虚拟制造技术与数字化工艺

虚拟制造技术与数字化工艺 本文介绍了虚拟制造的背景和它的定义，讨论了虚拟制造的流派、相关技术、应用领域它在数字化工艺中的研究与应用。随着全球竞争的增加，为了缩短产品的上市时间，在八十年代相继提出了FMS（Fexible Manufacturing System）、CIMS(Computer Integrated Manufacturing System)、CE(Conturrent Engineering)等新的概念，对它们的研究与应用，提高了产品的质量和生产效率。随着网络和生产技术的发展，在九十年代提出了敏捷制造AM（Agile Manufacturing）、精良制造LM（Lean Manufacturing）、分布式制造（Distributed Manufacturing）和虚拟企业VE（Virtual Enterprise）等新的研究领域，目前设计技术研究主要集中在详细设计阶段，CAD系统虽然提供了表示和操作复杂零件 的方法，但是它不能表示概念设计阶段的信息，在这种情况下，产生了虚拟制造VM（Virtual Manufacturing）。虚拟制造建立了计算机化的制造活动这样一个关键概念，它概括了对真实制造世界的对象和活动的建模与仿真研究的各个方面。虚拟制造的基础是用计算机支持的技术对所有必要的制造活动进行彻底的建模与仿真，其中建立计算机化的工艺过程，即：数字化加工过程是虚拟制造研究的核心基础工作之一。虚拟制造的定义 在Lawrence Associates的Virtual Manufacturing User Workshop报告中，VM被定义为：它是一个集成的、综合的可运行制造环境，用来提高各个层次的决策和控制。各部分的语义说明如下：环境 通过协同地提供分析工具、仿真工具、应用工具、控制工具、模型（产品、过程和资源）、设备以及组织方法的集合，用以支持构造和使用分布式制造仿真。层次 是指从产品的概念设计到回收利用、从车间到执行位置、从物质的转换到信息的传递等各个方面。控制 预测效果的真实性。提高 增加它的精度和可靠性。运行 用环境来构造和操作特定的制造仿真决策 是指改变（可视化、组织、定义和选择）后的影响。 综合 指真实的和仿真的对象、活动和过程的混合状态。上述关于VM的定义没有充分强调VM在预测过程、成本和质量方面的能力，而且它没有说明VM预测的可靠性和精度，因此它还存在下面的缺点：该定义限制了它处理的范围，并且提高了工程和制造之间的交互性。虽然它的最理想的定义达到了对VM最全面的描述，但是，根据不同用户的对象、技术背景和水平，VM应该有不同的定义。VM的定义应与特定用户的经验基础相联系，这里的制造应该是广义的、企业范围的“大”制造。因为在车间之外的重要活动也包含在建模、数据和仿真中。VM的定义必须与特定用户的经验和要求相联系，因此，VM不可能只有一种定义，对于每一个人来说，VM并不是完全相同的，所以应了解它与其他相关概念的区别。给出一个象VM这样覆盖面广的定义，是非常困难的。VM的定义不可能包含它的每一个方面。因此，为了更好地解释VM，下面对VM的内涵进行说明：通过基于建模的途径和利用仿真，VM主要是为了提高加工过程的质量。VM最重要的作用是为实施IPPD(Integrated Product Process Development)提供一个工具，特别是用于预测产品成本和控制功能。VM的基本目的是基于计算机模拟产品的开发环境，使得设计者在真正的加工之前就能够模拟地制造产品。这里的“产品开发”包括了与产品相关的所有活动，不仅包括技术上的和商业上的，而且包含了产品的设计和生产。但是，VM并不仿真所有的这些方面。VM是基于模型的制造，使用的工具反过来影响这些模型。最初始的工具是仿真，利用仿真可以降低制造成本，而且可以检查真实空间和虚拟空间的许多参数。从全局的观点来讲，在一个IPPD环境下，通过在计算机中完成“制造”，VM提供了对部分或全部设计过程的评价方法。1.VM的流派 VM的研究都与特定的应用环境和对象相联系，在VM的研究过程中，由于应用的不同要求，各有不同的侧重点，因此出现了三个不同的流派，它们是以设计为中心的VM、以生产为中心的VM和以控制为中心的VM。1.1 以设计为中心的VM 以设计为中心的VM是通过加制造信息到IPPD的过程和在计算机中进行“制造”，仿真多种制造方案和产生许多“软”的模型。因此它的短期目标是：为了达到特殊的制造目的(例如为了装配进行设计、精良操作或柔性等)，VM用以制造为基础的仿真来优化产品的设计和生产过程。它的长期目标为：VM在不同的层次上用仿真过程来评估生产情况，并且反馈给设计和生产控制。1.2以生产为中心的VM以生产为中心的VM是通过加仿真能力到生产过程模型，达到方便和快捷地评价多种加工过程的目的。它的短期目标是：VM是基于生产的IPPD的转换，用以优化制造过程和物理层。它的长期目标是：为了实现新工艺和流程的更高的可信度，VM是增加生产仿真到其它集成和分析技术。1.3 以控制为中心的VM以控制为中心的VM是通过增加仿真到控制模型和实际的生产过程，来实现优化的真实仿真。 1.4 三类VM之间的关系虽然三种VM的定义不相同，但是它们都涉及到虚拟产品生命周期中不同的方面，因此，它们具有下面的特点：以设计为中心的VM为设计者提供了一个设计产品和评估可制造性的环境，它的结果包括产品建模、成本预测等，所以，在设计中的潜在问题能够被发现，同时它的一些指标(例如成本等)也能被预测。为了生产出合格的产品而不做实际的样品，以生产为中心的VM为工艺计划和生产计划的生成、工艺资源的要求以及对这些计划的评价提供了一个环境，它能够更精确地提供成本信息和产品的供给计划。2. VM与其它相关技术之间的区别当前在先进制造技术的研究过程中，产生了许多新的概念，如IPPD、虚拟企业VE（Virtual Enterprise）、建模与仿真M&S(Modeling and Simulation)等。因此，为了更详细说明VM的内涵，需要了解VM与其它相关概念之间的关系。2.1 VM与IPPD IPPD是一种交错功能协调机理，它使得与设计和制造相关的信息可以在产品设计过程的各模块间流动。VM仿真制造、生产和装配过程，因此它必须有与上面信息的接口，但是VM并不是各模块的集合，也不能使信息在模块间流动。它们的关系如图1所示。图1 产品开发过程按照IPPD的观点，VM增加了IPPD的过程，它提供了一种方法将制造知识综合到产品开发的早期阶段。因此，它在IPPD中的作用是重要的。首先它允许IPPD直接通过模拟加工过程来设计、分析和制造产品，而不用关心实际的加工。其次，它允许IPPD在原型系统中任意层次上增加过程。IPPD的优势并不在于过程中模块的多少，因为几个最好的单个模型组合到一起并不是最好的。利用VM，IPPD可以逆向分析加工过程，而不用重构加工过程。按照并行工程CE(Concurrent Engineering)的观点，VM增加了上面提到的能力外，它共享的基础结构比CE所需要的更可靠。2.2 VM与M&S(Modeling and Simulation) VM依靠M&S技术模拟制造、生产和装配过程，使设计者可以在计算机中“制造”产品。M&S是VM的基础。VM是M&S的应用，但是它扩展了传统的M&S技术。在传统上，M&S建模的目的仅仅是为了仿真和相关的分析。而在VM中，使用主要部分已存在的模型，而不是优化的仿真。因为在VM中，由于其他的原因，模型是动态的，随着仿真环境的改变，它是变化的。2.3 VM与VE(Virtual Enterprise) 虚拟企业是敏捷制造的基本的动态组织形态，是指为了赢得某一机遇性市场竞争，围绕某种新产品开发，通过选用不同组织或公司的优势资源，综合成单一的靠网络通讯联系的阶段性经营实体。