Integrating Flexible Process Plans with Scheduling in Flexible Manufacturing Systems

This paper highlights the importance of integration between process planning and scheduling in flexible manufacturing systems (FMS). An effective integration increases the potential for enhanced system performance and enhanced decision making A framework that integrates flexible process plans with off-line (predictive) scheduling in FMS is presented. The flexibility in process planning, including process flexibility, sequence flexibility, and alternative machine tools, is discussed. The proposed framework consists of four integrated stages with the objective of reducing the completion time. The integrated stages include: 1. Machine tool selection. 2. Process plan selection. 3. Scheduling. 4. Re-scheduling modules. In addition, the paper proposes a new approach, namely the Dissimilarity Maximisation Method (DMM), for selecting the appropriate process plans for a part mix where parts have alternative process plans. The recursive structure of the framework provides a different approach, namely overlapping schedules, which considers a longer scheduling period as comprising several short scheduling periods. Knowing that neither the process plans nor the planned (predicted) schedules are truly followed on the shop floor, the related literature and the corresponding approaches are compared in order to envisage new approaches for closing the gap between process planning and scheduling.     

A structured approach to the automatic planning of machining operations for rotational parts based on computer integration of standard design and process data

The traditional procedure for developing a manufacturing process plan involves a number of interconnected steps beginning with the initial design and culminating in the instructions for the machine that makes the part. When performed manually, the procedure is very tedious, time consuming, and often, inconsistent. This paper presents an alternative method, called the Automated Machining-Operations Process-Planning System (AMOPPS), to automatically generate the process plan and the numerical control (NC) instructions to machine a part that has been previously designed by a computer-aided design (CAD) system. AMOPPS combines preset planning logic and data from three databases (viz., workpiece material, machine tool, and cutting tool) with appropriate data from a CAD database and information from the user about the workpiece to calculate the optimal machining parameters, print a process plan, print the corresponding NC program listing, and provide an on-screen animation of the cutting passes. Although AMOPPS is a prototype, it can be extended by adding other modules, and it does provide a structure through which a fully integrated manufacturing system can be developed.     

A process net model approach for multiple process plans

A process planning system that generates alternative process plans offers multiple process plans for a part, thereby providing the flexibility to cope with changes in shop floor status. In this paper, we introduce the concept of a process net as a model for the generation of alternative process plans. We also show the usefulness of the process net model in generating alternative process plans by implementing the developed system to construct process nets, and devising an algorithm to generate alternative process plans for rotational parts.     

Integrated manufacturing process planning and control based on intelligent agents and multi-dimension features

Dynamic manufacturing environments require a flexible process planning and control system in response to changing manufacturing resource availability, production uncertainty, and dynamic machining conditions. To address these issues, this paper proposes a novel integrated process planning and control method based on intelligent software agents and multi-dimension manufacturing features. An integration framework with three modules including generic process planning, shop floor process planning, and online process control is developed. An intelligent agent-based approach is adopted for achieving intelligence and autonomy of individual software modules and components. An ontology-based multi-dimension manufacturing feature model is proposed to facilitate the communication and collaboration between process planning and control, as well as to speed up the decision-making of intelligent agents. The feasibility and flexibility of the proposed method are validated through a proof-of-concept implementation.     

An integrated scheme for process planning and scheduling in FMS

Process planning and scheduling are the two important manufacturing functions involved in any shop floor activities. As functional integration is essential to realize the benefits of computer integrated manufacturing, a scheme for integration of process planning and scheduling has been introduced in this paper. The proposed scheme can be implemented in a company with existing process planning and scheduling departments when multiple process plans remain available on the shop floor. It consists of two main modules, introduced in detail in this paper. They are process plan selection module and scheduling module.     

