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.     

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.     

A Branch and Bound Algorithm Based Process-Planning System for Plastic Injection Mould Bases

This paper describes the use of artificial intelligence in the process planning of plastic injection mould bases. The computer- aided process-planning system, developed for IMOLD? will extract and identify the operations required for machining. These operations are considered together with their precedence constraints and the available machines before the process plan for the mould base plate is generated. The process plan is optimised by a branch and bound based algorithm. Overall machining time has been proposed as the objective function for optimisation. The ability of this algorithm to search intelli-gently for a feasible optimised solution is illustrated by an industrial case study. A brief comparison with a genetic algor-ithm based process planning system is also made. The result of this development will allow users to optimise process plans easily for any given mould base, with options to suit dynamic changes on the manufacturing shop floor.     

柔性流水车间设备利用率排产优化问题研究

针对具有工序约束信息的柔性流水车间的设备利用率优化问题,提出利用PSODE混合算法来解决该问题,全局优化过程采用群体优化算法,在局部优化过程中通过上下道关联工序约束信息来控制工件的分配,将并行工位总设备利用率作为适应度函数,构建了具有关联工序约束的柔性流水车间生产调度模型,确定生产工件的加工路径、加工顺序、开工时间和完工时间。通过多组方案数值计算结果对比分析,验证了PSODE算法解决柔性流水车间设备利用率优化问题的有效性。     

成批生产计划调度的集成建模与优化

针对多品种批量生产类型,建立了调度约束的生产计划与调度集成优化模型。模型的目标函数是使总调整费用、库存费用及生产费用之和最小,约束函数包括库存平衡约束和生产能力约束,同时考虑了调度约束,即工序顺序约束和工件在单机上的加工能力约束,保证了计划可行性。该模型为两层混合整数规划模型,对其求解综合运用了遗传算法和启发式规则,提出了混合启发式求解算法。最后,针对某机床厂多品种批量生产类型车间进行了实例应用,对车间零件月份作业计划进行分解,得到各工段单元零件周作业计划,确定了零件各周生产批量与投产顺序。     

MODELING AND IMPLEMENTATION OF A DISTRIBUTED SHOP FLOOR MANAGEMENT AND CONTROL SYSTEM

Adopting distributed control architecture is the important development direction for shop floor management and control system, is also the requirement of making it agile, intelligent and concurrent. Some key problems in achieving distributed control architecture are researched. An activity model of shop floor is presented as the requirement definition of the prototype system. The multi-agent based software architecture is constructed. How the core part in shop floor management and control system, production plan and scheduling is achieved. The cooperation of different agents is illustrated. Finally, the implementation of the prototype system is narrated.     

考虑配合加工的作业车间启发式倒排调度算法

目前对制造业领域作业车间调度问题研究中,配合加工增加了调度的约束,使调度的难度进一步加大。根据实际配合加工作业车间环境,建立了以最短加工时间为目标的调度模型,采用启发式倒排算法对其求解,该算法能保证工件的交货期,最后通过实例对算法进行验证并给出对比结果。     

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.     

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.     

A developed production control and scheduling model in the semiconductor manufacturing systems with hybrid make-to-stock/make-to-order products

Semiconductor manufacturing systems are one of the most complex production systems and this complexity increases when these systems produce both make-to-stock (MTS) and make-to-order (MTO) products in order to improve the production system utilization. To deal with this complexity, we present a dynamic production control and scheduling model for a semiconductor shop (fab) with hybrid MTS/MTO production environment. The proposed model encompasses two major modules: release module and dispatching module. The release module deals with two issues: prioritizing the MTS and MTO products in the job pool and determining when and which products can be released into the shop floor. The only considered issue of dispatching module is to prioritize the MTS and MTO products in the queue of each workstation whenever a machine becomes idle. To evaluate the proposed model, different performance measures for MTS and MTO products are considered. Moreover, a number of numerical experiments have been conducted by simulation studies. Simulation studies indicate that the proposed model outperforms other related well-known production control and scheduling policies in the literature.