improve the efficiency and the quality of production in plastic injection molding. This paper introduces an approach to generate spiral channels for conformal cooling. The cooling channels designed by our algorithms has very simple connectivity and can achieve effective conformal cooling for the models with complex shapes. The axial curves of cooling channels are constructed on a free-form surface conformal to the mold surface. With the help of boundary-distance maps, algorithms are investigated to generate evenly distributed spiral curves on the surface. The cooling channels derived from these spiral curves are conformal to the plastic part and introduce nearly no reduction at the rate of coolant flow. Therefore, the channels are able to achieve uniform mold cooling. Moreover, by having simple connectivity, these spiral channels can be fabricated by copper duct bending instead of expensive selective laser sintering.     

General frameworks for optimization of plastic injection molding process parameters

Plastic injection molding is widely used for manufacturing a variety of parts. Molding conditions or process parameters play a decisive role that affects the quality and productivity of plastic products. This work reviews the state-of-the-art of the process parameter optimization for plastic injection molding. The characteristics, advantages, disadvantages, and scope of application of all of the common optimization approaches such as response surface model, Kriging model, artificial neural network, genetic algorithms, and hybrid approaches are addressed. In addition, two general frameworks for simulation-based optimization of injection molding process parameter, including direct optimization and metamodeling optimization, are proposed as recommended paradigms. Two case studies are illustrated in order to demonstrate the implementation of the suggested frameworks and to compare among these optimization methods. This work is intended as a contribution to facilitate the optimization of plastic injection molding process parameter.     

An object-oriented approach to computer-aided design of a plastic injection mould

This paper describes a knowledge-based and object-oriented approach for the design of the feed system for plastic injection moulds. The gating system of a plastic injection mould plays a significant role in producing a quality part. Designing of this gating system entails a great amount of effort from an experienced designer and it is time-consuming. CADFEED (Computer-Aided Design of the FEED system of the plastic injection mould) is developed to accurately and efficiently design the type, location and size of a gating system of a plastic injection mould. This system provides an accurate and fast means of obtaining solutions based on the users' requirements, which are easily handled by the rating algorithm in the system. CADFEED generates acceptable solutions at a lower cost than most traditionally and commercially available analysis packages. This system can be used to verify designs proposed by the design engineers. It can also help novice engineers in the understanding of mould design. Another important feature of CADFEED is that it is a low cost system, which uses AutoCAD and an expert system shell on a personal computer. This feature makes CADFEED easily affordable by small-scale industries.     

A neural network-based approach for dynamic quality prediction in a plastic injection molding process

This paper presents an innovative neural network-based quality prediction system for a plastic injection molding process. A self-organizing map plus a back-propagation neural network (SOM-BPNN) model is proposed for creating a dynamic quality predictor. Three SOM-based dynamic extraction parameters with six manufacturing process parameters and one level of product quality were dedicated to training and testing the proposed system. In addition, Taguchi’s parameter design method was also applied to enhance the neural network performance. For comparison, an additional back-propagation neural network (BPNN) model was constructed for which six process parameters were used for training and testing. The training and testing data for the two models respectively consisted of 120 and 40 samples. Experimental results showed that such a SOM-BPNN-based model can accurately predict the product quality (weight) and can likely be used for various practical applications.     

Cost-effective design for injection molding

It is commonly agreed that a large proportion of the ultimate product cost is determined at product design stage. Therefore, a cost-effective design cannot be obtained unless all cost issues are resolved at early design stage. Therefore, instead of performing cost estimation after design, research presented in this paper aims to provide on-line cost evaluation and advisory to help product designers avoid cost-ineffective design. The objective can be obtained by (1) identifying factors that might affect product cost at each product design stage, (2) developing a design for cost effectiveness methodology that accommodates the concepts of concurrent engineering, and (3) developing a computer-based design for cost effectiveness system based on the proposed methodology. In this research, we focus on injection molding product design due to the advantages of injection molding process, such as high production rates, excellent quality and accuracy of the parts, and very long mold life. This paper first reviews and characterizes the conventional molding product development process with an emphasis on the identification of cost factors. Based on the results of process characterization, a cost model is developed, which depicts the relationships between cost factors and product development activities, as well as their relationships with product geometry. According to the product life cycle activities and the cost model, a design for cost effectiveness process is proposed. The process and the cost model are then employed for the development of a computer-based product design for cost effectiveness as one of the module of an integrated design for injection molding environment.     