动态联盟具有集成性和时效性两大特点。它实质上是不同组织或企业间的动态集成，随市场机遇的存亡而聚散。在具体表现上，结盟的可以是同一个大公司的不同组织部门，也可以是不同国家的不同公司。在VE中伙伴能够共享生产、工艺和产品的信息，这些信息以数据的形式表示，能够分布到不同的计算环境中。VE与VM没有很强的相互依靠关系。在信息的集成和共享领域，VE主要强调网络，而VM主要强调产品的设计，而且在设计阶段VM的重点是仿真产品的生命周期中的各个活动。 2.4 VM与VP(Virtual Prototyping) 虚拟原型(Virtual Prototype)是相对物理原型，具有一定功能的基于计算机的仿真系统。它主要用于测试和评价多种设计的指定特性。VP是使用虚拟原型的过程。目前，它主要用于缩短产品的开发时间和降低成本。在VP中，计算机辅助设计信息直接被传送到产品模型，而不用构造物理原型来检验设计的有效性和进行优化设计。如果虚拟原型是通过模拟工艺计划来构造的，那么VP就是用VM来产生的，在大部分情况下，VP比物理原型具有更大的优点，在虚拟产品周期中，VP是一个必需的组成部分。所以，VP的发展将增强VM的能力，反过来，VM为VP提供了一个应用环境。2.5 VM与AM(Agile Manufacturing) 敏捷制造作为一个新概念，其基本思想是通过将高素质的员工、动态灵活的组织机构、企业内及企业间的灵活管理以及柔性的先进生产技术进行全面集成，使企业能够对持续变化、不可预测的市场要求作出快速反应，由此获得长期的经济效益。由此可见，敏捷制造强调人、组织、管理和技术的高度集成，强调企业面向市场的敏捷性(Agility)。在一个企业的组织管理中，它的敏捷性可以用四个主要变量表示，即通讯连同性(Communication Connectedness)、跨组织参与性(Interorganization Participation)、生产的灵活性(Production Flexibility)和雇员的使能性(Employee Empowerment)。VM是敏捷制造的一种实现手段，是制造企业增强产品开发敏捷性、快速满足市场多元化需求的有效途径。 3. VM在数字化工艺中的应用 3.1 数字化工艺的概念对切削加工而言，早在本世纪初切削的工艺模型就引起研究者的关注，但一直到本世纪40 60年代，在切削机理方面的几项突破使切削研究有可能建立在材料的物理层面上，到本世纪80年代以后，随着计算技术和测量技术的进展，大量的工作集中在工艺过程的分析、建模与仿真，他们对不同的工艺过程（车、铣、钻、铸、冲压等）的不同方面（力模型、热模型、误差模型、材料变形模型等）及不同的加工材料（金属、复合材料等）做了大量的工作，取得了丰硕的成果，一些结果已应用于工业界，获得了满意的效果。然而，这些研究成果仍未大面积的推广应用，原因在于研究的不系统性。传统上，工艺的设计与校验典型地通过制造一个实物原型来完成，而基于工艺的可制造性评估则根据加工的成本和时间来确定加工的难度，加工时间和成本由零件材料、加工特征和加工参数的手册值决定，虚拟制造技术在多方面改进了传统的工艺设计和校验：通过“数字化加工过程”，不需要制造昂贵的实物原型就可在计算机上校验工艺设计；通过“数字化加工过程”不仅可精确地估计制造时间和成本，还可估计其它重要参数，如：零件质量；通过“数字化加工过程”可以更直观地“观察”加工过程，如磨削过程中单个磨粒的微观表现，切削中的应力与热流，卡具的变形。这些有助于我们更精确和更有创造性地设计加工过程。 “数字化加工过程”包含二层含义：一是刀具路径仿真，即建立工件/工具/机床的实体模型，刀具沿着由工艺确定的轨迹切削，一些不适当的刀具轨迹(刀具/夹具干涉)很容易地被发现；二是评估是否在加工工艺中说明的工艺参数是合适的，如大的切深会产生颤震，毁坏刀具、工件，高的进给率导致不可接受的表面粗糙度，研究者已经在刀具路径校验方面做了大量工作，也有大量工作是有关加工过程的物理效应模型，在虚拟加工过程中将表达切削的物理效应的模型和表达切削几何的实体模形结合起来，完整地表达切削。在虚拟制造环境下，物理模型与实体模型的规范描述和系统集成将不仅能评估现有的工艺过程，而且能为新工艺的创新与设计提供有力手段。3.2 数字化加工过程的系统结构。工艺过程数字原型是真实工艺过程在虚拟世界（计算机）的影射，模型反映的是工艺过程一个侧面的特性，因此工艺过程数字原型是反映工艺过程各个侧面特性的模型及其相互关系的集合。一般基本工艺过程可抽象地表达如图2。图2 单元工艺在上图，基本的加工过程可表达为：输入为毛坯，利用设备在工艺信息的指挥下加工出产品和产生废弃物；在右图，与加工过程相关的物理实体是工具（刀具与卡具，有时也包括机床）和工件，而所有与工艺过程相关的物理效应主要都发生在这些实体上，因此，我们可以基于工件、刀具和卡具产品模型来构造规范化的数字化加工过程结构，即将加工过程处理作为一个四维的过程，即：空间三维和时间维。任意一个工艺过程效应都发生在特定的位置和时间，因此任意一个工艺过程效应都可看作一个四维空间点上的属性，这样的处理使不同的模型之间建立了一种统一、规范而直接的对应关系，从而有利于较好描述具有多种物理效应和复杂耦合关系的工艺过程，建立结构化的加工过程数字原型，加工过程数字原型的结构如下图所示，分四层： 图3 数字化加工过程的系统结构 第一层为几何实体层，建立与工艺过程相关的物理实体的几何模型；第二层为运动学模型层，基于第一层模型和运动轨迹信息，建立几个几何实体之间相互运动的关系；第三层为物理模型层；基于第二层中几何实体之间的相互关系（时间轴上和位置上的）和工艺信息（材料、加工条件）建立物理效应模型（断裂、变形、力），这些物理效应彼此相互作用，构成了复杂的网络关系；在输出层，按特定的顺序搜集、排列第三层的输出，获得完整的工艺特性结果，如：按空间搜集所有留在毛坯上的材料，即为加工后工件形状。3.3 工件表面误差的分析实验 图4为棒铣刀加工表面的一个试验结果，图中比较了加工表面误差，理论与实验结果很一致。图4 棒铣刀加工表面误差比较主要参考文献1. Zheng L.， Liang S.Y.， “Identification of Cutter Axis.Tilt in End Milling*”Transaction of ASME， Journal of Manufacturing Science and Engineering， 1998.22. Zheng L.， Liang S.Y.， “Analysis of End Milling Forces with cutter Axis Tilt”Transaction of NAMRI/SME，Vol.23，1995 P137-1423. Zheng L.，Chiou Y.S.， Liang S.Y.