塑料挤出成型设备自动控制系统的改造

介绍塑料挤出成型设备的组成、结构特点．以及控制系统的改造。     

A new model based approach for the prediction and optimisation of thermal homogeneity in single screw extrusion

In polymer extrusion, delivery of a melt which is homogenous in composition and temperature is important for good product quality. However, the process is inherently prone to temperature fluctuations which are difficult to monitor and control via single point based conventional thermocouples. In this work, the die melt temperature profile was monitored by a thermocouple mesh and the data obtained was used to generate a model to predict the die melt temperature profile. A novel nonlinear model was then proposed which was demonstrated to be in good agreement with training and unseen data. Furthermore, the proposed model was used to select optimum process settings to achieve the desired average melt temperature across the die while improving the temperature homogeneity. The simulation results indicate a reduction in melt temperature variations of up to 60%.     

Control of properties in injection molding by neural networks

Adequate control of product properties in injection molded plastics requires very accurate predictions. The problem is that the mechanical properties of these plastics, such as tensile modulus, are highly non-linear with the process variables, hence they are tough to predict. Consequently, up to date, injection molding machines include only closed loop control of process variables. Control of product properties is virtually non-existent.

We show here for the first time, that mechanical properties, such as tensile modulus values, can be predicted using Artificial Neural Networks quite accurately within a reasonable time. This is a major step towards an integrated self-taught control mechanism for the injection molded plastics industry.     

复合材料液态浸渗挤压的开关控制系统

针对液态浸渗挤压复合材料成形过程实施难度大、质量难于控制的现状，开发了工艺过程开关控制系统，并编制了基于Windows 98操作系统、C Builder 5.0环境下可视化计算机开关量控制程序软件。利用数据采集系统进行关键参数监控，实时在线采集并同时显示3组工艺参数，计算机可按输入参数及现场情况控制成形过程。试验结果表明，该系统性能可靠，操作方便，为该工艺的实际应用奠定了基础。     

A fuzzy PID thermal control system for casting dies

In high-pressure die casting processes, proper control of die temperature is essential for producing superior quality components and yielding high production rates. However, die temperature distribution depends on various die design and process variables for which accurate models are normally very difficult to obtain. In this paper, a new intelligent control scheme is proposed for die thermal management. In this scheme, extra cooling waterlines controlled by a pump and solenoid valves are attached to the established cooling channels. A fuzzy PID controller is designed to minimize the temperature differences between channels. The experimental results obtained from a laboratory die casting process simulator indicate that the developed control system is capable of adjusting the desirable supply of cooling water into multiple cooling lines. Hence, the local temperature distribution of the die insert may become more homogeneous.     

Modeling of extrusion coating for applications in electronics manufacturing

This paper focuses on the development of a model of the extrusion coating process that can be used to generate an automated (as opposed to manual) procedure for determining the control setpoints for a desired deposition thickness and range of deposition materials. This model includes the dynamics of the bead formation process and the bead variation during the coating. The “bead” refers to the deposition material that collects in front and under the die head as the substrate is moved beneath it. Understanding and modeling the dynamics of the bead process as a function of the control‐variable settings is crucial in obtaining an automated procedure for setpoint determination in extrusion coating.     

Process and die profile design for tube extrusion of γ iron

This study is related to material modeling and die and process design of tube extrusion of γ iron. Strain dependent rate power law is used for material modeling whose coefficients are arrived at through genetic algorithm (GA). Die profile of the tube extrusion process is optimized to produce microstructurally sound product at maximum production speed and minimum left out material in the die. The design problem is formulated as a nonlinear programming problem which is solved using GA. Selection of the processing parameters is carried out using dynamic material modeling (DMM). Using this approach tube extrusion process of γ iron is successfully designed.     

直齿圆柱齿轮冷挤压成形腔参数优化

针对齿轮冷挤压技术存在的成形压力大和坯料填充困难问题,建立了流线型的直齿圆柱齿轮冷挤压成型腔几何模型,并对挤压过程进行了数值模拟。结果表明,流线型挤压腔能够在较小的成型力下保证挤压齿轮齿形填充饱满。通过对模拟过程的分析,研究了不同坯料放大半径  值对成型腔形状和挤压方式的影响,并通过对不同成型腔的数值模拟,得到最优的参数模型。     

Single screw extrusion control: A comprehensive review and directions for improvements