基才Pro／E三维钣金展开的CncKad数冲加工

详细介绍了采用Pro／E三维设计软件和CncKad数控加工软件辅助钣金件的设计与加工制造的完整过程。用Pro／E软件的钣金模块进行钣金件设计建模时,需要根据钣金材料和厚度设置折弯表程序,调用相应的折弯表,将钣金件展开成平整状态。Pro／E软件与CncKad软件集成后带有CncKad功能模块,将展开好的钣金件导入到该功能模块中,采用CncKad软件自动或者手动冲压功能加装模具,生成数冲程序,控制数冲机床加工钣金件。     

On-machine measurement using a noncontact sensor based on a CAD model

Once a machining process is finished, an inspection process is carried out to check whether the part is within dimensional tolerances. A coordinate measuring machine (CMM) is a general metrological device for assessment of dimensions on the shop floor. It cannot be ignored, however, that CMM measurements require significant resources in operating time and cost, which has led to many studies into on-machine measurement (OMM) systems. This study aims to develop an OMM system with a noncontacting laser displacement sensing apparatus and a computer-aided design (CAD) model for ease of operation, improved operating speed, and free form profiling. The system is composed of two software modules, one for sensor alignment with the machine tool and the other for measurement based on CAD/CAM (computer-aided machining). Consequently, the system was verified on the shop floor at a numerical control (NC) machining center.     

基于多智能体机制面向资源的CAPP系统研究

为提高在车间中执行的工艺规划的柔性和适应性,提出一个基于多智能体机制面向资源的CAPP系统的框架。该系统由分布式制定工艺任务的工艺信息代理和对应车间资源的资源代理组成。面向一个工艺任务,资源代理组成多个资源代理联盟,工艺信息代理通过选择资源代理联盟进行任务分配。重点研究了工艺规划和资源分配的并行,多代理之间多级协商的资源冲突消解策略,以及面向资源的工艺决策优化等关键技术。开发了原型系统以评价系统的性能,生成的面向资源的工艺方案输入车间调度系统。     

基于过程集成的闭环动态工艺规划系统

描述了一个在过程上实现工艺规划与车间规划集成的闭环动态工艺规划系统,建立了实用化CAPP系统的新模型,丰富了动态CAPP的概念。它能根据车间环境的状态,充分利用制造工艺和车间环境的柔性产生优化的工艺方案。系统在车间环境约束下采用专家系统技术进行非线性工艺规划,产生可选工艺路线和工序可选设备。在一个由工艺路线选择、设备动态优化选择和车间优化规划构成的闭环系统中,以高生产效率为目标,根据推广的关键路线分析的结果和一系列启发式知识动态地选择工艺路线和设备,最后获得有较高实践意义的结果。     

A Generative Computer-Aided Process Planning System for Prismatic Components

This paper deals with design and development of a generative computer-aided process planning (CAPP) system for prismatic components and named PSG-CAPP. The proposed CAPP system has been divided into three modules. The first module is concerned with feature extraction. The second and third modules deal with planning the set-up, machine selection, cutting tool selection, cutting parameter selection, and generation of process plan sheet. The whole CAPP system is developed using Visual Basic 6.0 as front end and Oracle 7.3 as back end. The SolidWorks98 plus has been used for modelling, and feature extraction has been implemented using a program written in Visual Basic 6.0. The speciality of the developed CAPP system is that it is linked with the CAD module and it extracts the majority of features automatically prior to process planning. The developed CAPP system has been tested with aerospace components. The main feature of the proposed CAPP system is its ability to handle a variety of prismatic components and generate process plans for them. A case study has been included to highlight the potential of the CAPP system. ID="A1"Correspondance and offprint requests to: Professor P. V. Mohanram, Department of Mechanical Engineering, PSG College of Technology, Peelamedu, Coimbatore 641004, India. E-mail: msadaiah@yahoo.com     