设计型专家系统的知识表示

本文从工程设计的实际过程出发，探讨了便于实现设计推理的知识表示。框架结构用于设计方案的描述和工程实例的存储，关联表示用于提出和修改方案。     

Expert systems: An application in flexible manufacturing

Flexible manufacturing systems (FMS) are needed to provide manufacturing operations with the capability to adjust, in real time, to changes in the manufacturing environment. Realization of the goals of flexible manufacturing is governed by the ability of the FMS to maintain adequate information on the factory to assist in generating scenarios from product planning to operations and performance. This leads to a view where the factory is represented as an integrated information system. To facilitate the analysis of information requirements and the design of information systems for flexible manufacturing, an expert support system (ESS) which can be used to model and study the various structures is described. This ESS uses the information cell model to build these information structures. Petri net representations of these structures and their interactions are then constructed. The ESS may now be used to exercise these models and study their performance using time and cost measures.     

A procedure for plastic parts demoldability analysis

The present work proposes a new systematic procedure for the geometric analysis of plastic parts that will be transformed by injection process. The procedure is based on visualization techniques such as slicing by parallel planes, Scan Line Segment and Z-buffer methods. By these procedures, the fitness of the part geometric design for manufacturing process is evaluated. Part demoldability and parting line are defined, with an outstanding improvement of the traditional methods used for mold design purposes. Therefore, this approach focuses on Design for Manufacturing research area.     

Instrumented film-insert injection compression molding for lens encapsulation of liquid crystal displays

A film-insert injection compression molding process was introduced to encapsulate cholesteric liquid crystal displays with flexible and rigid lens for full protection of displays to replace the currently used time consuming hand lamination technique. For this purpose, a new interchangeable cavity instrumented hot runner mold was designed and constructed. This complex method was carefully optimized considering challenges arising from an insert multilayer display with +80% liquid crystal content as well as different thermal expansion coefficients between the layers and the lens material as a high potential of delamination and warpage. Concerning the desired physical properties including transparency, low melt viscosity and melting temperature as well as a wide range of hardness grades from soft (flexible) to hard (rigid), three different hardness grades of thermoplastic polyurethanes were found to be the best candidates for this lens application. During proposed lens encapsulation, the pressure changes were evaluated with screw and mold movements using position detection via displacement transducers attached to track the mold closure and screw forward motion. The quality of encapsulation and shrinkage related problems, as well as their elimination, were all discussed. Display substrate material selection criteria for lowered warpage were defined with supporting thermal characterizations. Among the process parameters, tested also by applying the design of experiments with Taguchi method, mold temperature was found to be the most influential parameter on warpage, followed by pin gate opening time, packing pressure, and cooling time.     

Simulation and experimental study in determining injection molding process parameters for thin-shell plastic parts via design of experiments analysis

This paper deals with the application computer-aided engineering integrating with statistical technique to reduce warpage variation depended on injection molding process parameters during production of thin-shell plastic components. For this purpose, a number of Mold-Flow analyses are carried out by utilizing the combination of process parameters based on three level of L₁₈ orthogonal array table. In the meantime, apply the design of experiments (DOE) approach to determine an optimal parameter setting. In addition, a side-by-side comparison of two different approaches of simulation and experimental is provided. In this study, regression models that link the controlled parameters and the targeted outputs are developed, and the identified models can be utilized to predict the warpage at various injection molding conditions. The melt temperature and the packing pressure are found to be the most significant factors in both the simulation and the experimental for an injection molding process of thin-shell plastic parts.     

基于控制参数化的注塑工业过程最优反馈控制方法

本文针对一类典型的注塑工业过程系统, 研究了注塑填充过程中产生的熔体流动速度最优跟踪控制问题, 提出了一种基于控制参数化的计算最优反馈控制器设计方法以实现注塑过程中熔融聚合物流动前沿位移的最优跟 踪控制, 进而达到改善注塑零件性能的高效生产目标. 首先, 面向注塑工艺复杂生产过程建立了动态过程系统数学 模型, 提出了注塑机内部熔融聚合物流动前沿位置的动态最优跟踪控制问题; 其次, 设计了一种多级反馈控制律, 通 过控制参数化方法将控制反馈核进行了参数化表示, 将控制器设计问题转化为一序列最优参数决策问题; 然后, 通 过状态灵敏度方程分析方法, 求解出了目标函数及约束条件关于决策变量参数梯度信息的显式表达式, 并基于所提 供的梯度信息结合序列二次规划算法进行了高效优化迭代求解; 最后, 通过实验仿真验证了本文所提出的最优反 馈控制器设计方法的可行性和有效性.     

Knowledge and experience-based systems for analysis and design of microprocessor applications hardware

The potential of expert systems for the analysis and design of microprocessor applications is discussed. A prototype expert system, which designs microprocessor applications hardware, is described. Some general principles of expert systems are considered.