Polymer extrusion is usually a complex process, particularly due to the coupled nature of process parameters, and hence highly prone to fluctuations. Although a number of different approaches have been attempted in research/industry over the last few decades for extrusion control, it is still experiencing some problems in achieving consistent product quality. Presently, most of the polymer processing extruders are equipped with PID controllers mainly for the control of the screw speed and barrel temperatures in their set limits. It seems that only both of these controllers are commonly used as the major aids of process control to achieve the required melt quality. Although, the quality of the melt output (i.e., a thermally homogeneous melt output which is constant in quantity and quality over the time) is the key variable in polymer extrusion, only a few control techniques are available which make control decisions by observing the actual melt flow quality. Therefore, the development of new control strategies which consider the actual melt quality, perhaps incorporating industrially popular nonlinear techniques such as artificial intelligence, should be highly valuable. In this work, a critical evaluation is made on the state-of-the-art of the previous control approaches in polymer extrusion in industry and research while identifying their limitations. Then, some of the possible directions for future research and also to develop an advanced process control strategy are presented by eliminating a few of the existing limitations.     

An intelligent supervision system for open loop controlled processes

On-line manufacturing systems for continuous production are traditionally checked by constant time-based inspection and statistical process control processes. In the monitoring operation of large scale process plants, it is important to detect and locate process variables as they can significantly modify the operation and quality of the products involved. The present paper explores an alternative for monitoring these systems that uses the open loop control paradigm. The proposed method is defined and presented as an application for one particular industrial process—rubber die extrusion. The advantages of this method for this particular application, including its implementation throughout a multi-agent system, compatible with the HoloMAS paradigm for managing, modeling and supporting complex systems, are also discussed.     

Modeling and optimization of cold extrusion process by using response surface methodology and metaheuristic approaches

Obtaining the optimal extrusion process parameters by integration of optimization techniques was crucial and continuous engineering task in which it attempted to minimize the tool load. The tool load should be minimized as higher extrusion forces required greater capacity and energy. It may lead to increase the chance of part defects, die wear and die breakage. Besides, optimization may help to save the time and cost of producing the final product, in addition to produce better formability of work material and better quality of the finishing product. In this regard, this study aimed to determine the optimal extrusion process parameters. The minimization of punch load was the main concern, in such a way that the structurally sound product at minimum load can be achieved. Minimization of punch load during the extrusion process was first formulated as a nonlinear programming model using response surface methodology in this study. The established extrusion force model was then taken as the fitness function. Subsequently, the analytical approach and metaheuristic algorithms, specifically the particle swarm optimization, cuckoo search algorithm (CSA) and flower pollination algorithm, were applied to optimize the extrusion process parameters. Performance assessment demonstrated the promising results of all presented techniques in minimizing the tool loading. The CSA, however, gave more persistent optimization results, which was validated through statistical analysis.

     

Three-dimensional non-Newtonian computations of extrudate swell with the finite element method

Numerical simulations have been carried out for the extrudate swell problem in three-dimensional domains. The finite element method is used with streamline elements, which render the calculations fast and efficient for flows through long extrusion dies (no reservoir present). The method is first tested against purely viscous (Newtonian), viscoplastic (Bingham), and slightly viscoelastic (CEF model) results for the determination of extrudate swell from circular dies, which have a two-dimensional counterpart. Full three-dimensional die designs are also studied, such as extrusion from a square and a cross-shaped die.     

A mixed Eulerian–Lagrangian method for modelling metal extrusion processes

A mixed Eulerian–Lagrangian approach for the computational modelling of metal extrusion processes in complex three dimensional geometries is presented. The approach involves the representation of the workpiece as a pseudo-fluid, and requires the solution of non-Newtonian fluid flow equations in an Eulerian context, using a free-surface algorithm to track its extreme deformation during its extrusion. The solid mechanics equations associated with the tools are solved in a conventional Lagrangian context. Thermal interactions between the workpiece and tools are modelled and a fluid–structure interaction technique is employed to capture the effect of the fluid traction load imposed by the workpiece on the tools, and especially the subsequent adaption of the Eulerian mesh to account for the impact of die deformation. Two extrusion test cases are investigated and the results obtained show the potential of the model with regard to representing the physics of the process, the advantages of the model over a more loosely coupled approach, and the parallel scalability of the resulting software.     

Artificial neural networks to optimize the extrusion of an aluminium alloy

Extrusion of aluminium alloys is a complex process which depends on the characteristics of the material and on the process parameters (initial billet temperature, extrusion ratio, friction at the interfaces, die geometry etc.). The temperature profile at the die exit, largely influences microstructure, mechanical properties, and surface quality of an extruded product, consequently it is the most important parameter for controlling the process. In turn the temperature profile depends on other process variables whose right choice is fundamental to avoid surface damage of the extruded product. In the present work, two neural networks were implemented to optimize the aluminium extrusion process determining the temperature profile of an Al 6060 alloy (UNI 9006/1) at the exit of induction heater (ANN1) and at the exit of the die (ANN2). The three-layer neural networks with Levemberg Marquardt algorithm were trained with the experimental data from the industrial process. The temperature profiles, predicted by the neural network, closely agree with experimental values.     

