This paper presents an object-oriented modelling approach to production scheduling for FMS. The purpose of this study is to prepare a simulation tool to try a method of production scheduling that allocates jobs to the machines and cutting tools in an FMS. This model is developed by using Pharo as the language software for object-oriented programming through UML system design. This model consists of three types of classes. The first type is the Equipment-class, which related to the physical equipment in the FMS, for example machining-centers, cutting tools, pallet stocker, stacker crane. The second type is the Product-class that related to the information how to process the product. This class has sub-class such as process plan, machining operation and required cutting tools. The third class is the Production Planning and Controlling (PPC) class, which related to create the schedule to equipment. The PPC-class has sub-classes such as the daily order or job, job sequence, job allocation on machine and scheduling methods. A numerical example is provided in this paper to show that the object-oriented model for FMS and production scheduling is verified. The FMS consist of four identical machining centers and eight jobs. Each job has a process plan that requires some specific cutting tool types. The method for production scheduling in this model is Shortest Processing Time (SPT). The production scheduling performance is measured in this model.

This paper addresses a batch scheduling problem for a three-stage hybrid flowshop consisting of a machining stage processing common and unique components on unrelated parallel machines, an assembly stage combining the components into assembled products with complex assembly structures, and a differentiation stage processing the assembled products on dedicated machines to produce different product types. The common components are the same for all products and are processed in batches, while the unique components are dedicated to respective given product types and are processed individually (one-by-one component). The goal is to schedule all the products with different assembly structures to minimize total actual flow time (TAFT) defined as total time interval of components to be processed from their arrival times to their common due date. A non-linear programming model is proposed, where small size problems can be solved optimally using the LINGO software, and large size problems is to be solved using a heuristic algorithm. The proposed algorithm consists of two sub-algorithms. The first one is constructed using a shortest processing time (SPT) based heuristic to get a job sequence as an initial solution and the second one is to improve the initial solution using the variable neighbourhood descent (VND) method with neighbourhood insert and swap move operators. In solving the problem with the algorithm, two scenarios arise, e.g., the same and the different sequences for all stages. A set of hypothetical data is generated for different hierarchical assembly structures to test the model and the algorithm, and the results show that the different sequences for all stages obtain solutions with better performances than the same ones.

This paper discusses production scheduling problems on CNC-machines having a set of cutting tools in a Flexible Manufacturing System (FMS) to maximize the cutting tools utilization. This objective has been selected because it is frequently found that cutting tools are under-utilized as they are used far below their respective lifetime limits. We will consider the situation where several identical CNC-machines are operated in an FMS; each of which is equipped with the same cutting tool configuration. The jobs to be scheduled are machining parts, and each of the parts requires one to two stages of processes, and each of the stages consists of several sequential operations, where a specific operation requires a certain type of cutting tool. Whenever a certain cutting tool is being used, the time consumption will be accumulated to calculate its remaining lifetime. The assignment of an operation to a particular CNC-machine will be based on the sufficiency of the cutting tool remaining lifetime to complete the operation. We formulate the problem in a mathematical model and then solve it using a solution method based on the object-oriented modeling approach, where the FMS elements are grouped as classes of the objects, i.e. the CNC-machine, the cutting-tool, the product (job) and the storage classes. Numerical examples show that the proposed solution method can effectively solve the scheduling problem.

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