An image acquisition system for real-time seam tracking

Process planning is a function that establishes the technological requirements necessary to convert a part from its raw material to the finished form. Generally, the result of process planning is delivered to the workshop to guide the manufacturing process in the form of process plan. However, a part always has multi alternative process plans for the processing means and techniques are not unique, therefore, optimization and selection of process plans is an important task of flexible process planning. In this paper, the flexibility of process planning and the AND/OR network adopted to represent the flexibility of process plans were described, and a mathematical model for the optimization of flexible process planning based on the AND/OR network was established. On this basis, a new heuristic method, called cross-entropy (CE) approach, was proposed to optimize flexible process planning. In order to facilitate the implementation of the CE-based approach, the new sample representation and probability distribution parameter were introduced; meanwhile, the new sample generation mechanism was presented and the updating expression of probability distribution parameter was deduced. Case studies, used for comparing this approach with genetic algorithm (GA) and genetic programming (GP)-based approach, were discussed to indicate the performance and adaptability of the proposed CE-based approach in terms of the solution quality and computational efficiency of the algorithm. The results show that the CE-based approach is effective for the optimization research of flexible process planning.     

基于创成设计思想的可重构机床模块设置方法

建立合理的功能模块群是实现可重构机床方案重构的关键,基于创成设计方法建立了以镗铣加工为主的机床结构形态方案图谱,解决了机床模块划分时机床结构形态方案不足的问题。通过对机床结构形态方案的分析,划分出机床概念结构模块群;依据可重构机床模块功能自治原则,建立了机床概念功能模块群;将机床的概念功能模块、运动功能及被加工零件的工艺方案联系起来,建立了以工艺方案为依据的可重构机床功能模块群设置方法,并以某变速箱壳体件加工为例验证了该方法的可行性。     

A resource-oriented tolerance representation scheme for the planning of robotic machine tending operations in automated manufacturing systems

In this paper, we define a representation for tolerances associated with robotic machine tending operations. The intent of the representation and analysis presented in the paper is to assess whether a robotic material handler is capable of holding the accuracies required for loading and unloading a machine. This representation and analysis, therefore, provides the basis of a process planning system for robotic operations. This representation is critical for flexible and automated manufacturing because it enables automatic planning of unload and load operations from and to machining centers that are required for discrete part manufacturing. Planners can use this representation along with the specified tolerance criteria to conservatively assess if a given robot resource is capable of using a specific gripper to unload or load a given part from a given fixture on a machining center. For a new part, this assessment allows an automatic material handling operations planner to determine if reconfiguration or procurement of resources is required for the material handing of the new part or if simple reprogramming of the robot and machine resources is sufficient. Also, this representation helps providing flexibility to the manufacturing system control software in the case of the addition of a new machine to the manufacturing system. In this case, the new resource data would be input into the resource model, and the decision on the machine tending operations (loading or unloading) would be carried out in the same manner. This representation was tested successfully using an automatic operations planner at The Pennsylvania State University’s Factory for Advanced Manufacturing Education (FAME) lab.     

A Dynamic Programming Based Process Planning Selection Strategy Considering Utilisation of Machines

Computer-aided process planning (CAPP) has been recognised as a key element in computer-integrated manufacturing (CIM). Despite the fact that tremendous efforts have been made to develop CAPP systems, the benefits of CAPP in real-life manufacturing environments are not obvious. One of the main difficulties in applying CAPP in real manufacturing settings is the missing link between generated process plans and shop-floor activities. The assumptions that the shop floor remains static and there are unlimited resources available have caused a typical CAPP system to make a repetitive selection of the same most desirable machines for manufacturing different parts. When process plans for various parts are finally sent to the shop floor, process bottlenecks normally arise, making the generated plans ineffective. Some efforts have been made in the integration of process planning and shop floor activities; however, the problems associated with the lengthy time and impractical attempts at the generation of process plans, remain unsolved. Since in most cases, it is possible that several alternatives exist for machining a part by using different equipment, a stage-type network structure can be constructed. This paper introduces a dynamic programming based process plan selection strategy, enabling the efficient solution of this stage-type network prob-lem. In this proposed strategy, the use of workstations is also taken into consideration so that the resulting plan is valid for the conditions that exist on the shop floor at the time an order is released. A case study has been provided to substantiate the effectiveness of this proposed strategy.     