Energy-based control of a distributed parameter bi-zone model with moving interface

In this work, a model-based control of the melt temperature of a distributed parameter bi-zone model with moving interface of an extrusion process is studied. An energy-based controller is derived using internal energy as a storage function and controlled variable with the screw speed as control input. The stability of the controller is proved through the use of a Lyapunov-like candidate function. Finally, the practical usefulness of the method is illustrated by some closed-loop simulations of the experimentally verified model of the extrusion process. The interconnection of the moving interface is performed under the assumption of variable viscosity along the extruder and a finite-volume scheme is used for the discretisation of the dynamic model.     

Structural feature extraction in online extrusion of plastics

Structural features of plastics such as orientation, degree of crystallinity and spherulite dimension are influenced by basic extrusion conditions of temperature, screw speed, haul off speed, mass outflow and the nature of casting. These induced structural features in turn influence the post-extrusion processes which are an essential part of film-fibre production.A correlation between structural features and mechanical properties of extruded film has previously been established.A sensor, based on small-angle light scattering, using a laser source and microprocessor-based pattern processing has been designed for online control. Principles involved are described and circuit details included.     

Application of fuzzy-based Taguchi method to the optimization of extrusion of magnesium alloy bicycle carriers

By using fuzzy-base Taguchi method, this study investigates the optimal process parameters that maximize multiple performance characteristics index (MPCI) for hot extrusion of AZ31 and AZ61 magnesium alloy bicycle carriers. The larger-the-better quality characteristics of flattening strength and T-slot fracture strength as well as the smaller-the-better quality characteristic of extrusion load is considered in the MPCI. Through MPCI inference model, a manufacture method with less extrusion load and better mechanical properties under hot extrusion can be obtained. The signal-to-noise (S/N) ratios of the three quality characteristics??flattening strength, T-slot fracture strength and extrusion load??are calculated for the products based on experimental results. And the S/N ratio serves as the input variable to fuzzy control unit, and MPCI is a single output variable. The obtained MPCI is used to analyze optimal process parameters. This study finds combination of process parameters that optimizes MPCI, and conducts confirmatory experiments to prove the accuracy of optimal combination of process parameters thus selected. Finally, mechanical properties of AZ31, AZ61 magnesium alloy and A6061 aluminum alloy bicycle carriers are tested to identify differences among these three materials.     

塑料异型材挤出模工程图自动标注系统研究

塑料异型材挤出模结构相对固定,但其板块工程图冗余废线较多,尺寸标注处理繁 琐。以塑料异型材挤出模为研究对象,在UG 平台上构建了塑料异型材挤出模工程图自动标注系 统,并就以下方面进行了研究：提出板块冗余废线识别方法,并采用删除与转换两种方式实现各 视图废线的自动消除;提出孔定位标注元素识别方法,并采用四象限递增排布法实现孔定位尺寸 及其公差的自动标注;提出孔特征的识别与匹配方法,实现各板块孔特征规格、公差与文字的自 动标注。通过实例分析表明该系统极大减少了图纸设计工作量,有效提高了异型材挤出模工程图 的设计效率。     

基于TMS320F2812的挤出装置串行通信研究

膏体挤出自由成型是一种陶瓷零件快速制作工艺,挤出位置和挤出速度的控制以及挤压力的实时采集对于陶瓷膏体挤出装置的运行非常关键。本文采用了TMS320F2812DSP对挤出装置进行控制和数据传输,分析了控制任务的结构,研究了DSP与PC机之间的串行异步通信方案,详细阐述了数据传输格式和接收方式,并设计了上下位机的控制程序。对通信方案的实施结果表明:该通信方案准确有效,可以完成电机控制和数据采集。     

地铁屏蔽门人群挤压荷载测试系统的设计

为了解决当前地铁屏蔽门人群挤压荷载测试装置存在的自动化程度不高、产生的线荷载不精确不均匀的问题,综合计算机软件技术、自动控制技术和传感器技术设计了地铁屏蔽门人群挤压荷载测试系统.设计了计算机软件和PLC控制程序实现测试过程的自动控制.采用多点加载法,并对加载点引入闭环反馈控制来实现对荷载的精确控制.实验结果证明,设计的系统实现了测试的自动化,并解决了线荷载不精确不均匀的问题.