， “Three dimensional cutting force analysis in end milling ”，Int. J of manufacturing science， 1995，37(10)4. Beverly A. Beckert， Venturing into virtual product development， Modern Manufacturing， September 19965. Paul Dvorak， Engineering puts virtual reality to work， Modern Manufacturing， October 19976. Edward Lin， Inoannis Minis， Dana S. Nau and William Regli， Contribution to Virtual Manufacturing Background Research ， May19957. Virtual Manufacturing User Workshop， DoD Joint Directors of Laboratories， 25-26 Oct. 1994 Virtual manufacturing technology and digital technologyZheng li, Xu ping , lu , Jia qiu ,xu2006-2-2 This introduced virtual manufacturing background and its definition, discussed virtual manufacturing styles, relevant technology, applications in the field of digital technology, research and application.With increasing global competition, in order to shorten the products listed time in the 1980s have made Ltd. (Fexible Manufacturing System), CIMS (Computer Integrated Manufacturing System), CE (Conturrent Engineering), new concepts, and applications of their research to improve product quality and production efficiency. With the development of technology and production networks in the 1990s by creating a strong am (Agile Manufacturing), sophisticated manufacturing LM (Lean Manufacturing), distributed manufacturing (Distributed Manufacturing) and the virtual enterprise ve (Virtual Enterprise), a new field of study, the current study focused on the technical design stage of detailed design, CAD systems, while providing that the method and operation of complex components, But it can not express the concept design stage of information, in such circumstances, have tried to create a virtual (Virtual Manufacturing).Virtual manufacturing establishment of a computerized manufacturing activities such a key concept, which summarizes the world of real objects and manufacturing activities of the various aspects of modelling and simulation studies，Virtual manufacturing is based on the use of computer technology to support all the activities necessary to create a thorough modelling and simulation, in which a computerized processes, namely : digital plus The study process is to create virtual one of the core foundations.Virtual manufacturing definitionLawrence Associates in the Virtual Manufacturing User Workshop report, the VM is defined as : it is a master, integrated operational manufacturing environment to enhance all levels of decision-making and control. Semantic description of the various components are as follows : environment through concerted provide analytical tools, simulation tools, application tools, control tools, models (product, process and resource), equipment and the organization of the assembly methods, to support the construction and use of distributed manufacturing simulation. Levels Refers to the concept of products from design to recycling, from the workshop to implement location, material from the conversion to the transmission of information fields. control Forecast results authenticity Improved Increase its accuracy and reliability. operation Environment for the construction and operation of a specific manufacturing simulation decision-making Mean change (visualization, organization, definition and choice) impact. integrated That the real and simulated objects, activities and processes cocktailOn the above definition does not adequately emphasized tried tried in the forecast process, cost and quality capabilities, but it does not indicate the reliability and accuracy of forecasts VM, there are also shortcomings : The definition limits its scope to deal