Parametric process planning based on feature parameters of parts

This paper presents a model parametric process plan that is dependent on feature parameters of parts, and proposes a solution for the automated process planning of part families. Based on the parametric process plan templates for part families and the feature parameters of new parts, a prototype system is developed. First, parts are grouped into families considering their geometric or manufacturing similarities, and the parametric process plan template is pre-created for each family. Then, to plan the process of a new part, the system extracts feature parameters from its feature-based model and generates an a parametric process plan by searching the template library and solving related constraints. Finally, the system outputs the process plan sheets, if necessary. Although the system cannot creatively generate process plans for brand new parts, the system can meet two important requirements of the real industrial world to CAPP systems, that is good system performance and rapid response.     

A Cascading Auction Protocol as a Framework for Integrating Process Planning and Heterarchical Shop Floor Control

A new contract net-style auction protocol is proposed as a framework for integrating process planning and shop floor control in heterarchical manufacturing systems. Process planning is partitioned into on-line and off-line activities; off-line process planning decisions are represented in a graph format and used as input for on-line process planning activities performed by machine controllers. Triggered by the opening round of an auction, the final on-line stages of process planning are dovetailed with the resource allocation process in the shop floor control system. The auction process allows final process planning decisions to be based on timely information, relying on the distribution of static process planning information rather than the distribution of a model of dynamic shop floor status and allowing a controller to identify all the primary and secondary resources and operations that must be provided for the incremental processing of a part.     

Integration of process planning and scheduling in a job shop environment

Today’s manufacturing systems are striving for an integrated manufacturing environment. To achieve truly computer-integrated manufacturing systems (CIMS), the integration of process planning and production scheduling is essential. This paper proposes a framework for integration of process planning with production scheduling in a job shop environment for axisymmetric components. Based on the design specifications of incoming parts, feasible process plans are generated taking into account the real time shop floor status and availability of machine tools. The scheduling strategy prioritizes the machine tools based on cost considerations.     

用普通数控车床准确加工母线为非圆曲线的工件

讨论了用普通数控车床准确加工母线为非圆曲线工件的插补技术要点 ,编制了通用的加工程序生成软件。只需将工件的母线方程和几何参数输入该软件 ,即可生成NC代码加工程序 ,并可在计算机上动画模拟加工全过程。该软件应用于GSK 92 8型数控车床加工时取得了良好效果。     

基于多域互用的数控机床模块化配置设计

为实现数控机床各级功能部件的选型优配设计,提出一种多域互用的数控机床模块化配置设计方法。通过机床功能部件的机电液属性池定义模块,根据模块的隶属与层次关系创建产品偏序模板。定义关键模块、相关模块、虚拟模块,以表征各模块的优先级与重要性。根据零部件选型与优配约束,确定模块的实例化规则。由可比属性间的模糊隶属度推算两模块相关性,通过Karhunen-Loeve变换遴选出关键模块,根据支持矢量机多分类实现产品树重构。由布局设计促进模块实例化,由结构变异实现难直接重用零件的互用,根据设计需求输出模块化物料清单与装配体,最终实现多域互用的模块化配置设计。开发了模块化配置设计原型系统,应用于HMS系列某卧式加工中心设计,结果表明,通过属性—模块—模板的层级映射将已有的数控机床设计拓展到布局域—选配域—变异域多域互用的模块化配置设计,扩大了零部件借用范围,降低了不同布局的产品族间的非标件比率,有利于提高数控机床的设计效率和质量。     

Retrofitment of a CNC machine for hybrid layered manufacturing

Subtractive manufacturing [computer numerical controlled (CNC) machining] has high quality geometric and material properties but is slow, costly, and infeasible in some cases. On the contrary additive manufacturing (rapid prototyping) has total automation but compromises quality. A hybrid layered manufacturing process presented in this study combines the best features of both these approaches. It uses arc weld deposition for building near-net shapes, which are subsequently finish machined. Time and cost savings of this process can be attributed to reduction in NC programming effort and elimination of rough machining. It is envisioned as a low cost retrofitment to any existing CNC machine for making metallic objects without disturbing its original functionalities. Near-net shape building and finish machining happening at the same station is the unique feature of this process. A customized software generates the NC program for near-net shape building. The intricate details of integrating arc welding unit with a CNC milling machine are presented in this paper.