| Turning center is a new kind of machine tool equipped with dual-spindle and dual-turret. The turning center becomes popular used in industry recently, because it could perform both milling and turning operations. The distinguish feature is that turning center could perform simultaneous machining and parallel machining. In simultaneous machining mode, two power turrets(PTs) perform the same feature or two different features of one part cooperatively. In parallel machining mode, PTs perform different features of two parts respectively. By contract, using traditional machine tools, only one operation could be performed at a time. A turning center could be considered as a replacement for a milling and a lathe machine tool. Hence, turning center provides an excellent solution for geometric complicated mill/turn parts that have both turning features and milling features. The multiple functions require fewer setups, which reduce workpiece transferring and setup time significantly. Fewer setups could also eliminate or reduce setup errors thus increase the product accuracy. It could enhance efficiency, increase machining quality, reduce machining cost, and is valuable for small company with limit working area in workshop.In the face of process planning for the turning center, two tough issues will be encountered. The first tough issue is that it is difficult to recognize complicated intersecting features. The traditional feature recognize approaches focus on the geometrical information of design features, without considering the matching relationship between design features and the manufacturing resources, such as machine and tools. Thus, some complicated intersecting features of mill/turn part will be difficult to recognize. And even these features have been recognized, they are difficult to machine with the manufacturing resource constraints. The second tough issue is the process planning problem in simultaneous machining mode and parallel machining mode, which are two distinguish characteristics of turning center process planning. In these two mode, the manufacture resources such as spindles, turrets and tools are difficult to schedule. Besides, collision testing must be conducted between the turrets. Traditional approaches aim to solve process planning problems of one part, without considering characteristics of turning center process planning. Thus, this paper mainly focus on the following aspects.(1) A new feature recognition and mapping method is developed based on turning center processing capability to handle the complicated intersection features. The process design ontology model is first constructed as the foundation of knowledge expressing and reasoning for this research. The turning center processing capability model is proposed based on cutting forming function and cutting edges function. According to the turning center processing capability model the mapping mechanism between design features and manufacturing features are analyzed. The machining parameters such as processing methods, feasible cutters, TAD are determined for the surface of each design feature based on the turning center processing capability model. Finally, a clustering method based on ant colony algorithm is developed to classify the surface of a part into a set of manufacturing features.(2) A new process planning method is proposed for two spindles-one part mode. When turning center using dual-spindle hold one part, the dual-turret could perform operations simultaneously. The simultaneous machining would change the basic principle FIFO(first in first out) of operation sequencing in process planning. FIFO means that an operation could not start until the previous one in processing has been finished. According to the high flexibility of turning center, a 0-1 mixed integer programming mathematical model is established and the objective function is the lowest machining cost. A new edge-based selection strategy coding method is proposed to improve the GA, which resolves the illegal solution problem. Using the new encoding strategy, the population distribution characteristics of the initial solution is improved in order to avoid that the GA obtains local optimum.(3) A new process planning method is proposed for two spindles-two parts mode. Compared with the two spindles-one part mode process planning, the two spindles-two parts process planning can improve the machining efficiency and optimize the spindles and towers resources, which is a coupled problem between the process planning optimization and job shop problem. There are so many objective functions and constraints condition for the integer programming model, and it is difficult to resolve this problem. Therefore, the improved non-dominated sorting genetic algorithm is proposed to resolve this problem. Before the selection operators are carried out, individuals were stratified according to the relationship. The population diversity is guaranteed by the crowded degree calculation for non-dominated genetic algorithm.(4) An architecture is proposed based on temporal ontology model for turning center CAPP. Process temporal ontology model, part information model and machine processing capability are constructed. The mapping relations among these three models are also built. The new process scheme is designed for multi-type machine methods such as machining two parts with two spindles, machining the same feature for two towers. Three critical approaches, such as the feature recognition based on machine processing capability, the process planning for two spindle –one part mode, the process planning for two spindle –two part mode, are discussed in this paper. The proposed methods and theories are applied to some key parts of industrial to highlight the validity and feasibility.In this research, a new turning center oriented feature mapping method, the process design methods and thoeries for two spindles-one part mode, and the process design methods and thoeries for two spindles-two parts mode are developed. Some application cases demonstrate the validity and feasibility. The methods and theories proposed in this article could improve the company flexibility and the utilization of turning center. Besides, the process design of complicated mill/turn part is improved. |
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