with, and enhance the engineering and manufacturing world between. Although it tried to achieve the best definition of the most comprehensive description, but according to different user groups, technical background and level should be tried different definitions. VM should be defined with specific user experience associated with the manufacture here should be broad, enterprise-wide big manufacturing. Because in addition to the workshop is included in the modelling of important activities, data and simulation.The definition must be tried with the experience and requirements of specific user linked, and therefore can not be tried only one definition for each individual, VM is not exactly the same, it should understand the difference between it and other related concepts. Such as VM provides an extensive coverage of the definition is very difficult. VM definition can not include every aspect of it. Therefore, in order to better explain tried and tried by the content of a note : ways and through the use of simulation-based modelling, tried mainly to enhance processing quality. VM is the most important role for the implementation of IPPD (Integrated Produce Process Development) to provide a tool, particularly for products projected cost and control function.VM basic aim of computer-based simulation product development environment, allowing designers in the real processing can be simulated prior to manufacture products. Here, product development includes all activities relating to products, including not only the technical and commercial, and includes product design and production. However, the simulation does not tried all these aspects. VM model is based on the manufacture and use of tools in turn affect these models. Simulation tools are most initial use of simulation can reduce manufacturing costs, but can also check the real space and virtual space of many parameters.Speaking from the overall perspective, in a IPPD environment through the computer to complete the manufacture and tried to provide some or all of the design process for the evaluation methodologies.1. the school of VMVM research with specific application environment and associated targets in VM research process, because of the different applications, each with a different focus, resulting in three different styles, they are designed to center tried, for the production-centred and tried to control the center tried to1.1 To design for the center of VM.Tried to design for the center through the manufacturing process and the information in the computer to IPPD, create, a simulation of manufacturing programmes and many soft models. Therefore its short-term objectives are : To create a special purpose (for example, to assemble a design, sophisticated operation or soft), tried to create-based simulation to optimize the product design and production process. Its long-term goal : VM in different levels to assess the production process using simulation, and feedback to the design and production control. 