یک سیستم بر اساس حجم ماشین برای کاهش تعداد برگه های مسیر در برنامه ریزی فرایند

The paper focuses on the problem of choosing the manufacturing route in metal removal processes, which is very important for the Computer Aided Process Planning (CAPP) systems. A method consisting in establishing groups of precedence between machine operations has been proposed, in order to reduce the number of possible routes. This reduction is based on the elimination of the routes which are not technologically possible, despite being mathematically computable. A wide range of parts has been evaluated, using group technology for choosing the representative cases. For the different parts, the mathematically possible routes have been generated. Graph Theory has been used to determine the precedence between operations. The application of this method permits to reduce considerably the number of possibilities that must be computed, and therefore, the route sheet is obtained more quickly and the computational resources are used more efficiently.

The planning process is the act of preparing detailed operating instructions for turning an engineering design into an end-product, i.e. the part [1]. This implies the need to translate the design specifications of a part into the required manufacturing operating instructions, to convert it from the raw material to the part in its final state [2]. There is a great deal of manufacturing data in process planning, such as the identification of machines, tools, flanging, parameter selections for machining, operations, etc. [3] and [4]. All of this data has to be evaluated in order to select the sequence of operations that will make up what is known as the route sheet. The sequence is generally obtained to conform with particular objectives, such as, for example, the shortest time and/or the minimum cost. Process planning requires many kinds of human abilities, which are to be found in the figure of the process planner [2], [4] and [5]. The traditional approach to resolving the process planning task is the one found in a manufacturing company, when the plans are handed over to the manufacturing process experts who then specify the procedures to make the product. The process planners, using their experience and knowledge, generate instructions for the manufacture of the products based on the design specifications and the available installations and operators. The fact that there are few experienced process planners and that, when faced with the same problem, different process planners would probably come up with different plans is an indication of the heterogeneity that exists in process planning [2]. But, in short, consistent and correct planning requires two things: knowledge of manufacturing processes and experience. This has led to the development of Computer Aided Process Planning (CAPP) systems, which are becoming more and more important in this field.

This paper is a contribution to the subject of very high number of routes sheets alternatives to compute. This problem has been discussed for different authors, like Weill et al. [21], Alting and Zang [7], Gu and Norrie [1] and Halevi and Weill [22]. The initial approach of the paper is based on Sundaram [23] of ordering the operations. In this model we included the technological restrictions we analysed in an empirical study carried out in a machine workshop. It is true that, in some of the aforementioned studies, ordering the operations in the route sheet was looked at, but none of them proposed anything specific that offered consistent and coherent alternative route sheets. From our investigations, we have managed to place the manufacturing operations into four large groups. These groups contain operations that virtually always follow a certain sequential order in any manufacturing route, i.e. any operation from group 1 will always be followed by any one operation from group 2, and so on. These four groups of operations here provide us with the following advantages: (a) With the analysis of the technological restrictions, the number of possible manufacturing routes for a part is reduced. (b) The reduction in the number of possible manufacturing routes will more than likely lead to a reduction in the time taken to compute the planning alternatives, since they will only take into account the technological feasible routes. (c) This reduction in the number of possibilities makes production process planning easier. (d) The reduction is applicable to computerised planning systems (CAPP) and manual planning. The contribution and the results we obtained, will do improvements in computational characteristics of computer systems, will bring much more reliability and speed to the programming of CAPP systems. We think that this will lead to the wider use of CAPP systems which have failed to find their place among the most used management and planning systems in manufacturing companies, despite the enormous potential that, a priori, they have to offer. At last, our study have limitations as we explained before in the paper. We can summarise these limitations and we need to be borne in mind. First of all, the table of results we give here is only applicable in the area of manufacturing by metal removal, and second it is not possible to obtain a table of precedences that any part would comply with 100% but we have found very good solutions in a great number of cases. Therefore we think that more studies are needed to investigate the application of the methodology—which we believe to be perfectly applicable to any other area of our study—in other production areas and manufacturing systems.