A review on integrated process planning and scheduling <s> Statement of problems <s> Abstract Dynamic process planning is concerned with the integration of process planning with scheduling. This paper presents the computer-aided process planning (CAPP) system, PARIS, that is meant to be integrated with a scheduling system. The approach to dynamic process planning implemented divides the planning tasks into the two phases: static and dynamic planning. This paper discusses the overall approach and focusing on the details of the implementation of the static phase. An example is used to illustrate the concepts presented. <s> BIB001 </s> A review on integrated process planning and scheduling <s> Statement of problems <s> Abstract Computer aided process planning (CAPP) and scheduling are two major activities in a modern manufacturing system. The existing CAPP systems have not taken account of shop floor conditions while developing process plans. This paper discusses the importance of integration of scheduling and CAPP and proposes a method for the same. There can be several methods to machine a part and several machines capable of performing the process required to complete the part. Based on this concept, this paper suggests a method of scheduling and its integration with CAPP, so that on-line process plan can be generated taking into account the availability of machines and alternative routes. A scheduling factor for an operation and machine combination has been defined taking into consideration the actual working conditions and capabilities of the machines. Finally operation–machine assignment is made on the basis of these actual scheduling factors. This helps in generating more realistic process plans and helps in improving the efficiency of the manufacturing system as a whole. <s> BIB002
In traditional approaches, process planning and scheduling were carried out in a sequential way. Scheduling was conducted after the process plan had been generated. These approaches have become an obstacle to improve the productivity and responsiveness of manufacturing systems and to cause the following problems Rajotia, 2002, 2003) : 1 In manufacturing practice, process planner plans jobs individually. For each job, manufacturing resources on the shop floor are usually assigned on it without considering the competition for the resources from other jobs BIB001 . This may lead to the process planners favouring to select the desirable machines for each job repeatedly. Therefore, the generated process plans are somewhat unrealistic and cannot be readily executed on the shop floor for a group of jobs  . Accordingly, the resulting optimal process plans often become infeasible when they are carried out in practice at the later stage. 2 Scheduling plans are often determined after process plans. Fixed process plans may drive scheduling plans to end up with severely unbalanced resource load and create superfluous bottlenecks. 3 Even though process planners consider the restriction of the current resources on the shop floor, the constraints in the process-planning phase may have already changed owing to the time delay between the planning phase and execution phase. This may lead to the infeasibility of the optimised process plan  . Investigations have shown that 20-30% of the total production plans in a given period have to be modified to adapt to the dynamic change in a production environment BIB002 . 4 In most cases, both for process planning and scheduling, a single criterion optimisation technique is used for determining the best solution. However, the real production environment is best represented by considering more than one criterion simultaneously BIB002 . Furthermore, the process planning and scheduling may have conflicting objectives. Process planning emphasises the technological requirements of a job, while scheduling involves the timing aspects and resource sharing of all jobs. If there is no appropriate coordination, it may create conflicting problems. To overcome these problems, there is an increasing need for deep research and application of IPPS system. The IPPS introduces significant improvements to the efficiency of manufacturing resources through eliminating or reducing scheduling conflicts, reducing flow-time and work-in-process, improving production resources utilising and adapting to irregular shop floor disturbances  . Through the integration of these two systems, IPPS can provide better process plans and schedules than the traditional manufacturing systems to improve the productivity of the manufacturing system greatly. In the following section, the review on the research of IPPS is presented.