1.2 to the production center of VMProduction centred tried to increase simulation capacity by the production process models, and to facilitate quick assessment of multiple processing purposes. Its short-term objectives are : VM is based on the production IPPD conversion to optimize the manufacturing process and the physical layer. Its long-term goal is : new processes and procedures in order to achieve higher credibility, tried to increase production simulation to other integration and analysis technologies 1.3 To the control center of VMTo the control center through increased tried to control simulation models and the actual production process, to achieve the true simulation1.4 The relationship between the three categories VMAlthough the definition of the three tried different, but they all relate to different virtual product life cycle, therefore, they have the following characteristics : centred tried to design for designers with a design and evaluation can manufacture products of the environment, including the results of its product modelling, cost projections, therefore, the potential problems in the design can be found, while some of its indicators (such as cost, etc.) can also be predicted. qualified to produce products without doing the actual samples for the production centred tried to craft plans and the generation of production plans, processes and resources required for the evaluation of these plans provided a environment, it can provide a more accurate cost information and products supply.2. VM distinction between technical and other relatedCurrently in advanced manufacturing technology research process generated many new concepts, such as IPPD, virtual enterprise ve (Virtual Enterprise), modelling and simulation M&S (modeling and Simulation). Therefore, in order to explain in more detail the content tried, and tried to understand other related concepts relations.2.1 VM and IPPDIPPD is a cross functional coordination mechanisms, and it makes design and manufacturing-related information in the product design process modules mobile. VM simulation manufacturing, production and assembly process, it must interface with the above information, but the VM is not the module assembly, or in which information flows between the modules. As shown in figure 1 of their relationship. Figure 1 product development processIn accordance with the views of IPPD, tried to increase the IPPD process, which provides a comprehensive approach to creating knowledge in the early stages of product development. Therefore, it is important in the role of the IPPD. First it allows IPPD directly through simulation processes for the design, analysis and manufacture of products, instead of the actual processing concern. Secondly, it allows the prototype system IPPD arbitrary levels increase process. IPPD advantage does not lie in the number of course modules, as several of the best individual model portfolio together is not the best. VM,IPPD can use reverse analysis processes, instead reconstructs processing. In parallel works CE (Concurrent Engineering) perspective, tried to increase the above-mentioned capabilities, sharing infrastructure it needs more reliable than the CE.2.2 VM and M&S(Modeling and simulation)M&S tried to rely on simulation technology manufacturing, production and assembly process so that designers can in the computer to create products. M&S was tried foundation. VM is M&S applications, but it extended the traditional M&S technology. Traditionally, the aim was merely to M&S modelling simulation and related analysis. In VM, the use of the main part of the model has been in existence, rather than optimizing the simulation. Because in the VM, because of other reasons, the models are dynamic, changing with the simulation environment, it is changing.2.3 VM and VE(Virtual Enterprise)Virtual enterprise is the ability to create basic dynamic organization patterns refers to the opportunity to win a competition of the market, centering on some new product development, through the choice of different organizations or companies resources, integrated into a single network communications rely on the interim operating entity. Dynamics of integration and timeliness Union two characteristics. It is essentially a different dynamic between the organization or enterprise integration, with the market opportunities and assemble and part survival. In specific performance, allied with a large company can be different organizational departments, and can also be of different companies in different countries. Ve partners can share in the production, technical and product information, the information in the form of data that can be distributed to different computing environment. Ve and tried not strong interdependent relationships. In the area of information integration and sharing, the main emphasis ve network, and tried the main emphasis on product design, but the focus is at the design stage VM product life cycle simulation of the various activities.2.4 VM and VP (Virtual Prototyping)Virtual prototype (Virtual Prototype) is the relative physical prototype, with some computer-based simulation system functions. It is mainly designed for the testing and evaluation of designated properties. VP is the use of virtual prototyping process. Currently, it mainly for shorter product development time and reduce costs. In VP, computer-aided design information relayed to the product models directly, instead of tectonic physical prototype to test the effectiveness of the design and optimization of the design. If the virtual prototype simulation processes through the construction plans, then VP is used to generate the VM, in most cases, VP greater advantage than physical prototype in virtual product cycle, VP is a necessary component. Therefore, the development will enhance the VM VP capacity, which, in turn, tried to provide an application environment VP.2.5 VM and AM(Agile Manufacturing)Ability to create a new concept, the basic idea is to be adopted by the high-quality staff, dynamic and flexible organization, enterprise and inter-enterprise management and soft flexible advanced production technology to conduct a comprehensive integration that enables businesses to the constantly changing and unpredictable market demands rapid response, which was long-term economic benefits. So nimble manufacturing emphasis, organization, management and highly integrated technologies, emphasizing the ability of market-oriented enterprises (Agility). In a business organization and management, its four main features of the variables that can be used, together with sexual communication (Communication Connectedness), the cross-organizational participatory (Interorganization Participation), production flexibility (Producti